snip
Hello Bob, Sorry for being late, Paul answered it all, also regarding bsfc
being different at different engine operating conditions.
However, consider also this; you drive up a long hill, then turn around and
drive down again with the engine off. You covered twice the distance with only
slightly more fuel used going up. Your average fuel consumption is only a little
more
than half compared to the same distance traveled on a level road.
Of course, this is an extreme case. Normally the engine is not switched off.
The closest you come to above scenario is when the road has a slope (or grade),
that allows you on the downhill leg to be completely off the accelerator without
needing to step on the brakes and going the same normal travel speed. The air
butterfly will be closed and the fuel supply is nearly equal to idle. Very
little fuel is used going down. The total fuel used is more than per the above
scenario, but certainly less then you would need if the road was level and you
drive
the same distance (equal to up and down).
The total fuel consumption goes up from this minimum if the road is less
steep or if steeper.
The other point mentioned by Paul to increase fuel consumption dramatically
is to accelerate to say 40 or 50 mph, then shutting the engine down and letting the
car run down to a stop or near stop, then start up the engine and repeat this
procedure. You can?t do that in traffic of course, but at night on a lonely
road when you are low on fuel and there is no gas station in sight for miles
around. The gas mileage you get is in the range of being double.
Now, wouldn?t that apply to flying as well? I wonder if it would really work
too.
Assuming you fly level at a given cruise altitude. Now you apply more power
and climb, perhaps 2000 ft. Then you throttle back to say 1500 or less rpm (~2500
rpm for rotaries) but maintain speed with the elevator. After you are back to the
same cruise altitude, you apply power and climb up 2000 ft again and then you
throttle back. You repeat this as often as you want. Mind you, if you have
passengers,
they may ask what the hell are you doing? Nevertheless, it should get you further
for the same amount of fuel. Are there any takers out there to try that out? If
would be nice to have that theory tested.
Best Regards
Rolf Pfeiffer
Rolf
Interesting concept. Sounds logical but against the law of thermodynamics at
the same time. The success of this concept would be plane specific. It would
be dependent on many factors such as Hp/weight ratio, wing loading/wind area
ratio, drag. etc.
I would think that if it worked it would be taught to military pilots who
often found themselves in situations where they needed to stretch their
range to make it back to base. Any vets care to comment?
I would volunteer to try out the concept as I have probably the worst plane
to do it in. Cessna 150s have lousy glide ratios 7:1 and they are a wee
bit, ... OK a lot underpowered. I would have to climb in a slow shallow
cruise climb and decend at hmmm ... best glide speed is 67mph I believe.
Perhaps I'll give it a try on one of my flight legs in a more remote region
of the Southwest USA. Obviously I am going to have to stay lower than 3,000
at the ceiling and keep a sharp eye out. Approach Control may have a fit
though:)
Doug in Japan
Doug,
Thanks for your comments.
Sure it would be plane specific and would depend on many factors as you point out. The
same would apply to the car and road comparison as well, where the best slope of the
road would also be car- or even truck specific.
One thing puzzles me, that is your reference to a "thermodynamic" law. Could you
explain what you mean by that?
That the military does not use it does not automatically mean that it won't work
However, the jets are so heavy and their glide ratio so poor, it is likely that it
would not work with jets. On the opposite scale are gliders with an auxiliary motor.
Here the effect would probably be more than double, perhaps 3 or four times the
distance that can be covered compared to level flight with the engine always running.
As I said, it would be worth a try. We know it works for cars, perhaps it works for
planes as well.
Rolf
BTW guys I recalculated more accurately my mileage coming back from Aqua Caliente
after refilling the tank and it was 22.8 MPG
Paul Lamar
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