Braking Parachutes for Aircraft: Max Airspeed & Benefits

[Sojourner01]

I'm aware that some fast aircraft possesses drag 'chutes to slow them down on landing. I was pondering a few things about these...

At what maximum airspeed can aircraft that possesses them, deploy them?
Would it be useful to aircraft to be able to deploy braking 'chutes earlier and thus at higher velocities?

This, incidentally, does include more exotic 'aircraft' like shuttles and spaceplanes.

 

[AlephZero]

Obviously there is a max design speed for deployment, since the drag is going to be roughly proportional to speed squared. Early deployment would either destroy the chute, break the attachment cord, or give the pilot a sudden g force that could interfere with use of the flying controls.

As for earlier deployement, it's fairly easy to lose speed in a controlled manner while the aircraft is flying - just reduce engine power and put the nose up. Once on the runway, you don't have the "nose up" option, so if brakes or reverse thrust fail, chutes are a good backup system.

Also, a chute is very blunt instrument for speed control. The only options you have are first deploy it, then jettison it.

 

[3trQN]

Also, a chute is very blunt instrument for speed control. The only options you have are first deploy it, then jettison it.

What about sliders and devices that control chute deployment rate and the number of canopies?

I've never seen a vehicle chute up close, but skydiving chutes have a means of controlling the jerk and chute deployment, often deployed at ~100mph (not very fast i know)

Multi-stage deployment systems, with successive stages designed for tolerance in a specific speed range would allow much faster deployment too.

 

[Q_Goest]

Hi Sojourner01, I think you need to take a step back and ask, "what is a drag chute"?

If you consider all possible ways of converting the kinetic energy a space vehicle has upon reentry into thermal energy as being a "drag chute" then such things as hypervelocity drag chutes are already being used. The limitation isn't so much a mechanical one in which there's insufficient strength for construction of the device, the limitation is on the heat created when high velocity air is converted to heat. The device that does this conversion is going to get extremely hot. The drag chute in this case is the wings and body of the Space Shuttle for example.

If on the other hand you consider a "drag chute" only to be a fabric type of device that is deployed using some kind of theather, then perhaps we have to limit ourselves to the concept of a parachute.

Regardless of what type of device you're referring to, there's some limitation on it that is dependant on velocity because of the temperature the drag creating device will be exposed to. As velocity decreases, temperature becomes less of an issue, and mechanical strength becomes the primary issue.

 

[Sojourner01]

Thanks Q, heat was a factor I hadn't considered.

The thought had crossed my mind that perhaps some kind of device totally unlike a 'parachute' as we know them, and more like a long streamer with a large number of protruding baffles, could be made exceptionally strong and thus able to withstand massive drag forces at very high velocities. I'm inclined to think that in order to work, a device such as this would have to rely on fluid mechanical relationships very much more complex than intuition suggests.

 

[AlephZero]

What about sliders and devices that control chute deployment rate and the number of canopies?

I've never seen a vehicle chute up close, but skydiving chutes have a means of controlling the jerk and chute deployment, often deployed at ~100mph (not very fast i know)

Multi-stage deployment systems, with successive stages designed for tolerance in a specific speed range would allow much faster deployment too.

Remember you are trying to stop something with a bit more inertia than an average sized skydiver!

http://www.airsceneuk.org.uk/airshow02/elvington/elvington.htm
http://www.pioneeraero.com/2-17_air_bra.htm

 

[russ_watters]

Thanks Q, heat was a factor I hadn't considered.

The thought had crossed my mind that perhaps some kind of device totally unlike a 'parachute' as we know them, and more like a long streamer with a large number of protruding baffles, could be made exceptionally strong and thus able to withstand massive drag forces at very high velocities. I'm inclined to think that in order to work, a device such as this would have to rely on fluid mechanical relationships very much more complex than intuition suggests.

If you have a higher speed and need less drag, why not just use a smaller 'chute?

But in any case, for much higher speeds (like a fighter jet at just under mach 1), conventional airbrakes deploy and retract fast and produce a ton of drag. No need for a drag chute.