I have a BTE Flyin King that I have a 91 four stroke in now and wanted to dip my toe into the gas arena. I figured that the Flyin King might make a good platform for a gas engine trainer and wanted to know if anyone has installed a gas engine? If so what size? I was thinking of a 20 or similar. Thanks!

I am building a Flying King right now for a 20cc gas engine. The engine is a RCGF rear carb 20cc from Henry at Aerovate. The engine was bought from him while he was a U.S. distributer last year. I ran about three tanks through it to see how it ran and to check the needle settings. It will be a very good motor for the F.K. The model was built with the intent to put a gas engine on it even though Bruce Tharpe cautions against it. I laid the engine on the plans and cut the fuselage off to accomodate the length. Since the gas engine weighs quite a bit more than a glow engine shortning the fuselage is going to allow it to balance without extra weight. I am covering the fuselage now
(the rest is covered) and should be flying it in a couple months. By the way, I am covering with light weight polyester dress lining and useing polycrylic to adhere it. Works great.

spasmatic: Thanks for the reply. I was thinking of trying that exact engine as well, in fact I just clipped out an advertisement for it from one of the rc magazines. How does the engine fit in the "as built" engine area? ( I don't have any dimensions of the engine)I would like to try and avoid doing any surgery, except strengthening up the firewall a bit. Do you have experience with gas engines or is this your first one? If you do, I may ask for some suggestions as this will be my first. It's funny you say that Bruce cautions against using a gas engine for the FK, when I wrote him asking for recommendations he didnt say anything about not using one, but that he didnt know what would be a good fit. His only mentioned concern was of the fit in the cowl area. For covering, I used Monokote...it works good for me and I know what I am doing LOL!

Your question as to the fit in the existing engine compartment would have me recommend you don't. It would extend out the from so far there would have to be a lot weight added to the rear to compensate. The engine mounts on stand-offs is the reason for the reach. I have two other gas engines, a Fox 4.2 and Fox 3.2 I have flown for several years. This RCGF is much smaller but shows good potential, especially for the F.K. The 20cc when I was trying it out on the test stand would idle at 1800 and would touch 9000 on the top end. I did not hold it there but was curious. Later when it gets broken in good it should do better. Going back to surgery on the nose, it should not be too bad. I cut mine off with a coping saw with no problem. Just reinforce it well. The resulting cheeks were combined with a balsa block connecting the two sides at the top. After shaping and sanding it has made a very nice cowl. The engine fits completly under the sides and top of the cowl with a small cut-out for the muffler on the lower left side. I also made it a tail dragger with oversize tires to allow for prop clearance. At present there is a APC 15x6 prop. on the motor.

I wasn't sure if the standoffs were the only way to mount it; I guess I just figured since it was a small gas engine they would have given you some options. Would you happen to have any pictures of the front? How far forward of the windshield did you remove the cowl area? I built mine as a tail dragger, so I shouldn't have any issues. I also have big 5" tires on mine as well, looks cool and taxiis on grass real nice with ease. Thanks for all the info.!

I modified my mount some because the carb needles didnt have easy access. Basically extended the lower standoff about 1/2". Good little engine.
Edwin

Looks like a nice engine close up. Thanks for the pic edwin.

Pat

The front edge of my firewall is 2 inches from the forward bottom area of the windshield. If you cut your front off, allow the sides of the fuselage to extend 1/2 to 3/4 inch past the firewall to allow for triangular stock reinforcement. Follow the previous angle of the firewall (slightly slanted) and it will also have to be cut from larger stock. Going back to the engine, mine is a smooth running as any glow engine of similar size.

Be sure to reinforce the wing attachment points and the empennage (tail group) with triangle stock.

With that much extra weight on the model, it will be easy to exceed the VNe (velocity never exceed) of the model even in a slight dive. The result could be folding the wing, failing wing attachment points or losing the tail group. Not pleasant to contemplate.

Good luck with your conversion and keep us informed of your progress. We need pictures too!


Ed Cregger

spasmatic: Thanks for the info. Did you happen to do any reinforcement as NM2K suggested in the post after yours other than the firewall area?

NM2K: Thanks for the info. as well. I didn't think about the wing attach areas or tail area. The FK can take up to a 90 size engine as speced/built according to BTE. The gas engine that I am considering and that spasmatic is currently installing has about the same power output, but with a weight gain of course. With this in mind, do you think it is still necessary to do the additional reinforcement other than the firewall area? Mine is already built and is "simply" a conversion, so reinforcement may not be that easy.

In answer to your question of reinforcement, NM2K is correct about adding stress to an airframe and to be sure you haven't exceeded its ability to absorb it. He comments frequently on these threads and I have a lot of respect for him. In my build, I reinforced the firewall, added some gussets to tie the rear stringers? for some strength to the rear fuselage, and filled the gap the stab sits on. The latter two items may not be needed but I went ahead and did it. The FK is meant to be a sport slow flyer and I don't think we will be stressing it too much such as acrobatics. I am wary of the front attachment of the wing to the fuselage. It looks like a potential weak point but I'm sure if it was Mr. Tharpe would have modified it. I think in your case I would shorten the nose and go with it. If the tail shows signs of excess shaking or vibration then you could add support wired easiley. The motor we are using is about a pound heavier than a glow motor but otherwise things are pretty much the same as far as vibration goes. It will get much better fuel mileage with a smaller tank than your glow engine.

spasmatic: Again, didnt think about the use of flying wires, I will have to keep that in mind if the need should arise. I will definitely shorten the nose as recommended and strengthen th e area as required.

spasmatic: what would you recommend the firewall thickness to be 1/4", 1/2" ply?

I am using 1/4 inch 5 ply plywood for a firewall and it should be more than adequate.

After flying my Flyin' King with an OS 46LA for a year, I have decided to buy a petrol engine. For sport flying, I believe that the RCGF 15cc will be enough (it is probably a lot more powerful than the 46LA). Other candidates are RCGF 20cc and CRRC Pro GF26i. The question is how much more the 20cc and 26cc vibrate, and whether the airplane will shake apart. Having the extra power of a 20cc or even 26cc would be great for towing. How big is the difference in vibration between the 15cc, 20cc and 26cc?

I switched from a saito 120 to the rcgf 20cc rear carb on my rascal 110. I didnt notice any real difference in vibration. Later I went back to the saito 120 on my rascal. The little bit of extra weight put the rascal over the limit by just enough that I couldnt thermal very well anymore. Nothing wrong with the engine. Just a flying style difference. I'm putting the 20cc on bandito grande I built from the Doc Mathews plans at rcm.
Edwin

Hello,I just got a FK NIB kit and bought a Magnum .91 4s. Can you tell me what motor mount you used? I heard Dubro but the usable rail length seems a bit short. Seems like the front engine mount hole will be right at the front end. [email protected]