No, not tied to ground effect. Blowing the (strenghted, I suppose) flaps delays stall and achieves a higher lift coefficient. Old technology (F104, F4) bled and piped air from engine compressor to near flap hinge
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Air Force Pilot Screws Up - Wrong Airport
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mikewof
mikewof
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I watched the video, I noticed the solid flaps you described.
So lessee ... lift, gravity, thrust, drag ... the flaps extend into the path of the jet exhaust, a certain vector of that thrust then is directed downward, increases lift, but increases drag. In the video that looked to be at least 20-degrees or more of flap, is that normal for takeoff, or is it a short-runway thing?
The way they backed they reverse thrusted the plane, they only seemed to move it back a short distance. Is that common for takeoff or a flex of the ability?
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I'm going to guess since they could back up , they did so to get the max runway length.
They already fucked up once, why not take advantage of every bit of runway they could easily get.
mikewof
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It's hard to tell, but in the video it looked like they only backed up a bit, and had a good bit of runway behind them, and a good bit in front of them when they lifted. An airplane that big, I would have backed its tail was over the rhubarb ... it's just something in my head that screams at me that it's too big and heavy to take off in anything shorter than one of the runways at Denver International, let alone a runway at Centennial.
That takeoff, couldn't have been a better promotional piece for the folks at Boeing.
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They certainly only needed a portion of the 5,000' runway. They only need 3,500' to take off.
justsomeguy!
Super Anarchist
Wiki states that with a full load they need 12,000 plus feet of runway.
The plane must have been offloaded?
I'm thinking you are confusing it with the C5. A fully loaded 747 can take of in a little under 11,000'.
justsomeguy!
Super Anarchist
FRED is still FRED. I monitored the fleet of C-5As, Bs, Cs and Ms on a daily basis for years looking for engine issues, and there were days when not one of the first dozen or so C-5Ms were mission capable. The aircraft System Program Office, now Life Cycle Management, at Warner-Robins didn't understand the first fucking thing about Reliability Centered Maintenance. Maybe it's gotten better since 2014.
Charlie Foxtrot
Super Anarchist
New engines and avionics certainly helped. But, that old Rube Goldberg hydraulic system is still there.
Charlie Foxtrot
Super Anarchist
McDonnell Douglas. And, yes.
Boeing had the Powered Lift concept, which was very good very slow, but sucked rock at cruise.
Charlie Foxtrot
Super Anarchist
The 17s three piece flap system.
The Coandă Effect, since there appear to be other nerds here.
And hey, have a Weird Al ear worm while we're at it:
Think I'm just too white and nerdy
Think I'm just too white and nerdy
Can't you see I'm white and nerdy?
Look at me, I'm white and nerdy.
mikewof
mikewof
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The one in the OP was made by McDD?
Do you know how the system works? Is it that the jet engine hits the flap in its way, then makes the billowy cushion of ground-effect turbulence? I assume the need to contain the ground effect turbulence is why the plane has such a strong negative dihedral?
Any issue with that dihedral and the wingtip vortices with paratroops?
Charlie Foxtrot
Super Anarchist
Let’s unpack this, shall we?
The one in the OP was made by McDD?
McDonnell Douglas designed and built the C-17 (the plane in the first photo), based largely on the YC-15 flying prototype, which was developed by Douglas Aircraft. The C-17’s first flight was in September, 1991. Boeing <spit> bought McDonnell Douglas at the end of 1996. By that time we had the program under control and were pumping out money.
Do you know how the system works? Is it that the jet engine hits the flap in its way, then makes the billowy cushion of ground-effect turbulence? I assume the need to contain the ground effect turbulence is why the plane has such a strong negative dihedral?
Ground effect has very little to do with the 17’s performance; the wing is set far too high to have any significant benefit from the very short time the plane is in ground effect. The plane’s short field capabilities arise from the Blown Flaps. (Got the shirt “It’s Better Being Blown” before uppah management had a stroke.) https://www.globalsecurity.org/military/systems/aircraft/c-17.htm is a high level discussion of the externally blown flaps of the C-17 and the 17 in general. If you really want to get in the weeds, try https://www.globalsecurity.org/military/systems/aircraft/c-17.htm. We put together a really outstanding webpage (for 1996 or 97) on the Blown Flaps, but I guess Boeing killed that too.
Any issue with that dihedral and the wingtip vortices with paratroops?
The anhedral wing was chosen for maneuverability (all the cargo weight well below the wing would otherwise make the plane too stable) and to direct the apparent wind toward the wing root and the flaps. The 17 did have problems with paratroopers getting too close when using both paratroop doors. Even though the 17 is basically a flying knockwurst, it is also a very cleverly designed aerodynamic one. The slipstream recombined underneath the tail, dragging the port and starboard paratrooper sticks together. In a test, one troopie hit and collapsed the chute of another, who had to ditch his main and ride down under his reserve chute. Another time there were collisions, that I seem to remember resulted in bruises, a broken arm, maybe a short period of unconsciousness, and much heavy drinking. That issue was resolved by much larger airstream deflectors ahead of both paratroop doors and a maybe a change in speed and deck angle.
IMNSHO, the C-17 is the best airlifter ever, by a huge amount. It is a crying shame that Boeing, ‘Boma, and Airbus combined to kill the program. Talking to a friend that was still on the remnant of the program several years ago, all the Air Force can complain about is that there are just too damn few of the C-17s.
mikewof
mikewof
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Okay, so it's more complicated than just vectoring the jet exhaust downward from the flaps for extra lift, because that would make the plane harder to land?
In your links, it seems that the blown flaps are made of the flaps plus a controllable diverter of some kind in the jet exhaust. In the videos, it's odd to see such aggressive flap position on takeoff, but the effect is undeniable, that enormous bitch seems to just float off the runway.
With the negative dihedral, why did they mount the wings so high if it's too stable?
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