The A2A Simulations Community

Hi!

I bought Spitfire two days ago and it is a wonderful product, visually and physically. Because I am a fan of aerobatics I tried to test it in various manoeuvres. I managed to do a nice loops, rolls and split s. I was able to do a really nice hammerhead and tail slide which is not so common in many of FSX planes. Then I tried directional slips and similar manoeuvres. I observed something strange:

I tried to do a flat turn: it means I wanted to turn with my rudder only, keeping the wings levelled with ailerons. I was able to keep the plane in a level flight, the plane rotated a bit from the original direction but the velocity vector appeared to be stable and didn't want to rotate at all. So I was moving constantly in the same direction, but a bit sideways.
Additionally I think that it is to hard to roll the plane with the rudder only.

I think that maybe it is a known future and a limitation of the flight model, but I wanted to be sure and eventually report a problem.
On the other hand I've been flying with planes in FSX which were able to do a flat turn.

Have you observed anything similar?
(I have the correct realism settings, as in the manual.)

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Krzysztof Sobczak

Something that I feel has been "over" simulated is the usefulness of a rudder, especially on warbirds. The actual size of the Spitfire rudder is rather small, and the actual shape of it doesn't help much either. While it does have some decent rudder authority compared to many planes of the era, the reality is that the majority of high performance aircraft of this era suffer from a severe lack of rudder authority. It has enough authority that the plane will forward slip however.

For the most part, a rudder is made specifically to help coordinate the aircraft and provide some control during crosswind landings, as well as to correct the nose during a takeoff. In this role it succeeds quite well. The plane was never to my knowledge made to "flat turn," and it serves little purpose for a combat aircraft.

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As aerobatic instructors we have to deal with the question of "rudder only" flat turn all the time with new acro students.
The problem with rudder only turn is in how it's defined. If defined as a turn while maintaining a constant altitude as in a level turn, the ability to do that goes south in a heartbeat for most aircraft. If a descending rudder only turn is what is desired, it can be done in some aircraft with high thrust to weight ratios and extremely powerful rudder authority.
The problem with a neutrally mass loaded fighter like a Spitfire in attempting a rudder only turn is in the aerodynamics involved.
If a true flat turn trajectory is required, as full rudder is applied in these aircraft to start that turn, enough anti-turn aileron has to be instantly applied so as to kill the increased lift on the outside wing and thus prevent a lift vector split which of course constitutes bank. 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.
Dudley Henriques

Just to add to Dudley's excellent answer, the flat turn was made famous in the first instance by Werner Voss in his Fokker DR1. The big thing to note here is that the DR1 had a "full flying tail" type rudder..the whole surface moved and there was no vertical stabiliser to do what that does....ie help stop you skidding sideways. (note, Boelke and Immelmann had both used it before that in the Fokker E1 but Werner got "the big press coverage" because of his famous fight with 56Sqn later.)

A common defensive trick of good Spitfire pilots was to stand on the rudder to make it APPEAR as if they were turning..the incoming bullets would then pass inside them.

Pilots of modern aircraft (myself included until I did Tiger Moth time) usually have no idea what a rudder is really for..since adverse yaw has largley been designed out.

One last point...except for slow speed aerobatics, takeoff and landing, the Spit should be flown "feet off" the rudders. Any trim issue should be dealt with by using the rudder trim..to prevent fatigue.

regards

Darryl

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...Some say he never blinks, and that he roams around the woods at night foraging for Merlin parts...

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.


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 moment of drag perpendicular component equalizes the moment of 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.

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Krzysztof Sobczak

Zefirro, just as you may not be aware. Dudley isnt a PhD student, or a text book student. He is however...

"........an aviation consultant and former professional civilian pilot, having flown high performance aircraft for over forty years. He retired from flying in 1995.

Mr. Henriques is a past President of the International Fighter Pilots Fellowship. He has served in an honorary capacity as Maryland State Representative, Eastern Region Director, and Director of Special Projects, for the Combat Pilots Association of the United States.
He was an active member of the Professional Race Pilots Association, and the P51 Mustang Pilots Association.

Flying history
He holds commercial ratings for both single and multi-engine aircraft, and is a certified flight instructor. He has flown at least seventy different types of aircraft, including experimental, prototype, and fighters, both jet and propeller.

A specialist in aerobatic demonstration flying and aerobatic instruction, he has flown hundreds of air shows in aircraft ranging from a Pitts Special to a P51 Mustang fighter.

During the early sixties, flying a Mustang, he patented a three point reverse roll to knife-edge tactical pitch-out approach that became a trademark manoeuvre.

One of very few civilian pilots who have flown both American and foreign high performance jets, he has flown by invitation with the Canadian Jet Aerobatic Team Snowbirds, and the Naval Test Pilot School in the supersonic Northrop T38 Talon.

