Idle/Braking (was Re: Winter / Focus / Fuel/Electric.)

[John Ferrell]

RE: " As most modelers, I don't have math to substantiate it, but a clean
widebody does not add much drag.  There have been prior posts to this list
noting that a cleanly shaped widebody fuse contributes a small percentage of
drag to the overall airframe."

Well, if you you fly a Prophecy with a YS140 and a Focus with a YS140 at the
same weight, the Prophecy has lots of excess power. The Focus has enough. I
am not sure about that qualifier "cleanly shaped".  The Prophecy seems best
with a 15-12APC and the Focus with a 16-10 APC.  I don't see much difference
in the airplanes other than the fuselage.

I will be tucking away your response for further consideration because you
are one of those flyers I can watch and learn better than I can fly and
learn!

I gather that you are saying as far as you can tell, the slower the idle,
the better the braking? If so,  we are in agreement. The training manual is
wrong.

If you consider the situation of a windmill extracting the power from the
wind I would expect the power extracted to be proportional to the square of
the rotor velocity.

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: <davel322 at comcast.net>
To: <discussion at nsrca.org>
Sent: Thursday, December 04, 2003 11:05 AM
Subject: Idle/Braking (was Re: Winter / Focus / Fuel/Electric.)


> As most modelers, I don't have math to substantiate it, but a clean
widebody does not add much drag.  There have been prior posts to this list
noting that a cleanly shaped widebody fuse contributes a small percentage of
drag to the overall airframe.
>
> I found Amir's post interesting - the 1.2 number was derived (if I read
his post accurately) from actual experiments.
>
> From all the re-pitching of APC propellers I have done (with an old
Prather pitch gauge), I can tell you without a doubt that the reading on the
Prather does not match the stated pitch of the prop - my understanding from
APC is that the true pitch of the prop is the centerline of the prop
airfoil - which rarely matches the flat side (bottom) of the prop.  The
bottom of the prop is still a good reference tho.
>
> Idle speed - I'm pretty comfortable stating I can tell a difference in 200
RPM (give or take 10% of idle speed) on a pattern plane I am familiar with.
Similarly, I can tell the difference in braking with a 1" pitch change on
the prop (also give or take about 10%).
>
> Regards,
>
> Dave Lockhart
> DaveL322 at comcast.net


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