Constant Speed Propeller models

[dalgrim]

I've seen this asked many times here and the usual answer was always to make a v-pitch and map it to the throttle channel and then have the throttle follow a preset curve. While this worked ok, it was more of a "in-flight adjustable" at best. So I made a true constant speed model using a headspeed governor and using the knob for the rpm select. The governor controls the v-pitch servo. This way its constantly adjusting the pitch to maintain a constant RPM on the propeller, regardless as to where the throttle is. I uploaded the model to the swaps if anyone wants to see how its done. It could be done to almost any model though.

download link to the swaps:Download

As a side note I think I found a couple bugs in the governor object and would love to go over them with any developers that read these forums.

 

[jbourke]

As a side note I think I found a couple bugs in the governor object and would love to go over them with any developers that read these forums.

Go for it.

Jim

 

[dalgrim]

ok First the Armed input option does not seem to work at all. I've even tried setting it to a fixed output at any positive number but the governor will never arm.

Second no matter what the gain is set to once the target rpm is reached there is a very fast fluctuation from -100 to 100 trying to balance the governor at the target. In my understanding shouldn't the governor vary the correction according to the distance from the target. IE if the rpm is only a little off why give a -100 output? That will just let the rpm drop too far creating a need to give a larger correction +100 which will then rebound it back over the target. This is usually not noticed as the rpm on a heli is usually slow to react and as long as the governor makes the + correction in time it will remain relatively close to target.

Obviously what I'm doing using a governor to control a pitch servo is nowhere even close to how they were intended but it does expose these quirks.

v-pitch: when a vpitch prop is set to about 3 or less pitch there is also a rapid + - thrust oscillation.

I believe the formula for thrust (leaving out blade efficiency) is:
T=(pi/4)*(D^2)*{v+(Δv/2)}*ρ*Δv

where:
T thrust
D propeller diameter
v velocity of incoming flow
Δv additional velocity, acceleration by propeller
ρ density of fluid

so if a v-pitch prop is at 0 pitch its Δv would be 0 making the thrust always 0.

 

[Lorenzo Jones]

governor armed input channel

OK guys, six years later and Armed Input on the governor still doesn't work at all. Both in RF7.5 and RFX Beta.

Also the v-pitch prop graphics moves back onto the engine nacelle at steep pitch, at least on corsair and P-51 models.

like dalgrim (above) I am trying to set up a constant speed prop as that is what real airplanes use.