Getting 45 MPG at 207 MPH .... can you pulse and glide an airplane?

[MetroMPG]

Jesse: I'd read about this (changes in ATC to permit more efficient commercial "glides").

Thanks for the answers, everyone. I'm continually amazed at the collective knowledge here.

[bestclimb]

as far as drag in an aircraft goes there is two types. Induced and parasitic.

Induced is created when the wing is at a high angle of attack as airspeed increases this drag drops.

Parasitic is created by the fusulage and all the protrusions. It increases as the airspeed increases.

Both are on a curve. There will be an airspeed where the combination of the two are at its lowest.

Combine that with an engine that operates it's BSFC at that airspeed and Pulse and glide will not be nessisary.

The other thing you could do if the engine's bsfc rpm pulls the aircraft past it's lowest drag speed is climb. The thinner air makes the engine produce less power, the thrust is reduced due to lower pressure on the prop (or stream of jet exaust). There is less parasitic drag and the wing creates less lift.

The thinner air also means the indicated airspeed is lower (the aircraft "feels" less air moving over it) while the true airspeed goes up (actual speed the plane is moving through the air)

So what airliners are doing is one big "pulse" to get to an altitude that allows the plane to cover ground very quickly while flying in low drag. The fuel burned in the climb is almost always more than what was saved during the decent. But the fuel consumption is so low at altitude that it quickly makes up for the fuel used in climb and then some.

[bestclimb]

Originally Posted by Frank Lee

That is another reason why you generally can't just pluck an automotive engine out of a car and stick it into an aircraft. The duty cycles are waaay different, with the auto engine loafing along most of it's life with brief periods of higher load, and the a/c engine working pretty hard most of it's life, with brief periods of even higher load. That's why we ought not laugh too hard at an a/c engine that uses, say, 330 cubic inches to put out 100 hp. It's not because the engineers were dense.

a continental O-300 (opposed 300 ci) makes 145 a GO-300 (geared opposed) is good for 175hp the standard o300 has a TBO of 1800 hours at 2500rpm the GO300 gets 1200 hours at 3200 rpm I think.

lycoming gets 150 hp out of a O-320 and an O-360 is good for 180-200hp

these engines are making RATED (not peak) HP at 2500rpm

the 100hp engines are about 200-235 cubic inches.

[Bicycle Bob]

Air cooling limits the specific outputs as well, and keeping the revs down saves the weight and losses of a gear reduction for the prop. I think the aero engines sound better, too.

[Frank Lee]

Thanx for looking up the numbers; I didn't. I just recall that output/cid is low compared to other engines.

As far as the sound goes, I don't particularly enjoy listening to them.

[winkosmosis]

Well lookey here, a pointy nose.

[Bicycle Bob]

That's the shape of the landing gear mount, in a situation where it works OK.

[dcb]

so, if doubling your speed takes 4 times the power, roughly speaking, and power is proportional to fuel consumption, again roughly speaking, then with the right engine combo, you should be able to cruise @ 90mpg at 103mph and 180mpg at 52mph?

Would narrow wheels and direct drive, instead of wings and a propeller help or hurt mpg?

[Frank Lee]

Narrow wheels instead of wings will prevent flight! LOL

[Mustang Dave]

so, if doubling your speed takes 4 times the power, roughly speaking,...

Doubling the speed takes 8 times the power. Power is proportional to the cube of the speed, not the square.