Still on the theme of the right rolling moment observed on twin prop aircraft in X-Plane 12, at least the default B58, C90, as well as the 3 DC-3 addons I have tested, and other twin props which are freeware and available for instance from the Org repository, I have to say that the lift vector that is clearly visible as a the leading force when the flight model visualization mode is active, with it's origin on the port wing just behind the port propeller plane of rotation, is the justification "X-Plane 12 gives" to this "anti-torque" rolling tendency (I am assuming here CW rotating props).

I confess that my first reaction was to understand it as being plausible, probably depending on specific aircraft design, but from all of the sources / literature / comments from RL twin prop pilots , ... , it looked like such force couldn't compensate for the torque of both engines, at least at high power settings such as during climb, or at cruise regime, but in X-plane, even after setting to null the default trim tab settings that in Plane Maker were defined to overcome the torque effects, a right rolling moment is still present.

I read Janov's post yesterday at the .Org, : 

https://forums.x-plane.org/index.php?/forums/topic/270047-what-new-aircraft-would-you-like-to-see-for-x-plane-12/&page=13#findComment-2875696

and having been away from this subject for quite a while I started to think about it again. 

Actually, a few weeks ago I tested the very same effect in MSFS 2024, which with it's fine tuned flight model and the default Baron 58 already using the latest "CFD" approach, does exactly the same - rolls to the right at most power settings !

I even asked Copilot, and here's the result 🙂, bellow...

So, after all this swirl of arguments I raised and have been repeating in my posts, it can well be the case that I WAS WRONG !!! and indeed, depending on different factors, such a right rolling tendency ( probably yawing too due to the coupling ) may well be very realistic, which not only enhances X-Plane 12's updated flight dynamics ( I believe it didn't represent this when it was released, and I'm also 99% sure this was not the case in Xp11 ) BUT! also MSFS 2024's CFD approach which recreates the exact same effect when I take the default Baron 58 for a ride or the Beech Kingair now available in FS 2024 Standard Edition.

===================================I

 

Question asked to Copilot 🤣: In a twin prop aircraft with the propellers rotating clockwise as seen from the cockpit, what will be the prevailing forces resulting from the propellers rotation and what bank and yaw tendencies will result? Can the slipstream effect over the portion of the wing behind the propellers be able to counter the torque effect and create a right rolling moment instead of the one resulting from torque, to the left?

Copliot's Answer: Great question! Here's a detailed answer:

Forces Resulting from Propellers Rotating Clockwise

1. Torque Effect: As the propellers rotate clockwise, they generate a torque effect that tends to roll the aircraft to the left. This is due to Newton's Third Law, which states that for every action, there is an equal and opposite reaction.

2. P-Factor (Asymmetric Propeller Loading): This occurs when the descending blade of the propeller produces more thrust than the ascending blade, usually when the aircraft is climbing. For clockwise rotating propellers, this causes a yawing moment to the left.

3. Gyroscopic Precession: When the aircraft pitches up or down, the propellers act as gyroscopes. For clockwise rotating propellers, pitching down causes a yaw to the right, and pitching up causes a yaw to the left.

Bank and Yaw Tendencies

• Banking: The torque effect will naturally cause the aircraft to bank to the left.

• Yawing: The combination of P-factor and gyroscopic precession will also tend to yaw the aircraft to the left under most conditions.

Slipstream Effect

The slipstream effect refers to the airflow produced by the propellers as they rotate. This airflow can impact the wings and control surfaces:

1. Right Rolling Moment: The slipstream can generate additional lift over the portion of the wings directly behind the propellers. This may create a rolling moment to the right.

2. Countering Torque Effect: Whether the slipstream can entirely counteract the torque effect depends on several factors, such as the design of the aircraft, the power setting, and the speed. In many cases, the slipstream effect can partially counteract the torque-induced left rolling moment, but not entirely. Therefore, pilots often need to apply right aileron to maintain level flight.

In summary, while the slipstream effect can contribute to a right rolling moment, it typically does not fully counter the left rolling moment caused by torque. Pilots often need to use a combination of aileron and rudder inputs to maintain straight and level flight.

1 hour ago, jcomm said:

So, after all this swirl of arguments I raised and have been repeating in my posts, it can well be the case that I WAS WRONG !!!

Glad to hear that you could have Janov's answering you and explaining that in depth. Sometimes it's really better to be sure before reporting something as a bug 🙂

@jcomm at least you had the courage to admit it. Good on ya. 👍

I still suspect you were originally right, and the bug is actually there: i.e. a CW twin or single, barring any compensation with trims or asymmetric surfaces, should have a left rolling tendency, not a right one. Unfortunately I think only a real life flight test could put the matter to rest.

Will reply more extensively in the .org thread.

Who is Janov? Pardon the ignorance. 🙂 It's an honest curiosity. 

@BostonJeremy77, Janov is a RW airline pilot, I think presently in the 744 fleet, and one of the developers if the iXEG 737. I believe he now also makes part of the Laminar Research Team.

He has been cooperating on this subject, mostly at the .Org Forums.

Last findings on this "phenomenon" follow:

Actually in the default Baron, even with the default ACF file, the rolling tendency is minimal.

