Flying cars and jet-powered batwing

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wumpus
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Re: Flying cars and jet-powered batwing

Postby wumpus » Wed Oct 29, 2014 2:40 pm UTC

Note for drones larger than a quadcopter is suitable, I would like to point out the Scorpion UAV (an early 1990s drone).

This was a joint project between Scaled Composites and a company called Freewing (out of business). High speed flight is handled exactly like an aircraft. Takeoff, landing, and loitering can be done at a tiny stall speed with the propeller (can presumably be replaced with a jet, but takeoff and landing would have to change) providing vertical thrust and the wings providing whatever lift they can.

The catch is that wings pivot freely (the development Freewing was named after) and thus are perpendicular to the wind. The tail is also perpendicular to the wind due to leverage. Thus a servo placed between the fuselage/propeller/"fixed wing" and the tail simply points the propeller up or down. Tastes vary as how cool it is compared to a batwing, but it is certainly vastly easier to fly, maintain, and keep from crashing.

http://www.youtube.com/watch?v=1CuOxqtdyfs

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Re: Flying cars and jet-powered batwing

Postby Azrael » Wed Oct 29, 2014 2:44 pm UTC

stoppedcaring wrote:Are there particular figures you think are unrealistic?

All of them. You can't just assume that it will fly.

More specifically, you've hand-waived wing stiffness (no, saying you can toss titanium around over the fans doesn't actually solve the problem). Ignored that the fans themselves and the louvers (and controls) have weight. Oh, and forgot about any sort of aerodynamic calculations. Will your fan-embedded wings actually create lift?

You're just taking the specs from two airframes at opposite ends of the spectrum and saying something there's probably something in the middle (a complete tautology) and that the something is your batwing (complete nonsense without any sort of aerodynamic analysis). Dude, speculation is great, but all you're doing is making shit up. At least the "(engineering Heavy)" descriptor is gone, because you aren't engineering anything. You're Complete Guide to Star Wars Spaceship-ing.

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Re: Flying cars and jet-powered batwing

Postby stoppedcaring » Wed Oct 29, 2014 4:20 pm UTC

Tyndmyr wrote:The following is a TERRIBLE way to estimate carrying capacity.
stoppedcaring wrote:Once you subtract the weight of engines, armor, and armament, the airframes of the Apache and the A-10 both come to almost exactly 45% of the typical loaded weight, so I used 40% to account for the more compact design of our craft.


Carrying capacity is not really a flat percentage across all designs, nor is it strongly related to compactness. In fact, longer, less compact wings, are usually far more efficient, which is why cargo aircraft tend to have them. Sure, a heavier load tends to have tougher frame requirements, but this is kind of a wild oversimplification.

Eh...that wasn't an estimate of carrying capacity; that was an estimate of frame weight in comparison to typical loaded weight. The Warthog and the Apache couldn't be more different in design, but their body-weight-to-takeoff-weight ratios were literally within a single percent of each other. I've looked at various other attack aircraft, both fixed-wing and rotorcraft, and their bodies are consistently in that same 40-50% weight window. So without anything better to use, 40% seems like a reasonably good estimate for what the airframe and cockpit and rotors and skin would weigh. I can't think of any better basis for an estimate.

Stuff like carrying capacity, etc. isn't estimated as a flat percentage, but is built up from adding to that estimated airframe weight, using the lifting ability of the fans and engines as a total.

Armor has been added and removed to aircraft after construction for far more than 40 years. Damaged armor plate is usually not the biggest issue for field repair. The plate of armor is usually the bit you LEAST need to worry about being hit.

Sure, obviously armor is added and removed post-construction on a regular basis. My point wasn't that this is something novel, but that a ground-up design can allow for armor load to be customizable to the mission and designed to be swapped out in the field with minimal equipment. Current close air support craft can't really have their armor weight adjusted for mission requirements on the front lines. Making field repair easier is just a fringe benefit.

wumpus wrote:Note for drones larger than a quadcopter is suitable, I would like to point out the Scorpion UAV (an early 1990s drone).

This was a joint project between Scaled Composites and a company called Freewing (out of business). High speed flight is handled exactly like an aircraft. Takeoff, landing, and loitering can be done at a tiny stall speed with the propeller (can presumably be replaced with a jet, but takeoff and landing would have to change) providing vertical thrust and the wings providing whatever lift they can.

The catch is that wings pivot freely (the development Freewing was named after) and thus are perpendicular to the wind. The tail is also perpendicular to the wind due to leverage. Thus a servo placed between the fuselage/propeller/"fixed wing" and the tail simply points the propeller up or down. Tastes vary as how cool it is compared to a batwing, but it is certainly vastly easier to fly, maintain, and keep from crashing.

http://www.youtube.com/watch?v=1CuOxqtdyfs

Wow, that's cool! Not sure how well it would work for a manned system or an attack system, though; the larger you scale something up, the worse problems you have with really large moving parts. A scale model Osprey is vastly more stable than a full-size Osprey.

Azrael wrote:
stoppedcaring wrote:Are there particular figures you think are unrealistic?

All of them. You can't just assume that it will fly.

More specifically, you've hand-waived wing stiffness (no, saying you can toss titanium around over the fans doesn't actually solve the problem). Ignored that the fans themselves and the louvers (and controls) have weight. Oh, and forgot about any sort of aerodynamic calculations. Will your fan-embedded wings actually create lift?

The weight of the rotors, vanes, and control surfaces is part of the overall body weight estimate. Using body-weight-to-takeoff-weight ratios to estimate seems straightforward, but perhaps I could look at other ratios as well...body-weight/wing-area, body-weight/wingspan, body-weight/chord. I preferred takeoff weight, though, as it allowed me to include rotorcraft and that seemed important given the non-negligible weight of the rotor pair.

Perhaps wing stiffness and aerodynamic analysis seem less problematic simply because I know it's been done before. The Ryan XV-5 had a greater wingspan, lower chord, and greater wing loading, and its wings were thicker than would have been most efficient, but it still flew quite well. Sure, added thickness is going to result in more frontal drag (which I accounted for), but there's a broad range of aerodynamic designs to work with. I guess I would be less optimistic if nothing like the Ryan Vertifan had ever flown.

You're just taking the specs from two airframes at opposite ends of the spectrum and saying something there's probably something in the middle (a complete tautology) and that the something is your batwing (complete nonsense without any sort of aerodynamic analysis). Dude, speculation is great, but all you're doing is making shit up. At least the "(engineering Heavy)" descriptor is gone, because you aren't engineering anything. You're Complete Guide to Star Wars Spaceship-ing.

Well, in the absence of CAD with full wind tunnel simulation, using wingspan and wing loading and comparable lift coefficients and so forth is about the best we can do. The "batwing" design isn't set in stone; the various characteristics could be applied to a range of body configurations.

And "engineering heavy" was more about the prior discussion of the flying car than this. Although the math here is fairly thorough...

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Re: Flying cars and jet-powered batwing

Postby Zamfir » Wed Oct 29, 2014 7:27 pm UTC


Perhaps wing stiffness and aerodynamic analysis seem less problematic simply because I know it's been done before. The Ryan XV-5 had a greater wingspan, lower chord, and greater wing loading, and its wings were thicker than would have been most efficient, but it still flew quite well. Sure, added thickness is going to result in more frontal drag (which I accounted for), but there's a broad range of aerodynamic designs to work with. I guess I would be less optimistic if nothing like the Ryan Vertifan had ever flown

But that's the thing. People tried your plan. Their conclusion was to never try it again. Realistically no one would have tried it in the first place, if the US army hadn't been restricted to VTOL craft. They wanted to have their own jet fighter force anyway and were willing to pour liquid money down the drain for that purpose.

Perhaps something has changed in the mean time, but it's unclear what. You have a clear view what ailed the Vertifan? You have specific plans to circumvent those issues? Do you have a reason why your solutions have been missed by all those people working on VTOL craft for generations?

Your calculations are just circular reasoning. Your input numbers assume that you can solve all the related issues at no weight gain to the craft, and with extremely high efficiency all over. Then you calculate that if your design has no downsides, it would be really good. Yes, it would.

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Re: Flying cars and jet-powered batwing

Postby Azrael » Wed Oct 29, 2014 7:29 pm UTC

stoppedcaring wrote:Although the math here is fairly thorough...

At which point you need to give yourself a reality check.

No, your math is not very thorough. You can tell because, at best, you've compared a dozen or so specs between a couple of other designs and extrapolated linearly with excel. An aeronautic engineer this does not make.

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Re: Flying cars and jet-powered batwing

Postby stoppedcaring » Wed Oct 29, 2014 8:02 pm UTC

Zamfir wrote:
The Ryan XV-5 had a greater wingspan, lower chord, and greater wing loading, and its wings were thicker than would have been most efficient, but it still flew quite well. Sure, added thickness is going to result in more frontal drag (which I accounted for), but there's a broad range of aerodynamic designs to work with. I guess I would be less optimistic if nothing like the Ryan Vertifan had ever flown.

People tried your plan. Their conclusion was to never try it again. Realistically no one would have tried it in the first place, if the US army hadn't been restricted to VTOL craft. They wanted to have their own jet fighter force anyway and were willing to pour liquid money down the drain for that purpose.

Perhaps something has changed in the mean time, but it's unclear what. You have a clear view what ailed the Vertifan? You have specific plans to circumvent those issues? Do you have a reason why your solutions have been missed by all those people working on VTOL craft for generations?

There were a lot of things plaguing the Vertifan. The big three were insufficiently advanced electronics to stabilize flight (computers have come a long way in fifty years), insufficient power supply (GE's J85 was a reliable engine, but it was inefficient and the small fans produced little thrust), and a lack of a clear role (the 1960s were a rather different time militarily and the VTOL mode drank too much fuel to be used for ground attack). In the intervening period, helicopters did the same kinds of jobs much better, so VTOL jets weren't considered nearly so much in the close air support role.

