Luked

Nice sheet metal work Larry. I'm looking forward to more updates on this one.

Thanks for the report Joey. It's fun to hear stories from you guys that have flying planes. Helps with the motivation.

I've bent Lexan (polycarbonate) in our metal brake. Here's a video of a guy mending a piece:
 
http://www.youtube.com/watch?v=sNWqbAz6Lww
 
On our regular sized brake, you can bend 90 degrees in one bend. I was bending fairly thin stuff though. Probably about 1/16". Not sure how it would work on thicker material.

Hey Ed,
 
I'm not an expert, and I don't know what the thinking was in the design decisions. Something may have lead them to re-think their earlier assumptions. Here is my understanding of a strut braced wing in simple terms off the top of my head.
 
The part of the wing past the upper strut attachment is the easiest to understand because it's just cantilevered. All things being equal, the longer that section becomes, the more bending stress it will experience near the strut attach (the point of highest bending for that section). So, if you make the wing longer but leave the strut attached at the same distance from the root, the spar gets higher bending stress at that point.
 
The part of the wing that goes from the wing root to the strut attach point is a little more complicated. It's like a simply supported beam except that it has that cantilever section extending out to one side, and the strut is applying a compression force to it (when G load is positive). To get into the stresses on this part of the wing, you would want to do a shear and bending diagram (and free body diagram showing the strut forces), but basically, all things being equal, you can say the following. If the length of this section is increased, bending stress at the middle will be increased, and resistance to compression (buckling) will decrease.
 
The last thing to think about is the strut angle. As you move the strut upper attach point farther from the wing root, the angle of the strut becomes flatter. This part is hard to explain because you can't make as many simple blanket statements about it. A flatter strut angle means that a larger component of the force in the strut is compressing the wing spar, but as you move the strut out on the wing, it decreases the vertical force component needed to support the plane's weight because more of that vertical load is shifted to the wing root attach point. Also, the longer the strut, the less resistance it has to compression loads (negative Gs). It's kind of a balancing act.
 
Add to this that airplanes are loaded in many different ways as they fly through the air and make different maneuvers. The ailerons (flaperons for us) add additional up or down force at times for example.
 
Anyway, I've rambled enough. I hope I don't come off sounding like too much of a know it all jerk. This stuff is probably not that interesting to a lot of people. I like to talk about it though, and learn all I can. I probably misstated one of two things, so please let me know if I did. Also, keep in mind that the stuff above is very general concepts. Engineers consider many more factors in greater detail when actually designing an airplane.
 
Luke D.
 
 
 

Very cool!! Can you tell us more?

Thanks for the pictures Larry. That helps a ton. It will be a little while before I get to the struts, but I'll be coming back to this thread when I do.
 
Ed, I would have just used the stock Avid struts if I was going to go with the standard length Avid wings. The KF wings are longer though, and the struts attach farther out. This changes the angle, of the struts, so the forces should change. It also makes the struts longer, so they will buckle more easily in compression (negative Gs). That's my thinking anyway. If 1" x .049" tubing worked for the IV-1200, then I would think it would be adequate for my plane.
 
The lower attachment pictures are very interesting. I remember my engineering instructor saying that connections (vs. the members themselves) are usually where people run into problems.

I see it in the KF catalog. I might have to get it. They also have the model IV operating handbook. I wonder if that would be worth getting too.

Hey Ed, what's the Downs book?
 
Edit: I just confirmed your strut information Ed. I found it here (in the Model IV-1200 section):
 
http://www.avidfoxflyers.com/index.php?/topic/603-history-of-kitfox-structural-changes/
 
(Thanks Doug)

Thanks Larry. If you could check with him on the strut wall thickness, that would be great. I'm really leaning toward the longer wing. If I go that route, I would get the KF inserts.

That's really good information. I'd love to have that extra wing area, and it's good to know it's been done before. You wouldn't happen to know what size of tubing he used for the struts would you? I can figure out the diameter from looking at a Kitfox, but I don't know the wall thickness.

Hey Larry,
 
I was also wondering if your friend that put KF wings on his Avid used full length KF wings and KF struts.
 
Luke D.

I downloaded one of the mauals from the site a while back. Not sure which model it is for (doesn't seem to say), but I would guess this measurement is the same for all Avids except the Magnum.
 
There is a diagram that shows 80" from the end of the tube to the center of the bolt hole. Hope that's what you were looking for.

Yeah, I usually wouldn't give my personal number, but that's our business phone#, and it's all over our website anyway.

Hey thanks guys. Sioux201, I tried calling, but got your answering machine. You can give me a call at 541 926 7757, or just let me know the best time to call you.
 
Luke D.

Hey Ed,
 
Thanks for your reply. The reason I'm interested is because I'm trying to decide if I can put the longer KF wing on my plane without introducing forces it wasn't designed to take. I actually did what you said, and went and looked at a Kitfox here on our field. I'm not sure if it's a 4 or 5, but the uprights are 1/2" square tubing. ACS only lists .035" as an option for 1/2" square. My guess would be that's what they used. This KF has the long wings, so that's encouraging.
 
Luke D.

Nice! Sounds like this will improve the WB situation.This thing has come a long way since you got it.

Hey Joey looks good. Will this have much affect on CG? Sure will be a nice upgrade. Looks like they did a very nice job on the covering etc. How soon till flight test?

Thanks Leni. I'll post pictures and updates as I go. Got a little more done yesterday, but realized I need some more 7/8 shaft collars to move forward jigging up the new structure. Hope to get a goo rhythm and get something done on it each weekend.

Ahh, well I guess that complicates things a little. If there's not enough on the top of the wings to protect it from further corrosion then I would probably re-think things.probably depends on how long it would be till a complete paint job. I've used this stuff on old cars with amazing results. Old oxidized paint looked like new. I would only use if for a short term solution. I'm certainly no paint expert though.
 
http://www.amazon.com/Blue-Magic-TR-3-Resin-Glaze/dp/B000BOKO4W

Hey Leni I read through some of the comments on BCP (thanks for the link Larry). Like Larry said, I'll be the odd man out, and have a different opinion. Actually I'd be agreeing with one of the guys over there.
 
I'd be in favor of painting up just the tail feathers, and getting it in the air for now. Or, since you said you have some spare tail feathers, put them on for now, and get it flying. Advantages:
 
- Less weight
- Get flying sooner
- Still have the option to strip it and re-paint at a later date (also less weight)
- Less expense now
- Chance to do a good "shake down" and work out any bugs (make changes or repairs before you have new paint)
 
Either way will work fine though. This is just what I'd do.

Great paint job. I like the tail the best. It really highlights the round tail. I actually didn't used to like the round tails on Avids, but somehow they grew on me. I really like the color choices too.
 
Good job Cliff, and thanks for posting the pics Leni.

Well, after lots of planning and talking about my project, I finally got started actually doing something on it.
 
The first thing I did was to make a down and dirty rotisserie.

 

 

 

 
Since I decided to modify a significant amount of the forward fuselage, I needed to brace it up before cutting it apart. I used some clamp on shaft collars to attach the brace tubes.
 

 
Not sure if you can tell what's going on from the pictures, but I basically made some triangulated structures to replace the support that's currently coming from the overhead tubing structure.

 

 

 
Next step is to start cutting

Hey Trackwelder,
 
I kind of forgot about this. Some time after you started this thread, I talked to a Kitfox owner that has a friend with a KF powered by the Yamaha. I was surprised to learn there was one so close to me. I want to go check it out some time when I get a chance. He said the performance was impressive.
 
Luke D.

Thanks Ed!