Paul's explana= tion is all correct for non-counterweighted and non-feathering propellers.= =A0 For these type of props it is just the opposite, the spring and/or coun= terweights drives the prop course and the oil pressure drives the prop flat= .=A0 The reason I bring it up is, these type of props are becoming more com= mon.=A0 In the aerobatic world for example the trend is to use a counterwei= ghted prop to preclude over-speed in the event of oil pressure loss during = 'acro' maneuvers, which is common.=A0 On some of the high wing load= ed airplanes (like Lancair's) many pilots are using full-feathering pro= ps for much better glide in the event of an engine failure.

Mike Larkin

President

LAC

= Legacy Owner, Builder

Kitfox Owner, Builder

Glassair Owne= r, Builder

Import Jet, Owner, Restorer

Airline Test Pilot= , Airbus

On Wed,= Aug 21, 2013 at 5:10 AM, <vtailjeff@aol.com> wrote:

Thank you Paul!=A0

F= or the rest...refer to your propeller owner's manual... Not Glenda the = Good Witch of the Wind.

Jeff ;)

Sent from m= y iPad

On Aug 21, 2013, at 6:40 AM, Paul Miller &l= t;pjdmiller@gmail.= com> wrote:

M= aybe we should refer to the manuals on how props go to low pitch. =A0It ain= 't relative wind or any other kind of wind. =A0It is a "really big= spring" in the hub. =A0From Hartzell:

(2) Centrifugal twisting moment acting on the blades moves the blades to= a low blade angle (low pitch) to increase RPM. Since the centrifugal twist= ing moment is only present when the propeller is rotating, a mechanical spr= ing is installed within the propeller to assist movement of the blades to a= lower pitch position as RPM decays, and to reduce the propeller pitch to t= he low pitch stop when the propeller is static. With the blades at low pitc= h, the load on the starter when starting the engine is reduced significantl= y.=A0

(3) Oil pressure opposes the spring and centrifugal twisting mom= ent to move the blades to a high blade angle (high pitch), reducing engine = RPM.=A0

(4) If oil pressure is lost at any time, the propeller will move= to low pitch. This occurs because the spring and blade centrifugal twistin= g moment are no longer opposed by hydraulic oil pressure. The propeller wil= l then reduce blade pitch to the low pitch stop.

On 2013-08-20, at 1:45 PM, Jack Morgan <jmorgan1023@comc= ast.net> wrote:

If oil pressure fails, standard CS props are driven flat by the relati= ve wind ...

--
Mike Larkin
LarkinAviationConsulting
LegacyL2K@gmail.com
602-770-6054

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