It's only in the past decade that the military has begun actively looking for the next-generation counter-insurgency/close-air-support aircraft. They're considering fairly novel stuff, like attack helicopters with lift-producing wings and rearward-swiveling tailrotors, as well as convertiplanes and a fixed-engine tiltrotor to replace the Osprey.

It's possible that this exact design has been considered, researched, and rejected. Sure. But it's possible that it hasn't. Either way, I'm interested to know what problems or challenges there would be.

Your calculations are just circular reasoning. Your input numbers assume that you can solve all the related issues at no weight gain to the craft, and with extremely high efficiency all over.

Not sure I'm tracking you here. I'm not assuming high efficiency all over; I'm taking median performance specifications from a series of other aircraft and adding conservatism. Where am I assuming unreasonably high efficiency? It's not like I'm doing this to try and trick people into liking the design or giving me money or something; I'm actually interested in other people looking critically at the numbers themselves and coming up with specific problems I might not have anticipated.

Azrael wrote:Your math is not very thorough. You can tell because, at best, you've compared a dozen or so specs between a couple of other designs and extrapolated linearly with excel. An aeronautic engineer this does not make.

I never said I was an aeronautic engineer. But I think the math is a bit more thorough than you're assuming.

Since the whole body-weight-estimate thing seemed to be a sticking point, I checked a few other aircraft.

Body-weight/loaded weight:
  • A-10: 44.7%
  • F/A-117: 47.5%
  • Apache: 45.0%
  • B-2: 43.3%
  • F/A-18: 48.2%
  • Eurocopter Tiger: 40.6%
  • OH-58 Kiowa: 45.4%

Bodyweight/loadedweight is the only decent way to compare rotorcraft and fixed-wing craft with the same metric. I could do a comparison using wing area, but that would just be a rehash of wing loading, and we've already seen that the batwing design is within typical wing loading for this class of aircraft. The only other approach would be to try and estimate average density, but that would only be good for an order-of-magnitude estimate seeing that we don't have any way to calculate anything approaching precise volumes.

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Re: Flying cars and jet-powered batwing

Postby Zamfir » Thu Oct 30, 2014 7:39 am UTC

That body weight is an example of what I mean. Such a ratio is not really an input, it's a result. You want to build a machine that can perform a certain mission, at as little weight of its own as possible. If you pick a low number from that range, you're saying 'I am sure this concept would not have weight problems'.

That's not an input, it is one of the questions you need to answer. Why do you think this could be build at low weight? Why are people who actually know about this stuff still designing helicopters, if highly loaded ducted fans can be made to work so much better? It's not like they are unaware of the possibility, or that ducted fans are new and unexplored technology. Better engines don't fix this: the other possible solutions also benefit from better engines.

Or from another angle: suppose your plan was to build a non-vtol craft. By the same argument, you would go to that list, look at the numbers, and assumes that a 40 to 45% ratio would be achievable. Now you want to add a separate VTOL capacity to that structure. Two large fans with ducts and support structure (capable of lifting the entire craft), drive trains with gear boxes, louvres, a trust vectoring system, and the extra structure needed to work around the holes. And you go to the same table, and pick the same ratio.

In others words, your numbers say that you expect to end up at the same weight as without a complete secondary lift system. Yes, if that's possible, then it's a good idea to add such VTOL capacity to aircraft.

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Re: Flying cars and jet-powered batwing

Postby Tyndmyr » Thu Oct 30, 2014 2:09 pm UTC

stoppedcaring wrote:
Tyndmyr wrote:The following is a TERRIBLE way to estimate carrying capacity.
stoppedcaring wrote:Once you subtract the weight of engines, armor, and armament, the airframes of the Apache and the A-10 both come to almost exactly 45% of the typical loaded weight, so I used 40% to account for the more compact design of our craft.


Carrying capacity is not really a flat percentage across all designs, nor is it strongly related to compactness. In fact, longer, less compact wings, are usually far more efficient, which is why cargo aircraft tend to have them. Sure, a heavier load tends to have tougher frame requirements, but this is kind of a wild oversimplification.

Eh...that wasn't an estimate of carrying capacity; that was an estimate of frame weight in comparison to typical loaded weight. The Warthog and the Apache couldn't be more different in design, but their body-weight-to-takeoff-weight ratios were literally within a single percent of each other. I've looked at various other attack aircraft, both fixed-wing and rotorcraft, and their bodies are consistently in that same 40-50% weight window. So without anything better to use, 40% seems like a reasonably good estimate for what the airframe and cockpit and rotors and skin would weigh. I can't think of any better basis for an estimate.

Stuff like carrying capacity, etc. isn't estimated as a flat percentage, but is built up from adding to that estimated airframe weight, using the lifting ability of the fans and engines as a total.


That's because they design to maximize carrying capacity. What you are doing is the equivalent of assuming that because most big businesses are profitable, your different business will also be profitable(and more so!). You're not explaining HOW it's profitable.

How matters. It's kind of essential to any engineering. I don't demand the sort of rigor on a forum that you'd need for an actual design, but...wild assumptions are not very convincing support for your claims. If your design were remarkably similar to one of those designs, you could do some back of the envelope estimates based on that, but that's not the case here. There are a number of significant differences, meaning you can no longer rely on intuitive "eh, good enough" math to get a decent estimate. You can't simply assume that your design will yield results similar to other designs. For that, you need tests, simulations, or at least a fairly detailed mechanism description detailing how and why.

wumpus wrote:Note for drones larger than a quadcopter is suitable, I would like to point out the Scorpion UAV (an early 1990s drone).


Miniature predator kits exist. Only about six foot wingspan, but that's still enough to lift a camera or what not. Got one in my workshop...that one's unfinished though. Had one of the surfaces crack in shipping, hadn't gotten 'round to patching it up.

Scale models are a fun way to test stuff, of course. There are still issues of scale, so...it's not going to be exactly the same as a full scale deal, but yeah, using a mini drone model is a solid way to learn more.

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Re: Flying cars and jet-powered batwing

Postby Zamfir » Thu Oct 30, 2014 3:17 pm UTC

I found a nice example of the problem:
The basic model F35A has an empty weight of 13,200 kg, and a take-off weight of about 32,000 kg. Gives a ratio of 41%. Right in your table.

On the other hand, the F35B is the STOVL version. It cannot take-off vertically or hover, but almost. Its empty weight has gone up to 14,700 kg, while its take-off weight has gone down to 27300 kg. For a ratio of 54%. And this might well be the best-funded effort of its kind, ever.

For a Harrier (which does have vertical take-off capability) the numbers are 6400 kg and 9400kg for a ratio of 64%. Newer airframe and engine technology could probably brings down a bit, but apparently not enough to pursue this capbility in its successor.

That still doesn't give you a number to use, as your proposal is more ambitious than the Harrier. But it's a warning how a change in concept can affect the validity of assumptions.

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Re: Flying cars and jet-powered batwing

Postby wumpus » Thu Oct 30, 2014 4:14 pm UTC

stoppedcaring wrote:
wumpus wrote:Note for drones larger than a quadcopter is suitable, I would like to point out the Scorpion UAV (an early 1990s drone).
[...]

Wow, that's cool! Not sure how well it would work for a manned system or an attack system, though; the larger you scale something up, the worse problems you have with really large moving parts. A scale model Osprey is vastly more stable than a full-size Osprey.


For a manned system: It would either require some sort of helicopter-style cockpit (the fuselage is tilted at 60 degrees during takeoff and landing) or a pretty hefty redesign splitting the propeller and cockpit. In other words, a lot more complexity.
For an attack system: If you replace the propellers with jets expect to melt your runway. With a propeller it would work delivering inexpensive ordinance, but was designed more for surveillance (they were trying to also sell it to power companies to inspect power lines).
Scaling: I'm fairly sure it will scale well for at least designs with only 1 engine. There just isn't that much that can go wrong (well, when I was there the tail was too short. Scaled composites forced the plane to launch anyway and crashed the drone). The key point seems to be the tail servo, I can imagine multiple engines vibrating themselves out of alignment with the tail & servo could conceivably causing an issue. Having the propeller at the front of the fuselage and the whole thing at 60 degrees should help the whole "burning the runway" issues that VTOL have (and scaling moves the more powerful propeller away from the tarmac).

If I were to scale such a craft up (and make something I could pilot/ride in) I'd probably double down on the "leaf in the wind" idea behind the freewing itself possibly making the left and right wings independent (assuming the thing is scaled up enough to make it an issue, or perhaps to counterbalance multiple engines), the fuselage rotating freely wrt to the propeller in at least the manned edition, and if using multiple engines allow them to rotate separately. This is would be a huge engineering effort and a good example of the reason freewing is no longer in business (even if in the end you would have a much more useful plane).

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Re: Flying cars and jet-powered batwing

Postby stoppedcaring » Thu Oct 30, 2014 6:29 pm UTC

Okay, I think I have a better understanding of some of the objections; thanks for bearing with me.

Zamfir wrote:Body weight is an example of what I mean. Such a ratio is not really an input, it's a result. You want to build a machine that can perform a certain mission, at as little weight of its own as possible.

Suppose your plan was to build a non-vtol craft. By the same argument, you would go to that list, look at the numbers, and assumes that a 40 to 45% ratio would be achievable. Now you want to add a separate VTOL capacity to that structure. Two large fans with ducts and support structure (capable of lifting the entire craft), drive trains with gear boxes, louvres, a trust vectoring system, and the extra structure needed to work around the holes. And you go to the same table, and pick the same ratio.

In others words, your numbers say that you expect to end up at the same weight as without a complete secondary lift system.

That's a good point. Trying to come up with a ballpark estimate is hard, of course, and so this seemed like a reasonable approach, but I can see why it might appear overly optimistic.

