Aircraft Wood, again...;-)

[wolfy]

I own the only remaining Carbon Dragon (Jim Maupin) in australia. Despite the name there is very little carbon, mainly wood construction and very light.

 

[WaspAir]

Well, I guess wood is largely carbon (overlooking some oxygen, hydrogen, nitrogen . . .)

Looks like fun. I've never gone foot-launch.

 

[wolfy]

Ive never gone foot launch either, this one was built with the bomb bay doors covered.

 

[Aerofoam]

Is the Shepherd's crook shape formed by the rear keel/mast/engine mount area an artistic touch or an engineering decision?

Appreciate your brainstorming Mark

Jim

The curves are to keep continuous laminations through the entire length of a section from start to stop.
The internal laminations can have scarfed joints, or even butt joints as long as they are all staggered, the outer plies should be full length.
In reality they could be separate sections and get bonded after the fact, but the strength should be better if it is formed as
a single structure. I would fill the triangular voids with balsa, or foam to keep everything sealed.

 

[Aerofoam]

I own the only remaining Carbon Dragon (Jim Maupin) in australia. Despite the name there is very little carbon, mainly wood construction and very light.View attachment 1162712

Wasn't there an even smaller early version of this airplane?

 

[wolfy]

Wasn't there an even smaller early version of this airplane?

Not that Im aware of. Not from Jim Maupin and Erve Culver

 

[okikuma]

The Briegleb BG-12 (and BG-12/16) is another wooden wonder of that era.

JR,

Yes, you are correct. I had forgotten about the all wood Briegleb BG-12/16. At the beginning of WW2, Gus Briegleb also designed the all wood two place BG-8 glider for the USAAF Glider Training program. The USAAF tested the BG-8 glider. It performed too well to be a trainer so Briegleb Glider Company did not receive a contract. After the war Gus’ Sailplane Corporation of America designed and sold kits for the BG-6 and BG-7 gliders with the ubiquitous welded tube fuselage and wood wings.

After WW2 through the 1970s in Southern California, a vast majority of USAF, NASA, and local aerospace test pilots and engineers were heavily involved in soaring and flew out of El Mirage at the Briegleb Soaring Center. In fact in the early 1960s, Gus Briegleb was commissioned to build all the wood components for the NASA M2-F1 Lifting Body. The interior airframe of welded 4130 tubing was built by NASA, and Gus built the wood bulkheads and formed the mahogany skin.

A number of U.S. National Soaring Championships were held at the El Mirage Airport back in the 1960s - 70s.

I flew gliders out of El MIrage in the late 1970s - through the early 1980s.

Wayne

 

[Aerofoam]

JR,

Yes, you are correct. I had forgotten about the all wood Briegleb BG-12/16. At the beginning of WW2, Gus Briegleb also designed the all wood two place BG-8 glider for the USAAF Glider Training program. The USAAF tested the BG-8 glider. It performed too well to be a trainer so Briegleb Glider Company did not receive a contract. After the war Gus’ Sailplane Corporation of America designed and sold kits for the BG-6 and BG-7 gliders with the ubiquitous welded tube fuselage and wood wings.

After WW2 through the 1970s in Southern California, a vast majority of USAF, NASA, and local aerospace test pilots and engineers were heavily involved in soaring and flew out of El Mirage at the Briegleb Soaring Center. In fact in the early 1960s, Gus Briegleb was commissioned to build all the wood components for the NASA M2-F1 Lifting Body. The interior airframe of welded 4130 tubing was built by NASA, and Gus built the wood bulkheads and formed the mahogany skin.

A number of U.S. National Soaring Championships were held at the El Mirage Airport back in the 1960s - 70s.

I flew gliders out of El MIrage in the late 1970s - through the early 1980s.

Wayne

Did the Horten Ho4 ever fly there?
I know the Mississippi U campaigned it in the early 60's



My favorite is the Ho6 though, coolest thing ever IMO......Wood and cloth, Ridiculous aspect ratio and glide ratio.
They found it would flutter at about 80, but you could dive through the flutter and it was stable to speeds over 110.
I don't think they tried to push it harder than that.....

 

[WaspAir]

There were flying wings designed by Jim Marske back then.

 

[okikuma]

Did the Horten Ho4 ever fly there?
I know the Mississippi U campaigned it in the early 60's

View attachment 1162725

My favorite is the Ho6 though, coolest thing ever IMO......Wood and cloth, Ridiculous aspect ratio and glide ratio.
They found it would flutter at about 80, but you could dive through the flutter and it was stable to speeds over 110.
I don't think they tried to push it harder than that.....

