OPNLguy From , joined Dec 1969, posts, RR: Reply 1, posted (12 years 10 months 2 weeks 6 days 12 hours ago) and read 13731 times:
Basically, it's just the taxiing to, and turning onto the end of the takeoff runway, and commencing the the takeoff roll, all in one continuous movement, without stopping. Not an everyday occurence, especially at busier airports, but not a rare event either...
Mikeybien From , joined Dec 1969, posts, RR: Reply 3, posted (12 years 10 months 2 weeks 6 days 2 hours ago) and read 13651 times:
as you probably imagined, the alternatives to a "rolling" takeoff involve stopping at the threshold. At that point the aircraft is either throttling up and making a short field takeoff because it does not have the performance to do a rolling takeoff, or it was told by tower to "taxi into postion and hold" and is waiting for traffic to either get off the runway, or waiting for proper takeoff spacing.
STEINWAY From , joined Dec 1969, posts, RR: Reply 7, posted (12 years 10 months 2 weeks 5 days 10 hours ago) and read 13582 times:
Thanks for your answers, however I still don't understand the sentence where I heard about the rolling take off procedure :
"767 CROSSWIND TAKEOFF TECHNIQUE
For information Boeing recommends a rolling takeoff procedure when crosswind is > 20 kt. Engine surge can occur with a strong crosswind component if takeoff thrust is set prior to brake release." (from smartcockpit web site)
I understand a rolling take off would allow to avoid setting brakes before take off run, thus avoiding possible engine surge setting take off thrust, but could you explain why "Engine surge can occur with a strong crosswind component if takeoff thrust is set prior to brake release"?
Also why isn't it possible, on a crosswind non-rolling TO, to set the brakes at the beginning of the runway, release them and apply takeoff thrust only after.
Do you need to have the brakes set when you first apply takeoff thrust?
Mikeybien From , joined Dec 1969, posts, RR: Reply 8, posted (12 years 10 months 2 weeks 5 days 8 hours ago) and read 13565 times:
Ahhh... so that's what you wanted to know.
If an jet is running at full thrust with no forward velocity, it causes a vacuum at the inlet, sucking air into the engine. At a certain speed on the takeoff roll, the ram air becomes great enought that there is no longer a vacuum there. What does this have to do with crosswinds?
With no forward velocity and a heavy crosswind, the air is flowing across the inlet instead of toward it. The vacuum at the inlet changes the direction of the air as it passes by the inlet, and at a high enough crosswind it can cause the air to separate from the inlet and create turbulent flow (i.e. like behind a stalled wing). The turbulent flow is what leads to compressor stalls and surges in the engine.
So if the 767 does a rolling takeoff, by the time the engines are at full thrust the aircraft is already at a high enough speed to "feed" the engine with ram air.
The only other aircraft i know of with this problem is the C-5. Does anybody else know of any?
Kohflot From , joined Dec 1969, posts, RR: Reply 10, posted (12 years 10 months 2 weeks 4 days 4 hours ago) and read 13488 times:
Rolling TOs are SOP at AA? I guess it makes sense in some ways... but it seems like it'd be too vague. Can you do a rolling TO on a contaminated runway? If not, doesn't it open a gray area for a crew as to whether or not a runway is really contaminated, etc. etc.? Seems like it would just throw something else to think about in the already busy mix right before TO....