Design Challenge: Lightweight General Aviation Ejection Seat

[Scott Kenny]

At the low and slow end of the scale, we should consult BASE jumpers. Some of those "........." I am trying to think of a polite noun ...

"lunatic adrenaline junkies"

like to jump from less than 300 feet, starting at zero knots. They have learned most of the secrets to quick, reliable, on-heading openings at the bottom edge of the envelope. They will probably try to sell you a large (say 280 square feet), docile, 7-cell, square canopy with a few extra vents to speed up openings. Some use mesh sliders - to keep the suspension lines neat - while others discard their sliders completely for low jumps.
At the other end of the BASE envelope, some of them like to jump from 3,000 foot cliffs in Norway which means that they are opening at close to skydiver terminal airspeeds (say 130 mph). BASE jumpers add fabric sliders, etc. to soften openings.

I wonder if there is a way to attach a lanyard to a sail/fabric slider to pull it down at slow airspeeds???????
Do I get recognition on a patent for the idea?

At the top end of the skydiver scale, you have tandems which - on a bad day - can hit 200 mph. before deploying a huge (360 to 400 square feet) reserve. I have done that twice! The second time it took 4 days to straighten my neck! My neck still hurts some days.

The challenge is designing a canopy that will open reliably at both edges of the envelope. Back in the day, they used reefing ropes with explosive cutters to sequence openings. In a low-altitude, low-airspeed deployment, sequencing systems just blow all the cutters by the time the canopy reached line stretch. Then it opens quickly.
When deployment speed exceeds 200 knots, you want some of those cutters to delay for a second or 3.

Should have thought about the BASE jumpers for low and slow openings... Glad you did!

The biggest challenge comes when you deploy at low-altitude, but high airspeed. Then you need a canopy NOW! Because the alternative is a soft opening below ground level.

Yeah, that's the issue.

Especially a situation like the famous F16 Thunderbird ejection at Mountain Home AFB in the 1990s, where the plane had a massive sink rate when the pilot punched out. IIRC the pilot more or less just hovered on the rocket at ~300ftAGL till the seat separated, got half a swing under the parachute and landed.

Fortunately, most GA planes won't be that far into the "high speed" realm, but may still reach 400mph or so in a dive.

This reminds me of a conversation with Manley Butler a good 30 years ago. Manley said that he were to design an ejection seat for light planes (aerobats to warbirds) he would design and extractor system loosely based upon the Stanley-Yankee Extraction System.
In that case, I would start with a rocket with a canopy-breaker bolted to the top. The longer the rocket lanyard, the more time and distance you have to accelerate the pilot. No need for a fancy seat, just use his parachute harness to pull him out of the stricken airplane.

You can also deliberately use a stretchy rope between rocket and seat to lower the forces on the pilot in that case, at the cost of leaving the pilot in the plane longer.

Please note that I have packed and jumped early square parachutes with reefing lines (Para-Flite Strato-Cloud made during the 1970s), but they are a PAIN to pack and I doubt if any rigger younger than 60 years old has the first clue on how to pack them.

Have to call the old timers out of retirement for that one!

But I'd really prefer to have an easy-to-pack chute. Less to go wrong in a system that's already going to be complicated enough.

 

[Scott Kenny]

I agree, especially for high speed aircraft. However, for a system that needs to operate at 200 feet AGL and above and under 350 kts, the speed of a simple mechanical system could be adequate (Stanley Yankee charts for T-28 provided below). My thoughts are the activation system used in a Cirrus (handle pulling cable activated igniter), combined with the ballistics and mechanical seat structure of the Stanley Yankee extraction system (canopy jettison, seat fold, seat/harness release) would be simple, lightweight, and use the same install/maintenance practices that are already used by A&Ps for maintenance on Cirrus aircraft (i.e. BRS). There are numerous challenges of course, such as specific aircraft integration for canopy jettison, seat timing for harness release, and seat folding mechanism, etc., but these could be refined during seat development and testing.

Wow, is that successfully ejecting with a >5000fpm sink rate at 200ft AGL?!?

 

[riggerrob]

"lunatic adrenaline junkies"


Should have thought about the BASE jumpers for low and slow openings... Glad you did! ....

"Dirty, rotten, low-pulling BASE jumpers."
I have called more than one of them that --- to their faces.

It helps to remember that - up until 30 years ago - typically 30 percent of dead skydivers were listed as "low pull/no pull."
30-odd years ago Helmut Cloth introduced the Cybernetic Parachute Release System (CYPRES).
Any modern, light-weight, ejection seat needs to include some sort of Automatic Activation Device (e.g. CYPRES).

 

[Scott Kenny]

It helps to remember that - up until 30 years ago - typically 30 percent of dead skydivers were listed as "low pull/no pull."
30-odd years ago Helmut Cloth introduced the Cybernetic Parachute Release System (CYPRES).
Any modern, light-weight, ejection seat needs to include some sort of Automatic Activation Device (e.g. CYPRES).

Oh, absolutely. There is no way that I'd trust a pilot to even remain conscious on a zero-zero ejection. You need a LOT of force to throw someone clear of a plane and high enough to let the parachute open.