Viewing a single comment thread. View all comments

DreamyTomato t1_jdvw9hj wrote

Reply to comment by quietflyr in Does living in an airplane flight path, near an airport, pose a health risk? What happens to the lead from the jets fuel? by [deleted]

Why so much torque? Cars go up hills, but piston engines are pushing a propellor through air, which at LOW revs doesn't offer much resistance.

Or am I missing a point that cars have gearboxes and maybe planes have no gearboxes? So 2700rpm is the prop speed, same as the crankshaft speed?

(and I believe instead of changing rev speed, prop aircraft change the blade angle. So the engine stays at the same speed, but the load can vary greatly?)

1

quietflyr t1_jdvx47w wrote

An O-360 is a direct drive engine, the propeller is attached directly to the crankshaft. And that's the case for most light aircraft piston engines. Some (especially more modern ones) have a single speed reduction gearbox.

The only thing an aircraft piston engine does is turn a propeller through the air, and that absorbs nearly 100% of the power produced by the engine. Swinging an 80 inch diameter propeller at 2700 RPM will use a lot of power and required a lot of torque.

You raise variable pitch propellers or constant speed propellers. These are used on some piston engine aircraft (the rest use a simple fixed-pitch propeller) and all turboprop aircraft. They do vary the pitch of the blades to find the most efficient angle both in climb and at higher speeds, due to the mechanics of how a propeller works. But this doesn't really affect the fact that a ton of torque is required to turn the propeller.

5

motorslug t1_jdvxou6 wrote

That's correct. The bar majority of piston engine aircraft use a direct drive from engine to propellor. More complex aircraft use a constant speed propellor as a form of gearbox, allowing the blade pitch to be altered while maintaining a constant blade rpm.

2