I changed the subject because the topic changed...........  In response to Bill Kennedy

 

Bill,

 

Learning how to glide and the kind of prop used does matter.

 

Why?  Any Lancair is a slick plane and, as such, has a very low drag coefficient.  Thus, any other component of drag has a significant performance effect.  The prop is such a component.

 

The best glide speed range should be known and it is the target air speed after any engine mishap where the engine cannot be restarted.  Those aircraft equipped  with an AOA device probably have a indication of best glide regardless of aircraft loading. 

 

After achieving best glide, the next concern is rate of descent - a rate that is significantly affected by drag.  The prop pitch position and movement create greatly different levels of drag.  Thus, the following conditions should be examined: prop pitch and windmilling or stopped (whether the engine seized or a maneuver was used to stop the prop).   Consider the chart extracted from "Aerodynamics for Naval Aviators:"

 

Consider Constant Speed props first (prop pitch,windmilling).  For example, the Hartzell CS prop for a Lyc 320 has a flat pitch limit of 12 degrees and a coarse pitch limit of 40 degrees.  Using the chart above one can see that at 12 degrees, the windmilling prop has a great deal of drag while at 40 degrees the drag component is not much greater than that of a feathered prop.  The 40 degree position probably allows the prop to continue turning, thus keeping the pitch management oil pressure up.  And once the prop control is pulled to coarse pitch, as Bill Harrelson suggested, one should open the throttle to reduce engine intake stroke drag.  In my 320, the 0-thrust (engine approximately at idle) descent rate at best glide (about 107 KIAS) goes from 1500 fpm at cruise pitch to about 500 fpm at coarse pitch. 

 

A fixed pitch prop that is windmilling contributes a great deal of drag (look up the cruise pitch on the chart).  One should consider stopping the prop by leaving the throttle closed and carefully perform a climb maneuver (without a stall) to try to stop the prop from turning if the engine is not restartable.

 

If the prop is stopped, whether by maneuver or seizure, the drag is certainly less than a prop in cruise pitch that is windmilling.

 

Note that the aircraft performance (or lack thereof) of a stopped CS at flat pitch or fixed pitch prop at cruise pitch probably favors the fixed pitch prop.

 

Of course, the best engine failure performance condition is that with a feathered prop.   

 

Relatively speaking, remember that a C172, with its rivets, struts and wheels all contributing to drag, is less affected by drag from the prop in a failed engine condition.

 

Scott Krueger AKA Grayhawk

 

 

If you really want cheap insurance, learn how to glide and make a power off landing. Glide performance in a spin is really poor and the landing is no better (always fatal as far as I know). The kind of prop doesn't really matter. The pilot should be able to tell pretty quickly whether he can make a field or not, certainly 7,000 feet gives you plenty of time to analyze your glide. If you can't make it to the spot you want, land in a field. Airmanship is the best insurance I can think of.

> To: lml@lancaironline.net
> Date: Tue, 15 Dec 2009 16:33:59 -0500
> From: farnsworth@charter.net
> Subject: [LML] Re: Legacy Crash Watsonville?
>
>
>
> It is my understanding that the crash occurred close to the airport. I think
> I read it was about 1 mile. If that is true I think that the glide range
> difference between a standard constant speed prop and a feathering prop
> would have made the difference between making the airport and not.
>
> I believe it was reported that the pilot said he was at 7,000' when the
> problem occurred. The fact that he made it to within 1 mile of a safe
> landing with a standard prop (I don't know if he pulled his prop control
> back of not. I think the engine was not turning at the time of ground
> contact.)is evidence that the higher glide ratio of the feathering prop
> would have extended his range enough to land at the airport. With loss of
> oil pressure the feathering prop I have in my plane feathers automatically.
> It does not require me to pull the prop control back.
>
> Three years ago, at the Reno Air Races, Lee Behel was flying his Legacy in
> the valley to the West of Stead when he had an engine failure. It was touch
> and go on whether he would have an off airport landing or not. The
> difference was the feathering prop on his plane. If he had had a standard
> prop he would not have made the airport for an uneventful landing.
>
> I just think a feathering prop is cheap insurance.
>
> >
> > Lynn Farnsworth
> > Super Legacy #235
> > TSIO-550 Powered
> > Race #44
> > Mmo .6 Mach
> > Feathering Prop
>
>
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>
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