Engineering for occupant safety

[old man emu]

Protection from landing flat as in Thruster's illustration is pretty hard to design into an aircraft. I believe that flat pancake impacts are a little more common in gliders, for reasons I don's know, but they usually cause severe injury to the spine which can result in death. The spine can't handle vertical forces - see "hang by the neck".

 

Impacts of the aircraft at a nose down angle often result in the fracture of the airframe at the firewall, same as heavy landings on the nosewheel. Clearly the fact that there is a large mass attached to the rest of the airframe usually at only four points has some effect. 

 

Another common result is that the rear of the fuselage bends due to the tail section compressing into the forward section which has already stopped.

[RFguy]

The Cirrus SR20  is pretty good in this department.

 

Engineered crash seats for a flat pancake landing with the parachute.   DO not kneel on the seats when trying to get something out of the rear of the aircraft ../

 

The Tech and owners manual of the aircraft (something I read cover to cover on long journey's in my mates SR20)  tells you 

NOT to kneel or stand  on the seats because the honeycomb deceleration structure can be damaged

 

Obviously the knee in the seat generates a point load.

 

Edited April 5, 2021 by RFguy

[RFguy]

Ya know,  before I learned to fly, I used to think the Cirrus parachute system encouraged "MORAL HAZARD".  But my views have changed a little now I am "an experienced 90 hour pilot" . ha ha.

This time of year there is some fog here and there when I am flying around . If flying over a sea of fog , the first time you know where the ground is, is it when you hit it.... So now that adds more terrain that cannot be flown over in a single petrol engined airplane with no chute.  A twin is too much of a pain , the chute provides an out. 

 

 

[Geoff_H]

3 hours ago, Old Koreelah said:

Kevlar laminates are great at absorbing impact and then returning to the original shape, but It’s mongrel stuff to work with; you can’t tell by looking whether the layup is saturated with resin. 

It’s almost impossible to cut the raw fabric. Decades ago George from FGI told me the trick they learned when cutting the sails for Australia II: buy boxes of cheap scissors, cut a meter or so until the blade is blunt then get a new one.

I discovered another trick: extend your layup over a temporary boundary and when it’s hardened, cut it with an angle grinder.

Kevlar strerches and changes colour, hence you can see if it is damaged

[Geoff_H]

1 hour ago, old man emu said:

Protection from landing flat as in Thruster's illustration is pretty hard to design into an aircraft. I believe that flat pancake impacts are a little more common in gliders, for reasons I don's know, but they usually cause severe injury to the spine which can result in death. The spine can't handle vertical forces - see "hang by the neck".

 

Impacts of the aircraft at a nose down angle often result in the fracture of the airframe at the firewall, same as heavy landings on the nosewheel. Clearly the fact that there is a large mass attached to the rest of the airframe usually at only four points has some effect. 

 

Another common result is that the rear of the fuselage bends due to the tail section compressing into the forward section which has already stopped.

I think that flat pancake landings stem from spins that are not recovered in time.  Not usually taught or exercised these days.https://www.google.com/url?sa=t&source=web&rct=j&url=https://aviation-safety.net/wikibase/139874&ved=2ahUKEwj0mumb_OXvAhVw63MBHctKBi8QFjAAegQIAxAC&usg=AOvVaw2neq18dc8p_7Jc8AS4nUuk

[Jase T]

 

The USAF and the FAA tell us that the human body can survive sustained 9G declaration. To the point that it has become (I am led to believe) the requirement for structural integrity of seats and cockpit in N registered aircraft.  I can't find the study right now but will research it if anyone is actually interested, that looked at deaths related to deceleration in aircraft accidents. 100% of cases where the deceleration was 9G or less were survivable, yes higher transients up to the low 40's were survivable, albeit with some nasty injuries, but the tolerance was in the tenths of a second. I am talking sustained here. So, for my money the key is hitting the ground and stopping while sustaining 9G or less. At 50MPH you need 9.4 feet (all I could find was in US language) at 100mph you need 37.6 feet. So, the key is to arrive in control and as slowly as possible. Some of the 9.4 feet can be crumple zone of the aircraft, wings, and anything you need to hit to slow you down. But when you think about it 9.4 feet is not all that far if it means survival....

