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Stressed-skin plywood construction without lumber?

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mcrae0104

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The recent talk of Sitka spruce availability has me thinking of alternatives to aircraft lumber.
Not to steer this thread OT and away from plywood, but there are alternatives to spruce that are not "engineered products." Every now and then I revisit RS Hoover's blog and tonight I came upon this entry...

The Pee-Chay Catastrophe
 

TFF

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Built up ribs are about half the weight of a ply version. Ribs are pretty light. Ply ribs would be 5-20 lbs more a wing. Just depends on the wings. Skybolt and Starduster Toos can be built either way, and Sparcraft sold bootleg S1S Pitts wings with ply ribs.
 

Curt Curtis

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BBerson; sorry for the delayed response, also I am answering on yesterday's forum. I hope it works. I'm new on this forum and I'm not sure about the systems. The plane I have is Harry Tallman's design, and he was moving away from geodetic construction at that time which was about 1958. I worked with Harry Thalman on this airplane for several years in Salt Lake City, which was prior to my move to Phoenix Arizona. After Harry's crash and death this plane was involved in several owners. Years later I bought the pieces and move them to my place in Phoenix Arizona.

It has compound curves. Thalman built a large cement mold the size of the fuselage with copper pipes buried in the cement to heat the mold. It was formed in 3 stages, inside skin in one stage outside skin in another stage and bonding the aluminum hexcell in the final stage. Harry dreamed of certification and producing airplanes of this design. I do not know what will be the final outcome of the airplane pieces I have. I am not sure if I am capable of or interested in doing the final stages of the design and completing the airplane build. I am interested in discussions and opinions from participants in this forum.

I wish to know why you know about the Thalman T4? Years earlier, before I met Harry he told me of flying his airplane to Oregon and ended up in jail for flying his plane there. Oregon is possibly the birthplace of geodetic design and also possibly the birthplace of the home built movement. 3 times an individual flew his own home built airplane from Oregon to Washington DC attempting to get the rights to own and build your own airplane. His group finally succeeded and authorization was granted. Within a few months of that same year, Paul Pobernezy started the EAA.
 

TFF

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There is a fix for the Sparcraft ribs. Add Spruce capstrip on the vertical and perimeter of the rib and add gussets. So you got one big ply gusset rib shaped, a little bit of spruce, and some smaller gussets. It’s heavier for sure, but the Wolf Pro wings are ply ribs, so it still can be a good wing if suitably reinforced. Ever once in a while someone seems to find an unmodded Sparcraft . If someone gave me one, I would keep it. If I was building, it would be sticks.
 

BJC

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There is a fix for the Sparcraft ribs. Add Spruce capstrip on the vertical and perimeter of the rib and add gussets. So you got one big ply gusset rib shaped, a little bit of spruce, and some smaller gussets. It’s heavier for sure, but the Wolf Pro wings are ply ribs, so it still can be a good wing if suitably reinforced. Ever once in a while someone seems to find an unmodded Sparcraft . If someone gave me one, I would keep it. If I was building, it would be sticks.
That fix for the Sparcraft ribs adds weight, as you said. An after-the-fact fix; not a good way to start.

All the Wolf ribs and Wolf rib kits that I have seen are capstrip/trusses. Plywood nose ribs covered with plywood are used spar forward on the Pro. The ply LE adds significant strength.

If weight is a factor, capstrip/truss ribs will beat routed plywood every time, and, over the total aircraft construction time, will be minimal additional labor.


BJC
 

BBerson

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I wish to know why you know about the Thalman T4? Y
I joined EAA in 1974 and bought all of the design booklets and the geodetic articles that were reprinted in one of the booklets. I have had an interest in geodetic since then. My interest would be doing the strips in metal and I made many experiments. The geodetic may be outdated however, with a simple truss possibly being the superior (lightest) method.
I enjoy the discussion. In fact, search this forum for geodetic and it should come up several times.
 
