Wooden aircraft and crash safety

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wren460

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On a practical level, if you were to reinforce a wooden cockpit with some sort of resin and fabric to create a "crash cell" around the occupant, what would that entail? Here's the Evans VP-1 Volksplane, which is about as simple a wooden airframe as you are going to find. What would you have to do to create that crash cell. I suspect that it's a lot more work and a lot more additional weight than you might think at first glance.

View attachment 126998
At the minimum you would be wrapping the exterior of the fuselage (firewall to just behind the pilot) with a fabric reinforcement such as E-glass, S2-glass, Kevlar, Innegra, perhaps Dyneema or similar, each with differing properties and cost. More work? Certainly. Glassing the exterior is not so hard to accomplish. Glassing the interior is harder to accomplish but would provide a much stiffer structure due to the plywood skins acting like a sandwich core. One trick would be to apply the interior reinforcement layer on the plywood before installing it on the frame and then follow up with reinforcing the interior joints. Consider that with wood alone and no synthetic fiber reinforcements, at the minimum you will be applying varnish to seal the wood. Might as well be epoxy instead of varnish.

Yes, you would be adding some weight if also using standard 1/8" aircraft/marine plywood but one could also substitute a structural foam core for the plywood such as Divinycell in 1/8" or 1/4" thickness with composite skins on each side and likely beat the weight of the plywood alone. You would need one or more layers of reinforcement on the 45 degree bias to provide longitudinal shear resistance. Consider that if a 1/4" foam core is used, now you have an opportunity to radius the corners of the fuselage some more. Yes, a composite engineer should be consulted for which I am not.

It would be very interesting to build several proof of concept test structures and test them to destruction.....
 

Vigilant1

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Yes, you would be adding some weight if also using standard 1/8" aircraft/marine plywood but one could also substitute a structural foam core for the plywood such as Divinycell in 1/8" or 1/4" thickness with composite skins on each side and likely beat the weight of the plywood alone. You would need one or more layers of reinforcement on the 45 degree bias to provide longitudinal shear resistance. Consider that if a 1/4" foam core is used, now you have an opportunity to radius the corners of the fuselage some more. Yes, a composite engineer should be consulted for which I am not.
When we consider the unpredictable loadings in a crash and the value of having the structure hold together even after it has yielded, I suspect there might be some value in having a robust core that achieves some things we don't normally expect with foams (due to the ultimate tensile strength of the foam and resultant delamination of skins from it once fracture/peeling begins). In a sandwich panel under in-plane or out-of-plane loadings, having wood rather than foam is largely a waste of weight. But if keeping the skins adhered and at roughly the same distance from each other is important even after the skins start to crack in places, wood may have some value (as well as face fibers with good "toughness" properties after yield). I'd expect a corrugated core of E-glass (Innegra? Dynema?) might even be useful.

It would be very interesting to build several proof of concept test structures and test them to destruction.....
Yes, indeed.
 
Last edited:

TFF

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Lipstick.
I would think instead of adding, it would be better to make the composite do two things. Be the fuselage and be the crash structure instead of two separate structures. A redesign Looking at pictures of a VP fly reminds me of the Don Dwiggins book I would look at in the library as a kid. Nostalgia, which I am a fan of, but a stock VP is too crazy for me now. Whatever you do to it kills it some too. Something coming through the side ballistic like a limb might be ok with glassing, but reinforce longerons does nothing if the plane is already staying together. These are crashes that are not supposed to happen in any airplane. Nothing is going to keep ripping a wing off in one of these except not over G and not hitting something. Airplanes are not designed to be tanks. A roll bar tied solid would weigh quite a bit. That’s really what one needs. Warm and fuzzy weight takes away at performance that is not in abundance with a VP. Flying a stock VP is gutsy. That’s what it is. That roadster arm out the side looks cool. Not this day and age for me. Same thing I see with Wing Dings, and other early ULs. Something like 1 oz fg cloth as a surface on the fuselage instead of fabric I’m down with. Better life out of it than cloth and dope. You are not making it aviation stronger by slapping glass on it.
 

