Aircraft Wood, again...;-)

[WaspAir]

My recollection is that the Pietenpol had a reputation for never suffering an in-flight structural failure.

 

[Aerofoam]

Here is a doodling of a laminated frame, it would probably be .062" strips of Basswood and Spruce with strategic layers of CF.
It would be a big spring, so the suspension could be adjusted by the thickness of the layup, or made more flexible in the upper mast to absorb the 2/rev shake. The rear landing gear would be a single section arched laminated spring with upper control arms and dampeners.
It could be wide in the center as to not need forward control arms.
The clamping mold would be made from thick plywood layers and probably have inflatable bladders to apply the compression on the layup.
If it were me, I would vacuum bag it after pressing it in place with the bladders, then add more pressure after the vacuum was complete....
I think this would be quite a bit stronger than are 2" AL tubing and cheek plates. It may end up a little heavier, but not much...



While doodling, I remembered the Bowlus Albatross glider and the nice fuselage it had. Similar shapes can be made by "Torture Ply" or
"Cylinder Molding" layers of 1/8" Luan Mahogany on a form. Super rigid, strong and light. A monocoque could be made from these techniques.
The glider in the pic was most likely laid up strips over a light frame, but the ply method gets rid of the frame and is stronger....

 

[WaspAir]

Looks like the Albatross' little brother, a Baby Bowlus - they were molded. Sold as kits

 

[Mayfield]

Here is a doodling of a laminated frame, it would probably be .062" strips of Basswood and Spruce with strategic layers of CF.
It would be a big spring, so the suspension could be adjusted by the thickness of the layup, or made more flexible in the upper mast to absorb the 2/rev shake. The rear landing gear would be a single section arched laminated spring with upper control arms and dampeners.
It could be wide in the center as to not need forward control arms.
The clamping mold would be made from thick plywood layers and probably have inflatable bladders to apply the compression on the layup.
If it were me, I would vacuum bag it after pressing it in place with the bladders, then add more pressure after the vacuum was complete....
I think this would be quite a bit stronger than are 2" AL tubing and cheek plates. It may end up a little heavier, but not much...

View attachment 1162693

While doodling, I remembered the Bowlus Albatross glider and the nice fuselage it had. Similar shapes can be made by "Torture Ply" or
"Cylinder Molding" layers of 1/8" Luan Mahogany on a form. Super rigid, strong and light. A monocoque could be made from these techniques.
The glider in the pic was most likely laid up strips over a light frame, but the ply method gets rid of the frame and is stronger....

View attachment 1162694

Looks good Mark. How would the metal parts attach?

 

[Aerofoam]

Looks good Mark. How would the metal parts attach?

I think you could use the same type of AL brackets that are currently used for tube frames.
The areas of attachment could be thicker by adding tapered internal laminations to tailor the strength and eliminate point loading.
The arms could have linkage ends incorporated in the laminations, or just use side plates bolted through.
I am thinking in composite terms, so all of this would be vacuum bagged with epoxy and all holes would be sleeved with metal tubing.
Once the mold was made, the construction process would be relatively easy and not expensive.
If it was painted like a cloth airplane with an AL base coat and a light top coat, the UV exposure would not be an issue, but paint and epoxy are not light.....
I was also thinking the main landing gear could be a double wish bone and a single piece, so the only part with a linkage would be the upper control arm...

 

[Mayfield]

This is not a quibble Mark, but to a tyro, inflatable bladders and vacuum bagging sounds like it might be beyond the home workshop capability.

In macro terms, if there were hard orders for 10 frames or so, how much could someone with skills similar to yours, sell it for and still make it worthwhile?

Just a thought exercise.

Jim

 

[Mayfield]

Designed around aircraft quality wood, the wood frame would be about the same weight and a little stronger than the 6061 frames in common use. All this is just a quick and dirty calculation, and obviously there is more to it than just bending strength and no one should go out and build it.

Thanks Raghu,

This idea fascinates me. Not yet to the point of building a test article, but still fascinating. When I look at Mark's doodle of a one-piece frame, I am somewhat surprised it has not been done in wood or more likely glass of some type. To me, a non-engineer, it looks like a saleable concept if there is still an open frame market.

