Question about hard maneuvers!
Discussion
RIAT weekend and something that has often interested me, when you see higher performance planes doing air displays all the high G stuff is nearly all done at relatively low speed in full afterburner, for instance an Su27 display seems to be done entirely on full afterburner, is this because the computing power only really works at this level when the machine is in basically full military power?
Can these manouveres all be done on normal power ie mil, not afterburner?
Or is it basically because at full afterburner the air-frame is at maximum stress therefore enabling this stuff ONLY at this time, not in normal flight?
I was watching Elwyns excellent F18 footage and again most of the really hard stuff like mega pull ups, very quick and tight urns are all done on burner.
Always wondered why? And if there is a reason for it and can it all be done on normal power
Can these manouveres all be done on normal power ie mil, not afterburner?
Or is it basically because at full afterburner the air-frame is at maximum stress therefore enabling this stuff ONLY at this time, not in normal flight?
I was watching Elwyns excellent F18 footage and again most of the really hard stuff like mega pull ups, very quick and tight urns are all done on burner.
Always wondered why? And if there is a reason for it and can it all be done on normal power
Nothing to do with computing power.
Doing tight turns creates lots of drag, so you need lots of thrust to avoid slowing down.
The reason it's flown slowly is that (say) 8g at 500knts takes up a lot more space than 8g at 250knts, so it's not so good to watch as a display.
Doing tight turns creates lots of drag, so you need lots of thrust to avoid slowing down.
The reason it's flown slowly is that (say) 8g at 500knts takes up a lot more space than 8g at 250knts, so it's not so good to watch as a display.
Edited by Mave on Friday 15th July 17:58
Mave said:
The reason it's flown slowly is that (say) 8g at 500knts takes up a lot more space than 8g at 250knts, so it's not so good to watch as a display.
I dunno, being an old git, the min radius turns as part of a F-104 display, which took up at least 3 counties were 
were pretty spectacular......but then, that was in the days before all this electric jetrickery stuff came out....High g turns are often done at both high and low(ish) speeds at airshows.
A high g turn at high speed won't often look as if it is turning fast enough to suggest it is high g, but its just deceptive due to the radius of the curve being bigger due to the speed.
High g looks more impressive when at medium/low speeds because this gives better visuals from the ground as the airplane does much smaller radius turns.
As the above reply states, high g turns require lots of power in order to maintain momentum/airspeed. In order to do a high g turn it means the airplane must present much more of the wing surface in to the oncoming airflow, and with that there is much more drag. And this is effectively a huge air brake.
So in order to maintain momentum if the airplane is joining one turn with another, they often use afterburner. I'd say most modern military jets are capable of using full military power to maintain momentum in most of the high g turns you see at an airshow, but an airshow is all about visuals, performance and connecting one high g turn with another, so afterburner is much more effective for that.
A high g turn at high speed won't often look as if it is turning fast enough to suggest it is high g, but its just deceptive due to the radius of the curve being bigger due to the speed.
High g looks more impressive when at medium/low speeds because this gives better visuals from the ground as the airplane does much smaller radius turns.
As the above reply states, high g turns require lots of power in order to maintain momentum/airspeed. In order to do a high g turn it means the airplane must present much more of the wing surface in to the oncoming airflow, and with that there is much more drag. And this is effectively a huge air brake.
So in order to maintain momentum if the airplane is joining one turn with another, they often use afterburner. I'd say most modern military jets are capable of using full military power to maintain momentum in most of the high g turns you see at an airshow, but an airshow is all about visuals, performance and connecting one high g turn with another, so afterburner is much more effective for that.
Thought I'd put this F-16 example in for info.
If you look at the contour where PS = 0, this shows you how many g the A/C can pull at difference Mach numbers without losing or gaining energy. Above the line, the aircraft is losing energy (decelerating or losing altitude). Below it, the aircraft is gaining energy (accelerating or climbing).
You can see that below M0. 5, it can't maintain 4g even at full reheat - (but this chart is specific to a particular A/C configuration, it'll be different at an airshow with less fuel and ammunition
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