Originally posted by Widewing
Testing shows that the Ki-61 has a rather large turn radius compared to the others tested, while having the lowest wing loading (substantially) and just about the highest CLmax.
Just a word of warning here for the unwary with regard to aircraft parametric data. It is true that a low wing loading and a high Clmax are generally good when it comes to turning, but you can't draw conclusions about sustained turns based on those factors alone as safely as you can for instantaneous turns.
The reason is that it is possible for one aircraft to have a lower wing loading and a higher Clmax than another, yet still have a larger sustained turn radius and lower sustained turn rate.
The reason is due to the other variables involved. I can explain it easier with an example
Consider two aircraft, the first we will call aircraft A has a wing loading of 34 lb/ft^2 and a Clmax of 1.7 while the other we will call aircraft B has a wing loading of 36lbs/ft^2 and a Clmax of 1.6, which one would you expect to have the tighter sustained turn radius?
Well, aircraft A has a lower wing loading and a higher Clmax so you might expect it to have the smaller sustained turn radius.
Do you agree? If so, for this example, you would be wrong!!
In general it all depends on the variables that have not been considered.
In the example above you would probably be even more surprised if I told you that aircraft B was 1000lb heavier than aircraft A, with a lower Clmax and yet it still has a tighter sustained turn radius and a higher sustained turn rate.
Surprised? Good, then I have your attention. So what have we left out that makes so much difference?
Well we haven't considered the power plant or prop. The combination of a more powerful engine and more efficient prop can result in a higher sustained turn speed, which will increase the sustainable g, thus reducing the sustained turn radius and increasing the sustained turn rate.
We also haven't really considered the the entire wing geometry, only the area. If we begin to introduce other factors, such as the aspect ratio of the wing we will see that a higher aspect ratio will have a tendency to reduce the induced drag, thus increasing the sustained turn speed, which in turn will increased the sustained g which will reduce the sustained turn radius.
In the example I quoted above, I gave aircraft B (remember it was heavier, and had a higher wing loading and lower Clmax) a more powerful engine, a higher aspect ratio wing and a more efficient prop and it not only had a smaller turn radius, it had a much higher sustained turn rate. Contrary to the conclusion that would most likely be jumped to.
The important thing to remember here is that while wing loading, Clmax and power loading alone can give some indication of relative performance, it can do so only if all other factors are considered equal, when you consider dissimilar aircraft, the other factors are rarely equal, and if they vary considerably conclusions reached on limited data, such as wing loading and Clmax alone can be unsafe, so it is always wise to exercise some caution.
If in doubt, it is always better to use as much data as possible, and carry out a more detailed analysis, rule of thumb estimates aren't a good basis for making predictions about dissimilar aircraft performance.
Hope that helps.
Badboy
