Question to testers about FM?

[Weta43]

Kapuhy - you do know what AirTito does for a living don't you ?

[kapuhy]

Have no idea, but does it change anything? I can have MY opinion, and he can misunderstand me as well.

 

And he doesn't know what I do for living, too :)

[RvETito]

No worries, never meant to be disrespectful. It sure does pretty good what it is inteded for but the naval nature of the Kamov helicopters (except for the Ka-50) has led to the development of unique for their time SAU's- analogue computers for route flight where you can input by ground equipment waypoints (up to certain number), airfields, own ship position (ability to find it on it's own in 0/0 visibility), hover points (with ability to hover from one point to another in fully automatic mode)- a sort of a FMS, of course with some basic functions.

[Immermann]

In another thread there was a link to a demonstratiom video of the Ka-50. The pilot pushed a button below his right thumb now and then. Is that the force trim button?

(I didn't get an answer there.)

[AlphaOneSix]

In another thread there was a link to a demonstratiom video of the Ka-50. The pilot pushed a button below his right thumb now and then. Is that the force trim button?

(I didn't get an answer there.)

 

 

It sure does look like it to me, but I'm not absolutely certain. ;)

[EvilBivol-1]

Yes, it is.

[leafer]

What is force trim again?

[Sundowner.pl]

hmm, Acedy accidentally made it a bit complex.

 

Ok, so first, there are not many helicopters with pure Fly-By-Wire controls, actually I know only three - S-76, S-69 and RAH-66. Now most helicopters have actually mechanical connection to hydraulic control servos, and the FBW while exist, is only a backup system (like BUCS on Apache).

 

 

Now in helicopters that have force trim system - the cyclic and rudder pedals are centered by a feedback system. And what the 'Force Trim' button do, is sets the 0-0 position of that feedback system to the position where cyclic/rudder is currently.

 

For example, you're in a Blackhawk, hovering over a point while picking up downed airman using a hoist, you have a wind head on, so you normally would have to put cyclic forward to counter the drift. When you have found a position where you can keep the cyclic and the helicopter stay constantly in one place, you push the 'Force Trim' button, and it resets the feedback system, so in this 'new' position you don't feel resistance, this now becomes the new neutral cyclic position.

[amalahama]

NH-90 has FBW controls too.

 

Regards!!

[leafer]

Ahhh. Thanks, guys.

[RvETito]

Yep, no FBW on Kamov helicopters- rigid connection between cyclic/pedals and servo actuators. The resisting force comes from a spring in the trim mechanisms- like Acedy said, electro-magnetical brakes. By pressing the trim button the solenoid energizes and release the tension of all springs thus setting new 'neutral' (in terms of force) position. The cyclic's neutral position on some helicopters like Ka-32 and Bell-407 is indicated by a light on the lights warning panel.

[Nordic]

Are there any detailed drawings or pics out there about the trim mechanism? Would be interesting to see...

[AlphaOneSix]

It's not very interesting, really. A bellcrank attached to a flight control rod which is attached to a spring. The other side of the spring is attached to a magnetic brake. When you push the trim button, the brake is released and the spring is able to move with the flight control rod without any spring tension. When you let go, the brake engages and then that side of the spring can no longer move, so any movement of the flight control rod will have the force of the spring acting against it.

[Masak]

Excuse me guys, I’m a bit confused.:helpsmilie: Do I understand well that you described two different kind of force trim?

 

AirTito- after cyclic is moved to desired position against springs tension, force trim button is pressed to remove tension on cyclic and create a new neutral position

 

AlphaOneSix- force button is pressed to remove springs tension on cyclic (to let it move freely), cyclic is moved to desired position and force trim button is released to apply springs tension again to keep cyclic in that position.

 

I know the second variant from a short stick time on Mi-17 I been lucky to get. I think I remember a noisy sound of relay behind left seat every time force trim button is pressed and released.

 

Or is it just the same force trim system but used differently? But I have been told that to move cyclic first and then press FT button leads to overcontroling. Which is quite understandable (in Mi17) since cyclic is hard to move without FT pressed (same were pedals).

 

So, please guys, if I understood correctly and there are these two different force trim variants, could you provide me with some examples of using these on various helicopters? Thank you. Petr:)

[Flanker15]

Ok so let me get this straight.... Lets say you are hovering or something and the chopper is trying to yaw to the left a bit. You'd apply rudder until the movement stops then press the force trim button, after which the chopper won't keep moving even with the rudder centered. Is this right?

[Masak]

Speaking about Mi17 using pedals looks like this:

 

While hovering, chopper is yawing lets say to the left. You press FT button on your cyclic which allows you to apply right pedal (otherwise pedals same as cyclic feel to be kind of locked. you can move them but with large force). After stopping yaw you release FT button and pedals (same as a cyclic) stay in the position where they were at time you released FT.

 

So while in cruise you can use trim for trimming pedals and actually fly with your feet of the pedals.

[Yellonet]

Ok so let me get this straight.... Lets say you are hovering or something and the chopper is trying to yaw to the left a bit. You'd apply rudder until the movement stops then press the force trim button, after which the chopper won't keep moving even with the rudder centered. Is this right?

Yes. Maybe ;)

[RvETito]

Excuse me guys, I’m a bit confused.:helpsmilie: Do I understand well that you described two different kind of force trim?

