Civilian Avionics

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nehpest
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Civilian Avionics

Postby nehpest » Sun Feb 06, 2011 10:27 am UTC

Disclaimer: this seemed like the most appropriate forum for this topic, but if this would fit better elsewhere, please move it.

I'm part of my university's newly-formed High Speed Aircraft Club. Essentially, a bunch of aerospace engineering majors got together to build a Mach-capable unmanned test vehicle; we have a few design requirements as of now, shown here:

  • Must maintain Mach 1.20 for a minimum of 15 seconds.
  • Must have a minimum max altitude of 10000 feet AMSL.
  • Must weigh in at or under 350 lbs (? I might be misremembering that one).
  • 99% reliability; we're aiming for at least 99 flights before overhauling or scrapping the vehicle (of course, routine maintenance is expected to take place between flights - this is more "we don't want to crash"-type damage)
Since I'm the only electrical engineering student in the group, I was voted into being part of the electronics and avionics group. That's all well and good, but beyond the very basics I have no idea what sort of instrumentation or sensors would be useful on this type of craft. Obviously, we'll need altimeter, airspeed indicator, directional indicator, sensors for attitude, GPS, VSI, a tacho for the engine (we haven't decided whether to do a jet turbine or a rocket yet, so this may be superfluous), and a radio transponder (we're test-flying in southern and central California, if/when we get the go-ahead from the FAA). However, I'd dearly love any input you folks can give on the sort of instrumentation we should consider for our toy.
Last edited by nehpest on Sun Feb 06, 2011 8:17 pm UTC, edited 1 time in total.
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Re: Civilian Avionics

Postby Hawknc » Sun Feb 06, 2011 1:11 pm UTC

Depending on the type of propulsion, I'd imagine you would also want to keep an eye on the fuel system - fuel/air ratio, pressure, tank level etc. Good luck with it (especially getting FAA approval)!

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Re: Civilian Avionics

Postby The EGE » Sun Feb 06, 2011 6:09 pm UTC

With civilian GPS receivers, you're not able to use the device above 515 m/s (1000 km/h, Mach 1.5) and 18 km (about 59000 ft). Some receivers will still function at higher speed but lower altitude and vice versa; some will stop sending data if you exceed either. But, GPS has the capability to give you altitude, airspeed, position, and direction, within limits. I know a few folks who use GPS as a fairly complete avionics suite for high-power rockets; if you need I may be able to get you in contact.

I would recommend a jet engine over rockets for your primary powerplant. Jet engines have a fairly standardized design and it's real easy to get plans for miniature versions. Rockets are tricky for horizontal-motion systems. Solid-fuel rockets (like the standard APCP-fuel high-power rocket motors) only burn for a few seconds and cannot be shut off; liquid-fuel rockets are finicky, require expensive turbopumps, and are prompt to explode.

Solid-fuel boosters might be useful for the final sprint past Mach. However, they're expensive (a J570 load that gives 120 pounds of thrust for 2 seconds costs $70 per plus $110 for the reloadable casing; an L339 that gives 80 pounds thrust for 8 seconds costs $160 plus $300+ for the casing), require two levels of certification (which one of your team members may already have) and would make getting FAA approval trickier.
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Re: Civilian Avionics

Postby nehpest » Sun Feb 06, 2011 7:43 pm UTC

Hawknc wrote:Depending on the type of propulsion, I'd imagine you would also want to keep an eye on the fuel system - fuel/air ratio, pressure, tank level etc. Good luck with it (especially getting FAA approval)!


Excellent point - fuel is kinda important :lol: I'll edit this into the OP, that one of our other design constraints is that we're looking to get 99%+ reliability for the vehicle, since it's probably going to run in the neighborhood of 10k USD (yay charity and grants).

It occurred to me while I was sleeping just how much can happen in 15 seconds at Mach. I'm starting to wonder if human reaction times are going to suffice if something unforeseen happens.
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Re: Civilian Avionics

Postby Korrente » Sun Feb 06, 2011 8:11 pm UTC

If you're able to get newer parts try to spring for things with electronic sensors. Then you can route all of your ADC/AHRS and GPS information into one box. If you're able, look into how Garmin packs all their equipment into a G1000 system: every sensor feeds into one of two very small computers for processing. I don't know how you're planning to automate the thing, but if you're building your own FMS this way, you can just plug in whatever you need to add if it comes as an afterthought.

I would definitely not rely on GPS for things like altitude and heading. A digital pitot-static system shouldn't cost too much or be too hard to build, and it will give you way more accurate results (That said, I have no idea how to make a pitot tube work when air starts to compress at that high of speed). Use a small magnetometer for heading and it'll never fail. Accelerometers for pitch and roll as they're accurate and probably easier to read digitally than a gyroscope, not to mention less chance of failure. If you're going all-digital, a VSI is not needed, you can get that from watching altitude change.
They will probably require you to have some sort of Mode-C capability and there's not much you can do there to lose weight. It will have to be linked in to the static system to get its altitude. I would say you should try an ADS-B system as well just to freak out some airline pilots, but that will mostly stop working when/if your GPS stops.

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Re: Civilian Avionics

Postby nehpest » Sun Feb 06, 2011 8:31 pm UTC

The EGE wrote:With civilian GPS receivers, you're not able to use the device above 515 m/s (1000 km/h, Mach 1.5) and 18 km (about 59000 ft). Some receivers will still function at higher speed but lower altitude and vice versa; some will stop sending data if you exceed either. But, GPS has the capability to give you altitude, airspeed, position, and direction, within limits. I know a few folks who use GPS as a fairly complete avionics suite for high-power rockets; if you need I may be able to get you in contact.


I vaguely remembered there being limitations on the civilian version of the technology, but I didn't know what they were; thanks! As of now, we don't anticipate reaching M1.5 or anything close to that altitude (our design floor is 10,000 ft, but we haven't established a ceiling). As for the contact with GPS hobbyists, I'll bring it up at the next meeting, but I suspect we'll be very interested in talking to them.

I would recommend a jet engine over rockets for your primary powerplant. Jet engines have a fairly standardized design and it's real easy to get plans for miniature versions. Rockets are tricky for horizontal-motion systems. Solid-fuel rockets (like the standard APCP-fuel high-power rocket motors) only burn for a few seconds and cannot be shut off; liquid-fuel rockets are finicky, require expensive turbopumps, and are prompt to explode.


Interesting. During the first requirements meeting I went to, a couple of guys were making that argument, but in reverse: that jet engines are finicky and complex, while rockets would be easy. From having flown model rockets as a kid, I'm comfortable with thinking that solid-fuel rockets won't do here; it looks like some research is in order to figure out jets vs. liquid-fuel rockets.

