Scale Swappable P51 - Design, Build, Fly

by JasonEricAnderson | April 6, 2014 | (17) Posted in How To

The Goal

The P51 Mustang has always been my favorite of the WWII warbirds. There have been some amazing swappable Mustang designs here on FliteTest (See related articles at the bottom) but one of the things that really makes a mustang is the iconic leading edge of the wing. I wanted to design a swappable that could be as scale as I could make it using the standard FliteTest build techniques of A/B folds, 50% cuts, and crush bends. 

Design Process

To start with I needed some good reference drawings to model from.

After collecting reference material and research I was ready to start designing in SketchUp. I recorded this design process as time lapse videos that go through the entire process from start to finish. You can view these at the end of this article. I've also posted many screenshots of the development in the build thread in the forums. That link is also at the bottm of this article. I took a lot of inspiration from both the FT Spitfire and the FT Racer with some major changes to get the wing geometry to fit with the Mustang's look. 

I pulled my three views into SketchUp and blocked in the basic shapes as simple outlines. By doing this I was able to lock in the scale proportions before I got to deep into the construction. Then I refined and worked out the various details of how the wing geometry would look, the standard fuselage and more specific details like the belly scoop and turtle decks. 

Once the design went through a few revisions I used the Flattery plugin to export out the parts in a .SVG vector file. If you're not familiar with what a 'vector file' is click here. From there I used InkScape to clean up and arrange the parts into a printable format. Using the standard print and tape up technique I cut out the shapes and traced them onto my dollar tree foam board.

Build Process

The wing has been the most complex part of the build. I had a first prototype that opened up some flaws in my design. I went back to the model in SketchUp and revised it and printed/cut a new set of parts. The second build was solid enough that it was worth putting electronics into. 

Maiden Flight

Once I started installing the electronics I realized I didn't have a Y harness for the aileron servos. After building one and fiddling with the servo extensions I was ready to put in the power pod and take it for a test flight. 

Summary

Since I'd been flying mostly FT Flyers and FT Nutballs this was much more plane than I was used to. I'm very much a newbie pilot. As this is my first scratch build design I've learned a lot over the process. I've really enjoyed taking something from idea and seeing it built and flying. Designing something from scratch is an ongoing process. I'm sure I'll be making tweaks as I build more of these. This is a warbird and from what I've heard, it flys like a warbird. The wing root plate is the only really hard part of the build and it may take some tweaking to get it in place. Also, Be careful to keep a good even dihedral angle when you build your wings. The portion of the wing that sits inside the fuselage should sit flat and the wings should have a clear symmetrical dihedral. 

 

Quick links for this article

Gear list

UPDATE/SNEAK PEEK

I'm working on a 'body wrap' for this that could be applied with spray adhesive to up the scale look even more. Once this is complete I'll post a new article for it. In the mean time here's a sneak peek.

- Find this article & others like it at www.FliteTest.com -

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COMMENTS

alibopo on April 12, 2014
Nice job! Mega respect! - I'm still struggling to get my head around the computerised project-to-paper aspect of this process, so I'll be looking over the links you gave. I've no problem producing a final model, but reproducing the process in a format others can easily copy still has me stumped. With the actual flying, I can see you're on a very similar journey to me - the good news, it does get easier! :) Regarding your maiden in the video, that first fly-out was looking very good and stable - seems to me it all went a bit mad when you started trying to control things! :( I know that feeling! Looking at your initial throws, I feel you had a lot of movement dialled-in. Your wingtip ailerons will have LOADS of effect due to their distance from the fuselage and their healthy proportions. I reckon they could be dialled-down to HALF that range and still have lots of effect. Likewise the elevator and rudder. The FT Cruiser drawings have a particularly nice throw gauge, and I've used that for a lot of my builds to give me my LOW-range throws. It's worked very well. I wouldn't use the throw gauge from the Baby Blender, it's pretty extreme for an initial setting on a monoplane. Reduced throws gives you a much more manageable flight experience, and once you get your hands and eyes used to the new performance and handling of the new plane you can start to increase the throws. The only scare I had using limited throws was when I tried flying my Tribewt inverted - I just didn't have enough elevator to climb away from the ground! That gave me a few heart-stopping moments, until I remembered to roll-out! With a lot of these planes it's all bank-and-yank when flying at speed, which is very familiar ground for most flyers, but flying at lower speeds, you can't turn too fast, or let the wings tilt too much, or the plane just drops out of the sky. Flat-enough rudder turns will help keep the plane in the air. As part of my 'education' I spent (still spend) time on a simulator, working on rudder turns and flying as slow as I can. Most (but not all) of these low wing planes need a touch of opposite elevator to keep them from rolling onto their side, which is kind-of the opposite to flying bank-and-yank, so it really is worth practising in a simulator so you can mentally shift from one technique to the other without panicking. It's definitely paying-off for me when it comes to 'real' flying. All the best. Alibopo.
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JasonEricAnderson on April 13, 2014
Awesome input. I was thinking of making notes where you could have a fixed rudder and just go bank/yank from the get go. I'm still getting the hang of the rudder. I need to get the adapter for my T-six so I can practice on a sim.