No, we actualy talk about one and the same pricipals.

 

AirTito- after cyclic is moved to desired position against springs tension, force trim button is pressed to remove tension on cyclic and create a new neutral position

As I posted- 'neutral' in terms of force (controls tension). The purpose of this button is to reduce the load of the pilot so he doesn't get tired easily. Example- you're in hover against the wind, to keep constant position related to the ground you must use forward cyclic input. Assuming that the controls are trimmed for hover with no wind (no tension on the cyclic) moving it forward will cause tension. When you balance the helicopter for the given conditions you press the trim button and the tension is released- you may now even let go the stick- it has new nutral tension position set.

 

AlphaOneSix- force button is pressed to remove springs tension on cyclic (to let it move freely), cyclic is moved to desired position and force trim button is released to apply springs tension again to keep cyclic in that position.

 

I know the second variant from a short stick time on Mi-17 I been lucky to get. I think I remember a noisy sound of relay behind left seat every time force trim button is pressed and released.

 

Or is it just the same force trim system but used differently? But I have been told that to move cyclic first and then press FT button leads to overcontroling. Which is quite understandable (in Mi17) since cyclic is hard to move without FT pressed (same were pedals).

 

So, please guys, if I understood correctly and there are these two different force trim variants, could you provide me with some examples of using these on various helicopters? Thank you. Petr:)

 

Kamov and Mil helicopters use one and the same ЭМТ-2Е trim mechanisms- 3 of them for pitch, roll, yaw. The sound you've been hearing is from the solenoid energize.

 

I've heard for flight techniques with continously pressed trim button but this is what actualy can cause overcontrol- you don't have a feedback from the controls.

 

Hard to move the Mi-17's cyclic without pressing the trim button? You mean in flight or on the ground? With or without hydraulic power?

[Sundowner.pl]

Without hydraulic power you can't move them at all... I tried :music_whistling:

[RvETito]

Speaking about Mi17 using pedals looks like this:

 

While hovering, chopper is yawing lets say to the left. You press FT button on your cyclic which allows you to apply right pedal (otherwise pedals same as cyclic feel to be kind of locked. you can move them but with large force). After stopping yaw you release FT button and pedals (same as a cyclic) stay in the position where they were at time you released FT.

 

So while in cruise you can use trim for trimming pedals and actually fly with your feet of the pedals.

 

Nope, it doesn't work that way. FT doesn't lock your controls, it just creates artificial tension to provide control feedback to the pilot. It's not hard at all to move any of the controls without using the FT button to release the tension, the question is that if you have to do it lets say few hours a day you might get pretty tired.

 

Once again- the function of the trim button is to unload the pilot during sustained maneuvers- hover, coordinated turn, horizontal flight, climb and descent. You set the desired control input and press the button to release the tension. That's it.

 

So in the example you gave it should work like that- left yaw which you want to eliminate, then you apply right pedal input, you feel some tension (I can't recall now but it was few kgf, assuming you have hydro), once the yaw is ceased you press the FT button and the tension is gone- you have now set new balanced position with no tension on the controls. Note- the pedals won't be in the neutral position, only the tension.

[RvETito]

Without hydraulic power you can't move them at all... I tried :music_whistling:

 

You haven't tried hard enough, it's completely doable (first hand info). But you're usualy not allowed to do that because you can damage the servos. Though I see pilots do it all the time at preflight checks and haven't seen this causing a problem (Ka-32 and Mi-17).

[Sundowner.pl]

I was trying that few month ago in a Mi-14 - cold, on the ramp, couldn't move that fricking thing an inch. Was talking with an instructor pilot about that, and what he said is when all hydraulics are down in that chopper, well, enjoy the ride down, or if you have a chance, make use of that parachute, that you sit on it.

[RvETito]

I said that you can move the controls without hydro on the ground, not that you can fly it that way :D

[Masak]

Hi AirTito

 

My experience with Mi17 is very, very limited (couple hours on crew chief seat and approx. 40 min of stick time) and I do respect your knowledge and definitely don’t want to argue. But I really remember quite clearly how the pilots used a FT. In hover or in cruise anytime they wanted to change cyclic (or pedals) position, they pressed FT button, moved cyclic and released button. In this order. So in cruise it was needed once a while but in hover they pressed a released FT almost constantly. Before my flight I have been instructed: “First press FT, move cyclic, release FT. “ So I did. I have been also told, that sometimes beginners forget to press FT first, they apply force on cyclic (a large force because of resistance) and when they press FT- “KLAK”:)- resistance in cyclic disappears and cyclic moves inadvertently further then needed because of force applied by pilot to desired direction. That is overcontroling I mentioned. The overcontroling that you mentioned happened to me in hover because I didn’t use FT the way described above and held FT pressed instead. While in flight, with hydraulics working fine, there was very large resistance both on cyclic and pedals. With FT pressed there was actually no resistance at all. As long as you hold FT pressed.

The way of using FT you described seems to me to works with coolie hat- force decreases gradually, but with force trim button force disappears immediately which can lead to overcontroling.

 

Or, all it is just a different ways to use that damn force trim button….:)

[Yo-Yo]

all that you have written is well known but it's a matter of piloting style. THough as far as I know the style with pressed FT button is officially prohibited because of uncontrollable stick movement possibility w/o stick forces.