So, it does depend on how you are driving, and driving in hills can give
     > better gas milage than level ground under certain conditions.  But, I in
     > the more normal driving ranges, even with better bsfc goin uphill,
     > better gas milage is obtained driving on the flat.
     >
     > That was fun,
     > Bob White
     >
     > --
     > http://www.bob-white.com
     > N93BD - Rotary Powered BD-4 (soon)
     >

     You did a great job Bob.

     Paul Lamar

Nice work Bob, If I might relate this to aircraft though, I do NOT believe you can
make a similar arguement. The problem that would rear it's ugly head is the prop
disk. On most powered aircraft the highest drag component is the propeller in
decent.( A shallow decent not a intentional dive!) Unlike a car where you can
literally "put it in neutral" most aircraft don't have a clutch or transmission.
Indeed even if they did you would have to have a prop that would fully feather
to take advantage of the "downhill" portion of the run while the engine idled.
A practical example of this was printed in the Van's newsletter. There was a
US Representitve or Senator, (possibly state) flying his own aircraft.
(I already like the guy) He had a failure of his prop extension or the bolts. The
prop completely parted from the plane and fortunately didn't damage anything else
while doing so. He (sorry I can't remember his name) declared an emergency
and was closest to Truckee CA airport. Using his GPS's pre-programed glide range indication he informed the Airport that he would probably be about 2 miles short.
The glide range had been very accurate when practicing engineout procedures
previously. The short story is that he made the airport EASILY.
Talking to Van later he was told, "Sure the plane makes a MUCH better glider
without the propeller" I'm sure Vance can verify this as well. If you have to
prove this to yourself go up in anything with a constant speed. Idle the engine
and set best glide in corse pitch. Then set the prop to flat pitch and you will
think you just threw out an anchor! (be careful not to stall)!
Bill Jepson

 
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