P-51 Mustang Swappable Build with plans

by filken | September 10, 2013 | (25) Posted in Projects

I have a fever, and the only cure is more cowbell...and another swappable scratch build!

I want to start off by saying that if you are a compulsive plane builder and lover of war birds like myself, I apologize for doing this to you but this is a plane I just had to build. I bought my first plane a couple of months ago and when I was trying to decide what to buy I was looking at a P51 Mustang RTF but the guy at my LHS (and the price tag) talked me out of it because "a 4 channel is not a trainer". While the logic is sound, I am not always logical and I couldn't stop the craving for a P51. Since I love the swappable plane series and I already have all the electronics, it was not long before I couldn't resist the urge to design one of my own. Besides, if you have a Spitfire and a P38, you need a P51...right? Maybe the FT guys will make a foam board aircraft carrier for all these war birds. :)

Now, lets get to the build.

This one took substantially less time to design because I already had the techniques from my P38 design. I copied the dimensions for the P51 by stitching together a 3 view in Sketchup and tracing over the shape.



I am really impressed with how accurate Sketchup is. I can build a 2D wing design and then make it 3D and fold it over to make sure everything lines up. I can set wing dihedral and see how that affects the shape of the holes in the fuselage without having to build a bunch of prototypes. So far Sketchup has worked really well and I have gotten very consistent results. I have uploaded the 2D plans and 3D model to the Sketchup warehouse so if you want to modify the plans you can download them and play around. Even if you don't know how to use Sketchup you can download the 3D version as a reference. I madeverything except the poster board pieces in scale size so you can see where everything goes. 

I was a little more diligent this time to take pictures of the build process so I can give more detailed instructions.

Here is the info.

Wingspan: 38 7/8"

Length: 32 5/8"

Motor/Speed Controller: "The Beef" kit from Lazertoys.com for the Spitfire

Servos: 4 x 9 gram

Prop: 8x6

Battery: 2200mah 3 cell 25c LiPo

Removable wing

Center of Gravity: 2 7/16" back from the leading edge (in the center of the wing)

If you have a power pod already, great! If not, you will want to start with that. I added the build video to the related articles section so you can watch that if need be.

Build the wings using the same techniques FT uses on the Versa (also in the related articles below). If you watch that build video and use these plans you should get the desired result. I made the wing plans a little wide on the top surface because until my foam board stretcher arrives I am only able to cut things down if they don't fit. The center line of the wing is the inside, bottom plate of the wing so make sure you keep that reference point as close to the plans as possible.

Once you have the wings folded you can trim the excess to make the top edge parallel with the bottom. I used the sanding technique that was used on the FT Versa to get the desired wing dihedral.

There is a spacer in the plans that should give you the proper dihedral (5deg.). I taped the bottom surface of the wings together fist, folded them back, glued the edges, put one wing flat on the table and set the spacer under the other wing tip for support until the glue cooled.

Then I added another piece of packing tape down the center on the top of the wing for a little extra strength. Once the wings were assembled I glued a piece of poster board over the wingtip to finish it off and give it some strength like they did with the FT Racer. 

Then you can build the fuselage. Nothing too complicated here. Make sure everything is square or you will have a crooked tail and as any alley cat can tell you, a crooked tail is no fun.

Then you can glue the wing on. If you plan to have the wing removable just glue it on the bottom. If you glue the top you won't be able to remove the wing without a saw, and no one wants to carry a saw with them every time they fly.

Now that the wing is glued go ahead and cut through the fuselage just in front of the wing, parallel to the leading edge, and just behind the spacer at the rear of the oil cooler (the bump at the bottom rear of the wing) just like they do in the Spitfire build video.

I glued 2 spacer blocks in front and 1 in the rear beneath the skewers that hold the wing rubber bands for added strength. I also put in 2 squares on the top center of the wing like the Spitfire for alignment. I waited to install the tail until after the wings were in their final position because they can shift slightly after you make them removable.

After the wings are attached in their final (but removable) resting place you can install the tail surfaces. Check the fit on the elevator and make sure it doesn't bind with the fuselage or the rudder before you glue it down. Glue on the elevator first and line it up with the wings. Then install the rudder and be sure it is at a 90 degree angle with the elevator.

I glued the top section of the rudder first and once that was lined up and set I finished gluing the bottom piece of the rudder to the fuselage. 

