ORIGINAL: snacker
I put together my first fuel tank tonight and the metal tubes had to be cut back to about 1/4". I had to do this because it was running into the back of the engine and kinking the fuel lines otherwise. It's goinig on a Sig Sr Kadet with an OS .91. Could this present any problems? If so, how can I fix them? I don't want any fuel lines falling off.
Here's a pic. Not the greatest, but I think you can see what I'm talking about.
Measuring is ok, but nothing beats a test fit.
1/4" is getting close to too short. It would be better to have just a bit more tube and it's easy to find room for that. The fuel tank inserts into the fuselage right. So insert it 1/4" less than it'd be if bumped up against the inside of the firewall. Worried that it might not be supported by the round hole in the firewall? Fix that with a spacer. It's easy to make one.
You can either use a Forstner bit and drill an appropriately sized hole, or simply glue together the right thickness wood scraps with the right size hole inside them. Then glue the spacer to the inside of the firewall. Use epoxy. And after it's set, mix some more and coat the entire inside of the firewall, spacer and all, and the inside of the fuselage as well.
When you use a greatly larger engine than recommended for any model, you're bolting on a lot more than the structure was designed for. So you need to consider that the front of that airplane is going to need a bit of help. Do what you think would be necessary. Later on, you will have a chance to autopsy and see how your reinforcment worked. If it doesn't happen soon, then you'll get feedback from that. That suggests you did enough. If it does happen soon, that's also good, because you'll see early on if your improvements worked or not. And have a chance to refine your hot rodding skills.
Also, think about the prop that motor is going to prefer. Is the stock landing gear going to give enough ground clearance? It's especially critical on landing. Stock gear is often marginal for the recommended engine's weight. Or is usually marginal when a heavier engine is used. And that's not even considering the prop clearance, just the added weight.
Lot's of things happen when you hotrod an existing model design. And a little forethought can make the hotrod run. Without it, you wind up with a one-shot hotrod. You've already run into a very insignificant result of a shoehorn job. There are lots more to come.
Good thing about our hobby is that we can try almost anything we can come up with. Best thing about our hobby is that we can usually make almost anything work. And no research animals are killed in the testing. Well, other than a few earthworms on occassion.