Wooden aircraft and crash safety

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Sraight'nlevel

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That's a great idea. How about we also fill up the cockpit with packing peanuts before each flight. That would provide an additional measure of energy absorption before ones body impacts the interior of the fuselage. Ha, ha..........

Seriously though. There may be something to all that foam and fiberglass, check out this ultra hard Long EZ crash landing.


Whatta heck happened there ? Stall ?
 
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challenger_II

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Check out the undercarriage, on final approach: He's all set for landing, when he realizes the nose gear isn't down. Rather than do a "go-around", it appears the pilot tried to force the situation.
 

wren460

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Whatt heck happened there ?
Landing went bad but go around aborted too, perhaps engine issues? Pilot must have decided he had no choice but to put it down but was too slow which likely resulted in the Canard stalling before the main wing (intentional design parameter) hence the loss of pitch control and inability for the main wing to provide enough lift. I'm amazed he walked away just like a bull rider who gets slammed to the ground but stands up to the crowds cheer only to collapse after exiting the arena. Perhaps somebody on this forum knows more about this accident... I'm really curious about the pilots injuries. It is interesting to note that the body position in this type of aircraft might have been a factor in distributing the impact forces......
 

Ava

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....Nearly 100% of the fatalities occurred when the aircraft hit the ground...
Is this a corollary of: "Almost nobody has ever died from falling from a great height, it's that sudden deceleration that proves fatal--" or maybe vice versa?
 

Ava

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I am thinking about a de Havilland type wood structure. Would having the plywood inboard of the longerons in the cockpit area (which I prefer because it offers more options pertaining to the number, size, and location of stringers provide a safer (bathtub?) structure than having the longerons inboard of the plywood?
 

WonderousMountain

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The available Hemlock fir is fairly close grained and rather consistent in grains structure and can be found fairly clear of knots but not always in long lengths and is somewhat low in density but Hem fir is pleasant to work with having almost no splintering (unlike Douglas Fir) and is very low in resins or oils making for low odor and good bonding of joints. The NACA report 1941 says Hem Fir's strength is similar to Sitka Spruce.

So many possibilites.
Hemlock is reported to make fair plywood,
It would be easy enough to source local Alt
plywood rather than redesign all longerons.
 

Dan Thomas

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Ever seen plywood splinter? Instead of one or two long splinters from a longeron, you get thousands of shorter splinters. Might as well have a cactus in the cockpit.

The energy has to be dissipated somehow. The trick is to do that without presenting a lot of shattered and torn structure to kill the occupants. And you have to do it in a way that doesn't add a bunch of weight. You could have a safe, crashworthy airplane that will never crash because it's too heavy to fly.

The big OEMs like Cessna and Beech and Piper all use metal. Aluminum. They're the ones that get heavily sued if someone is maimed or dead in one of their airplanes, so they tend to use materials that will dissipate forces without turning into a thousand swords.
 

wren460

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Ever seen plywood splinter? Instead of one or two long splinters from a longeron, you get thousands of shorter splinters. Might as well have a cactus in the cockpit.

The energy has to be dissipated somehow. The trick is to do that without presenting a lot of shattered and torn structure to kill the occupants. And you have to do it in a way that doesn't add a bunch of weight. You could have a safe, crashworthy airplane that will never crash because it's too heavy to fly.

The big OEMs like Cessna and Beech and Piper all use metal. Aluminum. They're the ones that get heavily sued if someone is maimed or dead in one of their airplanes, so they tend to use materials that will dissipate forces without turning into a thousand swords.
And the Bigger manufacturers like Boeing are now heavily substituting aluminum with composites........
 

