Building more crash-worthy composite planes and cockpits

HomeBuiltAirplanes.com

Help Support HomeBuiltAirplanes.com:

litespeed

Well-Known Member
Joined
May 21, 2008
Messages
1,557
Location
Sydney
Winginitt,

I think others have made it abundantly clear-

This is about secondary safety, not primary. Primary safety is a given for this conversation.

If you have nothing to add about making a aircraft safer in a actual crash- please desist.

You are only going over rehashed ideas and stopping others from contributing and gaining some useful knowledge.

Forum members often stay back from commenting, when they feel others are pushing a agenda that is not on topic.

This is beyond thread drift.

If you wish to push your view - start a thread on your topic.

This is a community forum- not a platform to shout your ideas.

This is a friendly reminder, please accept it.

Moderators /staff may be less polite.
 

BJC

Well-Known Member
HBA Supporter
Joined
Oct 7, 2013
Messages
11,113
Location
97FL, Florida, USA
You were fortunate of not remembering. The last thing I remember after the mid-air was the ground about 3' in front of the nose or the aircraft coming at me at a very high rate of speed. Don't remember hitting the ground, just waking up with gasoline pouring on me. From then on I remember to much and wish I didn't. Living got very hard, and the mental trauma was worse than the physical even with having to get my heart beating again.
I had the exact, same, recurring dream for several months ... trapped in the airplane under water, unable to release the restraint system.


BJC
 

Winginitt

Well-Known Member
Joined
Apr 5, 2019
Messages
176
Winginitt,

I think others have made it abundantly clear- (You and 1 other)

This is about secondary safety, not primary. Primary safety is a given for this conversation. ( ?)

If you have nothing to add about making a aircraft safer in a actual crash- please desist. ( posted on fuel tanks,quick release,helmet,air bags,foam,fuel shut off ....and speed/control)

You are only going over rehashed ideas and stopping others from contributing and gaining some useful knowledge. (I think there are some people out there who are thinking about the relevancy of incorporating technology that decreases the requirements necessary for surviving after the crash. Look at all the tech Just Aircraft has incorporated and many home builders are attempting to emulate them. If just one home builder works to improve his airplane because of something I wrote, then I'm happy.)

Forum members often stay back from commenting, when they feel others are pushing a agenda that is not on topic. (Grown men are capable of posting if they want to. I have no agenda, I simply want to spur thought by the OP and hopefully other builders that the most important thing they can do is make their airplane controllable at the slowest speed possible and then most of the other dangers will become more easily manageable.

This is a friendly reminder, please accept it. (?)

Moderators /staff may be less polite.
( If the OP feels that the information I have posted is not helpful or of any interest to him, he needs to PM me and I will gladly respect his wishes. I don't think its your place to decide what may/may not be useful to him or other builders.)


Exerpts from " Small Airplane Crashworthiness Design Guide"
6.5.1.5 Energy-Absorbing Capacity of Forward Fuselage In consideration of the conservation of energy, the initial kinetic energy of an impacting aircraft must be accounted for in energy dissipated during the deformation of both soil and structure. The designer will realize that energy not absorbed by the ground will be absorbed by the aircraft’s crush zone, other areas of the aircraft structure, or in the cabin (occupied space). The goal is to avoid absorbing energy in the cabin (Uc in the following equation) and dissipate it or absorb it all in the crush zone and other parts of the fuselage. As a simplified model, the energy absorbed by the cabin can be expressed as: (6-15) where: UC = energy to be absorbed in cabin deformation. MA = mass of the aircraft vo & vf = initial and final velocity of the aircraft UG = energy absorbed in ground friction and earth plowing Pav = average force developed in the collapse of crush zone ahead of the cabin S = linear deformation (reduction in length) of the crush zone U’S = deformation energy in structure other than in the cabin or the crush zone.


Formula 001.jpg


where: UC = energy to be absorbed in cabin deformation. MA = mass of the aircraft vo & vf = initial and final velocity of the aircraft UG = energy absorbed in ground friction and earth plowing Pav = average force developed in the collapse of crush zone ahead of the cabin S = linear deformation (reduction in length) of the crush zone U’S = deformation energy in structure other than in the cabin or the crush zone

For the following reasons, several ACG members believed that 71 kts was too high for a design and test impact condition. (OP is proposing 90 mph)

Finally, there was a precedence of using stall speed (my suggestion is to design for mitigating stall speed as much as feasible)

noted that the impact speed range checked in the NTSB accident report contained or was just above the airplane’s published stall speed. As a consequence, the ACG chose Vso (stall speed) at the MTOW. (NTSB says stall speed and accident speed are usually close unless plane actually stalls, then forces become uncalcuble)

Winginitt: If you notice, all calculations originate from the speed/velocity of the airplane and its occupants .


