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Rudy Lee

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Apr 26, 2020
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I think all the poly-fiber stuff you thin with MEK. .......one possible solution is to use that 3m water base glue and consider latex as others have said..... or even "no finish" (if you keep it inside)
We will be thinning our poly-tak with their reducer. It says the mek wont work as a thinner. I don't think we really have an issue with melting as long as we cover the exposed foam. The main question is if we need to apply any chemicals to prime the fiberglass or could we just sand it?
 

Rudy Lee

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Apr 26, 2020
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23
Good to know that we can just sand and clean - thanks! Since we already have poly-tak, would you still recommend using 30nf? Is it that good? If so, awesome.
 

proppastie

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The glue binds the fabric... if you glue to the ribs before you shrink it I think you have problems.....the manual talks about rib stitch or other forms of fasteners to the ribs after shrink.....1" of poly tack to where it attaches to the LE and Trailing Edge overlap second piece (top, bottom) glue fabric together then shrink.... this is from the PolyFiber manual Rev 21 page 18-19.......but you are not supposed to mix systems.....so if you are going to forgo the possible melting of the ribs you probably need to look to the Stewarts manual (which I have not looked at)
 

TFF

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You need to test. I know stuff is expensive. If you had conventional wood, metal or composite ribs, there would be no worry. 30nf has lots of good qualities, and it is relabeled as the Stewart’s glue. Stewart’s did the leg work to see if it was safe for flying. Many have diverted in the homebuilt world to mixing methods. Some for better, some for worse. You need to test your chemicals. I’m not going to give a direct answer. It’s not about short cuts

You have to test to see if that is ok.
With one brand or another, they can’t recommend other products. If you were dealing with a certified plane it would be illegal. Too much work to use the wrong stuff and then tell the owner it has to be done over. In that respect, better can’t be an excuse.

There is a responsibility to the person flying the plane that there is no hidden issues. There is a responsibility to everyone for the hard work that may have to be done over with the wrong chemicals. You need to paint polytack on a test structure with fabric and paint the fabric with the Polyfiber system . There is a company that sells model airplane size quantities of polyfiber. Get some and see. Home for Poly-fiber Aircraft Covering System
 

Rudy Lee

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Apr 26, 2020
Messages
23
Thanks for all the advice - you are totally right, we definitely have a lot of testing in front of us. We'll try out the 30nf and poly tak and see how they turn out - we'll keep you posted :)
 

maya.ayoub.32

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Apr 6, 2020
Messages
60
Hello Home Built Airplanes Forum!,

Sorry for the lack of updates from the fuselage side these past few months!

Fuselage Updates
We’ve been designing and simulating our 4130 Chromoly Steel fuselage through Fusion 360. We needed to redesign our fuselage because our center of gravity was too far back, making the plane dynamically unstable in flight.

After simulating our plane at 3gs during flight, we’ve decided to stick with 0.625” (⅝”) diameter tubing with a 0.035” wall as many other ultralights, such as the Legal Eagle, have done. Based on our simulations and other comparable ultralight designs, the plane will be able to withstand these forces. To double check we’ll be joint testing, since Fusion’s simulations can be inaccurate around coped tubes.
Most recent design of the Fuselage:


Fuselage Simulation at 3.8 gs:



We’re working this week to add the struts and spars to the simulation since they will be working with the fuselage as one structure, hopefully helping everything withstand the forces.

Tail Questions
Simulations using XFLR5 told us that we needed a tail with an area of 4650 square inches, and our current design reflects this. However, after seeing the tails of the Legal Eagle and other ultralights, we are concerned by our tail size. At what point do we trust industry standard tail size over our calculations? Does anyone have any advice in terms of calculations to run to determine how large our tail area should be?
Our old fuselage incorporated a 1” OD aluminum tail to match the rest of the truss, however now that we’ve moved to ⅝” steel, we’re unsure of our next steps. We’re trying to keep the tail as light as possible so our center of gravity is as forward as possible (according to our XFLR5 simulations, the optimal center of gravity is at least 5.8” in front of the quarter chord). Until this point we’ve planned to use Airdome extruded aluminum hinges this forum previously recommended, however they only come in one size at 1” OD.

Below is an example from @radfordc back in May 2020:



We have a couple of possibilities for this which we’d love to get your opinions on:

Option 1
We could keep the same aluminum rudder, elevator, horizontal stabilizer, and vertical stabilizer at 1” x 0.035”:


We’re not expecting massive forces on our tail (likely under 50lbs), and the 1” aluminum should be comparable to the Legal Eagle’s ⅝” steel tail. The advantage of this method is to keep the tail as light as possible, as we could very easily weld our own hinges. For ease of transportation, we’re thinking of attaching the vertical stabilizer with a U channel so it is easily removable. We’re wondering if this forum can see any concerns with this?

Option 2

If a detachable vertical stabilizer would be unstable, we could keep it 5/8 OD steel then weld our own custom attachments between it and the rudder.

Again, the disadvantage would be weight as 5/8 “ steel weighs twice as much as 1” aluminum both of 0.035” wall.

Option 3
Just to throw it out there, the EMG-6 attaches their control surfaces using fork and eye bolts with a rotator bolt.



The advantage of this would be simplicity, however, it would have a lot of pressure and we mostly just wanted to put it out there in case there’s strong opinions for/against.

Option 4
Our last option would be to weld our own attachments and keep the tail 5/8 tail, however, the only advantage to this would be preventing galvanic corrosion and allowing us to weld. It would be more expensive and roughly twice as heavy.


