About the Propeller Article…
I WOULD LIKE TO CORRECT a possible
misconception about MT propellers in the
December issue. The author states, “About half of
the composite props I saw were made by MT of
Germany.” MT propellers use two types of blade
material—aluminum and what MT calls “natural
composite.” MT describes natural composite as
“high compressed wood in the root and lightweight
wood in the remaining body.” …MT blades are not
carbon fiber construction as typically thought of
when the aerospace term “composite” is used. The
blades are made of wood, plain and simple.
The final machined wooden MT blades are
covered in fiberglass, given a stainless leading
edge, and installed in the blade ferrule with
special lag screws. The blades are then installed
into an aluminum hub similar to a McCauley style
of hub (one piece). There is absolutely nothing
wrong with these time-tested wooden propeller
blades providing they are given the proper respect
and maintenance. This style of blade construction
was also utilized in the Aeromatic/Tarver and
Beech-Roby, to name a few, over 60 years ago.
_
William R. Goebel, EAA 109387
Rhome, Texas
The Pratt and Whitney PW1000G Engine
JUST RECEIVED THE JANUARY ISSUE. It looks
just great, however there is a serious technical
error on page 12 (AeroInnovations). You describe
a new turbofan engine by Pratt and Whitney
that develops 30,000
horsepower. That much is
okay… but your description
of the other engine
parameters is way off the
mark. You have written
that the engine only
weighs 220 pounds and
is only 19. 65 inches in
diameter….it is physically
impossible to develop
that much horsepower
in that small a package…. This engine would weigh
1,000 kilograms or 2,200 pounds. It would also be
5.0 meters in diameter, or more than fifteen feet.
_
Michael Tate, 634548
Pickerington, Ohio
PRATT & WHITNEY ENGINEERS DEVELOPED a
turbo fan engine with 30,000 pounds of thrust,
not horsepower as stated. Further, the design
exercise was to develop a quieter engine by
reducing the turbo fan rotational speed via a
gear reduction unit. This innovation lowered
the sound pressure by about 20dB. This engine
was not developed as a small lightweight engine
as the article stated.
This article summary was
incorrectly worded as you
and several other readers
pointed out. It was the
gear that was 0.5 meters
in diameter and weighed 100 kilograms, not
the turbine engine, and the 30,000 horsepower
should have been 30,000 pounds of thrust. We
apologize for these errors and promise more
discreet editing in future columns. For a direct
link to the original article on this subject, visit
www.SportAviation.org.
The AeroInnovations column in the magazine…
and in e-Hotline…is intended to offer innovative
ideas to members for review. EAA doesn’t
necessarily endorse the concepts, but rather shares
the information for member discussion.
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