Ava

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Ever seen plywood splinter? Instead of one or two long splinters from a longeron, you get thousands of shorter splinters. Might as well have a cactus in the cockpit...
Right... But while falling on a cactus is painful, it probably won't be fatal or debilitating, unlike falling on a javelin. The principle, I believe, behind tempered glass which shatters into a million tiny pieces rather than a few large jagged ones.
 

wren460

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I suppose this conversation could go on for some time. I think we were discussing what could be done to a wooden aircraft fuselage in order to reinforce it to include a "safety cell" for the occupants. Wood can splinter for sure. Aluminum can crumple for sure and it also likes to fatigue over time from repeated loading. Interestingly, if loaded to before the yield point, wood will not fatigue and can be said to not have a "fatigue life". The same can be said for most synthetic composites though I suppose the binders can decay and I suppose wood can rot. Personally I don't like working in aluminum and prefer composites to include natures composites. I'm thinking about readily available resources and economics. What kinds of materials are readily available to me including those which are easy to ship? Can I combine some materials in order to improve the overalls crash worthiness of the structure while at the same time improving the performance of materials which might be deemed non traditional such as alternative wood species.
 

wren460

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Right... But while falling on a cactus is painful, it probably won't be fatal or debilitating, unlike falling on a javelin. The principle, I believe, behind tempered glass which shatters into a million tiny pieces rather than a few large jagged ones.
Ya....I tried that once when I was a kid. That is I fell right into a Cholla Cactus. Boy did that suck. I wanted to die....

I see you are interested in Model A powered Pietenpol, is that not an example of making use of something more readily available? That is, once upon a time, the Model A engine?
 

Dan Thomas

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Aluminum can crumple for sure and it also likes to fatigue over time from repeated loading. Interestingly, if loaded to before the yield point, wood will not fatigue and can be said to not have a "fatigue life". The same can be said for most synthetic composites though I suppose the binders can decay and I suppose wood can rot.
Aluminum fatigues if it's overstressed long enough and often enough. But there are Cessna 172s flying around with way over 20,000 hours on them, some near 30K hours. One that operated in Belize was retired with over 30,000 hours. The highest-time DC-3 has over 91,000 hours on it. Plenty of airliners get up to numbers like that, too. An well-designed and built aluminum homebuilt is never going to accumulate enough hours to deal with fatigue issues.

I looked after flight school airplanes, and we had 172s with 12,000 hours on them when we sold them. We found it better to buy low-time airplanes with engines nearly run out, re-engine them, re-do the interiors and update the radios, than to start replacing all the worn-out cables and pulleys and paint on top of replacing the engine and interior and updating the radios. The old airplanes were fine for a PPL who might fly it 50 or 100 hours a year, but in a flight school, stuff has to be entirely up to snuff or you're forever grounding the thing to fix things found at inspections. Students hate that.

Composites suffer degradation in the sun. Temperature extremes cause stresses that can cause cracking or delamination. Wood rots. I had to replace enough wood when I restored my Jodel, which had spent some time tied down outside before I got it.
 

Wanttaja

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Is this a corollary of: "Almost nobody has ever died from falling from a great height, it's that sudden deceleration that proves fatal--" or maybe vice versa?
Kinda. Think it was Heinlein who said, "When it comes down to it, EVERY death is due to heart failure."

It's the loss of aircraft control at altitudes where a fatal impact is likely to occur. Traditionally, people were warned of the base-to-final turn. No question it's something to be watching, but I was surprised to discover that twice as many stalls occurred during the initial climbout...even when the engine was in 100% shape.

Ron Wanttaja
 

WonderousMountain

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Instructions on flying the Sorrell Guppy advises you to climb without pulling on the stick. It's undercamber WingsSet rises in level attitude. Flare directly before landing, no sooner.
 

Sraight'nlevel

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Friend of mine a trophy winner R/C scale modeller once said when I asked about the demise of his beautiful R/C plane: " It collided with the globe !".
 

BJC

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I am thinking about a de Havilland type wood structure. Would having the plywood inboard of the longerons in the cockpit area (which I prefer because it offers more options pertaining to the number, size, and location of stringers provide a safer (bathtub?) structure than having the longerons inboard of the plywood?
Makes inspections more difficult.


BJC
 
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