Manifold pressure and airspeed

[Pruciak]

Maybe to some its basic physics but currently I'm baffled by a question. I made a test yesterday: i set my RPM to 2000 throttle to about 50% i turned on level flight, was going about 500 km/h then at the same RPM i increased the manifold pressure and I started to gain speed, It's ok - basic knowledge but please someone explain to me why is this happening? I'm not changing the revolutions of the propeller, I'm not changing the blade angles of the propeller I'm just increasing manifold pressure, how come my airplane is gaining speed? Magic? Maybe I'm stupid as hell but I just can't figure out why is this happening... The blades of the propeller "cut" the air with greater force or something like that? Please someone elaborate.

[chris455]

With any constant speed propeller, irrespective of what rpm you have chosen, the propeller governor will endeavor to maintain the engine speed you have chosen using the propeller pitch control.

Increasing manifold pressures causes the propeller governor to increase the angle of attack of of the propeller blades to maintain the selected rpm. This results in bigger "bites" of air passing through the propeller disc, increasing thrust, thus airspeed ( all else remaining equal).

There may be more elegant ways of explaining this, but this is the gist of it.

Powerful thing, torque. ?

Hope this helps. There are some real "gearheads"  ( no disrespect intended) on the boards that may be able to break this down further still-

S!

 

Edited April 21, 2018 by chris455

[Pruciak]

Now i understand, thanks a lot!

[dogeness]

I am guessing you were flying a constant-speed propeller aircraft. In such aircraft, you set a desired RPM and the automatic governor will increase/decrease propeller pitch across various airspeeds in order to maintain that desired RPM. So, increasing or decreasing M.P. will not see an increase in RPM in the tachometer. It will, however, see an increase in the thrust. If you increased M.P. and there wasn't an automatic RPM governor, you would see your RPM rise. However, since there is a governor, on increasing M.P., the governor will change the pitch of the propeller to make it more coarse, which means there is more "resistance" to the spinning of the propeller. So, even though you have increased M.P., the propeller is still spinning at the same RPM.

[Pruciak]

I thought the blade angle stays the same all the time and that was my mistake.

[Mitthrawnuruodo]

 

 As has been said in the previous comments, you're seeing the torque increase while the angular velocity remains constant. Therefore, the power increases. 

 

Such systems allow efficient propeller and engine operation in all phases of flight. In principle, it's quite similar to the gearbox of a car (of course, the mechanism is very different).