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POH fuel flows
Bob,
Sorry that chart was so BIG... guess I need to learn how to make it "fit the window".
If it wasn't readily apparent after looking at the AA Intercooler Power Settings, as you can discern, the basic idea is to remember three power settings for any altitude based on 55%, 65% or 75%... e.g., it's always going to be 33" and 2400 RPM for 75%; 31" and 2300 RPM for 65%; and, 27" and 2300 RPM for 55% -- and their corresponding fuel flows, i.e., 88, 76 and 64 for Best Power (50 ROP), and if at or below 65%, peak EGT's resulting in 67 or 57 PPH respectfully.
Now, with respect to Cessna's POH... the chart for a stock airplane seems to have finite differences in BHP and Total PPH for a given altitude, ISA. So, let's just pick 10,000' and 18,000' for comparison and arbitrarily use 2400 RPM and 33".
At 10,000', Cessna POH shows 72% Best Power (50 ROP) with a fuel burn of 153 Total PPH for 2400 RPM and 33", and a TAS of 184 Knots. With the intercoolers the chart shows this same power setting giving 75% Best Power (50 ROP) and a fuel burn of 176 Total PPH, or 23 additional PPH (3.83 gallons per hour). BUT, the airplane equipped with the intercoolers is giving 195 KTAS instead of 184 KTAS as in the POH.
AHhhh, but drop the intercooled airplane down to 65% at the same altitude (30"/2400 RPM) where you can run lean peak EGT and your fuel burn is now 134 Total PPH with no penalty in airspeed... your speed is the same as the stock airplane at its slightly higher power setting... 184 KTAS ... and beating the stock airplane fuel flow by 19 PPH, or 3.16 gallons per hour. This latter figure isn't quite comparing apples to apples, because if you compare to the stock airplane's comparative per cent of power setting, the difference is only about a gallon per hour. So, it depends on how you want to skew the numbers.
OK, for 18,000' the stock airplane Cessna POH shows 71% Best Power (50 ROP) being developed with 33" and 2400 RPM, with a fuel burn of 150 Total PPH, resulting in 198 KTAS. With the AA intercoolers for the same altitude, 2400 RPM and 33" nets out 75% power and a fuel burn of 176 Total PPH- but you might need an extra 50 RPM spool depending on ISA conditions to keep MP steady, turbos spooled and pressurization happy, so running 32.5" and 2450 nets the same 75%. Again fuel burn will be 176 Total PPH, but speed will be 211 KTAS instead of the stock airplane's 198 KTAS, a distinct 13 knot advantage. Dropping the intercooled airplane down to 65% power results in 202 KTAS, and a fuel burn of 134 Total PPH, which is still better than the stock airplane at 150 Total PPH for 71% in addition to a slight speed benefit.
We very rarely run 75%... and unless we're going long, it really isn't economical to climb to the teens... but we like the pressurization and the turbos for mountain flying, and so we usually run 55% to 65%. At these power settings we can run lean and at peak EGT, thereby grabbing the fuel flow savings and also gaining speed over the stock airplane, at least at the higher altitudes.
If we run around local, say 5000' for a hop, we generally run 55% power which gets us down into the 114 Total PPH range, or 19 Gallons per hour and generally gives us about 160-165 KTAS on ISA days. Besides, we like to enjoy the ride, and these lower power settings are easier on the pocketbook and the noise levels are reduced too.
I beleive the intercoolers were probably the best investment on the P337 as it enables the engines to run cooler and promotes longer engine life. And there's virtually no maintenance to this item, as long as the rubber connection hoses maintain their integrity. Above all, as with any add-on equipment, if someone was in the market for a P337, I'd strongly suggest getting one with the goodies that you want already installed, as aftermarket installs now would be QUITE expensive, almost to the point of being cost-prohibitive. (Same with boots, RSTOL, etc.) And speaking of RSTOL, last time we checked it was around $14K+ for Robertson.
Well, there you have my nickel.
SkyKing
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