Design Challenge: Lightweight General Aviation Ejection Seat

Dynoman

Dynoman

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Over the last 60 years or so there have been a number of ejection seat designs for high speed military aircraft. These designs have eventually evolved enabling air crews to escape in zero-zero (i.e. zero airspeed-zero altitude) ejections conditions. The sophistication of some of the latest designs even have enabled air crew to eject upside down while descending toward the ground at low altitude. However, despite the proliferation of these systems in military aircraft there are very few ejection seats or systems that have been designed for light general aviation aircraft. The Cirrus aircraft company has developed their aircraft with Ballistic Recovery Systems (e.g. Cirrus and Cirrus Vision Jet aircraft) and other manufacturers have been incorporating BRS systems into their light aircraft designs. Unfortunately, most of these BRS designs have limited envelopes in which the pilot can safely deploy the BRS.

This thread is to discuss the possibility of a zero-zero or near-zero-zero ejection seat system for GA aircraft. Considering the weight and required sophistication of the design to eject, stabilize in a positive attitude and trajectory, and deploy a parachute or other decelerating device. The nearest design that I can find to the concept is the Russian NPP Zvezda SKS-94. https://russianpatents.com/patent/254/2540133.html

It can extract the pilot within 0.3 seconds as low as 33 feet altitude and costs $35,000 (1998 dollars). In 2015 Zvezda developed a pole system, which dates back many years to WWII and a compressed air version experimented with by Martin Baker.
 

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You might want to check out the Martin-Baker MK17. It is extremely light and used in the Grob G 120TP.
 
I was working in the warbird industry when (circa 1993) Sukhoi tried to sell some aerobats - to American customers - with Zvezda SKS-94 seat. I doubt if the seat ever received FAA certification. Remember that this happened back when the FAA insisted on removing all explosive/propellant charges from military-surplus ejection seats.

One day Manley Butler was musing about civilian ejection seats and insisted that he would only be involved in designing an extractor system. Hint: Mr. Butler had previously worked at US Navy Station China Lake perfecting ejection seats, drogue chutes, etc.

Definitely start with a Zvezda or Stanley style of extractor seat. Using a rocket to pull things to line stretch simplifies the ejection process. Install a canopy-breaker on the nose of the rocket. Pack the parachute canopy into the head-box. Packing the parachute canopy into a head-box eliminates a dozen problems related to stuffing a bulky canopy into a cockpit that is already snug. Limit the lower portions to a simple parachute harness IOW no rigid components below the rocket.
Stanley extractor seats were retrofitted to Douglas AD-1 Skyraiders during the Viet Nam War.
 
It's certainly possible to get rid of the hazard of compressed air and the complexity of certified civilian energetic material by going all electrics.

This original idea is to my knowledge yet unpattented.

Use a fast discharging unit (static discharge), connect a fast spinning electrical motor, use a single usage clutch. As engine rotation reaches over 10krpms, engage the clutch. The clutch is rigidly linked to a pinion and rack (straight gear) monted on the seat structure.

And voila, off you go. Quick calculation shows that a 100kg pilot with its seat can be quicked out by a single 1kg motor under a second. You'll probably need two motors to provide for the right impulse.

The advantages is long term safety, installed in the aircraft, ease of certification, no specific operator need for the system, aside of your usual qualified mechanic etc...

Copyright... Me
 
Explosives still have something like 100 times the energy density of electricity.
 
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Under 14 CFR Part 23, for the certification of general aviation aircraft, AC 23-19A allows for ejection seats in general aviation aircraft. The FAA does not have a standard for the design and certification of these systems, however they state that the Air Force Systems Requirement Document (SRD) provides the criteria that the seat must meet in terms of testing and verification. The SRD is specific to the system design, however the anthropometric requirements for g-loading, seat accommodations (crew percentiles) and measurements, and system speed and altitude requirements (operating envelopes) are established for all of the USAF designs.

Establishing a criteria is the first step for the design. BTW there are no textbooks on the subject of Crew Escape/Ejection Seats that I can find. If anyone knows of any let me know. The only things available are journal articles and system test reports.
 
