Wooden aircraft and crash safety

[wren460]

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

Ya, will somebody please light a fire under the butt of one Mr. Wainfan and his solution to this problem the FMX series............

 

[Wanttaja]

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.

Ya, will somebody please light a fire under the butt of one Mr. Wainfan and his solution to this problem the FMX series............

What features does the FMX have to alleviate stalls during initial climbout?

Ron Wanttaja

 

[Old Koreelah]

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...

I lined my Jodel’s cockpit with ply, partly for the extra strength, but mostly to reduce the chance of being impaled on slintered spruce.

 

[flitzerpilot]

Ava, if you're considering multiple stringers with external ply, (with or without maybe in-filled with balsa) that's moving a long way from the basic Pietenpol construction. BJC mentions the difficulty of inspection and others have commented on the possibility of injury from splintering of inboard ply-skinning. But, forgive me for mentioning the Flitzer again: the basic Z-21 has a flat-sided ply-skinned fuselage, thickness reducing as it extends aft towards the sternpost.

The move towards some greater crash protection involves a very substantial firewall bulkhead and internal plywood side-skinning which extends only as far as the lower main spar, so in the event of a survivable high impact, internal ply splintering should not come close to the pilot's torso. Happily this is yet to be proven. Additional inspection ports have since been included into Flitzer designs, namely foot well ports (*3 on the Stormcock side elevation) aiding maintenance and inspection of rudder pedals, brake levers (where fitted) and fuel cock, etc.

Several later Flitzer evolutions have abandoned the rear fuselage ply skinning for fabric over stringers.

 

[Ava]

....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?

Once upon a time will be in a few minutes... when I fire up Ole Piet and takeoff from the grass circle directly into the 10 mph wind on this cloudless morning. Model A Ford engines like ours are still around, and there are plenty of places to buy new parts-- like the pictured Edelbrock "high compression aluminum racing head."

High is a relative term: the original A head as properly mounted had a 4.2:1 cr, then a 4.6; B's are 5.9; C's are 6.9. About the same as the aftermarket 7.0:1 cr, and aluminum heads weigh half what the cast iron ones do. It's a nice torqey engine spinning a big 74" x 42" paddle making a whole lot of usable thrust at 1500-1700 rpm.

 

[Ava]

Ava, if you're considering multiple stringers with external ply, (with or without maybe in-filled with balsa) that's moving a long way from the basic Pietenpol construction...

You are going way beyond my thoughts. Which is fine, people never learn anything if everyone either agrees with everything or disagrees with everything they say (or just think about out loud).

Pietenpol fuselages-- at least the built up wood ones, there is a steel version for the AC-- have ply skinning (properly Haskelite, but that stuff is getting hard to source ) over the outside of the longeons and frames. I was just thinking that some of the de Havillands (like Fox Moths and Giant Moths) had the plywood inside of the longeons. In the cabin the ply was covered by doped fabric-- perhaps to contain splinters. When built per plans the requirement for inspection ports on a Pietenpol is really minimal. With the cables and tubes being inside the compartment or outside the aircraft, rather than hidden away.

 

[speedracer]

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.

I think he pulled up because he realized he had forgotten to lower the nose gear. That is a really, really long runway. Someone said that if an EZ pilot tells you he's never landed gear up, you're talking to a liar.

 

[speedracer]

Whatta heck happened there ? Stall ?

Long EZ's don't stall. They just don't. In mine I can pull to idle, hold the stick to the aft stop and make 60 degree banked turns with no departure.

 

[wren460]

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

I've never seen hem fir plywood though I imagine I'd like it. Too bad there are no plywood mills within a thousand miles of my location.

What features does the FMX have to alleviate stalls during initial climbout?

Ron Wanttaja

Far less likely to spin. 1,000 FPM mush.

 

[wren460]

Long EZ's don't stall. They just don't. In mine I can pull to idle, hold the stick to the aft stop and make 60 degree banked turns with no departure.

I have zero experience in this type of aircraft, only information found online. To my understanding the angle of incidence on the canard is set to a higher angle than the main wing and is intended to stall before the main wing resulting in an automatic nose pitch down stall recovery without any sort of main wing drop off, or if the stick is held full aft then an altitude diminishing mush. So, while the main wing may not stall, if the aircraft is too slow and too low when the canard stalls then you may have an ultra hard landing/impact as can be seen in the previously posted video.

