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Flap Setup Question(s)

Old 05-09-2016, 02:07 PM
  #1  
stanz358
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Default Flap Setup Question(s)

Hello Everyone - kinda new to the sport and this is my first go-round with flaps and have a few questions regarding setup. The aircraft is a PK Sport Cub and figured this would be a good plane to play around with flaps.

Is it standard practice to have a single servo operate both flaps or split on to 2 servos/channels. This particular setup is single servo which is mounted to the underside of the wing. Seems one flap is deflecting a bit more than the other because the plane wants to roll a little right when deployed. It's been a real pain measuring deflection, removing the wing, adjusting, mounting measuring and so on. It would seem if they were split on to their own servos/channel you could adjust travel on the transmitter which would make adjustment a lot easier?

I think I know the answer to this but just want to confirm. I have high and low rates setup as per the manual 100 and 70 with elevator mix also as described.

On low rates you're limiting surface travel from 100 down to 70. In order to get elevator mix correct on low rates, you have to adjust down elevator mix proportionally to whatever your low rate is set at since flaps are still deploying 50% and 100% no matter which mode you're in correct?


Thanks
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Old 05-09-2016, 03:44 PM
  #2  
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It used to be most common for us to use a single servo... when servos cost $50 for a cheap one and minimum wage was $1.25.
Now the second servo is possibly cheaper and lighter than the hardware to get away with using just one.
We still tend to use just one channel for flaps but if you have the spare and want to mix, that's fine too.

Difference in throw when using a Y will be due to a mechanical difference. Control horn a different distance from hinge line or servo arm not quite the same centering would be the most common.

While getting used to flaps... less is better.
Appx 5 to 10 deg for low deflection and 20 to 30 deg for high deflection when on a 3 position switch.
As you get used to flaps and what they do, stup up the deflections adjusting to what you want the plane to do.

Small deflection is mainly a tip-stall prevention tool. This will increase the effective angle of attack in the center part of the wing making it stall before the tips.
Large deflection is mainly for adding drag. Anything more than 40 deg you are primarily just adding drag.
In between is a mix of effects

Adding lift really isn't the job of flaps if they are not a type that also adds wing area. The multi-stage flaps of an airliner move back and down and significantly add to wing area allowing the plane to fly much slower.

Simple flaps that do not add wing area are NOT going to change the speed where the plane stalls. They will change how it acts when it stalls.

You can mechanically or electronically adjust the throws of the flaps.
Don't adjust flap-elevator mix based on throttle above 40% with flaps down. Flaps are for low speed. Very few planes will fail to nose-up if you deploy flaps at high speed.
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Old 05-10-2016, 01:09 PM
  #3  
stanz358
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Thanks - Plane was flying great without flaps but I'm determined to get these working correctly. I made some adjustments, flew it this morning before work and flew worse. Somethings not right. I have an elevator mix with the flaps and it (the elevator) was not going back to level when flaps were returned to up position. This is new twist. And the existing issue still exists - both flaps are not deflecting the same amount causing a slight roll. Tried measuring and adjusting with a ruler yesterday and that was difficult at best and with not so good results. Have to pick up a tool to measure deflection.

Thanks for taking the time to respond.
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Old 05-10-2016, 04:10 PM
  #4  
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Delete the flap -elevator mix. You really don't need it on a Cub unless the flaps are designed wrong.

Typical Cub behavior with flaps is:
At speed, the flaps will cause it to nose up.
But at proper approach speed the plane will naturally nose down appropriately.
More flaps and the plane will assume a more nose down attitude as the plane seeks its correct flying speed based on trim setting.

Large flap deflection is designed to allow a steep descent without building speed, thus above appx 35 deg the nose down angle can be quite noticeable and alarming if you are not used to it. This is why I say to start with modest to moderate flap deflection instead of max flaps (60 deg) which might have the plane assume a 45 deg nose down attitude hands off.

Its just a matter of getting used to the effect.
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Old 05-10-2016, 05:43 PM
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Personally I am all for single servo on flaps. Just make sure geometry is right.

The best way in my book is to have a single U torque rod. The centre has an arm for the servo link.

This way it is impossible to get misaligned or out of step flaps.... see attached.

Nigel
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Old 05-10-2016, 06:30 PM
  #6  
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Originally Posted by solentlife View Post
Personally I am all for single servo on flaps. Just make sure geometry is right.

The best way in my book is to have a single U torque rod. The centre has an arm for the servo link.

This way it is impossible to get misaligned or out of step flaps.... see attached.

Nigel
That design only works for wings that have no trailing edge sweep and no dihedral.. i.e. the hinge lines of both flaps need to be on the same axis.. which is quite limiting.

A more flexible design but still using a single servo is to have two seperate torque rods operated via a 'Y' shape pushrod with two clevises attaching separately to the two torque rods.

