FLITE TEST MASTER SERIES P-38 LANDING GEAR
By Rndurrant / April 21, 2021
It’s been fun following the Flight Test guys, and since December, I’ve had the opportunity to scratch build and kit build a few of their designs. I like the way they think, their sense of humor, and interest they have in people. However to me……landing on the belly of your aircraft is……well….a crash! To each his own in the RC world, and I understand their motives and do applaud them. They’ve given us great airframe designs, and left it up to us to use our imagination to do whatever we desire with them, and so we do……
The area I fly is not favorable to belly landings, as well as being a professional Aircraft Mechanic and inspector, I have to have landing gear on my planes. So when I set out to build the Flite Test P-38 Master series kit, landing gear installation was a foregone conclusion.
Now we all know that there’s more than one way to skin cat…..Don’t know why you would want to skin a cat, but suffice it to say that each one of us could come up with a way that would result in the same ending…a nude cat. So with the information in this article, I present my method of taking the clothes off of a kitty, or rather, present my method of installing gear on the P-38, and leave it up to your ingenuity to better my method on your own project, and wind up with the same result, a P-38 with landing gear.
I studied pictures of the P-38 Lightening with the aircraft at rest on the flight line, to get an understanding of gear location and airframe attitude. I then considered the parameters I had to deal with on my model of the P-38. For scale appearance the nose landing gear should be mounted in the removable nose section, but for strength, I chose to mount it on the forward bulk head of the main airframe just under the electronics shelf. This would simplify things greatly as well as provide the most strength.
Because the nose landing gear is in a position aft of the actual aircraft gear location, it necessitated moving the main landing gear back proportionally to provide the proper look, and stability tricycle landing gear is known for. So the geometry is not scale, but it works and looks nice enough.
MAIN LANDING GEAR INSTALLATION METHOD
Bear in mind that all of my measurements are subjective, and given merely as a basis for my installation. Adjust as needed or desired for yours, so I suggest you plan things out and come up with your own measurements, or you can use these if they are acceptable to you.
Strength and aesthetics were my top consideration. The gear had to function time after time, hard landings, rough terrain and whatever else may be encountered. Mounting the main gear to the engine nacelle on the model would eventually cause fatigue and failure as that structure is not strong enough to take the abuse of landing. Just as in full scale aircraft, the landing gear is mounted to the robust structure of the wing. So with all that in mind, let’s get started……..
Measure 10” back from the forward surface of the firewall of each engine nacelle and mark the seam of each tail boom in this location. This is where your main landing gear struts will protrude through the nacelle. Cut a W=11/8” x L=2 ¾” section, on center out of the bottom of the tail boom. Keep in mind that this cut out is NOT centered on the protrusion of the landing gear strut, and is mostly aft of the strut location to allow fitment of the strut support platform. This cut exposes the bottom of the wing and the tail boom longeron support mounted to the bottom of the wing which is your foundation.
Aircraft structures often use laminated honeycomb panels for rigidity, strength, and weight saving. Using this technique, cut 4 lengths of foam board the exact height of the longeron and 3 inches long. These will aid the tail boom longeron in support of the gear as well as distribute the forces over a larger area of the wing, and will be sandwiched between the bottom of the wing and the support platform.
The gear support platform is made from 1/8” aircraft grade plywood. Cut it: W-1 1/8” x L 2 3/4”, to fit nicely on the laminated support on the wing. Draw a line through the center of the plywood support longwise, or fwd to aft, this will be used to align it to the center of the longeron at installation as well as to index your main strut on center. Check the fit of your plywood to the wing support, making sure it will sit flat and align etc.
All of my landing gear struts are made from 1/8” rod, bent to give the height and support needed. Do a little pre-planning on the overall height of your main landing gear struts, including the wheels and tires you want to use. If you make them too short, the rudders may contact the ground when rotating for takeoff, or your props may strike the ground etc. Also note that the P-38 lightening sits a little nose high on the flight line, so plan your main strut length to account for a longer nose strut, so the aircraft will sit properly and make a more scale appearance.
With your Main Gear struts bent in this a manner, they will provide support for the landing forces vertically and horizontally (X, Y, and Z axis) for those who understand machining etc. Make sure that when bending the 2 main landing gear struts, that they are symmetrical so your plane doesn’t sit higher on one side than the other. Now you can hot glue, epoxy, or even wire your struts to the wooden support platform. I chose hot glue. As you can see the vertical strut is located on center of the platform and is at the forward end. This positioning will allow for the horizontal support of the strut, and is the reason I cut the opening in the boom mostly aft of the center of the strut.
