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XyZspineZyX
09-14-2003, 01:34 PM
In FB 1.11, every 109, including the K4, will have a RIGHT roll tendency with a LEFT yaw tendency, which is a little strange to me. I think the yaw and roll tendency is coupling to each other.
And when I turn off the torque&gyro option in difficulty setting, I found that, the 109 begins to roll LEFT with a LEFT yaw! That seems to say, it's the torque that gives the 109 the RIGHT roll tendency. Is it true? (remember, 109's prop is clockwise rotating from cockpit forward view, so the torque should give a LEFT roll tendency.)

Oleg or anybody, can you point out where I am wrong, or could you please kindly give me some explanations on this?

Thank you so much. And I will keep waiting here for some replies.

XyZspineZyX
09-14-2003, 01:34 PM
In FB 1.11, every 109, including the K4, will have a RIGHT roll tendency with a LEFT yaw tendency, which is a little strange to me. I think the yaw and roll tendency is coupling to each other.
And when I turn off the torque&gyro option in difficulty setting, I found that, the 109 begins to roll LEFT with a LEFT yaw! That seems to say, it's the torque that gives the 109 the RIGHT roll tendency. Is it true? (remember, 109's prop is clockwise rotating from cockpit forward view, so the torque should give a LEFT roll tendency.)

Oleg or anybody, can you point out where I am wrong, or could you please kindly give me some explanations on this?

Thank you so much. And I will keep waiting here for some replies.

XyZspineZyX
09-14-2003, 04:37 PM
i just curious why nobody mentioned this bug should be fixed from FB1.0 released untill now?

XyZspineZyX
09-14-2003, 05:01 PM
HQ1 wrote:
- i just curious why nobody mentioned this bug should
- be fixed from FB1.0 released untill now?
-
-

i can't recall precisely, but seems that IL2 also has this bug/problem?

XyZspineZyX
09-14-2003, 10:57 PM
i think they are trying to give planes the ability to perform snap stall rolls not only the 109 does it just about everyaircraft does it now in the game


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Good dogfighters bring ammo home, Great ones don't. (c) Leadspitter

XyZspineZyX
09-15-2003, 12:21 AM
BSHD

About the roll: there are two effects coming off the engine that cause a rolling moment. The first is the reaction to the torgue. If the propeller is turning clockwise from behind (from the pilots point of view), then the airplane will want to roll to the left. I believe you understood this part, from your description. This effect is actually not that big during straight and level flight at a constant propeller setting, but it tends to dominate when throttling up and as the propeller disc accelerates.

The second effect is usually more dominant in steady flight and works as follows. With propeller rotation clockwise again from the pilot's point of view, the air coming off the propeller has a rotational component that flows down the right side of the airplane, from right to left under the fuselage, upwards on the left side of the fuselage and from left to right over the top of the fuselage. This rotational component reduces the effective angle of attack at the root of the right wing, and it increases the effective angle of attack on the root of the left wing. The effect is that the left wing produces a bit more lift than the right, and the aircraft wants to roll to the right.

As I said, this second effect is usually the more dominating of the two effects at a constant throttle setting, but the relative strength of the two depends on the throttle setting, overall angle of attack of the aircraft and the location of the wing on the fuselage. The way you describe it in your post, it sounds like it is modelled correctly in the sim (unless of course there is documented proof that in the case of the 109, the first effect tended to dominate).

In regard to yaw: it is caused by the same effect that causes the asymmetric angle of attack at the root of the wing. As the rotational air continues down the length of the fuselage, it eventually hits the left side of the rudder (remember, it flows from left to right over the top of the fuselage). This means that the fin sees an effective angle of attack that wants to push the tail to the right, making the nose yaw to the left. The Bf-109 had an asymmetric fin that is thicker on the left side than on the right to help it counter this force, but depending on the throttle setting it will probably still want to yaw the nose to the left (especially when at full throttle).

XyZspineZyX
09-15-2003, 03:14 AM
Thx, Oryx:
I have had the same thought as you before. The flow you described is called slipstream. But when you turn off the torque&gyro option in difficulty setting, you will find that the 109 begins to roll to LEFT! That is to say, it's the torque that makes the 109 roll RIGHT! If the option title is not "torque&gyro" but "slipstrem", that makes sense. (no slipstream, there is only torque left and the plane begins to roll LEFT...)

