High altitude cruising

born2fly · #1 06-11-2009, 04:16 PM

I'm doing more work lately at "higher altitude" - - 11k, 12k, up to 17,500 (cannulas and no desire for IFR filing). My RV6 is (of course) a little mushy up there. I also notice that my leaning procedures don't work the same. Carbureted, LOP, LASAR, everything is just fine at <10,000, but the ROP-LOP range seems very small (30 degrees) at higher levels. Quarter-twist of the mix knob goes from smooth to rough.

Any thoughts or tips?

- - - sure is smooth up there - - -

G.

blandess · #2 06-11-2009, 04:27 PM

My thoughts (worth less than 2 cents sometimes)

is the carbureted engines don't schedule fuel as precisely as fuel injected versions do. Do you have an engine monitoring system of any kind? i.e. EDM 700, Dynon EMS? I would say better than 90% of the articles I read involve high performance engines, sometimes turbocharged, with engine management systems for the ROP/LOP ops. If you do have an EMS, then I would watch your EGT and stop when it tells you to or just before the roughness ensues. Anyone else have better ideas? Please correct me if I am giving out false information!

born2fly · #3 06-11-2009, 04:49 PM

Yeah, I have a good reliable JPI bar graph, and that's how I know the LOP-ROP spread is shrinking with altitude.

At low levels, I can lean the puppy to over 100 LOP, but at high altitude, if I get more than 20-30 LOP, it roughens up. So at high levels, I'm pretty much stuck with running near peak.

However, peak at low levels is 1530 or so, while peak at high levels is more in the 1440-1470 range.

I'm lucky to have the LASAR, it is good at lighting the fire and even though the engine is carbureted, it is reliably ignited and will always run evenly at LOP. My EGTs/CHTs are within 50 or so of each other (respectively).

I'm turning in 165ktas at about 7.5gph or less. So I know the engine is putting out good power.

G.

scard · #4 06-11-2009, 05:42 PM

CARB HEAT! We fly a lot above 10k', and it is a definite condition with our carburated O320 that we can lean a whole lot more with a little carb heat on up high. I'm pretty sure it is the turbulence, and not necessarily the heat that provides the obvious improvement in EGT balance. The difference for us up at 13k' with or without carb heat can be in the neighborhood of 1+gph.

RVadmirer · #5 06-11-2009, 06:02 PM

I was told carb heat richens the mixture. Doesn't this cancel out further leaning? I have flown my O-320-E2A to 17,500 with no issues that I was aware of.....

hevansrv7a · #6 06-11-2009, 06:03 PM

Quote:

Originally Posted by born2fly

...
At low levels, I can lean the puppy to over 100 LOP...

I'm turning in 165ktas at about 7.5gph or less. So I know the engine is putting out good power.

G.

1. Suggestion: according to the GAMI chart, you get the best SFC at around 50 LOP. Going to 100 loses some efficiency.

2. Question: 165 KTAS on 7.5 or less - at what altitude? What does it do at 8000 DenAlt? Those are good numbers!

Thanks.

born2fly · #7 06-11-2009, 06:29 PM

Yeah, I don't actually RUN at 100 LOP - what I meant was that it WOULD run there as opposed to rough-run. 30-50 (the cylinders aren't perfectly matched in a carb engine) is what I try for.

Carb heat WILL richen, but that's not the point. Carb heat warms the fuel-air mix and helps to facilitate even distribution, therefore more even CHT/EGT.

Another thing is part-throttle. This angles the carb butterfly and can sometimes increase downstream turbulence in the intake. More turbulence (to some degree) will also enhance fuel-air mixing, and consequently promote even burning.

YMMV of course.

My 7.5gph and 165ktas are typical at 6000-9000 feet, depending on temperature. Last week I made a trip with light winds and got nearly the same exact numbers from 9,500 all the way to 15,500. Amazingly consistent. I don't have a lot of experience at high levels yet to say whether this is repeatable. BTW - this is with a very heavy ship. Mine is fully insulated and carpeted, rear hatshelf compartment, two-axis autopilot, 2-part epoxy painted inside and out, full-IFR, oversize tires, and with nearly 100 pounds of baggage. Flying weight was probably close to 1800 pounds. I can usually get about 170+ktas at 7.5-8gph when I'm traveling lighter, just me and half tanks. It's a quick ship, John Hughes did a great job.

G.

wrongway john · #8 06-13-2009, 08:07 AM

Don?t hear much feedback from RV?s set up with turbos, but I?m sure some have went this route along with using oxygen. Curious if a few fly the 20-25,000 ft altitudes much, and what kind fuel consumption and speeds possible in that area.

Also, since the air is thinner at such high altitudes, would the VNE be a bit higher or is the difference so slight, as to not be of any help?

nucleus · #9 06-13-2009, 08:12 AM

Quote:

Originally Posted by wrongway john

Don?t hear much feedback from RV?s set up with turbos, but I?m sure some have went this route along with using oxygen. Curious if a few fly the 20-25,000 ft altitudes much, and what kind fuel consumption and speeds possible in that area.

Also, since the air is thinner at such high altitudes, would the VNE be a bit higher or is the difference so slight, as to not be of any help?

The VNE stays the same, based in true airspeed. I know a guy who recently sold his turbo RV-6 and he regularly cruised at flight level 250.

Hans

frankh · #10 06-13-2009, 10:48 AM

I'd love to see some pics of a turbo install..If only to smugly hear those wonderful words.."RV484 Hotel, climb maintain level 28 zero"...

Frank