# What is the maximum speed at which thrust vectoring can be used? Thrust Vectoring on the SR-71

The SR-71 is limited to a 45 degree bank turn at speeds in between mach 2.85 to ~3.2. This means the blackbird would take almost 5 1/2 minutes to make a 180 degree turn at mach 3. Would it be possible to add thrust vectoring to increase maneuverability and decrease such an exaggerated turn radius? What is the maximum speed an aircraft has used thrust vectoring?

• The problem is not the speed-per-se, but the G forces induced by the resulting maneuver. Given the same control surface deflection angle, the higher the speed the higher the G force exerted on the aircraft (and the pilot). In the case of the SR-71 the issue was also the small wing-area and as a result the low maximum allowed wing-loading, as answered on aviation.stackexchange.com/questions/8028/… Oct 22, 2023 at 8:04
• @DeepSpace in part, disruption of air flow into the engines at high bank angles and aoa is also a factor. Oct 22, 2023 at 13:43

Maybe not what you're after, but most launch vehicles use thrust vectoring as their primary control. It is also used by on-orbit spacecraft -- not always a gimbaled nozzle, but sometimes that way and other times as discrete thrusters.

I am sure some tactical missiles would meet your criteria of high speed uses of thrust vectoring.

Would it be possible to add thrust vectoring to decrease turn radius?

It depends.

Vectoring thrust does help in maximising the turn rate but according to which kind of turn is flown.

• In a instantaneous turn, i.e. a turn where we don't care about losing speed and/or altitude, then vectoring thrust maximises the turn rate if thrust becomes perpendicular to the flight path. Hawker Siddeley Harrier can employ this technique.

• In a sustained turn, i.e. a turn flown keeping speed and altitude (which I suppose is what you are considering), then vectoring thrust maximises the turn rate if thrust is aligned with the flight path. In a sustained turn as the one we are talking about with a so big turn radius, thrust is basically already aligned with the flight path and vectoring it wouldn't bring any noticeable improvement.

Obviously all this is true as long as the load factor and the stall constraints are respected. Generally speaking turn rate $$\dot{\psi}$$ equals:

$$\dot{\psi}=\frac{g\sqrt{n-1}}{V}$$

so that it increases with higher Gs (higher load factor $$n$$) but decreases with velocity $$V$$.

• When you use the variable Velocity (V), what unit is it in? Mph? Nov 2, 2023 at 12:25
• @SamJones: everything is in SI system, i.e. velocity in m/s, g in m/s² and psi in rad/s Nov 2, 2023 at 12:59