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alibopo on April 14, 2014
Hi, fixed rudder works fine for a lot of builds. There's some of my planes I hardly ever touch the rudder. But I get a lot of pleasure from take-offs and landings and I find I need a bit of rudder there for take-offs/landings and the odd bit of taxiing. You can't use bank-and-yank to change direction if your wings are almost touching the ground already. One of my planes almost refuses to change direction unless I use the rudder. Either from necessity or interest, rudder turns add a whole range of options to your flying. The funny thing is that you're already familiar with rudder turns from any 3-channel plane you've flown - but the common 'system' is to connect the rudder servo to aileron input on the receiver so it feels like bank-and-yank. This means the 3 channel skill-set transfers easily to 4-channel bank-and-yank. When that rudder moves to another transmitter control stick movement (4-channel) it takes time to work out you can fly the plane using either steering method, or with combinations of both. All part of the journey.
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alibopo on April 12, 2014
OOPs - it should read 'opposite AILERON' for the bit about rudder turns - note to self pay attention!
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808aerosquadron on April 12, 2014
"Chuck and pray." This may become the new Swappable mantra.

Nice design on the P-51. Looks like you have a winner design there.

Thanks for your Sketchup tutorials. They have been extremely helpful.
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BuckE67 on April 16, 2014
Good job man!
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thatjoshguy on April 11, 2014
Great work! Your SketchUp tutorials were a huge help to me!
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Flying Penguin RC on April 11, 2014
Really nice work there, love the canopy and scale wing. Your video reminds me of the maiden of my P51 design. Found out later the CG needed to be very far forward and yeah, they fly like war birds. Keep that speed up! I would call that one successful maiden flight. And 5 stars for sure.
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coldbloodedtx on April 11, 2014
Nice looking design, this will probably make my build table soon. This will look great flying alongside the BF109 swappable we're working on :)
What motor/prop/esc/batt combo are you using (I haven't read your entire build thread to dig it out yet). Looks like a Turnigy 2826, and I would guess 1400kv, assuming 8-9" prop but I figured I'd ask.
Also, props for posting your crashes. Good for folks to see the reality of learning to fly, and also the relative durability of foamboard construction.
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JasonEricAnderson on April 11, 2014
Good call. I updated it with my gear list. Thanks!
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Phoenix1962 on April 12, 2014
Nice job! Very much like the way I tackle a new design. Research,scale, draft, and initial build. Design flaws are dealt with as I do the initial build. The only difference is after using Autocad for fifteen years...... I just can't get used to Sketchup functions. LOL I've been collecting 3 view drawings for years, and have an extensive library to chose from. Again...........WELL DONE! Phoenix1962
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Balu on April 11, 2014
If the FT crew comes out with a P51 too, I'd love to see a comparison between the two planes.

As for you being a "newbie" - you definitely reached a new level in your RC ranks :)
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JasonEricAnderson on April 28, 2014
I can't wait to see the FT mustang.
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JasonEricAnderson on September 2, 2015
Sorry for the broken links to the plans. I've fixed them.
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Wim on August 20, 2015
Looks awsome. Links to the plans don't work anymore :(
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JasonEricAnderson

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Scale Swappable P51 - Design, Build, Fly