Bae-146 elavator

[Micky]

Hello
just a question about the elevator on the Avro...I heard that it was servo controlled so you don't have to have a hydraulic powered tab. But if that is so how come that while standing the elevator is fully deflected upwards? Ok there are controll looks but you would not put it on if the aircraft was fast enough for the servo tab to lift the elevator would you...so I am at a loss here and would be grateful if you could help me out...:O

Thanks micky

[B1/B2]

Hi there,

Not 100% I fully understand your question but to confirm; The 146/RJ does use the Servo Tab method (it's the inner of the two tabs) meaning the Elevator surface itself is only controllable with aerodynamic forces acting on it. If you were meaning "control Locks" (??), there is form of gust lock in that the P1 column engages in the footrest bar, however the elevator surface itself can still be moved. You are correct in saying the elevators normally (but not always) rests downwards (Nose up position) but this is purely to do with the large horn and elevator balance weights. (Or more common at present frozen Type 4 fluid).

Hope this kind of answers your question ....

Regards.

[alf5071h]

Micky, the 146/RJ servo tabs provide the aerodynamic force to move the elevator, the tabs are connected directly to the control column. There are no control locks and as B1/B2 indicates the column and tabs are ‘restrained’ in the centre of the pitch range so that on the ground the tabs do not get damaged by the ‘free’ elevators. The elevators themselves have ground gust dampers located within the tail-plane, these differ from the recently added in-flight dampers which are in the tail-plane / fin top fairing.

On the ground the elevator usually positions nose down (trailing edge up) due to the balance weights in the leading edge. However the elevators can move independently of the tab and themselves (left / right) even in low wind speeds, the gust dampers only prevent rapid movement. Although the servo tab is fixed with respect to the column, the elevator is free to move with respect to the tab. Thus with the column restrained, only the wind can move the elevator and not the tab, but each interacts with the other in strong winds.

For the aerodynamically astute there is also a spring (torsion bar) in the servo tab control, but that’s far too difficult to explain; thus for you and I, the 146/RJ only has servo tabs.

[Micky]

Thanks everybody:ok:
You all understud what I meant...
I just dident know why the elavator stood up when there is no direct link to the contoll colum.
So thanks a lot! I think the Bae is a interisting aircraft and whould love to fly it one day when I finish my Atpl....

Cheers Micky:O

[Volume]

If you look at this (http://www.airliners.net/open.file?id=812010&WxsIERv=Oevgvfu%20Nrebfcnpr%20ONr-146-100&WdsYXMg=JQY%20Nivngvba&QtODMg=Gbhybhfr%20-%20Oyntanp%20%28GYF%20%2F%20YSOB%29&ERDLTkt=Senapr&ktODMp=Znepu%2031%2C%202005&BP=1&WNEb25u=Thfgnib%20Orege%E1a%20-%20Vorevna%20Fcbggref&xsIERvdWdsY=Q-NJQY&MgTUQtODMgKE=%5BPnaba%2020Q%5D&YXMgTUQtODMgKERD=123&NEb25uZWxs=2005-04-07%2014%3A10%3A58&ODJ9dvCE=&O89Dcjdg=R1011&static=yes&width=1280&height=944&sok=JURER%20%20%28nvepensg_trarevp%20%3D%20%27ONR%20Flfgrzf% 20Nieb%20146-EW%2FEWK%27%20BE%20nvepensg_trarevp%20%3D%20%27Oevgvfu%20Nre bfcnpr%20ONr-146%2FNieb%20EW%27%29%20NAQ%20%28cynpr%20%3D%20%27Gbhybhfr%2 0-%20Oyntanp%20%28GYF%20%2F%20YSOB%29%27%29%20%20BEQRE%20OL%20 cubgb_vq%20QRFP&photo_nr=2&prev_id=816192&next_id=788332&size=L) impressive picture, you can notice that the deflections of the left and right elevator is different.
Is there no mechanical link between the elevators?
How are the right/left tabs connected?
If Airflow is non symmetric (yaw angle, rudder deflection), does this result in an asymetric elevator deflection? Is this intentionally and some sort of automatic load allevation, or is this just the price you pay for a simple design?

[alf5071h]

Volume, there is no physical link between elevators.
The primary aerodynamic link is via the servo tabs, which are joined by independent pitch control circuits via the flight deck control columns. In the event of a jam anywhere in the system even this connection can be split. There is a secondary ‘aerodynamic’ connection via the left and right trim tabs, which are connected and cannot be split. This to some extent keeps the elevators together in flight, but as indicated by the photo other effects could cause a small asymmetry, rudder, yaw, roll, etc.

With small asymmetries the difference in force (load) on each elevator is minor with respect to the total design load, the ‘springs’ in the servo tab circuit may provide some balance. The aircraft is certificated to cope with a jam (block) of one elevator and sustain safe flight by using the other; again the loads are within the design requirements.

With the autopilot engaged only one servo tab is controlled at the rear of the aircraft (different sides for 146 and RJ), the effect of this in theory, is that the ‘on-side’ tab moves first and the ‘off-side’ tab follows up via the full length of the pitch control circuit, but in practice there are no noticeable effects as shown by the exceptional performance of the RJ autopilot / autoland system.