ORIGINAL: armody
Hi all,
I read this thread about glow engines and gas engines, as glow engines have glow plugs, gas engines have spark plugs which I have seen being used in cars or in motorbikes, and gas engines are run by gasoline, am i right or wrong. I have seen higher displacement glow engines as well as lower, so are the gas engines. I have a question, that when the displacement or CC/CI inreases rpm decreases, the smaller the engine more the rpm. Does higher rpm make a difference in engine's performance, and can it take plane to a vertical climb up? or the gas engines with low rpms they have more power?. Why the rpm decreases when the size of engine increases?
Thanks
Mody
Larger engines have lower RPM because of the inertia of the piston. I have a .061 that spins up to over 20K and a 2.2 gas that only tops out at about 8K. The piston in the .061 has alot less mass and a much smaller stroke. That means that there is less inertia to overcome and that the piston travels a much shorter distance for each revolution. As far as the performance goes, there is a trade off. Engines do make more power at higher RPMS, but the efficiency of the prop decreases if the tips of the blades go supersonic. Also, larger engines usually have more torque. This means that it can turn a larger prop with a greater pitch at lower RPMs to get the desired thrust. As far as vertical performance, that depends on the plane. Any plane will go vertical with enough power. Most large aerobatic planes have gas engines and unlimited vertical.