sorslibertas

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Feb 1, 2022
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At the minimum you would be wrapping the exterior of the fuselage (firewall to just behind the pilot) with a fabric reinforcement such as E-glass, S2-glass, Kevlar, Innegra, perhaps Dyneema or similar, each with differing properties and cost. More work? Certainly. Glassing the exterior is not so hard to accomplish. Glassing the interior is harder to accomplish but would provide a much stiffer structure due to the plywood skins acting like a sandwich core. One trick would be to apply the interior reinforcement layer on the plywood before installing it on the frame and then follow up with reinforcing the interior joints. Consider that with wood alone and no synthetic fiber reinforcements, at the minimum you will be applying varnish to seal the wood. Might as well be epoxy instead of varnish.

Yes, you would be adding some weight if also using standard 1/8" aircraft/marine plywood but one could also substitute a structural foam core for the plywood such as Divinycell in 1/8" or 1/4" thickness with composite skins on each side and likely beat the weight of the plywood alone. You would need one or more layers of reinforcement on the 45 degree bias to provide longitudinal shear resistance. Consider that if a 1/4" foam core is used, now you have an opportunity to radius the corners of the fuselage some more. Yes, a composite engineer should be consulted for which I am not.

It would be very interesting to build several proof of concept test structures and test them to destruction.....

My understanding (at least in boatbuilding) is that wood should not be sandwiched in fibreglass, as it may encourage rot should there be any water ingress. Is it different for airplanes?
 

cluttonfred

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On the subject of cropdusters and safety, the great Fred Weick of Ercoupe fame also essentially developed the concept of the modern cropduster from a safety perpective during his time at Texas A&M. There is a chapter on it in his autobiography From the Ground Up (long out of print but that's what libraries are for). Highly recommended!

Texas A&M College Aircraft Research Center

Ag-1 aka Weick Ag-1, -2, -3 1950 = Agricultural plane. 1pOlwM; 225hp Continental E-225; span: 39'0" length: 29'8" load: 1200# v: 115/100/45 range: 400; ff: 1/x/50 (p: Ted von Rosenberg). Hugh DeHaven, Fred Weick. Might be considered as the mother of all modern ag sprayers in the world. POP: 1 [N222]. There followed Ag-2 with 450hp P&W R-985 in 1956, redesigned by George Wing at Transland Company (qv), and the 1958, Wieck-designed Ag-3, which became the prototype Piper Pawnee.
1656058776295.png
Source: American airplanes: Ta - Th

See also: Fred Weick - Wikipedia
 

flitzerpilot

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I can only comment on the design of the Flitzer types in terms of 'crashworthiness' of a wooden aeroplane.

1/ A biplane where the pilot sits close to the centroid of a staggered wing cellule, ie. effectively between the wings but with a good cockpit view in itself provides some crash protection. In addition, an 'A' frame or inverted Vee cabane supporting the upper wings is effectively a roll-over safety feature. Thus no specific roll-over pylon need be added, adding unnecessary weight and drag. Much of the cabane is buried in the forward decking so local drag is minimised.

2/ In a somersault (overturn) the cabane absorbs the main load in the vicinity of the cockpit and the fin post is sacrificial. Providing one is well strapped in and sits low, the head is not likely to be in close proximity to the ground.

3/ The 'crash cell', if one can term it that, is made up of an inner plywood skin on the first few fuselage frames ahead of the cockpit in addition to the external ply skinning. The engine itself and the engine mount will bear the brunt of a crash in any event while the choice of a steel tube undercarriage means that the 'toad stabbing that Bernie Pietenpol describes with a broken wooden undercarriage penetrating the cockpit is not a factor. Progressive frangibilty can be considered as 'built in'.