I was considering two main factors. Fixed-wing aircraft have a larger wingspan than optimal for cruise due to the need for a low takeoff speed; that's why some fighters and bombers designed for supersonic flight use variable-sweep wings. However, the Batwing is VTOL-only, eliminating the need for aerodynamic-only takeoff. Fixed-wing aircraft also typically have a long fuselage in order to accomodate the vertical and horizontal stabilizers; the flying wing approach eliminates the tail and nose entirely. All of that means added structural weight. Similarly, typical helicopters require a tail and tailrotor which add structural weight with no lifting benefit; the military helicopters I was using for comparison also had lift-neutral wing stubs.

If I was proposing a non-vtol flying wing, I would need a broader wingspan and a robust retractable landing gear system, but I would still end up taking a slightly lower percentage (probably 30-35%) due to the gains of eliminating the tail and fuselage weight. Similarly, if I was proposing a tailless helicopter, I would end up with around 35% due to savings from the tail structure. A ducted-fan VTOL flying wing incorporates the weight of the rotors as well as the weight of wings, but by eliminating the tail and the broader wingspan it should still be within the same range.

The Ryan XV-5 Vertifan had a very high empty-to-loaded ratio (54%), but this was the result of exactly what you're talking about: adding lift fans to an otherwise typical and ordinary airframe, with fuselage and T-tail and undercarriage.

I found a nice example of the problem:
The basic model F35A has an empty weight of 13,200 kg, and a take-off weight of about 32,000 kg. Gives a ratio of 41%. Right in your table.

On the other hand, the F35B is the STOVL version. It cannot take-off vertically or hover, but almost. Its empty weight has gone up to 14,700 kg, while its take-off weight has gone down to 27300 kg. For a ratio of 54%. And this might well be the best-funded effort of its kind, ever.

A good example, though I have been using a body weight that subtracted the weight of the powerplant, armor, and onboard guns, rather than the empty weight alone. I know what my engines weigh and I wanted to be able to adjust armor and guns; by removing all these, a broader comparison across aircraft designs was possible.

The P&W F135 turbofan/shaft weighs 1701 kg and the onboard GAU-22/A rotary cannon adds about 122 kg. I don't know the weight of armor, but a ballpark estimate of 300 kg is probably conservative; this means the actual body weight of the F35A is ~11,077 kg and the F35B is ~12,577 kg, for ratios of 35% and 46%.

Plus, the F-35 is designed for stealth and incorporates internal engines and internal weapon bays, which drives up body weight.

Why are people who actually know about this stuff still designing helicopters, if highly loaded ducted fans can be made to work so much better? It's not like they are unaware of the possibility, or that ducted fans are new and unexplored technology. Better engines don't fix this: the other possible solutions also benefit from better engines.

Not necessarily, or at least not as much. The static thrust equation is highly nonlinear. For a helicopter, the disc area is limited only by rotor blade strength, which allows for very large rotors and makes the power-to-weight ratio of the powerplant much less of an issue. But for a fan-in-wing design, there are very narrow constraints on disc area and so sustained hover requires a minimum power-to-weight threshold in order to be feasible. The GE3000 is the first turboshaft engine with a power-to-weight ratio and a specific fuel consumption capable of making this work.

A helicopter designer can increase static thrust by increasing disc area without significantly affecting weight; a ducted fan design requires a high power-to-weight ratio or increasing power will yield increasingly diminishing returns due to increased engine weight. The Vertifan, Harrier, and F-35B weren't designed for sustained vertical flight like a helicopter; instead, they burned a lot of fuel quickly for takeoffs and landings. The Batwing, on the other hand, is intended to burn the same amount of fuel in hover as it burns in cruise.

Tyndmyr wrote:There are a number of significant differences, meaning you can no longer rely on intuitive "eh, good enough" math to get a decent estimate. You can't simply assume that your design will yield results similar to other designs. For that, you need tests, simulations, or at least a fairly detailed mechanism description detailing how and why.


The empty-to-loaded weight estimates were never intended to assure feasibility, only to provide a framework. The end result is what needs to be assessed for feasibility, and there are a couple of ways to do this in the way you're suggesting.

One way is structural wing loading. Aerodynamic maneuverability is determined by overall wing loading, but structural integrity depends on the load on the wing minus the fan area. My estimated wing area was 20.2 m2 and the fan area is 13.26 m2, meaning the structural wing loading is 645.5 kg/m2. This is a lot higher than overall wing loading of typical fighters (simply because fighters must be maneuverable), but well within structural wing loading of wide-body airliners with wing-mounted engines.

Of course, g-force analysis is going to be much more complex than that...but as this is a ground support aircraft, not an air superiority fighter, it won't be subject to quite as much g-force. We want to be sure it can take off before worrying about gees.

Another, perhaps more rigorous approach, is to look at the pressure loading from torque on the mean aerodynamic chord of the aircraft. In order to support the weight of the aircraft in level aerodynamic flight, the wings must be strong enough to carry the full aircraft weight without bending at the point of greatest load. For the batwing and Vertifan, the point of greatest load will be the wing section containing the longitudinal diameter of the fans. For all other fixed-wing craft, the point of greatest load will be on the mean aerodynamic chord (MAC).

Since we aren't looking for an actual numerical value (e.g. for comparison to tensile strength or bending moment of some material) but just comparative ratios, I'll simply plot the static torque (wing load times wingspan outside of aerodynamic center in kg*m) to the estimated MAC length (in m).

Grabbing a range of aircraft...

Image

It looks like the loading on the Batwing at the highest-stress point would be well within the normal range. These are a couple of pretty powerful engines and the fans are large enough to produce a tremendous amount of thrust, so even if a little more weight needs to go into strengthening the airframe, I don't see it posing a problem.

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Re: Flying cars and jet-powered batwing

Postby stoppedcaring » Fri Oct 31, 2014 10:15 pm UTC

Here's a more typical 3-view mockup. I added an inverted V-tail which can be pulled up to augment as flaps for ground effect assist. I'm thinking control would be bleed-air only, but I suppose control surfaces might be necessary.

Image

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Re: Flying cars and jet-powered batwing

Postby Tyndmyr » Mon Nov 03, 2014 10:27 pm UTC

stoppedcaring wrote:I was considering two main factors. Fixed-wing aircraft have a larger wingspan than optimal for cruise due to the need for a low takeoff speed; that's why some fighters and bombers designed for supersonic flight use variable-sweep wings. However, the Batwing is VTOL-only, eliminating the need for aerodynamic-only takeoff. Fixed-wing aircraft also typically have a long fuselage in order to accomodate the vertical and horizontal stabilizers; the flying wing approach eliminates the tail and nose entirely. All of that means added structural weight. Similarly, typical helicopters require a tail and tailrotor which add structural weight with no lifting benefit; the military helicopters I was using for comparison also had lift-neutral wing stubs.


Your prioritization of problems seems off. For one thing, long wings result in great aspect ratios, which means better fuel efficiency if induced drag is a big concern. Wing length is mostly limited by structural considerations, not because short winged aircraft are inherently always more efficient. Worse efficiency necessitates carrying more fuel, etc. So, it is not reasonable to assume that you will necessarily have less weight due to your design...you need to get into the details to determine if you can save weight.

Long fuselages, likewise, are not inherently bad. For a given enclosed volume, long tubes are usually pretty efficient for reducing resistance, thus the shape of just about every rocket ever. And of course, you're still going to need control surfaces. Flying wing designs tend to be inherently less stable, requiring rapid computer controlled adjustments for flight. The additional(likely at least three redundant sets of) flight computers of course take up space/weight. In fact, it's VERY easy to eat space/weight on airframes, and even professionally made designs often end up growing and becoming heavier throughout the development process.

If I was proposing a non-vtol flying wing, I would need a broader wingspan and a robust retractable landing gear system, but I would still end up taking a slightly lower percentage (probably 30-35%) due to the gains of eliminating the tail and fuselage weight.


You generally are going to want a robust retractable landing gear system regardless. Non-retractable gear is usually hella inefficient on aircraft with any speed.

Similarly, if I was proposing a tailless helicopter, I would end up with around 35% due to savings from the tail structure. A ducted-fan VTOL flying wing incorporates the weight of the rotors as well as the weight of wings, but by eliminating the tail and the broader wingspan it should still be within the same range.




The Ryan XV-5 Vertifan had a very high empty-to-loaded ratio (54%), but this was the result of exactly what you're talking about: adding lift fans to an otherwise typical and ordinary airframe, with fuselage and T-tail and undercarriage.

The P&W F135 turbofan/shaft weighs 1701 kg and the onboard GAU-22/A rotary cannon adds about 122 kg. I don't know the weight of armor, but a ballpark estimate of 300 kg is probably conservative; this means the actual body weight of the F35A is ~11,077 kg and the F35B is ~12,577 kg, for ratios of 35% and 46%.


I don't know what the F-35 carries, but the F-22 had rubbish, and the F-35 was the follow-on air superiority/multirole design. Assuming much armor at ALL is sketchy. Armor may also vary between the different models(certainly many other factors do). It might have that much armor, it might not. Hell, it might change still. Nearly every airframe undergoes quite a lot of change, and the F-35 is still quite young. Certainly we have seen a trend away from armor, and the A-10 was something of an outlier on the side of having a lot. It's pretty much a cinch that it'll have less armor than that.

Tyndmyr wrote:There are a number of significant differences, meaning you can no longer rely on intuitive "eh, good enough" math to get a decent estimate. You can't simply assume that your design will yield results similar to other designs. For that, you need tests, simulations, or at least a fairly detailed mechanism description detailing how and why.


The empty-to-loaded weight estimates were never intended to assure feasibility, only to provide a framework. The end result is what needs to be assessed for feasibility, and there are a couple of ways to do this in the way you're suggesting.


Estimates are fine. I do not quarrel with the idea of estimating, but the manner in which it was done. You can round off insignificant digits, etc for ease of rapid calculation, etc(so long as you're aware of the added uncertainty in design), but you should be estimating based on the mechanism you plan to actually use, not by comparison to things you believe to be inferior without having done the math to demonstrate that.