Dynoman said:
Under 14 CFR Part 23, for the certification of general aviation aircraft, AC 23-19A allows for ejection seats in general aviation aircraft. The FAA does not have a standard for the design and certification of these systems, however they state that the Air Force Systems Requirement Document (SRD) provides the criteria that the seat must meet in terms of testing and verification. The SRD is specific to the system design, however the anthropometric requirements for g-loading, seat accommodations (crew percentiles) and measurements, and system speed and altitude requirements (operating envelopes) are established for all of the USAF designs.

Establishing a criteria is the first step for the design. BTW there are no textbooks on the subject of Crew Escape/Ejection Seats that I can find. If anyone knows of any let me know. The only things available are journal articles and system test reports.
Click to expand...
The only parachute design textbook - that I have read - is Theo Knacke's but it is far too general and theoretical. An engineer still needs to add a large dose of practical experience to design a parachute that will open at low altitudes and low airspeeds while not ripping the pilot's head off.
 
Using the Martin Baker Mk17 and the Zvesda SKS-94 as the baseline models:

Mk17 capable of launching a 100lb-250lb occupant clear of the aircraft from a position on the ground up to 18,000 feet with a speed range from 60kcas to 250kcas. Seat weight 90 lbs or 40 kg.

Zvesda SKS-94 weighs less than 40 lbs and can be operated between 33 feet altitude and 18,000 feet.

Obviously less weight and simplicity are objectives of the design based on the photos I’ve seen of the two seats. However, reliability and performance are it’s primary objectives. Designing these into a concept seat may simply be a refinement of existing seat designs with the application of the latest and best performing technologies.

The seat should be designed to fit and work inside aircraft that lends itself to the concept. For example a Cessna 172 or a Piper Pa28 wouldn’t enable an ejection and a BRS system would be more applicable in these cases. The concept seat should work on canopy equipped aircraft such as RV-10 or American General Tiger. Maybe an airframe should be designated to examine seat integration issues.
 
I found the AA-5B maintenance and POH online that will provide the structural components of the airframe and canopy for integration and the POH to look at aircraft performance. I'll sketch out a general layout of a seat that fits in the envelope of the cockpit dimensions with rails, telescopic ejection gun, and possible rocket motor.
 

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Preliminary ideas for seat design. Ideally an aerobatic aircraft or a small military trainer would be the best candidate. Considering that most general aviation accidents occur on takeoff or approach to land (i.e. stall/spin and engine loss) the seat would need to be safely used at low altitude and low speed. However, structural failure, particularly for an aerobatic aircraft would be the consideration for the higher end in the Vn diagram envelope.
 

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The seat envelope for the AA-5B is 20 inch width, 46 inch height, and 34 inch depth.
 
Concept sketch of the seat.

The seat features and justifications:

Twin Ejection Guns - Allows for a thinner profile of the seat
No Drogue Parachute - Low speed and altitude ejections
Bottom Main Canopy Loading/Ejection - Faster canopy deployment
Main Ejection Handle and Face Screen in Headbox - Provides face protection
Gen V Harness - One size fits all, single release fitting
Lightweight Construction - Reduces overall weight for ejection and aircraft
No Rocket Motor- Will require forward speed without motor Approx. 60-90 kts. Allows shorter seat.
Secondary Firing Handle - For spin ejection initiation
Seat Pan Hinge - Allows occupant to lower legs during ejection to reduce contact with aircraft panel
Minimal Flail Protection - Slow speed ejection
 

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Dear Dynoman,
You have some good ideas there, but I am not sure why you want to install a face curtain many decades after the USN eliminated upper activation handles from all their ejection seats.
Does anyone remember the USN's logic for eliminating upper activation handles??????
 
Integral helmet (no risk of facial injuries from shattered glass)?

Also @Dynoman : you can avoid the hinges. There are no hinges that will safely sustain the ejection induced load without being a design weak point.
 
I believe the Mk17, which is designed for small cockpits, has the seat pan either stay in the aircraft or is hinged in some manner as the occupant is propelled upward (the seat is still in development). The occupant exits the aircraft in a standing position to reduce the legs getting severed on ejection. I'll have to go back and try to find some information on the method of the seat pan giving way. I located a discussion on the Martin-Baker Mk-17 seat (I'll post it below) and I believe that is what they said.