Airplanes, by their nature, tend to hit the ground pretty hard. You might build a cockpit that can take the crash, but the sudden stop will still tear your insides apart and kill you.
Surviving the crash is heavily dependant upon acceleration, the structure not collapsing around you,
(which is the result of the velocity)

I'm designing a new experimental plane that will use carbon fibre extensively in the fuselage and wings so I figure that I might as well design it with improved safety built in.
(To me, that says he is open to any suggestions, not just encapusulating )

[B said:
"RSD[/B], post: 494654, member: 101182"]Surviving the crash is heavily dependant on impact speed and using crushable structures to decelerate impacts on the pilot
If you check back you will find that I have offered suggestions about restraints, fuel tanks,air bags,seat dampening and foam support,fuel shut off, quick release belts, as well as suggestions about keeping the airplane controllable to a slower stall speed by employing fences, spoilers, and Hoerner wing tips. If you read any of the "Small Airplane Crashworthiness Design Guide" you will quickly see that they say a major problem with any safety design is that loss of control results in a subsequent change in the angle of attack......and all calculations become moot !
In simple terms, it doesn't matter how much calculation and technology a builder uses if they can't keep control of the angle of attack....ie; stall/spin.

So since the OP is designing a new airplane from scratch and says he wants to incorporate as many safety features into the design as possible, I don't think its redundant to say that I think the singular most important thing he can do is find the best way to retain control of the airplane until it is flying as slow as possible and as near to the ground as possible. Those two things will be the starting point for all other calculations. The "Small Airplane Crashworthiness Design Guide" says:
in the 1967 Crash Survival Design Guide (Reference 3-7) required calculating the longitudinal and vertical changes in velocities from the average impact conditions of 71 kts and 31 deg.

The OP says he is thinking 90mph . My suggestion is that he attempt to build features that are effective at 90mph but try to design for scrubbing speed to a lesser standard.


Having said all that, if the OP feels that what I have been posting is not relevent or helpful to him, he should PM me and let me know. I will respect his wishes..........
 

RSD

Well-Known Member
Joined
May 19, 2019
Messages
211
Winginitt - I'm the OP and unfortunately you are broadening this topic more than what I was wanting which means that we are losing the focussed detail that I was wanting. If we can now get back to the original topic that would be appreciated.
 

Winginitt

Well-Known Member
Joined
Apr 5, 2019
Messages
176
Winginitt - I'm the OP and unfortunately you are broadening this topic more than what I was wanting which means that we are losing the focussed detail that I was wanting. If we can now get back to the original topic that would be appreciated.
Ok, sorry my info wasn't what you wanted.
 

henryk

Well-Known Member
Joined
Mar 8, 2010
Messages
5,228
Location
krakow,poland
If your wings can be kept level and your speed slows to 30 mph (or less), you have a much better chance of survival than an airplane that stalls at 45 and drops a wing....no matter what safety devices you incorporated. Its wrong to ignore those considerations.
=thru !!! for example=KASPERWING with Vmin =5 m/s impact energy is 1/4 of another aircraft
with V min=10 m/s (36 km/h !) and 1/10 iff Vmin=15 m/s (54 km/h)...

BTW=very big,but short overloud ("g") pulses are not danger for humans....
f.e,=>500 "g" !!!
25 "g" in a second can be deadly.

a="g"/9,81=0.5 V^2/s
 

Attachments

Last edited:

cblink.007

Well-Known Member
Joined
Jul 7, 2014
Messages
215
Location
Texas, USA
People forget (or choose to ignore) the wide gulf between the composite technology of INDY or F1 cars and what’s getting put into general aviation aircraft especially by homebuilders.
This was a crash that took place at well over 220 mph. Peak deceleration force on the driver? 214g. He survived, and eventually recovered to race again another day!


All this said, there are many composite E-AB's whose occupants walked away from 200+ mph crash events. The Rutan Amsoil racer crash being one of them.