One way is structural wing loading. Aerodynamic maneuverability is determined by overall wing loading, but structural integrity depends on the load on the wing minus the fan area. My estimated wing area was 20.2 m2 and the fan area is 13.26 m2, meaning the structural wing loading is 645.5 kg/m2. This is a lot higher than overall wing loading of typical fighters (simply because fighters must be maneuverable), but well within structural wing loading of wide-body airliners with wing-mounted engines.


Combat aircraft do not generally strive to have the maneuverability of a wide-body airliner. This is true of ground support roles as well as air superiority roles.

It looks like the loading on the Batwing at the highest-stress point would be well within the normal range. These are a couple of pretty powerful engines and the fans are large enough to produce a tremendous amount of thrust, so even if a little more weight needs to go into strengthening the airframe, I don't see it posing a problem.
[/quote]

Slapping big engines on a design does not make that design good.

I also suspect that with small wings, high wing loading, heavy reliance on active lift and so forth, a failure of one engine would result in a very swift death for everyone on board. Helicopters at least have autorotation, and most aircraft have a decent glide path and some degree of stability even with one or more engines out. This seems like it'd be as aerodynamic as a brick when you lose power.
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Re: Flying cars and jet-powered batwing

Postby stoppedcaring » Mon Nov 03, 2014 11:14 pm UTC

Tyndmyr wrote:...it is not reasonable to assume that you will necessarily have less weight due to your design...you need to get into the details to determine if you can save weight.

Long fuselages, likewise, are not inherently bad. For a given enclosed volume, long tubes are usually pretty efficient for reducing resistance, thus the shape of just about every rocket ever.

I think some of your quoting got mixed up in there. :)

Yeah, I would definitely need to go more in-depth into aeronautical engineering, or run this by an AE friend of mine, before claiming certainty about any of this. But I figured that the overall picture should be enough to see if there were any major challenges or issues or failure modes that would need to be addressed. Given everyone's fairly broad scientific acuity here.

Flying wing designs tend to be inherently less stable, requiring rapid computer controlled adjustments for flight. The additional(likely at least three redundant sets of) flight computers of course take up space/weight.

Well, the B-2 Spirit first flew in 1989. Nineteen eighty nine. Computer systems have come a LONG way in terms of miniaturization in the last quarter-century. Besides, this wouldn't be completely flying-wing; it does have an inverted V-tail as shown in the revised mockups above.

If I was proposing a non-vtol flying wing, I would need a broader wingspan and a robust retractable landing gear system, but I would still end up taking a slightly lower percentage (probably 30-35%) due to the gains of eliminating the tail and fuselage weight.


You generally are going to want a robust retractable landing gear system regardless. Non-retractable gear is usually hella inefficient on aircraft with any speed.

The keyword was not retractable, but robust. This aircraft is intended for vertical ground-effect takeoff and landing; the landing gear would be only for emergencies and so it doesn't need to be able to take hundreds of harsh landings.

Similarly, if I was proposing a tailless helicopter, I would end up with around 35% due to savings from the tail structure. A ducted-fan VTOL flying wing incorporates the weight of the rotors as well as the weight of wings, but by eliminating the tail and the broader wingspan it should still be within the same range.

The Ryan XV-5 Vertifan had a very high empty-to-loaded ratio (54%), but this was the result of exactly what you're talking about: adding lift fans to an otherwise typical and ordinary airframe, with fuselage and T-tail and undercarriage.

The P&W F135 turbofan/shaft weighs 1701 kg and the onboard GAU-22/A rotary cannon adds about 122 kg. I don't know the weight of armor, but a ballpark estimate of 300 kg is probably conservative; this means the actual body weight of the F35A is ~11,077 kg and the F35B is ~12,577 kg, for ratios of 35% and 46%.

I don't know what the F-35 carries, but the F-22 had rubbish, and the F-35 was the follow-on air superiority/multirole design. Assuming much armor at ALL is sketchy. Armor may also vary between the different models(certainly many other factors do). It might have that much armor, it might not. Hell, it might change still. Nearly every airframe undergoes quite a lot of change, and the F-35 is still quite young. Certainly we have seen a trend away from armor, and the A-10 was something of an outlier on the side of having a lot. It's pretty much a cinch that it'll have less armor than that.

Yeah, it was really hard to find much on the F-35's armor; I think that's probably still classified. But even if we say no armor at all, that's just 36% and 47%, so I don't think it matters.

One way is structural wing loading. Aerodynamic maneuverability is determined by overall wing loading, but structural integrity depends on the load on the wing minus the fan area. My estimated wing area was 20.2 m2 and the fan area is 13.26 m2, meaning the structural wing loading is 645.5 kg/m2. This is a lot higher than overall wing loading of typical fighters (simply because fighters must be maneuverable), but well within structural wing loading of wide-body airliners with wing-mounted engines.

Combat aircraft do not generally strive to have the maneuverability of a wide-body airliner. This is true of ground support roles as well as air superiority roles.

Fair enough. The cross-sectional strength is probably a better approach.

It looks like the loading on the Batwing at the highest-stress point would be well within the normal range. These are a couple of pretty powerful engines and the fans are large enough to produce a tremendous amount of thrust, so even if a little more weight needs to go into strengthening the airframe, I don't see it posing a problem.

Slapping big engines on a design does not make that design good.

I also suspect that with small wings, high wing loading, heavy reliance on active lift and so forth, a failure of one engine would result in a very swift death for everyone on board.

If you look back at some of the early discussion (or even if you don't), the goal was to have single-engine hover capacity. With both engines running, it's designed to cruise and hover at 45% from each, meaning that a single engine at 90% can also hover/cruise. Now, if both engines go out...yeah, that's probably a problem. Not the best glide ratio (though limited autorotation from the dual rotors might supplement your glide ratio enough to make it feasible). You better hope you have a nice level landing area and plenty of forward airspeed or that ejection handle is going to look awfully tempting.

(Edited to fix quote problems...sorry)
Last edited by stoppedcaring on Tue Nov 04, 2014 4:26 pm UTC, edited 1 time in total.

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Re: Flying cars and jet-powered batwing

Postby wumpus » Tue Nov 04, 2014 3:30 pm UTC

While I've heard you can make a brick fly with sufficient thrust, is it really necessary to propose such a craft with two separate engines with at least 111% thrust to weight ratio (after any losses due to angling the thrust >45 degrees), plus two additional "main engines" with [presumably] considerable thrust? Whatever happened to using lift, anyway? And do you really want to balance on a single [off center] thruster? I understand space-x took multiple careful tries to land an unmanned [balanced, on center] rocket with a [more or less] single thruster (and still has yet to land with the intent to reuse the craft), but this sounds like adding complexity for sake of complexity.

If you haven't tried it, I would also like to recommend the game Kerbal Space Program. Great fun for all your mad science designs (warning: part of this is due to primitive physics calculations. All absurdities are not expected to work once physics correcting mods are added). On the other hand, there is a reason that Randal Monroe mentions that "it worked in KSP" is a career limiting utterance at NASA.

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Re: Flying cars and jet-powered batwing

Postby stoppedcaring » Tue Nov 04, 2014 6:13 pm UTC

wumpus wrote:While I've heard you can make a brick fly with sufficient thrust, is it really necessary to propose such a craft with two separate engines with at least 111% thrust to weight ratio (after any losses due to angling the thrust >45 degrees), plus two additional "main engines" with [presumably] considerable thrust? Whatever happened to using lift, anyway?

No, no, it's not four separate engines. It has two compact GE3000-type turbofan engines for ordinary thrust in normal forward aerodynamic flight. Together they can produce up to 4900 pounds of thrust. This means a turbofan thrust-to-weight ratio of around 0.5, giving it a forward acceleration of half a gee. The estimated stall speed is 91 mph; above that, the craft flies solely on aerodynamic lift with no vertical thrust needed.

However, the turbofans can be selectively used as turboshafts, delivering up to 4,474 kW of mechanical power to the ducted fans in the wings. Because the ducted fans have a significantly larger area, they use that mechanical power to produce much more thrust: at 90% efficiency two 6.63 m2 ducted fans can turn 4.47 MW of mechanical power into nearly 18,000 pounds of thrust, allowing hover at only 45% power. At full throttle, vertical acceleration is nearly twice as high as an Apache. And because the thrust is produced using ducted fans, not jet exhaust, the downwash is not superheated as with existing VTOL jets. That's how it takes off vertically.

And do you really want to balance on a single [off center] thruster? I understand space-x took multiple careful tries to land an unmanned [balanced, on center] rocket with a [more or less] single thruster (and still has yet to land with the intent to reuse the craft), but this sounds like adding complexity for sake of complexity.

Both lift fans will operate in tandem no matter what. Coupled turboshafts run in parallel, so if you lose one engine, your remaining engine will still run both of the lift fans. Nothing is off-center. Of course, forward thrust will be a little off-balance, but that's nothing new for aircraft; just adjust trim and you'll be fine.

If this is confusing, here's a visual of how the operation modes work:
Spoiler:
Image

The blue circles are my kitschy way of denoting downward thrust from the ducted fans. Downward thrust is blue because it is regular air, not superheated exhaust. Single-engine operation is shown in red (as opposed to dual-engine operation in pink) because the single engine must operate at a higher power percentage to produce the same performance.

Turbine engines are designed for an optimal power output; above or below that level their fuel efficiency suffers somewhat. For these engines, optimal power would likely be tuned to around 45% so that cruise and hover would both be optimized for best fuel efficiency/endurance. Running on a single engine would require prolonged operation outside of the optimal range, reducing fuel efficiency, so you'd only want to fly this way if one engine crapped out.

The design concept was to have a plane that could hover with the same fuel consumption as in cruising flight, rather than having to go full throttle in order to barely get off the ground (e.g. Harrier/F-35/Osprey). Helicopters are great for hovering with low fuel consumption but lack forward cruise speed.

