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

Here is another story about CAFE Foundations way to measure "zero-thrust".
Check their website, http://www.cafefoundation.org/index.htm
 and read the report on Dave Anders RV-4 for a good aerodynamics "lesson"!
http://www.cafefoundation.org/aprs/RV-4.pdf
 Somewhere in there they mention the installation of a sensor that measures
against the prop backplate. When the prop is pulling it will pull away, if
it is idling it will push on the sensor - basically they use the movement
between the pressure bearings in the engine. The idea is to establish a
powersetting that neither "pulls nor pushes".......
To verify, that this will work they did a tow on a C-152 without a prop!!
http://www.cafefoundation.org/aprs/propless.pdf

There is also other interesting stuff to study on their. Probably not
everything is applicable to Rotaries, but a good read anyway!
And plenty of neat aircraft tested!! Generally rathre fast things!

Thomas J.

 
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