Can wake turbulence be good?

Pi1otguy

Pi1otguy

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Fox McCloud
Most migratory birds fly in a V formation because its more efficient. While the leader has to work harder, the other birds get "free" lift from the leader's wake. Specifically, the upward part of the spiraling wake.

Can manmade aircraft get such benefits (lower fuel consumption, less wear and tear, etc) from this kind of formation flight? Can humans perceive the "good" part of the wake in flight? Those of you who've flown in formation, do you specifically avoid the wake?

Disclaimer: Formation flight without proper training can be hazardous to your health, aircraft, and certificate. I'm not suggesting that ever
 
Do you know why sometimes one side of the V is longer than others when birds do the flying v formation?
 
I seem to remember reading somewhere that the Air Force tested the "extremely close formation flying" technique for more efficient flight when ferrying fighters from base to base. It actually worked - lower fuel burn, etc. - but the pilots were EXHAUSTED after the flight.

They abandoned the idea b/c the silly human behind the stick couldn't handle the super close proximity of the formation. Seems like some sort of computer driven autopilot could keep them separated, but even then it would be pretty high stress for the pilot sitting behind the screen that's controlling the stick.
 
Hmmm... it might work.
You guys try it first and tell me if it helps any... :D
 
SkyHog said:
Do you know why sometimes one side of the V is longer than others when birds do the flying v formation?
Click to expand...

cause theres more birds on that side! (one of my favorite jokes :))

I remember reading about a NASA project where they flew an F18 in the updraft portion of the wake of an airliner. fuel savings on the order of 20% I think. There definitely is power there.
 
20% sounds like a huge savings to me. I suppose to benefit from this updraft would require radio beacons and an autopilot to triangulate relative position.

Taking this to an extreme, would the wake still be usable at supersonic speeds? High efficiency super cruise? (thinks of the tight formations in Stealth B))
 
Pi1otguy said:
Most migratory birds fly in a V formation because its more efficient. While the leader has to work harder, the other birds get "free" lift from the leader's wake. Specifically, the upward part of the spiraling wake.

Can manmade aircraft get such benefits (lower fuel consumption, less wear and tear, etc) from this kind of formation flight? Can humans perceive the "good" part of the wake in flight? Those of you who've flown in formation, do you specifically avoid the wake?
Click to expand...
A. The leader doesn't have to work harder than he normally would, he just has to work harder than the rest of the birds because they're taking advantage of the wasted energy in his flight.

B. Yes, manmade aircraft can reap these benefits...flying in the "sweet spot" results in about a 2" MP reduction when flying a 450 Stearman in formation. That's somewhere between 5 and 10% (I can't remember the power settings we were using), and as posted previously, would probably be more substantial when flying formation with a much larger aircraft.

C. Yes, it's pretty easy to perceive the "good" part of the wake...it's where you have to pull the power back to avoid hitting the lead, and it's an "unstable" position--if you move laterally out of position, the airplane will want to increase the lateral movement out of position rather than try to return.

D. I still avoid the wake...even at 200 feet behind an airplane (the distance that gliders are towed), the wake is less well-defined, larger, and rougher. In close formation, you simply "fall out of the wake" (hopefully away from the lead plane rather than into it ;)), but farther back, it can cause some pretty serious upsets.

Fly safe!

David
 
A paper was published in the last few years using fighters and seeing very large savings (tens of percent). It's too hard to do for any length of time manually, so they used differential GPS.
 
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