Solid-fuel boosters might be useful for the final sprint past Mach. However, they're expensive (a J570 load that gives 120 pounds of thrust for 2 seconds costs $70 per plus $110 for the reloadable casing; an L339 that gives 80 pounds thrust for 8 seconds costs $160 plus $300+ for the casing), require two levels of certification (which one of your team members may already have) and would make getting FAA approval trickier.


I think this is actually the plan at the moment. One of the team leads is certified level 3 for high power rocketry, so using the boosters should be right up his alley. The expense seems like a concern, though. Fortunately, FAA approval isn't anywhere near my area of responsibility :mrgreen:

Korrente wrote:If you're able to get newer parts try to spring for things with electronic sensors. Then you can route all of your ADC/AHRS and GPS information into one box. If you're able, look into how Garmin packs all their equipment into a G1000 system: every sensor feeds into one of two very small computers for processing. I don't know how you're planning to automate the thing, but if you're building your own FMS this way, you can just plug in whatever you need to add. I would definitely not rely on GPS for things like altitude and heading. An digital pitot-static system shouldn't cost too much or be too hard to build, and it will give you way more accurate results (That said, I have no idea how to make a pitot tube work when air starts to compress at that high of speed). Use a small magnetometer for heading and it'll never fail.


The fact that I had to look up some of those abbreviations reminds me why I'm asking for help here :) I'll definitely look into how Garmin designed their system. Thanks for the ideas about heading and the pitot system - I'll bring those up at the next meeting as well.

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Re: Civilian Avionics

Postby The EGE » Sun Feb 06, 2011 9:24 pm UTC

Okay, L3 certed means he knows exactly what he's doing, and that he has access to bigger motors.


Jets have the disadvantage of being air-breathing and requiring the turbine assembly, but liquid-fuel rockets are infamous for being explodey, because one small failure has a higher potential for catastrophic failure.

Definitely keep us updated, this sounds like an awesomely cool project.
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Re: Civilian Avionics

Postby Solt » Mon Feb 07, 2011 2:12 am UTC

Ok, in your requirements you forgot the definition of "aircraft". Because I could fire a bullet past mach 1 and meet all but your reliability requirement. Likewise, a vertical rocket with parachute would have no problem achieving all those requirements but is by no means an "aircraft".

I'm going to assume that you mean a horizontal-flying lift-generating vehicle, powered by rockets, that uses aerodynamic actuators for steering. Personally I think the rockets are cheating, but you ARE on a budget.

You need angle sensors (pitch and roll) as well as gyroscopic sensors for both angles in order to improve your estimate of the true angle (your angle sensors, since they will essentially be estimating the angle based on gravity, will be noisy as fuck and completely unreliable. You need extra information to clean up the output). You might as well just buy a 2-axis Inertial Measurement Unit to do all that. You'll also want sensors on all your control surfaces so you can be sure of the true position of those surfaces.

The real question is, are you flying this thing manually via radio control or is it going to be automated? (Or semi-automated like UAVs where the operator tells it where to go and the plane avionics control the flight surfaces that make it go there)

nehpest wrote:I'm starting to wonder if human reaction times are going to suffice if something unforeseen happens.

In my opinion, definitely not. Even if you could react fast enough, I doubt any of your members has an intuitive feel for how a plane steers at 1+ mach versus civil aviation speeds. I am not an aerodynamicist, but I'm guessing that control surfaces produce bigger responses for the same angle as you go faster. A pilot would have to compensate for that if he wants to maintain level flight. Also according to wikipedia apparently control surfaces have no effect as you break the sound barrier. I don't know what's up with that but yea, also a potential problem for a pilot. I wouldn't trust this to a human personally, but for a bunch of students the controls problems are not trivial.

The EGE wrote:Solid-fuel rockets (like the standard APCP-fuel high-power rocket motors) only burn for a few seconds and cannot be shut off; liquid-fuel rockets are finicky, require expensive turbopumps, and are prompt to explode.


You can't really take off with a solid fuel rocket though. You'd only have a matter of seconds to get into the air and fly to your test area before the thrust pushed you past mach 1. You need to be able to throttle. Best would be a combination of sources- a jet engine or liquid rocket to maneuver, and a solid fuel rocket to break the sound barrier.
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Re: Civilian Avionics

Postby The EGE » Mon Feb 07, 2011 3:28 am UTC

Solt wrote:Ok, in your requirements you forgot the definition of "aircraft". Because I could fire a bullet past mach 1 and meet all but your reliability requirement. Likewise, a vertical rocket with parachute would have no problem achieving all those requirements but is by no means an "aircraft".

I'm going to assume that you mean a horizontal-flying lift-generating vehicle, powered by rockets, that uses aerodynamic actuators for steering. Personally I think the rockets are cheating, but you ARE on a budget.


I would personally tend to disagree; the fundamental part of an aircraft is that it uses a powerplant to force air over winglike surfaces to generate lift; that's what separates an aircraft from a rocket (which uses aerodynamic surfaces for control only). Granted, there are some that toe the line like SpaceShipOne and the X-15, and it's semantics anyway.

Solt wrote:The real question is, are you flying this thing manually via radio control or is it going to be automated? (Or semi-automated like UAVs where the operator tells it where to go and the plane avionics control the flight surfaces that make it go there)

nehpest wrote:I'm starting to wonder if human reaction times are going to suffice if something unforeseen happens.

In my opinion, definitely not. Even if you could react fast enough, I doubt any of your members has an intuitive feel for how a plane steers at 1+ mach versus civil aviation speeds. I am not an aerodynamicist, but I'm guessing that control surfaces produce bigger responses for the same angle as you go faster. A pilot would have to compensate for that if he wants to maintain level flight. Also according to wikipedia apparently control surfaces have no effect as you break the sound barrier. I don't know what's up with that but yea, also a potential problem for a pilot. I wouldn't trust this to a human personally, but for a bunch of students the controls problems are not trivial.


Control surfaces have less effect, but I don't believe they lose effectiveness entirely. I've sent a handful of rockets past Mach - that use fins for stability - and they retained attitude. I do believe there is some loss of effectiveness, though. The L3 team member is almost certainly familiar with transonic aerodynamics; it's pretty hard to keep an M motor under Mach.

As for steering at Mach 1+: You obviously will not have the same feel as with a real plane, but a good flight sim can give you some idea of what it's like at transonic speeds. Google Earth's flight sim - which is, happily, free - has an F16 which can break Mach.

