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Old Apr 19, 2013, 09:58 PM
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P-40 Warhawk, C/L to RC Conversion from 1962 Plans

Back in the early 60's my dad was looking at building some balsa planes so he purchased plans for a few different birds - the P-40, a Navion, the Cessna 130, and a few others.

Then came marriage, a house, kids, a career, and other associated issues to change his priorities. The plans were boxed up and forgotten. I remember as a kid in the 70's looking at the plans and thinking about someday building the planes. Then I grew up, started a family, and my priorities changed as well.

Now the kids are old enough to have their own interests and I'm free to re-kindle some of mine. Last year I got into RC planes and assembled a few foam birds. That led to ARF balsa kits (pre-covered) and then a few other laser-cut balsa kits, and now I have a decent hanger of planes. But nothing built from scratch.

A few weeks ago my dad stopped by and had the plans that he tucked away so long ago with him! A couple of them really got my attention, and I figured I'm far enough along in my abilities and patience to try building one. The easiest of the bunch is the P-40 control line, as it's a profile fuselage and pretty simple wing. The tail surfaces are simple as well.

First thing to do is get a set of plans I could work with since I didn't want to destroy the originals from 1962 (Model Airplane News). I looked and found the plan was available on the Outerzone, no original plan was actually required. I work in the construction industry so our Estimating Department could have scanned it for me if needed. They took the .pdf from Outerzone and printed a copy. I checked the scale on the newly printed plans (the scale isn't on the original plan page, by the way) and found it was too small. Turns out the original plan is also too small. I had one of our estimators re-print it to the correct size and found the original was way off. I don't know why they'd have done that back in the 60's - it's not like you could easily take the drawings in and have them scaled up at the local shop...

So now I have 3 good prints at the correct size. I don't want to build this as a control line plane - I get sick just thinking of spinning in circles! My plan is to convert it to RC by adding ailerons and a functioning rudder to go with the standard C/L elevator control. I'm figuring it would run well with a 1000mAh battery as it should end up a little heavier than my Mountain Models Switchback.

I'm starting with the wings, since they're the most involved part of the build. To make them I could start with new balsa from the hobby store, but I figured it would be fitting to start with some balsa my dad picked up a few decades ago. I have a few small sheets so I'll mix a few pieces in here and there.

As of this time the port wing is about 75% done. I'm deviating from the plans a bit, using some of the ideas I got building the Switchback. The leading edge isn't made from 1" wide strips of balsa, it's carbon fiber tube with a couple 1/8" spars between the CF and the main spars. Ailerons will be added once I have the main wing structure complete.

I may be walking blindly into a mine-field with this conversion, but I have high hope that it turns out well and flies acceptably well considering it was never designed for this kind of flight!
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Old Apr 20, 2013, 02:16 PM
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A little more quality time with the port wing and it's starting to take shape. I've never done this before so it's a bit of trial & error. I built the trailing edge of the wing pretty much as shown on the plans, with the exceptions noted on the previous post. I found I needed to do some trimming to the ends of the ribs to get everything to line up since the rib lengths weren't very accurate.

Once the TE was in place and all spars and stringers secured with glue I removed a section of the TE to make room for an aileron. It'll be sized somewhere close to the original P-40's dimension, although I considered going the full length of the wing. However I figured this would be waaaay too much for the plane (based purely on a wild guess). With the TE out of the way I added some new material to the tail of the ribs to tie it all together. A little bracing is added, and I can see the finish line for this wing.

Still to do: wing tip bracing, building the aileron and the aileron servo mount, and a few other small details before I can move on to the other wing.
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Old Oct 19, 2013, 11:20 AM
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It has been a while, but now that the building season is about to start it's back to the P-40 (along with a few other planes I'm working on). Here is the fuselage and horizontal surfaces. The profile fuselage is made from two 1/4" sheets of balsa glued together. Plans called for 1/2" which my LHS didn't have. You can see the separation line on the "chin" of the plane - the lower section will be removable in case the wing needs to be removed. There is still a lot of work needed on the fuselage such as rounding the edges, placement of electronics, covering, etc., but I want to finish the other wing first.
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