The face curtain was the preferred method as it's helps to keep the pilot in an upright position and the curtain prevents air from catching the helmet. The design is a for GA aircraft and aerobatic GA aircraft so face protecting helmets may be optional.

View: https://www.youtube.com/watch?v=XFzWAM5uWxQ
 
I understand that you want in fact the seat pant to give away under the ejection load to ease pilot extraction. But then wouldn't you be limited by the risk of spinal injuries? Being pulled away is rather different than being kicked in the butt.
 
Tomcat, you are correct! BTW I'm not sure how the seat pan operates. I assumed it was hinged. The harness reels would have to restrain the pilot sufficiently to prevent the pilot from slipping out. I would think ideally this would be across the chest and under the arms, however the Mk17 seat has what appears to be shoulder, lap belts, and through the leg straps. If that system would be too difficult to work than a leg restraint system may have to be considered.

The Zvezda SKS-94 appears to have the pilot eject without the seat pan.

View: https://www.youtube.com/watch?v=r_WBK6mtkWw

The KS-2012 design also has the pilot eject with the seat pan appearing to fold behind the occupant.

View: https://www.youtube.com/watch?v=jqv6U_esnWo
 
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Modern parachute harnesses put all the pilot's weight on his leg straps. Parachute suspension lines transmit loads down to riser straps that connect to the vertical main lift webs at collar-bones. The vertical MLWs transmit parachute loads from the parachute canopy down to the leg straps. An ejection seat might use a wider rigid seat-pan to distribute loads over a wider area than 2 inch wide leg straps.
The horizontal back strap (lumbar) and horizontal chest strap just prevent the pilot from falling (forward or backwards) out of the harness. V or X diagonal backstraps also prevent the pilot from falling out the back of the harness.
A few sport harnesses also have a belly strap running horizontally below the belly button. This belly strap helps keep the harness hip joints in correct alignment with iliac crests.

Aerobatic seat-belts also need a 5th strap - in the crotch - to prevent the waist belt from riding up above the pelvis.
Both seat-belts and parachute harnesses try to focus all the harness loads on pelvis bones.

Rob Warner, FAA Master Rigger: back, seat and chest ratings plus a handful of (really rare) lap-packs
CSPA Rigger Instructor
Strong Tandem Instructor Examiner.
More than 6,000 parachute jumps including 100 military jumps and more than 4,000 tandems
Private pilot
Retired military air frame technician on Sea King helicopters and CF-18 fighter jets
 
Riggerrob, that is great information!

In a typical ejection seat design the ejection gun or rocket motor load is imparted to the occupant by the seat. The thrust vector is designed to target the seat/occupant CG to reduce rotational moments. I have found a number of studies conducted on better seat pan/cushion and lumbar support designs to reduce back injuries. Of course the harness is designed to restrain the occupant to the seat with the focus on reducing compression loads on the spine by holding the pilot firmly to the seat. Additional restraints, netting, and covers are designed to reduce flail hazards.

In an ejection system designed to pull the occupant out of the seat while in the cockpit the harness is applying the load to the occupant during the ejection. Therefore, as you stated, the MLWs transmit the load to the leg straps. The KS-2012 system looks like that may be the case for their design.

Due to the narrow confines of a small cockpit I think that this design should be considered for incorporation into the proposed system as it appears to meet that criteria and is the least complex (reducing weight and increasing reliability).

Here is an interesting concept called the Yankee ejection system used on the AD-1 Skyraider. The seat pan fold straightens out as the pilot is raised almost like a lawn chair. Neat idea see 3:12 on the video). This idea uses a spin stabilized rocket that is deployed when the canopy is blown.

View: https://www.youtube.com/watch?v=8Yw8g1Soigk
 
For that, IMOHO, you should design the flight suit as an integral part of the ejection system. Leave the seat inside the plane (use the hinged seat pan to facilitate extraction in cramped cockpit as you envisioned) and pull the pilot away with the rockets with restraint connected to a reinforced flightgrows.
The difficulty would be to not decapitate the pilot or sectioning an arm or leg with the restraints given that loads on them would be much higher (and complex) than during a parachute jump.
 
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Yes Dynaman,
Thanks for posting that great film of Stanley's Yankee Extraction System.

