Speed Hold

[AeriaGloria]

Anyone got speed hold to work at any time? 
 

  I know it is intended to engage at the same time as altitude hold, and manuals have it supposedly being effective enough to hold you within +/-10kmh

   However, if I taxi along a runway, keep all my controls the same, but change speed with Wheel brakes and/or collective, I cannot get pitch channel to move even after a 100 kmh speed difference 

 

  I know it uses the pitch channel, and the pitch channel is also influenced by cyclic movement from the compensation transducers, so I performed my tests engaging altitude channel when my cyclic was in the needed position and not moving it. 
 

I can upload a track shortly, but wanted to see if anyone else had this experience or if it is a long known missing feature

 

[AlphaOneSix]

My documentation indicates that the KZSP indicated airspeed controller doesn't start working until 150km/hr IAS.

[AeriaGloria]

56 minutes ago, AlphaOneSix said:

My documentation indicates that the KZSP indicated airspeed controller doesn't start working until 150km/hr IAS.

Interesting, I’ll try it out 

[AeriaGloria]

   Here is a track. I tried to start various dives/climbs, and enabled roll/pitch and altitude channel when only at a stable pitch, trying to minimize as much pitch channel movement as possible from attitude hold/compensation sensors 

   From 150-300 kmh, could not see any noticeable change. Perhaps it is too small to see or the test isn’t correct, but I expected it to be noticeable since Mi-8/17 documentation including ED manual says speed hold should be good for +/-10kmh holding, and for Mi-24 this value is +/-5 kmh. In Mi-24’s case, the speed hold causes the pitch channel to deflect 100% at just a +/-6.6 kmh difference from the speed it’s turned on at.

   Most other channels between Mi-8/24 appear to be identical, roll channel attitude hold holding a 12.5 degree difference from set attitude, compensation sensors using 40% lateral cyclic to create 100% deflection at attitude turned on, and altitude channel causing a 100% deflection when only a 10m difference from initialized altitude, yaw channel heading needing a 7 degree difference for 100% deflection. The largest outlier being pitch attitude hold which is 3x more aggressive in Mi-24, 5 degrees vs 15 degrees. But its compensation sensor is also identical between Mi-8/24, causing 100% pitch channel deflection for 50% stick movement. 
 

  So for speed hold, I expected if not a similar value, to be within a similar ballpark. Here is a track 

kzspspeedhold.trk

[DeMonteur]

On 11/8/2023 at 3:56 AM, AeriaGloria said:

Anyone got speed hold to work at any time? 
 

  I know it is intended to engage at the same time as altitude hold, and manuals have it supposedly being effective enough to hold you within +/-10kmh

   However, if I taxi along a runway, keep all my controls the same, but change speed with Wheel brakes and/or collective, I cannot get pitch channel to move even after a 100 kmh speed difference 

 

  I know it uses the pitch channel, and the pitch channel is also influenced by cyclic movement from the compensation transducers, so I performed my tests engaging altitude channel when my cyclic was in the needed position and not moving it. 
 

I can upload a track shortly, but wanted to see if anyone else had this experience or if it is a long known missing feature

 

As far as I know speed hold is not installed on this version of Mi-8. It is sepparate switch left of the AP indicator. At least on Mi-171Sh from Ulan-ude.  I never heard or read that altitude hold is connected to speed hold also

Edited January 21 by DeMonteur

[AeriaGloria]

7 hours ago, DeMonteur said:

As far as I know speed hold is not installed on this version of Mi-8. It is sepparate switch left of the AP indicator. At least on Mi-171Sh from Ulan-ude.  I never heard or read that altitude hold is connected to speed hold also

 

From the DCS Mi-8 manual