Taking a Spam Can and Making it Crashworthy

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JayKoit

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I've finally finished reading the "Crashworthiness" and "Design for Crashworthiness" threads and have to say that was the most informative collection of posts I've read in a long time. Gave me a lot to think about regarding how safe to an airplane can theoretically be, how safe it possibly can be, and how unsafe many of the kits out there really are.

Before I get to the topic, I wanted to thank SVSU Steve, GESchwartz, Topaz, Dana, Vigilant1, wsimpso1, Orion, Autoreply, JimCovington, Aircar -- and everyone else who contributed to the crashworthy threads on this site. You've undoubtedly helped me to consider things I never thought about that will make my plane (once it's built) a safer airplane than it otherwise would have been.

I have been considering an all aluminum semi-monocoque plane for my first build for quite a while now (the Savannah VG, a Zenith 701 variant). I want to build this plane because it's a simple build -- every part is pre-drilled (with full size holes) and pre cut & formed, real world build times of 250-300 hours, multiple FWF kits with cheap engine options, and I can build the plane complete w/basic VFR for just over 30K.

However, after having read all that I've read, i realize that the plane's material & structure are not the most crash friendly. So, my costs will not stop there, because now I want to implement some additional safety features/mods to make my plane more crashworthy. I'd love to get some feedback from you guys about my ideas, and whether or not you think it will make my plane a safer plane. Understand that chewing up some useful load is not a concern for me, as this will be primarily a solo flying time-building plane for me. FYI the basic plane has a 600 lb useful load, and I'm a 165 lb pilot, so I have some room to work with.

Here's the list of mods/additions (and their links):

- Center "Y" stick so there's no impalation risk
- Second Chantz air propelled (not rocket) airframe parachute - Second Chantz Home
- four point airbag harnesses - LA MOUETTE - Ailes delta et ULM - Vol libre - Vol moteur
- Rubberized crash resistant fuel tanks - Manufatti Elastomerici Rinforzati - Merin S.r.l.
- 3-6" confor foam energy absorbing seat cushions - The seat pans might absorb a little too -- see link below
**for reference pictures to the seat pans here's a link to a build log for the Savannah: Build Log Page 6 just click the thumbnails to enlarge.

- And finally, the biggest task in the build: I'd like to replace all the aluminum angle/longerons inside the fuselage from the firewall to behind the seats (the whole forward lower fuselage, mainly) with similar sized chromoly 4130 angle or square, so i have a chromoly cage around me. . If you check out the build log link i listed above, you'll notice that the Savannah already has an upper frame of chromoly tube, I would just want to complete the cage by replacing those aluminum angles with chromoly, then maybe add a couple reinforcements that would connect the firewall attach points/engine mount attach points on the fuselage side to the chromoly cage, . In a sentence, create a chromoly cage without a major redesign -- just use chromoly where the aluminum stiffeners/supports already were. Would that work in helping the fuselage be less collapsible in the event of a crash?

It's also worth mentioning this plane is slow. Cruise is 85-90 mph, stall is ~35 mph. So I'm not sure what my impact speed would be in the event of a stall/spin, but with such a lightweight & dirty airframe probably slower than most -- so with all of these things implemented do I have a pretty decent crashworthy spam can?

Would love some feedback. Thanks!
 

autoreply

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Most of what you list makes a lot of sense.

I'm not that fond of airbags, but my knowledge there is hear-say. Wasn't one of our members (Holden) formerly in the airbag-business? You could maybe ask him. I'd favor (uninformed) a 5-strap belt.

Some aluminium foam or honeycomb under the seat might help a lot in a severe crash that demolished the safety cage.

I'd also look at preventing crashes. You have a proven engine (Rotax 912S right?) Fuel system without design faults? I'd have a good look at something like ADS-B or the Powerflarm. Most importantly, training. Investing 1000 dollars in training is buying you more safety as any possible safety feat.
 

Dan Thomas

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- And finally, the biggest task in the build: I'd like to replace all the aluminum angle/longerons inside the fuselage from the firewall to behind the seats (the whole forward lower fuselage, mainly) with similar sized chromoly 4130 angle or square, so i have a chromoly cage around me. . If you check out the build log link i listed above, you'll notice that the Savannah already has an upper frame of chromoly tube, I would just want to complete the cage by replacing those aluminum angles with chromoly, then maybe add a couple reinforcements that would connect the firewall attach points/engine mount attach points on the fuselage side to the chromoly cage, . In a sentence, create a chromoly cage without a major redesign -- just use chromoly where the aluminum stiffeners/supports already were. Would that work in helping the fuselage be less collapsible in the event of a crash?

It's also worth mentioning this plane is slow. Cruise is 85-90 mph, stall is ~35 mph. So I'm not sure what my impact speed would be in the event of a stall/spin, but with such a lightweight & dirty airframe probably slower than most -- so with all of these things implemented do I have a pretty decent crashworthy spam can?
There have been some aluminum or composite airplanes that had steel tube frames inside them. The Aero Commander Lark and Darter are a couple, as is the Glastar. The frame carries the engine, wings, and gear, and acts as a roll cage for occupant protection. You could weld up a frame that would fit inside the Savannah, then build the airplane around it normally. The frame would be only a roll cage, not any load path for the rest of the structure, but it would add 50 pounds, probably, and reduce the inside dimensions. Steel tube also has its risks; there have been people maimed or killed by broken tubing piercing soft pink bodies.

