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View Full Version : A 330 THRUST REVERSER AND PITCH UP???


JABBARA
3rd Dec 2016, 23:03
Extract from A 330 FCOM PRO-NOR-SOP-19 P 5/6

"A small pitch up may occur during thrust reversers deployment before nose landing gear touchdown"

My experience is just opposite, after extension of spoilers, when Thrust Reverser is deployed before Nose Landing Gear, nose drops faster.

Any idea?

Thanks

Sidestick_n_Rudder
3rd Dec 2016, 23:16
I can only confirm. Reverser selection causes an immediate nose drop and significant back stick input is required.

Having said that, I *think* the cause for the nose drop are the spoilers, which deploy upon rev selection. Maybe later the reverse thrust itself causes some pitch up, but I haven't noticed...

Chris Scott
4th Dec 2016, 00:23
Hi S_n_R,

FWIW I think the deployment of the Ground Spoilers (normally at main-wheel spin-up) is likely to produce a noticeable pitch-up, as it does on other Airbus types I've flown.

ahramin
4th Dec 2016, 00:55
Exactly. And if the spoilers are only at half, deploying reverse will bring them to full, causing the pitch up moment.

tdracer
4th Dec 2016, 04:19
No specific knowledge of the A330, but I was directly involved in wind tunnel testing during the investigation of the Lauda 767 crash (after a reverser deployed in-flight).
During that testing, with the reverser deployed, the airflow and lift was destroyed over a large portion of the wing. On a swept wing, I'd expect that sort of airflow disruption with T/R deployment to result in a significant pitch down - not pitch up - moment.
I suspect ahramin and Chris Scott are correct that it has to do with the associated spoiler deployment, not the T/R.

Chris Scott
4th Dec 2016, 09:34
Hi ahramin,

Like tdracer, I haven't flown the A330, unfortunately. So can you explain under what circumstances the Ground Spoilers, which are normally activated on touchdown by main-wheel spin-up, would only half-deploy?

Hi tdracer,

Perhaps we have to distinguish between the in-flight situation, when the a/c tends to rotate around its C of G, and the on-the-ground situation where its weight is mostly being supported by its main-wheels on the ground?

In the latter case (on the ground), it will rotate around the main-wheel axles as a pivot point.** Despite the chaotic airflow created by the fan-reverser deployment, the rearward thrust vector it produces is presumably directed above the pivot point. That should produce a slight pitch-up, but I cannot pretend to have noticed it on the A310 or A320.

Early main-wheel braking certainly generates a pitch-down which has to be countered with elevator to avoid a hard touchdown of the nose-wheels. On the A320, for example, medium autobrake tends to start before nose-wheel touchdown.

**[EDIT] In this case, probably the attachment point between the main-gear leg and the main-wheel truck (bogie)?

Sidestick_n_Rudder
4th Dec 2016, 13:57
Hi,

Partial extension happens only in case of assymetric touchdown and reverse selection - similar to the A320, at least current Mod.

The GND signal for full spoiler deployment comes either from wheel spin up, or (both MLG compression AND RA<6ft).

The latter takes time since MLG is double bogey and normally there's a significant delay between aft wheels touchdown, the front wheels touchdown and the oleo compression (hence usually two distinctive thumps on landing).

My theory was that reverser selection deployed spoilers before AIR/GND logic signal was processed, but I am not so sure anymore...

In any case, after reverse selection on touchdown of the aft MLG wheels two distinctive things happen:
- immediate touchdown (or rather thump!) of the front MLG wheels and oleo compression
- significant pitch-down moment which has to be counteracted by sidestick

If reverse is not selected, the pitching moment is close to neutral, similar to the A320. Perhaps the reason is loss of lift due to airflow disruption as Tdracer described... Never ever noticed any pitch-up though...


Where is A33Zab, when we need him:confused:

pineteam
6th Sep 2018, 18:48
Hello guys, I have the same doubt for the A320 and still did not find a definitive answer.. Why the deployment of the reversers would create a small pitch up?

Thanks

Chu Chu
7th Sep 2018, 00:16
Perhaps we have to distinguish between the in-flight situation, when the a/c tends to rotate around its C of G, and the on-the-ground situation where its weight is mostly being supported by its main-wheels on the ground?

In the latter case (on the ground), it will rotate around the main-wheel axles as a pivot point.** Despite the chaotic airflow created by the fan-reverser deployment, the rearward thrust vector it produces is presumably directed above the pivot point. That should produce a slight pitch-up, but I cannot pretend to have noticed it on the A310 or A320.



I guess I'm saying this two years too late, but I don't think this can be the whole answer. If it one only needed consider the torque about the main gear axles, the brakes on the main gear would have zero moment arm, and therefore have no effect on pitch.

If the gear were not on the runway, a rearward thrust vector below the CG would tend to produce a nose-down pitch. Gear rolling on the runway would do nothing to offset that; they'd just roll a little slower as the nose pitched down.

But I can't seem to sort through this entirely in my head -- obviously a downward force forward of the gear but aft of the CG would create a nose-down pitch.

pineteam
7th Sep 2018, 05:41
https://www.pprune.org/tech-log/545141-thrust-reverser-effects-touchdown.html

I think Goldenrivett got the right answer.




The turbulent airflow around the thrust reversers causes an increase in pressure under the wing. Since the engines are mounted inboard, the effect on a swept wing is to cause a mild nose up tendency. It is easily controlled by nose down elevators.

Uplinker
9th Sep 2018, 09:45
I always found that I needed to modulate the joystick in pitch to prevent the A330 nosewheel slamming down after reversers deployed.

Debapratim
13th Sep 2018, 04:07
Extract from A 330 FCOM PRO-NOR-SOP-19 P 5/6

"A small pitch up may occur during thrust reversers deployment before nose landing gear touchdown"

My experience is just opposite, after extension of spoilers, when Thrust Reverser is deployed before Nose Landing Gear, nose drops faster.

Any idea?

Thanks
Yah I Have Noticed It Too....... and the nose drops so much faster.....