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I was interested, how the Bf-109 would fare in the same experiment:

 

 

Vertical climb 1.8 ATA prop auto (rpm 2800) (MW-50)

 

00:35 IAS: 98 km/h / Pitch: 87 / AoA: -4,5 - stable - very slow right roll due to full right rudder

00:36 IAS :79 km/h / Pitch: 86 / AoA: -6,5 -stable -same

00:37 IAS :60 km/h / Pitch: 83 / AoA: -10,4 -stable -same

00:38 IAS :40 km/h / Pitch: 79 / AoA: -20,1 -rotation starts

00:39 IAS :30 km/h / Pitch: 77 / AoA: -27 -rotation accelerates

00:40 IAS :20 km/h / Pitch: 72 / AoA: +121 -rotation accelerates (much faster now then TF-51)

00:42 IAS :-46 km/h / Pitch: 65 / AoA: -148 -rotation around twice as fast as TF-51 very roughly 220 deg/second

 

Rotation at twice TF-51 speed continues, falling backward until nose falls down at 00:48 (and white smoke from the engine), then rotation slows and stops

 

 

No track this time, but view counts are low anyway...

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What I see here after these experiments is the following:

 

 

- Torque is modelled BUT for some reason the roll tendencies around the longitudinal axis are very weak or non existent even in the low speed, low dynamic pressure regime up until the point the aircraft exceeds stall AoA, then there is unstoppable rotation along the longitudinal axis due to torque

 

 

- Torque is unique to the aircraft (Bf-109 spins faster than TF-51).

 

 

I think, we could agree on, that the forces acting on the airframe by the relative flow at speeds of 50 km/h is quite low (whatever is the direction).

 

 

Also the difference in speed is very low between between the torque roll and no torque roll range (60 to 40 km/h, and 80 to 50)

 

 

Both the TF-51 and the Bf-109 seems to behave following the exact same pattern, even though they are quite different beasts.

 

 

 

Altogether it seems: Stall AoA acts as a trigger: If AoA > stall---> torque roll, if AoA<stall--->no torque roll

Edit: The problem: why is there no tendency to rotate left around the longitudinal axis before stall AoA is reached in the very low dynamic pressure regime.

 

 

 

Writing an effective bug report about this will be quite difficult.... IF there is a bug at all...


Edited by HWasp
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What I see here after these experiments is the following:

 

 

- Torque is modelled BUT is only effective once the aircraft is over stall AoA (positive or negative does not matter)

 

 

- Torque is unique to the aircraft (Bf-109 spins faster than TF-51).

 

 

I think, we could agree on, that the forces acting on the airframe by the relative flow at speeds of 50 km/h is quite low (whatever is the direction).

 

 

Also the difference in speed is very low between between the torque roll and no torque roll range (60 to 40 km/h, and 80 to 50)

 

 

Both the TF-51 and the Bf-109 seems to behave following the exact same pattern, even though they are quite different beasts.

 

 

 

Altogether it seems: Stall AoA acts as a trigger: If AoA > stall---> torque roll, if AoA<stall--->no torque roll

 

 

Writing an effective bug report about this will be quite difficult....

Reminds an old joke:

A scientist trying to find where the bug's ears are place it on a table and screams. The bug runs away. Then he rips off one of bug's leg and screams at it again - bug runs away. He rips off the second leg and screams at the bug - bug runs away. As he rips off the last leg and screams - bug does not run. So the scientists writes an article and states that the bugs have ears on their legs.


Edited by Yo-Yo

Ніщо так сильно не ранить мозок, як уламки скла від розбитих рожевих окулярів

There is nothing so hurtful for the brain as splinters of broken rose-coloured spectacles.

Ничто так сильно не ранит мозг, как осколки стекла от разбитых розовых очков (С) Me

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- Torque is modelled BUT is only effective once the aircraft is over stall AoA (positive or negative does not matter)..Altogether it seems: Stall AoA acts as a trigger: If AoA > stall---> torque roll, if AoA<stall--->no torque roll

 

This doesn't make sense to me. If torque would only be effective above stall AoA, why is that it's there during normal flight well below stall AoA.

Furthermore I do need quite a bit of rudder at 0deg AoA during a vertical turn, but it's difficult to tell if it's due to torque (doubtful since it doesn't noticable increase with decreasing airspeed), p-factor and/or slipstream.


Edited by bbrz

i7-7700K 4.2GHz, 16GB, GTX 1070 

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This doesn't make sense to me. If torque would only be effective above stall AoA, why is that it's there during normal flight well below stall AoA.

Furthermore I do need quite a bit of rudder at 0deg AoA during a vertical turn, but it's difficult to tell if it's due to torque (doubtful since it doesn't noticable increase with decreasing airspeed), p-factor and/or slipstream.

