Efficient altitude, reciprocating engines?
Joined: Dec 1998
Posts: 4,282
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From: Escapee from Ultima Thule
If you're paying for it wet then you've already paid for the fuel in the hourly rate. In which case you're best served by going like the clappers to get there & back as quickly as you can.
Fly at the Full Throttle Height (ahem....altitude) for max continuous power in nil wind. If wind then work out the difference in TAS gained or lost by climbing or descending vs. the beneficial effect of more tailwind or less headwind.
If paying for it dry ie you buy all the fuel, then you need to compare the fuel consumption at different power settings vs the flight time to see how fuel consumption costs changes wrt to the cost for the aircraft using the same speeds.
Fly at the Full Throttle Height (ahem....altitude) for max continuous power in nil wind. If wind then work out the difference in TAS gained or lost by climbing or descending vs. the beneficial effect of more tailwind or less headwind.
If paying for it dry ie you buy all the fuel, then you need to compare the fuel consumption at different power settings vs the flight time to see how fuel consumption costs changes wrt to the cost for the aircraft using the same speeds.
Joined: Aug 2000
Posts: 3,648
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From: UK
If you're paying for it wet then you've already paid for the fuel in the hourly rate. In which case you're best served by going like the clappers to get there & back as quickly as you can.
Economy cruise power < Performance cruise power < Maximum cruise power < Maximum rental power
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Going like the clappers
Irresponsible, and why FBO's always rent wet. If renters paid for fuel, with a lower overall rate for the a/c, some dolts would fly with pistons pinging, enjoying their extended time in the air. Pilots are responsible in the great majority, but taking a chance on the odd nitwit isn't worth it, believe me.
AF
AF
Joined: Jun 2003
Posts: 13,787
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From: EuroGA.org
2gph will fry your engine in 10% of its TBO
Irresponsible, and why FBO's always rent wet. If renters paid for fuel, with a lower overall rate for the a/c, some dolts would fly with pistons pinging, enjoying their extended time in the air. Pilots are responsible in the great majority, but taking a chance on the odd nitwit isn't worth it, believe me.
Thread Starter
Joined: May 2006
Posts: 779
Likes: 0
From: Londonish
Coming back to this - the thread was started with malice aforethought; I did the trip I had in mind this weekend - 8500 out, 9500 back. Fairly high OAT generally - 43C on ground / +20 cruise out, and 30/15 back.
Both ways the chart showed me to be above full throttle height, so I naievely expected to push the black lever fully forward and lean for max rpm.
Interestingly I had to keep the throttle some way back to keep the revs under the red line (cruise was at about 2650rpm, PA28-161). What did I miss?
POH showed 75% at full throttle/2700rpm. Was very thermic so didn't risk running at 2700 due to lack of wobble room...
Both ways the chart showed me to be above full throttle height, so I naievely expected to push the black lever fully forward and lean for max rpm.
Interestingly I had to keep the throttle some way back to keep the revs under the red line (cruise was at about 2650rpm, PA28-161). What did I miss?
POH showed 75% at full throttle/2700rpm. Was very thermic so didn't risk running at 2700 due to lack of wobble room...
Thread Starter
Joined: May 2006
Posts: 779
Likes: 0
From: Londonish
Sheer bl00dy minded determination 
- 40+OAT at 2000, felt a lot more inside. If I hadn't had 3 pax plus a whole weekend and accomodation booked at the other end I'd have stayed inside with the house with the aircon on.. Damn silly weather to go flying. I'd have sold body parts for oxygen and the horses to get above it all...
IAS was around 95kts, TAS nearer 110 (according to the twiddlable sub-scale, not particularly accurate). Acceleration from climb was painful to say the least - just slightly less painful than the climb.
As far as I know standard prop - graph was from the aircraft's own POH, but it was a rental. Weight - MTOW less whatever we burned in the climb - probably around 30ltrs. Running on regular 100LL avgas..
- 40+OAT at 2000, felt a lot more inside. If I hadn't had 3 pax plus a whole weekend and accomodation booked at the other end I'd have stayed inside with the house with the aircon on.. Damn silly weather to go flying. I'd have sold body parts for oxygen and the horses to get above it all...IAS was around 95kts, TAS nearer 110 (according to the twiddlable sub-scale, not particularly accurate). Acceleration from climb was painful to say the least - just slightly less painful than the climb.
As far as I know standard prop - graph was from the aircraft's own POH, but it was a rental. Weight - MTOW less whatever we burned in the climb - probably around 30ltrs. Running on regular 100LL avgas..