 
Last edited:

Vigilant1

Well-Known Member
Lifetime Supporter
Joined
Jan 24, 2011
Messages
4,851
Location
US
If the engine is up front, you would want the engine to break away for mass relief during an impact sequence.
"Mass relief?" It is a nice chunk of inertial mass up front that will be handy if going through trees, fences, structures etc. If plowing into dirt, etc it will be reducing the rate of deceleration of the rest of the fuselage, and the occupants.
Sure, the engine's mass increases the total kinetic energy of the crash. But if it is in front of the occupants and stays there, it should be an asset, not a liability. If it breaks off, it won't significantly increase the available effective crush area, etc.
 

cblink.007

Well-Known Member
Joined
Jul 7, 2014
Messages
215
Location
Texas, USA
"Mass relief?" It is a nice chunk of inertial mass up front that will be handy if going through trees, fences, structures etc. If plowing into dirt, etc it will be reducing the rate of deceleration of the rest of the fuselage, and the occupants.
Sure, the engine's mass increases the total kinetic energy of the crash. But if it is in front of the occupants and stays there, it should be an asset, not a liability. If it breaks off, it won't significantly increase the available effective crush area, etc.
Mass relief. A term I have heard ad nauseum from those aerostructures guys when discussing crash sequences & survivability during my time in military flight test. Also, if the engine (or any other mass-intensive object in the structure) has already impacted, it is not necessarily helping attenuate seconday impacts. That being said, if the engine mounting frame is designed properly, the mass of the engine is taken into consideration with respect to impact attenuation. That way, the frame attenuates the impact accordingly.

I forgot to mention retention straps (similar to those seen on Indy and Formula 1-type cars to retain wheels and engines in a crash sequence) to keep that kind of mass from preventing further damage post-impact, so thanks for keeping me honest!!
 

Vigilant1

Well-Known Member
Lifetime Supporter
Joined
Jan 24, 2011
Messages
4,851
Location
US
We all have to make our choices. If swinging on cable down into dirt, trees, or pavement in an aircraft fuselage and I could choose between having:
1) An engine in front that will detach on impact (with or without a tether)
or
2) An engine in front that will stay firmly attached and not move relative to the passenger compartment.

Then option 2 seems highly preferable. I don't want the thing flailing around in the crash zone. And, I appreciate that, all else being equal, a fuselage of greater mass will decelerate more slowly than one of lesser mass.
 

Scheny

Well-Known Member
Joined
Feb 26, 2019
Messages
201
Location
Vienna, Austria
About mass relief: before I knew what I do now, I once asked why a car with a 500lbs diesel engine needs the same crash structure as one for a 250lbs gas engine. Of course, the engine hits the target first and does not add this energy upon the crash structure.

So, having a plane with the engine in the front means that the safety cell is relieved from that mass. Mass relief makes sense, when the engine does not hit first, like for instance twins. In this case, it is beneficial if they rip off the wing and the cell less less to bear.

If you google crash pictures for carbon mid-engine cars, you will notice a lot of ripped off engines. The structure is built in a way, that it supports a high load in direction of driving (to avoid hitting the safety cell), but only minor loads from the side. This way, you have higher survivability in side crashes where humans are more prone to injury.

As for tether cables: they are used for others protection, not so much your own! They want to avoid that a ripped wheel hits one drivers helmet. By now they have this head cage in formula 1 as tethers where not enough.

The Beast One aircraft is built using as much formula cars technology as possible. One important aspect that I noticed is, that the energy absorbing parts (like the coolers on the side of these cars) are very good in absorbing, but prone to ripping off. So they have to be built to accept more energy from side than direct loads (for instance by adding more +/45° fibers).

And last: the front bulkhead of the Beast One has an angled lower side, so that it will slide above small rocks upon a forced landing. No better way to minimize loads, than to avoid them at all!
 

Riggerrob

Well-Known Member
Joined
Sep 9, 2014
Messages
1,410
Location
Canada
Yes, this is straying from the OP's question ....
A second reason to install engine straps is keeping the engine attached after a propeller throws a blade. A thrown blade can unbalance the prop so badly that it rips the engine off the firewall, creating a huge balance problem. Engine straps can help balance while you glide to a field.
 

Dan Thomas

Well-Known Member
Joined
Sep 17, 2008
Messages
5,295
Yes, this is straying from the OP's question ....
A second reason to install engine straps is keeping the engine attached after a propeller throws a blade. A thrown blade can unbalance the prop so badly that it rips the engine off the firewall, creating a huge balance problem. Engine straps can help balance while you glide to a field.
The formula air racers use a cable around the engine, bolted to the firewall. That's becaue they turn their O-200s at 4000+ RPM, and props are very highly stressed at that speed.

