How do you determine where the horizontal thrust line is??

Thanks Jumper.....

Mount the engine so that the prop shaft is in the center of the cowling and depending on the airplane some down thrust or the the shaft should be angled down usually 1 to 1 1/2*. Also most planes need about 1 1/2* of right side thrust.

How can you center the cowl horizontally, If you dont know where the thrust line? Isnt there a rule of thumb or something like that???

Jumper, it will depend on what you're building. Some planes (like trainers and other flat bottom wing planes) use down thrust while more advanced planed usually don't. Can you be more specific as to what you're building?

rule of thumb: the thrust line is usually in line with the stab. If you draw a line from stab location on your plans forward to the nose, that should be the center of the crankshaft. Adding down thrust or right thrust changes the engine thrust in relationship to the aircraft, but does not change the horizontal thrust line.

Hi Guys -

It seems to me that high winged planes (in relation to where the engine is mounted and thrust line) require downthrust. Consider that drag from the wing is coming from above which tends to pitch the nose up. Low mounted wings could have the opposite effect.

Ernie

Jumper -

There are some things that need to be cleared up about your question.

There is a fuselage reference/datum line, which is usually a horizontal centerline around which the structure of the aircraft is designed and built. The stabilizer is generally parallel to this line.

There is an engine thrust line which is a line that runs thru the crankshaft of the engine where a line on the plans may be drawn to represent the Thrust Line.

You may have a "horizontal thrust line" when these two lines coincide, but in most cases, the engine thrust line is adjusted to inprove the flying handling qualities of the aircraft.
Right thrust is used mostly to compensate for engine torque for conventional rotation engines.
Up thrust or down thrust is mostly used to compensate for pitch changes that accompany power changes. Generally the thrust line is adjusted so that it goes thru or slightly above the "vertical location of the CG". High wing airplanes generally have a higher vertical CG thus requiring downthrust; whereas low wing airplanes require little or no upthrust.

Got the picture?

Now if you can restate your question in terms of fuselage reference line (for measuring wing incidence angle) or engine thrust line (for measuring side and down thrust), then perhaps I can can have a better understanding of what you're asking.