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haughtney1
12th Jul 2006, 23:44
Having had a long day flying a bent aeroplane (anyone who flys 757's will know what I mean:} )
Im just wondering how a FBW aka airbus copes with a less than straight airframe..?

Mad (Flt) Scientist
13th Jul 2006, 05:20
No different in principle to offsets in cg - trimmed out long-term, shouldn't affect short term control loop behaviour unless the 'bend' is so gross as to be ridiculous.

Dani
13th Jul 2006, 08:06
from my uneducated perspective (pilot, no engineer) I would say it's even easier to "trim out" a bent FBW aircraft. There are no cables, pullies and poles to adjust to the new length after the bending. It's not uncommon that aircraft change their flight characteristic with age. But I would say Boeings are more bent than Airbus ;)

Dani

glhcarl
13th Jul 2006, 15:58
If the aircraft requires a excessive amount of trim to maintain level flight, it should be written up and corrected. The Structural Repair Manual provides a chapter with asymmetery checks to verify any permanent set that the structure may have taken over years of flying. Addtionally, trim bias can be built into the aircraft. This is usually accomplished on the first test flight. However, if the structure is in fact bent, it could be accomplished again. To establish the trim bias the aircarft is rigged completly prior to flight, During the flight, after cruse altitude and still air are reached, the aircraft is trimmed to fly stright and level, using roll and yaw trim. When the aircraft is back on the ground the roll and yaw trim heads are removed and the head is set back to zero and the amount of bias in the system is recorded.

javelin
13th Jul 2006, 17:56
We fetched a 321 back from TOU after a tailstrike repair last year. On the return, I noticed that something was not quite correct..........

The rudder trim was hanging out at about 3 units of trim - rather unusual and the beta target was split (slip ball).

Fortunately we had an engineer on board so we took the autopilot out (shock, horror) and experimented with various trim settings DFDR ing as we went.

Later turned out that there was a miss rig somewhere and it got tweaked in the hangar.

So, to recap, yep, you notice a bent aeroplane with FBW if you pay attention :ok:

Obi Offiah
13th Jul 2006, 19:37
.....Fortunately we had an engineer on board so we took the autopilot out (shock, horror) and experimented with various trim settings DFDR ing as we went.
.......So, to recap, yep, you notice a bent aeroplane with FBW if you pay attention :ok:

If the aircraft was initially trimmed prior to the tailstrike, but had its autopilot switched off, after the tailstrike would the FBW system automatically compensate i.e the pilot would only notice discrepancies via trim/flight control surfaces display?.

Obi

javelin
14th Jul 2006, 10:48
Er, what birdstrike - this was after a Tailstrike repair.................

Obi Offiah
14th Jul 2006, 15:22
Er, what birdstrike - this was after a Tailstrike repair.................

Yep, my mistake. I've edited the post. :ok:

Obi