I would just build the airplane as per plans, and get some good training in stuff like stalls and spins. There's nothing like experiencing the real thing to help you avoid an accident. All the fancy anti-death stuff doesn't seem to make a lot of difference in some airplanes; the Cirrus has a rather high accident rate despite the presence of its parachute. Rubber bladder tanks get torn by ripped aluminum. A good seat, and that four or five-point harness are good ideas. But most of all, good training pays the biggest dividends.

Dan
 

bmcj

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Taking a Spam Can and Making it Crashworthy

STEP 1 - Remove the engine.

STEP 2 - hmmm.... nevermind, step one pretty much fixed the problem.

;)
 

SVSUSteve

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Autoreply said:
Some aluminium foam or honeycomb under the seat might help a lot in a severe crash that demolished the safety cage.
Actually, the seat should stroke (attenuate/absorb energy) even if the safety cage is not catastrophically damaged. If it doesn't, you're likely to wind up with a dead or critically injured pilot or passenger inside the safety cage. It's not a backup to the safety cage. They serve two different primary roles. The cage is there to maintain a volume so the people inside do not wind up crushed. The energy attenuating seat is there to reduce the energy reaching its occupant.

Dan Thomas said:
Steel tube also has its risks; there have been people maimed or killed by broken tubing piercing soft pink bodies
The risk of that is fairly low. In 1800 cases, I've found four cases of clear cut, unequivocal penetration by structural components. There are two others in the aviation pathology literature, both of which involved ultralights. Two of the cases in my research database were also ultralights or basically "fat ultralights".

Dan Thomas said:
Rubber bladder tanks get torn by ripped aluminum
That is exactly why I didn't go with rubber bladders and designed a better system for the Praetorian and Vireo.

Dan Thomas said:
the Cirrus has a rather high accident rate despite the presence of its parachute
That's because they market the parachute as a solution to the common problems of GA when it is only amenable in a narrow subset of them. It's just another big source of post-crash fire ignition in anything like a stall/spin in the pattern.

Dan Thomas said:
A good seat, and that four or five-point harness are good ideas.
A good energy attenuating seat with heavily reinforced attachments for the seat itself and the associated five-point restraints is high on the list of improvements that are easily achieved.

Dan Thomas said:
I would just build the airplane as per plans, and get some good training in stuff like stalls and spins. There's nothing like experiencing the real thing to help you avoid an accident.
Why not do both? Training only goes so far and it can make a person more comfortable with operating closer to the margin of error (less risk averse). The "more training" crowd doesn't like to admit it but their solution is only a partial one just as crashworthy aircraft are only part of the solution. There needs to be both if we want to protect ourselves and passengers.
 

Max Torque

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SVSUSteve,

Can you post the basics - a simple guideline for builders - and maybe some pictures of what makes a good energy attenuating seat for a homebuilt, please? I've done the searches for "energy attenuating seats" and "crashworthy seats" and learned a lot, but I've also read lots of misinformation and old wives tales and would like some informed input aimed at homebuilders. Thanks.

Also, I am at a loss to find a source for 3/8" (or similar diameter +/-) breakaway valves (i.e. frangible self-sealing valves for installation at the tank) at a reasonable cost - reasonable being a couple hundred $ vs. several thousand $ - Parker/Stratoflex, et al, valves are available and go for several thousand dollars each. Talked to a rep and he said cost is the reason civilian manufacturers don't use them (normally). No big deal for the military which spends taxpayer dollars. Any suggestions?

Thanks,

Tom
 
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SVSUSteve

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Can you post the basics - a simple guideline for builders - and maybe some pictures of what makes a good energy attenuating seat for a homebuilt, please? I've done the searches for "energy attenuating seats" and "crashworthy seats" and learned a lot, but I've also read lots of misinformation and old wives tales and would like some informed input aimed at homebuilders. Thanks.
I am actually working on an article for EAA Experimenter about just that. I might be several months though before it's published since I am trying to take a logical approach to teaching folks with my series rather than just jumping about. However, I will do my best to get something up on this thread in the next couple of days. Work has been kind of nuts lately and I am actually just checking in here before heading to bed.

Also, I am at a loss to find a source for 3/8" (or similar diameter +/-) breakaway valves (i.e. frangible self-sealing valves for installation at the tank) at a reasonable cost - reasonable being a couple hundred $ vs. several thousand $ - Parker/Stratoflex, et al, valves are available and go for several thousand dollars each. Talked to a rep and he said cost is the reason civilian manufacturers don't use them (normally). No big deal for the military which spends taxpayer dollars. Any suggestions?
I know there are at least two manufacturers for auto racing versions of the breakaway valves but both are things I have learned of through second hand means (conversations with drivers and mechanics). One is supposedly Japanese and the other is Italian. I have never been able to find a direct contact address or number for either company.

