Yes the article by Bud and Jim in EF 89 is interesting. Those Whirlwind blades
are beautiful and the new ferrules are not protuding outside the spinner anymore
as they do with the WarpDrive blades, adding drag without thrust.
The possibility to upgrade an existing Airmaster/WrapDrive prop with the new
blades
is very tempting.
However the article is disapointing regarding the compared cruise performances
of the WD and WW blades. Both Bud and Jim say they see a few more knots at the
same power setting. I have analyzed in details the figures shown in the charts
for the Monowheel and here are my comments:
1. Some speed figures are very wide spread, sometimes 10 knots for the same
conditions,
probably because the air mass was not as stable enough during the testing.
As we are looking for a few knots differences, that makes the comparison
a little bit doubtful.
2. The tendency is a speed increase of 2 knots with the WW blades at altitudes
up to 14000 ft.
3. The testing was done on the Rotax 914 only. I assume there would be some
similar
speed improvement also with the normally aspirated 912S.
3. Surprisingly at 17000 ft. figures show that the WW are slower than the WD for
3 out of the 4 power settings used for the test.
So to summarize, sorry Bud, I do not see the 5 knots increase you are talking
about.
Regarding the alleged reduced fuel flow with the WW blades at a given power
setting at the same density altitude, this is just not possible. That is the
law of physics. If the fuel flow is lower, that is due to either a lower power
setting or an inacurate fuel flow meter, not to the better prop blades.
To conclude I pass the following message to Airmaster: with the Airmaster/WD
blades
on my Monowheel, 912 ULS, one on board, full fuel, I consistently get 140
kts TAS at full throttle, 5000 RPM at 8500ft density altitude. If I could get
the proof that those WW blades would increase my cruise speed by 5 knots in
those conditions, I would place an order immediately!
Remi Guerner
F-PGKL
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http://forums.matronics.com/viewtopic.php?p=469294#469294
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