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Guest Ron Freimuth

rate of turn DF727

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Here's one for you aircraft modeling gurus: I just got the DF727 and it seems like the rate of turn is very slow, even at large bank angles. I don't know if this is well-modeled or not. I was wondering what in the flight model controls this? Is it easily adjusted via the aircraft.cfg file? Mike

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Mike: I haven't fooled too much with flight dynamics tweaking, but I believe that the relationship between bank angle and turn rate is something that is dictated more by the .air file, and not so much the aircraft.cfg. I feel your pain though. ;-) I've run into this several times with otherwise fine planes. Still... that is a pretty fundamental thing to have incorrect, and there are MANY planes out there for download where bank angle/turn rate is broken. This makes no sense to me, given that turn rate and radius are directly related to bank angle, and they are the same for every aircraft at a given airspeed, but I guess many plane designers just don't know this, so don't test for it? It is probably not the most intuitive concept.... Anyway, perhaps the best approach is to politely e-mail the author of the .air file and let him know his plane violates basic principles of flight? Good luck.

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Yes it's a bug. I mentioned this "slipping" issue on DF Support forum and take some replys. Flight dynamics designer said it's already discussed before. ( find some topics but not an answer ) And it's looks like he's using another panel with DF727 :) And panel developer asked to check autorudder is on/off :) So, don't bother..

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Hmmm... this is interesting. I also just got a reply to this on the DF forum from one of the design team who said the rate of turn is perfectly fine. But it looks like you guys recognize this as an issue. IF it is a known issue with the aircraft I don't understand why they can't admit it and do a fix on the next update instead of giving the tired "tested by real pilots" line. Mike

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Hmmm... well, why not test it yourself. If you don't have your own set of test gauges, a tool such as AFSD will help. Clear all wind/weather and then enter a level and cordinated constant speed turn. Your test gauges/AFSD will spit out the current speed, AOB, and turn rate. Then compare these values with, say,https://ewhdbks.mugu.navy.mil/maneuver.pdf

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I will do the test. Related question: I have AirEd; does anyone know where within the air file to adjust the turn rate parameter? Mike

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Why do "sim pilots" always think they know more than real pilots about how an aircraft is "supposed to work?" :-erks

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With all due respect Bill, and I think I know where you're coming from here, but maybe your cynicism is not warranted in this instance? ;-) I think you'd agree that it doesn't matter what anyone "thinks," either the original poster, or DF's experts; their aircraft must obey the basic laws of physics. I simply suggested that the OP test it and see. That the aircraft is payware and that the designer got input and a thumbs up from a real world 727 pilot by themselves mean little. Yes, given DF's good reputation, I'd be inclined to say that the 727's flight dynamics are probably right, but if they're not, I doubt it would be the first time such a mistake was overlooked in a payware .air file....

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Did you ever consider that you're making standard turn in the right way.try to make a turn at 170kias, keeping this speed (increase pitch, increase thrust, small ruder to avoid aircraft glissing, keep the airspeed and the bank and altitude).if I

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You have to use the rudder to keep the turn coordinated in some planes WITHOUT yaw damper. But 727 has YAW DAMPERs to eliminate dutch roll and sleep/skid. You shouldn't touch the rudder pedals except takeoff/landing.

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I ran some quick tests last night with 3 different planes: PMDG 737, Feelthere ERJ, and the 727. I ran the tests with no weather loaded (i.e. calm), no traffic. All turns were done for 360 degrees at 20 degree bank. Altitude was 5000 ft and I held the IAS at 250 kts. Yaw dampers were on. Here are the results: PMDG 737 4 min 5 sec DF 727 4 min 50 sec ERJ 4 min 15 secAnd, yes, I am concerned about getting the basics of the flight model correct. I just get tired of the "tested by real pilots" excuse if there seems to be documented and repeatable problem: Another payware plane I have can maintain a 1000 ft/min climb with no elevator/trim/throttle input and with decreasing airspeed!! It continues up to the point it reaches set stall speed in the file then drops out of the sky. After investigating further it only does it with flaps at 10 degrees. I decreased the flap lift vector by about 30 % and it flew much better. This was confirmed by other users yet the manufacturer said there was no problem since "it was tested by real pilots". Mike

