VMU take offs, dragging the tail!

[swr_e007]

Hi,

I've been watching some videos of VMU take off on youtube, including the testing for VMU on the Airbus 380.

Search for 'vmu test' and there are at least three vids, Boeing 777, Airbus 380 and MD87.

Lots of sparks!

I was just curious. Is the technique of rotating until the tail skid strikes the runway something that a pilot would be expected to do if an emergency requiring an early take off was required? Say - some obstruction is spotted on the runway at or after V1 - would the correct procedure be to deliberately tail strike the aircraft to get unstuck asap? Is this taught to pilots as an emergency procedure?

Or is it just a certification test?

[Groundloop]

No.

But there have been lots of instances of pilots overrotaing by accident and scraping the rear fuselage along the runway. That is really what the test is for - to see that the aircraft will get off the ground despite bad piloting - they just don't say that on the TV commentary.

Example here:-

Photos: Boeing 777-2H6/ER Aircraft Pictures | Airliners.net (http://www.airliners.net/photo/Malaysia-Airlines/Boeing-777-2H6-ER/0632272/L/)

[emeritus]

As I have understood it, this test is carried out to confirm that the aircraft can take off within the scheduled takeoff run and not run off the end of the runway if it is rotated early to the extent that the tailskid contacts the runway.
This was introduced back in the early 50.s after a BOAC comet rotated early with the tail scraping the runway and the angle of attack and subsequent aerodynamic drag was such that the a/c failed to reach flying speed before it ran off the upwind end of the runway with I think some loss of life.
Googling comet crashes should produce more info.

Emeritus

[swr_e007]

Thanks for the replies...

But I was just wondering if rotating until you get a tail strike would give you the shortest take off run (ok...other than in an early comet!) - or would the aircraft actually unstick sooner with a conventional rotation? Is a tail strike always a dumb thing to do, if say you are past V1 and running out of runway?

[tom775257]

No, rotating early doesn't help at all; comet or not by increasing angle of attack you will increase drag and certainly risk dragging the tail which will increase drag!

There is one possible scenario that I can think of which rotating early will work well and that is with an increased climb (V2) performance... basically you stay longer on the runway than required with the decreased aerodynamic drag that provides then rotate above the speed needed to safely fly to get a better climb gradient (eg Malaga runway 31, long runway and terrain ahead). As a pilot you are not directly given information on this for each runway, so it would be guess work. Either way not trained and not recommended. If the runway was blocked I would call stop, if we were about to rotate and suddenly something came infront of us I would pull back hit TOGA and hope. In the middle... who knows.

BTW a trainer on the A320 once told me if really needed he would increase the slat/flap setting if 1+F takeoff to 3 due to something on the runway at high speed to reduce the speed required to take off. Nothing is officially trained for this (in my experience with 2 airlines).

Dragging the tail is never a good thing.