That's good news for tri-gear builders like me, but the _theoretical_
efficiency difference in cruise, 2 vs. 3 blade, is supposed to be very
small in favor of 2 blades, from everything I've read. Your test has
confirmed that both your ASI's are accurate, but how's about MP, RPM?
There's also issues of whether prop diameter is optimum for cruise on
both installations, and whether blade designs (they're airfoils) are
identical in efficiency for two different mfrs. Then there's any
build differences.
I'd think you could compare relative aerodynamic efficiency by
side-by-side, power off glide at same glide angle. Same fuel load and
adding back the 100# empty-weight diff with ballast even, to get
scientific. And need also a pitch setting for minimum drag both
props.
Regards,
Fred F., A063
Garry Stout wrote:
>
> Graham Singleton wrote............
> "I believe that a 3 blade composite prop will always be better than 2
> blade wood on an efficient airplane like the Europa. The intrinsic yaw
> vibration cause by any 2 blade prop will damage the laminar flow over
> the wings and result in a drag increase."
>
> I am not an engineer and won't try to be one, however I do have some
> real world experiences. Yesterday my good friend Bill Stewart and I
> took to the air in our Europa's for the purpose of comparing air speeds
> at comparable power settings. Bill has a monowheel with an electrical
> driven 3 blade constant speed prop - Warp blades, while I have a trigear
> with a 2 blade Whirlwind hydraulic constant speed prop. We both run
> 914's.
>
> We leveled off at roughly 1300 ft elevation and set our power at 30" MP
> and 5,000 RPM, which is our usual cruise power setting. We both
> indicated 130 kts and flew dead even, side by side. Our actual speeds
> were identical with neither plane gaining on the other.
>
> Conventional wisdom would tend to favor a higher speed in the mono due
> to less aerodynamic drag, and in our case the mono is roughly 100 lbs
> lighter than the trigear. One might therefore conclude that the 2 blade
> prop on the trigear is more efficient, making up for the weight and drag
> penalty.
> That's all I can figure out. Anybody out there have any other
> explanations for what we experienced?
>
> Regards
> Garry
> N4220S
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