Sensing lift on a wing

[Higgler]

I have a proposal that needs to sense the forces on a wing due to air turbulence which either enhances or degrades wing lift.
If I placed many sensors on top and bottom of the wing measuring the force applied to these spots (capacitance change due to air pressure, not G force acceleration), can a computer analysis of those forces give an assessment of the change in lift due to forces caused by turbulence?

i.e. is measuring the forces on different parts of a wing enough to calculated change in lift and then correct for it?

I read the Wikipedia lift description, but couldn't answer my question.

Thanks.

 

[IRstuff]

Seems to me that it would be too localized and inaccurate for determining what aircraft should do as a complete entity. Current autopilots make use of the full-body motion sensed by the gyros and accels to determine this.

TTFN

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[GregLocock]

I think strain gauging the spars would be a less haphazard approach.

Alternatively you may well find that detecting turbulence acoustically is a better approach, that's what we do in wind tunnels.

Cheers

Greg Locock


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[Higgler]

This is for tiny UAV's to help them handle turbulence better and auto adjust for it.

My first thought was accelerometers in a few places (4) along the wing, but that seems obvious and probably too simple.

it needs to be ultra light, so a simple printed circuit adhered with flexible adhesive forming an airgap at the sensor so that the turbulence pressure can move the membrane and it's capacitance will change quickly. Similar to a MEM's gforce sensor, but in a printed circuit, which could double as the skin of the UAV.

with alot of small squares or circles (0.1" to 0.5" sisze) of printed mylar attached to , you could sense the forces along the entire wing surface. Then you have to do something (have a fast processor and adjust control surfaces.

might be a foolish proposal, just looking for some clarity here.

 

[GregLocock]

What's the difference between a dynamic pressure sensor and a microphone?

Cheers

Greg Locock


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[IRstuff]

The problem is relating the measured turbulence effects with actual changes in aircraft dynamics. I think that it would difficult at best.

TTFN

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[MikeHalloran]

Isn't mylar film a little bit piezoelectric, like kynar is?

Okay, just skin the thing with kynar; piezo film seems to be available from many sources, in pieces large enough to skin a complete micro-UAV.

Subdividing the metallized faces could work to form individual sensors. I'd want to compare the weight accrued to arrays of capacitance sensors to the weight accrued to arrays of charge amplifiers, which might be simpler, but troublesome in high humidity.

Sounds like great fun.



Mike Halloran
Pembroke Pines, FL, USA

 

[kontiki99]

Not sure what exactly you are trying to see, but one time worn method is tufts of yarn and filming the patterns with an external camera. I don't know how scalable that it. It won't give you quantitative data but will let you identify when and where the areas of interest are.

 

[MiketheEngineer]

Maybe not what you are looking for - but I fool around with electric radio controlled helicopters.

You can buy "autopilots" for them very cheaply!!

And they do a remarkable job of stabilizing these very lightweight machines!!

Just a thought!!

 

[rb1957]

Do you want to know the local pressures, or the integrated load on the wing ? why not attach the wing to a small load-cell ?

when you say "turbulence", do you mean local turbulence (like separated flow, vortex generators, ...) or macro turbulence (like the wake of an airplane, storm, ...) ?

 

[aafuni]

With MAVs you don't really care what the lift is doing, just what the plane is doing. Rather than trying to detect variation in lift between the wings, just detect the roll response to this difference.

You don't need multiple accelerometers across the wing as you said, just one multi axis IMU (inertial measurement unit, basically a bundled accelerometer). The poling rate of modern arduino based systems are fast enough to correct for even minor changes in orientation, and correct for them before they become noticeable to flight.

If you just want to level out the flight of a R/C type MAV then you can simple use a cheap piezo-gyro. Put the gyro in line with your ailerons and as the plane begins to bank, the gyro with normalize the response, resisting deviations from level.

Your pressure based method would be very heavy and computationally intensive for a onboard AP system. I also believe you will have a lot of sensor noise to deal with as the pressure naturally fluctuates of the wing.

