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Sky Dancing

Turn Performance

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Quote Originally Posted by Nepe EAF51 View Post
Any turn has two characteristics: Turn Radius and Turn Rate.

Turn Radius: the radius of the circle you are flying in.
Turn Rate: how fast you are moving in your turn circle.

We want the maximum turn rate with the minimum turn radius. Both depends only on speed and G's (for a given altitude and weight)

In short, as your speed increases also does your turn rate, until you reach the limits of the plane (or the pilot): the max G's you can pull. This speed is called "corner velocity", and it is the speed that gives the maximum turn rate and the minimum (or close to) turn radius. Thats great, but...if you pull that turn your speed will inmediatly starts to decrease and now you are below corner velocity. That is, corner velocity gives an instantaneous turn, not a sustained turn. If you keep pulling max G's you will slow down until the plane is able to keep the speed: that is the "best sustained turn speed", and gives much less turn rate and approx the same turn radius than corner velocity.

So yes, a FW190 can turn better than your Spit, if he is at the corner velocity and you are not. He can turn faster than you and inside your turn circle. Only that he will not be able to hold that turn for more than a few seconds, as he will be burning speed like crazy.

BTW, if you pull max G's above corner velocity, your turn rate will be worse and turn radius much worse than at corner.

Now for the more detailed explanation:

Look at this Energy Maneuverability diagram:



horizontal axis: airspeed
vertical axis: turn rate (in degrees per second)
we also have lines por pulled G, and for turn radius (in feet)

The most external lines show the limits of the aircraft performance: it is impossible to fly outside those limits (or the plane will stall if you force it to fly there). You can see how the line starts at stall speed, rise until corner velocity, and then goes down until max speed is reached. The lines starting near 150 mph are those of Ps (specific power) = 0, and gives the best sustained turn: the plane can hold that turn as long as he has fuel. Above that line you have only instantaneous turns; below it, you can hold the turn as long as you wish.

You see that corner velocity for a La5FN is 350 km/h, but if you pull max (6) G's at that speed you will be losing speed and coming down the blue line until you reach max sustained turn rate speed (around 250 km/h). Notice that while you slow from corner velocity your turn rate decreases rapidly, but your turn radius is almost the same.

Now suppose you are in a turning fight, both you and the bandit are already at best sustained turn rate speed, riding the edge of the stall. If you relax g´s and get a little more speed, you give up both turn rate and radius: bad. But that Energy you are not using now you can convert into altitude. I do this often, letting the enemy gain slowly on me as he pulls max G's, while I make a bigger and slower circle, but gaining alt above him. Many times when he has come to near my 6 I will have some meters of alt advantage, and he will not be able to pull up his nose to firing position. It´s dangerous and depends on relative performance of planes, be warned.

Btw, about use of flaps (from Andy Bush):
flaps increase the G available at a given speed that is BELOW CV.
Why would you use flaps? To gain an improvement in available G at slow speed. What is "slow speed" Anything up to max flap extension speed and below CV. In this regime, you can expect to get an increase of one or more Gs with some flaps out.

What about using more than the first "notch" of flaps? As a rule, as you extend more flaps, you get a much higher increase in drag than you get an increase in G improvement...in fact, your G available may well decrease.

Could additional flaps be used? Yes, but only for very specific purposes...such as in a "who can fly the slowest" contest...or when trying to slow down quickly (but observe flap limiting speeds when doing this).

In summary, don't use flaps above CV...no need to. When below CV and also below the flap limiting speed, use a minimum flap setting to possibly increase your G available.
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