Page 2 of 2
Posted: Sat Feb 11, 2006 4:39 am
by blueldr
I question the loss of RPM on a colder than standard day. The power output is based on density and pressureand are supposed to be self correcting. On big radial engines the power check was made at field barometric pressure and the RPM was always supposed to be the same.
Posted: Sat Feb 11, 2006 5:35 pm
by dlinsley
Is that with a constant speed prop?
Posted: Sat Feb 11, 2006 7:20 pm
by lowNslow
dlinsley wrote:Is that with a constant speed prop?
As I remember the runup on the DC3, which has a constant speed prop, you would note the manifold pressure before starting the engine. You then would run the engine up to the noted MP before start and check the RPM with the props in the full forward position. I don't remember what the RPM was, but it was always supposed to be the same.
Posted: Sun Feb 12, 2006 4:51 am
by blueldr
Yes, that procedure is done with a constant speed prop too.
I cannot immagine any circumstance where the low pitch stop setting in a CS prop would allow the RPM to run up into the governing range of the high RPM setting of the governor. Most engines will run up static to 2100 t0 2300, but the high rpm setting of the governor will be well above that. Under these conditions no governing pitch change takes place, so the prop acts the same as a fixed pitch prop would.
Posted: Fri Sep 29, 2006 5:31 am
by futr_alaskaflyer
Anyone know of a rule of thumb to estimate the increase in static RPM per 1 inch of pitch?
IOW I want to repitch from 56 to 53 or 52. If I am currently getting 2230 static, what rpm can I expect at 52? Or is there any rule of thumb?
Posted: Fri Sep 29, 2006 6:20 am
by kloz
25 rpm per inch comes to mind.
Posted: Fri Sep 29, 2006 1:16 pm
by Bruce Fenstermacher
Had this conversation with a prop shop technician some time ago and seem to remember his rule of 50 RPM per inch. But there is more to it and no firm rule as it would change with a given prop design.
I'd talk to the prop shop that you where going to have do the work. I'll bet if they know what their doing they know what you might expect with a given change.
Posted: Sat Sep 30, 2006 12:27 am
by mrpibb
I had my prop pitched 53 to 50" on a em56 prop, I lost 15 mph in cruise but the squirrels dont throw acorns at me from the trees anymore
Posted: Sat Sep 30, 2006 2:27 pm
by GAHorn
mrpibb wrote:I had my prop pitched 53 to 50" on a em56 prop, I lost 15 mph in cruise but the squirrels dont throw acorns at me from the trees anymore
What! You never get far from the squirrels at THIS group!
