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Wing Spar - design / bonding pultrusions

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sming

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Well iirc there is now in the plans an alternate technique where you just wrap around a lot of carbon to the same thickness ;)
 

harrisonaero

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Aluminum loves to go to aluminum oxide over time. Don't rely on it for bonding unless you anodize first and even then you have other dissimilar material issues to deal with.
 

Foundationer

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As a proud englishman I am sad to have to say two things:
1. The French design some VERY nice aeroplanes.
2. It's really embarassing I don't speak much French - why does wingtip auto-translate to 'salmon'?
 

BJC

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2. It's really embarassing I don't speak much French
Don’t be; English speakers kept France a French speaking country.

French pilots seem to be winning most of the world aerobatic contests. The exception is Rob Holland, USA, who just keeps on winning the 4 minute free programs.


BJC
 

pictsidhe

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As a proud englishman I am sad to have to say two things:
1. The French design some VERY nice aeroplanes.
2. It's really embarassing I don't speak much French - why does wingtip auto-translate to 'salmon'?
Sounds fishy to me.

Aileron, empennage, decoupage. First three off the top of my head that you probably know...
 

mcrae0104

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"Merde!"*

*exclamation of amateur aircraft designer, looking for the elusive error in his Excel spreadsheet--that's on-topic for a spar design thread, non?
 

BoKu

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Why use phenolic which is usually cotton or paper based, instead of solid carbon or E glass ( no electrolysis) ?
Because you can buy reinforcements like Phenolic or Garolite in slabs as thick as 1" (and even thicker). Just cut it to shape, bevel the edges as required, and plop it into the lamination. There are several places in my glider where I use 5/8" thick Garolite. Laminating that much glass or carbon would take a lot of time better spent elsewhere.
 

wanttobuild

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Why use phenolic which is usually cotton or paper based, instead of solid carbon or E glass ( no electrolysis) ?

I think I like your idea, especially if you can install the hard point during the layup, meaning no secondary bond. Secondary bonding works but not as good as the part completed in one session.

I still have reservations about bushing installations in composites, can't seem to find the bulletproof installation that suits me. Lapping the spar roots and pinning them in place is one design element I have always admired. Have a look @ the RV12.
 

Lendo

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Feb 6, 2013
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Brisbane
Johnny, Phenolic board is strong and hard, it won't compress and if you use something like a Cotton weave even Canvas, the Phenolic resin saturates the fabric, Timber may split. I've seen fibreglass flow/ compress under load. Phenolic board is recommended for a reason, I don't know of anything else that can do a better job in Composites.
Whattobuild, I like the idea of Stainless Steel Bobbins to accommodate Pins in Carbon Composites, in situations of solid Carbon Tow windings. The steel takes the compression loads and the Carbon or Glass takes the stresses. They can be wound in without breaking any filaments in the Tow. Something I would use in a solid carbon Landing Gear leg. How in each case is the builders decision.
 

TLAR

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Sep 29, 2020
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Lendo
Now that sir is a very good idea 💡

Bobbin, yep that’s the ticket
 

Foundationer

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While I was in the wing I was thinking about bell cranks... So I got the old CNC running and made some to play with. What size bellcrank is a good compromise? I was thinking a nice 75mm arm. And 3mm 6082 rather than two bent bits of 1.5mm. I haven't quite worked out how to properly secure the bearing either.

The wife is confused about why I'm covered in glitter. I just said 'CHRISTMAS' and left hastily.
 

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slociviccoupe

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Palm Bay Fl.
While I was in the wing I was thinking about bell cranks... So I got the old CNC running and made some to play with. What size bellcrank is a good compromise? I was thinking a nice 75mm arm. And 3mm 6082 rather than two bent bits of 1.5mm. I haven't quite worked out how to properly secure the bearing either.

The wife is confused about why I'm covered in glitter. I just said 'CHRISTMAS' and left hastily.
What feeds and speeds are you running. With looks like no air or coolant mist. I have a cnc router table and have done aluminum but took forever at .002 depth per pass And if i remember 6 ipm with 11k spindle speed. Got through it and was being very conservative but it was my last 1/4" single flute spiral up cut carbide endmill. No air or lubricant. 110 passes each opperation through .5" thick 6061 t6.
 

Foundationer

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Definitely takes ages! I used a 1/8 single flute carbide slot mill at 18k rpm on .4mm DoC slotting, 1mm DoC clearing all at 1000mm/min except for boring down in tight holes which is half that. The reason there's so much 'glitter' is I haven't bothered to hook the vaccum to the front of the spindle - sucks most of the chips out and makes it run a lot nicer. The 3mm one took 15 minutes or so, the 6mm one with the deep clearing took over a half hour.

Those slot mills are under a pound each so I don't really care if chip recutting kills them quick.
 

Jonny o

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Oct 31, 2015
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Fairbanks, AK USA
Thanks Boku for the good tip on Garolite.

I used paper based phenolic in a boat and had corrosion problems with the bolts. Nice to see other types. The E glass version is one of the toughest on the chart. It's number 2 for tensile. Too bad compressive strength wasn't listed.

Jonny
 

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Jonny o

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Oct 31, 2015
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Fairbanks, AK USA
While I was in the wing I was thinking about bell cranks... So I got the old CNC running and made some to play with. What size bellcrank is a good compromise? I was thinking a nice 75mm arm. And 3mm 6082 rather than two bent bits of 1.5mm. I haven't quite worked out how to properly secure the bearing either.

The wife is confused about why I'm covered in glitter. I just said 'CHRISTMAS' and left hastily.

I have always wondered why, if there are no clearance issues, that a bell crank couldn't be a lighter weight, and stronger, hollow center triangle, instead of a V ?
 
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