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I just did a calculation where using basic physics one can derive the rate of turn as a function of bank angle and TAS rate (in degrees/sec) = 180*9.8*tan(bankangle)/pi*TAS The TAS has to be in meters/sec. I converted my IAS of 250 kts to TAS of 275 kt at 5000 ft by the tables. The above equation gives a rate of 1.44 degrees/sec Converting my test data: PMDG 737 1.47 degrees/sec DF 727 1.24 degress/sec FT ERJ 1.41 degrees/sec Mike

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> I just did a calculation where using basic physics one can>derive the rate of turn as a function of bank angle and TAS >> rate (in degrees/sec) =>180*9.8*tan(bankangle)/pi*TAS>> The TAS has to be in meters/sec. I converted my IAS of 250>kts to TAS of 275 kt at 5000 ft by the tables. The above>equation gives a rate of 1.44 degrees/sec>> Converting my test data:>> PMDG 737 1.47 degrees/sec>> DF 727 1.24 degress/sec>> FT ERJ 1.41 degrees/sec>>>> Mike>you make the test how I told you?And by the way. I talked to my teacher of engines (formed 727 captain at Transbrasil) and he said "do not exceed 25

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>You have to use the rudder to keep the turn coordinated in>some planes WITHOUT yaw damper. But 727 has YAW DAMPERs to>eliminate dutch roll and sleep/skid. You shouldn't touch the>rudder pedals except takeoff/landing. Actually, the DF 727 uses only the defective FS 'yaw damper'. Which does little but reduce rudder travel. It does not damp yaw nor does it provide turn coordination. Thus, there is some Yaw in turns, and that reduces turn rate from what it would be if the YD worked as it should. So, one has to use rudder to keep the ball near center if the turn rate is to come out right. I ran AFSD, but 'turn rate' was too unstable to be of much value. I ended up timing turns against the clock. I noted the XML A:Variable 'Heading Rate' appeared to be off by 20%. Also, MSFS 'autorudder' does nothing but lock out the rudder input, and force the Ball to the center. Another MS Fake! As a matter of fact, I've been testing a real Yaw Damper I coded in XML. The problem is it locks out JS rudder control. However, with my YD enabled, it takes less aileron to hold a bank in the 727 and Yaw is normally under 0.5 degrees. About a 3:1 improvement over no YD (or the defective FS YD). Watching the tail of the DF 727 I can see the rudder move to control yaw. It wags quite a bit if the air is turbulent or there are gusts. It moves some as one starts and stops turns; in a way that keeps Yaw low. I limited the YD so it moves the rudder about +/- 5.5 degrees maximum, which is similar to the limits in real AC. If the problem with getting manual input to the rudder with the YD can be solved, there should be functional YD's in some future FS AC. MS hadn't been able to make a working YD, they tried in FS9, but it does virtually nothing. One has to be able to feed back Yaw, Yaw Rate, set limits, etc. to do it right. Fortunately, similar PID controllers do work to provide appropriate SPD control. Something the MS Airheads also messed up. In fact, I expect to create a set of XML blocks so most all the 'autopilot' and other control functions in MSFS can be done correctly. And, be adjustable for the specific AC. That means stable Pitch Control, ALT control, Roll Control, and functions that can be created from them. ILS, GS, etc. Ron

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There's no need to do a standard rate turn test using the physics I outlined above. The equation works with any bank angle and TAS. It accurately predicts the turn rate. So, I can use it to compare to the sim data.Yes, TAS varies somewhat with speed, but the variation would not change the results much. Mike

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