Don’t get in a FlapSome players make good use of flaps, others don’t. For the most part, we learn how to employ flaps from experience, but in some cases, even after significant experience it is still all too easy to get it wrong. One reason for this is a lack of good information. My intention in this post is to begin to help fix that.
Firstly though, some general comments on the use of flaps in air combat. It is fairly commonly known that using flaps changes the camber of the wing and that this changes both the lift and drag. Most players are aware that the lift increases, and the drag also increases, but what is important is the ratio between the increase in lift and drag and that ratio is known as the aerodynamic efficiency. Depending on the type of flaps and how much they are deflected, the influence of the flaps on the profile and induced drag in proportion to the lift can result in either an increase or decrease in the resulting aerodynamic efficiency of the wing. What that means is that the use of flaps can be good or bad in terms of the price you have to pay for the increase in lift.
What does that mean in terms of air combat? During an engagement, the differences in lift and drag are apparent by the influence on the way our aircraft can turn. Employing flaps generally results in higher instantaneous turn rates, and a smaller turn radius. However, in the case of a sustained turn, while the turn radius is always reduced, the sustained turn rate may either increase or decrease.
In cases where a particular flap deflection results in a reduction in turn radius, and an increase in the sustained turn rate, it is very important to identify that, because it can be highly desirable to fly in that configuration. However, it is more common for a reduction in turn radius to be accompanied by a reduction in the sustained turn rate. In those cases it is essential to know when you need to minimise your turn radius, or when it is more important to maximise your sustained turn rate.
The answer is this… Generally, (I need to speak in general terms because there are exceptions and I will come to that later) it is better to minimise your turn radius in a one circle fight (nose to nose turns) and to maximise your turn rate in a two circle fight (nose to tail). This is a very important point, it is so important that many players lose fights because they fail to understand the subtleties of it.
In order to make best use of the differences in radius and rate caused by the use of flaps, it is necessary to know how your turn radius and turn rate are influenced by the use of flaps in a sustained turn. That information is conveyed most readily by means of a diagram showing the turn circle for a fixed time. That way the turn radii can be seen relative to each other, and because the circles are drawn for a fixed time, the differences in sustained turn rates will be apparent because some lines will extend farther around the circle than others. You can see this by inspecting the following diagram.
Here you can see that the F4U1D benefits from a tighter turn radius and an increased sustained turn rate when flaps are employed. You will notice that the best sustained turn rate occurs when the flaps are deflected by two notches. That’s the best place to be in nose to tail fight, because the way to win that kind of fight is simply to win the turn rate war. You need to gain angles on your opponent until you move around the circle onto his tail. In order to do that you need to know how to maximise your sustained turn rate. The diagram above shows you exactly how to do that.
You can also see that if you deflect the flaps on the F4U1D beyond two notches, you pay for it with a reducing sustained turn rate. Notice also that once you get to four notches, the fifth and final notch gives you a slightly tighter radius with an insignificantly small reduction in rate. So for this particular aircraft, once you enter a turn fight, you should use only two notches of flaps as long as you are turning nose to tail to optimise your rate, and if the fight goes nose to nose, such as in a scissors, where you need to reduce speed and minimise your turn radius, use full flaps.
Lastly, if the situation changes don’t be afraid to work the flaps. If the fight is nose to nose and you employ full flaps as appropriate in that case, but the situation changes to one where you find your self chasing the bandits tail, don’t be afraid to reduce your flap deflection in order to improve your turn rate, and thus out turn your opponent.
Having said that, few things in life are cut and dry, and even that wisdom isn’t always safe. It all depends on the aircraft. For example, take a look at the diagram for the A6M2 shown below:
You will see that this case is very different from the previous one. Instead of the flaps producing an increase in the sustained turn rate as it did in with the F4U1D, you now notice that as the flaps are deflected the turn radius tightens up as expected, but now the sustained turn rate drops also. You can see that while there is a significant drop in sustained turn rate for the first and second notch of flap deflection, the second, third and fourth positions all have very similar turn rates.
The conclusion you can draw from this is that for this aircraft, if you want to maximise your turn rate, don’t use your flaps at all. There is no sweet spot as there was with the F4U1D. Also, if you feel the need to deflect the flaps by two notches, you might as well go all the way, because you will get a tighter turn radius and your sustained turn rate won’t diminish any farther than it already has. However, in this case the turn radii are small and the reduction in radius at full flaps is significant and that presents another problem.
Continued...
