What determines the ITR and the STR is very simple. But you must go back to basics.
Both depend on the lift equation. The ITR ignores the drag side of life while the STR takes drag into account.
The lift equation has all that you need for a complete understanding of both:
L = CL1/2 rSV2
(sorry PPRuNe does not like the symbols. If you don't know the lift eqation then start by finding that out but here r stands for the air density and the V is a squared term)
The max ITR is what you get if you suddenly yank the stick back until you reach Cl max and stall the wing. In doing this the G meter will show some maximum value. Exactly what rate of turn that G value will provide is down to the laws of physics not aerodynamics so let us not get diverted into that other than to say that for a given G value the rate of turn will be highest at the lowest forward speed at which you can achieve that G.
As to how the G you can yank varies with all the other factors just go back to the terms in the lift equation. More density more G. More wing area more G. More V more G and naturally more weight less G. But watch the V term. As mach number is increased it is certain that the Cl max you get in your yank to the stall will decrease due to compressibility effects.
IF (and it is a big if) you now really feel happy with this appreciation of ITR then (and only then) you are ready to consider the STR.
The STR introduces drag effects. To sustain a turn rate you must have enough thrust to overcome the drag increase that will follow your yank to the ITR. Since you could well do your yank when you are ALREADY at full throttle you will quickly slow down and so will then be able to yank to less G. There will come a time where your thrust equals the increased drag from yanking and bingo you can sustain that reduced G.
Perhaps you can now see why in the test flying word the ITR is called the lift boundary and the STR is called the thrust boundary.
So in conclusion give a particular aircraft more thrust and you will increase the STR or thrust boundary. The effect of more thrust on the ITR will be negligible.
PS The aircraft's (structural) G limit will naturally limit any manoeuvres should it intersect the curves of ITR (very likely at high speed) or STR (possible with a VERY hiigh thrust to weight aircraft).
Last edited by John Farley; 15th October 2011 at 13:08.