What are boost tabs???
11-03-2011 | 02:18 PM
#51
Senior Member
RE: What are boost tabs???
ORIGINAL: iron eagel
Da,
Boost tabs were, if I remember correctly,only used on some experimental fighters and some racers (primary on elevator surfaces) just before hydraulic assist became the norm. Hughes did some of the first hydraulic assist systems, and it may even be some of his earlier stuff were boost tabs were used. That is basically the era you'd find any mention of it (end of the ''Golden Age''???) just before or near the beginning of WWI.
Da,
Boost tabs were, if I remember correctly,only used on some experimental fighters and some racers (primary on elevator surfaces) just before hydraulic assist became the norm. Hughes did some of the first hydraulic assist systems, and it may even be some of his earlier stuff were boost tabs were used. That is basically the era you'd find any mention of it (end of the ''Golden Age''???) just before or near the beginning of WWI.
Yup, and the problem is there isn't much mention anywhere of how they were sized etc.
pimminz, yes, for many years and years almost every surface had a trim tab, but I really was talking about boost/assist tabs, the ones iron eagel and I are talking about.
11-03-2011 | 02:47 PM
#53
RE: What are boost tabs???
Da,
I guess what we refer to as "boost tabs" are considered to be balance tabs.
The only article I have ever seen that had any reference to the setup and sizing is the one I posted before.
L = 1/3 to 1/2 of the span of the control surface
C= 15 to 25% of the chord of the control surface
This area can be up to 10% of the control surface but not less than 4%.
I guess what we refer to as "boost tabs" are considered to be balance tabs.
The only article I have ever seen that had any reference to the setup and sizing is the one I posted before.
L = 1/3 to 1/2 of the span of the control surface
C= 15 to 25% of the chord of the control surface
This area can be up to 10% of the control surface but not less than 4%.
11-03-2011 | 07:44 PM
#54
RE: What are boost tabs???
There does not seem to be much about on the size of the things. I guess you just size them pro-rata from what you see on the full size. Don't use the FW190A as an example though, it's only got fixed trim tabs...
Evan, WB #12.
Evan, WB #12.
11-04-2011 | 03:30 AM
#55
Senior Member
RE: What are boost tabs???
Unless someone is redefining the definitions of "balance" and "boost" there is no similarity between the two. Balance meaning to have equal force about a pivot point, boost being an augment to the applied force. In fact, most boost tabs will be counteracting to balance as they usually contribute more static unbalance to the assembly as they are adding mass aft of the hinge or pivot point. There is also a difference between static and aerodynamic balance and either one or both can be accomplished with different implementation of structure. For instance, static and aerodynamic balance can be obtained by properly weighting the area ahead of the hinge line where that type of balance is implemented.
11-04-2011 | 03:57 AM
#56
Senior Member
RE: What are boost tabs???
I think "boost" pertains more to model servos, as they "boost" the servo power/thrust. Hard to say they Boost the power to the control column or pedals. All semantics
11-04-2011 | 06:01 AM
#57
RE: What are boost tabs???
My understanding is they were first used to help pilots in "pursuit aircraft" overcome the force on the elevator when pulling out of a dive or other high speed maneuvers.
Evan,
The size can be pretty much anywhere within the parameters listed, it's the amount of travel or throw if you will that governs the force applied.
"The boost tab should normally have a chord of less then 25%, and an area between 4 and 10% of the control surface. About 6% seems to be a good compromise. If very large angular deflections are required of relatively wide chord ailerons, the boost tab area should be close to 10%. I discovered this recently as I fine-tuned a new sport design that was intended for fun-fly aerobatics. The boost tabs can be made full span without using impractically small chord just reduce the throw considerably. I've used full - span boost tabs on rudders; at 10% of the rudder chord, the throw needed for optimum balance was only about half that of the rudder itself. It's best to start with too little movement just to be on the safe side and gradually increase it until you have solid control response. " Carl Risteen
Evan,
The size can be pretty much anywhere within the parameters listed, it's the amount of travel or throw if you will that governs the force applied.