Now that all your wings and control surfaces are assembled you can work on the turtle deck. I tried to make it as simple as possible without sacrificing the look of the plane. If you have some suggestions or better ideas send them my way and I'll be glad to give them a try. This is quite similar to the turtle deck build for the Spitfire with a couple of added steps. There is a crease line in the piece that forms the cockpit that should line up with the crease line towards the top rear of the fuselage. The tail gets narrower and the cockpit slants in so it can be a challenge to get the cockpit square, but if you're careful it can look really nice.  I glued the fold at the top of the cockpit and held it in place to line everything up before gluing it onto the fuselage. Once it is set, glue it to the fuselage and check again to make sure it is straight. Then you can glue on the turtle deck formers on the front and attach the poster board. I used tape hinges like the FT planes, and put the front and rear turtle deck covers on first. They both just meet up with the cockpit and should make a nice curved surface for the cockpit poster board pieces to form over.

I had to glue the bottom edge of the poster board to make it stay, but that's partly because I used some pretty low quality tape. The nice thing about the tape coming off is that you can get everything formed and set and then slowly peel off one side at a time and glue it. After the glue cools you can take the tape off and you'll have a cleaner look (assuming you did a good job with the glue).

I waited until the end to install the electronics, but you can install them as you go if that works better for you. I just find it easier to get things finished if I'm not worried about screwing up a servo or tearing off a control horn. I also waited to cut the relief for the aileron servos because I have a grab bag of all different sizes and I wanted to make sure they fit nice and tight. The aileron servos should be in line with the spar and lay flat against the middle bend surface on the bottom of the top wing piece. I set them in place, traced around the outside, cut out a piece slightly smaller than the lines, and hot glued them in place. I didn't put the servo locations for the tail on the plans because it can vary from build to build. Once everything was finished I just lined the servos up with the control surfaces, traced them out, and cut out the holes.

And here is the finished product.


Here is how it looks once it's painted. 


As you most likely have noticed, it is a belly lander, but designing retracts for a foam board airplane is no small task, so if someone out there has some brilliant ideas, bring them on. I think we all would love something simple and functional for our war birds.

That's pretty much it. Thanks for reading! If you like it please rate the article and let me know if you decide to build the plane. It's always good to get feedback.


Maiden Flight

The maiden flight went super well. I ran the numbers through an online CG calculator and ended up super tail heavy and almost didn't get it back on the ground. It turns out that the P51 has a ballace point that's further forward than most. Once I fixed the balance it was a totally different animal. It's a rocket! I am using a 1250kv motor running off a 3 cell LiPo with an 8x6 prop and I can easily run at 1/4 throttle. Full throttle is a blast! It glides nicely and landings are gentle. This would be a great combat plane. I couldn't be happier about how this turned out. I don't think you'll be dissappointed if you decide to build one. This video was taken by my son with my cell phone so some of it is out of focus and it's pretty shaky but you should be able to get a general idea of how the plane flies. 


Now go fly!



P51 Mustang Complete Plans.pdf

The color sceme for the plans is as follows:

Blue = Score Cut

Red = Crease

Green = Poster Board





Nathan_116 on September 16, 2013
I like your newfound i by of designing. Again, a little work to add landing gear/retracts, split flaps, and a scale canopy and its would be phenominal. Now all this bad boy needs is a real airplane to be paired after. Btw, what version of the p51 did you model it after? Also, could you make a tutorial on how to use google sketchup. I keep tying to figure it out but can't. I've been tryin to design a p40 warhawk for atleast 6 months but haven't gotten past a simple outline.
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filken on September 18, 2013
I made it after the P51D. I just finished painting it and the canopy looks much more realistic. It may not be scale, but my intention was to make it easy to build while keeping the look as close to the real thing as possible. I actually have an idea for 1 way landing gear that basically would stay folded in until you want to land. You would still need to hand launch because they wouldn't be able to retract, but you could land on hard surfaces without destroying your belly. It may not work but I'm toying with the idea. I am by no means a Sketchup expert, but I have some tricks that I have learned that I could share. I may put together an article if I have some time.
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filken on September 18, 2013
I just updated the pictures to include the new paint job.
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Jaxx on September 19, 2013
This was already a great looking plane. Now it looks even better! Did you airbrush? Starting the build tonight.
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filken on September 19, 2013
I wish I had an airbrush but alas it is not so. I just used Minwax, rattle paint and masking tape.
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filken on September 19, 2013
Oh and let me know how the build goes/flies.
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Jaxx on October 5, 2013
Had the plans printed, but haven’t had a chance to put it together yet. I can't wait to get it done. I'll let you know how it goes. Thanks again.
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ttprigg on September 17, 2013
Great plane and we loved the "color commentary" during the maiden flight! I am interested in knowing more about your sketch-up design process. Your model looks awesome! What version of SU do you use? I am using v-7 (to maintain a DWG import function) maybe I need to upgrade.... You mention that you "fold" the model. Do you simply create separate panels at the fold lines and rotate them or is there a function that I am not aware of? I am working on a small DLG similar to the "Weasel" and I am trying to figure it out in 2-D (and trial and error...)
Thanks in advance for your comments.
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filken on September 18, 2013
I use SU 2013. What I do is make the wing in the general shape I think it will need to be in a 2D version and then make it a component. The key is to move the axes (blue, green, and red planes) to line up with where I want the wing to "hinge". If I select everything except the hinge line and use the rotate tool it works rather well. I usually make the spar in 3D before I fold the wing surfaces so I know where to stop. Then once it is folded I use push/pull to make the surfaces 3D. That also allows me to use the intersect feature to make the outline for the wing cutout on the fuselage.
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ttprigg on September 18, 2013
thanks I will give it a try- I think that a sketch-up article would be great (if you have the time). Maybe there could be a thread on the forum about useful design tools. I understand that David and Josh were using 2D graphic design programs to produce their drawings. I am sure there are "tricks" we could all benefit from. Thanks again for your work!
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Jaxx on September 16, 2013

This is awesome work! I've been checking the site several times a day ever since you told me about this article. It finally got posted! Thanks for this.
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filken on September 16, 2013
Glad you like it. Tell me how your build goes and let me know if you have any questions or suggestions.
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filken on September 19, 2013
I just updated the article with new pictures of the paint job.
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Pete7694 on September 16, 2013
Very nice plane, and I love your camera man. He is so cute.
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goeland86 on September 16, 2013
+1 thumbs up to the cameraman! "Stop making me dizzy, plane!" hahaha!
very neat design though, love the concept!
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sailorJohn on September 19, 2013
Wow every time I log in I see a plane I want to build, retirement can be sooo stressful. Good job.
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Flynn on September 23, 2013
Fantastic design! Thanks for sharing. Maybe you, or someone can do a video overview of designing and going from sketchup to the final pdf version? I've tried with Paint Shop Pro, but i'd like to know how its done. Just an overview would be great.
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filken on September 23, 2013
After I get the 3D plans the way I want them I copy and paste the faces and edges of all of the pieces I want to have in the plans into another SU model. Then I have to rotate them all so they are on the same plane. The trickiest part is accounting for the foam thickness and A or B folds and making sure the real life version doesn't end up 3/16" larger or smaller. I also add interlocking tabs and recesses for the pieces that fold, and 3/16" score cut lines for the folds. Sometimes if I am feeling spry I will fold the 2D version along the fold lines to make sure everything lines up. After I have the 2D lines created and double check the measurements I use the free CutePDF Printer application to "Print" the plans to a PDF. The trick here is to make sure the camera is on "Parallel Projection" and from a "Standard View" such as left, or right. The view you see on the screen is what will print so zoom and size the window appropriately. I like to use the cut lines feature of PDF printing so I go into Print Setup before I print and change the paper type to "Post Script Custom Page Size". That way I can specify the "paper" size in the PDF so it ends up being a single page. You also want to make sure that when you print it as a PDF you uncheck "Fit to page" and "Use model extents", and make sure the "In the printout" and "In sketchup" scales are both set to 1 inch. Otherwise the scale of the printout will be all wrong. I also check the box for "Use high accuracy HLR". If you want to make sure there isn't any color or shading in the drawing you can enable the styles toolbar and use wireframe mode to hide the faces. I also go into Window>Styles and change the background color to white and remove the sky and ground so I don't have to waste a ton of ink when I actually print it. Once it is in PDF format you can use your favorite PDF program and print it out as a poster at 100% with cut lines and it should be the exact dimensions of your drawing. Hope this helps.
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FASTCRASHER on September 20, 2013
awesome plane and video guy!
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Paulobrasil on September 22, 2013
Hi FIken,

I i use SU to do my drawings too, is a vary intuitive way do make the plans.