I had in mind an updated version of Stanley's Yankee Extractor system.
I would up-date it by packing the parachute canopy into a head-box.
Install a canopy breaker (chisel) on the top of the rocket. Maybe also glue some detonator cord to the inside of the canopy (al. British Harrier and Hawk).
Use the extractor rocket to pull the pilot clear of the flailing airplane ... then a second later ... release the rocket bridle(s} from the harness to allow the rocket to pull the head box to line-stretch. After line-stretch, the head box opens, exposing the parachute canopy to the wind. The head box and rocket separate from the pilot. This sequence could cut another second off of deployment time and further reduce altitude loss.
Since we are talking about an ejection/extraction system for a sport airplane, this means exit speeds less than 300 knots, ergo less risk of limb flail injuries. Though it would be nice to have strap(s) holding the pilot's head centered between the risers during line-stretch.
TomcatViP said:
For that, IMOHO, you should design the flight suit as an integral part of the ejection system. Leave the seat inside the plane (use the hinged seat pan to facilitate extraction in cramped cockpit as you envisioned) and pull the pilot away with the rockets with restraint connected to a reinforced flightgrows.
The difficulty would be to not decapitate the pilot or sectioning an arm or leg with the restraints given that loads on them would be much higher (and complex) than during a parachute jump.
Click to expand...

Dear TomcatViP,
Your suggestion reminds us of the torso suits worn by USN aviators for the last 50-odd years. They are basically vests that integrate the parachute harness, seat-belts, floatation, survival gear, etc. Like most vests, torso harnesses cover the shoulders and rib-cage and some versions also cover buttocks.
Dating back to the 1950s, RCAF CF-104 pilots strapped "spurs" to their feet. These spurs clipped onto straps attached to the bottom front of the ejection seat. During ejection, these straps and spurs automatically pull the pilot's feet towards the bottom front of the ejection seat, to reduce the risk of kicking the instrument panel.
AS for restraining limbs from flailing ... RAF Tornado pilots wear fancy mesh jackets that look like they are part of anti-flail restraints. Can a Brit confirm my suspicions??????????
 
Stanley Yankee ejection diagram. Riggerrob, I like the headbox parachute idea. The rocket assisting the deployment of the chute would save time.
 

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I drew a lightweight ejection seat that incorporates some of the features we discussed. It uses the Yankee ejection seat folding concept. The telescopic ejection gun behind the seat propels the pilot seat upward. The seat stops at the end of the pole. The head box with main parachute has small rocket motors on both sides of the box. They fire after the canopy is breached and continue to pull the risers and the pilot out of the cockpit. A timer sequences the main chute release from the box allowing the main to open.

I still have to include the harness, harness reel, and the emergence harness release cables from the sides of the seat. Also, diagram the ejection handle cable to the gun cartridge at the base of the telescopic pole. Also the seat sequencer. Most seats today use a complex system of explosive gas cartridges with gas expanding along lines to activate various systems. I'd like to do a more mechanical system.
 

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We have, as we would say but a while ago now, a shed load of really sharp folk on this here site. Proper edjucashonal and a privilege to see. Thanks to all of you.
 
The amount of brain trust available on this site is amazing. I'm appreciative to all who share their experiences and insights. Always something to learn! Happy Easter!
 
The length of the ejection gun may be 10-15 feet (similar in length to the SKS-94). The Yankee risers that are made taunt by the Yankee's rocket is approximately 20 feet (as viewed from the films). Therefore, the ejection gun and risers should be approximately 15-20 ft in length above the seat or the headbox should be on a longer pole to eliminate potential burns from motor ignition.
 
Dynoman said:
Here are the latest concept drawings.
Click to expand...
Just a minor point: at step 12, the head-box gets pulled off of the parachute canopy.
You still want to maintain tension on the canopy and suspension lines for an extra fraction of a second.
When deploying round (axi-symmetric) canopies, it helps to keep tension on the apex (top dead center) until it fills with air.
Hint: the US Army uses 80 pound break cord tied to the apex (top dead center) of round T-10 main parachutes.

