Trying to understand aerodynamics of Apache roll.

[DmitriKozlowsky]

After watching UK Westland Apache doing roll at airshows, I experimented in DCS. Fuel at 40%, center aux tank E, no weapons.  Climbed to 5000 AGL, and entry speed of 120 KIAS. 

Left full pedal , collective down, full left cyclic. Didn't roll. At near 90 deg bank, control became mushy and helicopter would not continue roll.

Left full pedal , collective middle, full left cyclic. Didn't roll. At near 90 deg bank, control became mushy and helicopter would not continue roll.

Right full pedal , collective middle-down, full left cyclic. Rolled nicely, and then stabilized itself, after release of cycling.

Not quite getting what is happening aerodynamically to the rotor disk, with full left cyclic, and full opposite pedal, that allows Apache to roll.

Cheers

[Leg2ion]

I think...

When the MR rotates, if there was no anti torque (tail) the airframe would rotate the opposite direction - so the main rotor rotates anticlockwise when viewed from the above, and the airframe would rotate clockwise. To counter this affect the tail rotor pushes the tail to the right in an anticlockwise rotation, so when you put some left pedal in - in normal flight - it pushes the tail to the right. 

When you increase collective pitch (as you initially pull into the hover as an example) you also have to introduce some left pedal to counteract against the increased torque - so if when trying to roll you are applying full left pedal then in effect you are introducing maximum anti torque thrust which is trying to push the tail to the right - or in this instance upwards, to maintain an upright attitude - so despite having full left stick over by going full left pedal you now have a rotor at the back end trying to maintain you upright.  By going right pedal you are unloading the anti-torque effect, so would allow the aircraft to continue on its manoeuvre without trying to fight against a left-hand roll.

In addition, I believe the tail fuselage is constructed in a profile that allows the AH to maintain straight (ish) flight if there is a tail rotor failure above around 50-60 kts - but not sure if this feature is modelled. If you look at the tail - it is basically a wing designed to provide lift to the right, so as you go near 90 it is acting in profile as a normal wing - so again would be attempting to maintain level flight and resist any attempt to further roll over.

I think...?

[bradmick]

100kts is the no slower than airspeed for tail rotor failure.

 

I think some of the issue is the extreme sideslip and where the input for the pitch is being made on the rotor disk relative to the fuselage. This imparts a rolling moment in addition to the pitching moment, and becomes more noticeable at speeds above 40 knots. That being said, there are a lot of really complex interactions at work because helicopters are evil. 

[SunDevilPilot]

No need for the full left or full right pedal. Especially if you went to zero collective…. There would be minimal torque with no collective. Leave some collective in there…. It will roll quite easily.