MD11 question

[Brandon]

Reading an incident report the other day about an MD11F that was being ferried with center engine inop. The crew elected to takeoff with the center main gear retracted to cut down on drag, but unfortunately that moved the cg aft of limits and when they applied full power and released the brakes it rocked back onto the tail.
Anyways, just wondering how they retracted the center gear? The article made it sound that it was something that could be selected from the cockpit. I am guessing seagull will have then answer to this one!

[seagull]

Button next to gear handle isolates it. Pin the other gear, pull the ground shift CB, select gear up, push the botton on the panel and then select gear down.

[USMCmech]

Question,

Why take off with the center gear up?

I imagine the load is not a problem if the aircraft is empty, but why bother.

Save on tires?

[A300Capt]

[ QUOTE ]
Question,

Why take off with the center gear up?

I imagine the load is not a problem if the aircraft is empty, but why bother.

Save on tires?


[/ QUOTE ]

I'll defer to Seagull for the correct answer but I would assume that a the center gear isn't required for weight since they're probably completely empty due to the 2 engine ferry and, b it's one less piece of drag in the slipstream in the event of one of two remaining engines failing.

[cime_sp]

Did it back on the tail or did the crew over-rotate. From what I understand, it can be done with the a/c that light.

[Brandon]

From the brief report I read (I think it was just a little blurb in a Business and Commercial Aviation) it sounded like it planted the tail when the brakes were released. I guess it could taxi fine, but when the 1 and 3 engines came up there would be a nose up moment and the number 2 engine which would normally create a nose down moment was u/s. I imagine the CG limits change when that nose down force from the center engine is missing. I think the report said they calculated the CG to be about 3% mac aft.

Anyways, if it did happen at power application...far better to find the error then than to have an uncontrollable pitch up at rotation with only 2 of 3 engines running.

[seagull]

That would do it, aft CG, thrust line on 1 and 3 below the CG, not enough airspeed to counter it with elevator (and you can get the tail if you're not careful with the elevator on losing #2 at rotation). CLG would be up for less drag. When we first got the airplane we'd keep it up for 2 engine inop approaches, but we don't do that anymore, MD11 has enough performance that it doesn't matter, really.