What are boost tabs???  
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What are boost tabs??? - 3/23/2003 4:40:36 AM   
karolh


 

Posts: 2416
Joined: 5/15/2002
From: Mandeville, JAMAICA
Status: offline 		I have read about boost tabs, but do not know what they are and exactly what they do. Please enlighten me . Thanks.
       Post #: 1

What are boost tabs??? - 3/23/2003 8:01:14 AM   
Tall Paul



Posts: 4701
Joined: 6/23/2002
From: Palmdale, CA, USA
Status: offline 		A boost tab relieves the load the pilot would feel in a pure mechanical control system.
Look at this one on an Edge 540..
It's hinged to the elevator, but attached rigidly to the stabilizer. As the elevator moves (in this case) down, the tab moves up. As it's located on the trailing edge, it possesses a good "hinge moment" for its size, and permits the pilot to deflect the control stick (and therefore the surface) further than he would be able to unassisted.

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(in reply to karolh)
       Post #: 2

What are boost tabs??? - 3/23/2003 4:34:23 PM   
Rodney



Posts: 4917
Joined: 12/8/2001
From: FL
Status: offline 		I use these quite frequently on large models, especially on elevator and rudder. They let a less powerful servo move a big surface. Just don't let the boost tab exceed 10% of the total moveable area or you will most probably get hunting or oscillation; the tab overpowers the servo.

(in reply to karolh)
       Post #: 3

Origin of boost tabs... - 4/3/2003 12:04:11 AM   
Jeremy Sebens


 

Posts: 91
Joined: 4/22/2002
From: Champaign, IL, USA
Status: offline 		Big airplanes like the China Clipper that came before the days of hydraulic assist had control surfaces too large for the pilot to be able to move them when in flight. To solve this, the ailerons were actually free floating, with a small tab at the trailing edge that was controlled. When deflected, this tab pushed the aileron in the opposite direction aerodynamically, thereby causing the airplane to roll. So it works like this:

1) stick goes left
2) left boost tab goes down (YES, down)
3) this pushes left aileron UP aerodynamically (NOW I get it!)
4) same thing in reverse on other side
5) plane rolls left

It's all about using leverage - that's why these planes had very large control surfaces chordwise - to get the torque that could be exerted by the boost tab up. All in all, it's a really elegant solution.

See if you can find a good picture of a china clipper parked - you might be able to see that both ailerons are drooping.

See, Dr. King - I was listening that day in Flight 2!

< Message edited by Starfire-RCU -- Apr 4 2003 5:36PM >

_____________________________

Landing: Contest of strength between planet and aircraft.
NOTE: To date, planet remains undefeated.

(in reply to karolh)
       Post #: 4

What are boost tabs??? - 4/24/2003 2:19:41 AM   
Forgues Research



Posts: 3414
Joined: 12/15/2001
From: Glen Robertson, ON, CANADA
Status: offline 		I have been using boost tabs for abut 15 years and they work.

Here is a better explanation
boost tab

Extra with boost tab

_____________________________

Evo Engines
http://forgues-research.com

(in reply to karolh)
       Post #: 5

What are boost tabs??? - 4/30/2003 8:50:56 PM   
Mike Ashcroft



Posts: 2
Joined: 4/30/2003
From: StockportCheshire, UNITED KINGDOM
Status: offline 		Some medium to large lowspeed aircraft have what is known as a 'spring/blow off servo tab'. This has a tab, as mentioned earlier, that operates in the opposite direction to the parent control surface but only comes into operation when the aerodynamic load on the main control surface is above a certain value. This means the pilot has direct contol over the surface at low speed, but at medium speed he is assisted by the servo tab. However another spring device comes into play when the aircraft is at high speed that allows the tab to blow back. This to prevent over- control of the surface at high speed and gives the pilot adequate 'feel' . The two 'springs' are usually in the form of torsion bars.

_____________________________

Mike Ashcroft

(in reply to karolh)
       Post #: 6

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