View attachment 1162726

Mark,

I honestly don't know if the Ho6 had flown at El Mirage. Later today, I will be at an event with a couple of old glider friends of mine. I'll make sure to ask them.

Wayne

There were flying wings designed by Jim Marske back then.

View attachment 1162727

JR,

As you know, majority of the Marske gliders were built out of wood. The Pioneer III & IV, and the Monarch were built from fiberglass and epoxy laminates.

Wayne

 

[okikuma]

The Evans VP-1 Volksplane is an all wood plans built experimental amateur built aircraft powered by a VW engine.

Wayne

 

[okikuma]

And the all wood Schneider DFS 108-14 SG-38 Schulgleiter.

Wayne

 

[okikuma]

So Jurgen, there are a few more people that agree with you and I that wood as an aircraft building material is still valid for the 21st century.

Wayne

 

[Aerofoam]

And the all wood Schneider DFS 108-14 SG-38 Schulgleiter.

Wayne

But this would be SO EASY out of foam and glass/carbon, and no flying wires.......

 

[kolibri282]

First I would like to thank everybody for their beautiful photos and stories, great stuff!

Next I would like to contribute some thoughts on wood vs. metal design.
Looking at the wooden gyro design in #22, I first thought that this would inevitably result in a heavier aircraft, so I started to calculate a simple example. The mast is mainly stressed in bending, therefore I omitted the tensile stresses and calculated an equivalent wooden mast for a bensen type aircraft. To avoid unnecessary complication the calculation assumes a 2 inch square profile with 3/16th wall thickness made from T-6061, for which I looked up a bending (tensile) strength of 45.000 psi (310 N/mm^2). The weight of a 3' length of this profile, at a density for aluminum alloy of 2710 kg/m^3, is 2.2kg.

Sitka spruce has been the premium choice of wood for building aircraft for a long time so this is the material I wanted to compare to. The bending strength is given in
- ANC-18. 'The Mechanical Properties of 174 Australian Timbers' by E.Bolza and N.H. Kloot 1963
as 10.400 psi (74 N/mm^2), density is 27 lb/cuft (432 kg/m^3).
You can look up my calculation in the octave/Matlab(R) program below. The result surprised me! Even a full, non hollow, wood section is considerably lighter than the aluminum mast (see below). Lastly I calculated a wood section where the inner half was removed, i.e. had a rectangular hole of half of the section width. Here are the results:

	aluminum	spruce full	spruce hollow
b [mm]	50.8	68.3	70
W [kg]	2.2	1.8	1.4

	aluminum	douglas fir full	douglas fir hollow
b [mm]	50.8	64.6	70
W [kg]	2.2	2.0	1.6

for the 2 inch (50.8 mm) aluminum section you need 68 mm spruce and 70 mm for the hollow section, weight is 2.2kg for aluminum, 1.8 kg spruce and 1.4 kg hollow.

It is not possible to split up a beam in two parts of half the cross section, as in the drawing in #22, where the mast goes to the keel, because then your torsional rigidity drops dramatically. It would also be very difficult to increase the cross section gradually, becausE you would have to glue end-grain which gives a much lower strength of the glue and there are, as far as I know, next to know rules for calculating the joint. If you want to go fully natural materials you could tie the connecting arc with some sort of rope. That might sound strange until you remember that the polynesian canoes, which crossed thousands of miles of the pacific ocean back and forth, where tied together by rope, not a single piece of metal was used. A somewhat more modern approach would be to use the good old gusset plate for this connection.

So much for my thoughts on wood design. Looking forward to your comments.

Jürgen


=== octave/Matlab(R) program ====
clc

gEarth=9.81;
f2m = 0.3048;
i2m = 0.0254;
i2mm = 25.4;

% distance down the mast where bending stress is evaluated
h = 3; % 3 feet mast length
b = 2; % 2 inch square tube
t = 3/16; % wall thickness

% all dimensions converted to mm
b=b*i2mm;
t=t*i2mm;
h=h*f2m*1000;

Is=1/12*(b^4 - (b-2*t)^4);

Ws= Is/(b/2);

As=b^2- (b-2*t)^2;

sigAl = 310; % N/mm^2
rhoAl = 2710; % kg/m^3

Wal = As*h*rhoAl/1.0e9; % konvert rho from kg/m^3 to kg/mm^3


% wood -> spruce
sigW = 72; % N/mm^2
rhoWlbc = 27; % lb/cuft
matStr = 'Spruce ';

% wood -> douglas fir
% sigW = 85;
% rhoWlbc= 32.5;
% matStr = 'Douglas fir';

rhoW = rhoWlbc*16; % 16 (kg/m^2)/(lb/cuft)


