John Theune wrote:
: I'd really like to see some number to support your conclusion. By my
: estimates 100 hrs * 11 gals per hour = 1100 gal per year. RG decreases
: fuel need by 5% or 55 gal * $3.50 = 192.50 per year in fuel savings.
: From the numbers throw about by my aircraft owning buddies the delta in
: ownership costs for a retract are much more then that.

: Assumptions in above: Fuel burn is about the same for 180HP engines in
: Comanche 180 and 172s with 180HP engine. Increased speed reduces need
: for fuel by 5% by higher speed in cruise, climb fuel burn is the same.
: Big YMMV is added

Not to be too argumentative, but 5% might not be the right number. A quick
example:
http://www.risingup.com/planespecs/i...plane432.shtml
http://www.risingup.com/planespecs/i...plane427.shtml

That's a PA-28-180 vs. a PA-28-180R. Cruise of 119 kts vs. 141 kts. That's
18% improvement in speed. Others are similar around 15%. So, multiply your fuel
savings by a factor of 3 and you get $600/year. That's starting to sound more in line
with the additional costs of a gear swing every year, some more lube, and a
replacement part averaging every 5 or so.

Just food for thought.

-Cory

--

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