uav emergency parachute

[johnthewelder]

would a uav the size in the photo,be recoverable with a parachute at 400ft. altitude?

[jtprouty]

John,

If you had a way to rapidly deploy a parachute I would think you'd have a good chance at recovering the aircraft. It would all depend on the speed of the plane when the chute is deployed. If you deployed a drogue chute and could unfurl your main fast enough you should be OK.

Jimmy

[clolson]

I did one quick parachute drop test with a 6lb airplane. I came away from that with a couple thoughts.

1. You are going to need a parachute that is probably bigger than you'd size it going just from your gut. The rocket guys have web sites that will size the parachutes based on weight, however, they want their stuff to drop pretty fast so it doesn't drift too far down range. You are probably going to want to go quite a bit bigger than whatever they suggest.

2. The attach point is extremely critical. For my test I thought I had everything centered and balanced exactly the way I wanted. I dropped it with the chute open, and it went into the ground with a nasty spiral. You don't want it to fall too nose down or too tail down or that part will end up absorbing the entire blow of the "landing."

3. I started wondering about some sort of spoilers or way to stop the wing from wanting to fly. Perhaps a properly sized chute at the exactly CG will take care of that problem?

4. Even dropping the airplane with the chute open (off a high ledge) it still took longer than I thought it should for the chute to fully open and fill with air.

It looks like you are thinking about a way to protect or save your baby in case of a problem in air. But I will claim that parachute recovery is trickier than it looks and if you aren't very careful, you could end up just making things worse for yourself.

I'd suggest starting much smaller and doing a lot of testing. You need a clean release mechanism and a chute that reliably and quickly deploys. How/where are you going to pack the chute? You'll need to come up with an appropriate chute size to balance decent rate, down range drift, weight, and packed up size. And building a reliable release/trigger mechanism isn't always a no-brainer either. You don't want a hatch popping off prematurely or getting stuck or rattling around in the wind.

My personal opinion is that if you are staying below 400' AGL, your margins are going to be extremely tight for getting a chute to successfully deploy off of such a large beast as your picture indicates. If the point is to save your butt in some unexpected situation, you are probably going to be much lower than 400' AGL by the time your finger finds the right switch. And your aircraft is going to spend much of the time in approach or climb out phases where a chute isn't going to do you any good.

Just my 2c ... :-)

Curt.

[jtprouty]

When I designed the Vector P UAS I designed a hatch into the aft portion of the fuselage that would open rearwards expelling the chute and it's drogue. The lanyards for the chute attach to the main wing spar which is on the CG. My reasoning was that the hatch would help fling the chute free of the airframe, keep the lanyards out of the engine and empenage, and, once the chute was deployed, the plane would land on its landing gear helping to absorb the shock of the premature landing. I'm more interested in saving the payload (and any unfortunate soles on the ground) than I am saving the airframe.

Speed rings can be put on the main lines of the chute to help control opening shock at higher speeds and won't appreciably slow the opening speed of the chute at lower airspeeds.

Unfortunately, I never got to test the system, just integrated it.

Happy flying,

Jimmy

[kd7ost]

I think there would be no trouble as long as the chute is given every chance to get out of the plane. I agree with JProuty that saving the cargo is important. I did some parachute drop testing a handful of years ago with a trainer. What I learned is that if you tie the chute on the spar that during descent the weather cock effect of the tail feathers caused the plane to come down in a nose low/tail high attitude. To flatten it out I would use a yoke like a kite string to pull from near the nose and near the tail section. The yoke would have to be fairly long to work effectively.

Deployment time is also like Jimmy planned. I used a servo to release the front of the hatch and once pivoted up it flew free though. (I didn't have a pusher set up like he designed for so no prop to get in the way) The parachute was tucked inside with a plastic (like thick RC windshield material) wrapped around the S folded chute. Not only did the hatch flying free acting as a drogue tied at the apex of the main chute, but rubber bands and the plastic sheet literally pushed the chute out through the opening. The chute was pushing up against the hatch trying to get out all the time. When the unit was activated the slowest action in deployment was the servo transition at the hatch. Once that hatch went free the chute was deployed inside of a second. Swinging under the canopy wasn't a big issue either. A bigger chute, slower descent, higher winds and load line length will dictate the amount of swinging. But once everything is drifting down wind equally the oscillation stops very quickly. I wouldn't use a bungee at all to help decelerate the opening shock. It's too many parts and a critical point of failure. Again, as Jimmy said a deployment ring around the shroud lines will do that and is error free. Unless your plane is going nose down at warp speed when the system deploys I don't think you would even come close to catastrophic impact. It's all about getting the chute out and into the airflow quickly.

The biggest issue is what on board the plane causes the chute to deploy at the right time, and only at the right time. You don't want the engine running when that plane is under canopy. And deploying accidentally on a take off run would toast you as well.

Dan

[johnthewelder]

I was reading that a parachute could be used and a self destruct if that fails.I agree that protecting others and saving the payload is important.But how can someone (civilian) use the self destruct idea? They use explosive bolts on spacecraft.Maybe some homemade explosive bolts made by using 22 cal. nail gun ammo,and an ejection system for the payload (electronics).They have made a chip with built in wi-fi so one chip can communicate with another chip on the motherboard without wires.Maybe the payload could be detached physically from the airframe using this new short distance wi-fi.

[macboffin]

I have a lot of experience with chutes on UAVs. Main points; "A" Attach via a strop/s to very strong point or points so that plane hangs nearly vertical ; slightly nose down best if you have a U/C. "B" reduce opening shock via slider ring over shrouds. "C" Chute size important ; allow about three feet chute area per lb weight.(For comparison think about a man-size chute, around 28-30 feet diameter). "D" Have a two/three second delay between engine-cut and chute ejection. "E" very good if you can rig a chute release either by a ground operated "Stinger" or remote control channel. This saves the plane/remains being dragged into the next county by the wind whilst you sprint after it.(Ask me why I recommend that?).

[Gary Mortimer]

I wondered if I had a simple chute, like a rocket one inside my Stick when the wings folded if it would have helped.

My main 'but' would have been, that as the wings went they took the receiver with them, I had made sure the aileron servo was secure, too secure!!

So I could'nt close the throttle.

My choice would be to have the aircraft arrive tail first to absorb impact rather than the engine and equipment.

If I had set that up I'm sure the prop would have chopped the chute attachments??

How about a hit the button instant airbag around the front of the airframe??

Happy New year to all,

G

[eflyingman]

I have a lot of experience with chutes on UAVs. Main points; "A" Attach via a strop/s to very strong point or points so that plane hangs nearly vertical ; slightly nose down best if you have a U/C. "B" reduce opening shock via slider ring over shrouds.


do you happen to have a picture of what slider rings would look like and how they are implemented?

thx.

[jtprouty]

The slider rings, or speed rings, can be as simple as a steel or plastic ring that goes around the risers or as complex as a round plate that has a hole in it for each individual riser to go through. They are placed where the risers meet the parachute and basically gather the lines together at the top, closing the bottom of the chute. When the chute is deployed the ring slides down the shrouds as the speed slows and allows the chute to open. The slower the speed the more the ring slides down the risers. Eventually the chute will open completely and the ring will be at the bottom of the lines.

Pretty simple but would need some experimentation to get the right setup.

Happy flying,

Jimmy

[jtprouty]

There's a webpage at http://www.butlerparachutes.com/pia99.htm that has information on full scale parachutes with slider rings.

Happy flying,

Jimmy