Posts: 39
Joined: Mon Feb 05, 2001 8:48 am

146 Trimtabs

Tue Dec 11, 2001 7:23 am

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Anyone know why there are two trimtabs on the each elevator? And why they seem to operate seperatly?
Posts: 702
Joined: Mon Jan 03, 2000 7:10 am

RE: 146 Trimtabs

Tue Dec 11, 2001 4:51 pm

The 146 is one of the few civil jets to have a fixed tailplane, perhaps this has something to do with it
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Joined: Fri Aug 17, 2001 11:25 am

RE: 146 Trimtabs

Wed Dec 12, 2001 3:07 pm

I don't have all the manuals I originaly thought I did, will go out to the archives next weekend and search again.

It's been 18 years since I last worked on this airframe, but as memory serves me.....

The elevators are free floating, no direct input from the yoke. The tabs are the only direct link to the yoke, ie. servo tabs. It is common to see the elevators split when parked tail into the wind or taxiing down wind. airspeed will fair the elevators and back pressure on the yoke will actually move the tabs down forcing the elevators up. Auto-pilot servo's also actuate the tabs.

Posts: 788
Joined: Sun Apr 08, 2001 4:11 am

RE: 146 Trimtabs

Wed Dec 12, 2001 11:30 pm

To add to Metwrench's explanation, the inboard tabs are the servo tabs, each side is connected to the same side control column, the columns being connected under the cockpit floor by spring-loaded disconnect system, in case of pitch system jam on one side.

60 lbs force will break out the disconnect, then you discover which side was jammed and which pilot still has pitch control.

Each servo tab circuit has a "blow back spring" to limit the tab's authority according to airspeed.

Trim tabs are the outboard sections, and are controlled conventionally by cables, rods and screw jacks. Inputs are the thumb operated trim switches, manual trim wheels, and the autopilot.

Regards - Musang

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