Recover System (Parashutes)

[libelulamodelos]

do you use these kind of systems, how ? where? home build? what else??

give me some ideas, to put in my uav project.

[kd7ost]

Now thats a cool topic.

What are you planning on putting it on? Electric? Gas, Glow? Engine in front? Behind? I have thought this through a lot but am not employing it.

Dan

[libelulamodelos]

i use a .60 osmax engine, an a futaba 6 chanel radio.., a pusher helice !!

[kd7ost]

a pusher helice !!

I don't know what that is?

Dan

[libelulamodelos]

yeea my english is not ok, i know a pusher helice.

http://www.todohobbies.com.uy/productos/catalog/product_info.php?products_id=1099&osCsid=6f6a370407cda7884421a7ef84c21fa9

[Medve]

if you are using something like an AP4, you can set up the mission servo to kill the power, and pop a 'chute. Right now, they only come with one mission servo option, but the designer is working to add a second. Another option is to have the servo stop the motor, and have the "rout" on the gps programmed for continuous circles. This should bring in down in a gentle circle as long as it's not too windy.

[clolson]

Anyone know how big of a chute you'd need to gently let down a Sig Rascal110 (maybe 13-15 lbs?) Do I need to tape a couple garbage bags together, or are there commercial chutes or deployment systems available?

I don't know that I'd install one tomorrow, but it would be nice to have some leads on this in case it became politically beneficial to install something on our university UAV.

Curt.

[kd7ost]

And the garbage bags might serve a dual role in case things don't work out well. :eek: :D

Just kidding Curt,

Try http://www.the-rocketman.com/chutes.html
and
http://www.spectrachutes.com/
and
http://www.spherachutes.com/

There's more. Just do a google search on "Parachute, Model rockets". The Rocketman chutes are very heavy duty and have only a few lines for ease of packing. I would recommend at least an R12 and likely a R14 if you want things coming down soft. They rate the chutes for a descent rate that gets a heavy duty high altitude rocket down without drifting into the next state. (A little on the fast side)

Dan

[clolson]

Thanks for the links Dan. Something like this might be perfect if you get caught with an engine outage at an awkward altitude. Or, if you or your system decides you have a hopeless failure. I'd hate to see what happens if you released the chute in a 120mph dive. Whereever your main attach point ends up, you might want to tie off the very end of the rope to the engine or engine mount some how so if things go really wrong you at least are letting the heavy stuff down slowly ... and all the balsa bit can float in the breeze.

You'd have to come up with something semi clever for stowing it and deploying it reliably ...

[LukeZ]

I've been thinking about this too, but have yet to do any empirical testing. I probably just need to build a small e-powered model just for testing of this kind of thing.

I really liked the approach Art took with his Glidersonde (http://members.shaw.ca/sonde/index.htm) to estimate wind speed and direction, and then have the on-board computer calculate the correct altitude and position to pop the chute such that it would float down to a specific landing site.

As has already been mentioned there's two big issues to consider: attachment point and how to deploy. Some of this might depend on what you hope your chute to accomplish - if only for backup, extra-horrible emergencies, that's one thing. Maybe some structural damage could be accepted. If it's wanted as the regular UAV landing method then perhaps the approach would differ. Of course if one could anticipate the chute being deployed in controlled circumstances it might make the hardware design a bit easier. For example, you could have the autopilot initiate an unpowered climb to bleed airspeed and then pop the chute at minimum forward velocity. This would decrease the shock to the system when the chute fills. But, if you think you might need it to save your skin on an uncontrolled dive at high speed... who knows!


Luke

[kd7ost]

Art's a master,

I would be happy to just have the glider deploy the chute once in the general area and down to 1000 feet agl. I'll walk the rest of the way because for me thats easier than the porgramming. ;)

In a powered UAV though, I figure the parachute would deploy (In my scenarios) in the event of some catastrophic failure. I would probably use the Basic Stamp to watch some functions and have it take care of the chute deployment sequence. It would have to take a combination of things to activate the chute in almost all cases that I can think of. The exception might be a catastrophic power failure. I would have the code even written so it has to go into flight mode before any chute deployment could even happen. Like, you have to be operating under failsafe conditions, (No pilot in command) before it's even armed. Then things like GPS failure would cause first an engine shutdown, then a chute deployment.

The chute tie down point would likely have to be incorporated into the spar. Thats a natural strong point. The rocket man chutes above are shaped in a way that allows a "soft" deployment in a big ballistic rocket. Failing that method, a deployment ring slid up the suspension lines will allow a chute to open more gradually so the desceleration isn't a violent shock. Once you pass the openning shock OK you got it made.

