What size engine should i use?

[Oske]

So im in the process of building a giant foamy plane. I really want to make it run off of a gas engine but thats something i have no clue about.

The wingspan is 90 inches, fuse is about 60 inches long and i estimate it will weigh about 1 kilogram when finished.

I dont want any specific engines, just want to know what size engine to look for.

 

[Montiey]

To start, find 2 planes with a similar wing style, and then the same wingspan, weight, etc. all as close as possible. It might be hard to find a model that is identical to what you're building, but if it gives a suggested motor, then you know where to start for your plane.

…Other than that, I have no experience with engines (the post is a glorified bump).

 

[Joker 53150]

First, when you say "gas" I assume you mean gas/petrol and not nitro. With that said, it'll depend in part on what type of performance you're looking for. For a 90" wingspan 1 kilogram (2.2 pounds) is super light so it won't take a lot of power. Since it's that light, you may also run into problems with wind blowing it around, something you probably already thought about. For engine size I'm guessing around 9 or 10cc would work. I'm running much heavier planes, in the 15 pound range, with 20-26cc gassers.

What type of foamy are you looking at, DTFB, fanfold, solid core, or...? If you haven't done gas before there are a lot of additional considerations (also known as expenses) to be aware of. Optical kill switch to keep things safe, an electric starter to make that chore much easier, a field box is certainly useful, high-quality oil to mix with the gas, etc. The gas engines also bring a lot of vibration to the party so your airframe will need to be able to handle it. The firewall especially, where it meets the rest of the fuselage. Again you may have considered all this, but I don't know your background so I'm just trying to point out some of the potential headaches.

 

[Oske]

First, when you say "gas" I assume you mean gas/petrol and not nitro. With that said, it'll depend in part on what type of performance you're looking for. For a 90" wingspan 1 kilogram (2.2 pounds) is super light so it won't take a lot of power. Since it's that light, you may also run into problems with wind blowing it around, something you probably already thought about. For engine size I'm guessing around 9 or 10cc would work. I'm running much heavier planes, in the 15 pound range, with 20-26cc gassers.

What type of foamy are you looking at, DTFB, fanfold, solid core, or...? If you haven't done gas before there are a lot of additional considerations (also known as expenses) to be aware of. Optical kill switch to keep things safe, an electric starter to make that chore much easier, a field box is certainly useful, high-quality oil to mix with the gas, etc. The gas engines also bring a lot of vibration to the party so your airframe will need to be able to handle it. The firewall especially, where it meets the rest of the fuselage. Again you may have considered all this, but I don't know your background so I'm just trying to point out some of the potential headaches.

First off, im using dtfb and really trying to make it steong but easy to build.

I didnt consider the wind but ill probably be flying in mostly calm weather.

As for the vibrations, ill probably take care of that with rubber bushings, even if it doesnt get rid of it itll probably help a lot.

Thanks for pointing that stuff out, i really dont want to forget anything and then have that sabotage everything.

On another note ive had people reccomend 20 or 30 cc engines, as they say the smaller ones are "less user friendly". The plane im using this engine for is supposed to be an all around cargo/utility plane, so is an engine that big practical or overkill (i was thinking of having at least a 1:1 t/w ratio, maybe even higher for glider towing)?

 

[Joker 53150]

Bigger engines require stronger construction, more weight, etc. I'm not saying it won't work, but 20-30cc seems awfully big for such a lightweight plane. You're looking at something about the size of a Senior Telemaster, and the one I've got to build will use a 20cc gasser, and many say 20 is overkill. Note that the Telemaster is a bit heavier than the foam you're looking at. For your final weight, if you're planning to use all the regular stuff for modern gas engines, figure in the ignition box, physical kill switches, optical kill switch, gas tank, gas lines, batteries (if you run 2, which is common for electronic ignition), plus the regular servos.

 

[Bricks]

Figure out how you are going to fuel proof this airframe I don`t think hot glue and gasoline may mix well for the weight of your plane with Glo I would be looking at a 46-55 size gas would be a 10cc all up weight once done I would guess in that 4-5 lb area.