Solt wrote:
The EGE wrote:Solid-fuel rockets (like the standard APCP-fuel high-power rocket motors) only burn for a few seconds and cannot be shut off; liquid-fuel rockets are finicky, require expensive turbopumps, and are prompt to explode.


You can't really take off with a solid fuel rocket though. You'd only have a matter of seconds to get into the air and fly to your test area before the thrust pushed you past mach 1. You need to be able to throttle. Best would be a combination of sources- a jet engine or liquid rocket to maneuver, and a solid fuel rocket to break the sound barrier.
[/quote]

Agreed. I'd vote for the jet, because if it fails you're more likely to have a glider, versus shrapnel.
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Re: Civilian Avionics

Postby Korrente » Mon Feb 07, 2011 5:10 am UTC

Control surfaces definitely do not lose all effectiveness past mach. Besides there are plenty of ways to keep subsonic flow over the wing surfaces long after the aircraft has gone supersonic. Not to mention that they're probably not going to be doing anything but tiny control movement at that high speed anyway. In my opinion, if you can keep the thing in range of a controller's radio to steer it (and provided you have some kind of camera to look through and telemetry read) you should be able to pilot it manually. It will make it sooo much easier to land and recover, not to mention that even if you decide to automate it and that system fails you will have a manual backup. Mach 1 is fast, but remember that people have hand-flown planes there before.

Thinking about that a bit, you'll definitely want something to prevent the operator from over-stressing the controls when at high speed...it'll be easy to push the joystick a little to hard and that translate to ripping a wing off... Just something to lessen the ratio of joystick movement to control-surface movement as the speed increases.

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Re: Civilian Avionics

Postby Sockmonkey » Mon Feb 07, 2011 5:48 am UTC

This might be helpful. http://aardvark.co.nz/pjet/links.htm
Also, you might try propellant like nitric acid and annaline. Those react on contact without a tricky igniter and you just need to pressurize the tanks slightly so you don't need a tricky pump. A couple valves and there ya go. Truax used that for some JATO units he designed.

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Re: Civilian Avionics

Postby mbrigdan » Mon Feb 07, 2011 6:31 am UTC

Some things you might want to consider:
It'll take VERY strong motors to move your control surfaces at those speeds.
At Mach exactly, airflow is chaotic or something like that, due to the plane being right in the shockwave. You may want to design your plane to get past this point as quickly as possible.
If you want to remote control the thing, you'll need powerful transmitters if you want to stay in range. This may require you to build your own transmitters and/or buy special licenses.
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Re: Civilian Avionics

Postby Sockmonkey » Mon Feb 07, 2011 7:48 am UTC

A few relay stations around the area you're going to fly in wouldn't hurt either. It's probably going to have to fly on automatic the whole time since if something that small is close enough to see clearly it's going to be zipping by too fast for human reflexes.
Last edited by Sockmonkey on Mon Feb 07, 2011 7:48 am UTC, edited 1 time in total.

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Re: Civilian Avionics

Postby nehpest » Mon Feb 07, 2011 7:48 am UTC

The EGE wrote:Okay, L3 certed means he knows exactly what he's doing, and that he has access to bigger motors.

Jets have the disadvantage of being air-breathing and requiring the turbine assembly, but liquid-fuel rockets are infamous for being explodey, because one small failure has a higher potential for catastrophic failure.

Definitely keep us updated, this sounds like an awesomely cool project.


He definitely seems knowledgeable from my first impression - the whole team does, in fact. It seems to be a bunch of fifth- and sixth-year seniors (California public education takes a while to graduate :roll: ). I'll certainly keep you folks updated as events progress!

Solt wrote:Ok, in your requirements you forgot the definition of "aircraft". Because I could fire a bullet past mach 1 and meet all but your reliability requirement. Likewise, a vertical rocket with parachute would have no problem achieving all those requirements but is by no means an "aircraft".

I'm going to assume that you mean a horizontal-flying lift-generating vehicle, powered by rockets, that uses aerodynamic actuators for steering. Personally I think the rockets are cheating, but you ARE on a budget.


The club seems pretty clear on what they mean by "aircraft" - most of them are aerospace engineering majors, though, so I suppose the term has a formal definition known to people in the field. The characteristics you listed all hold true for our intended vehicle, as far as I am aware; it hasn't actually been designed yet, but all of those seem in keeping with the requirements discussions we've had so far. However, the rocket vs. jet decision hasn't been made yet.

You need angle sensors (pitch and roll) as well as gyroscopic sensors for both angles in order to improve your estimate of the true angle (your angle sensors, since they will essentially be estimating the angle based on gravity, will be noisy as fuck and completely unreliable. You need extra information to clean up the output). You might as well just buy a 2-axis Inertial Measurement Unit to do all that. You'll also want sensors on all your control surfaces so you can be sure of the true position of those surfaces.


Gyros, check. What is the usual method of determining attitude in, say, single engine civvie craft? I assumed everybody used gyros for that; is there another method that's more common? As for sensors on the control surfaces, I agree wholeheartedly, and I suspect the ops lead will too.

The real question is, are you flying this thing manually via radio control or is it going to be automated? (Or semi-automated like UAVs where the operator tells it where to go and the plane avionics control the flight surfaces that make it go there)


I don't think that decision has been made yet, but from the discussions we've had I think we're leaning towards manual radio control. One of the members either knows of, or has access to, a radio control device with a 50 mile range. We believe at present that its range will be sufficient for our test flights (at Mach 1.20, 50 miles takes a bit more than three minutes to traverse, and we only need to maintain the speed for 15 seconds).

nehpest wrote:I'm starting to wonder if human reaction times are going to suffice if something unforeseen happens.

In my opinion, definitely not. Even if you could react fast enough, I doubt any of your members has an intuitive feel for how a plane steers at 1+ mach versus civil aviation speeds. I am not an aerodynamicist, but I'm guessing that control surfaces produce bigger responses for the same angle as you go faster. A pilot would have to compensate for that if he wants to maintain level flight. Also according to wikipedia apparently control surfaces have no effect as you break the sound barrier. I don't know what's up with that but yea, also a potential problem for a pilot. I wouldn't trust this to a human personally, but for a bunch of students the controls problems are not trivial.