"The boost tab should normally have a chord of less then 25%, and an area between 4 and 10% of the control surface. About 6% seems to be a good compromise. If very large angular deflections are required of relatively wide chord ailerons, the boost tab area should be close to 10%. I discovered this recently as I fine-tuned a new sport design that was intended for fun-fly aerobatics. The boost tabs can be made full span without using impractically small chord just reduce the throw considerably. I've used full - span boost tabs on rudders; at 10% of the rudder chord, the throw needed for optimum balance was only about half that of the rudder itself. It's best to start with too little movement just to be on the safe side and gradually increase it until you have solid control response. " Carl Risteen
11-04-2011 | 06:31 AM
#58
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From: Canon City,
CO
RE: What are boost tabs???
The weather here in Colorado took a turn for the worse a couple of days ago turning my flying field (cow pasture) into a quagmire. I decided to use the time to install boost tabs on all the control surfaces of one of my Frankenflyers. I hope it won't cause a crash, as I originally planned to do one control surface at a time to avoid being overwhelmed by potential control problems. My field is a tough place to fly if there are problems. The pasture is surrounded by rocks, cliffs, junipers, cactus, fences and power lines. The pasture is the only place where it is possible to land safely, that is why my planes are primarily Frankenflyers.
11-04-2011 | 07:47 AM
#59
Senior Member
RE: What are boost tabs???
Just don't hit any cows I Just put a tab on the rudder of my foamy Zoombi. The knifedge loops are more egg shaped, as on the downside, when it accelerates, I believe the rudder is blowing out, unable to hold the 45 degree angle. Soon as it warms up and the wind stops blowing today I'll give it a test run.
I Just put a tab on the rudder of my foamy Zoombi. The knifedge loops are more egg shaped, as on the downside, when it accelerates, I believe the rudder is blowing out, unable to hold the 45 degree angle. Soon as it warms up and the wind stops blowing today I'll give it a test run.
11-05-2011 | 02:22 AM
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From: Christchurch, NEW ZEALAND
RE: What are boost tabs???
ORIGINAL: Rodney
Unless someone is redefining the definitions of ''balance'' and ''boost'' there is no similarity between the two. Balance meaning to have equal force about a pivot point, boost being an augment to the applied force. In fact, most boost tabs will be counteracting to balance as they usually contribute more static unbalance to the assembly as they are adding mass aft of the hinge or pivot point. There is also a difference between static and aerodynamic balance and either one or both can be accomplished with different implementation of structure. For instance, static and aerodynamic balance can be obtained by properly weighting the area ahead of the hinge line where that type of balance is implemented.
Unless someone is redefining the definitions of ''balance'' and ''boost'' there is no similarity between the two. Balance meaning to have equal force about a pivot point, boost being an augment to the applied force. In fact, most boost tabs will be counteracting to balance as they usually contribute more static unbalance to the assembly as they are adding mass aft of the hinge or pivot point. There is also a difference between static and aerodynamic balance and either one or both can be accomplished with different implementation of structure. For instance, static and aerodynamic balance can be obtained by properly weighting the area ahead of the hinge line where that type of balance is implemented.
Rodney,
Aerodynamic 'balance' and mass 'balance' are two different things.
In aerodynamics, control 'balance' refers to the force required to move the control surface and how that force varies with speed, deflection, and G force (there's more). We are discussing tabs that affect this balance hence balance tabs. I agree thats not quite the same as balance about a pivot (see saw or teeter totter?) balance
Mass 'balance' is about balancing the control surface about the hinge ie pivot line. This is mostly done to prevent flutter.
Confusion can arise because a common method of aerodynamic balancing, the horn balance (eg the top of a cub rudder), is often used as a good place to install the mass balance weight. The mass is there to prevent or reduce flutter, the horn is there to reduce the control force.
You can't change the aerodynamic balance with weight.
Dave H
11-05-2011 | 02:42 AM
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From: Christchurch, NEW ZEALAND
RE: What are boost tabs???
ORIGINAL: gerryndennis
Iron Eagle you would be hard pressed to find a higher performance or heavier aircraft since the 30's or so that doesn't have (balance or servo) tabs of some sort, Nearly every WW II aircraft has them. Even the light low perrformance aircraft will have at least a plain trim tab.
Dave H
Iron Eagle you would be hard pressed to find a higher performance or heavier aircraft since the 30's or so that doesn't have (balance or servo) tabs of some sort, Nearly every WW II aircraft has them. Even the light low perrformance aircraft will have at least a plain trim tab.
Dave H
I was meaning balance and servo tabs of some sort, but I didn't write it very clearly. I agree with Pimmnz, they are very common right up to modern aircraft including those with hydraulically boosted controls.