Several Flitzers have overturned, due to various causes not endemic to the design; such as an improperly secured stick grip popping-off during the flare, pilot error, engine failure on approach on a brakeless Z-1 where lack of propeller slipstream ended with the a/c oveturned in tall crop, being blown off a hard runway in a gusting crosswind, etc. In none of these accidents was any injury suffered by any pilot. However, in a recent such accident caused by an improperly crimped Nicopress which allowed the right hand rudder cable to depart, the aircraft ground-looped violently and overturned and the pilot suffered damage to vertebrae in his neck. He is a tall individual and admitted that he had arranged his seating to be high in order to 'see over the nose'. This is the first time that anyone flying this type has been injured in over 30 years of the type being flown.

My recommendation has always been to sit as low as possible commensurate with the eye level being just above the fore-decking height. In normal cruise the a/c sits about a 1/2 degree nose down allowing a panoramic view between wings and wires, which is all you need. Happily the pilot in question is recovering.
 

Sraight'nlevel

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Excluding Dh Vampire and De Havilland Mosquito most wooden planes fly slow. That makes them safe alone...then many safety features like lifting fuselage.....and being a low wing monoplane may add to safety.

Then again there are so many wood types...like Yellow Balau....and Nordic birch that are very strong.....bonding them with fiber class cloth with resins...and making them plywood gives another extra advantage. Some say they are tougher than aluminium if you want them to be and you have the extra "dough" to accomplish it.
 

cluttonfred

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We had a couple of threads over the years on safety improvements for the Evans VP-2 Volksplane back when FritzW was active. The consensus was that building a VP-2 as light as possible was probably the best thing you could do for safety by improving climb performance, acceleration, and handling in a marginal two-seater.

One point that was made was the weakness of the 3/4" steel "roll bar" windscreen frame, but in practice that has not been an issue because of the infrequency of Volksplane rollover accidents. That may be because the weakness of landing gear design usually results in the gear collapsing or shearing off before it can flip the airframe. I am not sure if that was an intentionally-designed safety feature. :-\ .

On reflection, the only true safety modification I would make to the VP-2 is to add a small U-shaped steel tube to be rear cockpit bulkhead to raise the angle of the seat harness shoulder straps to prevent spinal injuries from compression in an otherwise survivable crash.


 

TFF

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While quite a few VP 1/2s have been completed, I don’t think most rack up the flying time. Lack of rollover events can be lack of flying. Most build them for the low cost. Flying out in the open that exposed has probably scared more out of the cockpit than enticed. Yes some will gravitate to it, but not many. Just looking at these things come up for sale, almost none are passing pilot to pilot. Most seem to be estate sales of sorts to people trying to capitalize on it being an airplane they bought cheap, Ha, Ha. Not understanding it’s a cheap airplane. A hoop behind the head ruins the lines. I would not fly one without one, and I would never expect to crash.
 

WonderousMountain

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My understanding (at least in boatbuilding) is that wood should not be sandwiched in fibreglass, as it may encourage rot should there be any water ingress. Is it different for airplanes?
That is what I heard, but after talking with Bieker Boats, I am told the problem of Water ingress is primarily a dock issue found where ventillation fails. Bieker runs structural textiles on both sides and most are CNC commercial Marine ply, similar to our aircraft grades. Additional lumber is selectively applied.
 

Dan Thomas

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That is what I heard, but after talking with Bieker Boats, I am told the problem of Water ingress is primarily a dock issue found where ventillation fails. Bieker runs structural textiles on both sides and most are CNC commercial Marine ply, similar to our aircraft grades. Additional lumber is selectively applied.
Water getting into fiberglass-covered transoms sends a lot of boats to the dump. Much of it gets in around the motor attachment bolts; they're not sealed. I recently restored an old outboard runabout and sealed the bolts with dumdum to keep the water out.
 

Old Koreelah

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I’m new to this thread, so apologies if I’m repeating what someone has already mentioned.

Home-builders would be hard pressed to beat low-tech fibreglass for airframe survivability. It absorbs crash impacts, protecting the occupants.
Perhaps the most crash-worthy recreational aircraft is the Jabiru; statistically, they are tied with Cessnas for having the least fatalities.
It’s been said that most Jabirus that crashed are back flying again- because damage tends to be localised, unlike sheet metal or wooden airframes- the fibreglass fuselage is easy to repair.
Another benefit is they float.
 