If you haven't tried it, I would also like to recommend the game Kerbal Space Program. Great fun for all your mad science designs (warning: part of this is due to primitive physics calculations. All absurdities are not expected to work once physics correcting mods are added). On the other hand, there is a reason that Randal Monroe mentions that "it worked in KSP" is a career limiting utterance at NASA.

I'll have to give it a shot if I get a chance.

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Re: Flying cars and jet-powered batwing

Postby Tyndmyr » Tue Nov 04, 2014 7:13 pm UTC

You don't think that having unpowered fans in the wings will affect lift/handling in level flight?

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Re: Flying cars and jet-powered batwing

Postby stoppedcaring » Tue Nov 04, 2014 8:11 pm UTC

Tyndmyr wrote:You don't think that having unpowered fans in the wings will affect lift/handling in level flight?

Not with the control louvers closed, no. The louvers will certainly increase induced drag during transition, but that's to be expected. Once transition is complete and they are closed, the fans are aerodynamically invisible.

In hovering flight, angling the louvers backward or forward will adjust pitch while producing forward or backward motion, shifting more power to one side than the other will induce roll with strafing movment, and angling the louvers in contrary directions will control yaw in place. Louvers can also be used as air brakes and the fans themselves can be activated to perform otherwise-impossible maneuvers in level flight. A lot of that would be computer-controlled, though.

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Re: Flying cars and jet-powered batwing

Postby wumpus » Tue Nov 04, 2014 9:18 pm UTC

Ok, while it still looks like an infinite sink of R&D funds (requiring entirely new technologies needed simply to make the explicitly require entire new technologies to work), it might be a bit more sane.

I'm curious if anyone has done much in the way of pulling power from [jet]turbines like that? Do you put the clutches in the ~50krpm sections or after gear reduction (the high speed clutch sounds like a nightmare, but always powering the gear reduction would kill efficiency). The thing that combines the two turbine outputs appears to be essentially the same as a car differential, but I have my doubts about combining engines with such a thing (and what does it do to your poor clutch and/or gear reduction) and can it operate (if necessary) at high rpm.

In the end, I can't imagine the R&D budget just to get the cool batwing effect. You might be 30 years too late, I'm sure there were plenty of generals in the Reagan era who would have swooned over a batwing and coughed up the billions.

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Re: Flying cars and jet-powered batwing

Postby Tyndmyr » Tue Nov 04, 2014 9:25 pm UTC

The Osprey has such an engine linkage, but it's not using jets. This DOES introduce a single point of failure if the linkage system jams, but at least the Osprey sort of has an unpowered glide path. I do not know if a similar system can be adapted to work for turbines, or what potential tradeoffs we're looking at for that. I suspect that this system will need to be fairly complex, especially if it needs to be able to run the whole aircraft if an engine goes out, as you then have to deal with very assymetric forces.

As for the landing gear...VTOL aircraft traditionally still have very similar landing gear to normal aircraft. If you're positing a significant weight savings there, you might want to look at say, Harrier landing gear or what not. A reduction in reliability is the kind of significant tradeoff that is available on many aircraft, but it's not usually considered worth pursuing.

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Re: Flying cars and jet-powered batwing

Postby wumpus » Tue Nov 04, 2014 10:54 pm UTC

stoppedcaring wrote:
Tyndmyr wrote:You don't think that having unpowered fans in the wings will affect lift/handling in level flight?

Not with the control louvers closed, no. The louvers will certainly increase induced drag during transition, but that's to be expected. Once transition is complete and they are closed, the fans are aerodynamically invisible.
...


I guess with the extra width needed for all that fan complexity, it should still be easy to wrap the fuel around the fans. It might take some sort of fuel cell* to keep the center of mass in the same place, but this plane is nothing but extra complexity. I still have to wonder if there is any room for anything else (mostly weapons. Passengers and cargo never seemed to be part of the design. Are all the missiles/shells alighned with the center of mass, or does it have to deal with a CoM change during flight?

* fuel cells are what mechanics call gas tanks on cars modified for racing, no relation to the electrical concept that resembles fuel-powered batteries. The simplest method of conversion is to stuff sponges into the thing, but the idea is to make something that works under high G-force and less prone to leakage. Are they used in aircraft as well? It would certainly help to pull from both wings while banking.

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Re: Flying cars and jet-powered batwing

Postby stoppedcaring » Tue Nov 04, 2014 11:02 pm UTC

wumpus wrote:Ok, while it still looks like an infinite sink of R&D funds (requiring entirely new technologies needed simply to make the explicitly require entire new technologies to work), it might be a bit more sane.

Well, "a bit more sane" is definitely a step in the right direction! :lol:

There would certainly be a significant R&D load in making this craft function, but I'm not so sure all these technologies are entirely new. None of them are, really. The GE3000 engine is in testing. Ducted fans are used in many applications and fan-in-wing designs have been tested in the Vertifan as well as other concepts. The challenge is putting it all together, combining experience from both rotorcraft technology and fixed-wing aircraft.

I'm curious if anyone has done much in the way of pulling power from [jet]turbines like that? Do you put the clutches in the ~50krpm sections or after gear reduction (the high speed clutch sounds like a nightmare, but always powering the gear reduction would kill efficiency). The thing that combines the two turbine outputs appears to be essentially the same as a car differential, but I have my doubts about combining engines with such a thing (and what does it do to your poor clutch and/or gear reduction) and can it operate (if necessary) at high rpm.

There are three basic ways to go about it. A shuttered-exhaust pneumatic drive is perhaps the easiest way of doing it; the Vertifan diverted the entire exhaust stream from the jet engine wash into the housing of the three fans:
Spoiler:
Image
This is similar to using bleed air like the stabilization jets on the Harrier. Another option is a hydraulic design, using the turbines to pressurize a fluid loop that drives the fans. The third option is to use a shaft assembly like you're talking about; that's what the F-35B does.

We've been pulling mechanical power off of jet turbines for years; that's what a turboprop or turboshaft does. The issue here, admittedly, is the need for a variable-speed fan; turboprops are designed to operate at a single speed while adjusting pitch to change thrust. The ideal system would probably be gear reductions off each turbofan (like a typical turboprop) linked into a single power-bearing axle running down the length of the vehicle, with the fans themselves being driven off the end of the axle using hydraulics. This combines the mechanical reliability of a gear-reduction and axle with the lossless variability of a hydraulic drive, without the frictional costs and failure modes of a long hydraulic system. If necessary, the gear reductions themselves could be direct-exhaust-driven. In any case, turboprops, propfans, and turboshafts are some of the most well-developed and well-researched modern technological systems around, so this would probably be fairly easy to solve.

In the end, I can't imagine the R&D budget just to get the cool batwing effect. You might be 30 years too late, I'm sure there were plenty of generals in the Reagan era who would have swooned over a batwing and coughed up the billions.

The specific batwing-type appearance isn't entirely necessary, of course. But the goal is to fit a growing need in the military: manned counter-insurgency close air support. Air superiority fighters and super-range heavy bombers are great and all, but they are most needed against another superpower, and despite current dour relations with Russia that's just not going to happen any time soon. Meanwhile, most current conflicts remain asymmetric, and the need for close air support and counter-insurgency aircraft burgeons. The batwing design (whether it looks like Batman's vehicle or no) promises the ability to outrun, outmaneuver, outfight, and outfly any helicopter while exceeding the ground support performance and endurance of a helicopter. You don't often hear of helicopters shooting down jets.

A very similar design was proposed not too long ago by Lockheed-Martin in the VARIOUS UAV. It's a VTOL drone with the same fan-in-wing design pioneered in the Ryan X-V Vertifan, but it is envisioned more for naval UAV roles. Its smaller wing area means smaller lift fans, making it unable to hover for extended periods of time like the batwing.

Tyndmyr wrote:The Osprey has such an engine linkage, but it's not using jets. This DOES introduce a single point of failure if the linkage system jams, but at least the Osprey sort of has an unpowered glide path. I do not know if a similar system can be adapted to work for turbines, or what potential tradeoffs we're looking at for that. I suspect that this system will need to be fairly complex, especially if it needs to be able to run the whole aircraft if an engine goes out, as you then have to deal with very assymetric forces.

The Osprey uses an axle that runs across the entire wing so that one turboprop can run the other propeller if its engine fails, but yeah, the linkage system is vulnerable.

This system wouldn't be terribly complex because there would only be a single driveshaft or drivesystem connecting both engines to the pair of fans. The fan control system doesn't care how many engines are delivering power to the drive system, and the engine linkages don't care what the fans are doing with the power they deliver. Assuming ground-effect operation is possible, functioning on one engine would be commonplace.

As for the landing gear...VTOL aircraft traditionally still have very similar landing gear to normal aircraft. If you're positing a significant weight savings there, you might want to look at say, Harrier landing gear or what not. A reduction in reliability is the kind of significant tradeoff that is available on many aircraft, but it's not usually considered worth pursuing.

Even a Harrier was still designed for horizontal takeoff and landing whenever possible. This would be more like helicopter landing gear: only used in emergencies or for light taxiing, not intended for regular repeated landings at speed.

wumpus wrote:
stoppedcaring wrote:
Tyndmyr wrote:You don't think that having unpowered fans in the wings will affect lift/handling in level flight?

Not with the control louvers closed, no. The louvers will certainly increase induced drag during transition, but that's to be expected. Once transition is complete and they are closed, the fans are aerodynamically invisible.
...


I guess with the extra width needed for all that fan complexity, it should still be easy to wrap the fuel around the fans. It might take some sort of fuel cell* to keep the center of mass in the same place, but this plane is nothing but extra complexity. I still have to wonder if there is any room for anything else (mostly weapons. Passengers and cargo never seemed to be part of the design. Are all the missiles/shells alighned with the center of mass, or does it have to deal with a CoM change during flight?

* fuel cells are what mechanics call gas tanks on cars modified for racing, no relation to the electrical concept that resembles fuel-powered batteries. The simplest method of conversion is to stuff sponges into the thing, but the idea is to make something that works under high G-force and less prone to leakage. Are they used in aircraft as well? It would certainly help to pull from both wings while banking.