% the first moment of inertia of the wooden beam
% must be 310/74 times greater than that of
% the aluminum beam for the same strength

Wsw = sigAl/sigW*Ws;

% Wsw = b*h^2/6 = b^3/6
% b is the third root of w
bW = (6*Wsw)^(1/3);

Ww = bW*bW*h*rhoW/1.0e9;

% second moment of inertia of hollow beam is
% I2 = (b^4 - (1/2*b)^4)/12 = 15/16*b^4/12
% thus moment of inertia is I2/(b/2)= 15/16*b^3/6

bW2 = (16/15*6*Wsw)^(1/3);
Aw2 = 0.75*bW2*bW2;
Ww2 = Aw2*h*rhoW/1.0e9;


fprintf('%s\n',matStr)
fprintf('b al %5.1fmm b w %5.1fmm b w2 %5.1fmm\n',b,bW,bW2);
fprintf('W al %5.1fkg W w %5.1fkg W w2%5.1fkg\n',Wal,Ww,Ww2);

 

[Aerofoam]

First I would like to thank everybody for their beautiful photos and stories, great stuff!

Next I would like to contribute some thoughts on wood vs. metal design.
Looking at the wooden gyro design I first thought that this would inevitably result in a heavier aircraft, so I started to calculate a simple example. The mast is mainly stressed in bending, thus I omitted the tensile stresses and calculated an equivalent wooden mast for a bensen type aircraft. To avoid unneccessary complicaton the calculation assumes a 2 inch square profile with 3/16th wall thickness made from T-6061, for which I looked up a bending (tensile) strength of 45.000 psi (310 N/mm^2). The weight of a 3' length of this profile, at a density for aluminum alloy of 2710 kg/m^3, is 2.2kg.

Sitka spruce has been the choice of premium wood for building aircraft for a long time so this is the material I wanted to compare to. The bending strength is given in
- ANC-18. 'The Mechanical Properties of 174 Australian Timbers' by E.Bolza and N.H. Kloot 1963
as 10.400 psi (74 N/mm^2), density is 27 lb/cuft (432 kg/m^3).
You can look up my calculation in the octave/Matlab(R) program below. The result surprised me! Even a full, non hollow, wood section is considerably lighter than the aluminum mast (see below). Lastly I calculated a wood section where the inner half was removed, i.e. had a rectangular hole of half of the section width. Here are the results:

Spruce
b al 50.8mm b w 68.3mm b w2 69.8mm
W al 2.2kg W w 1.8kg W w2 1.4kg

Douglas fir
b al 50.8mm b w 64.6mm b w2 66.0mm
W al 2.2kg W w 2.0kg W w2 1.6kg

for the 2 inch (50.8 mm) aluminum section you need 68 mm spruce and 70 mm for the hollow section, weight is 2.2kg for aluminum, 1.8 kg spruce and 1.4 kg hollow.

It is not possible to split up a beam in two parts of half the cross section, as in the drawing where the mast goes to the keel, because then your torsional regidity drops dramatically. It would also be very difficult to increase the cross section gradually, becaus you would have to glue end-grain which gives a much lower strength of the glue and there are, as far as I know, next to know rules for calculating the joint. If you want to go fully natural materials you could tie the connecting arc with some sort of rope. That might sound strange until you remember that the polynesian canoes, which crossed thousands of miles of the pacific ocean back and forth, where tied together by rope, not a single piece of metal was used. A somewhat more modern aproach would be to use the good old gusset plate for this connection.

So, some thoughts on wood design. Looking forward to your comments.

Jürgen


=== octave/Matlab(R) program ====
clc

gEarth=9.81;
f2m = 0.3048;
i2m = 0.0254;
i2mm = 25.4;

% distance down the mast where bending stress is evaluated
h = 3; % 3 feet mast length
b = 2; % 2 inch square tube
t = 3/16; % wall thickness

% all dimensions converted to mm
b=b*i2mm;
t=t*i2mm;
h=h*f2m*1000;

Is=1/12*(b^4 - (b-2*t)^4);

Ws= Is/(b/2);

As=b^2- (b-2*t)^2;

sigAl = 310; % N/mm^2
rhoAl = 2710; % kg/m^3

Wal = As*h*rhoAl/1.0e9; % konvert rho from kg/m^3 to kg/mm^3


% wood -> spruce
sigW = 72; % N/mm^2
rhoWlbc = 27; % lb/cuft
matStr = 'Spruce ';

% wood -> douglas fir
% sigW = 85;
% rhoWlbc= 32.5;
% matStr = 'Douglas fir';

rhoW = rhoWlbc*16; % 16 (kg/m^2)/(lb/cuft)