The idea that a bug has ears on its legs is starting to get new followers... :)

Ніщо так сильно не ранить мозок, як уламки скла від розбитих рожевих окулярів

There is nothing so hurtful for the brain as splinters of broken rose-coloured spectacles.

Ничто так сильно не ранит мозг, как осколки стекла от разбитых розовых очков (С) Me

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He means that you are talking about phenomena that are unrelated to torque. ;) E.g. Above stall AoA the plane rolls because one of the wings stalled. Not because of torque. Rudder in a vertical turn is again, different.

 

This being said, I've read so many accounts of pilots dying because they applied full throttle too fast just before touching down to go around, and turning their P-51 / 109 on their backs. Why isn't this possible in DCS? I don't get anything similar to this, not even a mild version of it.

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Torque can also be felt "by the negative"....

 

 

Set your prop aircraft ( P51d or TF51 ) trimmed as close as possible for level flight, at a given power regime.

 

 

 

Now decrease power, slowly down to iddle ( or more abruptly if you don't risk destroying your engine ), and watch the CW rotation due to factors such as the negative propwash (axial component), and the now "overdone" contribution of the aileron trim ( maybe also rudder trim ) and tail fin cant that are present to overcome torque and slipstream effects at cruise power settings...

 

 

The fact that that CW rotation starts developing, and you actually have to counter it with left stick and then by trimming, is a good "indication" of torque being present while in the regime you started with.

 

 

On most prop aircraft I've flown in ( as a pax, since I only own a GPL ) including glider tugs, it used to puzzle me when I started thinking about this stuff more from a "simmer" pov, how the combination of prop effects translated mostly into yaw, instead of roll, even in situations where the pilot firewalled the throttle in a quite abrupt way.


Edited by jcomm

Flight Simulation is the Virtual Materialization of a Dream...

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Why isn't this possible in DCS?

 

It definitely is possible. I just experienced this about a week ago firing up the Mustang after a long break due to this ****storm here. Trust me, this definitely can happen with our P-51 too if we mishandle her.

The DCS Mi-8MTV2. The best aviational BBW experience you could ever dream of.

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Reminds an old joke:

A scientist trying to find where the bug's ears are place it on a table and screams. The bug runs away. Then he rips off one of bug's leg and screams at it again - bug runs away. He rips off the second leg and screams at the bug - bug runs away. As he rips off the last leg and screams - bug does not run. So the scientists writes an article and states that the bugs have ears on their legs.

 

 

That's a good one!

I do apologize for my primitive methods. lol.gif

 

 

I was trying to isolate the effects caused by the propeller by getting the plane to a very low speed environment, ripping most of the legs.

The thing, that seems strange to me, especially with 109, is that while it is able to remain stable, not rolling around it's longitudinal axis at a speed of 60km/h (F2) in the vertical,then, at the top of the climb, it starts to rotate along the longitudinal axis at 200 to 250 degrees/sec (yes I have measured that with a stopwatchsmile.gif).

 

I am trying to talk about that strange 3 seconds, when the plane is almost stopped in the air. First it does not roll around the longitudinal axis, then it starts to roll with great force.

 

Please have a look at the attached track between 00:27 and 00:30, and if you have some more time for this, please help me understand, what is happening there, and why.

BF109 Test.trk

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The story also works with a frog.

you cut off one leg and you order her to jump, she jumps.

you cut off both legs and she becomes deaf.

 

But to return to the subject, you isolate a behavior without taking into account all the aerodynamic effects of which an aircraft is affected.

This is the problem with people who spend too much time in books, and do not practice real experiences.

The stuff when it moves in the mass of air does not have the same reactions as when it is on the ground.

What is mentioned about the excessive torque for warbirds with consequent barrel, comes from the moment when the plane is on the ground at very low speed. At that moment the aerodynamic effects are almost null.

In flight the fletching and the wings,even the fuse, come to counter the effects of torque.It is not difficult to understand.

Finally there is no instant effects, it is necessary that all the moments of couples harmonize taking into account the aerodynamic resistances.The which can take one or two seconds .

Say you well that if there was not some latency between the effects, the pilot would be unable to correct with accuracy, he would not have time.

 

For exemple:

nord3202.jpg

https://fr.wikipedia.org/wiki/Nord_3202

I did my graduate on this kind of plane, the axis of the engine was shifted compared to that of the fuselage, the vertical empennage was also shifted compared to the axis of the fuselage. All that to counter the reversing couple.(torque)

In spite of that we had to put the rudder and the trim on the bottom right, and the thing was going left during the takeoff.

In flight none of that would stop us from flying normally

Still with only 240 horses. So try to imagine with 1500 horses and more?


