Archived

This topic is now archived and is closed to further replies.

LAdamson

Shortfield takeoffs and torque

Recommended Posts

 

With some thread drift, leading back to roll in the Cessnas........here is a shortfield takeoff video in a Cessna. This is where torque effect would be the highest, as you rotate at a lower airspeed, with full power. Notice the yoke movement at rotation and climbout. Does your simulated plane, need more constant deflection to the right, than what's shown here?

 

Share this post


Link to post
Share on other sites
Help AVSIM continue to serve you!
Please donate today!

With some thread drift, leading back to roll in the Cessnas........here is a shortfield takeoff video in a Cessna. This is where torque effect would be the highest, as you rotate at a lower airspeed, with full power. Notice the yoke movement at rotation and climbout. Does your simulated plane, need more constant deflection to the right, than what's shown here?

 

I tried the default C172 in X-Plane, and the roll induced by torque engine seems to be very low.

 

The video is interesting. The C172 engine, with 160 hp at 2700 rpm, produces a torque of about 307 ft*lbs (calculations below). The C172 has a cabin width of about 3,28 feet, so in order to exactly compensate the torque of the engine, you'd need a passenger sitting in the right seat (about 1,64 ft from centerline) weighing ( 307 / 1.64 ) = 187 lbs. What do you see in the video? :smile:

 

Calculations: Power = Torque * Angular_Speed -> Torque = Power / Angular_Speed = ( 160 hp / 1.36 * 1000 ) [W] / ( 2700 rpm / 60 * 2pi ) [rad/s] = 416 N*m = 416/9.81 kg*m = 42.42 kg*m = 42.42 / 0.454 / 0.3048 ft*lb = 307 ft*lbs.

 

On the other hand in these other videos, with no right seat passenger, the yoke deflection on takeoff seems more noticeable and constant. I don't think it's crosswind (only and always right crosswind?), also because the deflection continues well after wheels are off the ground, when pilot should return to coordinated flight even with crosswind.

 

( minute 3:55 )

 

( minute 3:52 / 14:10 )

 

However, I'm not denying that the torque induced roll may be or feel exaggerate in X-Plane. I'm just wondering about the reasons for it.

Share this post


Link to post
Share on other sites

usually the word "torque" in a forum is followed by a visit from jcomm :Just Kidding:  :lol: where's jc? :lol:

Share this post


Link to post
Share on other sites

Same instructor. A different takeoff (shortfield) and less deflections

 

 

 

 

On our builders forum, the use of aileron trim is sometimes discussed. There are those who figure it's a waste. Take a RV8 for instance. Tandem seating, 200 HP, and still the short stubby wings. Since pilot and passenger are sitting on the centerline, some of these owners feel there is no reason for aileron trim. I put it in my 6. More for passenger or fuel imbalance, than anything. 6 is a side by side. Never really noticed a difference with a passenger or not.....roll wise. Pitch at rotation is what's noticed, as the load is moved more aft.

Share this post


Link to post
Share on other sites

I think these videos all suffer from low wind turbulence due to friction, so it's hard to get a feel of what is a wind gust, and is torque correction. The best thing would be to set the aircraft at like 2000 feet, mantain SLow Flight, and show the controls needed to mantain the aircraft flying level. We would get a proper idea of control inputs this way, without external interference! Who's first? =p

Share this post


Link to post
Share on other sites

Well seen Alec, and indeed I even had a lot of difficulty trying to find the yoke inputs.

 

But, then again, I'm also waiting for one of your chances to go up and test it yourself, after finishing the IFR exams ;-)

 

The aircraft you usually fly has considerable dihedral, so I guess it will be more difficult to test the rolling tendencies, while the yaw should be obvious at lower speeds, but of course all of this tests should be run, as you pointed out in your post, above the limit layer, preferably around 2500' if you're flying near a huge town with big buildings....

 

@BleedAir:  Here I am, according to your perfect forecast :-)  I'm almost "dying" with a terrible flu, at home, on what should be my first day of holidays :-(  Not even able to spend enough time in front of the monitor to enjoy 10.25b1 :-(

Share this post


Link to post
Share on other sites

Lol! The title of this thread had "Jcomm bait" written all over it. :-)

 

Get well soon, J!

Share this post


Link to post
Share on other sites

And here's a take-off/initial climb (in coordinated flight) with the default C172S in X-Plane:

 

 

The required yoke deflection is very small. From "data output", it's around 5% of total deflection. I wonder how much a 5% yoke deflection is appreciable in real life (genuine question).

Share this post


Link to post
Share on other sites

 

 


The required yoke deflection is very small. From "data output", it's around 5% of total deflection. I wonder how much a 5% yoke deflection is appreciable in real life (genuine question).

 

Exactly my point in another post Murmur. The C172 looks very plausible to me in terms of "torque effect". This is making me wonder why. True that it includes a default aileron trim tab of 0.008 and rudder tab of 0.005, which I believe are possibly somehow realistic, although in real life they should be bigger. The engine is also, again most probably like in RL, right canted.

 

This aircraft puzzles me a lot because it is an excellent example of what should happen to other prop aircraft in X-Plane 10. As I told, the A2A model requires a lot more yoke to counter the rolling tendency at lower speeds / climbing at high power than this one!

 

Where's the "Magic" in the default C172????

 

@HiFlyer: Thx Devon! :-)

Share this post


Link to post
Share on other sites

Be sure to catch the part about aileron roll...

 

Right, he doesn't mention roll nor aileron inputs. As I said in the above post, X-Plane default C172 requires about 5% of yoke deflection. How noticeable is a 5% aileron deflection in real life?

Share this post


Link to post
Share on other sites