Propellers almost never fail catastrophically if they're properly inspected and maintained. That said, I've come across some really frightening stuff in my years of aircraft maintenance. Found a crank bent by some old propstrike. Found props with numerous serious nicks in them. Found props with nicks very improperly dressed out, increasing the risk instead of mitigating it.

The propeller is easily the most highly stressed part of the airplane, so much so that the manufacturers (like McCauley, for instance) demand removal and NDT if the prop is oversped 15%. A 15% overspeed represents a 32% increase in centrifugal and twisting forces. The prop manufacturer considers 32% a serious deal; the rest of the airframe is usually good for 3.8 times its usual load factor, or 280% more.
 

Riggerrob

Well-Known Member
Joined
Sep 9, 2014
Messages
1,410
Location
Canada
Dear Dan Thomas,
A new "airframe is usually good for 3.8 times its usual load factor, or 280% more."
That margin of error declines dramatically after a few hard landings.
Anyone who exceeds the envelope - in an old airplane - is STUPID!
 

Dan Thomas

Well-Known Member
Joined
Sep 17, 2008
Messages
5,295
Dear Dan Thomas,
A new "airframe is usually good for 3.8 times its usual load factor, or 280% more."
That margin of error declines dramatically after a few hard landings.
Anyone who exceeds the envelope - in an old airplane - is STUPID!
The FAR 23 standard is 3.8G plus an additional 1.5 safety factor above that to allow for manufacturing flaws, corrosion, and hard use. That makes a new airplane theoretically capable of taking 5.7G without deforming anything.

Declines dramatically? I don't think so. Look at the thousands of Cessnas and other bushplanes that have been used really hard for decades, including some very hard landings, and they still don't fall apart. Inflight structural failures due to poor maintenance and inspections is not the airframe's fault. Loss of control isn't the airframe's fault. Any bonehead should know that an unusually hard landing should trigger a thorough inspection. In Canada we even have a law prescribing it. https://www.tc.gc.ca/en/transport-canada/corporate/acts-regulations/regulations/sor-96-433/standard-625/appendix-g.html

Airplanes are normally made of materials that have yield and ultimate strengths. Yield is where permanent deformation occurs, ultimate is where it breaks. A landing hard enough to reduce the strength of the structure would have to deform it. It would have to be strained, in other words, as opposed to stressed.

How many light airplanes do we hear of coming apart in the air, where the investigators didn't find serious pre-existing damage or corrosion? Or something left unsecured? Normally it's related to loss of control such as VFR into IMC and the almost inevitable spiral dive well beyond VNE where the pilot overstresses the airplane trying to pull up when the ground suddenly appears. That's not a fatigue issue; it's a PDM issue.
 

Victor Bravo

Well-Known Member
Joined
Jul 30, 2014
Messages
7,291
Location
KWHP, Los Angeles CA, USA
The formula air racers use a cable around the engine, bolted to the firewall. That's becaue they turn their O-200s at 4000+ RPM, and props are very highly stressed at that speed.
There was an old photo of a Formula One race airplane (late 1970's or early 80's) that was gliding back to the runway with the engine hanging down by that safety cable a foot under the airplane.

They outlawed metal propellers in F-1 almost immediately after that incident. A friend of mine (who just passed away and I posted about his loss on HBA) was the stress engineer who had predicted that metal propellers would fail after a fairly short lifespan at race speeds.

It's some serious s**t when you turn a 56 or 58 inch metal propeller at 4000+ RPM, then put turbulence and G's on it.

Sorry for the drift...
 

Old Koreelah

Member
Joined
Oct 4, 2013
Messages
11
Location
Australia
Yes, this is straying from the OP's question ....
A second reason to install engine straps is keeping the engine attached after a propeller throws a blade. A thrown blade can unbalance the prop so badly that it rips the engine off the firewall, creating a huge balance problem. Engine straps can help balance while you glide to a field.
Rotax carburettors seem to be mounted without clamps over their rubber sleeves so such an imbalance would cause sufficient engine vibration to almost instantly toss the carbies off, this stopping the engine before it rips itself away. On this basis I installed a small steel cable around my carbie to do much the same job.
 

roxburg

Member
Joined
Jun 2, 2020
Messages
8
I have a few personal comments about CRASHWORTHINESS and safety of small aircraft (<12,500lbs).

Some background information first:

My dad has been working on aircraft since he started building Mosquito bombers in WW2.
He completed a 400hp, LS3 Chevy V8 installation in his Cessna 172 last summer - 2019.
He has rebuilt 5 Cessna 172's over the last 40 years, as well as a homebuilt low-wing float plane.
He is 93 years old and still flying to Oshkosh, except this year due to the covid virus.

