Disable hydraulic system for testing?

[Bushmanni]

Anyone managed to land the Hawg in MRFCS? (in DCS) :P

 

 

[Eddie]

OK, this is probably my last tentative to explain what I'm experiencing. Maybe somebody will believe me. Maybe.

 

The plane is on the runway, ready for takeoff. Then:

 

The trim tabs are working just like they should, it's your understanding that is at fault.

 

In when MRFCS is enabled the elevators operate as normal, the only difference is that they are controlled by direct mechanical linkages to the controls rather than hydraulics.

 

Only the ailerons are moved by their trim tabs, the elevator trim tabs operate normally.

 

Have a read of the A-10A flight manual available HERE, specifically the Primary Flight Control system chapter.

[Fox One]

Have a read of the A-10A flight manual available HERE, specifically the Primary Flight Control system chapter.

 

I did. But please have another look at the fourth picture. That trim tab goes UP, shouldn't the force developed on it push the entire elevator's trailing edge DOWN?

 

For the n-th time: when I fly in manual reversion, if I trim the plane NOSE UP the effect on the plane is NOSE DOWN. And it actually makes sense. The trim tab goes UP and pushes the elevator's trailing edge DOWN!

[NoJoe]

I'm with Fox One on this issue, I still don't understand why moving the elevator trim hat toward nose up causes the trim tabs to move up (and thereby move the elevators down, causing the aircraft's nose to move downward).

 

I understand that in MRFCS the elevators are pilot-controlled by direct linkages, but when using the trim hat on the stick, it responds backward. So, if this is the correct behavior, why does the aircraft respond opposite to the trim hat inputs? Reading through the .pdf you linked, Eddie, makes me think even more that the pitch trim hat should still operate normally (see page 1-31 for a diagram of the trim system, and the Manual Reversion section on page 1-40 mentions pitch trim is still operated normally).

 

--NoJoe

 

Edited to add: Besides, since the elevator trim system is entirely separate from the elevator actuation system (in either normal or MRFCS modes), I see no reason why it would suddenly reverse operation when in MRFCS mode.

 

EDit 2: To easily see this reversal, watch which way the elevator trim tabs move with nose up trim hat in Normal mode. Now switch to MRFCS, wait for the hydraulic pressure to drop, and move the trim hat to nose up again: they now move the opposite direction from before.

Edited May 21, 2012 by NoJoe

[Fox One]

NoJoe, thanks man, I was beginning to believe I'm going crazy :D

 

What you wrote make sense to me 100%, I have also read carefully the flight control system chapter from that A-10A manual.

 

Request to any forum members reading this: please test the trim while flying in manual reversion mode and see if the plane's response to pitch trim inputs is normal or reversed. Please report your findings. Thanks.

[Eddie]

I don't really see what you two are saying to be honest.

 

When operating normally the elevator trim tabs are not used when trimming the aircraft, the entire control surface moves. It's only when in MFRCS that the trim tabs themselves are used, actuated electrically.

 

It works correctly in the sim. The only issue with MRFCS is that it is that the pitch oscillations are still too pronounced and difficult to counter.

[Fox One]

Eddie, then how do you explain that?

 

EDit 2: To easily see this reversal, watch which way the elevator trim tabs move with nose up trim hat in Normal mode. Now switch to MRFCS, wait for the hydraulic pressure to drop, and move the trim hat to nose up again: they now move the opposite direction from before.

[NoJoe]

When operating normally the elevator trim tabs are not used when trimming the aircraft, the entire control surface moves. It's only when in MFRCS that the trim tabs themselves are used, actuated electrically.

 

Ah, okay. That makes sense, looking again at the system diagram. However, I think the issue we're seeing is that in MRFCS, when you move the trim hat for nose up, the aircraft's nose actually goes down.

 

Is that the correct behavior? Because that seems wrong... Try it yourself: go into MRFCS while flying, then use the trim hat on the stick. Trim for nose up. What does the plane do? I'm curious if Fox and I are seeing different behavior than you are. :)

 

--NoJoe

[Yellonet]

Eddie, then how do you explain that?

In normal operation the elevator tabs only seem to move in relation to the elevators. The tabs are level to the aircraft body in most trim settings.

[Eddie]

Eddie, then how do you explain that?

