Opposite climb/descend reaction when using pedals

[DeMonteur]

I did some hovering practice with spot turns and I noticed strange behaviour of Mi-8 when applying rudder pedals. When I applied left pedal I noticed heli with left turn start to descend instead of climbing (due to decreased power required required by tail rotor). For the right pedal it starts climbing with right turning.

[iFoxRomeo]

I did some hovering practice with spot turns and I noticed strange behaviour of Mi-8 when applying rudder pedals. When I applied left pedal I noticed heli with left turn start to descend instead of climbing (due to decreased power required required by tail rotor). For the right pedal it starts climbing with right turning.

 

Actually this behaviour is correct.

 

Fox

[DeMonteur]

Actually this behaviour is correct.

 

Fox

And Why? Because from my point of view pushing right pedal causes the tail rotor to increase thrust-> more power needed. This means that when I apply right pedal with same collective setting i will take some power from main rotor to tail rotor so I should start descending.

[swatstar98]

And Why? Because from my point of view pushing right pedal causes the tail rotor to increase thrust-> more power needed. This means that when I apply right pedal with same collective setting i will take some power from main rotor to tail rotor so I should start descending.

 

No, you may actually use some engine power, but it doesn't mean it will affect the main rotor.

[DeMonteur]

Opposite climb/descend reaction when using pedals

 

No, you may actually use some engine power, but it doesn't mean it will affect the main rotor.

 

 

 

On Mi-8 tail rotor takes up to 30% of power. In real heli it is definitely noticeable in spot turns. Where you need change the power setting slightly to hold altitude.

Another thing is that pilots of Mi-8 use left pedal climb when they are close to power limits or on limits to increase power on main rotor. There can be also problem you do not have enoug right pedal. This is also pretty common problem on these helicopters.

 

 

Sent from my iPhone using Tapatalk

Edited June 30, 2019 by DeMonteur

[iFoxRomeo]

The Mi-8 has a clockwise turning main rotor. When you are hovering without adjusting collective pitch and push the left pedal, you are reducing your main rotor's effective rpm and thus reduce its lift. With right pedal input you increase the effective rpm and increase lift. Thus you descend while yawing left and climb while yawing right.

 

Fox

[DeMonteur]

Found an answer. It is caused by power governor. When I apply left pedal power demand reduces, RPM increases, power governor decreases power, so it results in less power on both rotors and results in descend.

https://www.rotorandwing.com/2011/11/29/height-variations-in-rightleft-spot-turns-with-rotors-turning-clockwise/

[iFoxRomeo]

And Why? Because from my point of view pushing right pedal causes the tail rotor to increase thrust-> more power needed. This means that when I apply right pedal with same collective setting i will take some power from main rotor to tail rotor so I should start descending.

 

It doesn't work that way. You cannot distribute power between MR and TR. They are both connected together via the main gearbox. This connection is fixed.

 

 

Found an answer. It is caused by power governor. When I apply left pedal power demand reduces, RPM increases, power governor decreases power, so it results in less power on both rotors and results in descend.

https://www.rotorandwing.com/2011/11/29/height-variations-in-rightleft-spot-turns-with-rotors-turning-clockwise/

Interesting.

From your perspective the governor does it. The reason for the climb/descend is the change in effective Rotor rpm. The governor simply does his job, by maintaining system rpm.

 

Fox

[DeMonteur]

It doesn't work that way. You cannot distribute power between MR and TR. They are both connected together via the main gearbox. This connection is fixed.

I know it is fixed connection. But when I apply left pedal tail rotor decreases pitch-> decrease its power demand and this should increase RPM of both rotors due decreased overall power demand.

 

Interesting.

From your perspective the governor does it. The reason for the climb/descend is the change in effective Rotor rpm. The governor simply does his job, by maintaining system rpm.

Fox

I am trying to find the reason why it works this way. I hope I will definitely try it next week on real heli. Funny

Edited June 30, 2019 by DeMonteur

[iFoxRomeo]

I know it is fixed connection. But when I apply left pedal tail rotor decreases pitch-> decrease its power demand and this should increase RPM of both rotors due decreased overall power demand.

 

 

If you are pushing the pedal to quickly for the governor (and engine spool up/down) to adjust, then the rpm will increase/decrease.

 

 

I am trying to find the reason why it works this way. I hope I will definitely try it next week on real heli. Funny

 

 

Again. RPM is supposed to be constant in the helicopter, which is very important. Governor maintains that as long as the engine(s) delivers enough power (ignoring other limitations for a moment). By adding or substracting effective rpm with a yaw movement right or left you change effective lift. Thus you climb or descend in this case.

 

 

Fox

[DeMonteur]

No, you may actually use some engine power, but it doesn't mean it will affect the main rotor.

It is enough power demand difference to affect your climb or descend. In real word heli definitely noticeable.

[AlphaOneSix]

When I applied left pedal I noticed heli with left turn start to descend. For the right pedal it starts climbing with right turning.

 

This behavior is correct.

[DeMonteur]

Finally I tested it yesterday IRL and it was same as in DCS. It was small but noticable descend in left spot turn and climb in right spot turn. Quicker turn was not possible due RL limitations.