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Mar 12, 2018, 08:04 PM
Scratch building addict
rotagen's Avatar

Finished!


She's done ! Came in at 6.8 ounces with 2s 850maH. I'm pretty stoked because my hayabusa at same wingspan is 7.5 ounces.

Normally I wait until first successful maiden to earn decals but it's a rainy day .. so go for it.
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Mar 12, 2018, 09:49 PM
Build, crash...repeat
AleRRon's Avatar
Very cool. It’s nice to save money in this hobby by scratchbuilding, but one gets even more out of it by conceptualizing, designing, problem solving, and learning along the way. Nice work. I’ve been chicken to try “wrapping” rounded fuselages and so far have gone rectangular cross sections for simplicity. I’ll have to try your method soon.
Did you cover everything with foam putty and then sanded, or just covered certain spots?
Mar 13, 2018, 12:54 PM
Scratch building addict
rotagen's Avatar
Initially I debated over trying to make the fuse using my little hot-wire table, by using 2 pieces of styro for the 2 sides and keeping one side flat from the factory for gluing. I did a large p51 fuse this way, with a central thin piece of tougher foam which included the vertical stab - and it actually took a lot of time to rout out the holes and do all the shaping/sanding. So I opted to repeat the method I used on the hayabusa since it flew so well. But it would be a cool thing to try to do it with hot wire and sanding, just coudn't get my head around how to hollow out the fuse etc and keep things straight.

I tried to minimize the foam putty and just covered my vertical and top/bottom "wrapping seams", which matched where I put the cross-section (1/4 pie) formers. Just used my fingers. the stuff sticks well, almost as sticky as lightweight spackle. I also had to put some putty below the nose to smooth it out because I messed up on the shape. Sands down almost as easy as the foam itself. I didn't even bother with this step on my hayabusa but I was trying a little harder since this is my first build thread.

The measuring of course took some time, but I made it easier on myself this time by making two 1mm depron pieces (one for each side of the fuse) , per each longitudinal section of the fuse. and had them meet on top and bottom. I think it took 5 poster board templates (5 shapes) to cover the fuse but that's because I had one between every cross-section.

Definitely try this method, the result is a great flying lightweight nimble plane. Don't hurry like I often do, or you'll get a little frustrated.
I'm always amazed at how stable the little warbirds are. I have a Nicesky p-51 in this same size range and if you throw it gentle, the wings don't drop even a millimeter, just goes perfectly straight.

Turns out I was very lucky on the CG, since I moved the servos way back, a 2S 850mah battery put it right on the mark.

Next time will be much faster since I saved all my templates on poster board. I don't have a scanner at the moment or I could put all the formers on card stock and scan them in - then it's just simply printing out keeping things at letter paper size - I suppose I could drag out my old crappy inkjet with scanner some day if ffolks demanded.
Last edited by rotagen; Mar 13, 2018 at 01:00 PM.
Mar 30, 2018, 02:14 PM
Scratch building addict
rotagen's Avatar

maidened


Well the maiden went OK but I am not at all impressed with the KF wing on this airframe.

Seems to be a lot less lift on the wings than there should be, I am comparing to my Nakajima of Identical size and wing area, and the Japanese plane is almost a full ounce heavier. This plane is a lot less floaty and seems to generate zero lift at below horizontal angle of attack. Twitchier as well, but that may be due to the long nose and smaller moment arm from tail surfaces to CG.

But I wanted to keep this one scale or I would have made larger tail surfaces.

I recorded a video, but I was thinking I may do a "before and after" vid.

Went back to my usual method of creating an airfoil
with a simple light foam strip down the wing at about 30% chord, and wrapping the upper wing surface using 1mm depron.

It's funny, the KF wing works great on my kung fu forward swept wing, but I have a feeling it is mostly due to the wonderful flight characteristics of forward-swept models, ie a smooth upper surface would have flown even better.

Now wrapped, pics attached, just have to paint. Luckily I came out pretty light so the KF layer's extra weight shouldn't cause too much problem.
Mar 30, 2018, 09:05 PM
Scratch building addict
rotagen's Avatar
Well the new airfoil made a huge difference, too huge in fact. The hand toss was super stable, unlike earlier with the KF wing, it flew perfectly straight without the slightest wing dip. But the CG is now too far forward at its former position, and I couldn't get altitude so it hit the ground at a shallow angle, wing break but nice and clean so it's fixable.

Makes sense, now the lift is greater and the nose will dip due to greater force pushing the nose down.

At the same time I wrapped the wing on my simple cutlass pusher build, made a huge difference, and that thing is super fun, stable, floaty and fast and lands at walking speed.
Apr 03, 2018, 03:33 PM
Scratch building addict
rotagen's Avatar
Well I decided to scrap this one after a couple nasty crashes. The KF wing flew, but the lift was very sensitive to pitch, and it just wasn't floaty the way I like them.

After I made a nice airfoil, I had difficulty getting the cg right and well.... stuff happens.

On to my next build !

But I thought I'd show the Nakajima maiden to show the potential of this build method for small warbirds.

Nakajima maiden (3 min 48 sec)


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