What are boost tabs???
 

I have read about boost tabs, but do not know what they are and exactly what they do. Please enlighten me . Thanks.

What are boost tabs???
 

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.

What are boost tabs???
 

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.

Origin of boost tabs...
 

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!

What are boost tabs???
 

I have been using boost tabs for abut 15 years and they work.

Here is a better explanation
boost tab

Extra with boost tab

What are boost tabs???
 

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.

RE: What are boost tabs???
 

boost tabs crashed my plane. beware!!!!

RE: What are boost tabs???
 

Boost tabs are very safe, if your airplane crashed because of the boost tabs, they weren't installed properly. Been using them for more then 20 years, never a problem ...

Roger

RE: What are boost tabs???
 

Boost tabs can be very beneficial, do you have any pictures of your failed installation? I can not even visualize how they could be a cause of crash if properly installed.

RE: What are boost tabs???
 

UNFORTUNATELY, 'anything' has caused a plane to crash !
At least for some folks.

I'm afraid fact, reason, logic, proof, etc. etc. has little to do with these claims.

They chose the airplane; they chose the equipment; they did the installation(s); they were at the controls; yet "they" are always able to define something else as being the 'cause' AND they can do so almost at the instant of the crash.
Sound familiar?

Oh well, ....................so what else is new in RC ?

Interesting sidelight, RF type or equipment brand may vary BUT the claims stay the same. :([X(]:eek:
26.995MHz to 2.4GHz same folks same results. [:o]

I guess we could award an "A" for consistency .

RE: What are boost tabs???
 

My small hitec servo failed on the boost tab and that is all I had powering my big elevators!

RE: What are boost tabs???
 

That will do it,

the reason for not going too small on servos, is not for the flight loads but rather because of vibrations, also if you do go small on the servo, make sure you mass balance the control surface properly.

On my 34% Turbo prop laser, I am using only one 75 oz. nylon gear servo per control surface. Two years now.

Roger

RE: What are boost tabs???
 

Just so we are clear, then, there are two ways of operating the tab. You can directly control the tab, and use it to move the surface. This requires that there be enough airspeed over the surfaces before the tab will move anything. The other way is to power the surface and mechanically connect the tab to assist the movement, sometimes called a 'balance tab'. Of the variations, there's plenty, but they all work in a similar fashion. Which way you go is then up to you, though as at least one has found, if the servo stops working it don't matter which bit you are controlling, it still won't move.
Evan, WB #12.

RE: What are boost tabs???
 

i was using a 75oz servo...

RE: What are boost tabs???
 

You had a "small" 75oz servo on a boost tab driving your big elevators???

What airplane? A picture would go a long way to clearing up how you got one boost tab to drive elevators. Or did you have a boost tab on each elevator half of those big elevators but being driven by one servo? If so a picture of the linkage over to the other tab would be worth seeing.

RE: What are boost tabs???
 

was this servo operating the elevator or the boost tab, ??? If the boost tab, it is quite big for the job, as an insight, on my 35% Yak 54, I installed a small hitec 81 servo directly controlling the boost tab on the rudder. The rudder itself was free floating. On the ground for rudder/tail wheel operation, I would need a blip on the throttle to get some air but it worked beautifully.
In the air it worked very powerfully, did some very nice Knife Edge.

There was one problem though, since the Rudder also had an aerodynamic balance on the top of the rudder, in straight flight it would tend to oscillate. What I needed to do was install dampers on the rudder itself..

A properly installed boost tab on a control surface, using only a 25 oz servo controlling the boost tab, gives the control surface as much as 5000 oz of torque.

So, it would be nice to see how every thing was installed....

Roger

RE: What are boost tabs???
 

I just crashed my new 40%r today....because of Boost Tabs..... I was using HS-56HBs on my Boost Tabs on all surfaces including throttle......apparently Boost Tabs aren't what they're cracked up to be......:(

RE: What are boost tabs???
 

Or something else in your case.......http://www.rcuniverse.com/forum/js/f...ey/msn/lol.gif

Funny that we fly planes with normal setups andhavevery fewproblems........

RE: What are boost tabs???
 

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RE: What are boost tabs???
 

Boost tabs have been employed on full-scale airplanes of much later vintage than the China Clippers. The DC-9, which later became the MD-80, uses a combination of boost tabs and servo tabs to control its ailerons and elevators. The elevators and ailerons are statically counterbalanced. The pilot has direct cable manual control solely over the servo tab, which is assisted by a separate boost tab. The result is relatively light control forces, weight reduction, and excellent feel. Should hydraulic oil be lost, the airplane remains fully controllable - a boost to safety as well.

RE: What are boost tabs???
 

I did everything that was called for to make the boost tab work right and it failed.

RE: What are boost tabs???
 

If it might be of any help, here is how I operated the boost tabs on one of my planes that worked very well.

RE: What are boost tabs???
 

Here is one I used successfully,

RE: What are boost tabs???
 

which part of the setup failed , if installed properly, they are bullet proof..can you post a picture of your setup...

Roger

RE: What are boost tabs???
 

Does anyone know the forces that are generated by the boost tab? It would be great to know how large a servo is required. I used a servo force program to try to get the numbers but it doesn't look like it is correct.