Winter / Focus / Prop Drag

[Doug Cronkhite]

None of this is really necessary. Good solid aerodynamic theory is all 
that is required. I have a paper written by George Hicks that will explain 
a lot of this if you're mathematically inclined. I'll send it when I get 
home. The short version is a 10 pound pattern aircraft turning a 17" prop 
at max drag rpm will be about 15mph slower than a stopped prop. There is a 
margin for error depending upon parasitic drag of the airframe itself as 
well. What that max drag rpm actually is however is unknown (to me 
anyway). 

More info when I get home.

-Doug


On Mon, 8 Dec 2003, Larry Diamond wrote:

> This has been a very interesting thread on Prop Drag Vs Idle..
> 
> Couple of thoughts...
> 
> 1) From a non-engineering mind or non-aerodynamics mind, Stop Vs Idle seems
> to be about the same as a motor vehicle. The vehicle slows better when the
> tires are not in a skid.
> 
> 2) If there is enough interest there is a way, not only to prove
> this theory, but show it's predictability with Prop Disc Size, Idle speed, #
> Blades, and to a limit that nature allows, Temperature and Humidity. Also to 
> show the relationships on how one effects the other or how a subset effect a 
> single item, or etc...
> 
> The question is, "Who is willing to take this on?"; and, is it of any real 
> value
> for us to understand. For my skill level the answer is "no". For the Top 
> Guns and Designers of Pattern Aircraft, this may be some interesting data to 
> have.
> 
> Here is what I think the experiment would take.
> 
> A) A committed top pilot and caller (Troy N., Dave L., etc...) that feels 
> this is needed data and is committed to flying the same exact way, with 
> precision, to gather the best data. Precision would mean time Vs throttle 
> setting, altitude, attitude, etc....
> 
> B) Flight monitoring system that can down load data to a PC for collection
> and archive. Accuracy and repeatability is critical.
> 
> C) A team of folks that can work together to collect the data and keep the
> pilot performing the sequences the exact same way every flight and every
> attempt.
> 
> There is a scientific process that (if successful) will not only allow for a 
> single solution, but will also offer a formula for a given platform by 
> changing a predetermined set of variables. The formula will also be good for 
> parameters beyond what was tested.
> 
> The key point here is, "This is a long tedious process and the level of 
> detail
> required, not only to task but also documentation, is very intimidating to
> most." However, if done correctly...It works with very predictable 
> solutions...
> 
> The down side...
> 
> The formula will not be the same for every plane, even if it's the same 
> model
> with the same set up built by the same person with the same jigs and tools 
> and using the same fuel. However, the relationships should hold true for 
> similar airframes.
> 
> Upside...
> 
> We would know that it's a scientific based conclusion and can offer
> what has the most effect, # Blades, Idle Speed, etc...
> 
> Depending on the desired output, it can take from days to literally months. 
> The more complex, the longer it takes.
> 
> I would be willing to offer some assistance and guidance, but would not 
> tackle on my own.
> 
> If you think you might be interested in this project, let me know off the 
> list.
> 
> Larry Diamond
> NSRCA 3083
> AMA 5024
> 
> 
> ----- Original Message ----- 
> From: "Del Rykert" <drykert at rochester.rr.com>
> To: <discussion at nsrca.org>
> Sent: Thursday, December 04, 2003 7:59 PM
> Subject: Re: Winter / Focus / Prop Drag
> 
> 
> > If you are looking for irrefutable proof go up in a full scale or for R/C
> > take a clean design with low idling engine up and do some downlines. Bump
> > you idle trim up on some and leave it as low as you can on others. Will be
> > more pronounced with 4 cycles turning big side blade props.
> >
> > For more proof..  Ever see what happens to a model that kicks back up in
> > the
> > air but the prop stays on windmilling...  You can't fly it any more except
> > like a ton of bricks.. If that doesn't convince you nothing will. I flew a
> > friends model that it happened to. It only broke the prop on landing in
> > weeds as it landed on its nose.
> >
> >      Del K. Rykert
> >      AMA - 8928
> >      NSRCA - 473
> >      Kb2joi - General
> >
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> 

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