Iron Eagle I guess you meant to say the Golden age prior to WW II.
Dave H
11-05-2011 | 06:29 AM
#62
Senior Member
RE: What are boost tabs???
ORIGINAL: gerryndennis
Rodney,
Aerodynamic 'balance' and mass 'balance' are two different things.
Exactly what I said, you are just confirming it.
In aerodynamics, control 'balance' refers to the force required to move the control surface and how that force varies with speed, deflection, and G force (there's more). We are discussing tabs that affect this balance hence balance tabs. I agree thats not quite the same as balance about a pivot (see saw or teeter totter?) balance
Mass 'balance' is about balancing the control surface about the hinge ie pivot line. This is mostly done to prevent flutter.
Again, exactly what I said except I did not mention flutter. Incidentally, while mass balancing my prevent the onset of flutter, it does nothing to prevent it. The flutter characteristics (susceptibility) depends more on mechanical structure as you want maximum stiffness with minimum weight. Anything will flutter given the proper stimulus, what you strive for in aerodynamics is to keep that frequency of susceptibility outside the range you will be operating in.
Confusion can arise because a common method of aerodynamic balancing, the horn balance (eg the top of a cub rudder), is often used as a good place to install the mass balance weight. The mass is there to prevent or reduce flutter, the horn is there to reduce the control force.
You can't change the aerodynamic balance with weight.
Dave H
ORIGINAL: Rodney
Unless someone is redefining the definitions of ''balance'' and ''boost'' there is no similarity between the two. Balance meaning to have equal force about a pivot point, boost being an augment to the applied force. In fact, most boost tabs will be counteracting to balance as they usually contribute more static unbalance to the assembly as they are adding mass aft of the hinge or pivot point. There is also a difference between static and aerodynamic balance and either one or both can be accomplished with different implementation of structure. For instance, static and aerodynamic balance can be obtained by properly weighting the area ahead of the hinge line where that type of balance is implemented.
Unless someone is redefining the definitions of ''balance'' and ''boost'' there is no similarity between the two. Balance meaning to have equal force about a pivot point, boost being an augment to the applied force. In fact, most boost tabs will be counteracting to balance as they usually contribute more static unbalance to the assembly as they are adding mass aft of the hinge or pivot point. There is also a difference between static and aerodynamic balance and either one or both can be accomplished with different implementation of structure. For instance, static and aerodynamic balance can be obtained by properly weighting the area ahead of the hinge line where that type of balance is implemented.
Rodney,
Aerodynamic 'balance' and mass 'balance' are two different things.
Exactly what I said, you are just confirming it.
In aerodynamics, control 'balance' refers to the force required to move the control surface and how that force varies with speed, deflection, and G force (there's more). We are discussing tabs that affect this balance hence balance tabs. I agree thats not quite the same as balance about a pivot (see saw or teeter totter?) balance
Mass 'balance' is about balancing the control surface about the hinge ie pivot line. This is mostly done to prevent flutter.
Again, exactly what I said except I did not mention flutter. Incidentally, while mass balancing my prevent the onset of flutter, it does nothing to prevent it. The flutter characteristics (susceptibility) depends more on mechanical structure as you want maximum stiffness with minimum weight. Anything will flutter given the proper stimulus, what you strive for in aerodynamics is to keep that frequency of susceptibility outside the range you will be operating in.
Confusion can arise because a common method of aerodynamic balancing, the horn balance (eg the top of a cub rudder), is often used as a good place to install the mass balance weight. The mass is there to prevent or reduce flutter, the horn is there to reduce the control force.
You can't change the aerodynamic balance with weight.
Dave H
11-05-2011 | 08:07 AM
#63
RE: What are boost tabs???
Iron eagle and Da Rock,
I was meaning balance and servo tabs of some sort, but I didn't write it very clearly. I agree with Pimmnz, they are very common right up to modern aircraft including those with hydraulically boosted controls.
Iron Eagle I guess you meant to say the Golden age prior to WW II.
Dave H
[/quote]
Yes in the period after WWI and before WWII...
The type of tabs I refer to as "boost tabs" used the tab surface to offset the force the pilot felt on the stick.
11-05-2011 | 11:29 AM
#64
RE: What are boost tabs???
