Spiral Slipsteam and trim tabs Oh wow!

I recently had an opportunity to be schooled by DCS again and wanted to share my findings on the P-47D because I think some folks will wonder about "phantom rudder movements". It deserves to be highlighted at the very least.

Most sim fliers in DCS will be aware of the pull to the left you get with propeller driven aircraft as you add power. Some of the non-aeronautical folks will slap a few fancy names out there, like Torque, gyroscopic precession, P-factor, and call it done. A fourth "left turning effect" took me by surprise, because at first, I thought I had take-off assistance on. My rudders were moving by themselves!

Spiralling Slipstream is modelled for the P-47D. The air wrapping around the P-47D fuselage now corkscrews and hits the tail, applying a turn. It also hits the rudder, deflecting it increasingly right into the airflow. More power, more air, more deflection. So that is pretty cool by itself.

The thing that really spun my head was the way that the rudder trim interacted with this corkscrewing airflow. Be mindful of how trim tabs work. Their surfaces deflect into the airflow creating higher pressure on the opposite side to pull the rudder at its pivot. So, with the default Take Off right trim applied, you see your pedals move, un-commanded, to the right, as you apply throttle.

Set your trim neutral, however, and your rudder no longer deflects right as much, under power. You are un trimmed.

This effect is pronounced when the aircraft is at high angle of attack, or slow to stationary with its tail down. Separate to this, P-Factor is also increased due to the tail low angle, because the downward moving side (right) of the propeller is taking a larger bite of air than the upward one when you are sat back.

Thankfully, the P-47D is fairly stable and there should be less accidents on the ground compared to other aircraft. But I had to chase this all down to understand it, as a layman sim pilot.

So, I guess the next step in the evolution of flight sims is a commercial affordable force-feedback rudder, that will let you feel that airflow these clever chaps at Eagle Dynamics are creating for us!

Awesome find, Pikey.

Probably explains why it gets so weirdly wobbly up above 35k under power. 2500rpm, 40in of boost, 200knots or so and it just feels really unstable. It doesn't trim at all properly or want to stabilise.

Welcome to RL piloting 101

ya baby ya

Conclusion: We do need Force Feedback rudder pedals. Yesterday.

Look to see that take off assist is still turned off. I found it ON for all my planes after the patch.

Yeah ffb pedals would be nice, and someone to make a P47 throttle quadrant.

Look to see that take off assist is still turned off. I found it ON for all my planes after the patch.

Never had I this happen to me. I wonder why this happens to some and some not.

Pikey interesting behaviour. Will look for it on my next fliight.

Fox

When I did my first flight I could not trim out the forces no matter what I did, was almost at full right rudder to keep straight and level.

Got really frustrated by it and was ready to throw in the towel, if I can trim the Spit hands off surely I can trim this... nope, tried re mapping the controls for trim as I could not hold the stick and trim at the same time ( using a twisty TM160000M just now)

Then I went into the setup usb controller to see what was happening in there and the rudder was not centred and I could not get it to re centre, I had to hold 1/2 to 3/4 right rudder to get the rudder centred, the controller would not auto centre at all. Eventually I downloaded a manual calibration utility for the TM16000M and manually set up my rudder and low and behold it now works fine.

That first hour or so was really frustrating and a source of much cursing of the P47 :) but now it flies like a dream and I can trim to hands off no problem.