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jcomm

And now for something completely different... the Torque...

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Everything can be said about X-Plane, Laminar Research, 3pds, etc...

 

The same happens with FSX, DCS, ELITE... any product in the market, I believe....

 

But we should be able to notice the differences where they are... And I, althought sometimes very critic about my sims, have to recognize, as I have done on other occasions, that Austin is really the most helpful flight simulator developer I have met so far!

 

A month ago when everybody was complaining about some weird behaviours of the A2A C172 for FSX, the A2A crew used their real aircraft, recorded a couple of movies and tried to explain that what users were finding weird was, after all, very realistic, at least in that particular Cessna they own.

 

Well, one of our friends here emailed Austin, just like I have done a few times, complaining about the overdone roll due to torque, and presenting his arguments.  Austin replied promissing a visual proof, and here it is:

 

YES WE CAN HAVE TORQUE ROLL!!!

 

Austin shows, and for me it is irrefutable, at least in as far as the C400 goes, and I can see exactly that same behaviour in the X-Aviation model I have for X-Plane 10, that the aircraft certainly has a roll due to torque from the engine!  It's recorded by himself, who decided to make a flight to prove to those who continue arguing against it, that INDEED there must be roll due to torque, and on some aircraft it can really be very evident!

 

I take my hat off to Austin for taking the time to record this movie and send it in a personal message to that friend of mine ( no, not the imaginary one... ).  I have asked his permission to post it here.  Should Austin want to, he could easily had drop it at some forum, but I truly believe his days are more than filled with programming and managing decisions, sometimes very complex I guess. So, a big thumbs up for Austin, and LR, and, as far as I'm concerned, another 500 points summing up on to my X-Plane 10 score :-)

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The argument never was about if some aircraft have torque roll ( I am sure the GeeBee did) but about aircraft that do not and the exaggerated effect in xplane.

 

The part that seems to be missed is this effect vanished about 6 months ago in one of the betas. All my Carenado aircraft perform fairly rw like-before this they were showing exaggerated and unrealistic uncommanded continual roll effects that made the sim totally unusable for me. Now at least fm wise I find things accurate enough to be able to use the sim without negative training occurring.

 

The argument above is like saying it rains every day in San Diego, taking a video on the few days it does, and then using it to prove that point. sure it rains in San Diego-though very seldom, and when it does it is very light. There is on a very rare occasion a downpour .:)

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.

 

Yes, we need more weather reports and less aerodynamic specialists flying the sims. :rolleyes:

 

Ray

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The argument never was about if some aircraft have torque roll ( I am sure the GeeBee did) but about aircraft that do not and the exaggerated effect in xplane.

 

For a good example of one that does not, at least not more than what shows in the X-plane 10 model, with no magic tweaks applied, take the C172 SP :-)  It's a good example of one that performs very well, at least taking for comparison the acclaimed A2A C172 ( which I also own and enjoy quite a lot ).

 

The X-aviation C400 can have some editing, but I've just done it and, trying to set a similar scenario that Austin took for recording his video, I was able to obtain almost exactly the same roll rates, pitch rates, etc...

 

I believe it's indeed possible to edit, using PM, most aircraft in X-Plane and bring them a lot closer to real.

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All day long..........I've been thinking, what's he doing with his feet? What's he doing with his feet?

 

 

Problem is, I seen this thread on my cell phone. I've been using too many cell minutes, and don't download U-tube anymore. So this evening, I check out the video on the big screen. And what does he do with his feet? Nothing!

 

 

The plane begins to yaw like crazy. When you yaw, there is roll coupling. Don't arrest the yaw, and you'll roll. It's the same way all of those cheap little R/C planes work. No ailerons, and just rudder. When you hit the throttle like that, the correct response is to lay on the right rudder. If there is any roll at all, then fine, just correct it. But in reality, you won't be worrying about ailerons and roll. You need to be thinking "rudder'!

 

 

For instance, let's say you're going to come up short of the runway, and you hit the power. Get on the right rudder quick, because you'll be heading right over the left runway lights, before you know it! Use the rudder, and you won't be feeling or seeing, a sudden roll. Just use aileron, and you'll be adding more drag, which means more yaw.

 

 

As I said, it's the same with R/C. I've been reading those R/C forums lately, because I got back into it. Since some of these airplanes get into the air, rather quickly, the pilots are not using rudder. Some of them put weights onto the right wing, to stop the roll. And then someone might tell them, to use rudder, to start with. It corrects the yaw, and the roll at the same time.

...and Austin finally checkmates.

Nope.....

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It's a good example of one that performs very well, at least taking for comparison the acclaimed A2A C172 ( which I also own and enjoy quite a lot ).

 

Please see my comments in the other XP thread about the A2A 172.  Meaning no disrespect whatsoever to A2A who've produced a fine product, it's WAY too early to anoint this plane as THE 172 flight model.  Yes, the plane is "acclaimed" and it should be with many, many fine features.  But I still view the flight model as a work in progress, not definitive.

 

Scott

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Larry,

 

I see your point, but really not the case here, if you allow me to disagree.... Yes I know what you mean, and of course I also know about RC aircraft ( used RC electric gliders some 25 yrs ago when I was not able to fly for real for quite a while due to the economical crisis in Portugal ( a situation that comes in tides, and is about to repeat in the near future again :-/ )... and they were cheap 2 channel models with good dihedral, and of course, no ailerons.

