Long CC, CSP, 75% power, or more?

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ScottVal

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Scott
Hello,
I'm planning a long CC flight tomorrow with a rented Piper Arrow with CSP. There is forecast a moderate headwind. The POH says to normally cruise between 55% and 75% power. But what if I cruise a bit over 75% power, to try to make better time on my trip? Obviously I'll be watching the engine gauges -- CHT, oil temp, tach, manifold pressure, etc. What do you think? Do you risk damaging the engine when you cruise over 75% power?

-Scott
 
How high do you plan on flying? Are you even going to be able to make 75% power?
 
Good question. Because of the forecast winds aloft, I'm not planning flying high, so, yea, I will be able to make 75% power.

This is my first solo long CC in a complex AC. This particular question has been bugging me, and I was wanting to see what people on the forum thought about this.

I probably should have asked my CFII; it's a little late to call him...

Thanks.
 
Since drag increases exponentially with a linear increase in velocity, your fuel burn will increase as well.

Your best plan is to limit continuous operation to the customary 75% power and plan your flight for the least amount of headwind.
 
Fuel burn will be substantially increased (not exponentially, it's a power law) at the highest throttle settings. But I guess if it's a rental that you're paying by the Hobbs hour, you can drive it like one.
 
Fly fast in a headwind, slow in a tailwind.
 
Yea, there is the fuel-burn issue. My FBO charges reasonable fees and I like them, so why put them out of business to save a few minutes of flight time?
 
pericynthion said:
Fuel burn will be substantially increased (not exponentially, it's a power law) at the highest throttle settings. But I guess if it's a rental that you're paying by the Hobbs hour, you can drive it like YOU STOLE IT.
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Fixed that for you.
.
As mentioned, depending on how high, you might not be making 75%. Also, leaning out the engine may help with fuel burn but may have you running hotter. The difference if fuel used probably won't be significant enough to break the bank. 7 vs 6 gallons an hour.
I was once accused of seriously leaning out the engine to save a gallon an hour. What they did not realize, I hardly ever ran above 2350 rpm nor did I ever lean below 3,000'. Why speed along and miss everything.
Enjoy the flight. Stroll, not run.
 
There is some risk of detonation above 75% power leaned. But you should see the temperatures and airspeed loss.
 
ScottVal said:
Hello,
I'm planning a long CC flight tomorrow with a rented Piper Arrow with CSP. There is forecast a moderate headwind. The POH says to normally cruise between 55% and 75% power. But what if I cruise a bit over 75% power, to try to make better time on my trip? Obviously I'll be watching the engine gauges -- CHT, oil temp, tach, manifold pressure, etc. What do you think? Do you risk damaging the engine when you cruise over 75% power?

-Scott
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Wet Rental? Redline throttle and MP the whole way, lean to 200 ROP.
 
Henning said:
Wet Rental? Redline throttle and MP the whole way, lean to 200 ROP.
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Just out of curiosity, what if the same plane is an equity share flying club plane with a wet rental? I ask because I am in planning stages for a long CC flight myself...
 
MarkZ said:
Just out of curiosity, what if the same plane is an equity share flying club plane with a wet rental? I ask because I am in planning stages for a long CC flight myself...
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If you have part of the equity WOT(or25" if you stay low), top of green RPM, 25°LOP.
 
Hello guys,
Time for the post-mortem. The head-winds were not as strong as I thought they'd BE, so I was able to cruise at higher altitudes, and the 75% power thing wasn't really an issue. Thanks for all the nice feedback.
-Scott
 
Now we know why no one wants to buy a rental. Let your conscience be your guide.
 
frfly172 said:
Now we know why no one wants to buy a rental. Let your conscience be your guide.
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Doesn't matter with an Arrow or most planes you can rent since they are rated for continuous duty at full power. These are engines that put out around 1/2hp per cubic inch, that's low stress.
 
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frfly172 said:
Now we know why no one wants to buy a rental. Let your conscience be your guide.
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Rentals seem to get longer lives out of their engines than non-rentals. For the low powered engines, not really a big deal.
 
Sluggo63 said:
Fly fast in a headwind, slow in a tailwind.
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That's weird, I usually end up going slower in a headwind than I do in a tailwind. At least it seems to take longer to get where I'm going.

But seriously, unless you're trying for max range and therefor flying at a rather low IAS the only thing you gain by flying faster in a headwind is getting there very slightly sooner and more points on the credit card you use to buy fuel.
 
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