Originally Posted by zippi

I gotta be honest guys, I have never seen a firewall so thin on a plane this size. Just doesn't look that structurally sound to me.

It's designed to be a 50cc airframe. The fact that we all tend to put a much bigger engine in it, is not part of the design.

If you use the original aluminum brackets to bolt the firewall to the motor box, you really don't need a big and heavy firewall because the bolts that hold the engine on the firewall are going to be very close to the aluminum brackets. And that is where the forces are directed to. I chose to glass the whole thing inside and out and now the glass takes all the forces instead of the aluminum brackets. I practically could have used balsa-wood as a "firewall" because the wood is only acting as a spacer for the glass weave on both sides.

Originally Posted by Low_Cal

Nice work! And that's exactly where they break, nose comes off by windshield.

Thanks! I have also seen a couple of pictures of broken fuses. However, i didn't saw the landings that came before. If you look at the construction of the plane, that is the point where the forces from the motor box and from the landing gear are transferred to the rest of the fuse and the wing. So that is the weak point and the only major difference in the construction to "normal" ARF's (Yaks, Extra's, Edges) where the wingtube is part of the motor box and the motor box is much better connected to the rest of the fuse.

Originally Posted by Low_Cal

All Pilot RC planes seemed to be built this way, very light weight to the point of being fragile. Not just the Super Dec. As for the cost, Chief Aircraft has some good sales on Pilot planes.

Bill Hemple RC has a lot of Super Decs of different sizes; might try one of those.

You are correct. They are 'build to fly, not build to crash'. but it's not nearly as bad as i made it sound.

I tend to over-think and over-engineer my planes. Normally i scratch build my own planes. Last year i built a 33% Pitts M12 that a flying buddy designed. Just because i had time to kill and i didn't want a Hanger9 Beast. My ARF's are all heavily modified. I could never just bolt the engine on, throw in a few servo's and fly it. So i like to modify an ARF to try to make it bulletproof without adding to much weight and easier to assemble on the field. They can't do that in China, because the price would go up.

So, in my opinion.. Is the stock Decathlon a bad airframe? No, far from it. The quality is great considering it is an ARF. If you fly the stock Decathlon like it is supposed to fly (50cc engine, no high-G maneuvers and smooth landings) I doubt it will break.

But for me, with the bigger engine, flying IMAC just for fun (except for some violent snap rolls in down lines), and wanting it to last. I saw room for improvement and had time to waste.

I did not have a change to look at the construction of the Hempel Decathlons so i cant say if they are different from Pilot-RC and don't have that weakpoint. In my mind i would be comfortable buying either one. Also considering the excellent support of both companies.

If you are going to way over power the plane outside of the recommended engines then yes you may need to beef up the firewall. I have never needed to beef up a PRC firewall when running recommended engines

The angle brackets are far more than enough. You can fiberglass it if you want. it will increase the rigidity over the whole area but fiberglass in of itself isnt stronger than the brackets at the joints

I appreciate everyone's comment on the plane. I have built a giant scale gasser or two in my time and I have seen a lot of damage to an air frame come from the vibration from a gas engine. I guess I'm old school and like my planes with a little more meat on the bones. I have had many 50cc & 60cc planes with metal brackets on the engine box as this has become common practice on a lot of planes now but the firewall itself was still 1/4" to 5/16" thick. Seems to me if the plane is built that fragile that Pilot took the cheap route to save on wood on the inside and make it pretty and attractive on the outside. This is still a very nice looking plane and I was thinking of putting a 70cc Twin on the business end so I'm still on the fence about buying this plane or not. It's was going to be a winter project so I'll think about it until flying season is over and make may decision. I'm also looking at the H9 100cc Decathlon with a DLE 111.

I don't think a 70cc twin will fit inside the cowl, unless you are willing to make holes for the sparkplugs. At least not a DA-70. I carefully checked into this, as my initial plan was to use a BME 95, which is the same width as a DA-70. I'm using a DA-85 single cylinder engine instead.

As for the motor box, the wood used is about the thickness of what you would see on a 30cc plane, not a 50cc. And most pilots are using an 80cc or 85cc engine. You can fly it on 60cc, but its not going to hang on the prop unless motor is piped and you are at sea level. Its not that hard to add more plywood to double up the motor box, but you need to add to some other areas as well.

If I were going to do it again, I'd get a 100cc size Super Dec from Bill Hemple Models or H9 and fit it with a 120cc engine.