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#1
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From my excruciating review of TCM manuals,
interlaced into T337D performance charts... 75% ROP will give around 150knots IAS @ 13.3gph (ea) x2 = 26.5 gph 65% LOP will give around 140knots IAS @ 10.3gph (ea) x2 = 20.6 gph In the turbo, (non-pressurized) TAS increases linearly @10 knots/5k ft Until you hit 25k (critical altitude), when engine poer starts to dropoff I've never taken it that high, that's a looooong way down if you want to stop! So for example, at 10k ft TAS 75%= 150+10x2=170k @ ROP = 26.5.3gph = 6.4 kn/gal TAS 65%= 140+10x2=160k @ LOP = 20.6gph = 7.7 kn/gal = 20% more range/gal = 6% reduction in TAS speed. ===== Applied to my theoretical 1400 kn trip (each way) from Wash DC to Denver and back... 2800 miles total... 75% = 2800/170k = 16.5 hrs @ 26.5 = 440 gals 65% = 2800i/160k = 17.5 hrs @10.3 gph (ea) =360 gals For ~80 gals extra (roundtrip ~$500?) ...I can cut the round trip time by just ~1 hours...? Questions become, 1) Am I willing to pay $500 to get an hour of my time back? ...nah, I'll just enjoy the cruise for another hour 2) If the airplane costs $200/hour (??), one less hour reduces the extra fuel cost by $200.... CONCLUDE => It does seem to suggest LOP at 65% and enjoy the extra hour of flight time... Thoughts?
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David Wartofsky Potomac Airfield 10300 Glen Way Fort Washington, MD 20744 Last edited by n86121 : 03-08-24 at 11:31 AM. Reason: errors 
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#2
03-08-24, 12:21 PM
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"Excruciating".... YEP
You have summed it up! In my senior years, I've reduced the story to a much shorter version. Higher POWER = Higher SPEED = Less TIME = More $$$ (In FUEL and probably MAINT.) Lower POWER = Lower SPEED = More TIME = Less $$$ (In FUEL and probably MAINT.) It's not black and white however in my opinion. There are infinite shades of gray and countless variables go into the longevity (or lack there of) of our engines. Heck, many variables we cannot even control. We simply do the best we can and continue learning all the time. It's part of the fun I suppose. Enjoy your flight. Bring a pee bottle. I'd hate for you to have to heat up your engines just to make it to the little "pilot's" room. ;o)
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