Re: [indoor construction] VP or VD

From: <mkirda_at_sbcglobal.net>
Date: Sat, 21 Jul 2012 14:03:18 -0000

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, "markdrela" <drela@...> wrote:
>
> --- In Indoor_Construction_at_yahoogroups.com, "Nick Ray" <lasray@> 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 - 07:03:21 CEST