Stanz358.. it sounds to me like you probably have stiff hinges and/or binding linkages. If you disconnect the servo pushrod all the surfaces must move freely. If they are stiff then you get differential movement and poor centering. Stiff surfaces are quite common on some foamy planes, you often need to move the surfaces by hand repeatedly to their extremes of travel to free up the hinges.
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Old 05-10-2016, 06:40 PM
  #7  
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In fact the single torque can work if split into two and the arms together ... so a single control rod connected. No need for twin rod yoke.

Nigel
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Old 05-10-2016, 06:41 PM
  #8  
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One servo not centering the same as the other can do it also.

One spline difference and adjusting for same at flaps up... they diverge as the flaps come down.

If its a half-spline issue, its not going to be the easiest to correct
You can correct for that with computer radio and using separate channels... programmable servos.. or altering the linkage geometry. (geometry is hardest because it means minute shift of control horn position)
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Old 05-10-2016, 08:05 PM
  #9  
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Originally Posted by solentlife View Post
In fact the single torque can work if split into two and the arms together ...
If it's split into two surely it's not a single rod anymore
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Old 05-10-2016, 08:12 PM
  #10  
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Originally Posted by JetPlaneFlyer View Post
If it's split into two surely it's not a single rod anymore
C'mon be fair ... just getting round your dihedral bit and avoid twin control rods / yoke from servo.

The point is to get identical movement on each flap.

Nigel
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Old 05-10-2016, 08:22 PM
  #11  
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There are all sorts of solutions,, including square tubes which can be used to make a sort of "universal" joint with just enough angle allowed that the dihedral doesn't bother the linkage. and we are back to a single pushrod.
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Old 05-10-2016, 08:57 PM
  #12  
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Originally Posted by solentlife View Post
C'mon be fair...
Maybe you should try explaining a little better.

...split into two and the arms together
What does that even mean? If you don't like a yoked control rod, just how would this work?
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Old 05-11-2016, 07:34 AM
  #13  
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Originally Posted by Turner View Post
Maybe you should try explaining a little better.
Everyone else appears to understand .....


What does that even mean? If you don't like a yoked control rod, just how would this work?
Am I boring you or something ?

Its an old solution to the problem of angled wings whether horizontally or dihedral'd.

Instead of a single torque rod doing both flaps - you create two same as the aileron style. You fit them so the control arms sit together and then connect your clevis or z bend through both .... no need for yokes / two control link rods.

If a yoke or twin control link is not set correctly as to position of the servo and its arms connection geometrically to the control linkage - you can get slight differences in flaps movement. Doing away with twin connection removes that and you get identical movement.

Been playing this control linkage game for many years - haven't found one yet I cannot mechanically solve.

Nigel
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Old 05-11-2016, 12:41 PM
  #14  
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Well I think I found a few potential issues - one solved, the other in the works. Being fairly new to all of this, I'm learning what I need to look for/pay attention to during setup.

The Sport Cub has a torque rod for each flap and connected to the servo with a y shaped push rod. On the pushrod is a nylon nut if you will with studs on each to attach the clevise.
Sure enough, one was several turns lower than the other which was causing 1 to deflect more that the other. I measured and confirmed that before and after the adjustment. Took it out for a few flights this morning before work and the tendency to roll a little with flaps deployed seems to be gone.

I took fhhuber's advise and scaled back on the % flap deploy to 25% half flaps, 50% full flaps but it still pitches up quite a bit. This is the first flap setup for me so it's a learning experience. I just want to make sure any mechanical or setup issues are out of the mix and the rest is up to me.

One other thing I noticed right out of the box. This plane comes with "flaps optional". You have to cut each flap free and then setup. On the left side, the foam under the hinge tape is so thin, and is almost seperating from the main wing. This is causing the left flap to be "flimsy" for lack of a better term compared the right. I'm wondering if there is enough force on that flap when deployed to cause it to flutter a bit?

Horizon is sending me a new wing. QC issues with 2 planes from them so far but their support is great.

Anyway - thanks for all advice as always. Learning a lot from these exchanges with you guys!
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Old 05-11-2016, 02:21 PM
  #15  
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Originally Posted by solentlife View Post
...You fit them so the control arms sit together and then connect your clevis or z bend through both .... no need for yokes / two control link rods.
Seems like the worst possible idea to me with absolutely no independent adjustment. I use two servos and two channels for maximum versatility.
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Old 05-11-2016, 02:39 PM
  #16  
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The thin foam hinge is normal foam variation... eventually these molded hinge lines always fail (may be a few flights, may be a couple of years.) Then you slice the control surface loose and re-hinge it with some other type hinge. I usually put in the CA type hinges because they are simple to work with.

The molding process for the foam leads to some variation in thickness of the wing and ALL of that variation shows in the hinge line of the flaps. Sometimes it will be paper thin. Sometimes it may be approaching 1/4 inch. Ideal is 1/16 inch for a good solid hinge line that isn't excessively hard to flex.
They can't prevent this variation...


