Roll-on technique
Following 411A's remarks, here's a slightly bigger chunk of his quote from Old Smokey (post #23):
...the "Roll-On" Takeoff (not Rolling). That is, a Takeoff where the aircraft enters the runway at the nominal Takeoff commencement point already rolling with residual speed from the taxy.
For a 90 degree or 180 degree turn to line-up, this is obviously not practical or safe...
...I recall working on one Douglas jet aircraft where the AFM stated that the Maximum Achievable Takeoff Weights were (1) Roll-On Takeoff, (2) Standing Start, and (3) Rolling Takeoff in that descending order. The AFM went on to explain that a properly executed Roll-On Takeoff was one where the aircraft had a minimum speed of 10 knots at the normal SOT.
[Unquote]
This "roll-on" technique is precisely what I try to describe in post #33 – the Boeing-recommended technique I was taught (like 411A?) for the JT3D-powered B707-320B/C.
Whether Old Smokey is right to say that the 90-degree-turn case is not practical or safe, I'm not sure. Achieving a minimum 10kt demands a slightly less-sharp alignment, so the turn is not completed until a little bit further along the runway centreline. The main issues are probably: (1) integrity of nosewheel steering; (2) strain on L/G (B707 legs are short); (3) possible asymmetry of spool-up leading to loss of control.
As for the 180-degreee-turn case: it depends on the situation, the comfortable radius of turn the aircraft can achieve, and pavement width. If the runway has a very short spur just downwind of the most-downwind entry point, the take-off run can sometimes be maximised by entering the runway and turning the long way round (270 degrees or more). This works very well at a steady speed. On completion, a large aeroplane will have overshot the centreline, of course, but can be gently nursed back as it accelerates.
If, however, the thrust levers have been "stood up" before the aircraft is pointing in a safe direction, it becomes a fairly demanding and vulnerable manoeuvre.
Last edited by Chris Scott; 22nd November 2008 at 11:10.
Reason: Clarification in last sentence