Let’s talk Aerodynamic Trim and Nose to Tail Trim

[rweaves6]

As a fixed wing pilot, I’m a little confused with the two methods of trimming a rotary craft. In a fixed wing aircraft, having the ball centered means you’re coordinated and efficient, neither any skid or slip happening, the aircraft is moving forward with the tail tucked in nicely behind. 

Now how does this translate to the helicopter? I understand keeping the ball centered means the helo is trimmed aero and keeping the nose on the velocity vector is nose to tail. 

Is aero trim similar to when you approach an airfield in a fixed wing where you’re coordinated and crabbing to allow for wind. Then when you near touchdown and straighten the nose to point down the centreline, would this now be similar to nose to tail in the rotary? Are we rolling the helo slightly more to maintain nose to tail? 

*Edit*
My question is, are not both trim modes essentially Nose to tail trim? One is nose to tail to the desired heading and the other is nose to tail to the desired track/ bearing? 

Edited March 31, 2022 by rweaves6

[S. Low]

Brad is an Apache pilot, he details it out here I think:

edit - this post explains that the crabbing is a bit much right now. But if you scroll down I think he explains crabbing more. It’s due to all the forces acting on the aircraft. Need one trim for rockets and another for efficient flight I believe 

 

Edited March 27, 2022 by S. Low

[rweaves6]

Edit to my original post. I realize now where my confusion sits. My question is, are not both trim modes essentially Nose to tail trim? One is nose to tail to the desired heading and the other is nose to tail to the desired track/ bearing? 

[kgillers3]

Correct, ntt the aircraft is not in coordinated flight in relation to the winds and the torque effect, just trying to get the aircraft to fly long axis through something for landing and you can’t see your tail, so if your nose made it through your tail will likely make it through. If the ball is centered aircraft is in trim in relation to winds and torque effect which unloads the higher speed you go, in dcs it’s a bit extreme of a “crab” but life goes on. 

Edited March 31, 2022 by kgillers3

[jacobs]

I'll take advantage of this post to question: should be strive for aero trim? Is it more effective? Or is it just a matter of preference and there is no problem in trying to achieve nose to tail trim (damn that decentralized ball)????????

[bradmick]

2 minutes ago, jacobs said:

I'll take advantage of this post to question: should be strive for aero trim? Is it more effective? Or is it just a matter of preference and there is no problem in trying to achieve nose to tail trim (damn that decentralized ball)????????

You should always fly in aerodynamic trim. Nose to tail trim is used when you’re down low close to objects and trees. Coordinated flight is better for getting the lowest drag from the aircraft in forward flight. It is also preferred when shooting rockets because it provides a favorable relative wind to the rocket.

[jacobs]

Just now, bradmick said:

You should always fly in aerodynamic trim. Nose to tail trim is used when you’re down low close to objects and trees. Coordinated flight is better for getting the lowest drag from the aircraft in forward flight. It is also preferred when shooting rockets because it provides a favorable relative wind to the rocket.

Ok, that's really interesting, because if I'm flying into combat and I may have to WAS' rockets at any time and start PEW PEW, isn't it more helpful if I'm already at nose to tail trim? 

 

I'm still inclined to screw with that slip ball...

[bradmick]

1 minute ago, jacobs said:

Ok, that's really interesting, because if I'm flying into combat and I may have to WAS' rockets at any time and start PEW PEW, isn't it more helpful if I'm already at nose to tail trim? 

 

I'm still inclined to screw with that slip ball...

No, because now your fuel burn is going to suffer.

[26-J39]

What confuses me in DCS is that when you trim coordinated, in external view you clearly have a massive crab, as opposed to NTT where flight looks "coordinated".

How does flying crabbed be classed as "aerodynamic" and more fuel efficient?

[bradmick]

Math. Helicopters are really complicated. You have main rotor torque which initially decreases as the aircraft accelerates from the hover into forward flight, reaching its lowest point at max endurance/rate of climb airspeed. The tail rotor is constantly being used to counteract that torque effect, this imparts a constant yawing moment on the helicopter. The helicopter also wants to drift right at all times. This requires left cyclic to counteract it. The combined effects of the above combine to cause the aircraft to fly slightly crabbed at all times. The aircraft will be most efficient when it is aligned with the incoming wind, which is achieved by maintaining the helicopter in aerodynamic trim (centered ball) otherwise you’re going to be skidding and slipping all over the place and incurring a drag penalty. You have to actively be on the pedals to keep the aircraft from skidding/slipping in forward flight as a result of increasing/decreasing the torque for higher/lower airspeeds. There are a lot of forces at play that cause the aircraft to fly (and this is true of all helicopters with tail rotors) the way they fly. 

[cobrabase]

Foolish question but if one is in cruise all trimmed and on holds and then rapidly need to turn to a new course should we should disengage the holds then physically hold the trim down as we maneuver and then release to re-trim onto a steady course?

Edited September 1, 2023 by cobrabase

[bradmick]

Press and hold the force trim interrupted, when you return to level flight, release the force trim and then the holds automatically start doing work again. There’s no reason to turn them off, as pressing the force trim interrupt prevents them from doing any work.

Edited September 1, 2023 by bradmick

[cobrabase]

2 minutes ago, bradmick said:

Press and hold the force trim interrupted, when you return to level flight, release the force trim and then the holds automatically start doing work again. There’s no reason to turn them off, as pressing the force trim interrupt prevents them from doing any work.

 

Understood good Sir!  

I just wanted to confirm what I thought I heard on one of your excellent videos.  : ) 

[Sobakopes]

В 31.03.2022 в 21:55, bradmick сказал:

You should always fly in aerodynamic trim. Nose to tail trim is used when you’re down low close to objects and trees. Coordinated flight is better for getting the lowest drag from the aircraft in forward flight. It is also preferred when shooting rockets because it provides a favorable relative wind to the rocket.

If you shoot rockets while crabbing they are going to deviate sideways.

1 they have lateral speed component relative to your crosshairs line

2 upon leaving the tubes rockets encounter lateral wind component which produces their additional deviation towards wind and additional deviation

It doesn't matter on choppers that compensate via computing like hind ka50 Apache but on huey hip you ought to trim nose to tail if you ever wanted to use static non computed crosshairs.

But then, nose to tail only compensates for inherent helicopter crabbing and it still doesn't compensate for lateral wind which again produce effects 1,2. Which one could overcome via trial and error trimming or lateral correction 

Edited September 2, 2023 by Sobakopes

[bradmick]

In the Apache you shoot rockets in aerodynamic trim. The rocket steering cursor is your friend here.