Placing engines high on the fuse like an A10?

[SpaceToad]

Hey all,

So I am working on an A10 project, and this also applies to passenger aircraft like Airbuses and Boeings... How do you get away with having engines mounted high above the center of mass without having much torque from the engine?

[Plusck]

If you look closely at a drawing of an A10, the actual thrust vector from the engines isn't actually that high off the centreline of the aircraft. The intakes are higher (mainly for survival purposes: it's very hard to hit the intakes from the ground because they are just above the highly-armoured wing, above and behind if the A10 in question happens to be coming to say hello to you and your tanks) but the jet exhaust is significantly lower and directed straight back, not down.

So yes, the A10's arrangement is not the most efficient, and it probably relies on the significant lift of its wings to help stability under high thrust, but the A10 as a whole was made for survival and extreme maneuverability at low speeds, and the elevators being positioned just under the jet exhaust probably multiplies that maneuverability and control.

Likewise with big jets: the engines and the central fuel tank are the heaviest bits of the plane, and so they are not that far at all from the centre of mass. I would assume that at maximum thrust this will tend to push the nose up, but that also seems to be pretty much desirable behaviour.

Edited March 30, 2016 by Plusck

[Clockwork]

I've had first hand experience wih A-10s, and I've wondered blut the placement of the engines as well, but looking at pictures of it, the engines are actually very close to being in line with he (presumed) center of mass. If you're using pylons, I'd put them closer to the middle of the fuselage (very slightly off above) and at a very slight angle upward. The tops of the engines of the real A-10 are only very slightly above the top of the fuselge. I hope that description made sense! Good luck.

Edited March 30, 2016 by Clockwork

[steuben]

you can also angle your engines so that there vertical thrust offsets the torque they put into the system. Though the way I do it is to slap on enough gyros to offset the torque. KER would help you there.

[PnDB]

@steuben has the right idea.  If you look at a diagram of the A-10 engine, the exhaust direction is angled slightly upward, pointing the thrust vector pretty much straight through the plane's center of gravity.  Radio control planes with pusher-props mounted above the fuselage do this as well.

From Wikimedia -- trace a line down the center of the engine exhaust tube and see where it passes through the plane: