The Torques and other convolutions on MSFS's FDM...

#1
I remember, but I can't recall exactly which record, that we lost at least one record from fs9 into FS10 that could be used to fine tune slipstream - not engine / prop torque - over tail surfaces.
Back then I and Ron Freimuth made a few tests to determine the net effect.

In MSFS, ported to nowadays platforms, torque ( from engine / prop ) vanishes with increasing IAS, being nill above Vs0, which results in rather unrealistic behaviour of powerful prop aircraft, like but not only ww2 fighters, if their throttles are "cycled" in flight above that reference speed. Firewall the throttle of your climbing P51d, and then retard it to idle and your wings will stay level, as if "nothing had happened"...

In fs9 there could at least be some effect from the slipstream on the vertical fin - we could detect some yaw moment.

So, question is, how do you FDE gurus cope with it ? I've seen at least one ingenious workaround with an Aerosoft D-400, which silently deflected the rudder to reproduce the slipstream effects...

Yet another kind of effect that can supposedly be fine tuned using the proper regs is control surface effectiveness with dynamic pressure, and in particular rudder efficiency. This can, I believe, be used to fine tune for instance the feel while taxiing a taildragger, which at taxi speeds has it's rudder mostly ineffective and relies only in a steering tailwheel and / or asymmetric braking.

I used just a couple of ww2 fighters in FSX. The A2A p51d, and Bernt Stolle's fine tuned Flight Replicas Bf 109 K-4, the latter being by far my preferred rendition of a powerful ww2 fighter in FSX. From what I recall - it's been a long time since I used it - it behaved quite plausibly while taxiing, and during takeoff and landing, requiring correct techniques to be applied, such as differential braking and locking the tailwheel during takeoff and landing.

But I wonder if there is in FSX actually a way of properly reproducing propwash effects as a function of propwash speed, including asymmetric hit of various aircraft surfaces, some countering the torque, others "helping" it... like when the low section of the left wing is hit by the swirling propwash from the front prop ( on cw rotating prop aircraft ) or the tail surfaces get hit on their port side by that same swirling propwash ( again assuming frontal cw rotating prop )...

How do you cope with these effects and try to fine tune it ?

Also, can that new "Simln SDK" be used to overcome limitations inherent to the core FDE ?

Thanks for any hints, answers, suggestions, comments.... :)
 
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Roy Holmes

Resource contributor
#2
In 1541 you have Cmde due to propwash and CMq due to propwash
In 1544 you have Cnr due to propwash and Cn dr due to propwash.
They used to be part of 1101 but they are still there.
The most effective way to get a tail dragger to turn on the ground is a blast of throttle plus full rudder.
Roy
 
#3
Great Roy!

Thx for the eferences - I really have to start Reading the old docs again :)

What do you presently use for AIR file editing ?
 
#5
@fs1 Thx for the good news fs1 ! BTW: I remember you from the early eighties :) but I started seriously only around the time of your great grand child fs4...
 
#6
1. In MSFS, ported to nowadays platforms, torque ( from engine / prop ) vanishes with increasing IAS, being nill above Vs0,
2. I used just a couple of ww2 fighters in FSX. The A2A p51d, and Bernt Stolle's fine tuned Flight Replicas Bf 109 K-4, the latter being by far my preferred rendition of a powerful ww2 fighter in FSX. From what I recall - it's been a long time since I used it - it behaved quite plausibly while taxiing, and during takeoff and landing, requiring correct techniques to be applied, such as differential braking and locking the tailwheel during takeoff and landing.

3. But I wonder if there is in FSX actually a way of properly reproducing propwash effects as a function of propwash speed, including asymmetric hit of various aircraft surfaces, some countering the torque, others "helping" it...How do you cope with these effects and try to fine tune it ?

4. Also, can that new "Simln SDK" be used to overcome limitations inherent to the core FDE ?
1. That's definitely not the case.
2. Funny that you mention the 109, since this is a really old FDE (almost 10 years old) and I've improved my FDE design in the meantime quite a bit. Looking at the 109 FDE today I'm not definitely satisfied with it anymore.
3. You are simply expecting too much from FSX IMO ;).
4. When I worked with Milviz a long time ago, the SimIn SDK turned out to be very useful but it can't overcome basic flaws e.g. it can't simulate things that aren't there.
Unfortunately it's too complicated for me because I have to idea about xml and/or gauge design.
 
#7
Thx Bernt,
would really like to be able to try those modified Bf 109 FDEs...

Regarding torque effect in MSFS/ P3D, from Yves guide the formula he was able to derive makes it null at vs0 * 1.5

1) From Yves document:

"
This is the roll moment due to propeller torque.
 It applies to propeller planes only.
 The roll effect is at its maximum at zero airspeed. It decreases linearly with airspeed (TAS) and becomes zero at flaps_up_stall_speed (TAS) from [reference Speeds] multiplied by 1.5. The effect remains zero above that speed."
 
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#8
I've never modified the 109 FDE.
Ok, there's a big difference between VST0 and VST0 * 1.5! However I can't replicate the observation that the torque effect is nil above VST0 * 1.5.
But since the clean stall speed in the cfg file is only there to adjust the torque effect, you can increase it to any value you like, so the effect is e.g. more pronounced at higher speeds.
 
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