Honestly, if need be, theoretically one could source out a valve of their own design. I might actually think about doing that for the Vireo project....
 

Toobuilder

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...I'd also look at preventing crashes. You have a proven engine (Rotax 912S right?) Fuel system without design faults? I'd have a good look at something like ADS-B or the Powerflarm. Most importantly, training. Investing 1000 dollars in training is buying you more safety as any possible safety feat...

+1 on this. The single biggest safety threat in any non combat airplane is the pilot. You can have all the safety features in the world, but they are generally used only AFTER the pilot screwed up. Fix the first problem, and the need for the safety backup features is significantly reduced.
 

Hot Wings

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Also, I am at a loss to find a source for 3/8" (or similar diameter +/-) breakaway valves (i.e. frangible self-sealing valves for installation at the tank) at a reasonable cost - reasonable being a couple hundred $ vs. several thousand $ - Parker/Stratoflex, et al, valves are available and go for several thousand dollars each.

8mm works for my application but is too small for most common aircraft engines. These can be found for a "reasonable" price - $200 on eBay right now.
 

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Max Torque

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Okay gang, I found Staubli SPT05 Ball Locking Dry Break Plug and Socket for about $300 per fitting (socket and plug) as used in race car fuel breakaways. They come in AN4 and AN6 sizes. That would amount to about $600 for two fuel tanks. Still a bit expensive, but lots more affordable than Parker/Stratoflex.
 

SVSUSteve

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Staubli SPT05 Ball Locking Dry Break Plug and Socket for about $300 per fitting (socket and plug) as used in race car fuel breakaways
I think that could be the "Italian" company that I was referred to (not sure if it is actually Italian or not; I could have sworn the racing guys told me "Raubli" which would explain why I didn't find anything when I went looking). Where did you happen to find them just out of curiosity?
 

berridos

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I am really dubious about a troublefree wetwing. on the other side a bladder fuel cell could be heavy and maybe expensive. One idea I had to avoid the baffling problem is to build a rubber bladder with an access door of maybe 5 in. Once I introduce the folded bladder tank thru a 5 in opening in the root rib we could create baffling by introducing several explosafe or similar foam round tubes that fit thru the acces in the root rib and the bladder acces hole until we fill the bladder. I found the same list with addresses.View attachment L1_Approved_materials_tank.pdf

http://navyaviation.tpub.com/14018/css/14018_151.htm

http://navyaviation.tpub.com/14018/css/14018_152.htm
 
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Hot Wings

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Where would you attach the break valve cables in a detachable wing?
What we really need is a small inexpensive version of this safety valveFuel connect 1.JPGwhich has a problem with leakage if partially disconnected by a pull that is not linear and the center sleeve gets bent.
The Parker valve fuel 2.JPGdoesn't have this problem but is not as simple to make. Neither version needs the lanyard for activation.
 

cheapracer

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For what it's worth ...

I watched a competition once where University students were competing in making a front car's bumper as crashworthy as best they could on a budget and the winner and by far the cheapest was the team that used empty aluminium drink cans. They put pin holes in each end of the unopened cans and blew out the fluid and wrapped them together in bunches in packaging tape. A lot of energy was dissipated through the air in the cans first compressing and then escaping as they crush. Very little weight of course.
 

SVSUSteve

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For what it's worth ...

I watched a competition once where University students were competing in making a front car's bumper as crashworthy as best they could on a budget and the winner and by far the cheapest was the team that used empty aluminium drink cans. They put pin holes in each end of the unopened cans and blew out the fluid and wrapped them together in bunches in packaging tape. A lot of energy was dissipated through the air in the cans first compressing and then escaping as they crush. Very little weight of course.
The issue with that (or any energy attenuation system to be honest) is, while it may attenuate energy, the resulting impulse may be "shaped" in such a way or still significant enough to cause serious injury. I would not use it in safety critical systems without extensive testing. Remember that bumpers are not designed specifically to protect the occupants. Their purpose is more to minimize cosmetic damage and repair costs.
 

cheapracer

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Remember that bumpers are not designed specifically to protect the occupants. .
Maybe I didn't explain it properly sorry, my bad, the pyhsics Students designed and were required to crash simulate on computers and then to actually build their impact structures replacing the front bumper specifically to help disipitate a crashing car's energy. They were designed specifically to aid in the protection of occupants, they were not ornaments, they were in fact rather ugly!

Substances such as various foams, wood, cardboard and various aluminum shapes were tried by the teams but the cans came out in front. A g-meter was used.


I would not use it in safety critical systems without extensive testing. .
Sounds you work for a Goverment department maybe?
 

SVSUSteve

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Sounds you work for a Goverment department maybe?
Nope. You build a couple of, for example, the seats, load them up and test them. It is no different than the structural testing we do on an aircraft (sandbagging for static loads) to verify our calculations. You can run all the computer simulations and do all the math but until you experimentally verify the results, it is a big question of how it will actually perform. I don't know about you, but I don't think the first test should be one with a person at risk.

Can you point me to the actual data from the tests you mention? News reports are often blatantly wrong or at very least misconstrued.
 
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