Gary and Chris,
Here is detailed info from my most recent long trip
(ARR-EDC-PLK-ARR). Perhaps you can deduce more as the RPM was in the 2480
to 2500 range for all legs.
ARR->EDC 820 NM 4.7 hrs block to block. Flown at 6500 MSL to avoid
higher headwinds at higher altitudes and LOP (economy) to eliminate a fuel
stop. Conditions were constant for the entire trip and all four data
points are very similar. OAT 19C, Dalt 7500, KIAS 168, KTAS 187, 24.8" MAP, 2480
RPM, 7.4 GPH and 24.5 DBTDC. Actual flight time was 4.3 hours and I
put 32.1 gallons at EDC having been left with a reserve of 9.9 gals.
EDC->PLK 440 NM 2.4 hours block to block. Flown at 9500 MSL to use
the winds and ROP (best power) to go fast. OAT 16C, Dalt 11000, KIAS
163, KTAS 190 (Ahhh, over PGO GS 208 Kts), 22.1" MAP, 2490 RPM, 8.5
GPH and 27 DBTDC.
PLK-> ARR 380 NM 2.2 hours block to block. Flown at 7500 MSL and
ROP. OAT 18C, Dalt 8700, KIAS 171, KTAS 194, 24.1" MAP, 2500 RPM, 9.8 GPH
and 25 DBTDC.
Scott Krueger
IO 320, 9:1 CR, unfiltered ram air, dual Plasma III EI, Hartzell
CS prop, uh, a few drag reducers....
In a message dated 11/26/2011 9:23:27 A.M. Central Standard Time,
casey.gary@yahoo.com writes:
Scott,
Thanks for the information. I took your numbers and did a crude
reqression analysis and came up with the following: The advance
increases by 2.2 degrees per thousand rpm above 1700 and 0.85 degrees per
inche of manifold pressure below 28. Just gives a rough idea of how it
works.
Gary
From Scott:
Restricting my comments to Lycoming engines (320, 360), one would note
that 25 DBTDC is the fixed timing delivered by standard magnetos and that
timing is adequate for a wide range of engine operations. My injected 320
engine has a 9:1 CR and uses a base timing of 20 DBTDC. Normal ROP cruise
settings in the 4000 to 9000 MSL range and 2500 RPM (say 21 to 25 MAP), the
timing is between 24 and 26 DBTDC. At takeoff and low altitude race power
settings (2760 -2600 RPM, WOT, 28-30 MAP), the timing is about 22-23 DBTDC. At
leaned idle/taxi power (<10" MAP, <1100 RPM) the timing is about 34-35
DBTDC. At altitudes 10000- 14000 MSL, 2500 RPM, WOT and LOP the timings are
generally 29-31 DBTDC.
Scott Krueger