Propwash speed...

[jcomm 5,923]

I give up :-(

 

Where's the dataref for propwash speed ?

 

You know we can enable display of this important variable in the Data Display menu, but heck!  Where's the corresponding dataref ?

 

Any hint really welcomed....

 

Why?  I was trying to implement my paperwork on fine tuning of the prop effects, using propwash speed as one of the variables...

[Murmur 3,941]

Well, actually I couldn't find such dataref as well. Maybe you could try to use engine torque as a proxy for propwash? After all, the two should be strictly correlated.

 

As a sidenote, I'm in the final phases of my LUA flight model analysis plugin. It will be very accurate, with hard numbers, making possible to compare X-Plane C172 flight model with the real aircraft (in normal flight regimes).

 

I already had some preliminary results. I'll have to do a more detailed analysis, but at this point it's unclear if X-Plane propwash model is indeed flawed, or if it's correct and the problem lies elsewhere. Infact, looks like the defaul C172 is a lot more stable in yaw than the real aircraft. This _could_ be the cause for the lack of propwash effects AND for the poor ground model behaviour in crosswinds.

 

As I've said, at this stage I didn't make a detailed analysis yet, but I will be able to do that in a few days hopefully. I can already analyze pitch, roll and yaw moments on the aircraft as of now, but I'll still have to finish the two remaining parts (forces on the aircraft and controls effectiveness) before I make the entire analysis.

[jcomm 5,923]

Looking fwd for your results Murmur!

 

Also learned that some "hidden effect" , supposedly unwanted got obliterated by the latest beta 11...

 

Although apparently it only affected the behavior when flying without rudder controllers, one never knows....

 

Fixed for Beta 11:

• The new “automagic” rudder code has been removed. This code tried to manage the rudder for you if (and only if) you don’t have a rudder axis installed. Austin didn’t like how the planes flew with the code in place and we had reports of problems with third party aircraft, so rudder management without a rudder axis now works like 10.36.
• Instead: Austin has tightened up the ground steering of the Cessna 172. The original purpose of the rudder management code was to allow us to use the Cessna 172 as the default plane even if users are flying with the mouse. With the tightened up ground handling it should be easier to take off with less rudder input.
• Screenshots and movies now live in the Output folder, along with all other output from X-Plane. This avoids clutter in the main X-Plane folder.
• Fixed high/low idle panel button.
• Fixed bug where inserting the DVD at the product key prompt would not take us out of demo mode.
• Fixed bug that prevented sim startup on Windows XP. (1812).  If you are using Windows XP, please upgrade – Microsoft has EOL’d Windows XP and isn’t going to provide security patches!
• Requesting a water start now prefers seaports to sea lanes to avoid mixed land/water airports where X-Plane’s water data may be out of sync with the airport data. Sealanes are now drawn differently from airports on the local map to make it clear how an airport is built.
• Fixed opening a second replay with the same aircraft as the current replay (1762).
• Fixed ISE6 UDP packet.
• Fixed labeling in date/time window.
• Aurora Borealis drawn to the south in Southern Hemisphere.
• We now render the correct missing flap in a flap-fail.
• Arrow keys in the ATC window no longer move camera (1811).
• Scrolling fixed in advanced joystick screen (1721).
• Transponder fail message visible in the IOS.
• Improved diagnostics for UDP in the operations and warnings menu – the preference to log UDP traffic is also saved with the sim.
• CALI statement in FDR files is now wired up.

[LAdamson 240]

 

 

Well, actually I couldn't find such dataref as well. Maybe you could try to use engine torque as a proxy for propwash? After all, the two should be strictly correlated.
 

 

I doubt it. The moment the wheels leave the ground, the torque ( the need....... of feeling like you must use right yoke or trim) will be gone, while the feel & look of needing right rudder will be very noticeable, until airspeed is gained.   Other than that, I just can't get my mind involved in repairing simulated physics.  I just have too many hobbies for an old guy, and still work full time. Otherwise, it might be interesting. 

[Murmur 3,941]

I doubt it. The moment the wheels leave the ground, the torque ( the need....... of feeling like you must use right yoke or trim) will be gone, while the feel & look of needing right rudder will be very noticeable, until airspeed is gained.   Other than that, I just can't get my mind involved in repairing simulated physics.  I just have too many hobbies for an old guy, and still work full time. Otherwise, it might be interesting. 

 

The amount of propwash should be directly correlated with the torque the engine is outputting. This does not mean that the two phenomena have the same effect on the flight dynamics.

[LAdamson 240]

The amount of propwash should be directly correlated with the torque the engine is outputting. This does not mean that the two phenomena have the same effect on the flight dynamics

So many variables. Once forward motion of the airplane is added, the static rpms of the prop increase. Seems that torque from the engine would still be the same.  For instance, 2350 rpm at full throttle while sitting still, and then onwards to red line (2700 rpm) for cruise.

[jcomm 5,923]

So many variables. Once forward motion of the airplane is added, the static rpms of the prop increase. Seems that torque from the engine would still be the same.  For instance, 2350 rpm at full throttle while sitting still, and then onwards to red line (2700 rpm) for cruise.

 

Exactly Larry, and one of the reasons I am exploring that "propwash speed" data in x-plane, available and apparently very plausibly calculated, but yet unknown to me in terms of it's dataref counterpart... It's also high at the top of a powered step climb...

