Thank you much for your answers. You wrote a lot of informations and I am sure that for many people those information will be helpful but unfortunately there is nothing new to me. I know how to perform flat turn, which actions are needed. I know also a difference between World War I, nowadays aerobatic planes and Spitfire and I don't expect to meet the same in all cases. I never thought that a flat turn is something popular and I tried it in Spitfire a bit incidentally. I would like to add that I have read the manual and I know that I should avoid using rudder during normal flight.
Dudley Henriques wrote:
This causes a side slip condition and the influx of tremendous fuselage drag. Even if the power to weight ratio is strong enough to produce a nose rate and change in the velocity vector, the combination of the fuselage drag and inadequate rudder authority will result in at the least a forward slip and at best a descending slipping turn that should eventually stabilize into a sustained descending side slip.
Do you have something that illustrates that, with proper forces? I am a PhD student in physics and I must say that I am not satisfied fully with the answer and I can't imagine that.
The only problem may come from a drag and an engine power insufficient to keep the speed above the stall speed. If the power is enough to deal with the additional drag, and if there is a "nose rate" then the plane should rotate. There is no force that prevents the rotation until a kind of "equilibrium" or rather a stabilisation is reached in which a drag perpendicular component equalizes the perpendicular component of the force from the rudder. (I keep in mind that stabiliser+rudder AOA and airspeed also changes and the rudder can loose efficiency in manoeuvres like that). That's the moment in which the angular speed stabilizes but it is non-zero. I don't care the angular speed - it can be low. I don't expect to turn in 10 seconds, even I don't expect 60 seconds - in fact I expect a turn with a really big radius with Spitfire. But I don't expect that planes fly sideways.
So I'll be very thankful if you have any pictures explaining why a plane can be unable to do a flat turn if the power is sufficient to keep the speed above the minimum speed.
Welcome to our forums, and know as well that your questions and observations are also welcome here. It is actually through your exact type of input that we are better able to deal with the factors that define A2A as a design team totally devoted to providing the sim community the finest and most accurate product available.
This being understood, let's revisit this flat turn issue for just a minute and see if perhaps we're not so far apart in our thinking. For the purposes of this post I will be focused ONLY on the Spitfire as the test vehicle.
As I said in my initial explanation on the issue of rudder only turns, in discussing this issue, it is of paramount importance that the exact definition for the term "turn" be established up front so that the aerodynamics involved can be clearly defined, as there exist on the planet extremely high performance aerobatic aircraft that posses thrust to weight ratios and rudder authority capable of FORCING such turn.
If we define the term "turn" as a permanent change in the aircraft's heading performed without any loss of altitude, we have an aerodynamic situation that is extremely difficult to achieve for most aircraft, the Spitfire among them. The exact point where the Spitfire's rudder authority becomes insufficient to overcome the fuselage drag being produced by complementary yaw and continue to produce turn with the wings held at 0 bank is difficult to define, but it is an absolute certainty that any heading change achieved through the use of rudder alone will also result in a considerable loss of altitude.
So yes, in the respect that a heading change can be achieved with rudder alone, that is correct. The amount of that heading change however is subject to extreme losses in other aerodynamic assets.
All this having been said, and because the issue of a flat turn wasn't part of our normal flight testing during the Spitfire Beta process, I just performed a flight test in the our Spit Mk2b to ascertain the flight model in the regime we have been discussing and I find a flaw in the flight model that substantiates at least in part the points you have made does indeed exist. I am not seeing the exact behavior with full rudder application to induce complementary yaw that I would expect to see in the actual aircraft.
I have spoken to Scott on the phone and we will be working to change the FM to a more accurate representation for this behavior.
I will speak for both Scott and myself in thanking you for taking the time to pose your questions on our forum. By your participation you have made it possible for us to make an excellent A2A Spitfire even better than it was.