Edited by cromhunt
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The story also works with a frog.

you cut off one leg and you order her to jump, she jumps.

you cut off both legs and she becomes deaf.

 

But to return to the subject, you isolate a behavior without taking into account all the aerodynamic effects of which an aircraft is affected.

This is the problem with people who spend too much time in books, and do not practice real experiences.

The stuff when it moves in the mass of air does not have the same reactions as when it is on the ground.

What is mentioned about the excessive torque for warbirds with consequent barrel, comes from the moment when the plane is on the ground at very low speed. At that moment the aerodynamic effects are almost null.

In flight the fletching and the wings,even the fuse, come to counter the effects of torque.It is not difficult to understand.

Finally there is no instant effects, it is necessary that all the moments of couples harmonize taking into account the aerodynamic resistances.The which can take one or two seconds .

Say you well that if there was not some latency between the effects, the pilot would be unable to correct with accuracy, he would not have time.

 

 

Dude, are you for real? :lol:

What aircraft do you fly, and how many hours did you log on warbirds to have that condescending tone? Also, how can isolating an effect to study can be a problem? What kind of messed up logic is that?

 

I was trying to keep my posts focused and polite as much as I can, since I don't like it how all the threads about FMs turn into a throwing of ....s.

 

And also, just to be very clear about that, I have the greatest respect for the people creating the flight models of DCS birds, especially ED's. I am aware of the great complexity of the subject, and I find the overall quality amazing. I have the best of intentions here.

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[quote name=

For exemple:

 

https://fr.wikipedia.org/wiki/Nord_3202

I did my graduate on this kind of plane, the axis of the engine was shifted compared to that of the fuselage, the vertical empennage was also shifted compared to the axis of the fuselage. All that to counter the reversing couple.(torque)

In spite of that we had to put the rudder and the trim on the bottom right, and the thing was going left during the takeoff.

In flight none of that would stop us from flying normally

Still with only 240 horses. So try to imagine with 1500 horses and more?

 

 

That is a very nice plane. I had my basic training with a nice taildragger as well, even though 185HP only. Good times.

 

I really wouldn't like to start a fight about who has what flying experience, but please, keep in mind, that there might be other people around with actual flight experience.


Edited by HWasp
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That's a good one!

I do apologize for my primitive methods. lol.gif

 

 

I was trying to isolate the effects caused by the propeller by getting the plane to a very low speed environment, ripping most of the legs.

The thing, that seems strange to me, especially with 109, is that while it is able to remain stable, not rolling around it's longitudinal axis at a speed of 60km/h (F2) in the vertical,then, at the top of the climb, it starts to rotate along the longitudinal axis at 200 to 250 degrees/sec (yes I have measured that with a stopwatchsmile.gif).

 

I am trying to talk about that strange 3 seconds, when the plane is almost stopped in the air. First it does not roll around the longitudinal axis, then it starts to roll with great force.

 

Please have a look at the attached track between 00:27 and 00:30, and if you have some more time for this, please help me understand, what is happening there, and why.

 

The joke, actually, is not about METHODS - it is about WRONG CONCLUSIONS derived from right observation. As you see high AoA's at very low speed, it means nothing regarding wing autorotation because of insufficient dynamic pressure. So, the effect you saw was almost pure torque. Not a yaw-generating P-factor or slipstream causing yaw (yaw cases roll if not neutralized, but you need enough airspeed for the airframe to see this effect).

 

Your methods even allow to see differences between P-51 and 109 rotation, but you did not remember that MOIx of P-51 is much greater because of guns and undercarriage 109 does not have so far from X-axis. 109 has more power, so - greater torque.

Ніщо так сильно не ранить мозок, як уламки скла від розбитих рожевих окулярів

There is nothing so hurtful for the brain as splinters of broken rose-coloured spectacles.

Ничто так сильно не ранит мозг, как осколки стекла от разбитых розовых очков (С) Me

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The effect that makes the aircraft roll around it's longitudinal axis is pure torque, as you say, I did not mean to disagree about that.

What I was trying to point out with my posts, is that I miss this torque (trying to rotate the aircraft around it's longitudinal axis), while in the very low speed segment of the climb.

 

 

What I am trying to understand is, what is the force/forces, that are able to counteract this strong torque during the final slow speed segment of the climb, where dynamic pressure is already insufficient, as you say, before the rotation about the longitudinal axis starts.