This is where an extractor rocket is better than an ejector gun. But we have agreed to disagree on the relative merits of the two different systems.
 
riggerrob said:
Does anyone remember the USN's logic for
Click to expand...
When your hands are up on the hinges of the ejection seat curtain, the force of the air current can be so great that your arm will be torn off the hinge and inevitably broken by the air current. When you hold the handles from below, then even if your hand slips, there is constructive protection - hand scatter limiters that prevent your hands from being injured.
With the upper position of the hands, it is much more difficult to constructively make the limiters of the spread of the hands than with the lower one. So, nothing personal - pure physiology and concern for the budget, broken hands can be very difficult to treat and training a combat pilot costs a lot of money.
Dynoman said:
Here is an interesting concept called the Yankee ejection system used on the AD-1 Skyraider. The seat pan fold straightens out as the pilot is raised almost like a lawn chair. Neat idea see 3:12 on the video). This idea uses a spin stabilized rocket that is deployed when the canopy is blown.
Click to expand...
This is no longer a concept. A similar system K-37-800M, ejection-damping system (К-37-800М, катапультно-амортизационная система) was developed by Zvezda back in the USSR and implemented on attack helicopters of the Ka-50/52 type:
www.arms-expo.ru

К-37-800М, катапультно-амортизационная система

Назначение Катапультно-амортизационная система КАС-37-800М обеспечивает: комфортное размещение с надежной фиксацией экипажа в кабине; безоп...
www.arms-expo.ru www.arms-expo.ru


View: https://youtu.be/Eet10UdjetU


moreover, it has been successfully used during the current war.

By the way, maybe you should study the literature on ejection seats. I don’t know what was published in the West, but in Russian quite good popular science books like this one were published on the history of the development of ejection seats:
1.
Development of aviation means of rescue ( Развитие авиационных средств спасения):
www.centrmag.ru

Развитие авиационных средств спасения Агроник А.Г., Эгенбург Л.И.

Купить Развитие авиационных средств спасения. В книге приведены характеристики авиационных средств спасения.
www.centrmag.ru www.centrmag.ru

2. Means of rescuing the aircraft crew.(Средства спасения экипажа самолета) - rare

Moreover, in the process of searching for these two books on internet , I came across a Russian article on a topic of interest to you:
MEANS OF RESCUE OF THE CREW OF ULTRA-LIGHT AIRCRAFT

M. V. Sosunov, journal "Problems of Flight Safety" (СРЕДСТВА СПАСЕНИЯ ЭКИПАЖЕЙ СВЕРХЛЕГКИХ ЛЕТАТЕЛЬНЫХ АППАРАТОВ М. В. Сосунов, журнал «Проблемы безопасности полетов»)

СРЕДСТВА СПАСЕНИЯ ЭКИПАЖЕЙ СВЕРХЛЕГКИХ ЛЕТАТЕЛЬНЫХ АППАРАТОВ, М. В. Сосунов :: ПБП :: Aviahumanfactor.ru

СРЕДСТВА СПАСЕНИЯ ЭКИПАЖЕЙ СВЕРХЛЕГКИХ ЛЕТАТЕЛЬНЫХ АППАРАТОВ, М. В. Сосунов, ПБП, Человеческий фактор в авиации и космонавтике
www.aviahumanfactor.ru www.aviahumanfactor.ru
 
Amusing how he also suggests parachutes as a rescue system for motorcyclists.
Thanks for posting those links. It is very difficult to find books about Russian parachuting. Sadly, few people outside of Eastern Europe can read the cyrillic alphabet.
 
riggerrob said:
Amusing how he also suggests parachutes as a rescue system for motorcyclists.
Click to expand...
As l understand rescue crews
of ultralight trike, 2-axis microlights, flex-wing trikes, microlight trikes, deltatrikes, motorized deltaplanes e.t.c.
is a certain problem, so why not?
riggerrob said:
It is very difficult to find books about Russian parachuting.
Click to expand...
All this book available for free download in the Russian segment of the Internet. At the same time, everyone decides for himself the issues of observing copyright, but it is worthwhile to understand that these books were published back in the days of the USSR.
riggerrob said:
Sadly, few people outside of Eastern Europe can read the cyrillic alphabet.
Click to expand...
The currently available text recognition systems in PDF and djvu format e-books later allow the use of automatic computer translation programs into the desired languages, although of course it is better if the text is recognized in the scan itself. So I don't see any problems.

In principle, if someone points to any research literature on the history and development of ejection seats published in the West, I would be very grateful.
 

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