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On Fri, 14 Nov 2008 07:25:03 -0800, Alan Baker
wrote: In article , Alan Baker wrote: In article , Stealth Pilot wrote: On Thu, 13 Nov 2008 22:20:25 -0500, wrote: How does a person determine what the proper height of an engine should be when building an airplane? If a particular engine design mandates the prop is 4 inches, say, lower than where it would be with the ----------------------------------------^^^^ engine originally installed, what effect will it have on handling, and what changes in downthrust might be advised? Draw few diagrams of the situation and you'll see what I mean. I'm not even going to try to draw that situation here. Basically, if the thrust line was already above the CoM and you move it up, then the change is smaller than the arctangent of h/l and if it was below the CoM the change is a little greater than the arctangent. Did a quick little check: As an example, a Cessna 150 is about 25 feet long and from looking at wikipedia's little jpeg, the centre of mass should be about 5 feet behind the propellor disc. So if you raise the thrust line 4 inches, you need to angle the engine up an additional 3.8 degrees; arctan(4/60). alan his corvair engine has the thrustline lower than the original O-200. so that would be down an extra 3 degrees. Stealth Pilot |
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