Jim

 

[Aerofoam]

This is not a quibble Mark, but to a tyro, inflatable bladders and vacuum bagging sounds like it might be beyond the home workshop capability.

In macro terms, if there were hard orders for 10 frames or so, how much could someone with skills similar to yours, sell it for and still make it worthwhile?

Just a thought exercise.

Jim

So, I am recalling making laminated archery bows.
A true 2" x 6" rough cut board has the finished shape cut from the center using a bandsaw.
The 2 sides, front and back are separated by about 1/2", and mounted on a thick plywood back.
This is the mold, the laminations go in edge wise, so you are looking at the side of the bow.
The entire mold is waxed and a section of motor cycle inner tube is attached to the rear side of the mold and waxed.
The wood laminations including the center block for the handle are slathered in epoxy and put in the mold.
Once lined up properly, the inner tube is inflated, clamping the whole mess together.
Some people put plastic wrap in the mold to keep it free of epoxy.
After a 24 hour cure, the part is removed, the handle carved and the bow limbs are tapered, sanded etc....

This would be a giant mold laying flat as a big work table and you would have to crawl around on it to get it loaded
and ready. Non of it is rocket science, but it can be finicky...
I could build the mold in a couple days, I would probably want to enlist a friend who is good with Solid Works to model the frame and do some strength modelling to pair it down to minimum effective dose plus 20%. I have a feeling is may be too springy though, so strength won't be an issue once there is enough mass to not be so springy...
Carbon fiber on the outer layers would stiffen it a great deal.

I guess the attractive thing about this technique is that it does not require CNC machining, or highly technical tools of any kind.

On the other end of the spectrum,
I have been contemplating a mold, is the same over all frame shape, but rounded hollow tapered tubes with flats at the attachment points. This would be a clam shell set of molds and the end frame would be a one piece carbon fiber/rohacell hollow frame.
This would be much like the high end carbon bicycle frames, but much larger diameter tubes with a high degree of taper from the mid sections to the extremities.
I think the entire frame could weigh less than 40lbs including brackets.
Unfortunately, this either requires complete CNC modelling, then very expensive CNC machining of the cavities out of AL, or butter board, which now costs more than AL.
Or, more realistically, I would hand shape a plug and pull a mold from it out of massive amounts of fiberglass.
The first method could cost over $100k. The second method would require about 2 weeks of my time and less than $3k in materials....

I was just talking to a friend who's UAV just was the first to fly into the stratosphere on electric power.
He has an airplane with a wing over 70ft. in span and the entire aircraft weighs 180lbs. The battery weighs 80 lbs. of that total.
It's hard to wrap your head around those numbers!!!

 

[Aerofoam]

On the cost issue, I really have no idea what getting the quality wood laminations would cost, but, once the mold was finished, I would guess the cost would be around $2k per frame, if it was a frame kit, just the part, not pre drilled, sleeved, etc. Although it might be a good idea to standardize it to known cheek plates for the rotor head, like Dennis's or Domi, etc. because the mast would not be easily replaceable, so one set of holes is all you get....
Then it could be pre drilled and there would be less variations floating around...
I think the rest would be up to the builder since people have differing ideas on what they want to bolt on......

 

[Aerofoam]

Looks like the Albatross' little brother, a Baby Bowlus - they were molded. Sold as kits

I thought I recalled them being molded ply, but I know I have seen pics of a framed version too. maybe those were the bigger ones?

 

[okikuma]

Here is a doodling of a laminated frame, it would probably be .062" strips of Basswood and Spruce with strategic layers of CF.
It would be a big spring, so the suspension could be adjusted by the thickness of the layup, or made more flexible in the upper mast to absorb the 2/rev shake. The rear landing gear would be a single section arched laminated spring with upper control arms and dampeners.
It could be wide in the center as to not need forward control arms.
The clamping mold would be made from thick plywood layers and probably have inflatable bladders to apply the compression on the layup.
If it were me, I would vacuum bag it after pressing it in place with the bladders, then add more pressure after the vacuum was complete....
I think this would be quite a bit stronger than are 2" AL tubing and cheek plates. It may end up a little heavier, but not much...