I think of a hatch over the chute holder that is hasped with a micro servo in the front. Make the hatch an airfoil shape so it's always trying to lift anyway. That uses dynamic flight forces to do the deployment job for you. Pin it in the front so when it deploys it lifts from the front. As soon as it catches air under it, it's flying loose. Have the hatch be the drogue chute for your main chute. Tie a short, (2 to 3 foot) lanyard to the apex of your main chute. Have your main chute S folded into a slick walled shallow box so nothing hangs it up on the way out. Once it gets just a little air in the folds, it's coming out.

Dan

[kd7ost]

yeea my english is not ok, i know a pusher helice.

http://www.todohobbies.com.uy/productos/catalog/product_info.php?products_id=1099&osCsid=6f6a370407cda7884421a7ef84c21fa9

Thats OK, I don't speak Spanish at all.

Do you have a picture of your plane? We don't see many .60 size pushers planes.

Whatever you do with the deployment system, you have to make sure the propellor is not turning when the parachute comes out. The engine shutting off might be the reason the chute deploys. But if it's a different problem, you have to make sure the failsafe system shuts down the engine. I would make closing the throttle servo to shut down happen first even if it's an engine failure. Put it in a sub routine. Then a delay of a few seconds. This makes sure the prop is not turneing anymore. Then let the parachute deploy.

Like this.

Failure condition exists.
goto chute deployment

:chute deployment
shut down engine
pause 3 seconds
operate hatch servo
end

Dan

[LukeZ]

Hey Dan, that's a pretty good idea about using areodynamic forces to lift the hatch, and then using the hatch as a drogue. Hmm, I'm glad this thread got started.

You mentioned a deployment ring slid up the suspension lines. Is that basically just a ring to prevent the suspension lines from spreading too fast, but as the ring slides down they would open more? I've never heard of that but I guess it would work, so long as the ring didn't get tangled somehow. Wouldn't want to use a keychain ring I suppose, since the sharp edge could get caught.

I was thinking I would also want maybe a length of bungee in the line - I did this with my little model rockets as a kid. Only I think I just used a bit of rubber-band.


Luke

[kd7ost]

Luke,

I think any steel ring would work OK as long as like you said, it isn't sharp. You can get welded steel rings from farm supply stores etc. It works exactly as you describe. It prevents the chute from openning fully in one big whap. But as it fills with air it starts to spread the suspension lines and starts the ring sliding down to the tie point. The farther is slides, the more the chute can open. I think it takes a couple of seconds for full deployment instead of a millisecond. (Or whatevr) Thats a lot of variation but basically it decays the full openning long enough to spread the forces of impact (openning shock) over a longer time frame. Smaller pull for a few seconds instead of massive force in a 1/4 second or whatever the times are. It's a common practice when you have big fast loads going at warp speed and you need the chute openning forces to be spread out to minimize high amplitude instantaneous stress.

Is it the chute or the airframe holding up that concerns you?

Dan

[LukeZ]

Is it the chute or the airframe holding up that concerns you?The airframe. If the thing deploys in an orderly manner then ok, I don't see much of a problem. But if the plane is in a dive or even just cruising along at 60 miles an hour that could be a lot of Gs.

You know, it wouldn't be too hard to put an accelerometer in a testing plane and measure just how many Gs it would be, now that I think of it.

Another thing I've wondered about some is balancing the aircraft underneath the chute. I certainly wouldn't want it landing tail first or anything. At the same time, the location you may want to tie off at, such as the spar, may not be the C of G. So I'd think there would be some trade-offs, just as with most things.


Luke

[alexcmag]

yeea my english is not ok, i know a pusher helice.

http://www.todohobbies.com.uy/productos/catalog/product_info.php?products_id=1099&osCsid=6f6a370407cda7884421a7ef84c21fa9

Helice (in portuguese or spanish) is Propeller (in english).

[kd7ost]

Helice (in portuguese or spanish) is Propeller (in english).

Thanks alexcmag

I needed an enterpreter.

Dan

[kd7ost]

The airframe. If the thing deploys in an orderly manner then ok, I don't see much of a problem. But if the plane is in a dive or even just cruising along at 60 miles an hour that could be a lot of Gs.

You know, it wouldn't be too hard to put an accelerometer in a testing plane and measure just how many Gs it would be, now that I think of it.

Another thing I've wondered about some is balancing the aircraft underneath the chute. I certainly wouldn't want it landing tail first or anything. At the same time, the location you may want to tie off at, such as the spar, may not be the C of G. So I'd think there would be some trade-offs, just as with most things.