I have no idea who they're going to have piloting if we do indeed go with the manual route, but I assume (read: hope like hell) that they will be trained not to destroy our new toy. It's true that the control surfaces get wonky as you're going through Mach 1, as mbrigdan mentions below. However, they work properly once you're out of the chaotic regime. The details of all that are beyond my paygrade, and are the aerodynamics team's problem anyway :lol:

I agree about the non-triviality of the controls problems we'd face designing it to be [partially] autonomous. I don't think we have any controls specialists onboard just yet, but I'll probably find out this week.

The EGE wrote:Solid-fuel rockets (like the standard APCP-fuel high-power rocket motors) only burn for a few seconds and cannot be shut off; liquid-fuel rockets are finicky, require expensive turbopumps, and are prompt to explode.


You can't really take off with a solid fuel rocket though. You'd only have a matter of seconds to get into the air and fly to your test area before the thrust pushed you past mach 1. You need to be able to throttle. Best would be a combination of sources- a jet engine or liquid rocket to maneuver, and a solid fuel rocket to break the sound barrier.


I am pretty sure that a solid rocket, if it's to be used at all, would only serve as a boost to break through the sound barrier. Like I mentioned a bit ago, I don't think we know exactly how we're going to propel this beast yet. Thanks for all the insight!

The EGE wrote:
Solt wrote:Ok, in your requirements you forgot the definition of "aircraft". Because I could fire a bullet past mach 1 and meet all but your reliability requirement. Likewise, a vertical rocket with parachute would have no problem achieving all those requirements but is by no means an "aircraft".

I'm going to assume that you mean a horizontal-flying lift-generating vehicle, powered by rockets, that uses aerodynamic actuators for steering. Personally I think the rockets are cheating, but you ARE on a budget.


I would personally tend to disagree; the fundamental part of an aircraft is that it uses a powerplant to force air over winglike surfaces to generate lift; that's what separates an aircraft from a rocket (which uses aerodynamic surfaces for control only). Granted, there are some that toe the line like SpaceShipOne and the X-15, and it's semantics anyway.


We're certainly going to be generating lift with the wings.

Control surfaces have less effect, but I don't believe they lose effectiveness entirely. I've sent a handful of rockets past Mach - that use fins for stability - and they retained attitude. I do believe there is some loss of effectiveness, though. The L3 team member is almost certainly familiar with transonic aerodynamics; it's pretty hard to keep an M motor under Mach.

As for steering at Mach 1+: You obviously will not have the same feel as with a real plane, but a good flight sim can give you some idea of what it's like at transonic speeds. Google Earth's flight sim - which is, happily, free - has an F16 which can break Mach.


I'll bring up the training issue to the club's ops chief, but I suspect he's already thought of it. He's scarily-well-prepared. Most likely it's something we'll have to work out further into the project, as right now we don't know anything about how the vehicle will handle, or even what's to be driving it.

I'd vote for the jet, because if it fails you're more likely to have a glider, versus shrapnel.


That's a most excellent point. Converting this thing into tiny bits of red-hot metal over California's central basin would not make us any friends in the FAA, or a few other government agencies. Also, there's that whole "California likes to catch on fire pretty often" issue.

Korrente wrote:Control surfaces definitely do not lose all effectiveness past mach. Besides there are plenty of ways to keep subsonic flow over the wing surfaces long after the aircraft has gone supersonic. Not to mention that they're probably not going to be doing anything but tiny control movement at that high speed anyway. In my opinion, if you can keep the thing in range of a controller's radio to steer it (and provided you have some kind of camera to look through and telemetry read) you should be able to pilot it manually. It will make it sooo much easier to land and recover, not to mention that even if you decide to automate it and that system fails you will have a manual backup. Mach 1 is fast, but remember that people have hand-flown planes there before.

Thinking about that a bit, you'll definitely want something to prevent the operator from over-stressing the controls when at high speed...it'll be easy to push the joystick a little to hard and that translate to ripping a wing off... Just something to lessen the ratio of joystick movement to control-surface movement as the speed increases.


You're absolutely right about maneuvering at speed: it's not going to happen. Apparently, the "Mach 1.20 at 15 seconds" requirement is predicated on us going for a Guinness World Record of some kind; we have to make three passes in the presence of the judges, and the passes have to last 15 seconds minimum with an average speed of Mach 1.20. Our flight plan is going to look like a race track: 2 long straightaways in which we'll go full throttle, and two U-turns to reorient the plane (so as not to move it out of range of the controller). We'll probably be quite happy to avoid the stresses that go along with supersonic maneuvering (though, knowing the structure lead, we'll probably design for them anyway).

Sockmonkey wrote:This might be helpful. http://aardvark.co.nz/pjet/links.htm
Also, you might try propellant like nitric acid and annaline. Those react on contact without a tricky igniter and you just need to pressurize the tanks slightly so you don't need a tricky pump. A couple valves and there ya go. Truax used that for some JATO units he designed.


I'll toss the link and the idea to the propulsion group and let you know what they decide, whenever they get around to deciding!

mbrigdan wrote:Some things you might want to consider:
It'll take VERY strong motors to move your control surfaces at those speeds.
At Mach exactly, airflow is chaotic or something like that, due to the plane being right in the shockwave. You may want to design your plane to get past this point as quickly as possible.
If you want to remote control the thing, you'll need powerful transmitters if you want to stay in range. This may require you to build your own transmitters and/or buy special licenses.


Agreed about the actuators. Agreed about getting past the chaotic regime ASAP - I think that's what the rockets will be for, if we go with them at all. As for the transmitters, I am under the impression that we've solved it fairly satisfactorily.

Again, many thanks for all the ideas and suggestions, folks! I promise to keep you all updated on our progress if you promise to keep the ideas coming.
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Re: Civilian Avionics

Postby Sockmonkey » Mon Feb 07, 2011 7:54 am UTC

If the rocket is just for the boost up to speed then a ramjet might be a good way to go. It's crowbar simple and mach 1 is the beginning of the speed range where they don't suck.

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Re: Civilian Avionics

Postby Carnildo » Mon Feb 07, 2011 10:37 am UTC

Sockmonkey wrote:If the rocket is just for the boost up to speed then a ramjet might be a good way to go. It's crowbar simple and mach 1 is the beginning of the speed range where they don't suck.

Crowbar simple from a theory standpoint, but the engineering details involved in making one reliable and efficient are non-trivial.

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Re: Civilian Avionics

Postby Hawknc » Mon Feb 07, 2011 10:50 am UTC

nehpest wrote:Again, many thanks for all the ideas and suggestions, folks! I promise to keep you all updated on our progress if you promise to keep the ideas coming.