Tape a ruler to the bottom of the tail boom with the end at the strut location, set at 10 inches from the face of the firewall. Check the strut assembly fit first, by inserting the strut into the tail boom and on to the support on the wing, ensuring the vertical strut contacts the ruler. The ruler will position the main gear exactly at 10 inches on both sides keeping your main landing gear aligned with each other. If everything looks satisfactory, apply a liberal amount of hot glue to the surface of the wing support and re-install the strut assembly, keeping the centerline drawn on the plywood aligned with the center seam of the longeron, and the strut up against the end of the ruler. Eyeball the installation making sure everything is as you like. Just like John says….”hold this for 2 full minutes”.
At this point you have a couple of options, you can re-install the piece you cut out of the tail boom by cutting clearance for the strut and gluing it back in place, or leave it out if you like. Mine will be reinstalled.
Repeat this process on the other side.
NOSE LANDING GEAR INSTALLATION
Attaching the nose landing gear to the bulk head of the main frame follows the same basic principles as the main gear installation. Using plywood attached to the airframe for strength and rigidity.
Placing a piece of paper against the forward surface of the bulkhead, trace around the skin of the airframe to provide the initial shape for your pattern. Now draw another line the thickness of the foam board inside the traced line and cut this smaller shape out. Test fit making sure it fits the bulk head while positioned up against the bottom of the electronic shelf. Ensure there is enough clearance around the edges for the nose cone section to fit. Remove the foam board paper from the lower portion of the bulk head. If you leave the paper on, your landing gear will only be mounted as strong as the paper adhesion to the foam, so I removed it
Using the paper pattern you made, place it on some 1/8” aircraft grade plywood and trace the shape. Cut this shape out and check the fit on the bulk head. Make sure there is enough edge clearance to allow the nose cone to fit. Once you are satisfied, you can hot glue or epoxy the wood to the bulk head.
As stated before the P-38 lightening sits a little tail low – nose high on the flight line, so plan your nose strut overall length to make the aircraft sit properly if you like. Notice that the nose wheel on the P-38 is slightly smaller than the main wheels, so you’ll need to account for that also when measuring your nose strut over-all length.
I have a TIG welder, so I made my 1/8” rod a “T” strut to support both vertically and horizontally. You can simply bend your wire to get the support you need, just like the main landing gear. I also wanted to rake my nose strut forward a little to add stability and give the gear a more scale appearance.
To measure for the nose strut, I positioned my plane on its mains with wheels and tires mounted then set the airframe at a slightly nose high angle until it looked the way I wanted it to. Once that was set, I measured from the bottom of the electronic shelf to the ground, and accounted for raking my strut forward. This will give you an initial over-all strut length. Now Divide the diameter of your chosen nose wheel and tire assembly by 2, and take the result and subtract it from the over-all length of the strut you measured, to give you the axel position of the nose strut. This bit of figuring will give you the over-all length of the strut assembly after all your bends are made and wheel and tire mounted. If you want to make your nose strut straight down, that’s fine too.
Once you have your strut bent the way you need, fit check with a nose wheel installed and tape or hold the assembly to the bulkhead mount surface. Your plane should be sitting as planned. If not you can rake your nose wheel aft or fwd a little if you like to get the stance you want. If you don’t have your wheels yet, simply cut some circles out of foam board the size you want and glue them together to use as temporary wheels for fit checks and planning. My wheel diameters are: Mains - 2 ½” diameter; Nose 2” diameter.
Note- subtract ½” from the first leg of your strut if you bend your upper support like the picture, leave it if you weld your upper support like I did
Once you’re happy with the look and fit etc. glue the nose gear strut to the bulk head and make sure everything is centered nicely…..”hold for 2 full minutes”.
Now, all that is left is to modify the nose cone bulk head to fit your new installation. The ply and rod sit proud on the airframe bulk head so you’ll have to remove some paper and foam from the nose cone former to allow it to fit flush to the airframe once again. I removed the paper on my nose cone in the area that the ply and rod would contact, then very carefully, using a wood burner tool, simply melted the foam away in the areas I needed until the nose cone slipped right over the gear and mount. Be very, very careful using this technique, the foam quickly vanishes away around the tool so work with a piece of scrap until you get comfortable, before doing it on your airplane, or use a different technique.
You’ll also have to open the bottom center of the nose cone enough to allow the strut to clear.
One other addition I made while installing landing gear was to add alignment pins to the nose cone to main bulk head fitment, then I installed some pretty strong magnets to keep it all tight together. Something you might consider on your build also.
This installation provides a nice strong landing gear foundation for your P-38. The nose gear is rigid on my plane but you could easily modify it to rotate if you wanted it to steer etc. I’ve found that differential thrust programming steers the plane very well so you don’t really need to have active steering unless you really want it. To keep things simple I left it rigid and it works really well.
And that’s my way of skinning the proverbial cat.