 

As per the -1.

 

PITCH CONTROL SYSTEM

.......If both hydraulic systems are lost, pilot pitch

trim inputs will automatically operate the two

elevator trim tabs via two additional trim motors to

provide pitch trim. The geared/ trimmable elevator

tabs are mounted on the outboard trailing edges of

both elevators . The tabs are trimmable in manual

reversion, and geared in the powered flight control

mode . This reduces elevator aerodynamic loads to

levels satisfactory for instantaneous transfer from the

powered mode to MRFCS. Refer to PITCH MRFCS

section for additional description of pitch manual

reversion operation......

 

....Because that seems wrong... Try it yourself: go into MRFCS while flying, then use the trim hat on the stick. Trim for nose up. What does the plane do? I'm curious if Fox and I are seeing different behavior than you are.

 

When you trim in MRFCS the trim tabs move correctly, the nose pitches down when trimming up due to the same effect that the aileron trim tabs use to move the aileron itself. The airflow over the trim tab pushes the elevator down. This requires the pilot to pull harder on the stick to maintain level flight (remember there are no hydraulics to help you out at this point, only muscle power to move a heavy jet through the sky).

 

Now as I mentioned before, the effect is magnified somewhat by the known issue with MRFCS that I mentioned earlier. I should be possible to counter the aerodynamic effect on the elevators, whereas at the moment it is almost impossible to counter the effect at full trim deflection.

 

The way the controls operate is fine, it's the physics under the hood, so to speak, that are at fault somewhat.

[Fox One]

In normal operation the elevator tabs only seem to move in relation to the elevators.

 

Of course, in normal operation they are moved by the elevator itself through a mechanism, and they move in opposite direction from the elevator to reduce the hinge moment on the elevator and thus reduce the necessary force of the actuators to move elevators.

[Yellonet]

Ah, okay. That makes sense, looking again at the system diagram. However, I think the issue we're seeing is that in MRFCS, when you move the trim hat for nose up, the aircraft's nose actually goes down.

 

Is that the correct behavior? Because that seems wrong... Try it yourself: go into MRFCS while flying, then use the trim hat on the stick. Trim for nose up. What does the plane do? I'm curious if Fox and I are seeing different behavior than you are. :)

 

--NoJoe

In MRFCS I too get nose up on nose down trim. I don't know if this is how it should be in reality, but it seems wrong.

What happens is as the tabs move up, the elevator pushes down which in turn pushes the nose down.

[NoJoe]

the nose pitches down when trimming up

 

Huh, okay. If you say that's how it is in the real plane I'll believe you. As a pilot, that just seems wrong that the system would be designed that way (especially considering that since the trim tabs are trimmable only in MRFCS mode, they would be designed cause the aircraft to respond opposite to pilot input?).

 

I... Are you SURE? It seems so ... is it really designed that way? :helpsmilie: I would also be very interested to hear from other folks who have either actually flown the Hawg or work on them (Paul?).

 

Anyway, thanks for your input, and thanks for your patience, Eddie! :thumbup:

 

--NoJoe

[Yellonet]

Hmm... so the inverted trim functionality is how it should be.

Makes you wonder why there's no function that inverts the movement of the trim tabs when entering MRFCS. Seems a bit dangerous as it is...

[Eddie]

The thing to remember is that the effect is exaggerated. Were it not for the known bug, it'd barely be noticeable.

 

I will say however this is only my understanding of how things are based on the -1 and previous feedback from the devs (yo-yo for example).

[Corrigan]

Hmm... so the inverted trim functionality is how it should be.

Makes you wonder why there's no function that inverts the movement of the trim tabs when entering MRFCS. Seems a bit dangerous as it is...

 

Absolutely. Like you don't have enough on your plate already when you've lost all hydro, in addition to having to work a completely unintuitive system. It even says explicitly on the bloody stick that the nose should go up.

Of course, I'm just a layman.

