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goneflighting
22nd May 2015, 19:17
Hi all,

Can anyone explain why the left elevator drops just as the brakes are released? (starts at the 2:00 mark)


https://www.youtube.com/watch?v=A3JTItFiNtY

Mach E Avelli
22nd May 2015, 23:39
I haven't got two minutes to watch the video, but would suggest that it is sheer coincidence, possibly due to a wind gust. Have you observed this over many flights, or just the one?
The elevators float freely, but there is a disconnect between control columns in case of a jam somewhere in the circuit. The FCOM cautions about doing flight control checks in strong tailwinds, because it is possible that the controls will disconnect. They can be reset from the cockpit if this happens.
One for an engineer to answer more completely.

AerocatS2A
23rd May 2015, 00:24
The elevator control circuit is only linked to the servo tabs. The elevators themselves are free to flop around in the breeze independently.

Mach E Avelli
23rd May 2015, 05:18
Thanks Aerocat - much better explanation and in fewer words!

goneflighting
23rd May 2015, 09:22
Thanks! Solid old school design then. Just a bit disconcerting seeing the elevators doing opposite things on the takeoff roll!

dixi188
23rd May 2015, 09:39
DC-9s and MD-80s do the same thing.

AerocatS2A
23rd May 2015, 13:00
No problem. I'm not an expert but do have the misfortune of being current on the type ;).

TheiC
23rd May 2015, 23:06
That's no misfortune. Enjoy it while you can. It's a real pilot's aeroplane.

AerocatS2A
23rd May 2015, 23:45
I did wink...

I don't dislike it, but I do miss having an autopilot that does what you tell it to do. The RJ is ok.

skyhighfallguy
24th May 2015, 04:50
aerocats

I didn't care for the autopilot on the BAE146 either. It hunted in level off.

The MD80/DC9 (actually they are both DC9), if you look carefully as the runway is taken, just before the takeoff comences, both elevators go to full nose down.

There is a hydraulic ram which, when the yoke is full forward, pushes both elevators to full nose down. Full forward yoke is usually done to make the elevators symmetrical and to test the hydraulic ram.

this design feature is to facilitate stall recovery at very low airspeed or when the tail might be blanked.

I am trying to think of something good about the BAE146.

play final jeopardy theme ad nauseum.

717tech
24th May 2015, 12:39
I am trying to think of something good about the BAE146.
It's got four Thrust Levers :ok:

illusion
24th May 2015, 12:52
7000 pound ain't thrust, it's a gust from a cow's bottom..........

Yamagata ken
24th May 2015, 13:03
I liked the 146s very much. They did a very good job taking me to minor airports in Australia's NW, and (better) taking me home again after my shift had finished. I had the pleasure of being the sole passenger on one flight, and the Qantas Ladies put on a lovely caberet song-and-dance for my benefit during the flight briefing.

Thank you BAE. As a user they took me there, and they took me home. :)

BARKINGMAD
24th May 2015, 22:06
The autopilot was not at fault in the level off.

It was the trim system which was slow to react, so the 'frame would climb slightly above alt and eventually find itself back to datum.

The easy way of overcoming this was to use the trim wheel gently in the nose down direction during altitude acquire, until the mini indicator showed it was in trim.

Problem solved without expensive mods!

Yes, it had was known as 5 APUs in close formation, but I had the pleasure of hearing the relieved comments from SLF counting the "donks" as they boarded, in the weeks following the tragic Kegworth accident.

A great plane to start ones airline career, simple unsophisticated auto system which had to be watched, thereby inculcating a way of operating which stood me in good stead when subsequently I became "Boeing'd"............. :ok:

TheiC
24th May 2015, 22:28
5 APUs in close formation

Surely: four oil leaks connected by an electrical problem.

Either way, a fine aircraft. Only rapid development left its technology too rapidly outdated. It's redundancy, practicality, performance, and passenger appeal, made it a winner in its own field.

It's easy to be critical of the 146 for having too wide an envelope, being too easy to pole around the sky, allowing abrupt, steep, approaches, which don't meet the stabilised criteria. Another view is that it's the final pilot's aeroplane, enabling the trained aircrew to manoeuvre at their will to meet demands, while their A and B colleagues have to deal with such narrow margins that automation becomes the only means of achieving reliable results.

