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

[Dean Pappas]

Let me add to that,
As an example, I replaced the aged and cracking chin cowl on the old  Maya II with a smooth round one (oval hole for the front corner of the head). The original had a big opening, no more than a half an inch behind the prop. I was always leaning on the engine for all it was worth. The revised cowl was more football shaped, and the plane went faster and climbed better. It could have as much to do with the chin (cheeks) interfering with the prop as anything else. The total frontal area did not change.
Dean




-----Original Message-----
From: davel322 at comcast.net [mailto:davel322 at comcast.net]
Sent: Thursday, December 04, 2003 4:26 PM
To: discussion at nsrca.org
Subject: Re: Idle/Braking (was Re: Winter / Focus / Fuel/Electric.)


John,

Thanks.

Yes, the slower the idle, the better the braking (at least within the range of 1,000 to 2,000 RPM).

I certainly agree with you that a Focus is more power hungry than a Prophecy (I've flown both quite a bit).

"cleanly shaped" - my words and a bit ambiguous - some clarity warranted.  "Cleanly shaped" has more to do with the shape of the nose than the total fuse volume.  "Traditional" 2M planes like the Prophecy, Elan, Omen, older Typhoons, Finesse, etc had relatively smaller fuses and streamlined noses.  In that same era, a Hanson Excess had a huge fuse - but was still easy to power (with careful building to keep the weight down) because the nose was nicely "cleaned up" - streamlined.

The earlier "widebodies" had much more fuse area and retained the streamlined nose - examples being EMC (very big at the time), Fashion, Hydeout, newer Patriots, etc.  More recent widebodies have less streamlined noses - Smaragd and Focus (not really a widebody to me, but less streamlined nose) for example and need substantially more power to fly nicely.

A Partner has more side area than a Smaragd - but it is easy to power - the nose is more streamlined than a Smaragd.  A Hydeaway has more side area than a Hydeout - but it barely takes any more power - the nose is still streamlined.

Adding fuse volume will increase drag, period.  However, if the fuse retains a nice airfoil shape (cleanly shaped), the increase in drag is relatively small.  Increasing fuse volume with a broader/blunter/wider nose (aka Smaragd) will rapidly increase fuse drag (and the need for more power).  Increased drag can be a good thing for some airplanes, some pilots, some schedules, etc.

Better / more clear?  Better yet would be a re-post by anyone who kept the prior info on drag contributions by various parts of airframe.

Regards,

Dave Lockhart
DaveL322 at comcast.net

> 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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