Could you make the rwy an inch or two longer?

[ZeroAltitude]

Just found a link to an interesting video on pprune.
Takeoff of a fully-laden IL76, and it uses not every foot, but literally every inch of the runway:

http://au.youtube.com/watch?v=aWtdtuspnoM

[3WE]

I recall Don or someone saying that on heavy jets, due to very large induced drag and "backside of the powercurve" issues, that pilots will tend to maximize takeoff rolls. Not that they couldn't take off sooner, but the plane accelerates better without the wings "plowing" up the air, and then with a delayed liftoff, the plane is in an attitude that results in less drag, better climbs and faster speeds.

So, we may not be seeing the plane loaded to the hilt and "living on the edge" with respect to getting airborne, just "living on the edge" with respect to getting extra airspeed.

[Gabriel]

3WE,

It's true that, when the runway is comfortably long, sometimes pilot accelerate beyond Vr (but below max tire speed) before rotating for the reason you said. However, to me this doesn't look like one of those cases because:
- The pilot taxied to the very edge of the runway, it even looked like a couple of tires could have touched the grass. No one would do such a thing if the runway is comfortably long.
- One you rotate several knots past Vr the takeoff should look clean: The nose goes a bit up and up you go right away. In this case the aircraft rotated several seconds before lifting off, and then it looked like it didn't want to leave the ground.
- If you are already Vr and accelerating down the runway for a late rotation (basically for "comfort") it's Ok, but no sane pilot would let it roll to the very last inch of runway when the aircraft was already past Vr for several seconds!

[aardvark2zz]

I would have thought Vr is the optimum speed for rotation and that rotating before or after is not optimum for obstacle clearance.

In other words rotating later doesn't give you better performance due to higher speeds (greater drag due to wheels).
.

[GerryW]

3WE,
............................. but no sane pilot would let it roll to the very last inch of runway when the aircraft was already past Vr for several seconds!

No sane but Russians. I saw them a lot, when they were still allowed with their Il 76 here in Luxembourg, performing some stunts here.

[Gabriel]

I would have thought Vr is the optimum speed for rotation and that rotating before or after is not optimum for obstacle clearance.

In other words rotating later doesn't give you better performance due to higher speeds (greater drag due to wheels).
.

Well, that's not.

Vr is defined in terms of V2, Vlo, Vmu, Vs, Vmc and achieving 35ft over the runway surface just at the threshold of the runway if an engine fails at V1.
The aim ov Vr is to leave the ground as soon as possible (and with legal safety margins).

V2 is the speed achieved at 35ft in case of an engine failing at V1, and has to meet certain criterion of contability and margins over stall, and in that way, limits V1 and Vr (perhaps the airplane could lift off slower but if it doesn't reach the V2 criteria at 35ft then you have to increase V1 and Vr to get a complying V2).

V2 is not the best climb speed either. It's the minimum safe speed to climb with an engine failed. The obstacle profile allowed is limited by a climb at V2, what doesn't' mean that other faster speed could give a better climb profile.

That means, if an engine fails at V1, you know that rotating at Vr will assure you lifting off within the runway, achieving V2 immediately after, and avoiding obstacles by keeping V2.

Note that the typical initial climb speed is not V2 but V2 +10 / +20. Now if you loose an engine at V1 you would probably not want to trade altitude (or climb rate) for more speed beyond V2, but if you already achieved more than V2 you would not slow down to V2 again. If the runway is long (the weight is not limited by runway length) an an engine fails at V1 you may still keep it running a bit longer on the runway past Vr to achieve a more comfortable speed for the climb. An the same with all engines running.

For that I'd say that the pilot flying would have full awareness over the remaining runway and would finally rotate with a very comfortable margin so the airplane lifts off with a good bunch of runway remaining.

[ZeroAltitude]

No sane but Russians. I saw them a lot, when they were still allowed with their Il 76 here in Luxembourg, performing some stunts here.

Did anybody notice, in the video, the voice from the "off" commenting "The vodka burner is rolling"?

[Giles]

the controllers commentary make it funny


"we have smirnoff"

"you can lift it up anytime you like"

"gee i hope ive got enough to film the crash"