Given the number of aerospace engineers, rocket scientists and enthusiasts and students of the same that inhabit these forums, I doubt you'll be short on suggestions. :P Please do keep us informed, I'd love to know more about how you're designing the fuselage and lifting & control surfaces. As others have mentioned, there will be huge forces on the aircraft in the transonic regime so having a reliable manufacturing process is equally as important as the theoretical design.

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Re: Civilian Avionics

Postby p1t1o » Mon Feb 07, 2011 12:21 pm UTC

This sounds like a very exciting and interesting project!

Keep in mind that the poster doesn't seem to be responsible for the physical details - sounds like they have a pretty accomplished team of aeronautical engineers for all that stuff!

My two pence would be :
- for your telemetry, you'll need to be able to communicate quickly and reliably over distances on the order of at least 10Km (the circuit described will be around 6 or 7 km long, with you in the middle?), probably more for safety.
-you might want some pressure sensors on certain points on the wings and fuselage for confirmation that you have definitely broken the local sound barrier, and for other useful data on airframe performance.
-one of the biggest challenges designing supersonic aircraft back in the day was stability in the transonic and supersonic regimes, so its possible that your engineers might want an accurate reading of which direction the aircraft is pointing (as opposed to just which direction it is moving in) to detect things like flutter and other oscillations.
-I think it'd be cool to stick a microphone in there somewhere, firstly it might sound interesting as you break mach1, secondly, it might give useful data, such as the detection of dangerous levels of vibration.

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Re: Civilian Avionics

Postby idobox » Mon Feb 07, 2011 1:35 pm UTC

About the radio transmission, you have to make sure the doppler effect won't be a problem.
Mach 1 is about 1ppm of light speed, so frequencies will shift by that amount. Some radio-equipment, especially in the mm band, and with high bandwidth can have problems with that.
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Re: Civilian Avionics

Postby Mr_Rose » Mon Feb 07, 2011 2:01 pm UTC

People have been saying that liquid rockets are too fiddly and solid too uncontrollable; has anyone considered a hybrid? As in solid fuel liquid oxidiser?
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Re: Civilian Avionics

Postby Velifer » Mon Feb 07, 2011 2:05 pm UTC

nehpest wrote:What is the usual method of determining attitude in, say, single engine civvie craft? I assumed everybody used gyros for that; is there another method that's more common?

Yes. They're called "windows."

Cool project. Can you tell us who's helping to fund it?
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Re: Civilian Avionics

Postby Korrente » Mon Feb 07, 2011 4:41 pm UTC

nehpest wrote:What is the usual method of determining attitude in, say, single engine civvie craft? I assumed everybody used gyros for that; is there another method that's more common?


A gyro system will require motors or a vacuum system to get it spinning, and then more sensors to read their movement (usually it's just slaved to a moving card on the instrument panel, but not in your case). Using accelerometers to measure change in pitch/roll and rate of turn will definitely suit you better. You go from a 3-pound hunk of 10000rpm metal to a few tiny sensors

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Re: Civilian Avionics

Postby GenericAnimeBoy » Mon Feb 07, 2011 4:48 pm UTC

Velifer wrote:Yes. They're called "windows."

Reliance on visibility through the windows to provide attitude and collision avoidance information (ie: VFR) is contingent on weather conditions. All but the lightest civilian aircraft have an "Artificial Horizon" gyroscopic attitude indicator. http://en.wikipedia.org/wiki/Attitude_indicator

EDIT: The Wikipedia article I linked has some interesting information to the effect that mechanical gyros are beginning to be supplanted by integrated systems that use solid state or MEMS accelerometers which are lighter and more reliable. Might be a good line of research.

Also, yes, my internal sarcasm detector is broken. :roll:
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Re: Civilian Avionics

Postby Korrente » Mon Feb 07, 2011 5:07 pm UTC

Yes, MEMS, that's what I'm getting at. Had no idea what they were called, but they don't spin, they rarely break, they're very light, and they're very cheap.

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Re: Civilian Avionics

Postby nehpest » Mon Feb 07, 2011 7:29 pm UTC

Carnildo wrote:
Sockmonkey wrote:If the rocket is just for the boost up to speed then a ramjet might be a good way to go. It's crowbar simple and mach 1 is the beginning of the speed range where they don't suck.

Crowbar simple from a theory standpoint, but the engineering details involved in making one reliable and efficient are non-trivial.


I'm (fortunately) not involved in propulsion, but I'm pretty sure a ramjet isn't going to happen for precisely that reason.

Hawknc wrote:Given the number of aerospace engineers, rocket scientists and enthusiasts and students of the same that inhabit these forums, I doubt you'll be short on suggestions. :P Please do keep us informed, I'd love to know more about how you're designing the fuselage and lifting & control surfaces. As others have mentioned, there will be huge forces on the aircraft in the transonic regime so having a reliable manufacturing process is equally as important as the theoretical design.


My understanding on the fuselage is that we're going to use some kind of ultra-strong carbon fiber skin with foam interior. I'll verify that at the meeting.

p1t1o wrote:This sounds like a very exciting and interesting project!

Keep in mind that the poster doesn't seem to be responsible for the physical details - sounds like they have a pretty accomplished team of aeronautical engineers for all that stuff!

My two pence would be :
- for your telemetry, you'll need to be able to communicate quickly and reliably over distances on the order of at least 10Km (the circuit described will be around 6 or 7 km long, with you in the middle?), probably more for safety.
-you might want some pressure sensors on certain points on the wings and fuselage for confirmation that you have definitely broken the local sound barrier, and for other useful data on airframe performance.
-one of the biggest challenges designing supersonic aircraft back in the day was stability in the transonic and supersonic regimes, so its possible that your engineers might want an accurate reading of which direction the aircraft is pointing (as opposed to just which direction it is moving in) to detect things like flutter and other oscillations.
-I think it'd be cool to stick a microphone in there somewhere, firstly it might sound interesting as you break mach1, secondly, it might give useful data, such as the detection of dangerous levels of vibration.


Pressure sensors, good to know. I'm sure the aero guys will know better than I do about what sort of sensors and telemetry they'll want, but I'm mentally preparing for it in advance... it'd be nice to have something constructive to bring to the meetings, and you folks are awesomely helpful in that regard :)

Attitude sensors as well as direction-we're-moving sensors? That sounds important. I'll bring it up, though I don't know offhand how such sensors are different. Yay learning experience!

A microphone (and very likely 1+ video camera[s]) seem like awesome ideas.

idobox wrote:About the radio transmission, you have to make sure the doppler effect won't be a problem.
Mach 1 is about 1ppm of light speed, so frequencies will shift by that amount. Some radio-equipment, especially in the mm band, and with high bandwidth can have problems with that.


