Quote:
Originally Posted by Blackdog_kt
You might be on to something here.
Adverse yaw is encountered in all aircraft, but maybe the Spitfire's famous wing is partially to blame in this case?
From the wiki:
Why do we care? Well, because more lift means a bigger forward/backward component in the diagram, which means more adverse yaw. If the Spitfire's wing is capable of higher lift than other aircraft (for a given airspeed range, conditions, etc etc) then it will also be prone to more adverse yaw, which means you need to use the rudder more or have oscillations when it goes back to neutral behavior.
I don't know exactly how the Spit's wing compares to other aircraft, so if anyone could shed some light maybe we could track down if this is the cause of the instability. In the case that the Spit wing is better at producing lift then incurring extra instability during rolls would be accurate. There's no such thing as a free lunch in physics 
On a more humorous note
Good one  |
Spitfire wing produces a lift equal to the plane's weight in horizontal flight. Maximum lift is produced in sharp turns; the plane's great wing area with the accompanying lift producing capacity does not make for any increases of adverse jaw effect in low-G regimes. On the other hand, as you can see from your diagram, a plane with a bigger wingspan (and aspect ratio) does have the best chances for an increased adverse yaw because of a longer moment arm of the ailerons/wing outer panels relative to the CG/aircraft axis. Gliders and Ta 152H, for example, come into that category.
The Spitfire had differential Frise ailerons- that means most effective means available to counter the adverse jaw. Frise has a price of increasing the rolling plane's drag, but Mitchell obviously accepted this trade-off knowing that a fighter has to hit something, too.
Spitfire wings were an excellent and beautiful design, but that ellipse is not such a magic as it's fame implies. It was a quite thin profile, large area and low wing loading that did much more for the efficiency of it's wing's then their elegant elliptical planform, which probably did more for the Spit's high unit price.
Twisting the tips of a conventional tapered wing-planform brings it very near to the optimal elliptical lift-distribution*, at a fraction of the cost of a wing with an actually elliptic geometry. This goes even for the squared-off wingtip planforms, which do not spoil the lift distribution much additionaly, either (Bf109, P51).
Mitchell knew that very well, for sure, but went over to the elliptical wing after additional guns have been demanded - and he had no room for them in the original tapered wing. Moreover, the ellipse solved the structural problems of a thin profile and made his already excellent wing concept a couple of additional percent better aerodynamically; I imagine nobody asked much about the unit price at that time, anyway.
Rarely used for the reasons mentioned, the elegant ellipse of the wings made the Spit recognizably different from the other planes, and the chance to create a bit of magic around this has not been missed in a wartime, of course.
This famed ellipse of the Spitfire's wing found a way into the British hearts so deep, that redesigning the Typhoon into Tempest, Camm took the semi-elliptical planform partly to inspire confidence of his customers in the ministry, I suspect.
Nothing occurs to me as a possible cause for any increased adverse yaw in the spit's wing aerodynamic.
Like almost all fighters, Spit has had a lean stability for the sake of being more manoeuverable. Many pylon racers of the period were much more radical in that sense. Polikarpov designs, especialy the I16 had quite narrow stabillity margins, almost like racers.
Adverse yaw is only one of the disturbances (like gusts, gyroscopic effects, etc) which the stabilizing surfaces have to overcome, and the gyroscopic precession after a pedal has been kicked should be more noticeable on any prop plane than the adverse yaw.
Real Spit probably felt the adverse yaw properly only when rolling quite fast. So, you barking under a wrong tree, my lads
* When the lift-force distribution along the wingspan has a shape of an semi-ellipse, it s an optimal case, with the lowest induced drag, i.e highest lift-producing efficiency.