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Author Topic: Profile fuse thrust line to wing center line  (Read 1653 times)

Offline Gerald Schamp

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Profile fuse thrust line to wing center line
« on: December 22, 2016, 08:30:52 PM »
This has probably been asked already, but here goes again. On a profile fuse plane, where should the engine thrust line be compared to the wing center line. Engine, LA .46, wing area 600 sq. in. Looking over some plans there seems to be a number of locations that work, but considering the engine weight, hanging on the side of the fuse, roughly a 56 inch span, plus or minus. A number of designs seem to be almost in line with one another and others are more what a built up fuse plane would be. Also this would have wing mounted landing gear, two inch wheels, etc. 

Online Tim Wescott

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Re: Profile fuse thrust line to wing center line
« Reply #1 on: December 23, 2016, 12:41:01 AM »
I suspect that the ones that are the same as for a full-fuse plane aren't thinking about vertical CG, while the ones that put down a bit are thinking about vertical CG.

AFAIK, getting the vertical CG right is more important than the location of the thrust line (although there's certainly folks who have built planes with the wings and tail all in line with the prop axis -- but I think that the guys that do that give a thought to getting the vertical CG where it belongs.
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Offline Dave_Trible

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Re: Profile fuse thrust line to wing center line
« Reply #2 on: December 23, 2016, 06:55:59 PM »
I think this is difficult to say without seeing on paper what you are working with.  Just think of it this way and you should be close enough in most cases:
On most full body airplanes the wing will be between 1/2" and 1" below the thrust line.  Going more than 1" like on some semi-scales can be done using some dihedral to bring the average centerline more near the thrust line.  This works in general terms where inverted engines, pipes and mufflers hang below the thrust line (landing gear too) which tends to pendulum outward as the airplanes fly in a circular tethered path.  This rolls the airplane in toward the pilot a little if not corrected by lowering the tether point to compensate. 
On the profile the engine cylinder lays horizontal so plays a much smaller part- actually near zero except for a hanging muffler.  The tank and fuel charge as well are along the thrust line.  Really all that now lies below are the wheels.  Much less drop of the wing centerline is then called for,  say half as much to nothing if light wheels are used.  Many good profiles are mostly co-planer.  I still like a little drop for the landing gear and engine torque which will roll the ship the same direction.  Just a little though- maybe 3/8" on a 'normal' .35-.60 size profile.  Beyond that you are into minor trimming with tabs or tweeking.

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