Hmm, that's a good point; I hadn't considered Doppler shifts. I'll have to ask the guy with the transceiver if it can handle or be made to handle high relative velocities.

Mr_Rose wrote:People have been saying that liquid rockets are too fiddly and solid too uncontrollable; has anyone considered a hybrid? As in solid fuel liquid oxidiser?


I'll be honest, my knowledge of amateur experimental rocketry isn't up to snuff on how those work. Do hybrid rockets have similar weight and complexity issues vs. straight liquid-fueled rockets?

Velifer wrote:
nehpest wrote:What is the usual method of determining attitude in, say, single engine civvie craft? I assumed everybody used gyros for that; is there another method that's more common?

Yes. They're called "windows."

Cool project. Can you tell us who's helping to fund it?


Probably VFR isn't going to cut our safety requirements :D We're being funded (at the moment) about half and half by the school's ASI (shameless plug) and our student chapter of the AIAA (also shameless). Since we're in the greater LA metro area, we are planning to go to some of the more affluent areas and look for private sponsors, but I don't think we have any particular plans in that regard just yet.

Korrente wrote:A gyro system will require motors or a vacuum system to get it spinning, and then more sensors to read their movement (usually it's just slaved to a moving card on the instrument panel, but not in your case). Using accelerometers to measure change in pitch/roll and rate of turn will definitely suit you better. You go from a 3-pound hunk of 10000rpm metal to a few tiny sensors


Ah, yes! I read about MEMS last night after I stopped paying attention to the fora. Obvious benefits aside, that weight reduction is also very attractive. Three pounds less weight translates into just a little bit more acceleration, which is awesome.

GenericAnimeBoy wrote:Reliance on visibility through the windows to provide attitude and collision avoidance information (ie: VFR) is contingent on weather conditions. All but the lightest civilian aircraft have an "Artificial Horizon" gyroscopic attitude indicator. http://en.wikipedia.org/wiki/Attitude_indicator

EDIT: The Wikipedia article I linked has some interesting information to the effect that mechanical gyros are beginning to be supplanted by integrated systems that use solid state or MEMS accelerometers which are lighter and more reliable. Might be a good line of research.


We'll almost certainly have an artificial horizon indicator at the ground station; after all, these guys have spent the last 3+ years being indoctrinated into the best practices of the aerospace industry. I wonder if any of them have piloting experience... :?:
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Re: Civilian Avionics

Postby p1t1o » Mon Feb 07, 2011 8:00 pm UTC

nehpest wrote:Attitude sensors as well as direction-we're-moving sensors? That sounds important. I'll bring it up, though I don't know offhand how such sensors are different. Yay learning experience!


The sort of thing you will need are things like angle-of-attack sensors - this will show the difference between the the way the aircraft is pointing and the direction the air is flowing. Looks something like this:
http://commons.wikimedia.org/wiki/File: ... ator_1.jpg

And take a look at pitot sensors/probes (essentially just a pressure sensor on the end of a stick), they will give an airspeed reading (ask your guys about indicated and true airspeed) based on the actual air flowing past the aircraft rather than speed along the ground. In fact, just found this one that incorporates an AoA vane too:
http://en.wikipedia.org/wiki/File:Airspeed_p1230157.jpg

All these sensors need to be placed at appropriate places on the airframe so get usable data from the airstream so make sure the right people know what you need, holes need to go in the right places :wink:
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Re: Civilian Avionics

Postby gorcee » Mon Feb 07, 2011 8:20 pm UTC

You'll also need things like: control surface deflection sensors, landing gear sensors, airframe loading sensors, fuel rate sensors, skin temperature sensors, etc. etc. etc.

The most complex part of building an aircraft is configuring the flight control system. Lockheed hires more computer scientists than aerospace engineers. Getting flight controls certified is a massive and expensive effort.

To understand the sensors that you would need, you'll need to understand control systems and vehicle dynamics modeling. The sensors you need are the sensors required to fill out your observability matrix.

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Re: Civilian Avionics

Postby Mr_Rose » Mon Feb 07, 2011 9:00 pm UTC

nehpest wrote:
Mr_Rose wrote:People have been saying that liquid rockets are too fiddly and solid too uncontrollable; has anyone considered a hybrid? As in solid fuel liquid oxidiser?


I'll be honest, my knowledge of amateur experimental rocketry isn't up to snuff on how those work. Do hybrid rockets have similar weight and complexity issues vs. straight liquid-fueled rockets?

Not really; that's the genius of them. You get a relatively easy to handle and form rubber compound as a fuel with a hole, or series of holes through it, and pump oxidiser down it. Half the plumbing (and therefore complexity) of liquid-fuelled rockets plus the ability to switch the thing on and off or, if you're ambitious, throttle.
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Re: Civilian Avionics

Postby idobox » Tue Feb 08, 2011 12:07 am UTC

About localizing your aircraft, civilian GPS won't work out of the box, but civil aircrafts know where they are. I don't know what system they use, but it's probably worth looking at it.
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Re: Civilian Avionics

Postby p1t1o » Tue Feb 08, 2011 2:38 pm UTC

Civil aircraft do use GPS.

There are some pretty handy ones here, specifically for aviation:
http://www.transair.co.uk/

Back in the day, before it was integrated in a fleet-wide update, RAF tornados and harriers were "upgraded" with garmin handheld GPS in the cockpit.

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Re: Civilian Avionics

Postby Solt » Tue Feb 08, 2011 9:06 pm UTC

Korrente wrote:
nehpest wrote:What is the usual method of determining attitude in, say, single engine civvie craft? I assumed everybody used gyros for that; is there another method that's more common?


A gyro system will require motors or a vacuum system to get it spinning, and then more sensors to read their movement (usually it's just slaved to a moving card on the instrument panel, but not in your case). Using accelerometers to measure change in pitch/roll and rate of turn will definitely suit you better. You go from a 3-pound hunk of 10000rpm metal to a few tiny sensors


What.


IMU = gyro + accelerometers. And it's no bigger than an inch square.
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Re: Civilian Avionics

Postby Korrente » Tue Feb 08, 2011 9:38 pm UTC

What what?

I'm talking about not using typical iron-gyros, which is the usual method of determining attitude in single engine civilian aircraft. I fear an IMU that small would, like others have said, produce too much noise to be useful in this application. Maybe I'm wrong but wouldn't a gyro small enough to fit three on a square inch precess (and become inaccurate) extremely quickly due to the plane's movement? I still say a MEMS box is definitely the way to go: they work for models, they work for the aircraft I fly, they work for 747s. A good one's a little larger than a cubic inch but they're extremely accurate.