Helicopter and attack aircraft tanks already use self-sealing foam-embedded cell tanks in order to prevent leaks or ruptures or explosions if they are hit by gunfire. I'm not sure exactly how it all works, but I know it does.

As I've pointed out in the overall specs, the engines are large enough that space is going to limit what you can carry before weight will. As shown in the mockups here, the cockpit is slung under the front of the craft. There would be a bay immediately behind the cockpit for internal carry and I'm guessing there would be a few hardpoints, either on the outside of the wings or underneath, though the placement of the fans does limit hardpoint capacity. There could also be hardpoints on the sides of the cockpit just behind the windows.

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Re: Flying cars and jet-powered batwing

Postby Tyndmyr » Wed Nov 05, 2014 7:50 pm UTC

stoppedcaring wrote:The specific batwing-type appearance isn't entirely necessary, of course. But the goal is to fit a growing need in the military: manned counter-insurgency close air support. Air superiority fighters and super-range heavy bombers are great and all, but they are most needed against another superpower, and despite current dour relations with Russia that's just not going to happen any time soon. Meanwhile, most current conflicts remain asymmetric, and the need for close air support and counter-insurgency aircraft burgeons. The batwing design (whether it looks like Batman's vehicle or no) promises the ability to outrun, outmaneuver, outfight, and outfly any helicopter while exceeding the ground support performance and endurance of a helicopter. You don't often hear of helicopters shooting down jets.


I dare say we already have a more practical solution to asymmetric air power, and it's called drones.

Also, hard points at wingtips almost invariably have MUCH lower carrying capacity. Your fans take up the prime hardpoint real estate. Additionally, the support issues introduced by fan placement make wingtip hardpoints a particularly problematic choice for you.

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Re: Flying cars and jet-powered batwing

Postby slinches » Thu Nov 06, 2014 2:52 am UTC

I guess I'll start off by saying that I am an aeronautical engineer (caveat: I haven't done any preliminary aircraft design since my senior project).

Unfortunately, I don't have the time to invest right now to actually go through the design trade-offs to see whether any of what you're saying makes sense. Although, I can tell you that you'll have a hard time using the GE3000 to produce forward thrust since a standard turbofan modulates thrust by changing fan speed and that is a single speed turboshaft engine. You'd likely need to hook it up to a separate pair of propellers, ducted fans or propfans that can control thrust with blade pitch. That's a lot of added complexity (read: cost) on top of already hideously expensive engines.

The other things I can comment on at a glance are that stability and transition to forward flight will be major problems. As it's drawn, the center of mass looks to be very near the center lift for the fans which means you'll have to add extra control jets (huge reduction in efficiency) to have any pitch control in VTOL mode. The issue with transitioning to forward flight will be dealing with the airflow distortion into the fans while they're still needed for lift. Ducted fans (especially highly loaded ones) are prone to stall with high angles of attack at the inlet.

I'll try to find some time to take a better look at what you have later on. It does seem like you've put quite a lot of effort into figuring this out. I know I have a couple of good books I can point you to for doing your sizing studies, at least.

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Re: Flying cars and jet-powered batwing

Postby Zamfir » Thu Nov 06, 2014 3:28 pm UTC

More related to the original topic: Ive got a job interview coming up with a flying car company

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Re: Flying cars and jet-powered batwing

Postby slinches » Thu Nov 06, 2014 4:37 pm UTC

Neat. Is it Pal-V?

A drivable autogyro does seem like one of the more plausible options for a flying car.

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Re: Flying cars and jet-powered batwing

Postby stoppedcaring » Thu Nov 06, 2014 5:01 pm UTC

Zamfir wrote:More related to the original topic: Ive got a job interview coming up with a flying car company

Seriously? Dude, that's awesome. Which company? Or can you say?

Tyndmyr wrote:
stoppedcaring wrote:The specific batwing-type appearance isn't entirely necessary, of course. But the goal is to fit a growing need in the military: manned counter-insurgency close air support. Air superiority fighters and super-range heavy bombers are great and all, but they are most needed against another superpower, and despite current dour relations with Russia that's just not going to happen any time soon. Meanwhile, most current conflicts remain asymmetric, and the need for close air support and counter-insurgency aircraft burgeons. The batwing design (whether it looks like Batman's vehicle or no) promises the ability to outrun, outmaneuver, outfight, and outfly any helicopter while exceeding the ground support performance and endurance of a helicopter. You don't often hear of helicopters shooting down jets.

I dare say we already have a more practical solution to asymmetric air power, and it's called drones.

Drones are great for precision strikes, but they don't serve terribly well in a gunship role. Air support is more than just dropping shells or rockets on a target; helicopters can loiter alongside a ground team and provide covering fire and precision strikes in real-time. High-flying loiter drones in the skies above might be able to deliver a strike in 90 seconds; an Apache hovering a few dozen yards away can deliver the same strike in 9 seconds. Also, some helis can also airlift out wounded men, drop off additional supplies, and so forth; the modest cargo bay in the batwing would be just large enough for this.

Hard points at wingtips almost invariably have MUCH lower carrying capacity. Your fans take up the prime hardpoint real estate. Additionally, the support issues introduced by fan placement make wingtip hardpoints a particularly problematic choice for you.

Yeah, you're right. Wingtips might be limited to autocannons with one medium-load hardpoint under each wing just outside the fan; the rest of the hardpoints would have to be on the sides of the cabin/belly. It might be possible to mount an additional missile hardpoint between the engines but I'm not sure how well that would work. Capacity is probably going to be a small bomb/cargo bay plus 4 heavy hardpoints plus 2-3 light hardpoints.

If a mission REALLY required a lot of hardpoint space, it might be feasible to temporarily mount wingstubs on the sides/undersides of the cabin (since it doesn't touch the ground) at the expense of reduced performance.

slinches wrote:I guess I'll start off by saying that I am an aeronautical engineer (caveat: I haven't done any preliminary aircraft design since my senior project).

Unfortunately, I don't have the time to invest right now to actually go through the design trade-offs to see whether any of what you're saying makes sense. Although, I can tell you that you'll have a hard time using the GE3000 to produce forward thrust since a standard turbofan modulates thrust by changing fan speed and that is a single speed turboshaft engine. You'd likely need to hook it up to a separate pair of propellers, ducted fans or propfans that can control thrust with blade pitch. That's a lot of added complexity (read: cost) on top of already hideously expensive engines.

Thanks for commenting -- I appreciate all the expertise I can get, haha. I have a pretty solid math/physics/research background but the engineering stuff is self-taught so I know I'm out of my league here.

As far as the engine is concerned, yeah, I don't think we could just drop in a pair of stock GE3000s at all. It would have to be designed as a combination turboshaft-turbofan (or, as you suggest, a combination turboshaft-propfan). On that note, since you're the AE here, are variable-pitch ducted fans a thing at all, or are ducted fans all invariably fixed-pitch? Variable-pitch fans would really add a lot of stability, simplicity, and reliability.

The other things I can comment on at a glance are that stability and transition to forward flight will be major problems. As it's drawn, the center of mass looks to be very near the center lift for the fans which means you'll have to add extra control jets (huge reduction in efficiency) to have any pitch control in VTOL mode. The issue with transitioning to forward flight will be dealing with the airflow distortion into the fans while they're still needed for lift. Ducted fans (especially highly loaded ones) are prone to stall with high angles of attack at the inlet.

I wonder if there would be a way to control stationary pitch by adjusting the louvers properly. If it was possible to set different parts of the louver assembly to different angles, that might shift pitch without inducing forward or backward translational movement:
Spoiler:
Image
But I don't know whether that would work the way I'm envisioning it.

So airflow over the top of a ducted fan (parallel to its plane of rotation) can cause stall? Hmm, that's definitely a problem to consider. The computer control of that whole transition is going to be pretty complex.

I'll try to find some time to take a better look at what you have later on. It does seem like you've put quite a lot of effort into figuring this out. I know I have a couple of good books I can point you to for doing your sizing studies, at least.

Thanks, I look forward to whatever considerations you (and everyone else here) can provide.

slinches wrote:Neat. Is it Pal-V?

A drivable autogyro does seem like one of the more plausible options for a flying car.

A drivable autogyro with folding rotors and computer-controlled autopilot-heli-mode for VTOL is promising.

Rotors that fold and clamp to the sides of the vehicle, a ducted pusher fan that folds out into a makeshift tailrotor during heli-mode takeoff. It could work. Another option would be compressed-air tipjets, though this is noisier.

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Re: Flying cars and jet-powered batwing

Postby slinches » Thu Nov 06, 2014 8:02 pm UTC

stoppedcaring wrote:On that note, since you're the AE here, are variable-pitch ducted fans a thing at all, or are ducted fans all invariably fixed-pitch? Variable-pitch fans would really add a lot of stability, simplicity, and reliability.

Variable pitch ducted fans do exist, but aren't very common. The best example I can think of right now would be shrouded tail rotors on some of the newer helicopters.

I wonder if there would be a way to control stationary pitch by adjusting the louvers properly. If it was possible to set different parts of the louver assembly to different angles, that might shift pitch without inducing forward or backward translational movement:
Spoiler:
Image
But I don't know whether that would work the way I'm envisioning it.

Thrust vectoring can work as a control mechanism, but in this case it wouldn't be effective in pitch control (yaw would be okay). There likely isn't a long enough moment arm between the fan center of lift and CG. It's sort of like trying to balance a stick on end. As the stick gets shorter, quicker and larger vectoring control changes are needed to maintain stability. Current state of the art in this area is VTOL rockets, which are fairly stable by comparison.

Alternatively, you could move the wings up above the CG, closer to the configuration of a helicopter. That way it would be inherently stable.

A drivable autogyro with folding rotors and computer-controlled autopilot-heli-mode for VTOL is promising.

