# Performance question C172

#### highflying

##### New Member
I dont know why I am having trouble with this but can someone help me with this question.

At 65% power, 7500 feet, standard temperature what is your

RPM, Fuel Consumption, TAS?

If yo can explain to me how you got it that would be great also. Thanks for the help

#### MidlifeFlyer

##### Well-Known Member
[ QUOTE ]
I don't know why I am having trouble with this but can someone help me with this question.

At 65% power, 7500 feet, standard temperature what is your

RPM, Fuel Consumption, TAS?

If yo can explain to me how you got it that would be great also. Thanks for the help

[/ QUOTE ]I don't have a POH or PIM handy, but if I remember correctly, the cruise performance charts are pretty easy to read. How far have you gotten?

#### highflying

##### New Member
Well not to far. I mean I know how to use the performance charts but I can seem to figure out the 65% power. I mean if I could figure that out then the rest would be easy at least I think

#### jetman

##### New Member
From 172P POH

6000...63%..2400RPM 107ktas 7.0gph
69% 2500 rpm 113ktas 7.8 gph

At what rpm u would find 65%? from the chart u c that 6% rpm difference corresponds to 100rpm so 2% = about 35rpm
or 2435 rpm[65%]
Speed seems to increase 1k per 1% of increase power so at 65% 109 ktas and so goes for fuel about7.3 gph

8000...66%..2500 rpm.112 ktas....7.4gph
if u want to be exact u should use the 60% values and interpolate [ 2400 rpm106k 6.7g]and come up with something like
8000 65% 2485 rpm111ktas 7.3gph]

6000 65%2435rpm 109kktas 7.3gph
8000 65%2485 rpm 111ktas 7.3gph
Divide all the values by 4to find diff for avery 500ft and substract from the 8000 ft values [8000-500=7500ft]
2470rpm...110.5ktas
7.3gph
Good luck /// [ double check numbers calculations where done in my very tired head
in a hurry ]

#### highflying

##### New Member
Thanks for the help. I thought that was how you do it but I wanted to make sure there wasnt an easier way before I started do all the math work. Thanks again!!