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This is the data from a previous 109 flight, with about the exact same dynamics as the one in the track. (different times though)

 

 

00:36 IAS :79 km/h / Pitch: 86 / AoA: -6,5 -stable -same --no roll left<----

| This is the area I'm on about, no tendency to roll left due to torque

 

00:37 IAS :60 km/h / Pitch: 83 / AoA: -10,4 -stable -same--no roll left<----

00:38 IAS :40 km/h / Pitch: 79 / AoA: -20,1 -rotation starts

00:39 IAS :30 km/h / Pitch: 77 / AoA: -27 -rotation accelerates

00:40 IAS :20 km/h / Pitch: 72 / AoA: +121 -rotation accelerates (much faster now then TF-51)

 

 

During the climb there is full right rudder only, no other strong control imputs.

 

My point is: Why does that rotation to the left caused by the torque starts only that late? I would expect a strong tendency to rotate left around the longitudinal axis throughout the low speed climb, getting stronger, and soon unstoppable.

 

 

I think there might have been a misunderstanding between us, about what I'm trying to point out, so I'm going to edit my previous posts


Edited by HWasp
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It's not about who has the most experience, but how you interpret that experience, your conclusions, to use a word used by "yo-yo".

I'm just pointing out that you can not talk about an effect or a reaction on an airplane without taking into account all the parameters that make up the aeronautical flight.

You can not isolate an effect without defining the conditions under which it occurs, and after doing a demonstration of the effect in flight near zero speed (video) .It is obvious that in the configuration you have chosen, the aerodynamic effects are almost null, and so it is the propeller causes the barrel.

That does not mean that the importance of this effect applies to all configurations.

DCS does what it can and actually for the moment it's not bad, assuming they are able to integrate all the calculations and results. But it's still a game or a simulator, if you prefer, and this that we see on the screen depends on the computing power of our computers.

So necessarily limited.

 

PS:The first post of this topic spoke of a weak reaction of the game in conditions apparently similar to the real flight. And I observed that if you do not take all the parameters of the flight into account, and in particular the aerology which is very simple in DCS, it is not worth comparing.

Criticism is easy but art is difficult.


Edited by cromhunt
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Dude, are you for real? :lol:

What aircraft do you fly, and how many hours did you log on warbirds to have that condescending tone? Also, how can isolating an effect to study can be a problem? What kind of messed up logic is that?

I would take cromhunts posts with a (big) grain of salt since he made questionable posts (in a condescending tone of course) about aerodynamics in the past and admits on his own webpage that he's a rather bad pilot IRL.

 

Copy & paste from cromhunt:

--------

The most newer that i flew was the Piper cheyenne 2.With his two turbo prop 750 hp it gave a good sensation of power but above the flight level 100 it was imperative to put the autopilot on because it was impossible to maintain the line on manual.Flying with this kind of plane seems more balistics than aerodynamic

--------

 

That's nonsenes as they wouldn't have certified this aircraft if you can't fly it without AP. I did find the PA-31T as easy to hand fly as any light or heavy turboprop. Apart from this, the Cheyenne II has only 620hp...


Edited by bbrz

i7-7700K 4.2GHz, 16GB, GTX 1070 

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This is the data from a previous 109 flight, with about the exact same dynamics as the one in the track. (different times though)

 

 

00:36 IAS :79 km/h / Pitch: 86 / AoA: -6,5 -stable -same --no roll left<----

| This is the area I'm on about, no tendency to roll left due to torque

 

00:37 IAS :60 km/h / Pitch: 83 / AoA: -10,4 -stable -same--no roll left<----

00:38 IAS :40 km/h / Pitch: 79 / AoA: -20,1 -rotation starts

00:39 IAS :30 km/h / Pitch: 77 / AoA: -27 -rotation accelerates

00:40 IAS :20 km/h / Pitch: 72 / AoA: +121 -rotation accelerates (much faster now then TF-51)

 

 

During the climb there is full right rudder only, no other strong control imputs.

 

My point is: Why does that rotation to the left caused by the torque starts only that late? I would expect a strong tendency to rotate left around the longitudinal axis throughout the low speed climb, getting stronger, and soon unstoppable.

 

 

I think there might have been a misunderstanding between us, about what I'm trying to point out, so I'm going to edit my previous posts

The second thing you did not take in account is inertia. The experiment was dynamic.

The correct flight experiment showing the amount of torque must be:

Set 46/2700 rate

Trim at 150 mph IAS using slip and turn indicators (both to 0)

Watch the "red square" (in game controls indicator)

The same for 130

The same for 100 or any low IAS you can maintain.

Enjoy.

 

By the way, the real plane flies cruise with the ailerons almost in neutral and requires only small right deflection as the plane gets airborne at TO speed and power.

Ніщо так сильно не ранить мозок, як уламки скла від розбитих рожевих окулярів

There is nothing so hurtful for the brain as splinters of broken rose-coloured spectacles.

Ничто так сильно не ранит мозг, как осколки стекла от разбитых розовых очков (С) Me

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