F33 2500 RPM settings?

[Bob Lierschaft]

I am a new owner and am now actually flying the airplane! My IO-520OBB is recently overhauled (60hrs) has a Ram Cam and tuned exhaust). On my first trip I did 2 legs one at 7,000 and one at 9,000. at both altitudes I get about 1" more than book (Ram Cam & tuned exhaust helps)I used 2,500 RPM and max throttle - at 7k I had 23.7 MP 176+ tas and at 9k 22 MP and 172+ tas. My Garmin G500 ADC gives my a TAS that is very accurate - confirme with GPS wind and GS.

Question - by being 1" over book am I exceeding 75% power at 9k? 2,500 RPM seems smooth and I like the speed for trips - any problems with this? (35 years ago we were taught to baby our engines and run at 2300 RPM??

Any problem with using 18" MP and 2,200 RPM down low sightseeing (I am concerned about low rpm with the continental?) A training school had an engine failure and low rpm was sited as the problem - they were using 2,200 to save fuel. Really would appreciate several opinions.

[Tom Pelz]

Bob,

I routinely fly my engine at 2100 RPM for approaches.   No problems.  This is with a 520 and now a 550 engine.  At 2100 RPM, I am at 18 inches MP.   I think the problem is that there used to be an engine setting for the 550 that was quite unusual.  2100 RPM and 25 in MP.

I also fly at 2500 RPM at 10 - 14 K altitude at full throttle and 11.5 - 12.0 GPH fuel flow .

At 9K altitude, 2500 RPM, you are not making 75% power.  

DO you have GAMI injectors.  IF so fly lean of peak (I have been doing this for over 13 years without a problem (and saving a lot of gas.  I often fly from Wisconsin to the West coast.  I usually will burn 50 gallon less fuel for the round trip by flying lean of peak - and the engine runs cooler).

Part of your increased MP is from your intake air filter.  Keep it clean, don't switch to a Brackett filter.  That will reduce your MP.  (on the other hand, if you live in a highly dusty area, maybe the Bracket filter would be best as it might be better a keeping the sand/dust/other garbage out of your engine).

If you are uncomfortable about LOP operation, check into the advance pilot seminars.  They will convince you that LOP is a more sensible way to fly.

Tom

Tom Pelz2011-06-06 22:39:04

[Bob Lierschaft]

Just found this SB from Continental and talked to them - they are now recomending not less than 2300. Interesting read - it is CSB09-11

regards

bob

SUBJECT: MINIMUM CRUISE RPM LIMITS

PURPOSE: To inform operators of the possible long term effects of low engine RPM in cruise conditions. To establish limitation of minimum engine RPM in cruise.

COMPLIANCE Upon issuance of this bulletin

MODELSAFFECTED: O-470-G; IO-470-N; IO-520-BB, CB, MB, P; IO-550-A, B, C, D, E, F, G, L, M, N, P, R; IOF-550-B, C, D, E, F, L, N, P, R;

TSIO-520-AE, BB, BE, CE, DB, EB, JB, KB, LB, NB, UB, VB, WB; LTSIO-520AE; TSIO-550-A, B, C, E, K; TSIOF-550- J;

TSIOL-550-A, B, C

Teledyne Continental Motors (TCM) has examined recent occurrences of crankshaft counterweight release and subsequent engine stoppage in two high time IO-520 and two high time TSIO-520 engine models. Investigation and reported service history lead us to believe that these occurrences are associated with engine operation at sustained cruise engine RPM of less than 2300 RPM. Power settings of less than 2300 RPM have been within the recommended cruise range allowed by TCMa

[Tom Pelz]

Bob,

Note it says CRUISE.  I only use 2100 RPM for approaches and some times descents.   When descending, I like to keep the MP and the MP within two (1900/17 /2100 / 19).  This permits me to keep some power to help keep the egine warm on long descents.  (I believe that cracked cylinder heads occur when the power is reduced too abruptly or the cylinders are allowed to get too cool on long descents.)

So when I know that center is going to drop me too quickly (a slam dunk), I gradually reduce MP and then RPM.  IF I am at 2500 and 19 inches (full throttle) already, I reduce the RPM, and then begin my descent, after I have attained a slower speed.  As the MP increases as I descend, I keep the MP at 17 - 19 inches.  I often do not push the mixture in until I have need for more speed or my EGTs get under 1250 F, then I only add enough to keep the EGT between 1250 and 1300.

I think that the reason for the notice from Continental occurred because they had a stated power setting of 2100 RPM and 25 inches.

It would be interesting to read what Mike Busch says about this RPM limitation.  He routinely flies his T310 at less than 2300 RPM and high MP

Tom

[Bob Lierschaft]

Tom

Sorry I meant only in cruise. I use the same settings as you on approaches etc.

nice day for a change I think I will go flying!

regards

bob