As an aviation writer, Mr. Henriques has written extensively for the fighter communities of both the Navy and the Air Force. His nationally distributed articles on both the Blue Angels and the Thunderbirds during the fuel crisis of the early seventies, were of direct assistance to both these military aerobatic teams in maintaining their respective missions." (http://wikibin.org/articles/dudley-henriques.html)

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I never said firmly that there is something wrong, but there is something that I don't understand and I am not satisfied by the explanation. He wrote about being an flying instructor, so I wrote that I am interested in physics (since I am a PhD student) and I am not satisfied completely. I would like to know more and I explained my point of view. There is never anything wrong in asking or discussing. So I don't get why I have to believe just by showing me some titles. I was learnt that it is good to ask questions, even if an asked person is a Nobel Prize winner. And by the way, maybe we are speaking about two bit different things.

I just want to add, that I never wanted to make a 360 flat turn, but I was interested in something general, simply a small turn. If I am not able to make a 20 degree turn then I ask myself: why am I not able to do that? Is the physics model incorrect or is this something related to the real physics of the plane? From what I met in my experiences with flight simulators (even from a developer-programmer point of view) there are more often incorrect physics models than planes described physically with all details.

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Krzysztof Sobczak

Interesting post )

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.
Sincerely,
Dudley Henriques

Thank you very much for your answer. I am sorry that I wasn't enough strict from the beginning and I called it a flat turn, but that was the first term that I found to explain the problem. In terms of continuous stabilised turn you are of course right.

As I wrote in the first line of this topic: I find your job - the whole team - as an outstanding one. I love this plane and I really appreciate your professionalism, perfectionism and commitment in creation of the most precise and realistic planes. Thank you much. I hope that my words were not to unkind, but, exactly as you, I like to be perfect in everything that I do.

Once again thank you for your response and I am glad that my observation could be at least a bit helpful.

Krzysztof Sobczak

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Krzysztof Sobczak

You are very welcome. Enjoy the Spitfire, and because of your input, we'll be making it even better.

All the best to you,
Dudley Henriques

Interesting thread,

I also noticed that the Spitfire is extremely stable along the yaw axis. Haven't read any detailed reports about the Spitfire but e.g. the Bf 109 has an almost neutral yaw stability.
On the A2A Spitfire when pushing the rudder to the stop and thereafter releasing it, the fuselage doesn't swing through the original heading a single time but dampens out immediately which seems a bit strange for such a small tail.
Furthermore I'm surprised that the elliptical wing and the dihedral don't produce any roll moment when yawing the plane with full rudder deflection.
Again with the Bf 109 and e.g. the FW 190 it's even possible to roll the plane with the rudder alone.
Presently it's not possible to slip the Spitfire due to the very weak rudder but AFAIK the RW Spitfire doesn't like to be slipped at all....
A final question concering torque.
When flying just above stall speed at idle and I'm slamming the throttle fully forward while keeping the speed, there's also no roll moment.

Apart from these few points I'm VERY impressed. With the accusim module the immersion is unbelievable realistic. Thanks for this great plane!

Best regards

Bernt

To add to Bernt's comments - particularly this note:-

Yes - I would expect the same too.
Commenting on the OP's original post - I would only expect to be able to get a flat 360 turn from something like an Extra 260 or 300: there are a number of excellent aerobatic monoplanes around nowadays that have the power, the rudder authority, a well-back CG - to do the maneuver - and all having almost zero degrees dihedral - which is the major key, along with a 60 - 80% area rudder. This is the combination that will give a flat turn. The Spit comes nowhere near to meeting that criteria, and so I would expect merely a pro-rudder roll - because of the dihedral - followed by a forward slip. The Spit was never intended as an aerobatic aircraft: indeed most aerobatic aircraft of the day were biplanes!

Now I have to go and try a flat turn (plus a hammerhead, a chandelle and a whip stall) in the new bird, of course....

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pj



i7-2600K@4.9gig, ASUS P8P67 B3 DL; EVGA GTX580; 8gig Corsair Vengeance C8@1600; Win 7-64; TH2G w/3x19" VA926; Homebuilt cockpit; 6-pack throttle quadrant; TrackIR5 & EZCA; No blurries.[/font][/size]

Just to add my 2c worth to this.

I've not been able to get the Spitfire to do a flat turn when flying horizontally, but I once managed an incredible "hammerhead" turn when trying to do a wing-over. I think I kicked the rudder slightly just to co-ordinate the turn or correct a bit of drift. The result was entirely accidental but looks great!

Take at look at my first A2A video here at around 3:14.

My gut feeling is that the A2A flight model is accurate (I wouldn't *really* know). FSX limitations aside, it appears to be the most accurate Spitfire flight model in any sim that I've played - including the combat sims. I'll be interested to compare this with Oleg Maddox's Spitfire in "Cliffs of Dover", when it comes out.

At the end of the day, no (hobby) sim can entirely reproduce the myriad forces that affect an aircraft. To me, "suspension" of belief" is what it's all about. The A2A Spitfire does that for me - where many others just feel like they're "flying on rails".

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www.nzfsim.org

But even the Bf 109 was able to do a 'flat turn' despite the rather small tail (with a speed loss of approx 20kts AFAIR)
It's interesting that the Realair Spitfire and the A2A Spitfire are both reported to be flying very realistic but it's e.g. not possible to slip the A2A version but the Realair one slips very nicely.

Now THAT is strange...the A2A bird sideslips very nicely on my setup?

Darryl

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...Some say he never blinks, and that he roams around the woods at night foraging for Merlin parts...