windmilling propeller effect....winter/focus/fuel/electric

[White, Chris]

Hi John,
I'm not sure you want to go there after the discussion I just had with our
propulsion/Aero engineering manager. He's going to provide some data which I
will be happy to forward to you.  In our aero-modeling of twin propeller
aircraft these effects must be modeled realistically to satisfy FAA cert
requirements.
Chris

-----Original Message-----
From: discussion-request at nsrca.org
[mailto:discussion-request at nsrca.org]On Behalf Of John Ferrell
Sent: Thursday, December 04, 2003 8:41 AM
To: discussion at nsrca.org
Subject: Re: Winter / Focus / Fuel/Electric.


I ask this question each time I see the opportunity. One of these days some
one is going to answer it with the math, I hope!

Flight training standards for full scale teach that a windmilling prop has
more drag than a stopped prop. Training execises sometimes refer to setting
power to "zero thrust" rather than idle.

I suspect that the difference is small, I am just curious. Nearly all of my
personal flight time in full scale aircraft was in high wing Cessnas or
Beech Bonanzas. The Cessnas are just too draggy in general for me to tell
much about the question.

In the case of the Bonanza I could argue the question both true and false.
For a give airspeed the Bonanza has two different flight attitudes, one
requiring considerably more power than the other. Bonanza pilots refer to
this as "being on the step". Most training manuals deny the condition, most
Bonanza pilots take advantage of it. The books are not always right.

There does seem to be better braking in the Bonanza with a little power but
the airplane is so clean that a slight change in attitude masks tiny power
changes.

Contrary to earlier practices, I never felt it wise to totally shut down the
engine in flight. Aside from the obvious risk of failing in restart the
sudden chilling of the cylinders shows up as expensive welding repairs on
the next overhaul.

IF there is an optimum power setting on a pattern plane in regard to braking
that is the setting we should be using rather than the slowest idle.

In the current period of Sumo style airplanes the effect is probably
insignificant.

John Ferrell
6241 Phillippi Rd
Julian NC 27283
Phone: (336)685-9606
johnferrell at earthlink.net
http://home.sprintmail.com/~johnferrell/dixiecompetitionproducts/
NSRCA 479 AMA 4190  W8CCW
"My Competition is Not My Enemy"


----- Original Message ----- 
From: "Adam Glatt" <adam.g at sasktel.net>
To: <discussion at nsrca.org>
Sent: Wednesday, December 03, 2003 11:16 PM
Subject: Re: Winter / Focus / Fuel/Electric.


> John, experimentation or theory, though I have yet to hear anyone
> qualify the statement that a slow turning prop causes more drag than a
> stopped one with an explanation.
>
> John Ferrell wrote:
>
> >As I am sure you are aware, full scale pilots have been taught for many
> >years that a windmilling prop creates more drag that a stopped prop.
> >
> >How do you determine what rpm generates the most drag?
> >
> >John Ferrell
> >6241 Phillippi Rd
> >Julian NC 27283
> >Phone: (336)685-9606
> >johnferrell at earthlink.net
> >http://home.sprintmail.com/~johnferrell/dixiecompetitionproducts/
> >NSRCA 479 AMA 4190  W8CCW
> >"My Competition is Not My Enemy"
> >
> >
> >----- Original Message ----- 
> >From: "Doug Cronkhite" <seefo at san.rr.com>
> >To: <discussion at nsrca.org>
> >Sent: Wednesday, December 03, 2003 4:28 PM
> >Subject: RE: Winter / Focus / Fuel/Electric.
> >
> >
> >
> >
> >>Well.. you fix that by setting a good idle speed before you take off.
You
> >>never let the motor stop in flight for a few reasons.. 1) as you
> >>described, it looks weird.. 2) a stopped prop is not the best solution
for
> >>downline breaking.. 3) the start/stop is hard on the gears..
> >>
> >>-Doug
> >>
> >>
> >
> >
> >=====================================
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> >#
> >
> >
> >
>
>
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