Thrust Reversers Triggered on takeoff

[anthony_d]

Evening,

Just bought the CRJ, and after a couple of nights of reading manuals and flying about I'm settling in nicely. Really nice plane with almost no extra toll on my framerates

One thing I've noticed. On a couple of takeoffs with thrust reversers armed, they kicked in.

This happened on what was admittedly a bumpy runway, when the wheels bounced off the runway and then hit the runway again, the thrust reversers kicked in. At first I thought that maybe having one of my CH Yoke levers configured for reverse thrust came off it's zero setting a little. Then I disabled the thrust reverser axis and tried again.

Different bumpy runway, was just rotating to takeoff when my main undercarriage left the runway and greased the tarmac again. Reverse thrusters kicked in straight away.

There was also one instance when lined up with the runway, I entered the thrust limit into the MCDU, but entered it into the wrong box (top left corner instead of top right), thrust reversers kicked in and dragged my plane backwards kicking and screaming for about 1/2 mile while I panicked at the scene unfolding!

Is this supposed to happen?

Anthony

[Cameron]

Hi, Anthony,

The center console contains the ability to arm the thrust reversers automatically upon landing. They will come out when a hard, pronounced "thump" has been had. It sounds like the bumps you had on the runway caused this.

This is covered in the manuals as well. Just ensure to disarm this functionality while on the ground if you're going to be departing from such a runway and all should be good.

[anthony_d]

OK that makes sense.

On the theme of reverse thrust. When I was in flight, I was able to (inadvertently) operate the reverse thrust levers (using the reverse axis), causing the reverse thrusters to kick in. According to the manual (page 23) this should only be possible if the throttle is in the idle state. They weren't idling.

Never knew reverse thrust in flight was possible. I thought normally a weight on wheels interlock prevented this,. But I guess it sounds plausible for rear engined planes to have this feature.

Edited January 31, 2012 by anthony_d

[Cameron]

I can't speak for your situation, but the manual is correct in that it shouldn't be happening when outside of idle. Go up in flight and see if you can do it again in the pattern. Shouldn't be able to.

[anthony_d]

OK, I've just tried this out again, and here's some steps to reproduce :

1. Configure an axis input for reverse.

2. Load up the CRJ, getting into a flight ready state, take off and establish straight and level flight with some thrust.

As per manual

3. Reduce throttles to idle, engage the reverse thrust with the reverse lever and observe reverse thrust engaged.

4. Place reverse lever back into normal position and confirm that throttle demands are available.

Now here's the bug.

5. Place the throttle out of idle, and move the reverse thrust lever out of it's normal position. Observe the reverse thrust indicators flash on the engine instrument panel, only while the lever is being moved. Also observe that the normal engine thrust is being interrupted when the reverse thrust lever is being moved.

6. With the reverse thrust lever stationary, but in a reverse demand (not normal) position, confirm that the engines responds to normal throttle demands.

7. Place reverse thrust lever back into normal position.

Here's another bug found

7. Perform steps 3 & 4 again, but this time observe how the throttles can't be operated once the reverse thrust lever has been put back to the normal position.

8. Nudge the reverse thrust levers forwards a little in the VC. Confirm that the throttles can respond to demand once more.

Edited February 1, 2012 by anthony_d

[Japo32]

Well, I know reversers can be deployed in flight, but i would never do it.

To assign reversers to a joy, better choose the option of toggle than axis. Axis always produce little peaks that can make mad any good programming.

Let the auto reversers come when landing and with throttles when activated you will be able to input thrust then, when you want to switch them off, just press that toggle button so the throttles will recover their original function.

[philipp]

OK, I've just tried this out again, and here's some steps to reproduce :

1. Configure an axis input for reverse.

This is not supported. Reversers have to be activate by the command sim/engine/reverse_toggle (in a standard installation assgined to the dot key on the keyboard). We don't use X-Plane's default reversers, because we wanted to be able to simulate the reverser doors being hydraulically actuated, the interlocking mechanics of the throttles, and the auto-reverse system for rejected takeoffs. There is no way we could do all this with X-Plane's default simulation.

Your hardware throttle (or it's reverse axis) doesn't have the interlocking mechanics. You will notice that it works as expected if you use a hardware throttle axis as a throttle axis (not reverse axis) and the standard command (which you can of course map to a joystick button if you like).

Philipp

[anthony_d]

OK, I removed the reverse axis and configured the reverse toggle. Manual reverse thrust now works as you describe.

However auto reverse thrust upon RTO or landing doesn't work anymore. Strange. Auto spoilers work fine on landing.

Also, the reverse thrusters seem to bring the plane to a halt rather quickly on full blast (with mass of 39000lbs) - maybe using 400meters of ruwnway after touch down.. Is this how it is in real life?

Edited February 2, 2012 by anthony_d

[Cameron]

The CRJ is a relatively quick aircraft to throw down. They CAN throw some punch in reverse mode.

As described in the manual, auto reverse will not deploy on every touch down (be sure that it's activated to begin with). It will ONLY deploy on what it determines are hard enough landing to justify that what you're hitting is really intended as ground. If you grease it...chances are you're going to need to manually deploy.

[anthony_d]

Interesting. I haven't seen the selective deployment described in the manual anywhere (but it is mentioned in the tutorial that gentle landings will deploy). Just tried a few more landings, sometimes it deploys and sometimes not.

[mutestyles]

As long as you dont overrun the runway its all good.