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Re: Civilian Avionics

Postby Solt » Wed Feb 09, 2011 5:03 am UTC

Korrente wrote:Maybe I'm wrong but wouldn't a gyro small enough to fit three on a square inch precess (and become inaccurate) extremely quickly due to the plane's movement? I still say a MEMS box is definitely the way to go


We're probably talking about the same thing. I've only used solid state gyros, so MEMS if you want to use that term. In fact I've never had the chance to see an old fashioned gyro for myself. The times, they are a changed.

Edit: well, not exactly solid state. They have moving parts internally obviously but they come in IC packaging.
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Re: Civilian Avionics

Postby Sockmonkey » Wed Feb 09, 2011 1:08 pm UTC

This guy built his own self-balancing scooter. Some of his open-source coding for the thing and information about the sensors he used might be helpful. http://tlb.org/scooter.html

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Re: Civilian Avionics

Postby Hemmers » Wed Feb 09, 2011 2:47 pm UTC

Solt wrote:I am not an aerodynamicist, but I'm guessing that control surfaces produce bigger responses for the same angle as you go faster.

Yeah. On light aircraft with direct controls you can feel the airflow pushing back - the stick is firm in your hand. When you bring the aircraft up the the stall, you can mush the stick all the way round the box with absolutely no effect, because not enough air is flowing over the control surfaces.

It's not a bigger response per se, just a faster one. If you're flying along at 60 knots and put on y-degrees of roll, you'll roll at a given rate (1 roll per z metres travelled).
At 600 kts, the effect is exactly the same, but you're covering those z metres 10x faster, the roll rate (z) is the same, but will take less time - but the same response nevertheless.

Minimum airspeed is also one of the reasons gliders need a wingman to hold and run the wing-tip until you're going quick enough that the control surfaces can be used to keep the craft level.

This is also the reason as others have already mentioned that you'll need a pitot tube:
Indicated Airspeed != Actual Ground Speed

GPS will give actual speed over ground (SOG), your Pitot will tell you what your airspeed is.


Because these speeds mean your control inputs are much faster and the whole aircraft is basically more sensitive, you'll almost certainly need a gyroscope package to monitor pitch/roll/yaw and feed into the control stack, so you're essentially looking at a fly-by-wire concept.
On the upside, the Ardupilot project already has a UAV on a board with a full guidance package. Don't know how it will cope with M+ or if it's really suitable, but it's worth looking at for ideas on implementation, as indeed is the whole DIY Drones site.

Solt wrote:Also according to wikipedia apparently control surfaces have no effect as you break the sound barrier. I don't know what's up with that but yea, also a potential problem for a pilot. I wouldn't trust this to a human personally, but for a bunch of students the controls problems are not trivial.


Yeah, this was a problem when they first developed supersonic a/c.
In WW2 a few Spitfires got close to M1 in steep dives and the control surfaces pretty much jammed. RAF solved it with fully-moving tail planes rather than the traditional elevator tabs at the back of the tail planes (which the Americans promptly stole for their M1 aircraft).

This will be for their aerodynamicists to work on and specify rather than the avionics team.
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Re: Civilian Avionics

Postby p1t1o » Wed Feb 09, 2011 4:06 pm UTC

Hemmers wrote:Yeah, this was a problem when they first developed supersonic a/c.
In WW2 a few Spitfires got close to M1 in steep dives and the control surfaces pretty much jammed. RAF solved it with fully-moving tail planes rather than the traditional elevator tabs at the back of the tail planes (which the Americans promptly stole for their M1 aircraft).


This effected the elevators and was caused by shockwaves that form over the tailplane moving differently on the upper and lower surfaces, as speed increases shockwaves move back, the upper one reaching the elevator first, forcing it down and steepening the dive.

There was also the problem of wing twist, as control moments increased at high speed, the force produced by an aileron when a roll was desired would twist the whole wing, effectively making it into one giant aileron, but acting to roll the aircraft in the opposite direction (!).

Interesting stuff this.

Slightly OT but one of my favorite anecdotes involving aerodynamic heating - the sprint anti-ballistic missile developed by the US during the cold war accelerated to mach 10 in a handful of seconds. Largely due to it starting in the thick lower atmosphere, aerodynamic heating heated it so hot that an oxy-acetylene torch would have cooled it down.

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Re: Civilian Avionics

Postby gorcee » Wed Feb 09, 2011 6:09 pm UTC

All this talk of gyros is kind of silly, considering any weight gain saved is going to be much smaller than engineering the control surfaces to meet free-play specifications. All-moving horizontal tail free-play limits are [imath]/pm 0.017^\circ[/imath], or a total of [imath]0.034^\circ[/imath]. In order to meet that, you're going to need some seriously beefy electrohydrostatic actuators. I don't believe that any current production aircraft meet this specification, because they are waived by wind-tunnel testing.

But to get such a waiver for a supersonic vehicle, you'll need to do transonic testing. There's one (well, two, kind of) wind tunnel in the US that has continuous dynamics testing, and it costs around $80,000 per day to operate, and that doesn't include the cost of constructing the model.

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Re: Civilian Avionics

Postby nehpest » Thu Feb 10, 2011 2:16 am UTC

gorcee wrote:All this talk of gyros is kind of silly, considering any weight gain saved is going to be much smaller than engineering the control surfaces to meet free-play specifications. All-moving horizontal tail free-play limits are [imath]/pm 0.017^\circ[/imath], or a total of [imath]0.034^\circ[/imath]. In order to meet that, you're going to need some seriously beefy electrohydrostatic actuators. I don't believe that any current production aircraft meet this specification, because they are waived by wind-tunnel testing.

But to get such a waiver for a supersonic vehicle, you'll need to do transonic testing. There's one (well, two, kind of) wind tunnel in the US that has continuous dynamics testing, and it costs around $80,000 per day to operate, and that doesn't include the cost of constructing the model.


I'm posting from my phone so I won't respond directly to everybody's posts, but I wanted to let ya'll know that our next full meeting, so I'll be able to provide a full update after that.

Also, re wind tunnel testing: this is one area in which we're quite fortunate. We have a supersonic wind tunnel right here on campus that can exceed our current design goals; I've read some of the masters theses from previous years, and learned that it's apparently pretty nicely appointed. University policy is that we're free to use it as long as we don't interrupt any faculty usage.