P.S.
1. How to judge that between slipstream and torque, who dominates? Is there any "theory"?
2. What do you mean "fin", what is that? It's vertical stablizer or level stablizer? I am not native English speaker. Sorry.

XyZspineZyX
09-15-2003, 03:19 AM
In addition:
It might also be a bug of "torque&gyro" option, which is supposed to be "slipstream on/off" option.

XyZspineZyX
09-15-2003, 03:27 AM
Hi BSHD

Usually, when people talk about Torgue effects, they actually mean all the "by-products" of generating thrust, which includes slipstream effects, torgue effects, gyroscopic effects, etc. I believe the option toggles all of these effects in the sim on and off.

- 1. How to judge that between slipstream and torque,
- who dominates? Is there any "theory"?

No simple theory that I know off. You can do a fairly complex analysis to predict the rotational component of the flow, then use something like a panel method analysis to calculate the induced effects on the wing and how much rolling moment that produces. It goes a bit beyond what I can quickly explain here on the forums. I have no idea if this is what Oleg's team did when creating the flight models, or whether they used reports from test pilots. (The latter doesn't always include enough detail).

- 2. What do you mean "fin", what is that? It's
- vertical stablizer or level stablizer? I am not
- native English speaker. Sorry.

Yes, I meant the vertical stabilizer.

Regards,
Oryx

XyZspineZyX
09-15-2003, 03:58 AM
Oryx:

If the torque&gyro option turns off all the things like slipstream, real torque, gyro effects, the fighter should be precisely centered. But it's not the case, the 109 begins to roll left and yaw left, also, the "yaw indicator" and "bank indicator" (i mean the little ball at the bottom and the vertical bar in the middle, i don't know their English name) shows the 109 is rolling to left and yawing to left.

1. About the theory, I think it must be complex enough and it's impossible for me to understand such a difficult in English. So, I let it be. But the point you mentioned is really significant, to use the (test) pilots' reports. In some articles I read, they say, they need to step on the left rudder very very strongly in high speed dive, I used to think it's because of the fixed right trim on the rudder, now I think it's also because of the slipstream caused right roll tendency.

2. You said the make the fin "left thicker than right" to trim the rudder? I don't know what it means.

XyZspineZyX
09-15-2003, 04:06 AM
Thanks for the info Oryx, great stuff. Consider it stored in memory (to be probably forgotten tomorrow, not your fault of course, I blame the ready availability of miscellaneous drivel data that keeps slipping into my brain and pushing out stuff like this that I find important).

XyZspineZyX
09-15-2003, 06:20 AM
BSHD

Remember that there are also fixed trim tabs on the 109. If the torgue effects (all the effects associated with them), are "turned off", then the fixed trim tab settings probably over-compensates, unless the simulated Bf-109 is "re-trimmed" when turning off the engine effects. Since I don't know for sure what is turned off with the realism setting option and if the fixed trim tabs are "readjusted" so to speak, I can only speculate. I wouldn't place too much importance on what the sim does when the realism settings are turned off and to be honest, I have never tested it myself. In general, it looks like the behavior with the torgue and gyro-effects turned on is correct (at least in a general way).

- 2. You said the make the fin "left thicker than
- right" to trim the rudder? I don't know what it
- means.

Try to find some high-quality detail drawings of the Bf-109 - the better ones usually show this. It is probably less easy to see it in photographs unless you can somehow find a picture taken right from above. Basically, the vertical stabilizer of the Bf-109 is not symmetrical. The left side is thicker than the right, so that the vertical stabilizer has a certain amount of camber to the left.

If airflow hits the vertical stabilizer at an angle (as explained earlier), then the vertical stabilizer will produce a side-force in exactly the same way that a wing produces lift. Of course, this is not wanted and one way to compensate is to try and align the vertical stabilizer with the local flow by mounting it at a slight angle on the fuselage (in this case with the leading edge pointed to the left). Some WWII fighters do in fact follow this approach.

