Wooden spring/Wittman gear?

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RogFlyer

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Another place to look for information regarding timber laminate and designing for this application might be bow-making. My uncle made competition bows of all types from the 60's to the early 90's. The compound bows in particular were very robust and took a hell of a lot of force/stress and deflection at light weights.

All the way through, the timber layers were laminated with Resorcinol resin, which were tightly clamped in forms and oven cured.

I don't know about energy absorption/damping - I would think not much, as for a bow one would want as much stored energy as possible to transfer to the arrow.
 

Aviacs

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Oct 21, 2019
Messages
114
Thank you all for all the interesting information and links!

It is fascinating to see that wooden gear ideas have been tried, some were used and some may be yet. Somewhat clear paths to success exist, but as with any part that tries to use materials efficiently (low weight, small frontal area of cross section), there is no free slam dunk. :)

David B - My impulse is somewhat similar - the original builder and some subsequent owners of my Sonerai 2 spent time making small aero effiencies that apparently added up to a fair amount of extra speed. One of the mods was simply to put some sort of stiffeners in places over the gear, and then fabric wrap & dope it to cover the brake lines as well. I don't like that since it hides potential corrosion; & will have to strip it anyway doing inspections toward a US airworthiness cert. Manifestly it makes sense to simply put the airplane back together as practically as possible using existing parts and accepting less streamlining while getting it back in the air. I, too, don't want to afford Grove, and they are not streamlined anyway though the internal drilling instead of external brake lines is worth a few kts. Apparently there may well be aero as well as weight improvements to be had from wooden gear, at some not insignificant cost of experimentation.

The other & actually more pressing area i have to address for the airplane is a new canopy raised, or tall enough to fit me under.
For some reason, i find it easier to plan & dither about familiar materials, like wood....

Practically what will happen, is efforts to get the airplane back flying and signed off.
Then use info gained here to pursue (or knot) more quixotic ideas for improvements.

Rogflyer - The connection to recurve bows struck me immediately with the pictures of failed wooden gear sections, and the arced solution to shape: I inherited a Chinese horn/wood/sinew archery bow (wood-fiber composite, e.g.) and researched them at one time. There are now modern makers using traditional natural materials. The original shape of such a bow is very much like the ideal laminated gear shape, and for the same reasons. Picture includes light and heavy versions
1617514327698.png


smt
 
Last edited:

RogFlyer

Member
HBA Supporter
Joined
Jun 27, 2017
Messages
21
Location
Lewisham
Thank you all for all the interesting information and links!

It is fascinating to see that wooden gear ideas have been tried, some were used and some may be yet. Somewhat clear paths to success exist, but as with any part that tries to use materials efficiently (low weight, small frontal area of cross section), there is no free slam dunk. :)

David B - My impulse is somewhat similar - the original builder and some subsequent owners of my Sonerai 2 spent time making small aero effiencies that apparently added up to a fair amount of extra speed. One of the mods was simply to put some sort of stiffeners in places over the gear, and then fabric wrap & dope it to cover the brake lines as well. I don't like that since it hides potential corrosion; & will have to strip it anyway doing inspections toward a US airworthiness cert. Manifestly it makes sense to simply put the airplane back together as practically as possible using existing parts and accepting less streamlining while getting it back in the air. I, too, don't want to afford Grove, and they are not streamlined anyway though the internal drilling instead of external brake lines is worth a few kts. Apparently there may well be aero as well as weight improvements to be had from wooden gear, at some not insignificant cost of experimentation.

The other & actually more pressing area i have to address for the airplane is a new canopy raised, or tall enough to fit me under.
For some reason, i find it easier to plan & dither about familiar materials, like wood....

Practically what will happen, is efforts to get the airplane back flying and signed off.
Then use info gained here to pursue (or knot) more quixotic ideas for improvements.

Rogflyer - The connection to recurve bows struck me immediately with the pictures of failed wooden gear sections, and the arced solution to shape: I inherited a Chinese horn/wood/sinew archery bow (wood-fiber composite, e.g.) and researched them at one time. There are now modern makers using traditional natural materials. The original shape of such a bow is very much like the ideal laminated gear shape, and for the same reasons. Picture includes light and heavy versions
View attachment 109245


smt
Aviacs - wow, that takes me back. In the very early days, for pocket money, my cousin and I used to cut ox-horn strips and taper plane them, as well as scrape and polish sinew strips. Both glued with animal (casein?) glue to the laminated wood cores. Towards the end, the tension side was carbon fibre tow and the compression side was etched strips of some exotic microstructure alloy (around 1GPa(!) compression stress, but fatigue cracked quickly at relatively low tension). Both materials were ruinously expensive in the late 80s/early 90s. The carbon fibre was imported from Japan, if I remember correctly, and the alloy from Sweden. My uncle had a series of bow/material design books from the 20s/30s and early 40s, when there was a revival in bow making and quite a bit of engineering research done, much of it in the US.
 

nikolai

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Joined
Apr 28, 2020
Messages
8
The possibility/puzzle of making a wooden gear for my Sonerai2 project is intriguing
(not a need - already have 2 aluminum sets, 5/8" as well as spare 1/2")

However, there seems to be a fair amount of speed in fairing the gear and brakelines.
Streamlined wooden gear legs could incorporate internal brake lines, just like the gun drilled aluminum versions, and maybe save a few lbs.?

