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Old 07-17-2018, 03:35 AM   #61
msalama
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OK, not a troll. Accepted.

Quote:
must be compensated for with rudder and a bit of aileron as speeds builds.
This is exactly what I have to do with the Mustang, every single takeoff. So the phenomena are there.

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in a single engine prop require trim changes in all three axis
And again, if I change the power settings in any way, I'll need to trim all three axii when airborne in the Mustang. So again, the phenomena are there.
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Old 07-17-2018, 03:43 AM   #62
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Quote:
wonder howtorque is being calculated in DCS
I'd say pretty convincingly. Check the BST helo FMs for example.
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Old 07-17-2018, 05:04 AM   #63
David OC
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Quote:
Originally Posted by bbrz View Post
Of course it does matter. It's essential to observe the need for increased aileron input with decreasing airspeed. Again, it's an important factor in any vertical maneuver IRL.

This is for sure not documented anywhere since such a 'test' would be meaningless IRL.
There's no use for such a maneuver in a P-51 and I don't think that especially with the high value of these vintage P-51s anyone would even think of trying that.
Furthermore it puts a lot of stress on the airframe, prop and prop shaft.

The point I'm trying to make is that the complete lack of torque in this situation is a basic bug in the FM of (at least) the TF-51. This makes me wonder how torque is being calculated in DCS.

If this bug lies in the core of the DCS flight modelling, aerobatic planes like Yak-52 and the Christen Eagle wouldn't make much sense if they couldn't be flown in a realistic way.
Wasn't the Yak-52 built for a commercial client for aerobatics etc? If so, these would have been the first things picked up when doing all the testing you would think? Especially considering they did IRL flight testing also.
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Old 07-17-2018, 05:35 AM   #64
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Quote:
Originally Posted by David OC View Post
Wasn't the Yak-52 built for a commercial client for aerobatics etc? If so, these would have been the first things picked up when doing all the testing you would think? Especially considering they did IRL flight testing also.
Let's wait and see. Certainly not a first day buy anymore for me
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Old 07-17-2018, 06:06 AM   #65
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Yeah, it was a commercial project for a party training RL Yak-52 pilots. And as such, it must've been developed pretty comprehensively and accurately, or said party wouldn't have accepted it at all. So to assume there'll be, say, no torque modelling present is just ludicrous IMO.

And about this complaint here: the guy says there's no torque, yet I need to always input rudder and aileron when taking off + trim for takeoff as per the book, and trim all 3 axii if I change any power settings in flight. Sure, you can always debate whether the effects and symptoms are correctly presented; but claiming none exist is, again, just ludicrous.

And that's my $0.0002. Au revoir gents and gentettes
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Old 07-17-2018, 06:07 AM   #66
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[QUOTE=bbrz;3568374]Of course it does matter. It's essential to observe the need for increased aileron input with decreasing airspeed. Again, it's an important factor in any vertical maneuver IRL.


We are NOT talking about the same thing here. The purpose of this test is to try and narrow down the problem. I wanted to get the aircraft in a zero speed condition, and then test the torque there. How I got into that situation was NOT part of the test this time!

What this shows me, is that the torque itself is there, and if there is a problem, it might be around the effects that counteract torque in flight.
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Old 07-17-2018, 06:42 AM   #67
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Quote:
Originally Posted by HWasp View Post
What this shows me, is that the torque itself is there, and if there is a problem, it might be around the effects that counteract torque in flight.

Or... not a problem but rather a well programmed feature that doesn't get modeled right in many flight simulators...


A good example are the slipstream effects, and the asymmetric "hit" in the lower surface of the left wing, left sections of the fuselage and, above all, left vstab and rudder surfaces ( for the areas above CoG )... These all tend to counter torque , in the presence of slipstream, which is actually maximized at high power ratings and lower TAS...


I still remember well when along it's v9 iteration, Austin introduced torque in X-Plane :-/... It took years to correct, and we're still dealing with the rest of the effects...


That's why DCS, and sorry but I really have to mention it here too - IL-2 BoX - are light-years ahead of most civil sims in modelling these and other effects.


I also still remember the first time I met the effects of deflected propwash during takeoffs under strong crosswinds with exactly these same P51d.... Have you tried it ? Get your P51d in the rw with a 10m/s wind from, say, your 10 o'clock, and see what goes on when you add takeoff power ...


Ah, and BTW, torque should also be countered using RUDDER, not ailerons ! It's obvious if you take into account adverse yaw from the wing the get's it's aileron down to counter the torque ( left in a CW rotating prop aircraft ), and well explained here for instance...


So, not saying it's perfect, but it certainly must be really close to it in as far as it is possible with such a program...

Last edited by jcomm; 07-17-2018 at 09:05 AM.
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Old 07-17-2018, 09:04 AM   #68
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Trying to narrow this down with some further unprofessional tests. See attached track.



1st vertical / power 100% prop. max rpm

00:43 - IAS: 100km/h / pitch: 76 / AoA: 10,2 --- stable
00:45 - IAS : 80km/h / pitch: 73 / AoA: 8,8 ----stable
00:47 - IAS: 52 km/h / pitch: 65 / AoA: 15,2 ---stable

At this point as AoA goes above 20 rotation to the left starts

00:50 - IAS: -46km/h / pitch 74 / AoA -106 --- continous rotation to the left approx 100-180 deg/second (did not measure that)

00:52 - IAS: -47km/h / pitch 66 / AoA +178 - continous rotation to the left

00:56 - IAS: 123km/h / pitch 1 / AoA -72 - still continous rotation to the left, at this point the nose drops below the horizon

00:57 - IAS: 150km/h / pitch -30 / AoA +25 - As AoA is back in range the rotation decreases rapidly

00:58 -IAS :187 km/h / pitch -67 /AoA -1 - stable dive, rotation stopped

Next vertical without engine power (throttle idle, prop min. rpm)

01:38 -IAS :58 km/h / pitch 73 /AoA 15,2 --stable
01:39 -IAS :37 km/h / pitch 72 /AoA 32,3 --stable, no roll
01:40 -IAS :28 km/h / pitch 71 /AoA 63 -- no rotation
01:42 -IAS :-65km/h / pitch 53 / AoA 123 - nose dropping, no roll, no rotation
Nose dropping to stable dive


I think this shows the following:


-The continous rotation to the left is caused by the torque, not any other effect, being stalled or anything else (we knew that of course)


-Being in the 50 km/h speed range, basically zero speed, the rotation due to the torque starts only as the AoA increases above stall AoA.


Pleas do watch the track and excuse my bad flying.
Attached Files
File Type: trk TF-51 tailslide Test.trk (412.2 KB, 4 views)
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Old 07-17-2018, 09:42 AM   #69
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Quote:
Originally Posted by HWasp View Post
Trying to narrow this down with some further unprofessional tests. See attached track.


Excellent data ( even if not "professional" ) .


I will not be able to try your track, but I agree from the observations that something looks wrong indeed !


Thx
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Old 07-17-2018, 09:47 AM   #70
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Thanks for the tests, very explanatory on the fact that the P-51 in DCS has the effect of the implemented torque.


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