Su-27/33 Drifting Sideways on Takeoffs

[Cmptohocah]

There is a weird tendency of the Flanker to drift to one side during takeoff roll (even with no winds) when the nose wheel steering is disengaged.
The drift stops at around 80-100km/h IAS. This only happens when the NWS is off. If left on, this does not happen.

Step to reproduce:

1. lock nose-wheel-steering into takeoff position (управление колесом - off)
2. start the takeoff run
3. airplane starts to were of to the side and rudder input is needed
4. sideways motion stops at around 80+ km/h

Steps when it does not happen:
1. keep the NWS in the ground position (управление колесом - on)
2. start the takeoff run
3. no rudder (steering) input is needed

This weird behavior happens on both Su-27 and Su-33.

Edited May 3, 2022 by Cmptohocah

[Ironhand]

Interesting. The only times I’ve noticed any drift with NWS disengaged are when I either 1) takeoff with full afterburner or 2) don’t wait for thrust to equalize prior to releasing the brakes during a full mil takeoff. In the former case, the longer you wait prior to releasing the brakes, the less of a nudge to one side or the other you experience.

I’ve attached two TRKs. One for full mil takeoff and one for AB. I flew the full mil takeoff first. I then replayed the TRK and took control after NWS was set to disengaged. In theory, at least, that made the two lineups on the runway identical.

In the full mil takeoff, the Flanker runs arrow straight down the runway prior to wheels up. In the AB takeoff, because the thrust wasn’t fully equalized prior to brake release, there’s an initial nudge to the right but not enough to move me off the runway prior to takeoff. At no point did I touch the rudder pedals during the takeoff roll in either TRK.

If I get a chance later, I’ll try the AB takeoff with NWS engaged just to see what happens.

Su-27 NW Steering Off--Full Mil.trk Su-27 NW Steering Off--AB.trk

Edited May 3, 2022 by Ironhand

[Cmptohocah]

44 minutes ago, Ironhand said:

Interesting. The only times I’ve noticed any drift with NWS disengaged are when I either 1) takeoff with full afterburner or 2) don’t wait for thrust to equalize prior to releasing the brakes during a full mil takeoff. In the former case, the longer you wait prior to releasing the brakes, the less of a nudge to one side or the other you experience.

I’ve attached two TRKs. One for full mil takeoff and one for AB. I flew the full mil takeoff first. I then replayed the TRK and took control after NWS was set to disengaged. In theory, at least, that made the two lineups on the runway identical.

In the full mil takeoff, the Flanker runs arrow straight down the runway prior to wheels up. In the AB takeoff, because the thrust wasn’t fully equalized prior to brake release, there’s an initial nudge to the right but not enough to move me off the runway prior to takeoff. At no point did I touch the rudder pedals during the takeoff roll in either TRK.

If I get a chance later, I’ll try the AB takeoff with NWS engaged just to see what happens.

Su-27 NW Steering Off--Full Mil.trk 60.53 kB · 0 downloads Su-27 NW Steering Off--AB.trk 58.87 kB · 0 downloads

 

Hmm.. you might be on to something there. I don't really wait for the power to stabilize - could be that this is the cause. I will do a test to confirm it.

[Ironhand]

No. You are correct...at least where AB takeoffs are concerned. With NWS engaged, there is no push to either side. TRK attached.

Su-27 NWS ENGAGED--AB.trk

[Cmptohocah]

I did some test-takeoffs where I waited for the engines to stabilize and indeed there's no drifting tendency any more (without NWS engaged), so thanks for that.
Funny that when having the NWS on, this does not happen for some reason

Edited May 13, 2022 by Cmptohocah

[Dragon1-1]

Disabling NWS on FC3 planes seems to be dodgy. Some time ago, the F-15 had serious problems landing without NWS, which was a problem because actuating it after touchdown typically ended badly (normally you'd use the rudder alone, without NWS). IIRC, this was fixed at some point, but the issue may remain in other FC3 aircraft.

[Brzi_Joe]

Late to the party, but just for others with problems at takeoff (presented as left engine fire, but really takeoff problem); My left rudder pedal partially broke, and I was sometimes unintentionaly breaking. I had many days with frustration, but calibration site showed my faulty left pedal (huge dead zone didn't help). I repaired broken parts with super glue and some pulver, no more problems for me.

But as above said, press and hold breakes, wait for booth afterburners, and then start rolling.

Edited June 5, 2022 by Brzi_Joe

[Cmptohocah]

On 5/30/2022 at 5:08 PM, Brzi_Joe said:

....

But as above said, press and hold breakes, wait for booth afterburners, and then start rolling.

Or as an alternative, keep the NWS engaged and turn it off at 80km/h.