Which airplane?

George Patterson wrote:
: You can get a mogas STC for the 152.

... from Petersen for 91 fuel, no?... isn't the 152 a high-compression
Lycoming O-235 at 110hp? 8.5:1 or 8.7:1 CR IIRC.

: I've seen car engine conversions. Are their TBO really high as in cars?

: Not usually.

Usually the auxiliary components and/or the packaging fail as I understand it.
Retrofitting an auto engine to an aircraft requires very careful packaging to get the
power/weight ratio comparable to an aircraft engine. That careful packaging works on
pretty slim weight margins, so engineering it well is required.

: Whats a good choice on a serious
: budget? Or rather; whats the cheapest way to fly 600km or so with two
: people? four people?

: Probably the old Hershey-bar Cherokee (150 or 160hp). That's a pretty good two
: person plus luggage aircraft. It'll burn more gas than the 152, but it'll
: usually make that trip without a fuel stop. It'll carry four in a pinch, but you
: may have to leave the tanks less than full. If you buy one of the later 180 hp
: models, that's a true four-seater.

Perhaps *slightly* more gas, but not much if flown the same speed. Speed drag
is the biggest fuel consumption in cruise, so comparing apples to apples is probably a
better range/fuel economy question. Cruising a Cherokee-160 at 115mph is about 55%
power, or pretty much the same 6-7 gph you get with a 152 at 75%. Airframe drag
determines speed.

Bottom line... going faster takes power, and power=fuel burn. The only
*significant* difference is airframe drag. I constantly have to explain that to
people saying a Cessna 150/150 has "horrible range." Actually, the only difference is
20-40 extra lbs hanging off the nose. Throttle back and you get basically the same
range. Power requirements (due to drag... the main component at cruise) go as the
*CUBE* of velocity... 2x as fast requires 8x the power. Or, the other way is that 2x
the power will get you 2^(1/3)=1.25x as fast. Going from 100hp-150hp gets you all of
1.5^(1/3)=1.14, or 14% faster at 50% more fuel burn.

-Cory

--

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