I'm capable of doing the craft work, it's my business.
However, i have not seen how a set of spring gear is actually designed? Parameters? Cook book estimations of landing loads & how much extra margin to add?
Any insights or link to resources?

Thanks!
smt

PS: I did several attempts to search the forum re "wooden gear legs" and permutations with no hits.
Then i googled the world, and it sent me back here to this: Laminated wood landing gear which i am reading now.

Still interested in any further info and comments.
some historical facts.
aircraft S-4 Petrel
USSR, 1927. The chassis spring is made of ash.
 

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Aviacs

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Oct 21, 2019
Messages
114
My objectives for the project would be to
1.) streamline the gear including/especially cover the brake lines and see if it makes a difference
2.) at no weight penalty compared to the existing 5/8" gear mounted on the plane.

It occurs to me, given that there is a spare original/unused 1/2" aluminum Sonerai 2 gear here;
& that a solid wooden gear would almost certainly be thicker than an original gear by a significant amount;

Therefore it might be practical to answer my experimental questions in the original direction merely by fairing the 1/2" gear with light wood such as mahogany, or even balsa if the wood was 'glassed over. (Piles of light-ish weight redwood and mahogany here, no balsa but i think prices are back down on balsa since the scarcity a few years ago for wind turbine blades?)

Tough issue is that it would stiffen the legs and move more stress to the bends at the mounting points. Which is where the thinner (1/2" thick) gears seem to collapse on a hard landing. Bob Aymar gave me his S1 sans engine (some45 years ago) which he had pancaked into a berm at FDK when the continental A65 quit. For years i used those bent gear as a source for cheap thick pieces of aluminum for small parts.

smt
 

rv7charlie

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Nov 17, 2014
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Location
Jackson
The online images of Sonerai 2 gear legs look almost identical in concept/design to an RV8 leg. The RV gear legs use a hollow fiberglass streamline profile that is closed on the trailing edge with piano hinge. It's secured at the fuselage & wheelpants by the intersection fairings. Simple to install; simple to remove to inspect the gear leg. If you feel you need more flexibility in the fairings, epoxy/polyester aren't the only binders you can use to create a non-structural fiberglass reinforced part. (hint hint)

Charlie
 

Aviacs

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Oct 21, 2019
Messages
114
epoxy/polyester aren't the only binders you can use to create a non-structural fiberglass reinforced part. (hint hint)
Which note also prods me to remember the blow-mould/form option.....
And the fact that such fairings might well be symmetrical as otherwise makes the suggestion stronger.

Hmmm.

Although i confess confusion about other binders than typical vinyl/epoxy/polyester that are senssible?
smt
 

rv7charlie

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Messages
1,427
Location
Jackson
Honestly, my 1st preference would be to look at adapting existing stuff, like the Van's RV8 fairing (they'll sell to you) or adapt something from the light plane world, like these strut fairings. The strut fairings aren't split, but it shouldn't be too difficult to slit them and insert a doubler or a run of piano hinge as a closure method.

If you really want to roll your own, I'd experiment with techniques used by others to make diffusers (inlet ducts) for air cooled engines. There's a thread on VAF by Dan Horton where he uses 'glass cloth and (IIRC) a 2 part urethane product that cures into a rubbery substance. Makes a strong but flexible 'thing' in the shape of the mold. The process is just like a 'glass layup; you just wet out the 'glass cloth with the urethane instead of epoxy. Others have done the same thing with far less investment by just wetting out the 'glass with high temp silicone (or regular silicone, if temp isn't an issue). Since there are now paint-able silicone caulks on the market now... Just think outside the aviation box for something that starts as a liquid & cures semi-rigid.

I made a strong, 'glass reinforced 'hinge' for the alternate air door on my injected RV6 by wetting out a couple of layers of 'glass cloth with red RTV. I have *not* made anything as long and potentially floppy as a gear leg fairing, so I can't promise it will work. But if I needed a custom fairing & nothing off the shelf would fit, I'd certainly risk the price of a tube of caulk & a couple of square feet of 'glass to experiment. ;-)

BTW, 'glass isn't the only reinforcing material available for non-structural stuff, either. It's just (probably) the most convenient, familiar material to homebuilders because they have some lying around. Outside the box...
 

Aviacs

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Oct 21, 2019
Messages
114
Thank you for the links!

The rest of your note jogged some 50 yr old memories..organic chem lab.
I was more into motorcycles, english sports cars, and construction in the summers, than my studies at the time.
But i did a series of experiments modifying styrene monomer & polyester to increase the polymer chain lengths until coming up with various rubbery results, that yielded some interesting fiberglass options. For years i kept a couple pieces in the metal shop, lost since in a move. My dad was a chemist, though; so it was the last thing that interested me & I've long forgotten anything i ever knew. Went into construction instead, don't regret it.

smt
 
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