Rotors that fold and clamp to the sides of the vehicle, a ducted pusher fan that folds out into a makeshift tailrotor during heli-mode takeoff. It could work. Another option would be compressed-air tipjets, though this is noisier.

I think they'd likely just target short takeoff and landing rather than true vertical lift. For a private/commercial aircraft it's probably not worth the added complexity to fully power the main rotor, but a small electric motor (possibly the same one that operates the folding mechanisms) could be used to help spin up the main rotor and shorten the takeoff roll.

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Re: Flying cars and jet-powered batwing

Postby stoppedcaring » Thu Nov 06, 2014 9:14 pm UTC

slinches wrote:
stoppedcaring wrote:On that note, since you're the AE here, are variable-pitch ducted fans a thing at all, or are ducted fans all invariably fixed-pitch? Variable-pitch fans would really add a lot of stability, simplicity, and reliability.

Variable pitch ducted fans do exist, but aren't very common. The best example I can think of right now would be shrouded tail rotors on some of the newer helicopters.

Yeah, the line between ducted fan and shrouded rotor is awfully thin. I'm guessing that getting into variable-pitch tends to decrease your maximum design efficiency.

This is just complete spitballing, but I wonder if two stacked blisks (of equal or different blade counts) could be designed to create an effective-variable-pitch system by changing their clock position relative to each other. E.g., when the blade edges are closely aligned, they exert less force on the airflow; when they are offset, they exert greater force:
Image
I don't know if that would produce the equivalent effect of a variable-pitch prop or if it would just hurt efficiency.

I wonder if there would be a way to control stationary pitch by adjusting the louvers properly. If it was possible to set different parts of the louver assembly to different angles, that might shift pitch without inducing forward or backward translational movement:
Spoiler:
Image
But I don't know whether that would work the way I'm envisioning it.

Thrust vectoring can work as a control mechanism, but in this case it wouldn't be effective in pitch control (yaw would be okay). There likely isn't a long enough moment arm between the fan center of lift and CG. It's sort of like trying to balance a stick on end. As the stick gets shorter, quicker and larger vectoring control changes are needed to maintain stability. Current state of the art in this area is VTOL rockets, which are fairly stable by comparison.

Alternatively, you could move the wings up above the CG, closer to the configuration of a helicopter. That way it would be inherently stable.

Oh, you mean the vertical center of gravity? The ducted fans are certainly positioned at the longitudinal center of gravity -- they have to be -- but the vertical center of gravity is probably going to be a good deal lower.

A drivable autogyro with folding rotors and computer-controlled autopilot-heli-mode for VTOL is promising.

Rotors that fold and clamp to the sides of the vehicle, a ducted pusher fan that folds out into a makeshift tailrotor during heli-mode takeoff. It could work. Another option would be compressed-air tipjets, though this is noisier.

I think they'd likely just target short takeoff and landing rather than true vertical lift. For a private/commercial aircraft it's probably not worth the added complexity to fully power the main rotor, but a small electric motor (possibly the same one that operates the folding mechanisms) could be used to help spin up the main rotor and shorten the takeoff roll.

Without VTOL, flying cars can never be used for short hops within a city; you have to go to and from an airfield every time you want to fly.

What about those compressed-air tipjets? If the engine had to store up energy for vertical flight in a tank, I mean.

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Re: Flying cars and jet-powered batwing

Postby slinches » Fri Nov 07, 2014 4:54 am UTC

stoppedcaring wrote:This is just complete spitballing, but I wonder if two stacked blisks (of equal or different blade counts) could be designed to create an effective-variable-pitch system by changing their clock position relative to each other. E.g., when the blade edges are closely aligned, they exert less force on the airflow; when they are offset, they exert greater force:
Spoiler:
Image

I don't know if that would produce the equivalent effect of a variable-pitch prop or if it would just hurt efficiency.

You could design a variable effective camber rotor that way, but I doubt it would be very efficient. You're probably better off with a static variable guide vane, if that is even worth the added weight.
Oh, you mean the vertical center of gravity? The ducted fans are certainly positioned at the longitudinal center of gravity -- they have to be -- but the vertical center of gravity is probably going to be a good deal lower.

How so? It appears that both the bulk of the fuselage and the engines are above the lift fans in your drawings.

Without VTOL, flying cars can never be used for short hops within a city; you have to go to and from an airfield every time you want to fly.

This is why I'm not holding my breath for flying cars. Even if an efficient means of vertical flight is possible, the regulations and air traffic control problems will take decades to resolve. (not that I mind exploring the technical possibilities)

By the way, here are a couple of good references for preliminary aircraft design:

"The Elements of Aircraft Preliminary Design", Roger D. Schaufele ISBN:0-9701986-0-4
This book has quite a lot of practical design information in the form of tables and charts. Although, it's primarily focused on standard fixed wing commercial aircraft.

"Aircraft Design: A Conceptual Approach" by Daniel P. Raymer ISBN: 1-56347-829-3
Is a bit more comprehensive and even has a chapter on VTOL aircraft, but it's not quite as approachable.

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Re: Flying cars and jet-powered batwing

Postby stoppedcaring » Fri Nov 07, 2014 10:26 pm UTC

slinches wrote:
stoppedcaring wrote:This is just complete spitballing, but I wonder if two stacked blisks (of equal or different blade counts) could be designed to create an effective-variable-pitch system by changing their clock position relative to each other. E.g., when the blade edges are closely aligned, they exert less force on the airflow; when they are offset, they exert greater force:
Spoiler:
Image

I don't know if that would produce the equivalent effect of a variable-pitch prop or if it would just hurt efficiency.

You could design a variable effective camber rotor that way, but I doubt it would be very efficient. You're probably better off with a static variable guide vane, if that is even worth the added weight.

*googles* Oh, a static variable guide vane looks cool. I'll need a cover of some kind over the top of the ducted fan anyway, to close in aerodynamic lift mode, so I wonder if a radially-oriented guide vane could do it. If I'm understanding correctly, partially closing the vane will lower the amount of air accessible to the fan, reducing the load on the fan so that thrust and power consumption decrease despite the fan remaining at the same speed?

Oh, you mean the vertical center of gravity? The ducted fans are certainly positioned at the longitudinal center of gravity -- they have to be -- but the vertical center of gravity is probably going to be a good deal lower.

How so? It appears that both the bulk of the fuselage and the engines are above the lift fans in your drawings.

The lift fans are as far up on the wings as they can go; they're angled inward slightly, but still mounted on the "shoulders". At least, that's the idea. The engines are the only significant weight higher than them; the entire belly, cockpit, and fuselage are all slung underneath.

By the way, here are a couple of good references for preliminary aircraft design:

"The Elements of Aircraft Preliminary Design", Roger D. Schaufele ISBN:0-9701986-0-4
This book has quite a lot of practical design information in the form of tables and charts. Although, it's primarily focused on standard fixed wing commercial aircraft.

"Aircraft Design: A Conceptual Approach" by Daniel P. Raymer ISBN: 1-56347-829-3
Is a bit more comprehensive and even has a chapter on VTOL aircraft, but it's not quite as approachable.

Thanks, I'll see what I can dig up.

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Re: Flying cars and jet-powered batwing

Postby Zamfir » Sun Nov 09, 2014 10:57 am UTC

Well, you can reduce the power consumption of a fan by restricting the air flow going in, but that is a highly inefficient method. In many cases, you reduce output a lot with only a minor decrease in input.

Good guide vanes are designed to prerotate the flow going into the fan, typically against the direction of the fan's rotation. A normal fan takes in roughly axial flow, and the exit flow has a rotation in the direction if the fan. This is similar to how a fixed wing generated lift by turning the incoming airflow downwards. With the guide vanes, the fan takes in counterroating flow and the exit flow is close to axial, for a similar change in rotation over the moving fan.
This two-stage setup can increase efficiency, since the rotational energy in the outflow would otherwise be a loss term. But of course, the guide vanes have friction that counteracts this advantage.

By rotating the guide vanes, you cn increase or decrease this prerotation, and by extension the load on the moving blades. This is a similar effect to rotating the angle of the moving blades themselves, and also similar to changing the angle of attack of a fixed wing.

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Re: Flying cars and jet-powered batwing

Postby ucim » Mon Nov 10, 2014 2:46 am UTC

It seems to me that you're trying to solve the wrong problem. Of course the problems mentioned will need to be solved, but they are not the showstoppers, IMHO.

1: Weather. We drive in just about any weather. Flying (an airplane) in weather requires advanced training, and flying it in some kinds of weather also require advanced equipment. Airframe icing is often a (light plane) showstopper in the Northeast (US) for example. And flying in or near a thunderstorm is pretty much attempted suicide. So, even after your engine problems are solved, you will still have to deal with this.

2: Air traffic. It's 9 am and all your neighbors get in their flying cars and take off from their driveways, each then scooting in a different direction at twice highway speed. It's like a hundred people driving around in a parking lot, with no lanes marked, with the exception that threats come from all directions, and if one vehicle "makes contact" with another, they both crash on somebody's house. Later that day, everybody comes home tired, and do the same thing in reverse. And at night, they do it yet again, coming home slightly tipsy from the wine they had at the restaurant. (Note - the effects of alcohol are amplified at altitude). Oh, and there are things like trees and power lines in the way.

3: Practicality. Air and road are two very different media. A flying car is a combination of a poor airplane and a poor car. It will be (almost by definition) worse at everything it does than a single-purpose vehicle. So, how good is the best single-purpose vehicle that accomplishes the part of the mission that involves its chosen medium? How good would it be with all the technological advances required of a flying car? These are the engineering obstacles to overcome, but even when that happens, #1 and #2 remain. And if the answer is "computers will control everything" then you haven't worked with computers much!

One benefit to all this; commonplace flying cars will never be retro. They will always be future tech.