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Curt Curtis

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BBerson this construction is still geodetic. The construction method used was to use very thin 5 inch wide veneer strips, they run spirally around the fuselage same as geodetic, but there is no space between the 5 inch wide strips. They run continuously with no gaps between the 5 inch wide strips. All is glued together with 3/8 of an inch hexcell filler. Harry Thalman was a strong believer in geodetic construction for the lightest possible weight. Even his wing construction was geodetic.
CURT
 

BBerson

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BBerson this construction is still geodetic. The construction method used was to use very thin 5 inch wide veneer strips, they run spirally around the fuselage same as geodetic, but there is no space between the 5 inch wide strips. They run continuously with no gaps between the 5 inch wide strips. All is glued together with 3/8 of an inch hexcell filler. Harry Thalman was a strong believer in geodetic construction for the lightest possible weight. Even his wing construction was geodetic.
CURT
Well, I suppose you can call that geodetic. Most would call it sandwich monocoque.
I wonder if the Northrup molded plywood planes also used opposed diagonal veneers?
Is that 3/8" Hexcell filler a honeycomb?

BJC, the patent is interesting. It said the strut depth is greater than the width.
 

Bill-Higdon

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Some information on the Thalman T4 geodesic designed airplane. I worked with Harry Thalman on his airplane and own the airplane he was building to replace the one he crashed and was killed in. The fuselage is a plywood sandwich construction built in a heated cement mold. In about August 1962 EAA magazine had a in-depth article on the geodesic construction methods. I am interested in a discussion concerning this airplane. Tom Nalevamko is familiar with the Thalman T4 and I have had contact with him.
CURT
Curt, I'd like to see more on this. Several of my mentors were friends of Harry, and Early was one of my mentors as well. I seem to remember seeing the remains of the plywood version in the weeds at Skypark in my youth.
 

Curt Curtis

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Bill Hidgon - BBerson - Tom Nalvanko; The plywood remains that you saw in the weeds at sky Park was possibly the T4 airplane parts that I have. Which is basically a stressed plywood skin, some of it is wound in spiral wood strips which are preformed into a honeycomb monocoque sandwich type of construction.
Harry Thalman's geodetic airplane that he was flying was based at sky Park. I flew in it only one time. He frequently bragged about its rate of climb as well as its cruise speed.

I helped Harry Thalman build fittings for the plywood plane. Most of my effort, however, was to help build a cement floor in the hen coups at his father's place to provide a place to continue building the plywood T4 airplane. Harry talked frequently about his trips to Oregon to visit George Yates. Harry also was very interested in Russell bourkes two stroke Scott's yoke engine and made trips to Petaluma, California to follow that development.

I did hang out some with Earl player and was familiar with his player special geodetic airplane. Earl player was a neat happy guy to hang out with. When I moved from Salt Lake city to Phoenix, Arizona, the EAA chapter was trying to find a way to get the player special shipped back to Oshkosh since Earl donated it to the EAA Museum. I understand it is there now being restored for display.
CURT
 
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Bill-Higdon

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Curt, I'd like to see more on this. Several of my mentors were friends of Harry, and Early was one of my mentors as well. I seem to remember seeing the remains of the plywood version in the weeds at Skypark in my youth.
I hate Spiel Chezck I meant Earl.
Curt, it's good to see the info you provided. As a side note in the late 60's & early 70's I toyed a geodetic copy of the Piper Skycycle, and pod for a Bowlus Baby Albatros knock for a set Tcraft wings. I got as far as using CDX plywood rings & redwood fence for mock ups.
 

Curt Curtis

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Bill-Hidgon; I see you tinker and experiment. I knew you meant Earl. My drunk dragon got Thalman right once but misspelled later. and I did not notice. Crap happens. My issue and question, should this project continue or should I make furniture or use it for firewood? I would be interested in someone to continue to build this project.

CURT
 

Orsovolante

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Some reflections.
I have often read the word "sustainable". Well I believe that the only thing that is more sustainable in plywood is the possibility of using less valuable and faster growing plants, such as birch, compared to fir. For the rest there is a lot of glue and energy-consuming processes, which are used for its construction.
Surely the plywood has also been used to make fuselages with working leather. I have fixed and dealt with several gliders that used this technology. I remember a K6 glider that had amazed me with the ridiculous thickness of the skin and the absence of side members in the back of the fuselage.
In my opinion, in an amateur construction, plywood could be used effectively to make the wing ribs, with CNC cutting, those of the fuselage, perhaps interposing foam or honeycomb panels.
If you really want to minimize the use of wood then you might as well use glass or carbon pultruded for industrial use. They are found practically everywhere and I believe that even those without certification have a greater resistance to stress than aeronautical timber.
 
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