: I bet if you run a 180hp cherokee at the same TAS as a 140/150/160,
: the fuel burn will be damn close to the same. The 180 simply provides
: the option to run at a higher power setting, and hence higher speed
: and fuel flow.

: This same story probably extrapolates to the Cherokee 235.

It does. Take any specific airframe that has the options of different engines. The PA28 with a
150/160/180/235 hp engine will cruise the same speed with the same fuel burn at a constant *total* hp. For example,
75% in a 160 hp, 65% in a 180 hp, and 45% in a 235... all will be 8.5 gph. Drag power goes as the cube of the speed.
Consider a PA24 (available with a 180/250/260/400 hp engine)... it scales with the cube.

The only difference is that compression ratio is "free" power... more "bang for the bang." A 160 hp will have
the same fuel flow gph as a 150 (percentage-wise).

- Cory


--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************