View attachment 1162693

While doodling, I remembered the Bowlus Albatross glider and the nice fuselage it had. Similar shapes can be made by "Torture Ply" or
"Cylinder Molding" layers of 1/8" Luan Mahogany on a form. Super rigid, strong and light. A monocoque could be made from these techniques.
The glider in the pic was most likely laid up strips over a light frame, but the ply method gets rid of the frame and is stronger....

View attachment 1162694

My friend Jeff Byard owns a beautifully restored Bowlus BA-100 Baby Albatross that he flies regularly at Mountain Valley Gliderport, Tehachapi, CA. I will never loose my sense of awe over the craftsmanship that was performed when the glider was first built.

Mark, perform a good search on how Hydulignum was exactly produced. That process would serve well in construction of your laminated airframe.

Wayne

 

[Aerofoam]

My friend Jeff Byard owns a beautifully restored Bowlus BA-100 Baby Albatross that he flies regularly at Mountain Valley Gliderport, Tehachapi, CA. I will never loose my sense of awe over the craftsmanship that was performed when the glider was first built.

Mark, perform a good search on how Hydulignum was exactly produced. That process would serve well in construction of your laminated airframe.

Wayne


View attachment 1162697
View attachment 1162698

Wow, that's eye candy!
What's the glide ratio of that plane?

 

[WaspAir]

I thought I recalled them being molded ply, but I know I have seen pics of a framed version too. maybe those were the bigger ones?

Maybe - I think it had spruce bulkheads with mahogany ply covering.

 

[WaspAir]

Wow, that's eye candy!
What's the glide ratio of that plane?

19:1 at 35 mph was claimed. Haven't had the chance to fly one to confirm that personally, but would love to get the opportunity!

The Super had much more wing (62 vs. 44 ft span) and produced about 29:1 at around 47 mph. Cost went way up, too.

 

[Aerofoam]

19:1 at 35 mph was claimed. Haven't had the chance to fly one to confirm that.

That's not bad, I wonder what modernizing it could achieve?
I like the Archeaopteryx....but it would look better with the Bowlus fuselage...

 

[WaspAir]

A more modern airfoil would help. It's a very low speed aircraft and would not penetrate well into headwinds, but some impressive flights have been done in them anyway.

 

[okikuma]

Maybe - I think it had spruce bulkheads with mahogany ply covering

Mark,

Jeff's BA-100 is definitely a work of art.

JR,

You're correct 19:1 to 20:1 are the numbers I've seen printed. I too certainly would love to have the chance to fly at BA-100. In reality, I'm way too large to be granted such an invitation.

As printed in Wikipedia and confirmed to me by Jeff,

“The famous aerodynamicist Irv Culver told Albatross owner Jeff that the problem came from three sources. First, the rotation axis of the all flying horizontal tail was located at 35% chord instead of slightly in front of the aerodynamic center at 25% chord. Second, the horizontal tail rotation hinge had high friction. Third, the relatively soft pitch axis cable control system stored elastic energy reacting the friction in the tail hinge. As the pilot tried to input pitch controls into the unstable tail, the friction of the tailplane hinge prevented initial movement which then stored up energy in the control cables. The pilot then applied more force to get the desired reaction. Eventually, the high friction would break loose and the horizontal tail would move much farther than desired due to the higher than necessary force applied by the pilot and releasing the force in the control cables. The resulting over control often resulted in PIO and when near the ground would likely damage the aircraft. Culver instructed the owner to move the hinge axis forward to 24.5%, add a downspring to the pitch control, and liberally lubricate the hinge axis before each flight to reduce friction. According to Byard, the plane flies significantly better with the improvements.”

Wayne

 

[okikuma]

Besides the BA-100, the two of the most wonderful all wood experimental amateur built gliders I have seen up close were the Woodstock and the Cherokee II.

Wayne

 

[WaspAir]

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

 

[Mayfield]

On the cost issue, I really have no idea what getting the quality wood laminations would cost,

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