# Mock up suggestions......

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by MadProfessor8138, Jul 4, 2019.

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1. Jul 4, 2019

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So I'm thinking of mocking up an airframe that I've been designing and thought I would ask for opinions.
The real airframe will eventually be constructed of 4130 tubing with an aluminum tailboom.
I've thought of 2 different approaches to mock up a full scale airframe.

1. Wood :
A. Wooden dowels glued up in place of the 4130 tubing.
B. 5"-6" pvc pipe for the aluminum tailboom.

2. EMT....electrical metal tubing :
A. EMT brazed in place of the 4130 tubing.
B. 5"-6" pvc pipe for the aluminum tsilboom.

Should I go wooden dowel or EMT ?

Kevin

2. Jul 4, 2019

### Victor Bravo

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I vote for dowels. Slightly more expensive than EMT, but a lot lighter (to move the mock-up around the shop, hang it from the wall, etc.), PLUS you can glue it with CA or hot glue to make faster progress. Also a lot easier on the hole saw blades you will use to cope the joints.

3. Jul 4, 2019

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I'm kinda leaning towards the wooden dowels too....I'm currently building a wooden aircraft and to be honest,i just like working with wood.

Two issues that I'm concerned about though.......

1. The airframe has some curves and the dowels will need to be bent.
I'm currently researching whether or not dowels can be bent with steam or ammonia.

2. I actually plan to build a full scale airframe to sit in so I can adjust measurements here and there.
Not sure if the dowels will be strong enough for this.

Kevin

4. Jul 4, 2019

### Victor Bravo

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The dowels will not be curved because a proper "space frame" truss does not have any curved pieces.

5. Jul 4, 2019

### akwrencher

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On the plus side for wood, steaming isn't very hard, or try some fabric softenrr. My late uncle used it many years ago to soften an oil frame for his boat that was giving him trouble. I like the idea of the emt myself though. It wouldn't be terribly hard to tack weld it together with a wire feed. I don't see why you would need to cope the ends for a mock up. No flight loads. Downside is it's probably galvanized, which sucks to weld. Not good for the old lungs.

6. Jul 4, 2019

### pictsidhe

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Wood is good!

Pvc pipe is light, glueable, bendable with heat. Could also be pop rivetted with gussets.

The EMT I've seen here ia galvanised. That isn't much fun to weld.

7. Jul 4, 2019

### Bill-Higdon

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Down side to PVC is it's flexibility, something the FMX-1 Group learned the hard way, it was ok for a first quick & dirty check but that's about it

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8. Jul 4, 2019

### TFF

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PVC. Coping the joints and gluing will get you just about the same experience as 4130 and all sorts of sizes. Long too. It will be cheaper too. Dowels, I hate the wood they use for hardware store dowels. They are not straight. They are some type of foreign junk wood. I look at them for RC projects all the time and pass.

Wood is normally my go to for mocking something. I think The PVC will work through the problems better and will be easier to scrap without feeling bad. You don’t want to be attached to the mock up.

9. Jul 4, 2019

### TFF

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On the bending of 4130 airframe parts, how much bending are you wanting? Anything fancy will need a mandrel bender. Anything tighter than Cub tail parts will kink up.

10. Jul 4, 2019

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Everyone is bringing up some good points and I appreciate the input.
I see pros and cons with each material that could be used for the mock up...

PVC......
Pro :
2. fairly cheap
3. easy to work with
Con :
1. Flexibility
2. pieces tend to not be straight...memory from being stacked in a pile

EMT.....
Pro :
2. fairly cheap
3. can be drilled for bolts and rivets
4. can be bent fairly easily
5. can be welded or brazed
6. Light weight
Con :
1. precautions must be taken if welded or brazed because its galvanized....not difficult to do,just an extra step

Dowel.....
Pro :
1. I like working with wood
Con :
1. material will have to be ordered in for the lengths desired...not much available locally
2. they tend to not be straight
3. can be expensive if not careful
4. any bending may turn out to be problematic

After searching through past threads I ran across a mock up that Toobuilder had done with EMT....he had some nice results.
After looking at the pros and cons list....the EMT seems to be the better choice of the materials.

Kevin

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11. Jul 4, 2019

### Victor Bravo

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So now after this discussion, you owe us all to see what it is you are designing

12. Jul 4, 2019

### Hot Wings

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A soak in muratic acid, picked up at the hardware store with the EMT along with a length of plastic gutter and ends (for the soaking trough), takes care of the zinc.

13. Jul 4, 2019

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I'm versed in welding galvanized metal so it wont be too much of an issue....the muriatic acid does do wonders....

Kevin

14. Jul 4, 2019

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Victor Bravo.........I'm reluctant to post anything on the forum pertaining to the 2 designs that I'm working on....sadly.
Each one of the designs has a few issues that I'm still trying to find the answers to....no design is strictly straightforward,there are always complications.
I posted in the past hoping to receive some helpful suggestions and input from everyone but it quickly turned into a discussion ranging from ....you aren't a BIG name in aerospace so you can't possibly design anything....you're going to kill yourself....if you dont use carbon fiber and unobtainium costing $millions$ then it will never be airworthy.....etc,etc,etc.
I would truly LOVE to post my ideas because I know there are individuals on here that could easily answer questions to a few areas that I'm having problems with....but being a public forum,you tend to get overwhelmed with all of the naysayers derailing the thread and trashing it up instead of actually contributing useful information.

Kevin

15. Jul 4, 2019

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You know what....I'm going to post a tad bit of info anyways.
You guys have tried to help with suggestions for a mock up and deserve to know what I'm working on.
I wont post any of my design sketches right now but this will give you an idea of what I'm designing...

Design 1.....A10 Warthog

Design 2....Ultrabat

This is a new rendition of an old design...

Kevin

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16. Jul 4, 2019

### Hephaestus

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Since it's mock-up and you'll be tweaking.

I vote emt and plumbing strapping/self drilling screws. That way you can take it apart and refit / adjust easily as you go and find issues to resolve.

17. Jul 4, 2019

### wb2754

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If you have a router, you can make round dowels whatever length you need.
3/4 in. sq wood would work well.
Maybe a little biased....building an all wood LSA Maranda.

18. Jul 4, 2019

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Not biased.....lol
I'm building an all wood Ragwing Stork RW19.....
Im actually in the shop right now with my kiddo and we are laminating the elevator halfs.....

Kevin

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19. Jul 4, 2019

### BJC

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We?

20. Jul 4, 2019

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