For those seaking an hydaulic prop I note that MT now offer an hydraulic
prop for the Dyn Aero range of A/C. Its use prevents the use of a Vac
pump (which I don't want in any case) its a little heavy considering the
prop itself and the hydaulic governor etc.. In favour its very fast
changing pitch and has the MT quality. I am not convinced that two
blades are more efficient than three. Especially on the Rotax 912S which
has a higher reduction ratio. It may be more efficient to have two
blades at high speeds but my money is on three blades in the takeoff and
climb phase. For us in the UK that's a major consideration. I'll put my
three blades up against two any day of the week.
Jerry
lts@avnet.co.uk
http://www.avnet.co.uk/touchdown
----- Original Message -----
From: Terry Seaver
Cc: Europa Mail List ; Whirlwind propellers
Subject: Re: Whirlwind prop for motor gliders?
Bob Jacobsen wrote:
The factory Tri-Gear Europa was damaged in a landing at Lakeland
before
Arlington and did not fly out. It had nothing to do with the engine
- the
nose gear had a weld fail. It does have a Whirlwind prop that was
undamaged
in the incident (one advantage of 2 blade props!)and the plane will
be at
Oshkosh.
The Airmaster and some of the other electric VP props do fully
feather.
Currently the Whirlwind does not offer this although Bob from Europa
Lakeland said there has been some talk of it - maybe in the future?
The
Rotax is easy to stop the prop turning and won't start windmilling
again -
that is what saved the prop on the factory tri-gear. They were able
to stop
it before landing when they knew the gear had a problem. Remember
though
that even a two blade prop presents a lot of drag if it's not fully
feathered.
Bob Jacobsen
A131
We chose the Whirlwind prop because it has
the lightest weight (and the weight is further back),
has very good performance (two blades are more
efficient than three), and is hydraulic. I had
some concern that the electric props would not keep
up with the speed changes during aerobatics
(if you can't do some occasional acro you might
as well take the bus).
The early reports from the factory say that the
difference in glide ratio between feathered to
non-feathered is estimated to be 27:1 vs 25:1.
If true, I don't consider the lack of feathering a
show stopper.
There is no doubt that the prop will stop at some
low speed, the important question is; at what speed
does it begin windmilling again ? 80 kts would be
great, that would allow you to slow down to optimum
gliding speed to stop the prop, and allow air restarts
by diving to 80+ kts. 45 kts on the other hand would
be a real problem, with the engine turning over most
of the time.
Terry Seaver
A135
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