Wanttaja

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Home-builders would be hard pressed to beat low-tech fibreglass for airframe survivability. It absorbs crash impacts, protecting the occupants.
Perhaps the most crash-worthy recreational aircraft is the Jabiru; statistically, they are tied with Cessnas for having the least fatalities.
Only seven Jabiru accidents in my 1998-2020 homebuilt accident database. Not enough to draw any conclusions.

However, as far as fiberglass for airframe survivability, the jury is still out. Lots of factors involved in the survivability of accidents, including (as I've posted often before) the aircraft configuration (high/low wing) and the performance level of the aircraft. Probably the best straight-across comparison is the Beech Bonanza vs. the Cirrus designs--same configurations, same general performance. 30.6% of all Bonanza accidents have at least one fatality, vs. 33.7% of Cirrus accidents.

Both both have nearly TWICE the fatality rate of the plain 'ol metal Cessna 210...another high-performance aircraft.

Aircraft Model​
Fatality Rate​
Cessna​
All​
14.1%​
172​
11.0%​
172 R&S​
9.8%​
182​
16.6%​
182 S&T​
16.4%​
210​
17.2%​
Beech​
All​
27.6%​
Bonanza​
30.6%​
Cirrus​
All​
33.7%​
Diamond​
All​
15.7%​
Mooney​
All​
24.5%​
Piper​
All​
17.9%​
J3​
5.1%​
PA-28​
17.8%​
Arrow​
22.4%​
Homebuilts​
All​
24.0%​
Vans​
27.3%​
Glasair​
30.8%​
Lancair IV​
52.2%​
2-Seat Lancair​
42.2%​
Zenair (All)​
15.2%​
Zenair CH-701​
11.7%​
Searey​
19.0%​
Kitfox​
13.9%​
Sonex​
28.6%​
Velocity​
19.0%​
The production aircraft figures are for ten years (2007 through 2016), the homebuilt results are 23 years (1998 through 2020).

Ron Wanttaja
 

sorslibertas

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Joined
Feb 1, 2022
Messages
7
Only seven Jabiru accidents in my 1998-2020 homebuilt accident database. Not enough to draw any conclusions.

However, as far as fiberglass for airframe survivability, the jury is still out. Lots of factors involved in the survivability of accidents, including (as I've posted often before) the aircraft configuration (high/low wing) and the performance level of the aircraft. Probably the best straight-across comparison is the Beech Bonanza vs. the Cirrus designs--same configurations, same general performance. 30.6% of all Bonanza accidents have at least one fatality, vs. 33.7% of Cirrus accidents.

Both both have nearly TWICE the fatality rate of the plain 'ol metal Cessna 210...another high-performance aircraft.

Aircraft Model​
Fatality Rate​
Cessna​
All​
14.1%​
172​
11.0%​
172 R&S​
9.8%​
182​
16.6%​
182 S&T​
16.4%​
210​
17.2%​
Beech​
All​
27.6%​
Bonanza​
30.6%​
Cirrus​
All​
33.7%​
Diamond​
All​
15.7%​
Mooney​
All​
24.5%​
Piper​
All​
17.9%​
J3​
5.1%​
PA-28​
17.8%​
Arrow​
22.4%​
Homebuilts​
All​
24.0%​
Vans​
27.3%​
Glasair​
30.8%​
Lancair IV​
52.2%​
2-Seat Lancair​
42.2%​
Zenair (All)​
15.2%​
Zenair CH-701​
11.7%​
Searey​
19.0%​
Kitfox​
13.9%​
Sonex​
28.6%​
Velocity​
19.0%​
The production aircraft figures are for ten years (2007 through 2016), the homebuilt results are 23 years (1998 through 2020).

Ron Wanttaja

At a glance, it appears that there is a correlation between fatality rate and speed.

is there a breakdown of in which stage of flight the accidents happened?
 
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