lml@lancaironline.net ?????????????

Adding to Robert's correct comments below, both the MT and Hartzell governors control engine RPM using a centrifugal weight type RPM sensing device. This technique changes the oil pressure supplied to the prop depending on engine RPM only. The system works the same regardless if the engine or the propeller is driving the crankshaft rotation as long as oil pressure is being produced by the rotation.

If oil pressure fails, standard CS props are driven flat by the relative wind while aerobatic props have counter weights mounted on the blades themselves which drive them to full course. The aerobatic governors control oil pressure opposite normal governors...... more pressure gives flatter pitch. This change is required for aerobatics so a temporary loss of oil pressure won't allow the engine to overspeed under high power.

Hope this helps clear up the confusion below.

Jack Morgan

On Aug 20, 2013, at 6:00 AM, Lancair Mailing List wrote:

From: Robert R Pastusek <rpastusek@htii.com>
Subject: RE: [LML] Re: Fw: [LML] Re: FW: [LML] Flaps on take-off?
Date: August 19, 2013 5:17:41 PM EDT
To: Lancair Mailing List <lml@lancaironline.net>

Wolfgang,
My MT prop/governor does not work as you describe below. Specifically, if the engine is turning (with oil pressure), I can control RPM within the mechanical stop limits built into the prop hub, and total power/drag. Idle power/min RPM/120 KIAS glide gives me 600-650 RPM; Max RPM in that configuration gives about 2600 RPM, and the drag increase is significant. At a bit above idle power, max RPM is limited to 2700 by the governor, all the way up to max power. Min RPM is maintained as power is added…for a while…but I’ve never gone much above idle power. with the prop at min RPM…hard on the engine…and it’s not a useful datapoint, but I suspect it will maintain 650 RPM through full power??

Bob

From: Lancair Mailing List [mailto:lml@lancaironline.net] On Behalf Of Wolfgang
Sent: Monday, August 19, 2013 12:40 PM
To: lml@lancaironline.net
Subject: [LML] Re: Fw: [LML] Re: FW: [LML] Flaps on take-off?

Where did the 320 and 172 information come from ?

Fixed pitch props will continue to windmill but what about constant speed ? - - I haven't tried this with a non-responsive, non seized engine.

The next question is what is the blade angle, resulting from a wind driven constant speed propeller, for the "max" rpm and "min" rpm lever positions.

The control loop gain will be "adverse" in that scenario (wind driven vs shaft driven).
. . . in the wind driven mode - as the rpm decreases - the pitch is made to go flatter - making the rpm decrease more - - -

After consulting with H&S Prop Shop here in Michigan, the light goes on.
It does not matter where the RPM lever is set.
With a non-responsive engine, the blades will go to the minimum pitch set by the physical stop in the prop hub,
. . . typically 10-15 degrees depending on setup for the particular installation.

Now a feathering prop is a different ball game . . .