So, I would agree that under normal weight and balance conditions and if properly constructed, a Long EZ won't fully stall.

 

[wren460]

Once upon a time will be in a few minutes... when I fire up Ole Piet and takeoff from the grass circle directly into the 10 mph wind on this cloudless morning. Model A Ford engines like ours are still around, and there are plenty of places to buy new parts-- like the pictured Edelbrock "high compression aluminum racing head."

High is a relative term: the original A head as properly mounted had a 4.2:1 cr, then a 4.6; B's are 5.9; C's are 6.9. About the same as the aftermarket 7.0:1 cr, and aluminum heads weigh half what the cast iron ones do. It's a nice torqey engine spinning a big 74" x 42" paddle making a whole lot of usable thrust at 1500-1700 rpm.
View attachment 127090

I think that is way cool! I really like the Pietenpol design except for the cockpit access at my age and frame size.

 

[Dan Thomas]

You don't have to stall an airplane to crash it. Just get it too slow and the sink rate will get high enough to bust everything. The Ercoupe was stall-proof, but they would pancake in if the pilot got it too slow on final. There have also been plenty of ordinary Cessnas and the like damaged that way.

 

[wren460]

Innegra impact test. The sample is one layer of 4oz Innega laminated on each side of 2lb density extruded polystyrene foam 1" thick. The hammer weighed 55 oz on the head end. Notice the groove in the laminate sample where I folded the sample multiple times.

 

[radfordc]

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

Looks like it's true that a Piper Cub can just barely kill you!

 

[radfordc]

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

Is there any data that shows ULs are safer than GA planes?

 

[speedracer]

I have zero experience in this type of aircraft, only information found online. To my understanding the angle of incidence on the canard is set to a higher angle than the main wing and is intended to stall before the main wing resulting in an automatic nose pitch down stall recovery without any sort of main wing drop off, or if the stick is held full aft then an altitude diminishing mush. So, while the main wing may not stall, if the aircraft is too slow and too low when the canard stalls then you may have an ultra hard landing/impact as can be seen in the previously posted video.

So, I would agree that under normal weight and balance conditions and if properly constructed, a Long EZ won't fully stall.

When the canard stalls it drops about 4", then (unstalls), flies and stalls again. It does this about 4 times a second. It's called a "canard bob". The guy in the video just flew it into the ground.

 

[Tom DM]

Whatta heck happened there ? Stall ?

No : forgot to lower the nose wheel on landing and then to fly the aircraft

 

[Tom DM]

Looks like it's true that a Piper Cub can just barely kill you!

Thanks: I have an appointment with one and must admit some rustiness... last flight with the type was about 49 years ago.

What could possibly go wrong?

 

[wren460]

When the canard stalls it drops about 4", then (unstalls), flies and stalls again. It does this about 4 times a second. It's called a "canard bob". The guy in the video just flew it into the ground.

Ya I've seen that demonstrated in Velocity aircraft but I would imagine if the aircraft is too slow, card stall recovery would not occur hence diminished pitch control. I suppose the deployed spoiler did not help either.

 

[Ava]

Ya I've seen that demonstrated in Velocity aircraft but I would imagine if the aircraft is too slow, card stall recovery would not occur hence diminished pitch control. I suppose the deployed spoiler did not help either.

On Ole Piet, the envelope is 15" aft of the leading edge to 20" back. Taking off at 870 pounds which is solo and full fuel I'm at 15.88" which will move on up to 15.41" if I run the tank dry. Putting someone in the front cockpit only moves the CG back a bit less than an inch. So, I'm always riding on the front edge of the CG range. I mention this because Speedracer said a VE won't "truly" stall.

My power-off stalls are benign. There is not enough elevator to keep the airplane stalled indefinitely. Just keep the wing level and as the nose falls the airplane makes enough lift to unstall itself. An extra 175 pounds up front and inch of aft CG movement just slows the process down without really changing it.

In a power-on stall there is more torque to contend with-- in order to keep the wings level-- and the elevator is more effective at keeping the nose up because of the effective wind, but starting out at a safe altitude... (pause) a safe altitude...that isn't an issue either.

But, to this noob with 39.0 total hours, it sure looks like what the guy in the video did was get distracted trying to get that front gear down on final and stall-- or maybe as it was suggested stall-recover-stall-recover-stall-recover-stall-recover-stall-- into the field