-AAFuni

 

[Higgler]

I'd posted this a half hour ago, but it didn't make it thru.


Here's the verbage of what's needed;
Design a concept for equipping small and micro Unmanned Aerial Systems with equivalent capability to sense and respond to small scale turbulent motions in the atmosphere.

so it seems that micro uav's can't handle turbulence and limits their applicability. The requirements sometime hint that current methods don't work.

rb1957, I believe turbulence is due to wind gusts when you are flying right next to and into a building. These are micro uav's, 12" in size typically.

aafuni, seems like you have experience here. I agree the computational challenge in evaluating 10-20 sensors is a limit, and just a few is much friendlier for a real solution. I'd hazard a guess that the wind gusts affect micro-uav's so quickly that the response time might need to sense forces on the tip of a wing before the wind gust hits the opposite wing (purely a guess).

 

[aafuni]

May I ask what this is from?

 

[Higgler]

It's a SBIR for the Army.
sometimes the requested technology is pie in the sky and totally unrealizable, but that's partly the nature of SBIR's. Asking for new technology.

Topic Number: A11-015 (Army)
Title: Direct Sensing of Micro Unmanned Aerial Vehicle Lift

 

[rb1957]

that sounds interesting ...

is the problem that inertia effects are swamping aerodynamic effects ? is the gust picking up the UAV like a toy (such as it is) and throwing it ?

or is it an aerodynamic problem ? is the gust acting on the UAV like a micro-burst, essentially stalling the wing ??

or both !? wing stalls so there's nothing to react the inertia load (so Newton takes over, and the UAV accelerates out-of-sight), or vice versa ?

intersting, verryy interesting

 

[IRstuff]

I'm not convinced that current UAVs can't "handle" turbulence. The issue, invariably, is SWaP, so they could probably do it, but it might be too large, too heavy, or too power hungry or all three. Even a simple quartz rate gyro might be too much weight penalty.

Certainly, UAVs in the Shadow-class and above can deal with whatever comes along.

TTFN

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[Higgler]

I really can't answer the questions rb1957.I'd expect all your assumptions are correct.

These microuav's fly through turbulence just inches away from structures and the ground. I'm guessing that's the challenge. Reaction time needs to be quick, and they also have to be able to take a hit, then restart.

Sounds like one could improve in the flight characteristics for normal turbulence, but to stop a gust from blowing a microuav into a wall from 10 inches away sounds impossible. I think it'll need to fly backwards too.

It feels to me like that improvement is what they're looking for, not a solution.

 

[rb1957]

how do yo guys calc stability for microUAVs ? it's an awfull long time since i did an aero. calc, but i remember (perhaps faultily) that conventional airplane configurations (tailplane, or canard) are stable (ok, not always) ie the H.Stab naturally counters the up-set moment due to a gust. now i imagine in this app you're looking at flight-path deviation which would be less for a more stable plane, yes? if this fixes your problem, it'll create another ... the damned thing will be too stable and won't want to maneouvre ! ... maybe varible stability ??

 

[rb1957]

thinking about this problem, i think you want to control the flight-path; i think it's less of a problem of lift force. i don't think you can create a driven system that will sense the gust and react quickly enough to prevent an excessive deviation from the flight-path (ie crash into the building inches away). i think you need novel aerodynamic solutions, like the Virgin galatic sub-orbital plane ... with it's variable configuration (the tails can unlock and rotate about the fuselage to create a high drag return mode).

maybe you wnat something like blow-out panels in the wing surfaces, so that the high pressure of the gust isn't reacted by the wing surface (and so doesn't affect the airplane's CG ??

 

[Higgler]

Just heard from the tpoc.
They want a sensor set to add to the body of the micro uav. No particular microuav has been designated.

Once in place, they'll later develop the control computer to adjust the control surfaces.

rf1957, I think you're correct, something novel is needed.

But designs of microuav's take a long time to get results. This is a low budget "see if you can make a sensor" project.