Hi Ed, Dave
You are both making reference to the same FAA approved Overhaul Manual,
Form X-30010 of 02/80.
If you refer to page 106, the table of "Test Operating Limits"
following overhaul calls for magneto drop testing "at Full Throttle
(RPM)" which is specified in the top column as 2275-2325 for the C-75
and 2575-2625 for the C-85. They specify that such testing on the C-90
and 0-200 be done at 1800 RPM.
They repeat this on the following page in their "Start Oil Consumption
Determination" table following the Period 5 Warm up.
In my experience, mag drop is not significantly different over 1700
RPM. With reference to Ercoupe Instruction Manual recommendations of
"full power" runup, remember that the long props swung by the 65 HP
original Ercoupes could not turn up as fast as the later C-75 and C-85.
Since full power runups are even more damaging to (the original)
wooden props than today's metal ones, it may well be that the adverse
effect on propeller service life of increased static RPM from increased
horsepower was never reexamined by ERCO.
Consider that the 0-200 spins the smallest diameter prop the fastest
(additional ground clearance) and the C-90 spins a 71" prop. These
engines are of higher compression and displacement because of greater
stroke than the C-75 and C-85. If 1800 RPM is considered sufficient
for their testing, it makes absolutely no sense to me to subject the
same 71" prop on a C-85 to possible foreign object damage during full
throttle operation up to 2625 RPM sitting on the ground, or the 73" or
74" prop on a C-75 at 2325 RPM.
I took the trouble to go further into my files and drag out my 1980
version of the FAA approved Continental Operator's manual, Form X30012.
There, big as life, on page 15 again appears the direction to check
magneto drop at 1700 RPM. (This is the recommendation in the Flight
Manuals for the Alons and M10s). I am not aware of a later version.
On page 16 Continental suggests then increasing RPM to 2200 RPM to
check operation of the Mixture control, but the wording used suggests
this pertains to engines with Marvel carbs in referencing "idle
cutoff". I would ignore this inasmuch as Forney, Alon and Mooney
specify no such testing.
Interestingly, Forney recommends 1500 RPM for their mag checks, the
figure Ed used. If I were contemplating using a dirt strip I would
check in advance (on a hard surface) what kind of mag drops occur at
1200 RPM and, if satisfactory, use that RPM on dirt or gravel strips.
When all else fails, use judgment ;<)
William R. Bayne
.____|-(o)-|____.
(Copyright 2009)
--
On Nov 18, 2009, at 22:05, Ed Burkhead wrote:
In the Overhaul Manual for the C-75, C-85, C-90 and O-200, Section VII
OPERATING INSTRUCTIONS (page 40), it instructs the operator to “open
the throttle gradually until the engine is running at approximately
1200 R.P.M. Do not exceed this speed until oil temperature has
reached 75° F.” In the next section, “GOUND TEST,” it says to do the
mag check but nowhere does it say to increase the rpm above 1200 rpm.
http://www.pj260.com/Continental/O-200%20Manual.pdf
Ed
On Nov 19, 2009, at 00:35, [email protected] wrote:
Bill,
Strange that they didn't carry it over to the Feb 1980 copy of the
A/C/O-200 Overhaul Manual I have (Form X-30010). I looked at Para 7-4
under "Ground Test" on Page 39-40, and it does not specify what RPM at
which to perform the mag check. Thanks for your reference. I have
copies of several checklists being used by others and they seem to use
anywhere from 1600-2000 RPM. The 415-D AFM says Full Thottle approx.
2050 RPM, the 415-C Instruction Manual says Full Throttle 2000 RPM
approximately, so that's probably where I got the 2000 RPM I used in
my checklist. That seems excessive to me, so I would probably go with
the lower RPM in the TCM document.
Thanks,
Dave
