MT Propeller
Jesse Shookman
this type of prop. I recently sent MT a big long e-mail of questions,
which they will answer eventually. I also hope to talk w/ them in
person at this year's EAA.
See below for my questions to MT and their initial response.
I think the most intriguing thing I read on MT's website is the fact
that their "natural composite" props have no known speed limitations.
They don't say they do or they don't, just that they don't know.
They've never had one fly off or apart, or had one show signs of
structural failure after testing, and I assume that also includes
customer experience as well. That is a great to know, especially when
considering constant speed vs fixed pitch. All you really have to
worry about is what is happening to the engine, not your prop ...
although you can be sure I'll take plenty good care of my MT when I
buy it!
Jesse Shookman
I have several questions for you, so I apologize in advance for the
lengthy e-mail. My questions all pertain to aerobatic aircraft,
specifically 2-place biplanes like the Pitts and Eagle, and also
smaller single seat aircraft like the Laser 200 and Pitts S-1S. I
have my own Google discussion group for the Laser 200, and hope to
post any information you provide there.
First off, in a small aircraft like a Laser 200 or Pitts S-1S, do you
find the benefits of a constant speed prop outweigh the extra weight
of a governor and more complex prop hub? I noticed in the fixed pitch
prop section of your website that you state ...
"Because of the high vibration damping characteristics of wood, no RPM
restrictions are needed. Blade tip fatigue failures, as they often
occur with metal propellers are unknown."
This statement leads me to believe that the only RPM restrictions
would be those of the specific engine. Any specific information you
can provide on this subject specifically related to aerobatics?
You've mentioned on your website that your propellers can weigh up to
50% less than metal props. Also mentioned is that your governors are
lighter than most brands too. Which other popular governor brands are
you referring to, and how do the weights compare?
"The polar moment of inertia of the natural-composite propeller is
considerably lower compared to metal propellers, which results in a
much smoother run."
I've read from some of the Christen-Eagle google group members that
because of the low polar moment inertia of MT props that they don't
windmill very easily, and that one should make sure to have their idle
set well before proceeding w/ aerobatic flight, otherwise if the
engine dies one might have to use the starter to get the engine going
again. Thoughts on this?
"The governor produces usually oil pressure to increase pitch.
However, blades having counterweights installed i.e. for aerobatic
aircraft or twin engine aircraft always turn into high pitch position
without oil pressure and therefore use oil pressure to decrease
pitch."
For aerobatic aircraft w/ loss of oil pressure your governing systems
go basically into feather? Is this correct, and if so, why is this
the case? Drag considerations? Does this have anything to do w/ the
prop not being able to windmill easily? I was under the impression
that most single engine CS props went into fine/flat pitch w/ loss of
oil pressure.
"An unfeathering accumulator with compatible governors can also be
installed in aerobatic airplanes in order to prevent a RPM drop during
certain high or zero G aerobatic maneuvers. This unfeathering
accumulator maintains the oil supply to the governor for 5-10 seconds,
when the governor becomes short of the oil supplied by the engine."
Do you see many aerobatic aircraft installing accumulators? Is it
worth the extra weight? Can you provide aircraft examples, or
specific flight examples where the accumulator was paramount?
What are the drag vs performance considerations w/ 2 vs 3 blade
props? Square blade tips vs normal blade tips?
Have you tested 2 and 3 blade props on a 230 HP Lycoming IO-360. What
about the 250 HP Superior XP-400 SRE Engine?
http://www.xp-360.com/index.asp?content=15
Thanks much for your time,
Jesse Shookman
Jesse Shookman
thank you for your request.
I will forward your request to our engineering and they will answer
your
question. As we are close to Oshkosh and therefore already fly end of
next
week to the USA we maybe answer after our return your questions.
Sorry for any delay.
MT-PROPELLER
Entwicklungs GmbH
Eric Greindl
Airport Straubing-Wallmuehle
D-94348 Atting - Germany
phone: +49-9429-9409-19
mobil: +49-160-90709719
fax: +49-9429-8432
www.mt-propeller.com
Jesse Shookman
flies Unlimited w/ an Extra 300 in Germany.
Martin said the cruise between the 2 and 3 blade MT's is similar, but
that the 3 blade is better at generating power at low RPM's. He also
said the 3 blade has better breaking action on downlines.
There is also the issue of weight ... 3 blades are heavier than 2. W/
the Laser, maybe a 2 blade prop is all that is needed.
I will post the MT part number for the 3 blade prop here soon. Martin
said he has friends flying in Advanced right now w/ 3 blade MT Lasers.
Jesse Shookman
"Dear Jesse,
For the Laser 200 we have the following 2 props for sale:
3-bladed 74 inch diameter
MTV-9-B-C/C188-18a - USD $11,650
Composite Spinner - USD $1,250
The 2-bladed 76 inch diameter
MTV-15-B-C/C193-34 - USD $9,200
Composite Spinner - USD $1,200
The 2-bladed propeller has a weight of 53 lbs, the 3-bladed 66 lbs.
The governor which will work for both systems is our P-880-( ) for USD
$1,480, and has a weight of 2,2 lbs.
Please tell us, if your governor is front- or rear mounted to have the
correct reduction gear ratio.
With best regards,
MT-Propeller Entwicklung GmbH
Martin Albrecht
Vice President / General Manager"