Low RPM's during run up/take off

[hilltop170]

wldlndfirefghtr-
I will be flying 15D today and I will get some data for you to compare. It has an EM 7655 on the O300-D at about 350 hours SMOH with new ECI cylinders flown regularly, Horizon digital tach that takes input off of the mag switch, not the engine. I will get data at 1720'msl at Fredericksburg and at 710'msl at Pecan Plantation. The temp should be close to standard, it's 55F right now.


T82, Fredericksburg, 1720'msl, 60°F,
Static 2285rpm
TO 2315rpm
FT @ 5500', 57°F, 2665rpm, 9.2gph
FT @ 3500', 62°F, 2700rpm, 9.2gph
FT @ 2000', 65°F, 2710rpm, 9.5gph

0TX1, Pecan Plantation, 710'msl, 70°F
Static 2330rpm
TO 2350rpm

[blueldr]

Richard,
With a fuel burn that high, what kind of true air speed does it settle down to? Whats your burn leaned out at cruise power? True Air speed?

Ever tried to figure the gas mileage? Or NMPP (Nautical Miles per pound) of fuel ?

[hilltop170]

Dick-
I did not calculate TAS today, I was just looking at rpm at different conditions. It indicated 118-120 at full throttle and 105-107 at 2500rpm, both leaned just rich of engine misfire. Fuel flow at 2500rpm leaned just rich of misfire is 7.2 - 7.5gph depending on altitude. With the tailwind today, ground speed was 129mph which yielded 17.9mpg, better than my pickup.

[GAHorn]

Dick-
I did not calculate TAS today, I was just looking at rpm at different conditions. It indicated 118-120 at full throttle and 105-107 at 2500rpm, both leaned just rich of engine misfire. Fuel flow at 2500rpm leaned just rich of misfire is 7.2 - 7.5gph depending on altitude. With the tailwind today, ground speed was 129mph which yielded 17.9mpg, better than my pickup.

You gots a Cheby... right?

[hilltop170]

Sí!

[Joe Moilanen]

Anyone have specs on what the static RPM should be on a 0300D with a 1A175/SFC 8043 prop?

Joe

[hilltop170]

What static are you getting with a 8043?

[ron74887]

Joe, by the STC on the 0-300-D the 8040 prop has a static of 2380 to 2480. (seaplane) No data on the 43. 43 was not approved by Cessna- whoever got it approved should have the data with it. Ron

[Joe Moilanen]

I'm getting about 2300, maybe a hair more at times, I'll do some more research and see if I can get some harder numbers.

Thanks!

Joe

[ron74887]

Joe, 23 sounds about right for a 43 pitch since a 40 is between 2380 and 2480. you are 3/4 the difference. I don't have all my info here and don't know the difference in a normal 51 vs a 55 in rpm's. I would think you are very well in the ball park. Sorry all my info in on the computer at the office. Ron

[Joe Moilanen]

Joe, 23 sounds about right for a 43 pitch since a 40 is between 2380 and 2480. you are 3/4 the difference. I don't have all my info here and don't know the difference in a normal 51 vs a 55 in rpm's. I would think you are very well in the ball park. Sorry all my info in on the computer at the office. Ron

Thanks Ron!!

Joe

[wldlndfirefghtr]

Richard,

Really appreciate the data. Makes me a bit less concerned, but still need to get back up and fly 26D and see where she sits. Everything is pointing to normal, just lower compressions due to sitting. When I get back up I'll post some numbers as well.

Thank you again.

Jason

[wldlndfirefghtr]

All,

Went up today, again right at gross, DA about -1900. Takeoff rpm 2100, slowly climbing on take off roll, around 1000' just hitting 40mph. Aborted takeoff followed by 2 high speed taxis.

Well I suppose next step is to pull the prop and check the pitch. Suggestion was to also see if the brakes were dragging. CFI believes it to be an engine performance issue, not producing power/not feeling the acceleration. I'm at a loss. Here was what was done previous to this flight;

(O300D) Performed compression test (68, 62, 72, 63, 67, 63) re-timed both magnetos to 28 degrees BTDC. Cleaned , re-gapped plugs, cleaned treated for corrosion, performed bore scope inspection on exhaust system for obstructions- none found, ops checked carb heat box and carb throat for obstructions and defects- none found. Inspected throttle, mixture, carb heat control travel limits and stops, performed static run up, satisfactory.

Mechanic believes prop to be a cruise, based on eyeballing it, no note of re-pitching in prop logbook.

Thinking of getting 2nd opinion....

Suggestions......

Thanks again.

[n2582d]

re-timed both magnetos to 28 degrees BTDC. ... Suggestions...

The right magneto should be timed to 26 degrees.

[Bruce Fenstermacher]

Jason, I reread this entire post. How long have you had this plane? In other words do you know the plane to have produced more RPM with this prop?

If the answer is yes it made more RPM under the same circumstances then either it is a recording error or something not quite right.

Both mags timed at 28° is not quite right.

A leaking carb heat valve is not quite right. Disconnect scat duct from carb box to see if it makes a difference on a test run high speed taxi.

Running rich is not quite right. Lean for best RPM on the ground and see if that makes a difference. If it does then I'd be looking at the carb venturi or just the over all condition of the carb. Your primer, if leaking can also be a source or a rich running engine. It could be disconnected for testing purpose and eliminating it from the trouble shooting process.

If static RPM is OK but you don't develop RPM on the roll and your ground roll is extended, I'd look at dragging brakes, tire inflation and even pilot technique.

It would also be nice to know what pitch prop your trying to turn. This info could explain a lot.