Power setting on 914 UL with c/s prop
in General Tech Discussion
11 years ago
As y'all can see, this is my first post in this forum. If I post something that's been discussed ad nauseam already, accept my apologies and, please, point me in the right direction. My cursoray search didn't turn up anything suitable.
Here's my question:
I am flying a gyroplane, powered by a Rotax 914 driving a constant speed prop. Reading in the Rotax manual, I find a table giving power settings which are recommended for fuel economy. I did a very careful series of flight tests, measuring fuel flow and airspeed over a large range of RPMs and MAPs. (BTW, I can upload the graphs of IAS as a function of MAP and RPM as well as fuel flow if the disccussion warrants.)
Now, I find that the power settings recommended by the Rotax manual are anything but ideal for my configuration. And that's not surprising, since they only take the engine into account, not the enire aerodynamic efficiency of the aircraft at various speeds, which has a large effect.
It turns out that my most efficient power setting (giving the highest miles-per-gallon or liter/100 km or range) is 4500 rpm at 35 inHg MAP resulting in 20.5 l/h.
My question now is this: what are the limits beyond which I have to worry about too low rpm for too high a manifold pressure? Are there other factors to take into account which preclude certain power settings for cruise (all at or below 5500 rpm, of course, and at or below 35 inHg).
Any input or pointers in the right direction are appreciated.
Thanks, -- Chris.
Here's my question:
I am flying a gyroplane, powered by a Rotax 914 driving a constant speed prop. Reading in the Rotax manual, I find a table giving power settings which are recommended for fuel economy. I did a very careful series of flight tests, measuring fuel flow and airspeed over a large range of RPMs and MAPs. (BTW, I can upload the graphs of IAS as a function of MAP and RPM as well as fuel flow if the disccussion warrants.)
Now, I find that the power settings recommended by the Rotax manual are anything but ideal for my configuration. And that's not surprising, since they only take the engine into account, not the enire aerodynamic efficiency of the aircraft at various speeds, which has a large effect.
It turns out that my most efficient power setting (giving the highest miles-per-gallon or liter/100 km or range) is 4500 rpm at 35 inHg MAP resulting in 20.5 l/h.
My question now is this: what are the limits beyond which I have to worry about too low rpm for too high a manifold pressure? Are there other factors to take into account which preclude certain power settings for cruise (all at or below 5500 rpm, of course, and at or below 35 inHg).
Any input or pointers in the right direction are appreciated.
Thanks, -- Chris.
