Small project update

[Luked 71]

Well, things seem pretty quiet around here, so I thought I would show a little of what I've been working on. I finally got back to work on the Avid. Now that all of the stress calculations are done (mostly) for the new landing gear/seat truss, I wanted to see how it would fit with everything else on the plane.

 

I made up a solid model of the fuselage. I'm also planning some other changes, and want to make sure all of the changes work together. Once I have all of the changes modeled, I'll be ready to order some tubing, and start cutting and welding

 

Here is what I have so far.

 

[akflyer 1427]

Damn!  Kind of impressive to see someone actually doing some real engineering when making changes!  Will be interesting to see what you come up with for stresses on the cabane vee.  The one from Airdale has the cabane vee pulling in a straight line across the center, but I am certain that if you drop that centerline down (like Piper did on the cubs) then it will put much less stress on the seat truss and the gear attach points. 

 

[Luked 71]

Hey Leni,

 

This is actually for a bungee style gear, so the geometry of the tubes is different. The main part that I re-designed though is the truss that the bungees wrap around.

 

It shouldn't be hard to do a truss analysis for a "bush gear style" though. If someone had some dimensions of their gear, I can see what I can come up with. There are some limitations to doing very simple truss analysis (joints method), but it can be pretty useful if you understand those limitations.

 

Just to be clear, I'm not an engineer, but I took 2 years of engineering about 20 years ago before I went a different direction (long story). beyond what I learned in school, I'm self taught.

 

Luke D.

Edited 30 Jul 2014 by Luked

[akflyer 1427]

I do believe the original designer was self taught.... and he has made some amazing designs.   Maybe when the guys get back from OSH they can post up some numbers for you to play with and see what you come up with. 

 

[Luked 71]

I think there are some actual engineers on the forum aren't there? It seems like I remember some members mentioning it. It would be nice to get some input from them as well. I've documented all of my calculations pretty clearly, so others could review them.

 

My brother is a professional engineer, and he has reviewed them with me (pointed out a couple of mistakes). We both know there are some assumptions made to simplify things a little, but otherwise, the results seem pretty useful.

Edited 30 Jul 2014 by Luked

[EDMO 1078]

Luke,

     After just a quick glance at your drawing, I think you need to move the rear of your overhead tubes to the outside corners of the rear spar crossover tube - going to the center gives no rigidity.   I can post a photo of mine if you want - but not saying mine is the only way to make them.

     With all your calculations, have you guestimated the bare fuselage weight?

EDMO

[Luked 71]

Hi Ed,

 

I'm not sure I understand which tubes you mean. maybe you could show a picture. The solid model in the picture is mostly just my starting point. It is exactly as the fuselage came from the Avid factory. Except for the following changes:

 

- Tail was stretched 16 inches by previous owner (this is pretty easy to spot in the picture).

- Some tubes in the floor and firewall area are not shown because I just haven't added them yet, or because they have been removed on the real plane.

- The landing gear / seat truss is my new design.

 

I'm going to be adding some new tubes in the front area to make up for some of the nose wheel structure I removed.

 

One nice thing about solid modeling this think is that the software calculates the weight of everything for you. It will also tall you the center of gravity. The weight is still pretty meaningless at this point though because I have a lot more to add.

 

One more edit: There are two tubes I still need to add right under the rear spare carry through. These will change the picture a little in that area 

Edited 30 Jul 2014 by Luked

[EDMO 1078]

Luke,

     I was referring to the tubes at the top of the cabin, commonly called "headache bars" - I took the photo, but will have to wait for my daughter to get home to post it - my old brain just cant remember how to do that.

     I put a slight upward bend in mine to match the wing profile - figuring that in case of a rollover or crunch, the tubes would bend up away from my head instead of down.  Some have these tubes in a double-"Y" shape and connect to all 4 corners - mine are larger tubes and go from about center of windshield in two places to the top corners of the rear spar tube.  There may be better ways to make them?  Might be good to think about having to crawl out the top?

     Don't be confused by my photo - I raised my roof and wings 6 inches.

     I will just add the photo to this post later today.

EDMO

Edited 30 Jul 2014 by Ed In Missouri

[Luked 71]

Thanks for the picture Ed. It's nice to see what you've been doing on your project. I think you'll see what Avid was doing better when I get those two other tubes in that are missing. I'll probably post an updated pic on Monday. I didn't really pay much attention to that area yet because I've mainly been focused on the landing gear

Edited 31 Jul 2014 by Luked