What are Torque, P-Factor, Slipsteam and Gyroscopic effects?
#1
(10-05-2018, 12:01 PM)jcomm Wrote: In my opinion ELITE offers a very plausible implementation of the so called "prop effects" or "the torques" on prop aircraft, of various types.

It's hangar is made up of some rather significant GA-class representatives, from single prop to twins. I do miss, btw, the two French modules that were present in ELITE v8 - the TOBAGOs used at most flight schools here in Europe. Maybe they can be added in the future as add-on modules ( ? )

There are actually 4 basic factors present in the aerodynamics of a prop aircraft:
  • Engine and Propeller torque
  • Propeller P-Factor
  • Propwash / Slipstream  effects
  • Gyroscopic effects
ELITE models all of these in a rather plausible way, and we can actually test it.

P-factor is present in any aircraft with propellers, being it during takeoff or inflight whenever there is an angle between the relative wind and the propeller axis of rotation, although it is particularly noticeable in taildraggers, which do not make part of ELITE's fleet.

The kind of flight dynamics model used in ELITE is a lot closer to the one which was the base for MSFS and now also P3D, and many other flight simulators, including the full Level-D sims, the only difference laying in the parametrization used or the various aspects modelled, regarding lift, drag, thrust, etc... These so called "table-based" approaches rely strongly on available data obtained from expensive flight tests, a reason why while in MSFS we can have a 777 that already costs a good deal of $$ it couldn't compare to only the dataset used for a Level-D sim for that same aircraft, provided at "lottery" figures to the bigger developers on that market ( CAE, Thales, … )

Well but I still believe propwash effects are taken into consideration in ELITE, at least in as far as they were present in MSFS up top version 9 ( they were cut in MSFS X unfortunately :-/ ). In real life they are connected to the spiralling/swirling air mass projected behind by the propeller and hitting, sometimes asymmetrically, various surfaces of an aircraft, wings, fuselage, tail surfaces...

Finally the gyroscopic effect is present specially at higher power settings and lower speeds / higher AoA, and acts pretty much like we learned at highschool.

P-Factor, Gyroscopic, propwash and torque all contribute in an aircraft with a clockwise (cw) rotating prop (as seen from the cockpit admitting the propeller is ahead of it towards the nose of the aircraft) to the "left turning tendency" felt more aggressively during takeoff but present also at any other phases of flight

Aircraft are designed to minimize these effects at their optimal cruise settings, based on power and speed / AoA, as well as density altitude. They can offer movable trim surfaces for elevator, rudder and aileron (aileron trimming not present in ELITE, although it should be there for the Baron, Seneca and B200...) or ground adjustable trim tabs, that can be set by the manufacturer, aircraft maintenance units or the crew while on ground to compensate for the type of flight being done, or rigging.

But inflight whenever there are power or speed variations, as altitude / air density varies, or simply due to external perturbations like wind shear and turbulence, frequent adjustments are required. 

Some aircraft also have their vertical fin at an angle to the imaginary aircraft longitudinal axis and/or their engines/prop axis also tilted ( to the side and up or down ) to compensate for prop effects in cruise.

For aircraft equipped with rudder trim, at each flight regime it should be used to fly wings level and compensate for the effects mentioned above. Of course when the aircraft is perturbed by wind variations / turbulence the state of equilibrium will be lost, and the pilot has to regain control and re-trim.

I actually find ELITE does a much much better job at reproducing aircraft stability compared to either MSFS or X-plane, and it does so in a way that is clearly tailored to cope with it's main objective - being an IFR training tool.

Of course the "table-based" approach used in  ELITE is good just within the so called "IFR flight envelope" which means basically that no manoeuvres  involving aerobatics which might approach stalls or even post-stall situations, inverted flight and higher than usual pitch, bank and yaw angles, can be expected to give a plausible response by the core Flight Dynamics Model because there is no valid data for such non-normal situations.

Just as a side note, X-plane includes a very interesting tool that allows for the visualization of some of these effects. It's the "Flight Model Visualization" that can be activated in outside views of the aircraft in various modes and show, for instance, the propwash, the various lift, drag and thrust forces translated into canonical components, and so on... A nice didactic feature provided by that sim.




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#2
Many thanks for that in-depth tutorial jcomm Thumbup 

Will be useful for my re-learning the basics curriculum.

Will discuss with you on this when I get to it in the future.




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#3
(10-27-2018, 03:46 PM)Simicro Wrote: Many thanks for that in-depth tutorial jcomm Thumbup 

Will be useful for my re-learning the basics curriculum.

Will discuss with you on this when I get to it in the future.

You're welcome Simicro!

I leave here also a very good video on the subject:

https://www.youtube.com/watch?v=o8sc3VlZPUc
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#4


Thanks jcomm for the link to the video. Best visual and animated explanation I have ever seen Surprised




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