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Fuel vs. Engine and Airframe Time

LegacyDriver

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Without engine mx cost numbers in front of me this is always a tough one to figure out. I was hoping some of you guys had a rule of thumb on this one that might be generally applied to jets.

When you pull the power back to save gas you also add time to the airframe and engines. My question would be something along the lines of:

Which costs more, burning fuel to go fast or wasting airframe/engine time to go slower?
 

rettofly

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Power by the hour....

LegacyDriver said:
Which costs more, burning fuel to go fast or wasting airframe/engine time to go slower?

My last job required slowing down on repo flights "to save fuel". The job before that demanded max cruise at all times "because fuel is cheaper than flight time".

Can't wait to find out how my next job looks at this.
 

Flying Illini

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Good question...if your engines are on MSP, do you really care?
 

HMR

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Do the math for your A/C. In my plane (Astra) the difference between what the book recommends for power settings vs. balls-to-the-wall is 5 maybe 7 knots. On a 5 hour flight that equals a time savings of .1 yet we burn over 100 gallons more fuel. Your mileage may vary.

Also, since all our flight planning is based off book numbers, why fly anything other than "book" power settings?
 

LegacyDriver

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Well, as I noted in a previous thread our book numbers aren't very accurate at times so other than setting fuel flows and going I don't know how much help they are. (Our GDC numbers are dead on.)

For example, the other day we were doing 485 KTAS in our descent (they left us lower for a long time so we had time to compare). The book showed a MAX of 472 KTAS.

I imagine with fuel so expensive right now it certainly helps to save it, but if you are pushing yourself more quickly toward an inspection or part replacement is it worth it? MPS cares for the engines, but what about the airframe and such?
 
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HMR

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LegacyDriver said:
Well, as I noted in a previous thread our book numbers aren't very accurate so other than setting fuel flows and going I don't know how much help they are.
Your book numbers "aren't very accurate"? That sounds like it could be a liability issue for the manufacturer. How are you supposed to come up with an accurate flight plan?
LegacyDriver said:
MPS cares for the engines, but what about the airframe and such?
Are you seriously concerned about time on your airframe?What's the difference in time savings between LRC and full-throttle in the Legacy? After several years of flying I bet it would only add up to a few dozen hours.
 

falconpilot

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How much are you slowing down....???? It takes 60kts to make up 10min..(Gen rule of thumb) I don't think it matters that much... How much could you be saving??? And if your engines are on MSP, who cares.... We always try to go fast everywhere unless we're on a long intl trip...
 

LegacyDriver

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I am betting even I am cheaper than even a lightbulb--a dim one at that! :)

60 knots for 10 minutes. Have to chew on that one.

I am guessing burning an extra 400 pounds to save a few minutes would be an obviously bad mood if you are empty I would think.
 
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