 

I also know what you mean because I myself, not as a pilot but as a very interested, and sometimes cooperative :smile:  right seat passenger, have had the chance to notice a lot of yaw, and not that much ( if any ) bank in aircraft like the DR-400 or the Rallye 180 GT that were used to tow our gliders.

 

That is why I think that, this video Austin recorded is also a good example of exactly what he's trying to prove - that on at least some aircraft the torque manifests primarily in rolling moment and not that much yaw.

 

We can see that by checking the syntectic turn coordinator of the G1000 display. It's easy to see that while there is yaw, the amount of yaw is not as much as I've seen on those DRs and Rallyes... and the aircraft starts rolling immediately as Austin pushes his throttle!  Yes there is yaw, and yes some of the roll will result from yaw-induced roll, but there is also a lot of roll induced by the torque.

 

On those DR-400s, Rallyes, I did notice that the roll develops rather late, after the yaw had started. If rudder was not used for a while, and the aircraft was left sidesliping, then yes, a roll would start, but certainly not immediately like in the C400 video!

 

So..... what can we do about it?  I think I have my answer now, or at least that's how I am dealing with it right now - I use the artificial stability section of Plane-Maker, after having used the settings of fixed aileron and rudder trim  tabs that I guess or know from other sources that the real aircraft has. I sometimes even cant the engine, if it is not already canted.

 

The default C172 is a good example. If we fly it just as it comes with XP10, it's already very plausible, I believe, or at least according to the oppinion I got from a friend pilot with lots of ours on that model, and from the A2A C172 ( which I know has been criticized for the rolling tendencies by most FSX users ... ).

 

I still think that this video really shows what it is meant to show.  Austin recorded it at 6000', so no limit layer effects, started at the speed I guess is more prone to such a noticeable effect, and the roll started the moment he pushed the throttle, while the yaw was not that pronounced. The X-Aviation model shows practically the same effects, with perhaps a bit more of rolling moment, but I edited it with PM and am satisfied with the results.

 

Bottom line: Of course X-Plane does not do it PERFECT! But!!!! We can use the tools that come with it to fine tune an aircraft to behave plausibly, in this and other areas.

 

If, in the future, Austin adds more detail to the modelling of prop effects, and even takes into consideration more variables, we can come up with models that require less fine tuning when they're directly designed based on RW data. That will be wonderful, of course, but it the mean while, I can perfectly live and feel happy with what I have :-)

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The plane begins to yaw like crazy. When you yaw, there is roll coupling. Don't arrest the yaw, and you'll roll. It's the same way all of those cheap little R/C planes work. No ailerons, and just rudder. When you hit the throttle like that, the correct response is to lay on the right rudder. If there is any roll at all, then fine, just correct it. But in reality, you won't be worrying about ailerons and roll. You need to be thinking "rudder'!

 

I think you could be partly right. The ultimate proof should be something like that:

 

.) Trim the C400 for hands off coordinated level flight at an airspeed close to max efficiency.

 

.) Advance to full power and, after speed has stabilized, trim again for hands off coordinated level flight.

 

Does the aircraft need a change in aileron trim? If the answer is no, then X-Plane is wrong.

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I see your point, but really not the case here, if you allow me to disagree....

 

 

Okay...........putting it another way; what would of happened, if Austin applied right rudder?

 

 

I don't think the plane is quite slow enough, to show the torque effects, like you'd get from a P-51 Mustang, when full power is applied at slow airspeed. Of course the C400 engine wouldn't have enough power to roll the plane over, anyway.

 

So, what's the course of action here? When applying power to climb, or increase airspeed......do we just use aileron, or go for the rudder? I'll go for the rudder first, and use any aileron (without really thinking about it, of course :smile:) as nessesary. But "rudder" will be on my mind, as the first defense.

 

More rudder stuff:

 

http://www.airbum.com/articles/ArticleRudder.html

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Excellent articles, both but specially this last one Larry!!!

 

In gliders, we are well used to use uncoordinated inputs in order to keep our turns coordinated. On a very high aspect ratio model, specially the older ones, it's puzzling to see the amount of cross-control one uses to keep the yaw string aligned with the longitudinal axis of the glider!

 

This second article is also very good in explaining why a sideslip maneuver, that could easily trick someone's thoughts about the danger of entering a spin, is, after all a great way of losing excessive height, preferably without gaining excessive speed ( we do it with the manche sometimes all the way back on some gliders - scarry, I know, but very safe!!! ) 

 

And that paragraph on the safer stall when entered in a sideslip is also very interesting! Excellent article !!!

 

Now, back to X-plane and torque... I have been doing some tests, outputing sideslip angle data and I believe there is enough evidence to say that one of the problems is that X-Plane props yaw / sideslip less than they should due to the "prop effects".

 

In trying to overcome this limitation, which has been extensively discussed here and at other X-Plane forums, I will try to find a way to apply "Puffs" to a prop aircraft and force the yaw .

 

My idea is to place a puffer near the central part of the vertical fin, and adjust it's power as a function of other variables that are associated with a stronger spiraling slipstream asymmetric effect on various aircraft surfaces.

 

I want to be able to get:

 

1) realistic yaw due to prop effects, that can be countered with realistic use of rudder.

2) This being sufficient to overcome, on most aircraft and flight situations, any rolling moment due to torque from the prop.

3) and... the result being an aircraft flying wings level and coordinated, as opposed to what we get when we apply rudder to overcome the prop effects, and level wings, ending up with a ball fully displaced to the left!!!

 

I will be trying to find any Puffer specialists among the X-Plane user community :-)

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