Engine Offset Question

[homme de fer]

I asked this question in the general forum and it was suggested that I move it here.

Gentlemen,

I'm building a pattern plane (a 40 size) but no where on the plans does it tell me how much right thrust and down thrust to put in.

Any suggestions?

Marc

P.S. The plane is a pattern plane from the mid 80's and I believe it is calling for 0 offset for down and right thrust. Am I best to leave it like that? Is there an advantage to having down and right thrust?

[Sonic Boomer]

Hey Marc, in my experience with .60 size older pattern airframes, I started with 0 degrees down and betweeen 2 and 3 deg. right . From that point, I fine tuned according a detailed and progressive timming chart. I can't remember where I got the chart but will check mine to see if I can find a source for you. With a .40 size airframe as you are planning to use, thrust issues are less of a factor. I would suggest you build as per plans, and shim to adjust as neccessary to achieve accurate flight, esp vertical up and down lines.

Boomer

[homme de fer]

Thanks for the help. My only issue with making changes is that I hav to build a cowl out of balsa which will make any changes to the angle of the engine very difficult.

I think I'll go with 2 degrees of right thrust to start and get creative with the cowl in case I need more changes in the future.

thanks,

Marc

[byrocat]

Marc, before you get too far along with the kit, check to see just how much material you have to remove for 2-right/2-down versus 0-0 thrust angles. If it's not too much, work with a single cowling.

Just make sure that the cowling is removeable and not permanently fixed until you've got the angles right.

Otherwise, I've got two suggestions:
1) don't finish the cowling until you're satisfied with the thrust angles. This gvies your room to make adjustments to the plates/gaps, etc. before you do the final detialed finishing.
2) make a spare cowling before you start the trimming process. Once you've got everything right, then you have a good cowling to fix correctly.

Making replacement cowlings is not hard, especially if you have an original to use as a model or mold master.

BTW, have you been able to measure the kit and see if the angles are in the drawings or if everything is drawn 0-0? Contacting the manufacturer and/or designer may resolve this.

[homme de fer]

Thanks for the tips byrocat,

The good thing here is that I'm working from plans; not a kit. So I can make the cowl up as I go. I'm going to try to make a balsa cowl that attaches to the fuse with screws from the inside. I saw some plans on how it's done and it doesn't look too difficult. The plans call for the cowl to be glued on but I don't like that idea.

Secondly, I want to try my hand at making a fiberglass cowl. So, I'm going to use some green styrofoam and sand to shape then practice glassing it. If it works out nice, I'll use it, if not, I'll use the balsa cowl.