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Re: Flying cars and jet-powered batwing

Postby Zamfir » Wed Nov 12, 2014 4:40 pm UTC

I had the interview today. Very preliminary, it's not even clear if there would be a fitting position for me. But it's interesting anyway. It didn't feel like vaporware at all, as far as such things can be judged from such a talk. They have working prototypes, and they are working with quite some people at making the design good enough for sales and series production. They seem to have good and diverse funding, a careful approach to attract funding and on spending the money. Serious potential customers, I got the impression they even have definite customers. He said that investors and customers are overlapping groups. Kickstarter for rich people :) We've talked about what customers want with their vehicle, how customers go about getting an airstrip, deal with noise complaints from the neighbours (bribe them).

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Re: Flying cars and jet-powered batwing

Postby stoppedcaring » Wed Nov 12, 2014 10:26 pm UTC

Zamfir wrote:Well, you can reduce the power consumption of a fan by restricting the air flow going in, but that is a highly inefficient method. In many cases, you reduce output a lot with only a minor decrease in input.

Good guide vanes are designed to prerotate the flow going into the fan, typically against the direction of the fan's rotation. A normal fan takes in roughly axial flow, and the exit flow has a rotation in the direction if the fan. This is similar to how a fixed wing generated lift by turning the incoming airflow downwards. With the guide vanes, the fan takes in counterroating flow and the exit flow is close to axial, for a similar change in rotation over the moving fan.
This two-stage setup can increase efficiency, since the rotational energy in the outflow would otherwise be a loss term. But of course, the guide vanes have friction that counteracts this advantage.

By rotating the guide vanes, you cn increase or decrease this prerotation, and by extension the load on the moving blades. This is a similar effect to rotating the angle of the moving blades themselves, and also similar to changing the angle of attack of a fixed wing.

Okay, that makes a lot of sense. I assume that prerotating the air in the opposite direction decreases the load on the moving blades compared to axial inflow? That could allow for a pretty significant effective angle-of-attack range. And I'd presume the aeronautical engineers would be able to tune it pretty specifically to the various requirements.

I'm thinking something like this should work: vane blades that fold flat via a shiplap design, but open up to produce a variable-pitch system that can rotate all the way in the opposite direction. Efficiency would probably drop off sharply on either side of a 45' angle, but that's to be expected. Tilting more toward the full-closed flat position would correspond to reducing the load on the fans, making the transition from hover to forward flight simpler (because they just need to be slowly closed as aerodynamic lift takes over thrust).

singleviewcolorwithvanes.png


Back to the subject of the flying car...

ucim wrote:1. Weather. We drive in just about any weather. Flying (an airplane) in weather requires advanced training, and flying it in some kinds of weather also require advanced equipment. Airframe icing is often a (light plane) showstopper in the Northeast (US) for example. And flying in or near a thunderstorm is pretty much attempted suicide. So, even after your engine problems are solved, you will still have to deal with this.

2: Air traffic. It's 9 am and all your neighbors get in their flying cars and take off from their driveways, each then scooting in a different direction at twice highway speed. It's like a hundred people driving around in a parking lot, with no lanes marked, with the exception that threats come from all directions, and if one vehicle "makes contact" with another, they both crash on somebody's house. Later that day, everybody comes home tired, and do the same thing in reverse. And at night, they do it yet again, coming home slightly tipsy from the wine they had at the restaurant. (Note - the effects of alcohol are amplified at altitude). Oh, and there are things like trees and power lines in the way.

Certainly, something like this would start out as a police/emergency responder sort of thing, opened up later to only a handful of people with pilot licenses, and so forth and so on. The point is to get SOMETHING up and running.

3: Practicality. Air and road are two very different media. A flying car is a combination of a poor airplane and a poor car. It will be (almost by definition) worse at everything it does than a single-purpose vehicle. So, how good is the best single-purpose vehicle that accomplishes the part of the mission that involves its chosen medium? How good would it be with all the technological advances required of a flying car?

Even if we forget about the car side of things, it's the "flying" bit that's important. To my knowledge, there is no manned VTOL craft capable of fitting into a garage. Anywhere. We need to rectify that. :)

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Re: Flying cars and jet-powered batwing

Postby wumpus » Thu Nov 13, 2014 2:37 pm UTC

stoppedcaring wrote:Even if we forget about the car side of things, it's the "flying" bit that's important. To my knowledge, there is no manned VTOL craft capable of fitting into a garage. Anywhere. We need to rectify that. :)


I really don't think that the horseless carriage had to fit in a horse's barn to replace the horse. The cost of a garage is so far less than your hypothetical batwing (even in New York City where a garage adds something like $1M to the price of a house according to a somewhat recent nytimes article. A batwing will likely be true even if someone has a private garage in Tokyo.) that this couldn't possibly be a real condition. Even for something derivative of the scorpion I mentioned (simple single propeller engine), the cost of the aircraft will still likely exceed the cost of the garage (paying for the R&D will be huge).

I have to assume at least one of the selling points of such a "flying car" is to go rather fast (100-200mph at least). This likely means that such a craft wants to be longer and thinner than a regular car (although this isn't absolute). You can get away with a lack of crush zones if you drop the whole "car" idea and stick to VTOL aircraft, which might buy back some space, but you almost certainly need the wings for sustained high-speed level flight.

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Re: Flying cars and jet-powered batwing

Postby stoppedcaring » Thu Nov 13, 2014 5:26 pm UTC

wumpus wrote:
stoppedcaring wrote:Even if we forget about the car side of things, it's the "flying" bit that's important. To my knowledge, there is no manned VTOL craft capable of fitting into a garage. Anywhere. We need to rectify that. :)


I really don't think that the horseless carriage had to fit in a horse's barn to replace the horse. The cost of a garage is so far less than your hypothetical batwing (even in New York City where a garage adds something like $1M to the price of a house according to a somewhat recent nytimes article. A batwing will likely be true even if someone has a private garage in Tokyo.) that this couldn't possibly be a real condition. Even for something derivative of the scorpion I mentioned (simple single propeller engine), the cost of the aircraft will still likely exceed the cost of the garage (paying for the R&D will be huge).

I have to assume at least one of the selling points of such a "flying car" is to go rather fast (100-200mph at least). This likely means that such a craft wants to be longer and thinner than a regular car (although this isn't absolute). You can get away with a lack of crush zones if you drop the whole "car" idea and stick to VTOL aircraft, which might buy back some space, but you almost certainly need the wings for sustained high-speed level flight.

The batwing is the military close-air-support concept; the flying car is a separate discussion. Things kind of diverged in this thread.

As far as flying cars are concerned, fast is important, but being able to hop over traffic is a big part of it. The point of the garage comparison is not cost, but space. If we're ever going to have any sort of flying personal transport vehicle, it should ideally be able to take off and land from a single parking space or two spaces at most.

The comparison between planes, cars, and a flying car is comparable to the comparison between railroads, carriages, and horseless carriages. To be successful, horseless carriages had to be able to integrate (to some degree) into the existing horse-and-buggy-based infrastructure. Being able to fit on a driveway, take off and land from 1-2 parking spaces, or drive in a single lane of traffic (if that's an option) is part of fitting into the established infrastructure.

The only thing that currently comes close is the Martin Jetpack. It's intended to be rolled out first for firefighters and emergency responders. It just lacks any sort of cruising capacity.

If you start with a motorcycle concept rather than an ordinary sedan concept, you don't have to worry about crumple zones.

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Re: Flying cars and jet-powered batwing

Postby wumpus » Fri Nov 14, 2014 12:23 am UTC

Yes, parking is obviously going to be important. Another thing is how you sell enough to get a "flying car making startup" started up. I'd probably look at Elon Musk's decision that electric cars are going to be expensive for awhile, so try to compete with Porsche buyers instead of Prius buyers. If I was trying to not only build flying cars, but simultaneously build a startup that makes flying cars I would ponder why cars that cost more than airplanes seem to outsell airplanes. I suspect that it is mostly because you can show off such a car by just driving it (the other is time&money: choose at most one). People only see you and your aircraft at airports (who likely already have a plane...). Sell the most dramatic entrance and you will have a backlog of orders well until you are officially "started up".

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Re: Flying cars and jet-powered batwing

Postby ucim » Fri Nov 14, 2014 5:01 am UTC

stoppedcaring wrote:Certainly, something like this would start out as a police/emergency responder sort of thing...
Sounds good, but it's because that's a "money is no object" kind of application. And even so, money is an object. Is it better to have one flying car, or six ordinary police/emergency helicopters?

stoppedcaring wrote:As far as flying cars are concerned, fast is important, but being able to hop over traffic is a big part of it.
No, being the only one who can hop over traffic is the big part of it. Just picture everyone having that ability, and using it at the same time! It's pretty self limiting, and it's not pretty.

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Re: Flying cars and jet-powered batwing

Postby wumpus » Fri Nov 14, 2014 2:35 pm UTC

ucim wrote:
stoppedcaring wrote:Certainly, something like this would start out as a police/emergency responder sort of thing...
Sounds good, but it's because that's a "money is no object" kind of application. And even so, money is an object. Is it better to have one flying car, or six ordinary police/emergency helicopters?

Note that medivac can likely get away with STOL (assuming the hospital can build whatever they need and that the medivac and takeoff and land on a road). The thing to remember is that a helicopter fights the air every inch of the way while an airplane tends to ride the air. For less dense areas, gaining speed from using wings (let alone the relative safety of planes vs. helicopters) would make them more cost effective (after startup costs. The startup costs are likely the killers, thus my notes above on building high-cost flying cars).
ucim wrote:
stoppedcaring wrote:As far as flying cars are concerned, fast is important, but being able to hop over traffic is a big part of it.
No, being the only one who can hop over traffic is the big part of it. Just picture everyone having that ability, and using it at the same time! It's pretty self limiting, and it's not pretty.

Jose

If you are effectively adding lanes vertically, it should help. Obviously this assumes a significant time hopping over time on the ground. Unfortunately, I think the only "real" flying cars on or near the market are autogyros that effectively only do this (I think they are more or less off road vehicles that fly to ignore otherwise impassible terrain).


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