Recent ArticlesScale Swappable P51 - Design, Build, Fly
SketchUp for RC Aircraft Design Tutorial #7
SketchUp for RC Aircraft Design Tutorial #6
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
Battery: 2200mah 3 cell 25c LiPo
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.
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!
The color sceme for the plans is as follows:
Blue = Score Cut
Red = Crease
Green = Poster Board