[Fox One]

When you trim in MRFCS the trim tabs move correctly, the nose pitches down when trimming up due to the same effect that the aileron trim tabs use to move the aileron itself. The airflow over the trim tab pushes the elevator down. This requires the pilot to pull harder on the stick to maintain level flight

 

So the pilot flies in manual reversion mode, pulling quite hard on the stick to mantain level flight. Then he tries to relieve some of that necessary force, his arm geting quite numb. And he uses the trim as he did thousand times, cause he remebers he read in the Dash-1 that in manual reversion the trims still work. And guess what? Instead of releaving some of the necessary force pulling on the stick, it actually makes the necessary force HIGHER! Gee, those Fairchild designers had some great logic, no doubt about that.

 

It doesn't make any sense. If it was that way, i would just release a technical order for A-10 fleet to simply reverse the wires entering the elevator trim tab's motors! :D Really simple, easist to implement T.O. !!!!

[Eddie]

...It even says explicitly on the bloody stick that the nose should go up....

 

It also says on the stick the left wing should go down when pushing the trim hat left. However in MRFCS it doesn't. ;)

 

If you're flying in MRFCS, you can't really go hands off the stick. Remember it's an emergency backup system designed to enable you to get away from the enemy, and maybe back to base.

 

It doesn't make any sense. If it was that way, i would just release a technical order for A-10 fleet to simply reverse the wires entering the elevator trim tab's motors! :D Really simple, easist to implement T.O. !!!!

 

As I've said at least 3 times now, it's only as bad as it currently is in the sim due to a known bug. If it were that bad on the real aircraft it wouldn't work the way it does. IRL MRFCS is used all the time, both for training flights and functional check flights without issue. Using MRFCS to fly straight and level or make slow controlled manoeuvres is fine. But anything else and maintaining control will be difficult.

Edited May 21, 2012 by Eddie

[NoJoe]

Well, I am very interested to hear what some of the devs say about this issue. It seems like we've all gone about as far as we can go by reading the Dash 1, and the MRFCS trim functionality is very unintuitive as it stands now.

 

It kinda hits that "this seems wrong" alarm bell. :)

 

But again, I do want to thank you, Eddie, for your input and your patient replies! I for one really appreciate it. :thumbup:

 

--NoJoe

 

[EDIT, I can't type]

[Eddie]

and the MRFCS trim functionality is very unintuitive as it stands now.

 

Indeed, but when the issue with pitch oscillations is fixed (whenever that is), the system should work as you'd expect it to.

[Yellonet]

Absolutely. Like you don't have enough on your plate already when you've lost all hydro, in addition to having to work a completely unintuitive system. It even says explicitly on the bloody stick that the nose should go up.

Of course, I'm just a layman.

I guess it's one way of separating the wheat from the chaff :D

[Fox One]

it's only as bad as it currently is in the sim due to a known bug.

 

Translation: the only bug is that in manual reversion when using pitch trim the elevator's trim tabs move in the opposite way they should, you were right from the beginning, thanks for wasting your time :D:D:D:D:D

[Sierra99]

Hey folks!

 

I would like to experience what it is like to fly without the hydraulics driving the control surfaces. Is there a way? A switch to flip? I mean theoretically the control surfaces will barely react at high speeds, I wanna experience that. :)

 

Also - how does trimming work without the hydraulics? Do I use the same keys? Or is there a separate trimmer? I saw a trimmer-like thing on the emergency panel but I have no idea how to use it.

 

Thanks a lot in advance!

 

LAWL... I tried this earlier tonight... Started out straight and level... Finished up as a smoking hole! Landing with 1 elevator, no rudders and 1 engine was WAAAAAY easier!

 

I've never seen a plane pitch forward that fast after a little stick input!

Gooood luck with your experiment!

[Depth]

Translation: the only bug is that in manual reversion when using pitch trim the elevator's trim tabs move in the opposite way they should, you were right from the beginning, thanks for wasting your time :D:D:D:D:D

 

Normal mode:

Trim input for Nose Up

Trim tab moves up

Increased airflow hits trim tab, generates downforce on elevator

Elevator locked by hydraulic pressure

Downforce on elevator transferred to tail

Nose moves up

 

Manual Reversion:

Trim input for Nose Up

Trim tab moves up

Increased airflow hits trim tab, generates downforce on elevator

Elevator not locked by hydraulic pressure, elevator moves down

Increased airflow hits elevator, generates upward force on tail

Nose moves down

 

How do you not understand this?

[ralfidude]

Here, just watch this. Its all there.

 

 

 

 

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