% the first moment of inertia of the wooden beam
% must be 310/74 times greater than that of
% the aluminum beam for the same strength

Wsw = sigAl/sigW*Ws;

% Wsw = b*h^2/6 = b^3/6
% b is the third root of w
bW = (6*Wsw)^(1/3);

Ww = bW*bW*h*rhoW/1.0e9;

% second moment of inertia of hollow beam is
% I2 = (b^4 - (1/2*b)^4)/12 = 15/16*b^4/12
% thus moment of inertia is I2/(b/2)= 15/16*b^3/6

bW2 = (16/15*6*Wsw)^(1/3);
Aw2 = 0.75*bW2*bW2;
Ww2 = Aw2*h*rhoW/1.0e9;


fprintf('%s\n',matStr)
fprintf('b al %5.1fmm b w %5.1fmm b w2 %5.1fmm\n',b,bW,bW2);
fprintf('W al %5.1fkg W w %5.1fkg W w2%5.1fkg\n',Wal,Ww,Ww2);

I would work in laminations because it equalized the wood as far as tension, twisting and other forces are concerned. It also stabilizes and somewhat weather proofs the wood. Cloth can be added for other tension, or torsion benefits.
Also, the mast would probably benefit from being 3x3 at the base/keel junction and reducing to 1 x 3 above the seat/motor mount, with the width staying 3". The base section could have strategic hollow sections for weigh reduction.
This would allow the fore and aft motion to absorb the 2.rev shake.

I love lashings as fasteners, it's a lost art and actually stronger than rigid plates.
I removed all the hardware from the 12' long dagger board on my 44ft. trimaran and replaced it with a 2" diameter glass lined hole to attach the line that retracted the 200lb. Douglass fir/Fiberglass board.
You could inspect it in seconds and it did not corrode, or fatigue like the metal plates that had been there.

While we are on Doug. Fir, the old growth is remarkably strong. My trimaran had 2 clear 6" x 12" x 27' old growth Douglas fir beams that formed the main structure of the amas and box beam assembly. They were subjected to up to 60,000lbs of force with the 13ft. leverage arm from the center of the boat. The growth rings were less than 1/16".
The newer fir which grows very fast in full sun with plenty of water, can have rings that are 3/8" to 1/2" and the strength isn't in the same galaxy of old growth fir.....

 

[kolibri282]

This would allow the fore and aft motion to absorb the 2.rev shake.

Young has introduced the idea of making the mast as flexible as possible to absorb rotor shake, so my favourite idea is to use a single piece of bamboo for the mast. You'd have:
- a naturally tapered cross section
- a naturally hollowed cross section
- a round cross section which is the optimum for a mast,
...in terms of bending and aerodynamics
- a single piece, no glue lines

the results for a quick and dirt bamboo calculation, bending strength 130 N/mm^2 density 630 kg/mm^3 assuming that the cross section is 2/3 of the full section are (preliminary)
Bamboo

	aluminum	bamboo full	bamboo hollow 2/3
b [mm]	50.8	---	53
W [kg]	2.2	---	0.9

It is almost midnight and I will try a better calculation tomorrow.

PS: Tonight we went to a concert by Avi Avital, mandolin, and Ksenija Sidorova, accordeon, just awesome.

 

[WaspAir]

To state what may be obvious, wood was largely abandoned for aircraft not for any inherent flaws in the material but because of the expensive skilled labor it required.

 

[Aerofoam]

Young has introduced the idea of making the mast as flexible as possible to absorb rotor shake, so my favourite idea is to use a single piece of bamboo for the mast. You'd have:
- a naturally tapered cross section
- a naturally hollowed cross section
- a round cross section which is the optimum for a mast,
...in terms of bending and aerodynamics
- a single piece, no glue lines

the results for a quick and dirt bamboo calculation, bending strength 130 N/mm^2 density 630 kg/mm^3 assuming that the cross section is 2/3 of the full section are (preliminary)
Bamboo

	aluminum	bamboo full	bamboo hollow 2/3
b [mm]	50.8	---	53
W [kg]	2.2	---	0.9

It is almost midnight and I will try a better calculation tomorrow.

PS: Tonight we went to a concert by Avi Avital, mandolin, and Ksenija Sidorova, accordeon, just awesome.

Bamboo is a great material for strength and weight, you could make lug intersections like a bike frame and build the whole frame from bamboo glued into the lug joints which could be welded AL, or composite.

The only issue with bamboo is it dries out and starts splitting. In Az. this process doesn't take very long.....

 

[Mayfield]

I believe the Demoiselle was made largely of bamboo.