But there is yet another modification required in the Baron 58 ACF. The right engine is located further from the center than the left one ( 5.89 ft vs 5.83 ft ) which IRL is counter intuitive because the critical engine is the left one, and a longer arm on the right engine makes it even "more critical"... But I have edited it and now they're both at 5.89 ft from the center.

With all default trim tabs zeroed in Plane Maker and the lateral arms of both engines equal, the Baron does not show any right rolling tendency and instead rolls and yaws left at higher power settings, as I believe it is supposed to be the case with the real Baron 58 (?)

Then in the default Beechcraft C-90 the tests have shown that even with all of the default trim tabs zeroed in Plane Maker the aircraft banks right at any power settings. I confirmed there's no asymmetry in the location of the engines, nor any lateral cant.

So, among the default twin prop aircraft in X-Plane 12.1 beta the one that exhibits this right rolling tendency is the C-90.

Other addon aircraft, like the VSkyLabs DC-3, LES DC-3 and Airworks DC-3 all have the same effect, even when the trim tabs are zeroed in Plane Maker.

Out of curiosity ( the following is A JOKE!!! ) MSFS copied so closely X-Plane ( end of JOKE !!! ) that in FS 2024 Standard Edition which I own, both the default Baron 58 and Kingair 350 bank madly to the right at the full range of power settings !!! 🤣

I can't find out why because being cloud-based / encrypted modules I can't open their "aircraft.cfg" and check for any inconsistencies...

Edited February 22, 20251 yr by jcomm

2 hours ago, BostonJeremy77 said:

Who is Janov? Pardon the ignorance. 🙂 It's an honest curiosity. 

Janov is pretty much a huge influence in Laminar. Behind most of the flight models, input on wEather,wed, and many other things. Hes often in Austins ear when he can prove things are wrong.

6 hours ago, BostonJeremy77 said:

Who is Janov? Pardon the ignorance. 🙂 It's an honest curiosity. 

Some say he works part time as the Stig, and keeps Chuck Norris in his car boot, apparently Chuck isn't dead, he's just to afraid to move. All we know for sure is he goes by the name @Janov

Edited February 23, 20251 yr by mSparks

Got ya. Thanks for the info! I am now flying almost exclusively in XP12 since discovering Map Enhancement. As a matter of fact, I am doing 3x around the world to visit all continents' major parts (except for Antarctica)... There are so many aircraft that I still want to get: Toliss A330, Rotate MD-88, Rotate MD-88, XCrafts Embraer family, Flight Factor 777, Toliss 319 and 320 (I only own 321 CEO and NEO). I am even toying with the idea of Magknight 787 (though that one is probably on back burner as I heard it was less than ideal and I don't want to buy junky stuff)... I think the 777, the 330, and the McDs are the priority. 

4 hours ago, BostonJeremy77 said:

Got ya. Thanks for the info! I am now flying almost exclusively in XP12 since discovering Map Enhancement. As a matter of fact, I am doing 3x around the world to visit all continents' major parts (except for Antarctica)... There are so many aircraft that I still want to get: Toliss A330, Rotate MD-88, Rotate MD-88, XCrafts Embraer family, Flight Factor 777, Toliss 319 and 320 (I only own 321 CEO and NEO). I am even toying with the idea of Magknight 787 (though that one is probably on back burner as I heard it was less than ideal and I don't want to buy junky stuff)... I think the 777, the 330, and the McDs are the priority. 

I LOVE Xp12, and thanks to you it's even better since I started using the Apple maps instead of Google-1 with Map Enhancement !!!

 

Hi Jcomm,

I think your favourite guide to aerodynamics Mr Denker (See How It Flies) may have a word or two to say about the loose use of terminology; "engine rotational inertia should not be confused with propellor drag" (see sections 9.5 and 9.6). Whether that has a significant effect on the overall outcome I don't know. I am still struggling intuitively with the concept of "torques flowing in a closed circuit and cancelling".

Cheers Tim

3 hours ago, jcomm said:

I LOVE Xp12, and thanks to you it's even better since I started using the Apple maps instead of Google-1 with Map Enhancement !!!

 

Nice! You like Apple Maps? I do too! Even in Greenland it was good. I keep using them going forward!

1 hour ago, thepitts said:

torques flowing in a closed circuit and cancelling

It's a bit misleading because the red arrows in Fig 9.15 suddenly disappear in 9.16. This isn't exactly correct. The brake shoe mounting brackets would have the same red arrows in 9.16 because they're rigidly connected. The difference is that the other end of the bracket is attached to the other side of the rotational system (fuselage) as opposed to a separate component (the ground in 9.15) and cancels out the opposite red arrows of the fuselage in 9.15. 'flowing' maybe isn't the best word here given that we're looking at solid structures. Think 'summation'. The red arrows are all still there in 9.16. He just doesn't draw them because the net sum of all arrows combined is zero.

And if you really want to get nerdy, zoom out to a full-earth view for 9.15 and you'll see the planet rotating like a really...really big propeller spinning at imperceptibly small RPM. But only if the airframe is floating freely. As soon as you remember gravity and build a stand to hold up the airframe, you've arrived at 9.16.

Unfortunately not a smart enough nerd or though I am trying (---or so my wife says.)

Conceiving the Earth rotating like a really really big propeller at imperceptibly low rpm....you've got to love physics !

Cheers Tim