Edited April 5, 2021 by Jase T

[RFguy]

if you pancake (say a stall in a pullout from a dive) or stall spin near the ground,  I think you're gonna die. unless there is a fair slab of decel room.

 

 

 

[rgmwa]

What happened to the Do-Maw project? Haven’t heard anything for a long time and couldn’t find the thread. He put a lot of thought into occupant safety.

[Geoff_H]

Everything you need to know about designing for crash survival.

https://www.google.com/url?sa=t&source=web&rct=j&url=https://apps.dtic.mil/dtic/tr/fulltext/u2/a218434.pdf&ved=2ahUKEwie-cbGoObvAhUm8HMBHZtuBM4QFjACegQIBRAC&usg=AOvVaw3cFHOGbCb_0w_GSjU22SZb

[kgwilson]

4 hours ago, Geoff_H said:

I think that flat pancake landings stem from spins that are not recovered in time.  Not usually taught or exercised these days.https://www.google.com/url?sa=t&source=web&rct=j&url=https://aviation-safety.net/wikibase/139874&ved=2ahUKEwj0mumb_OXvAhVw63MBHctKBi8QFjAAegQIAxAC&usg=AOvVaw2neq18dc8p_7Jc8AS4nUuk

Not necessarily. Many result from flat spins. You can get in to a flat spin when stalling or spinning where the aircraft is in a balanced state and begins to rotate around the yaw axis, especially if the CoG is well aft of the cockpit and the fuselage is fairly level. Power, aileron and elevator don't help and in some designs especially if in that configuration the rudder is shielded by the horizonal stabiliser. In this configuration the airflow is at 90 degrees or thereabouts to the control surfaces rendering them ineffective.

 

This has killed many pilots and instructors. If the CoG can be shifted forward you may be able to get the nose to drop and full down elevator will then assist to get forward airspeed again. That's hard to do but has been done successfully by pilot & passenger climbing on to the glare shield. More commonly the aircraft continues a flat spin & goes straight down and the subsequent impact kills the occupants instantly.

[Marty_d]

2 hours ago, rgmwa said:

What happened to the Do-Maw project? Haven’t heard anything for a long time and couldn’t find the thread. He put a lot of thought into occupant safety.

That was Head In The Clouds, I think. 

[pmccarthy]

7 minutes ago, Marty_d said:

That was Head In The Clouds, I think. 

I cannot find HITC or his project using search. I remember he got deleted a decade ago and came back, wonder what happened this time.

[ClintonB]

His project was interesting and looked to be progressing well. Shame not to see it completed or closer.

sometimes things get in the way, I did a hour or two on my Bushbaby on the weekend and achieved some tasks.

now need to make a list so jobs can be completed. 7 years and no air time. Needs to change.

 

[Head in the clouds]

16 hours ago, rgmwa said:

What happened to the Do-Maw project? Haven’t heard anything for a long time and couldn’t find the thread. He put a lot of thought into occupant safety.

I'm glad someone remembered 😊. Yes, always been concerned about the number of apparently unnecessary fatalities. My take on it is a very strong crash cage around the occupants, good harnesses, rear head support, flail protection as far as practical, and most particularly as much underseat impact absorption as possible. To that end my latest design also incorporates a large amount of landing gear suspension movement with gas struts, but that's not practical for all aircraft configurations.

14 hours ago, pmccarthy said:

I cannot find HITC or his project using search. I remember he got deleted a decade ago and came back, wonder what happened this time.

I'm still here, I've never been 'deleted' as far as I know, though a few people have expressed that desire from time to time 🤣. I did get suspended for a month around that time, for having a contentious opinion.

 

The DooMaw project has been on hold for a while, boy how a couple of years passes in a flash when you're busy! I've just been too involved with my drafting work and developing a new marine business lately. But DooMaw is still alive and well and will be completed in due course. There's the covering and painting of the fuselage still to do, final fitup of the engine, instrument panel and wiring to finish, and the wings to build.

 

Here is a link to the DooMaw - building a STOL thread. There are references to the crashworthiness design features throughout the thread, chromoly structures aspects are earlier in the thread and the seat impact absorption stuff is on Page 11.