Right now, our biggest concern is keeping our center of gravity as far forward as possible, since our calculations tell us we need it to be around 5.8” in front of the Quarter Chord. Because of the weight concerns, we’re leaning more towards the aluminum tail, however, we’d love to hear from the experts what would be more practical.

Galvanic Corrosion:

Basically all of these options result in aluminum and steel being in very close contact, so we were wondering if this forum had any suggestions in preventing galvanic corrosion?

Thank you as always for all your insightful feedback!
 

Aerowerx

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Did you think of this?

Keep your 5/8" tubing and use the 1" OD hinges. Then find some 1" tube that will fit over the 5/8" as a bushing. You would only need a small length which should not affect the weight by a significant amount.
 

BJC

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You might want to include all attachment points (engine mount, seat, restraint straps, landing gear, wing, wing struts, tailwheel, fuel tank attach, tail wires, etc.), before finalizing the truss. You may end up moving a few clusters and adding some more diagonals.


BJC
 

TFF

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Does the regular Legal Eagle use a steel tail? The LE /XL uses an aluminum tube one. As for corrosion, paint on both surfaces should be enough to insulate the metals. They can corrode, but unless the conditions really warrant it, it will not be an issue.
 

maya.ayoub.32

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Did you think of this?

Keep your 5/8" tubing and use the 1" OD hinges. Then find some 1" tube that will fit over the 5/8" as a bushing. You would only need a small length which should not affect the weight by a significant amount.
Great Idea! We were initially thinking of creating our own hinges to meet our needs- what do you think of this? The hinges are made out of two tubes welded together which should be easy to construct and we saw others doing on their own Legal Eagles. It depends on if a detachable vertical stabilizer (VS) is safe, though, because that dictates if the VS would stay 5/8 or if we can switch it to 1" aluminum. As of now, we're leaning towards keeping the whole tail 1" aluminum then using the existing hinges, however, if the VS was welded straight on would keeping the in 5/8" then welding our own 5/8" OD to 1" OD hinges work?
 

maya.ayoub.32

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Apr 6, 2020
Messages
60
You might want to include all attachment points (engine mount, seat, restraint straps, landing gear, wing, wing struts, tailwheel, fuel tank attach, tail wires, etc.), before finalizing the truss. You may end up moving a few clusters and adding some more diagonals.


BJC
Yeah, this is actually a great idea. We currently have some members working on the landing gear and engine mount, then we're adding the struts just for simulation purposes. You bring up a really great point that we should wait for their placements to be finalized as well and simulate it all at once to ensure safety - thanks for the tip!
 

maya.ayoub.32

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Apr 6, 2020
Messages
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Does the regular Legal Eagle use a steel tail? The LE /XL uses an aluminum tube one. As for corrosion, paint on both surfaces should be enough to insulate the metals. They can corrode, but unless the conditions really warrant it, it will not be an issue.
They're made of 6061 T6 aluminum tubing, which I totally forgot about! You're totally right they use zinc-based paint on their pop rivets for corrosion purposes, which I don't see a problem using on our too. Thank you for the reminder and insight! Do you have any recommendations on whether or not to implement a removable vertical stabilizer? We're not very concerned about the actual attachment at this stage, but the decision dictates the material of the VS which will affect our center of gravity, thus affecting the placement of our pilot/nose.
 

bmcj

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I love Poly Fiber, but have you ever looked into Oratex, you can find a few Oratex discussion threads here on HBA. It might check all the boxes for your use.
 

TFF

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The issues with removable tail parts is good attachment and easy and safe rigging. Taking something apart always has an issue of forgetting to attach something. Forget a bolt or nut or like. Covering that is all you need to do.
 

Aerowerx

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Great Idea! We were initially thinking of creating our own hinges to meet our needs- what do you think of this? The hinges are made out of two tubes welded together which should be easy to construct and we saw others doing on their own Legal Eagles. It depends on if a detachable vertical stabilizer (VS) is safe, though, because that dictates if the VS would stay 5/8 or if we can switch it to 1" aluminum. As of now, we're leaning towards keeping the whole tail 1" aluminum then using the existing hinges, however, if the VS was welded straight on would keeping the in 5/8" then welding our own 5/8" OD to 1" OD hinges work?
It might be better to use the existing hinges on 1" aluminum, if your weight works out OK. If you make your own hinges I would be concerned with binding issues.
 

proppastie

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I love Poly Fiber, but have you ever looked into Oratex, you can find a few Oratex discussion threads here on HBA. It might check all the boxes for your use.
I have looked at Oratex very expensive....but what the heck its an airplane.....Poly-fiber is well known.....I am currently looking at Hipec....as they claim you do not have to rib stitch and if it glues down as well as they say I will not tape over my rivets on my LE. ....there are so many rivets for my stiffeners I would be better to put down the felt or 2 layer of cloth on my LE.
 

proppastie

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Does anyone have any advice in terms of calculations to run to determine how large our tail area should be?
speed, length of the arm (distance) to the CG. .....copy similar speed sized aircraft ....however it might look also to scale a certified aircraft because homebuilts experimental are not necessarily same ( as docile ) designed..... There is a chapter in Glider Criteria P20 on "balance loads"....But I have not studied it as I copied the Carbon Dragon which is a very slow aircraft with large tail surface and arm because it is so slow. Plans from my signature block at the Irish site.
 
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