IronEagle, the period you are referring to was when the tab ideas were developed. I think even some of the late WW1 airplanes were using adjustable tailplanes, certainly many had offset fins to counter yaw trim. Fokker pilots were known to carry a bit of U/C bungee to assist with elevator trim...So far as what the difference is between a balance and servo tab is, I think, and only think, that a balance tab is operated by the surface movement, whereas the servo tab is the pilot operated device, which then moves the surface. My own experience is that models, generally, have no need of the things other than reproduction on a scale model, as we have a rigid, servo operated system with a rigid trim system, in other words, the tab is physically unable to do what it was originally intended.
Evan, WB #12.
Evan, WB #12.
11-05-2011 | 12:28 PM
#65
Senior Member
RE: What are boost tabs???
Here's some pics I mentioned from post 56. Knifedge loops are now round and surprisingly, about a 1/3 smaller with full rudder throw. I think it's worthwhile on oversize surfaces like many 3D planes.To keep it light, I used carbon fibre rods with heatshrink for hinges. Horns are hotglued into the surfaces. Alignment is so the tab is a little past where the tab is aligned with the airflow at full rudder throw.
11-06-2011 | 05:56 AM
#66
Senior Member
RE: What are boost tabs???
Flypaper2, your pictures show the same technique I have used on ailerons and on rudder. On my planes I set up the throws so that the tab was always very close to the same angle as the fixed part of the surface; i.e. when the movable surface was at full deflection, the tab was still parallel to the fixed portion of the surface it was attached to. I did not experiment much with aspect ratio of the tab, just kept it at less than or equal to 10% of the rudder/aileron but I suspect that the aspect ratio may have some effect on efficiency. In any case, it let me use rather moderate powered servos to do a gigantic job on the big planes. In former tests, I found that if I exceed the 10% rule it was easy to get over control with steady or uniform response to control almost impossible. When overdone on the elevator, level flight was nigh on impossible, tended to gallopeither climb or dive in an oscillatory fashion.
11-06-2011 | 12:38 PM
#67
Senior Member
RE: What are boost tabs???
Just got back from our first indoor flying of the season. Not too much carnage Yes the rudder on the Zoombi is roughly 8 in. high with a 5 in. chord. The tab is 1 by 4 in. This one at full deflexion is a little past the neutral point. I thought it might be too much, but it turned out fine. Rudder goes back to neutral and stays there fine. Servo is the Hobbyking HXT 900.
Yes the rudder on the Zoombi is roughly 8 in. high with a 5 in. chord. The tab is 1 by 4 in. This one at full deflexion is a little past the neutral point. I thought it might be too much, but it turned out fine. Rudder goes back to neutral and stays there fine. Servo is the Hobbyking HXT 900.
11-06-2011 | 05:10 PM
#68
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From: Canon City,
CO
RE: What are boost tabs???
I flew my old Frankenflyer today with boost tabs on all control surfaces. It flew fine with no issues. The ailerons are driven by standard size servos and responded better at high speeds, I get a faster roll rate. The rudder was more responsive as well, I could do knife edges when I had troubles doing so before the addition of tabs. I had no problems with oscillations on any axis. I flew just before dark so had no chance to do any tweeking. I will try increasing the throws one axis at a time and see how it goes. Now the tabs are now adjusted to stay parallel to the airflow, I will push it beyound that and see what happens. The plane is driven by a converted Ryobi 31cc weed eater engine and is heavy. I think from my limited experience with the boost tabs so far, they are worth the minor effort to install them on large scale airplanes.
11-09-2011 | 05:18 AM
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From: Christchurch, NEW ZEALAND
RE: What are boost tabs???
ORIGINAL: pimmnz
IronEagle, the period you are referring to was when the tab ideas were developed. I think even some of the late WW1 airplanes were using adjustable tailplanes, certainly many had offset fins to counter yaw trim. Fokker pilots were known to carry a bit of U/C bungee to assist with elevator trim...So far as what the difference is between a balance and servo tab is, I think, and only think, that a balance tab is operated by the surface movement, whereas the servo tab is the pilot operated device, which then moves the surface. My own experience is that models, generally, have no need of the things other than reproduction on a scale model, as we have a rigid, servo operated system with a rigid trim system, in other words, the tab is physically unable to do what it was originally intended.
Evan, WB #12.