 

Propwash speed is maximal at full break power, and starts decreasing as you gain speed, become airborne, ... It becomes negative at low power / idle inflight situations like for instance idle descents...

 

I was going to use it together with torque, to fine tune the asymmetric slipstream effects over the tail surfaces, left wing and fuselage, on a CW-rotating prop aircraft ( prop installed ahead of the wings and along the aircraft longitudinal axis, even if with some cant, which would also be taken into consideration...)

[Murmur 3,941]

I was going to use it together with torque, to fine tune the asymmetric slipstream effects over the tail surfaces, left wing and fuselage, on a CW-rotating prop aircraft ( prop installed ahead of the wings and along the aircraft longitudinal axis, even if with some cant, which would also be taken into consideration...)

 

I found a dataref that seems to be strictly correlated to propwash value:

 

sim/flightmodel/engine/POINT_side_wash

 

It's a 8 elements array (so probably one element per each engine), however looks like it's not writable.

[jcomm 5,923]

And Andy, at the .ORG, just posted this:

 

http://forums.x-plane.org/index.php?showtopic=88719&p=946844

 

That other dataref mentioned by Andy comes in handy too :-)

 

[by Andy Goldstein @ .ORG]

"The spiral component is sim/flightmodel/jetwash/ringDVinc - 80 element array for 10 elements each of 8 props."

 

Thx Murmur, and indeed I had that dataref on my list, but was unsure, and still am, about what it really means.

 

We will have to explore further.

 

The idea is making the yaw dependent on it. The asymmetric slipstream hitting the tail ( mainly vertical stab and rudder, but also de left wing and left pan of the horizontal stab, on a CW prop aircraft ) helping to counter the rolling moment from torque at higher power settings and slower speed ranges is what I would like to take int account...

 

And... Austin and Ben just confirmed:

 

[by Austin and Ben]

"sim/flightmodel/jetwash/DVinc”

 

yah… difficult name to guess! ;-P

but that is it, in meters per second, for jets and props both!

 

ben: this should prolly be named “propwash or jetwash” or similar… in mters per second behind props or jets

 

There are so many details of the deep X-Plane flight dynamics engine to explore, simply waiting for someone to pick them and start giving good use to whatever they may be used for...

 

Last Minute:

 

And Austin just explained that other dataref Murmur :-):

 

[by Austin]

"that is the SWIRLING of the wash

the helix angle is the arctangent of the lateral swirl and the wash itself"

[strider1 575]

 

And Andy, at the .ORG, just posted this:

 

http://forums.x-plane.org/index.php?showtopic=88719&p=946844

 

That other dataref mentioned by Andy comes in handy too :-)

 

[by Andy Goldstein @ .ORG]

"The spiral component is sim/flightmodel/jetwash/ringDVinc - 80 element array for 10 elements each of 8 props."

 

Thx Murmur, and indeed I had that dataref on my list, but was unsure, and still am, about what it really means.

 

We will have to explore further.

 

The idea is making the yaw dependent on it. The asymmetric slipstream hitting the tail ( mainly vertical stab and rudder, but also de left wing and left pan of the horizontal stab, on a CW prop aircraft ) helping to counter the rolling moment from torque at higher power settings and slower speed ranges is what I would like to take int account...

 

And... Austin and Ben just confirmed:

 

[by Austin and Ben]

"sim/flightmodel/jetwash/DVinc”

 

yah… difficult name to guess! ;-P

but that is it, in meters per second, for jets and props both!

 

ben: this should prolly be named “propwash or jetwash” or similar… in mters per second behind props or jets

 

There are so many details of the deep X-Plane flight dynamics engine to explore, simply waiting for someone to pick them and start giving good use to whatever they may be used for...

 

Last Minute:

 

And Austin just explained that other dataref Murmur :-):

 

[by Austin]

"that is the SWIRLING of the wash

the helix angle is the arctangent of the lateral swirl and the wash itself"

 

 

Can you edit the number using the deta ref editor ?

[jcomm 5,923]

No, not these datarefs, I can't interfere with the calculated values, but I wouldn't want to do it, yet, I can use those calculations, which are valid, to change those datarefs Austin made available for fine tuning of prop aircraft :-)

[strider1 575]

No, not these datarefs, I can't interfere with the calculated values, but I wouldn't want to do it, yet, I can use those calculations, which are valid, to change those datarefs Austin made available for fine tuning of prop aircraft :-)

How do you fine tune the prop ?

[jcomm 5,923]

How do you fine tune the prop ?

 

Not the prop :-) but rather the datarefs that Austin made available, around 10.30 I believe, for creating moments / applying forces that can, composed with the final force vectors calculated by X-Plane's FDM, be used to overcome any effect we feel overdone, or create / increase one we feel underdone ...

 

If, for instance, I find that a prop model has less yaw as a result of the prop slipstream / wash over some of it's surfaces, then I can use those datarefs to make that yaw moment more significant.  If I find that there is, on a given model, way too much roll due to torque, then I can compensate it again with those forces.

 

But, in order to create compensations that have the least possible impact / cancellation factor on other aerodynamic forces, we can try to look at other variables, instead of just taking the magnitude of "torque" into consideration.