Fuel / KG

[Xcel]

^^ rutan

weird...

Best way I understood it was - we used to put the fuel samples in the fridge for 5 minutes cause otherwise even our @15 temps wouldn't make sense on those hot days and with the friction on the front container from the tanker it was way off. Cool the sample down so the sg was within spec so we could accept the fuel. If hotter than his calculated @15 we would be getting ripped off cause the volume over such a large amount of fuel would be out and theoretically wouldn't fit in the tank... As the sample was from the owest point it was closest the road and the front so was the hottest. By the time we let the fuel in and it mixed with the colder fuel it would always fit.

[Ex FSO GRIFFO]

Hey 'Rutan' I never thought of that when I was flying higher performance, 'carby' pistons.

However, if it works for you...I wonder just how much fuel you actually saved?
Care to elaborate?

Half a circuit's worth...or more..?

The only comment I would make is that the use of the Carby Heat delivers unfiltered air - so you wouldn't want to have any 'dust' around....

Cheers

[rutan around]

Griffo, back in those days I didn't fly enough to think about quantifying fuel savings. Perhaps the Piper Comanche association could help here. We didn't use carby heat till we were above the dust layer. I think what was at play was that the heated induction air weighed less, so the MP decreased, which meant the mixture (fuel flow) could be reduced. The power remained the same because the better atomized fuel/air mix burned more completely and sooner. A bit like modern coal powered ships. They don't shovel lumps of coal in - they crush it to a talc-like powder and blow it in, achieving quick and complete combustion. Another 'trick' that helps is not quite full throttle. The following excerpt from the Cessna Pilots Association elaborates.

Lean of Peak (LOP) In A 182

Tech Support,
In a recent E-ATIS (13:51), Mike Busch answered a question regarding LOP operation in a 182Q (see below). However, he did not address the advantage, if any, of operating full throttle LOP given the difficulty of operating LOP at all in the 182Q. Is there an advantage? I operate my 1977 182Q LOP on most flights. I take a cautious approach by operating in the 62-64% range where per the POH I have the freedom to operate lean. Fuel flows are, say, 8.4-9.2 gph depending on weather and altitude and I make about 110 knots. The CHTs are acceptable; the EGT diff reading varies... 60 is great, 80 is typical, and I switch to ROP if I can't stay under 100. Of course, with a Skylane this requires partial carb heat such as 46-48 degrees IAT. These settings seem to keep my plugs clean, valves cool, fuel costs low, etc. I have tried the transition to full throttle LOP operation but given the above and at my typical altitudes (2,500-4,500), it seemed difficult. Is there sufficient additional advantage to switch to the full throttle settings?

Here is what was said in E-ATIS

“Your O-470 engine is very difficult to operate LOP without unacceptable roughness. It is only possible to control power with the mixture control when you're operating LOP. You cannot practically use the LOP procedures I was discussing in ATIS on your O-470.”

Thanks in advance,
David R.

David,
For O-470 engines operated LOP, it's best to operate them at "almost WOT." Starting at wide-open throttle, pull the throttle back slowly until there just the slightest reduction in indicated MP(a needle's width at most). This provides "almost WOT" operation, but cocks the throttle plate in the carburetor throat just enough to cause turbulent airflow, which improves fuel atomization and mixture distribution.

The other O-470 "trick" for operating LOP is to use just a touch of carb heat, again to improve atomization and mixture distribution.

Mike Busch, CPA Tech Rep.



Mike,
Thank you for responding to my question. I can certainly try the almost WOT. Given my current numbers with just carb heat, would you expect a noticeable improvement if I can position the throttle plate? Also, since the difference between 22-23 MP and almost WOT is big at 2,500 ft, are there tricks to help smooth the transition? Would it help to lean ahead of time to flows that are typical of either ROP or LOP operation? Since I am able to fly LOP with the settings I posted in my first message, I wondered whether I would see any improvement in efficiency or smooth engine operation by adding WOT on top of carb heat. For me at least, the transition from cruise power to WOT at 2,500 ft. is difficult. I wondered whether I should lean to my typical LOP fuel flows first before changing the throttle. Difficult = Like flooring the car, steering, and trying to adjust the radio at the same time! Having established cruise altitude and prepared for my leaning procedure (close cowl flaps, adjust carb heat, etc.), I have my hands full just scanning for traffic, maintaining altitude, and tracking my EDM readouts.

Thanks in advance,
David

David,
Operating at or near WOT is always more efficient, all other things being equal. The difference in efficiency can be large with turbocharged engines, is much smaller with normally aspirated engines.

For normally aspirated engines, the major loss of efficiency comes in flying at low altitudes where partial throttle is a consideration. If you are flying at efficient higher altitudes, you'd never consider operating at less than WOT anyway.

Mike Busch, CPA Tech Rep
Cheers RA
PS For the record back then we didn't dream of running LOP because it was "verboten"

[Ex FSO GRIFFO]

Thanks for that - and especially for the references.

Mike Busch certainly, is well regarded.

Cheers