Grumman Bearcat R/C

Hello everyone, 

Here is my model of a Grumman F8F Bearcat. The intention was to make something similar to the Multiplex Dogfighter/Funracer/RaceWulf series, with similar performance, but then printed. Radio setup is exactly the same as on those planes. The wing is detachable from the fuselage with nylon bolts. 

Wingspan is 914mm

Length is 702mm

***NEW VERSION HERE https://www.printables.com/model/455109-grumman-bearcat-rc-v2***

I printed mine entirely from PETG and this was a mistake. It turned out way to heavy at 1900 grams flying weight. I will try one in LW-PLA in the future. I had the idea that if I print everything with just one perimeter and enough reinforcements, that I would end up with a stiff and light airframe. It's not light! Because the tail is pretty heavy I had to add 200gr of lead in the cowling to get the centre of gravity correct.

As reinforcements I used carbon fibre tubes. The wing joining tubes are 8mm. In the wing there is a tube of 10mm at the thickest point and rear spar made from a 8mm tube. The ailerons are reinforced with a 4mm tube.

In the fuselage there is a main tube from 12mm. 2 8mm tubes help to keep it all together. The belly is reinforced with 2 6mm tubes and the hatch with an 8mm tube.

The stabiliser has a 5mm tube as spar. The elevators a 4mm tube. A small piece of 3mm rod is used to align the stabiliser. 

The fin has a 3mm rod as spar and a 2mm alignment rod. The rudder is reinforced with a 2mm rod. 

I added 2 different fuselage split ups. In the end I used the B version for my model. 

Canals for servo wires, cut-out's for nuts and wing bolts and a strap for the battery are foreseen.  The cowling is open and exhausts are open as well. There is a third exhaust hole at the rear of the wing so enough air flow can go through the fuselage for cooling. 

I tried to make integral hinges for all flying surfaces. They were to stiff so I sliced them and made them with silicone. 

Cut-outs for Hitec HS-55 servo's are foreseen for the ailerons, elevator and rudder. 

The hatch is detachable and an opening is foreseen for a magnet to hold it. 

I only posted step files. My print files will only give you a plane that is too heavy.

For those who want to try it anyway these were my print settings

• Layer height 0.15mm for the fuselage, 0.2mm for the wings and tail
• 1 Perimeter
• 4 Top and 2 bottem layers
• between 4 and 2% infill depending on the part
• adaptive cubic infill and rectilinear on fuselage part 1
• support on build plate for the first fuselage part and everywhere for the second and last

Update on the maiden flight

It flew! I put it on a dolly to launch. Because of the high weight we didn't dare to hand launch it. First we put it on a small dolly but this was not really a succes. Have laugh with the below movie ;-)

Then we used a larger dolly to launch larger gliders. After lift off it pulled left and in a good climb but it was super nervous. I put the centre of gravity at the aft of the range of what I calculated (55 to 75mm at the wing root) to be flyable. I didn't dare to add even more weight. This was another mistake. Power to weight ratio was no problem. The aft cg however was and I think I put it in an accelerated stall before crashing it eventually. 

Here is a video of the drama

The prototype is total loss. The lead sled is dead. But it proved that the aerodynamic concept is sound. It managed to pull 1,9kg in the air. Now it just has to go on a massive ‘crash’ diet ;-) For the fuselage I know how to do it, for the tail however I have no idea's yet so input is always appreciated. Feel free to experiment as well with the provided files.

Here is a thread on RCGroups about it. Watch it for further evolution of the model. Work on the V2 has already started. I gained 115gr aft of the cg by redesigning the fuselage structure. 

https://www.rcgroups.com/forums/showthread.php?4321997-Grumman-Bearcat#post50766583

Tom