IronEagle, the period you are referring to was when the tab ideas were developed. I think even some of the late WW1 airplanes were using adjustable tailplanes, certainly many had offset fins to counter yaw trim. Fokker pilots were known to carry a bit of U/C bungee to assist with elevator trim...So far as what the difference is between a balance and servo tab is, I think, and only think, that a balance tab is operated by the surface movement, whereas the servo tab is the pilot operated device, which then moves the surface. My own experience is that models, generally, have no need of the things other than reproduction on a scale model, as we have a rigid, servo operated system with a rigid trim system, in other words, the tab is physically unable to do what it was originally intended.
Evan, WB #12.
That's exactly the reason that trim tabs (or the trim function on balance or servo tabs) are, at best, useless or, at worst, dangerous on models. I remember an article in RCM&E back when large models where rare and large servos didn't exist. A couple of modellers had built a large Lancaster and used the scale elevator trim tab to trim the model nose up by setting the tab trailing edge up! It worked until the day they flew the model faster than before and 'the tail took over'. What really happened, obviousely, is that the trim tab did what it's meant to and drove the elevator down against the (weak) elevator servo causing the crash.
As for balance and servo tabs, as evidenced by the people posting here, it seems that they are very useful on models. Allowing larger and faster models (higher control loadings) achieving full control deflection with smaller, lighter servos and linkages.
I may have misunderstood your post but while I agree that on a model a trim tab is 'physically unable to do what it was originally intended', there is no reason why a balance or servo tab can't.
My understanding of the difference between balance and servo matches yours.
BTW you are spot on with the WW1 bungy cord trim, we do that on some of the Vintage Aviator aircraft at Masterton. Not that we fly stsraight and level that much, but its handy on a long transit.
Cheers
Dave H
11-09-2011 | 05:48 AM
#70
Senior Member
RE: What are boost tabs???
Reading the biography of Pappy Boyington of Baa Baa Blacksheep fame, When he had to take a long mission after a mean nightbefore hangover, He used to tie rubber bands from the stick to whatever was handy to keep the Corsair trimmed while he had a light snooze. When it started to drift off he said he could feel it and would tighten one up a bit.
11-09-2011 | 06:53 AM
#71
RE: What are boost tabs???
We seem to shift between full scale tab comments and actual use of tabs in our models
aerodynamic counterbalances are used in some micro designs -to remove loads on the tiny servo motor setups (the 6400 series rx/esc/ servo setup on UMX Extras is an example).
These make a big difference whre the "tab" approach can not.
The coupled tab reduces loads at small surface deflections- the " forward the hinge line" approach becomes more effective as deflection increases
We have been playing with the various aids developed for use on indoor aerobatic models
some of these seem wierd but in using them - they do work
fences , drag plates, angled tip plates for side force etc., all interesting approaches to increasing control and or controlling speed.
You can control a model quite effectively with simply changing drag at various points - -just like sticking your arm out on a bike - it causes a shift in center of drag.
aerodynamic counterbalances are used in some micro designs -to remove loads on the tiny servo motor setups (the 6400 series rx/esc/ servo setup on UMX Extras is an example).
These make a big difference whre the "tab" approach can not.
The coupled tab reduces loads at small surface deflections- the " forward the hinge line" approach becomes more effective as deflection increases
We have been playing with the various aids developed for use on indoor aerobatic models
some of these seem wierd but in using them - they do work
fences , drag plates, angled tip plates for side force etc., all interesting approaches to increasing control and or controlling speed.
You can control a model quite effectively with simply changing drag at various points - -just like sticking your arm out on a bike - it causes a shift in center of drag.
11-09-2011 | 07:07 AM
#72
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From: Mason,
MI
RE: What are boost tabs???
Look 5:57 into this video where Steve Hinton shows a BOOST tab on a Corsair. That's good enough for me.
http://www.youtube.com/user/comaz#p/a/u/0/nubn_QpkHnI
http://www.youtube.com/user/comaz#p/a/u/0/nubn_QpkHnI
11-09-2011 | 08:52 AM
#73
Senior Member
RE: What are boost tabs???
ORIGINAL: JL1
Look 5:57 into this video where Steve Hinton shows a BOOST tab on a Corsair. That's good enough for me.
http://www.youtube.com/user/comaz#p/a/u/0/nubn_QpkHnI
Look 5:57 into this video where Steve Hinton shows a BOOST tab on a Corsair. That's good enough for me.
http://www.youtube.com/user/comaz#p/a/u/0/nubn_QpkHnI
Yeah, those are on the ailerons. Earlier on in this discussion is at least one picture of the ones on the elevators.