Willy Messerschmitt opted for another solution. Instead of mounting the vertical stabilizer at an angle, he opted to use a non-symmetrical vertical stabilizer that naturally wants to produce "lift" or rather "side-force", to the left. By choosing the correct amount of camber, he could mount it pointing straight forward while it still compensates for the cross-flow. The overall result is very similar to mounting a symmetrical vertical stabilizer at an angle.

Both of these methods still have the problem that at some throttle settings they will over-compensate and at others, they will undercompensate. For that reason the airplane is still not trimmed for all speed/throttle combinations. The fixed trim tab allows for a bit of tuning on the ground, but there will still be flight regimes where some rudder input is needed. This brings me to your other point:

- the (test) pilots' reports. In some articles I read,
- they say, they need to step on the left rudder very
- very strongly in high speed dive, I used to think
- it's because of the fixed right trim on the rudder,
- now I think it's also because of the slipstream
- caused right roll tendency.

Actually, it is the opposite here - it is the lack of slipstream effect that causes the yaw to the right. At high speed, the cross-flow component of the flow becomes less as a percentage of the free-stream velocity component. In consequence, the angle with which the flow hits the vertical tail is reduced. Think of it this way:
> the cross-flow component is more or less dependent on throttle setting only.
> the free-stream component is the same as the speed at which the airplane flies.
> As you go faster, the cross-flow component stays more or less the same for a given throttle setting, while the free-stream component increases.
> The angle between the two flow components therefore becomes smaller at higher speeds.

The above is an over-simplification, but it captures the most important result. The result is that at high speed that unsymmetrical airfoil (and right rudder trim) starts producing too much force to the left on the tail, which pushes the nose over to the right. To compensate, the pilot has to hold in left rudder.

This also means that it is possible to require right rudder at slow speed and high throttle setting (as in a climb), but left rudder at high speed and high throttle setting (as in a powered dive). Whether this cross-over in trim occurs obviously depends on exactly how the fixed trim tab is set up.

Unfortunately, it is very difficult to explain this stuff without pictures...

Regards,
Oryx

XyZspineZyX
09-15-2003, 07:28 AM
Mr. Oryx:
I have to say, your theory is super super clear to me! Excellent comments! Thank you very much!

Just 2 points to make it more precise:
1. you said, "it is the lack of slipstream effect that causes the yaw to the right". It might be "... causes the yaw to the left". The slipstream effect to the fin is "yaw to left".
2. you said, "This also means that it is possible to require right rudder at slow speed and high throttle setting (as in a climb),". In low speed climb, it's a little tricky, the plane is yawing to left, so you need to step right rudder, but at the same time, the plane is right rolling (because of the slipstream effect on the wing), so you need to step left rudder or push the stick to left. In FB, I usausally push the stick to left time by time and the right roll is compensating the left yaw in a way. http://ubbxforums.ubi.com/infopop/emoticons/icon_biggrin.gif

About the case when the torque&gyro option is turned off, anyway, I will let it be, though it's still a little weird to me. http://ubbxforums.ubi.com/infopop/emoticons/icon_smile.gif (without any torque or its by-product, the fixed trim tab and the asymmetrical fin of 109 should make the plane yaw to right, but unfortuanatly, we see 109 yawing/rolling to the left. It's not the bug of torque&gyro off situation? http://ubbxforums.ubi.com/infopop/emoticons/icon_biggrin.gif)



Message Edited on 09/15/0306:46AM by JG54_BSHD

XyZspineZyX
09-15-2003, 09:07 AM
does anyone notice that 109's right wing drops firstly when stall is coming in FB?but i think it should be left wing drops firstly in real life.

XyZspineZyX
09-15-2003, 09:37 AM
HQ1 wrote:
- does anyone notice that 109's right wing drops
- firstly when stall is coming in FB?but i think it
- should be left wing drops firstly in real life.
-
-


why? why did you say so? it seems that the slipstream will give more down-pressure to the right wing, than to the left.

XyZspineZyX
09-15-2003, 12:40 PM
here is an article .from this you can find what i said.

