Wing Spar - design / bonding pultrusions

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Foundationer

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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 ?
Because a bellcrank looks like what I made* I never really thought about this. Seems like something that'd be fun to play around with in some kind of generative design environment and see what the computer thinks it should look like. I bet whatever the result is would really upset an inspector.

*Edit: In my head
 

Jonny o

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Because a bellcrank looks like what I made* I never really thought about this. Seems like something that'd be fun to play around with in some kind of generative design environment and see what the computer thinks it should look like. I bet whatever the result is would really upset an inspector.

*Edit: In my head


Yes, an upset IA ( inspector ) was what I ended up with during an inspection of my airplane. He didn't have a reason why they couldn't be triangles. Just: "That is not normal". I found a different inspector. They are still working fine.
 

TLAR

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Yes, an upset IA ( inspector ) was what I ended up with during an inspection of my airplane. He didn't have a reason why they couldn't be triangles. Just: "That is not normal". I found a different inspector. They are still working fine.
Have a look at the Bearhawk lsa aileron bellcrank made out of 4130 tube
 

Foundationer

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Another sort of spar related question: Anyone got a link to what you would use to support a 3/4 * .035 pushrod in the middle of the wing? I assume some kind of linear bearing or PTFE block or something? It'll go in and never be seen or accessed again so I don't want to guess at that bit and have it fill with dust or something after a year.
 

BJC

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I think that BoKu also posted a sketch of his homemade version. It might be worth a few minutes with the search function.


BJC
 
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Foundationer

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And while I've got questions that don't really deserve their own thread... Does anyone know a rough guess for micro/paint weight per unit area on a fairly decent to begin with wing?
 

BoKu

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I think that BoKu also posted a sketch of his homemade version...
 

Foundationer

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Thanks for that!

Your hinges for the flaperons in the wing of the HP24 - are they some kind of bushing (bronze?) wrapped in carbon and the carbon bonded to the wing skin or some other cunning concoction?
 

BoKu

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Thanks for that!

Your hinges for the flaperons in the wing of the HP24 - are they some kind of bushing (bronze?) wrapped in carbon and the carbon bonded to the wing skin or some other cunning concoction?
Yes, that's about what my gudgeons are. I make the material in 10" chunks using a 5/16" rod as a mandrel. Once it has cured I extract the mandrel and cut it into 5/8" wide pieces, ream the bore and insert the porous bronze bushings.

The pintles are molded into pockets in the lower flaperon skins during the layup.
 

wsimpso1

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It'll go in and never be seen or accessed again so I don't want to guess at that bit and have it fill with dust or something after a year.
Don't like that at all. Moving parts that can wear out or damage mating parts and no way to look at it during the test flight program and then annually thereafter? Whether you use an idler or set of rollers or a bushing, I am very uncomfortable with "never seeing it again". Rollers can seize, sliding surfaces can capture dust and/or aluminum oxide and abrade the the tube, and bearings can wear out and get loose. You want to catch these early and be able to fix them or maybe even upgrade the system later. A nice inspection cover and a few screws or even silicone attachment is easy and light.

Billski
 

BoKu

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Don't like that at all. Moving parts that can wear out or damage mating parts and no way to look at it during the test flight program and then annually thereafter?...
Well, that's pretty much how all production sailplanes are. There's sometimes an inspection hatch or window for the bellcrank, but the push-pull tube guides are deep inside with no provisions for inspection or repair save borescope cams and holesaws. When something goes bad you cut the wing open, fix it, then repair the hole. The linear bearing push-pull tube guides I use are based on ones that appear to have good service history in that kind of operational environment. I've seen nylon guides harden and crack, and three-roller guides freeze up, but the linear bearing guides seem pretty solid.
 

wsimpso1

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The OP said "never see it again". That implies no access... I suppose it is tough to imagine zero access for a modern borescope.

In sailplanes, the operator still has a functional check, and a way to inspect and repair as needed. That is different from "bury it and never look at it again", which is where my alarm bell went off.

I do suppose we do "cut and repair" to refuel submarines and fix failed human parts. We would still need to know it is a rare event rather than a regular thing...

The fact that linear bearings are pretty much trouble free is an important point for design of the OP's system IFF he is doing the whole thing as in a sailplane. Deviate anywhere, and the assumptions on reliability are lost, you start over, and regular inspection really ought to be provided for until reliability is demonstrated. I have this vision of an 0.035 wall tube being worn away. Without a visual check once in a while to catch a worn tube, it could locally buckle and lock the ailerons... that high value failure mode should justify some fuss.

When the linear bearings common in sailplanes do have issues, what are the failure modes, and how is it detected prior to major control issues? Yeah, lots of FMEA in my history...

A regular borescope inspection could stand in for a normal port and cover until a repair is indicated. The builder could even build the skin with port prepared but not cut similar to what is done with fabric, then the port is cut only when and where needed.

Billski
 
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Foundationer

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I was being a bit facetious when I said they were going to be stuck in there never to be seen again. But they're definitely high up on the list of parts that will be difficult to fix if there's a problem.
 

User27

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BoKu is describing accurately what is done in most sailplanes designed in Germany, and in several of their light aircraft. Some (Grob) use nylon balls running inside an aluminium tube with the aluminium control rod running down the middle. There is pretty much no way to inspect of change these bearings without cutting a hole on in the skin. They often last > 6000hrs. It is clear when the balls start to degrade as the stick feels like it is running in gravel. There is plenty of time to fix it, they don't self destruct immediately. Most homebuilts don't see 1000hrs, let alone 6000! Fixing holes in a composite skin is relatively straight forward, any composite repairer can do it. Installing an inspection hole is also only slightly more work. If the bearing are properly spec'd there should be no need for routine access.
Most German sailplanes don't require the aileron bellcrank bearings to be inspected until 3000hrs, and some (Schempp-Hirth) at 6000 hrs. At that point holes have to be cut, many install access panels, some make the smallest inspection hole possible (say 40mm dia), seal the edge with balloons and cover the hole with a self adhesive vinyl patch. If any parts replacement is required hole may have to be enlarged and a proper cover plate made.
 
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