I did one Sptitfire and have a same tail have you describe, What do you think about to push the wing position 15mm back to make the balance more ease to find?
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filken on September 23, 2013
Are you talking about moving the wings back on a Spitfire or a P51?
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Paulobrasil on September 23, 2013
Yes , i think the battery weight is not enough to proper balance the plane, and do not want to increase it.
The idea is to move the wing a little back, so the lever for the front weight will be bigger, and compensate it.
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Foam Addict on September 16, 2013
Very cool, I need to build a few friends for my spitfires!
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completemadbastard on September 19, 2013
Hey, FT guys! As soon as you kit this, I'm buyin'!
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Flying Penguin RC on September 16, 2013
Nice job on the P51
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185Dave on September 17, 2013
Very nice job. real good work. Keep the wind at your back.
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agiordan on October 22, 2013
Great Cameraman and great plane design. I decided to build it and so far it looks great. Not quite done, just need electronics. Question, what did you finally use for the CG? You initially posted 2 7/16" back from the leading edge. Is that what you ended up using? Thanks.
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filken on October 22, 2013
iI never got around to actually measuring the cg before my plane met the ground in a forceful way, but a good starting point is about half way between the spar and the leading edge.You may have to move it back a tad but this plane does not fly well with aft cg so as they say it's better to be nose heavy than tail heavy. Let me know how it flies. I'm interested to hear what your experience is.
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agiordan on October 23, 2013
Electronics arrived today so will be finishing it up in the next couple days. I'll start at the half way point and go from there and will post results. Thanks for the response and a big thanks for sharing!
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mboomrang on October 15, 2013
Great cameraman! Completely awesome!
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Gryf on December 13, 2013
"Why are they shooting off fireworks when it isn't Halloween?" I loved that... Another great design and build, and the usual excellent cinematography and commentary. Cheers!
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ankit dhama on December 15, 2013
hiii you say in this post that you make plane tail heavy but i see in video that tail heavy planes are so hard to fly so is no difference in tail heavy and nose heavy
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filken on December 15, 2013
Actually there is a big difference between nose heavy and tail heavy. To quote David "A nose heavy plane flies poorly, but a tail heavy plane flies once". Flite Test did a great video on how a tail heavy plane behaves. http://www.youtube.com/watch?v=00CGAPOp7A0 . If it's tail heavy it will want to climb and stall and the elevator will be extremely sensitive. At first the P51 was tail heavy and I almost wasn't able to land it. After I fixed the balance issues it flew much better. Each plane is a little different so you have to experiment with it to find out what works best. I hope this helps.
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Yogenh on February 6, 2014
I would love to see a twin mustang. Is that something that you will try??
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filken on February 9, 2014
Not trying to kill your dream but I don't really think that would work out too well. I think that the wingspan and overall shape of the plane would be too short to lend itself well to a twin setup. The P38 had a pretty high stall speed and the wingspan was 25% greater than the Mustang. I also try not to break too much new ground with plane designs. I'm no aeronautical engineer, I'm just copying what others have made that works. Don't let me stop you though! Just because I can't do it doesn't mean it's not possible.
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Gantorin on December 16, 2013
DUDE!!! I love it. Great job... I am so using this for my second build. AGAIN... Awesome job!
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ATCr on December 27, 2013
Do the plans print on a single large sheet? Do you have a PDF version that prints on multiple regular 12x8.5 sheets of paper?
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flight monkey on December 20, 2013
You have the best Copilot !! Awesome build!!! I love warbirds. This is next project. Thanks
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skindoc on March 5, 2014
Filken - love your designs and your son is a real character ! Great job on both projects !
Are you cutting your plans to foam board with a laser cutter or knife ?
Thanks !
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chobson303 on March 15, 2015
This is an easy build. Cut out the pieces Friday night and had it built minus the electronics on Saturday. I did have two minor problems because is didn't completely read all the build instructions. I used an A fold to put the fuselage together instead of a b fold which made the fuselage a bit narrower. I don't thing it's a big problem. My swappable unit still fits inside. I also didn't put any dihedral in. I guess I could go back and fix that but I'll try to fly it as is. Other than that it looks like a winner.
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P-51 Mustang Swappable Build with plans