Is mig-21 direct controlled and what is an ARU?

[Alfredson007]

.. or what ever it would be called. What i am trying to ask, is there any "filtering" or "automatization" or "fly-by-wireism" in mig-21, or is it just stick and rudder? What about the ARU? What does it actually do?

 

Thanks. Still having fun in my 21!

[Art-J]

A bit of everything.

 

Rudder - direct, mechanical. You can move it when "cold and dark".

Ailerons - direct, but hydro boosted, so hydro pressure required to operate within full range.

Stabilators - nondirect, hydro-boosted. Input goes through ARU-3 automated regulator, which dynamically changes ratio between stick and stabilator deflection, depending on speed and altitude, in order to provide optimal pitch control over all range of speeds and altitudes the plane can fly with.

[Alfredson007]

Okay thanks! I think the ARU isn't playing a huge role though, since when i put it on manual, it doesn't do anything dramatic, compared to when i disengage the "traction control" in Su27 for example. Or is the Leatherneck's model still incomplete in this sense?

[Art-J]

I haven't played with ARU enough, or read about the real thing to form an opinion.

 

One has to remember, however, that the old -21 most probably has much higher static stability margin than any next gen fighter like Su-27, designed to be almost unstable and requiring some fancy control augmentation systems to keep the plane from tumbling over itself.

[Luzifer]

The ARU changes the ratio between stick deflection and elevator deflection. So it adjusts a mechanical lever or something. There is still direct (hydraulic boosted) mechanical linkage from stick to elevator.

 

It is not in any way comparable to FBW or even stability augmentation. The only way it contributes to stability is by limiting elevator travel at high speeds and thereby giving the pilot finer control, which would reduce the possibility of pilot induced oscillations.

[EagleFox]

ARU is engaged i think at subsonic speeds becuase the elevators are whole horizontal stabilizator

and without ARU there would be a lot of pilot enduced oscilation. I think its like that don't quote me on this.

[Hadwell]

I think the ARU is broken right now, doesn't do anything, on or off, get full range no matter what... ARU is supposed to automatically limit elevator movement so you're less likely go over the 30 degree AOA limit, but as it is now, no matter what, you need to keep an eye on the AOA and watch how much you pull back on the stick, so you don't turn your plane into a falling leaf.

Edited January 13, 2016 by Hadwell

[RoflSeal]

That's not completely true, if I put ARU to manual and maximum, and pull a level turn on slow speed, I can barely get over 20 AoA, whilst If put it to minimum, I pull easilly over 30 AoA.

[grunf]

I think the ARU is broken right now, doesn't do anything, on or off, get full range no matter what... ARU is supposed to automatically limit elevator movement so you're less likely go over the 30 degree AOA limit, but as it is now, no matter what, you need to keep an eye on the AOA and watch how much you pull back on the stick, so you don't turn your plane into a falling leaf.

It does limit the elevator movement, it can be easily seen in the external view.

[Darkwolf]

ARU works. In dogfight, i sometimes put in max, which allows me crazy turn. :P