Re: Re: [indoor construction] VP or VD

From: Fred or Judy Rash <frash_at_chartertn.net>
Date: Sat, 21 Jul 2012 11:02:55 -0400

If you have a choice between Drela and Rash, always pick Drela.

Fred Rash

On 7/21/2012 10:03 AM, mkirda_at_sbcglobal.net wrote:
>
> Not being able to sleep last night, I was reading old posts and ran
> into this one. I dropped the data below into a spreadsheet and ran
> some calculations and got this:
>
> cm in Drela P Chord cm Chord IN
> 1.79 0.6981 83.72 39.85808722 3.53 1.3767
> 3.38 1.3182 77.07 36.07645866 5.87 2.2893
> 4.96 1.9344 70.81 34.92171369 7.54 2.9406
> 6.54 2.5506 65.06 34.46181123 8.58 3.3462
> 8.12 3.1668 59.87 34.28376074 9.05 3.5295
> 9.71 3.7869 55.24 34.28583424 9.05 3.5295
> 11.29 4.4031 51.14 34.33524276 8.68 3.3852
> 12.88 5.0232 47.51 34.45561892 8.03 3.1317
> 14.46 5.6394 44.3 34.57800208 7.14 2.7846
> 16.04 6.2556 41.46 34.72532129 6.04 2.3556
> 17.62 6.8718 38.93 34.8766222 4.67 1.8213
> 19.21 7.4919 36.66 35.03603496 2.68 1.0452
> 20 7.8 35.62 35.11276938 1.46 0.5694
>
> Averaging the Pitch, it is very close to 35 inches and pretty close to
> Helical.
>
> Tried running similar data in Fred Rash's PropMaker program and found
> a very different pitch distribution: I cannot easily copy the data,
> but Pitch ranges from 53 near the center to 41 at the tip.
>
> Both are roughly 17.5" props. Both have max chords of around 3.5"!
>
> Has anyone built props like these for F1D? It would be very
> interesting to see given the widest prop outline I have seen is 2.75".
>
> Regards.
> Mike Kirda
>
> --- In Indoor_Construction_at_yahoogroups.com
> <mailto:Indoor_Construction%40yahoogroups.com>, "markdrela"
> <drela_at_...> wrote:
> >
> > --- In Indoor_Construction_at_yahoogroups.com
> <mailto:Indoor_Construction%40yahoogroups.com>, "Nick Ray" <lasray_at_>
> wrote:
> > >
> > > With the 9cm max blade cord, would you use a lower pitch prop
> > > than the typical 32-36" range seen with F1Ds?
> >
> > For a given diameter, a wider blade dictates a higher pitch, not a
> > lower pitch. The baseline min-D prop I looked at has the following
> > chord and pitch angle distributions:
> >
> >
> > # r[cm] c[cm] beta[deg]
> > 1.79 3.53 83.72
> > 3.38 5.87 77.07
> > 4.96 7.54 70.81
> > 6.54 8.58 65.06
> > 8.12 9.05 59.87
> > 9.71 9.05 55.24
> > 11.29 8.68 51.14
> > 12.88 8.03 47.51
> > 14.46 7.14 44.30
> > 16.04 6.04 41.46
> > 17.62 4.67 38.93
> > 19.21 2.68 36.66
> > 20.00 1.46 35.62
> >
> > The P/D is roughly 2.2 over most of the blade, hence the wide chords.
> >
> >
> > > Also, is a Symmetrical prop still the most efficient?
> >
> > Propeller theory says nothing about the spar position on the chord.
> > That's a matter of flex under load.
> >
> > > Lastly, how would gradual change in diameter verses
> > > a prop folding at set intervals of torque effect the efficiency?
> >
> > How the diameter is scheduled shouldn't matter too much, since the
> > prop does OK at any diameter.
> >
>
>
Received on Sat Jul 21 2012 - 08:02:57 CEST