Flying Black 6

Republished with kind permission of Paul Coggan from Warbirds Worldwide #21



The Bf109 is a fascinating aircraft. It was produced in greater numbers than any other fighter aircraft, and was the main single-engined fighter opponent of the Spitfire and Hurricane in the Battle of Britain. Ever sinec I first flew a Spitfire I had a great desire to fly the '109. I soon had the opportunity to fly a Hispano HA-1112M1L Buchon and this made me even more curious about what a real Bf109 was like to fly.

John Allison did not have to ask me twice if I would like to be the other pilot to fly the Bf109G-2 that had been rebuilt by Russ Snadden and his team at RAF Benson. I still feel very privileged to be able to fly this aircraft so when I was asked to write an article for Warbirds Worldwide on flying it, how could I refuse!

The Bf109G has conventional elevators, ailerons, and rudder. Pitch trim is achieved by a variable incidence tail plane, and there is a ground adjustable fixed tab on the rudder and on the aileron for yaw and roll trim. The wing trailing edge incorporates manually operated simple flaps and radiator cooling is controlled by split flaps on the trailing edge which droop with the main flaps to increase flapped area. The outboard half of each wing leading edge incorporates an independent automatic slat, which extends at low speed or in hard manoeuvres. The main undercarriage legs retract outwards and when fully lowered the mainwheels feature a marked toe-in, i.e. the wheels are closer together at the front than at the rear. I believe that this unusual characteristic is caused by the problems of fitting the wheel well and undercarriage leg pintle into the wing due to the position of the main spar. The tailwheel is lockable from the cockpit. The engine is a Daimler-Benz DB605, driving a VDM variable pitch propeller which rotates clockwise when viewed from behind.

On approaching the aircraft it looks sleek, compact, and quite small compared to other World War II fighters. These characteristics are emphasised by the cockpit, which is small, cramped, and neither the seat nor rudder pedals are adjustable. Once the canopy is closed, there is very little headroom either. I am 6feet 3 inches tall, and to the question "How do I fit in it?" all I will say is that 'where there is a will there is a way!' However, the cockpit of this particular airframe is almost totally original, the only significant difference being that the gunsight has been removed and a Becker VHF radio and standby magnetic compass fitted in its place. This degree of originality adds much to the feel and character of this airframe and sets it apart from many rebuilt warbirds that have modernised cockpits, a practice that I dislike greatly. It must be added that this original cockpit has all of the labelling in German, airspeed in kilometres per hour (kph) and altitude in Kilometres. Manifold air pressure is in atmospheres (ata), 1 atmosphere being 30 inches of mercury.

Starting the engine requires one or two willing helpers standing on the starboard wing root to wind up the inertia starter with a crank-handle. The engine is then primed with about 10 strokes of a Ki-gas type pump, the fuel pump switched on and the starter handle pulled which engages a clutch connecting the inertia starter to the engine; hopefully the engine starts! There are two points about this starting procedure. Firstly, you cannot overprime the engine. Secondly it is not feasible to take the aircraft away from Duxford without the groundcrew!

Taxying is achieved using differential braking via rudder pedal mounted toe brakes. The aircraft is reluctant to turn sharply and my technique is to apply full rudder in the required direction of turn to give me better leverage and to then stamp on the toe brake. This is aided by pushing the stick fully forward to unload the tailwheel, an action which is totally unnatural to someone used to the Spitfire! However, the '109 is tail heavy and the tail never lifts. It is during taxying that the very poor forward field of view is first realised. You can see virtually nothing within 30 or 40 degrees either side of the nose, definitely worse than anything that I have ever flown.

Take off is made with 1 degree nose up tailplane trim, 20 degrees of flap lowered and always with the tailwheel locked. After lining up the throttle is smoothly opened to 1.1 ata, controlling the moderate left swing with rudder. Once the take-off power is set and the aircraft is directionally under control, the tail is gently raised just clear of the ground. The aircraft lifts off at around 150 kph with slight back pressure on the stick. This may sound simple, but is one of the most difficult tasks in flying the '109. If any swing is allowed to develop the toe-in on the outside wheel turns the aircraft even more i.e. it is directionally unstable. It will then roll about the outside wheel, leading to the classic ground loop. This problem is accentuated because the forward field of view is so poor that it is difficult to detect any swing starting. The only saving grace is that the lockable tailwheel gives some directional stability, and so it is kept on the ground for as long as possible. The gyroscopic effect of the propeller and loss of directional stability from the tailwheel once the tail is raised is marked, hence the tail is raised very gently and only slightly.