Aviation is also in my blood - I joined the RCAF in 1966 and worked as an aircraft mechanic
in a fighter squadron on the F104 ‘Widowmaker’. There were lots of crashes and I was on crash
recovery for 10 years. We were always on site within minutes after the body-bags were removed.
Then I switched to a helicopter search and rescue squadron (lots more crashes & body-bags)
for 2 years and finally changed my career direction to NDI (Non-Destructive Inspection). I
spent the next 30 years trying to find defects, before they became failures. I am a licensed,
journeyman auto mechanic with inter-provincial red seal, since 1975. I have also
owned and operated a 705 international charter airline, a commercial aircraft maintenance
company and an NDI company.

Without Prejudice:
Here are my thoughts about what equipment I would choose to install, to protect the lives of my
family members and myself when flying in a small single or twin aircraft.

1. Personal safety equipment – use all the research NASCAR has completed to protect their drivers.

A) Helmets with head and neck restraints – what is holding your head back in a 10g or more sudden stop?
How many years and deaths did it take, before helmets became a mandatory requirement to drive a
motorcycle in North America?
B) 5 point seat belts on every seat, anchored to the carbon fibre frames.
C) High back carbon fibre seats with side projections (10 times stronger and lighter than steel)
D) Ortho-pneumatic seat cushions, constantly massaging my aching butt and back during long flights.

2. Airframe modifications: Use the research that the glider and automotive industries have developed.

A) Like the glider cockpit frame I noticed in a previous response on this subject - Use Hybrid carbon/basalt
fibre composites to build an inner frame shield around the passenger compartment. It would include significant
‘U’ shaped side/bottom/top longitudinal anti-intrusion beams (like most cars today). Plus circular frames
to stabilize the longerons and maintain overall fuselage shape. Let the aluminum exterior be the part
of the aircraft that does what it does best – absorb impact energy. Let the hybrid composites protect
me and my family.

B) Whole aircraft ballistic recovery parachutes – don’t leave home without them. I would much rather
hit the ground at 5m/s or less, than 100 or more meters per second.

C) Heads up display (HUD) for airspeed, altitude, attitude and direction – up on the windscreen – so I never
have to look down at my instruments during the most critical times (40% of accidents) - landing and takeoffs.
There are models available for less than $300.00 right this minute. I know because I just assembled my
Stratux AHRS & GPS (with ADS-b in&out) and with a Hudly windshield projector it works in broad daylight.
I’ll have the options of weather, terrain if I need it, situational awareness of other aircraft around me (ADS-B)
and my EFIS instrument information up on my windscreen - where it always should have been. You can buy
little screens to mount on your helmet (with all the above information) just like motorcyclists have
used for years. You can even get a HUD in your new Buick, BMW or Mercedes.

D) Automotive, water-cooled, aluminum block engines (twice the power, using less and cheaper auto fuel).
Computerized fuel injection (no more fuel mixture control). I would install a manual throttle control system,
just because I would never want a complete power failure, if there happened to be a computer malfunction. I would
also install an aftermarket computer engine control system (ie: a company in Calgary builds a bullet-proof product).
Propeller speed reduction gearboxes and composite propeller (no overhaul or life limited prop parts) with
hydraulic pitch angle and full feathering capability. Supercharged, so I can take the aircraft up to 25K
feet (with oxygen), above most bad weather situations. Automotive style heat and air conditioning.
LED lights, 100 amp alternator and all the wiring and EFIS instrumentation able to handle 12 to 32 volts (Garmin 600).
New CHEVY LS3 engine long blocks only cost $5kto$7K and they always last at least 3000 hours.
You can just throw it away and put on a brand new one for about 1/5 the cost of the antique air-cooled engine overhaul.
They also burn very little oil - more environmentally friendly and changed every 500 hours. I usually replace my
oil filters once a year, whether it needs it or not.

E) Vortex generators on all flight control surfaces. Reducing the stall to the lowest possible speed while
maintaining directional control of the aircraft.

Why does the small aircraft industry always have to be 2 or 3 decades behind the rest of the transportation
industry, especially when it concerns occupant safety and new technology?

I hold the FAA and Transport Canada 100% responsible for this problem.
 

BJC

Well-Known Member
HBA Supporter
Joined
Oct 7, 2013
Messages
11,113
Location
97FL, Florida, USA
Welcome to HBA.

Sounds very ambitious. Please start a build thread to show us how it all works.


BJC
 
2
Top