Luke

Mass is a big factor too. I think even if the plane is going real fast you should be OK as long as you tie into the main spar.

When I was in the Army I jumped out of C-130 and C-141 aircraft at 150 mph. (130 knots) We jumped static line so your chute opened real fast. You would go from about 150 MPH out the door to descending under the parachute within ~2 to 3 seconds. As a larger than average guy I jumped out with all my gear strapped on me at close to 280 pounds. The full force of the deceleration came from two 2 inch wide straps located either side of your manhood. :eek: (It was up to each person exiting the door on that pass to make sure everything was properly placed before the green light came on ;)) (edited this in) This ~2 to 3 second deceleration made it very bearable.

That’s a lot of force exerted in a very short period of time and usually it left bruises but never hurt anyone bad. (We always breathed a sigh of relief actually at the "impact of opening shock" as we called it. It meant you weren't going to feel the impact of terra firma :D ) (edited this in) If you had hit the ground without a chute you would only be going maybe 100 to 120 mph but the deceleration would be instantaneous and would kill in almost every impact.

I just laid this story out here as a point of reference. People can envision the stress of something like this and relate to it even if they haven’t done it. A 20 pound plane traveling at 80 mph won’t come close to that kind of stress force. As long as you tie off at a strong point in the plane, and select a method that allows the chute to deploy over a several second timeframe that will work fine. Your tie off method in the plane could also be spread around. That would keep the forces from being concentrated in just one spot. It’s simpler too than trying to put a bungee in line with the weak points where it ties to the frame and to the parachute suspension lines. You just have to spread the deceleration out over a several second time frame. It’s like the mechanics of a crumple zone in a car. Once the openning shock is over with, your home free. How tough the system needs to be will depend on your static weight at the highest point of stress. This will be a factor of mass(weight) x speed x deceleration (how fast you bring it to a stop)

If the chute is secured at the center of lift on your plane, that should get the plane descending in a horizontal manner. Unless the chute is too small for your plane. If it descends fast, the weather cock effect will still take place in the plane aerodynamics and it will nose down. You may want to have a kite yoke type of a tie off to address that. One line at the LE and one farther back. But the main lift line still centered over the Aircraft center of lift.

Dan

[LukeZ]

Having multiple tie-off points would be ideal - the only thing there is that you pretty much have to run lines external to the fuse. This could create drag and/or be unsightly. But I suppose you could tape them down; then, when the chute deployed, the force would simply rip the tape off.

Even with only one tie-off point this may still be necessary, as it might not always be possible to locate your chute box at the exact location of your tie-off point. In fact if you want to attach to the spar this is probably never going to be the case.

If you had a crumple-cone on the front of your craft (especially if you were using a pusher design), then I suppose you could attach the chute to the tail and have it come down nose first. But it would be hard for me to see how this wouldn't result in some kind of damage somewhere to the craft. But, if you're just using it for emergencies that would probably be ok - at least your many thousands of dollars worth of electronics inside should be fine.


Luke

[ElectroLawndart]

Hi All,

You could use the technique we used in model rocketry.
Have the A/C seperate itself in to a few pieces. ie: seperate the wing and tail booms from the fuselage. All the parts are still tethered together but on a long string. This seperates the landing impact into a higher number of smaller impacts. The fuse can come down on a crush cone nose, the wing structure doesn't have to cope with the mass of the fuse on landing, etc. Just make sure the heaviest parts are at the bottom. No sense having the wing touchdown nice and soft only to have the fuse and motor come crashing down on it. :eek:

Dart

[kd7ost]

do you use these kind of systems, how ? where? home build? what else?? give me some ideas, to put in my uav project.

libelulamodelos,

It looks like you got some idea's here to work with anyway. If it was me I would put a well built chute in a compartment under a flyaway hatch just behind the trailing edge. I would use a nylon strap secured to the aircraft tying into the main wing spar between the fuselage wall's. Size of strap and parachute would depend on weight of aircraft. That strap can lay down with velcro right on top of the wing where it enter's into the front of tha hatch down to the chute. I might use a deployement ring if it's a conventional chute, or I would just use a Rocket man chute which is designed to deploy a little slower than normal. Thats one tough chute too. If you have a little plane, I wouldn't worry about too much. The recovery system has weight to it.

Obviously there are other idea's that have other factors to work with. I say it's a potentially complex process or potentially simple. It's all what you make it.

Dan

[libelulamodelos]

yea i got some ideas right now, i will start to do it, in few days photos from my project.

sorry for my sintaxis :)

Helice (in portuguese or spanish) is Propeller (in english).

thanks..