Pitching up is... you are still too fast for the flaps. That thing will hang in the air going VERY slow.

Take it high. No flaps. See how slow you can make it hold altitude. Add flaps.
Get used to the flaps that way.
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Old 05-11-2016, 03:42 PM
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Originally Posted by Turner View Post
Seems like the worst possible idea to me with absolutely no independent adjustment. I use two servos and two channels for maximum versatility.
Yer takes yer choice ....

Whatever you prefer.

Properly made and fitted - there is no need for independent adjustment ... but of course if you cannot make them / fit them properly - then go for independent means.

As to maximum versatility ?? On Flaps ? They only go up and down together ... what else do you need ?

Nigel
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Old 05-11-2016, 04:31 PM
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Well...

I play games with flaps.

Full function 4-servo wing sailplane programming

Ailerons
Flaps
Ailerons follow flaps (butterfly)
Ailerons move opposed to flaps (crow)
Flaps follow ailerons (full span ailerons)

I've used that on a Cub before. It works. Doesn't gain you a lot except the airbrake effect of crow mode can let you dive vertically at a low speed.

But, its entertaining (to me)to experiment with all of the possibilities
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Old 05-11-2016, 05:18 PM
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Originally Posted by fhhuber View Post
Well...

I play games with flaps.

Full function 4-servo wing sailplane programming

Ailerons
Flaps
Ailerons follow flaps (butterfly)
Ailerons move opposed to flaps (crow)
Flaps follow ailerons (full span ailerons)

I've used that on a Cub before. It works. Doesn't gain you a lot except the airbrake effect of crow mode can let you dive vertically at a low speed.

But, its entertaining (to me)to experiment with all of the possibilities
Fair enough ... no argument there ...

My point is that they move together ideally as one. Whether you have full movement UP and DOWN ... spoilers / flaps ... up to you but the idea for OP is to get identical movement on his flaps.

Turner seems to have a bee in his bonnet that my suggestions are no good .. all I can say to that - is they have stood the test of time ... thousands of models through many years have proven them.

I agree that today we have lighter and more versatile gear we can put in the models - but I like to play simple for simple functions. Which is what mine does.

Nigel
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Old 05-11-2016, 07:14 PM
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Originally Posted by solentlife View Post
...All I can say to that is they have stood the test of time. Thousands of models through many years have proven them...
The OP has a plane with two servos for flaps. Your solution is for him to convert his dual servo foam wing to a single servo with torque rods and no possibility of adjustment between the two control surfaces. This is not a solution at all.
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Old 05-11-2016, 08:26 PM
  #21  
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Huge Sport Cub thread over at RCG. I'm sure those guys have seen just about every possibly flap problem with the Sport Cub ans they'll be glad to help you sort it.

http://www.rcgroups.com/forums/showthread.php?t=2139067
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Old 05-12-2016, 07:34 AM
  #22  
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Originally Posted by Turner View Post
The OP has a plane with two servos for flaps. Your solution is for him to convert his dual servo foam wing to a single servo with torque rods and no possibility of adjustment between the two control surfaces. This is not a solution at all.
Now you are really annoying me - go back and read post #1 - where he says he has SINGLE SERVO.

Nigel
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Old 05-12-2016, 03:41 PM
  #23  
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My mistake. So why would he change to what you describe? He has a system which provides independent adjustment. The problem he has should be quite simple to fix. It may just need adjustment. He may have a stiff hinge or some other binding issue. How hard could it be to sort out.

Again you offer no solution.
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Old 05-12-2016, 03:54 PM
  #24  
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Originally Posted by Turner View Post
My mistake. So why would he change to what you describe? He has a system which provides independent adjustment. The problem he has should be quite simple to fix. It may just need adjustment. He may have a stiff hinge or some other binding issue. How hard could it be to sort out.

Again you offer no solution.
Excuse me T ... so I am not allowed to offer alternative ? Maybe you should tell the others to stop offering theirs as well ...

And lets be honest - you've got it wrong from the start and offered no solution whatsoever ... just seemed to want to make a crusade out of my suggestion.

This is Wattflyer and we do not copy the antics of RCG here. If you do not agree with my method - then enlighten properly and fairly why it is not a viable method. Which so far you have not done.

I can recall many models over many years with single control rod on dihedral and non-dihedral models ... swept back and swept forward wings. It works. It requires no adjustment of individuals unless you install poorly.

In fact if you do like Skyartec and many others do - you can have my version but with clevis ends instead of buried L of the rod. The torque rod then sits forward of the hinge line ... so that a short control link rod can go to clevis on the flap ... THEN you have your adjustment as you seem intent on insisting on.

Their are many ways to do flaps with and without dual servos ... I have just offered one with variations.

Why you seem so determined to ridicule me I am really at a loss to understand. Especially when you cannot even read the OP's post properly !!

Nigel
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Old 05-12-2016, 05:29 PM
  #25  
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well... this isn't helping any more....
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