I hadn't had that thought before, but now I have, I'm feeling quietly refreshed.

Octane
24th May 2015, 22:42
My brother liked flying the 146, thought it was solid, enjoyable aircraft to fly. Except that each aircraft in the fleet had different cockpit fitouts!

717tech
25th May 2015, 00:35
7000 pound ain't thrust, it's a gust from a cow's bottom..........
6970lbs actually!

I'm enjoying my time flying the BAe146. It's a very hands on Aeroplane.... Keeps you honest.

Lord Spandex Masher
25th May 2015, 01:11
The autopilot was not at fault in the level off.

It was the trim system which was slow to react, so the 'frame would climb slightly above alt and eventually find itself back to datum.
:ok:

Not quite. Whilst the trim wasn't brilliant and caused a certain amount of porposing, especially close to the barbers pole, the reason for the climb after altitude capture was due to a lack of PE correction in altitude hold. An increase in speed caused a climb and vice versa, one of the reasons for lack of RVSM approval.

We used to select an altitude 100' below the clearance and once captured the acceleration from cruise to climb speed caused a 100' climb. Conversely if you climbed at high speed and then decelerated (usually when you switched on the anti ice :}) you would descend slightly.

It is one of the best handling airliners and it had switches which you could actually see in the dark and geared turbo fans, which ain't anything new Messers Pratt and Whitney.

AerocatS2A
25th May 2015, 01:48
Not quite. Whilst the trim wasn't brilliant and caused a certain amount of porposing, especially close to the barbers pole, the reason for the climb after altitude capture was due to a lack of PE correction in altitude hold. An increase in speed caused a climb and vice versa, one of the reasons for lack of RVSM approval.

Correct. If you don't accelerate after level off then it holds the selected altitude just fine.

There are a number of ways to deal with it. You can set 100 low on the altsel as described by Lord Spandex above, you can manually select alt hold while in the capture mode when approx 100' below the set altitude (works best with low rates of climb), or you can just let it capture and accelerate and then re-arm the altsel and pitch back to it.

My main annoyance with the autopilot is its VS mode. When you select VS there's some delay between pushing the button and the final VS that gets set, so unless you have the VS nice and stable right where you want it, it's a bit of a lottery as to what you'll end up with. Not to mention that if in VS and you select F18, the aeroplane will balloon up as the autopilot servos are not powerful enough to hold the selected VS against the trim changes as the flaps run. Once they have run it might settle back to the original VS, or it might not. When you've come from a Dash 8 will give you what ever VS you set in fpm, the 146 system is a bit of a step backward.

The RJ fixes both of the above problems, but it doesn't seem to be as nice to hand fly for some reason.

As for redeeming features, it's airbrake makes it very versatile, it will slow down like a turboprop if you need it too.

fruitloop
25th May 2015, 02:00
"geared turbo fans"
A brilliant design that took nearly 20 year before it was appreciated..

ANCPER
25th May 2015, 08:50
"while their A and B colleagues have to deal with such narrow margins that automation becomes the only means of achieving reliable results."

Whatchewtalkingbout!

Flown all three and you certainly don't need the autos for A or B.

BARKINGMAD
27th May 2015, 21:50
L S M.

Whilst there may have been PE correction problems with the leveloff/acceleration, how come the simple expedient of "helping" the trim with a manual input also solved the problem?

I only flew the 146 and not the RJ, for 9 years and this technique never failed.

I can't recall if the 'frame had a THS, or was trim applied to the infamous tabs on the elevator, with all the slack accumulating over time making this phenomenon more likely?

Otherwise a great little over-engineered craft which was/maybe still is a pilots' aeroplane. :)

Lord Spandex Masher
27th May 2015, 22:37
I don't know, I never used that technique for levelling off.

I distinctly remember using a big handful of ND trim to stop the porposing at high(!) speed and it seemed to cure that, for a while at least.

I can't remember why it worked or even if I knew why it worked.

Toruk Macto
29th May 2015, 14:45
The way it landed was good for the ego