EDIT: Now that I have a keyboard...

p1t1o wrote:And take a look at pitot sensors/probes (essentially just a pressure sensor on the end of a stick), they will give an airspeed reading (ask your guys about indicated and true airspeed) based on the actual air flowing past the aircraft rather than speed along the ground. In fact, just found this one that incorporates an AoA vane too:
http://en.wikipedia.org/wiki/File:Airspeed_p1230157.jpg

All these sensors need to be placed at appropriate places on the airframe so get usable data from the airstream so make sure the right people know what you need, holes need to go in the right places :wink:


That AoA vane looks like it will do it - somehow I suspect the aero guys know about it already, but it's good for me to know now. The holes are really what's on my mind - I suspect the body foam isn't exactly cheap, given what they're saying it can do, so I don't want to say "Oh, yeah, guys - I need you to drill a hole through that expensive foam so I can run a cable to the XYZ widget" after the body is already fabricated.

gorcee wrote:You'll also need things like: control surface deflection sensors, landing gear sensors, airframe loading sensors, fuel rate sensors, skin temperature sensors, etc. etc. etc.

The most complex part of building an aircraft is configuring the flight control system. Lockheed hires more computer scientists than aerospace engineers. Getting flight controls certified is a massive and expensive effort.

To understand the sensors that you would need, you'll need to understand control systems and vehicle dynamics modeling. The sensors you need are the sensors required to fill out your observability matrix.


Good points all. I wouldn't have thought of landing gear sensors, but it is a silly oversight in retrospect - we're not going to break Mach at all with big clunky wheels disrupting our airflow, obviously. However, I don't know what skin temp sensors are meant to accomplish. Does that have to do with the aerodynamic heating p1t1o mentioned?

I haven't had a class dealing with control systems yet; what sort of knowledge is prerequisite for learning about them? If by vehicle dynamics you mean things like airflow simulations and things of that sort, I don't think I'll be involved in it; if not, would you clarify what that is?

Mr_Rose wrote:Not really; that's the genius of them. You get a relatively easy to handle and form rubber compound as a fuel with a hole, or series of holes through it, and pump oxidiser down it. Half the plumbing (and therefore complexity) of liquid-fuelled rockets plus the ability to switch the thing on and off or, if you're ambitious, throttle.


Fascinating. This seems like a good idea to toss to the propulsion guys.

Re: GPS. We're almost certainly going to have GPS aboard.

Re: gyros, MEMS, and accelerometers, oh my! The consensus forming in my head is that big spinning gyroscopes are a poor choice, and that a combination of IC gyros and accelerometers will give me the best performance for my weight and space. Is that about the size of it?

Sockmonkey wrote:This guy built his own self-balancing scooter. Some of his open-source coding for the thing and information about the sensors he used might be helpful. http://tlb.org/scooter.html


I dug through that site, and it's extremely interesting and informative. If I had more disposable income and less self-discipline, I'd be buying equipment and parts to build myself one. Thanks for that, Sockmonkey!

Hemmers wrote:Yeah. On light aircraft with direct controls you can feel the airflow pushing back - the stick is firm in your hand. When you bring the aircraft up the the stall, you can mush the stick all the way round the box with absolutely no effect, because not enough air is flowing over the control surfaces.

It's not a bigger response per se, just a faster one. If you're flying along at 60 knots and put on y-degrees of roll, you'll roll at a given rate (1 roll per z metres travelled). At 600 kts, the effect is exactly the same, but you're covering those z metres 10x faster, the roll rate (z) is the same, but will take less time - but the same response nevertheless.


That all jives with what I thought I knew about aerodynamics, sweet. A childhood spent playing with flight sims wasn't completely in vain!

Because these speeds mean your control inputs are much faster and the whole aircraft is basically more sensitive, you'll almost certainly need a gyroscope package to monitor pitch/roll/yaw and feed into the control stack, so you're essentially looking at a fly-by-wire concept.
On the upside, the Ardupilot project already has a UAV on a board with a full guidance package. Don't know how it will cope with M+ or if it's really suitable, but it's worth looking at for ideas on implementation, as indeed is the whole DIY Drones site.


This is extremely interesting, and will be shared tomorrow if I can squeeze it into the agenda.

This will be for their aerodynamicists to work on and specify rather than the avionics team.


Quite true! However, I'm all for it if people want to throw suggestions out that I can communicate to the team.

p1t1o wrote:Slightly OT but one of my favorite anecdotes involving aerodynamic heating - the sprint anti-ballistic missile developed by the US during the cold war accelerated to mach 10 in a handful of seconds. Largely due to it starting in the thick lower atmosphere, aerodynamic heating heated it so hot that an oxy-acetylene torch would have cooled it down.


Is this something we'd have to contend with? We'll be going almost an order of magnitude slower; I don't know what sort of accelerations we're expecting, though.
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Re: Civilian Avionics

Postby Sockmonkey » Thu Feb 10, 2011 9:15 am UTC

IIRC a team working on an M3+ missle in the 60s used a commercially available car manifold paint for certain high temp areas. Remember, engineering solutions are everywhere. Even in apparently unrelated areas.

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Re: Civilian Avionics

Postby p1t1o » Thu Feb 10, 2011 9:40 am UTC

nehpest wrote:Also, re wind tunnel testing: this is one area in which we're quite fortunate. We have a supersonic wind tunnel right here on campus


This. Is. Awesome.


nehpest wrote:However, I don't know what skin temp sensors are meant to accomplish. Does that have to do with the aerodynamic heating p1t1o mentioned?


Yup, temperature can effect structural strangth, flexibility and so on, you need to know that it is not going to fly apart if you speed up. Wind tunnel testing though will be a good indicator of how much heating will take place - see below.

nehpest wrote:
p1t1o wrote:Slightly OT but one of my favorite anecdotes involving aerodynamic heating - the sprint anti-ballistic missile developed by the US during the cold war accelerated to mach 10 in a handful of seconds. Largely due to it starting in the thick lower atmosphere, aerodynamic heating heated it so hot that an oxy-acetylene torch would have cooled it down.


Is this something we'd have to contend with? We'll be going almost an order of magnitude slower; I don't know what sort of accelerations we're expecting, though.


Hehehe, nope, the above is an extreme example. For a body at around mach one, I imagine the heating will be on the order of a hundred or so degrees celcius, give or take a bunch, depending on the planned altitude. Also your aircraft will accelerate alot more slowly, allowing heat to equilibrate somewhat. The sprint missile accelerated at 100gs and had a heat shield that boiled off to remove excess heat, plus, it only had to survive a maximum of about 15 seconds from launch to intercept anyway.


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