Once airborne, engine handling is markedly different from similar British and American engines, due to the lack of a constant speed unit on the propeller. The operating philosophy is that the engine has a running line of optimum rpm for a given manifold pressure; 2000 rpm at 1.0 ata, 2300 rpm at 1.15 ata (max. continuous) and 2600 rpm at 1.3 ata (30 minute limit). These rpm are also the minimum for the manifold pressure without overboosting the engine. The pilot sets the manifold pressure with the throttle, and engine rpm is controlled either automatically (when it is governed to the running line) or manually. Manual control is by a rocker switch on the throttle and this varies the propeller blade pitch. Once set, the propeller runs with fixed pitch, RPM increasing with increasing airspeed and vice versa. Cockpit of blade pitch is on a clock. For example, 12:00 is set for take-off and 11:45 for landing. Initially, we always flew the aircraft with manual RPM control, until we were happy with the automatic control functioning. In a display, 1.15 ata is set and RPM controlled manually to 2400-2500 to prevent overboosting. This requires a setting of around 11:05 at high speeds such as for loop entries, and an increase to around 11:20 over the top of a loop. This results in a lot of head-in-cockpit time and propeller adjustment during a display, greatly increasing the workload.

The Bf109G is heavy to manoeuvre in pitch, being similar to a Mustang. At 520kph it is possible to pull 4g with one hand, but I find it more comfortable to use both hands on the stick for looping manoeuvres, normally entered at 420kph and 3g. Pitch trim changes with speed are moderate, and the tail plane trim wheel mounted abeam the pilots' left hip is easy to use. For a display, I run it at 420-450kph in trim, and then do not retrim. This causes no excessive stick forces during the display. Overall the aircraft is straightforward to handle in pitch.

Roll performance is similar to a Hurricane or elliptical wing tipped Spitfire. A full stick roll through 360 degrees at 460kph takes 4 to 4.5 seconds without using rudder, and needs a force of around 20 lbf. One interesting characteristic is that rolls at lower speeds entered at less than 1g, such as a roll-off-the-top or half Cuban, have a markedly lower roll rate to the right than to the left. Therefore, I always roll left in such manoeuvres.

There are two problem areas in yaw control with the '109. Firstly, directional stability is low and marked slip ball excursions occur with any changes of speed or power. Also, there is moderate adverse aileron yaw (right yaw when left aileron is applied, and vice versa). The rudder force to centralise the slip ball is low, but constant rudder inputs are required during manoeuvres to minimise sideslip. If the slip ball is not kept central, the lateral force on the pilot is not uncomfortable and no handling problems occur, but it looks very untidy in a display. At the top of a left wing-over, you are very cross-controlled, with left aileron and lots of right rudder applied. This lack of directional stability makes it hard work to fly the aircraft accurately and neatly, although there are no safety problems. However, it must have made accurate tracking for a guns 'kill' very difficult. I suspect that many '109 kills were made at very close range! It also says a great deal about the shooting skills of the Luftwaffe Aces. The second problem is the lack of a cockpit adjustable rudder trimmer. The fixed tab is set so that the rudder is in trim during the cruise, reducing footloads during long transits. However, for all other airspeed and power combinations, a rudder force must be applied. This is an annoying feature, and I am surprised that a rudder trim tab was never fitted to later models such as the Gustav.

The idle power stall characteristics of the aircraft are very benign and affected little by undercarriage and flap position. Stalling warning is a slight wing rock with the stick floating right by about 2 inches. This occurs 10klph before the stall. The stall itself is a left wing drop through about 15 degrees with a slight nose drop, accompanied by a light buffet. All controls are effective up to the stall, and recovery is instant on moving the stick forward. Stall speeds are 155kph clean and 140kph with gear and flap down. In a turn at 280kphwith display power set, stall warning is given by light buffet at 3g, and the stall occurs at 3.5g with the inside wing dropping. Again, recovery is instant on easing the stick forward. One interesting feature is the leading edge slats. When these deploy at low speeds or in a turn, a 'clunk' can be heard and felt, but there is no disturbance to the aircraft about any axis. I understand that the Bf109E rolled violently as the slats deployed, and I am curious to know the difference to the Gustav that caused this.

