Hi Hartmut,
I respectfully disagree with some of what you suggest here. Here's why:
It's been a long time since the Ercoupes left the factory, and some
"good flying techniques" have changed with increased experience and the
necessity to burn 100 LL fuel instead of 80/87.
The Approved Flight Manuals for both the Alon and M10 do not lump tests
for "function" and "performance" together as you propose. I believe
the full power static run up necessary only to verify proper operation
of everything following each Annual Inspection, but that's merely my
personal opinion.
Alon and Mooney each specify 1700 RPM for checking both mags and
carburetor heat function. When the run up R.P.M. recommendation is
specific (not a range), and the acceptable mag drop is a single "not to
exceed" value (although an unspecified range of lower values is OK), it
would seem to me that each of these individual numbers IS to be
"satisfied". While a range of propellers and pitches is allowed per
TCDS 787, and allowable static RPM varies between them does not change
the single MAXIMUM allowable magneto drop deemed acceptable at 1700
R.P.M. applicable to all.
The "power check" is part of the take-off (as follows): "It is
important to check full-throttle engine operation early in the take-off
run" as both Dave and Ed earlier suggested. "When take-offs must be
made on a gravel surface, it is important that the throttle be advanced
slowly. This allows the aircraft to start rolling before high R.P.M.
is developed, and the gravel will be blown back of the propeller rather
than pulled into it." If the pilot routinely follows this practice,
day after day, he/she will know immediately in the first 100 feet of
the takeoff whether or not the engine is developing full power.
If the runway is short, the take off weight high, the density altitude
high, etc., each such challenge is best addressed in advance and in
appropriate detail on the ground. Once the takeoff run is initiated,
the pilot's single option if full power is not being developed is to
abort the takeoff with maximum possible runway remaining.
The fact that most Ercoupes do not have the C-90 engine or the Marvel
carb does not cloak or dismiss such other wisdom as these later, more
complete manuals have to offer the eager Ercoupe owner of today. The
danger associated with a lack of mag drop should be more widely
acknowledged and disseminated.
At some point the best pilots pick up the spoon and feed their own
desire for excellence. You, Hartmut, have repeatedly done this; and
each time graciously shared the results. Please accept my belated
thanks.
Regards,
William R. Bayne
.____|-(o)-|____.
(Copyright 2009)
--
On Nov 20, 2009, at 05:18, Hartmut Beil wrote:
Guys
We have to look at the purpose of the run up to come to a usable
solution.
Two reasons come to my mind:
1. we test for function of all crucial parts. Magnetos and Carburetor
heat .
2. we test for take off performance.
For the first test we don't need a full throttle run up. We have to
notice a drop during the magneto test to verify that both are working
and can be switched off.
And the carburetor heat is tested also by noticing the drop in rpm.
The magneto drop should not be excessive, a drop of more than 100 rpm
would indicate a non firing or barely firing spark plug. That's why
you do the run-up.
Not to satisfy some numbers.
Since the Ercoupe brakes are suited for slowing the plane down, but
not so much for holding the plane at full throttle in a static
position, it is common sense to do this kind of run up at a lower rpm.
I am using 1600 rpm and I am seeing magneto rpm drops between 25 and
75 rpm. Anything more and I have to look deeper into the issue. Think
about it, you don't do a full throttle run up in a tail dragger
either.
As for the performance test, I do briefly a full power test where and
when applicable before take off to be sure to reach the recommended
static rpm. That rpm value differs between the allowable engine
propeller combinations.
For the latter reason, I am also inclined to say that the experienced
drop in rpm when doing the magneto test also depends prop pitch.
So in result, there is no strict rpm to do the run up with. Nor is
there a rpm number of magneto drop that you should or should not see.
Rather than requiring a certain rpm number, I would recommend using
always the same number when doing the run up. Learn what the drop
usually is and be alert when it is different from the usual.
Hartmut
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