Back in the circuit, the '109 is straightforward to fly, except that it takes around 25 secs to lower the flaps, using a large wheel mounted next to the tail plane trim wheel and on the same shaft. A curving final approach is flown at 200kph, and once aligned with the runway the forward field of view is poor. The threshold is crossed at 175kph, the throttle closed, and the aircraft flared to the 3 point attitude. The '109 floats like a Spitfire and controls are effective up to touchdown. After touchdown, directional control is by using differential braking. The three point attitude is easy to judge, and although it bucks around on rough grass it does not bounce significantly on touchdown. however, the landing is not easy. From approaching the threshold up to touchdown the forward view is very poor, and it is difficult to assess drift. if the aircraft is drifting at touchdown, the toe-in on the wheel towards which it is drifting causes a marked swing, and you are working very hard to keep straight and avoid a ground loop. Each landing is a challenge, and just a bit unpredictable. Hard runways have higher friction than grass surfaces, and so the wheels dig in even more if drifting on touchdown, making ground-loops more likely on runways than on grass. The possibility of drifting on touchdown increases with a crosswind, and so for these two reasons, we are only flying the Gustav off grass and with a 10kt crosswind limit. I have flown the Buchon off the runway, and landed with a 10kt crosswind on concrete, but it is something that I would never do out of choice!

The Buchon flies very much the same as the Gustav, although directional stability is even worse. The biggest differences are engine handling and cockpit noise levels. The Buchon is very noisy due to the high exhaust stacks of the Merlin, the low exhausts of the DB605 giving a considerably quieter cockpit.

In summary, the Bf109G is a demanding aircraft to fly. The workload is high maintaining directional control on take-off and landing, although in flight the stalling and pitch characteristics are god. I would advise anyone planning to fly a '109 to get lots of experience and confidence in other large piston-engined taildraggers first. However, if its peculiarities are understood and the take-off and landing limits are strictly adhered to the '109 can be operated perfectly safely. I treat the '109 with greater respect than anything else that I fly, but the challenge of trying to fly it well gives me greater satisfaction and enjoyment than probably any other aircraft. But I am never satisfied- I now have an ambition to fly an Emil; the Bf109E.

WW Dave Southwood.



(I would like to thank Paul Coggan, former Editor and Publisher of Warbirds Worldwide and now with Aeroplane, for his kind permission to republish this 1992 article by Dave Southwood on flying the magnificent Messerchmitt Bf109G-2 W.Nr. 10639. -LMR)


erich brown also wrote an article about flying bf109 i remember he have the same experience on get into stall flying 109.

XyZspineZyX
09-15-2003, 04:15 PM
Yes, very informative article.
I found one thing interesting. "At the top of a left wing-over, you are very cross-controlled, with left aileron and lots of right rudder applied." This is exactly the same as in FB. When at the top of the wing over, the air speed is quite low and plane is controlled by air flows very strongly. The slipstream hitting the rudder makes 109 left yaw and the slipstream hitting the wing makes 109 roll right, so the writer said:" use left aileron and right rudder".

About the left wing stall, the reason MIGHT be, when at the edge of the stall, the AOA of the wing is at the uplimit. That is to say, increasing the AOA anymore will DECREASE the lift. As what we discussed before, the slipstream gives the left wing a bigger AOA than the right wing, so the left wing will enter stall earlier than the right wing.

I am still not clear about a part in the article, 'cause of my poor English. "One interesting characteristic is that rolls at lower speeds entered at less than 1g, such as a roll-off-the-top or half Cuban, have a markedly lower roll rate to the right than to the left. Therefore, I always roll left in such manoeuvres." What does roll-off-the-top or half cuban mean? Why are they less-than-1-G manuever?


BTW, in such a long article, I didn't see any "obvious" words about the torque or slipstream effects that make the 109 roll to right in low speed. A little disappointed.

Message Edited on 09/16/0302:25AM by JG54_BSHD