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Mushy control stick
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Paul Petty

Joined: 11 Jan 2006
Posts: 226
Location: Mississippi

Posted: Tue Jul 17, 2007 1:57 pm Post subject: Mushy control stick

Hey gang,



After Charleys first flight in the Kolbra the only complaint he had was mushy responce from the stick. Well we figured alot of this is his lack of time in a Kolb type aircraft and his comparing it to the RV8 or even the jets he flys on a regular basis.  After John H stopped by and it was discussed we or John rather found some movement in the control tube that sticks out the back and connects to the aileron push pull tubes. Right away we all agreed "There is your mush". Then it was suguested that more support be added back there. I started thinking of a way to fix this. To back up a bit remember than we changed the configuration of this area by running the control rod through a nylon bearing and making it fixed at the aft point. This leaves about 8" of the 4130 tube un-supported. However I got to really thinking about the steel tube and thought hmmm man there is no way that the 4130 steel tube is "flexing" that much. 



Now here is my thinking.. I am thinking that because the control tube is supported by a ridgid mount aft vs the slider for the flaperons, the flex or mush is coming from the lack of support at the other end of the control tube up near the rubber U-Joint. This makes perfect sence to me now that I think about it. The rubber U-joint is supported less than 3" in front but nothing of support to maybe 4' aft. This would make alot of stress on the U-joint and explain the flexing. 



Any of you guys think Im on the right track here?



As soon as I can get back to the airplane and have some help I will confirm this therory and report back. 

The only reason for this post about this issue is this....



Other Kolbs with flapperons when the flapperons are extended may encounter the same mushy feel. might want to get a buddy to hold the aileron and another to move the stick side to side and watch the movenent at the U-Joint to see if the tube is trying to warp up/down or sideways. 



If my theroy is confirmed I will make a nylon bearing and mount it to the tail boom up close to the U-Joint to prevent this flexing.

_________________
Paul Petty
Kolbra #12
Ms Dixie
912 UL 70" warp

Paul Petty

Joined: 11 Jan 2006
Posts: 226
Location: Mississippi

Posted: Tue Jul 17, 2007 2:01 pm Post subject: Re: Mushy control stick

PS....



This may be Kolbra only related and maybe only to Ms. Dixie due to mods so dont freak out!

do not archive

_________________
Paul Petty
Kolbra #12
Ms Dixie
912 UL 70" warp

lucien

Joined: 03 Jun 2007
Posts: 721
Location: santa fe, NM

Posted: Tue Jul 17, 2007 8:47 pm Post subject: Re: Mushy control stick

When I first started flying my FS II, I noticed the stick was rather "springy" in the aileron direction. It isn't what I'd call mushy, but definitely springy...



Once I started relaxing and looking around a bit, I took it up and did some full-deflection wing rocking to get an idea of the aileron response. I noticed the ailerons hardly defected at cruise even with the stick against the stop to either side. 



I think some of the spring is twisting of the torque rod between the stick and the bellcrank in the back that attaches to the pushrods. Probably the rest is absorbed elsewhere, just in the general play in the aileron linkage.

I don't think there are long portions of unsupported rod, but there might be towards the back....



So some of the flexing you're having could just be the tube itself?



That's my only quarrel with the plane at all, and even so with gap seals on the ailerons there's still a good bit of aileron control.



Otherwise, I love the design of the ailerons. Very simple and virtually no maintenance. No linkages, pullies or pushrods in the wing anywhere, it's all outside the plane for easy inspection and lubrication, etc.



LS

_________________
LS
Titan II SS

JetPilot

Joined: 10 Jan 2006
Posts: 1246

Posted: Wed Jul 18, 2007 5:44 am Post subject: Re: Mushy control stick

I have the same springy feeling in my MK - III Xtra.   There is a lot of aileron deflection on the ground, but in the air the ailerons dont deflect that much even with stick deflection.  In my case, all the linkages are steel, well supported, and have almsot no play.  I do have the seperate flaps and ailerons though, and im sure most of my "SPRINGY" feeling is comming from the aluminum tubes on the wing that go out to the aileron.  There must be 6 feet of aluminum tube there before it gets to the aileron, and 6 more in the aileron itself...  That could cause a LOT of spring like twist.  There is not much I can do about this exept go to a thicker tube, but that would involve a lot of work and given the leingth of it, some springy feeling would always be there.    I am going to add aileron spades to the counterweights to take much of the air loads resistance off the ends of the tubes and prevent it twisting so much.  That should make for much lighter and more pleasant aileron forces.



Mike

_________________
"NO FEAR" - If you have no fear you did not go as fast as you could have !!!

Kolb MK-III Xtra, 912-S

lucien

Joined: 03 Jun 2007
Posts: 721
Location: santa fe, NM

Posted: Wed Jul 18, 2007 6:28 am Post subject: Re: Mushy control stick

I should mention, speaking of control forces, that my FS II has the lightest forces in all axes of any plane I've flown so far.. The compromise there is it doesn't have huge amounts of control, but of course then again, it's not a Pitts and wasn't designed to be... 



My titan tornado, for example, has vastly more control, but the stick is a lot heavier in comparison, even with the spades on the ailerons.....



I also kicked around some thoughts of modifications of the aileron system on the FS II to take out some of the flex and give more deflection. But that would put me in test pilot territory, with new unknowns as far as additional stress on the ailerons, hinges and possibly even the wing panels and who knows what else........



Also, since the Kolb has been flying for a long time as-is, I figured it's all working as designed.  So I haven't messed with it.



I still haven't flown in the big Kolbs yet, so I don't know how they are as far as amount of control available and etc. A couple friends of mine in TX have an older MK III and I noted the same flexing in the ailerons. But they fly that plane in conditions I wouldn't think of going up in in my FS II, so....

LS

_________________
LS
Titan II SS

Richard Pike

Joined: 09 Jan 2006
Posts: 1670
Location: Blountville, Tennessee

Posted: Wed Jul 18, 2007 6:35 am Post subject: Mushy control stick

How do you think the wingtip vortices will interact with those spades?



Richard Pike

MKIII N420P (420ldPoops)



---

_________________
Richard Pike
Kolb MKIII N420P (420ldPoops)
Kingsport, TN 3TN0

Forgiving is tough, being forgiven is wonderful, and God's grace really is amazing.

Dennis.Kirby(at)kirtland.
Guest

Posted: Wed Jul 18, 2007 6:53 am Post subject: Mushy control stick

<< ... at the other end of the control tube up near the rubber U-Joint.

 	  Quote: 	
		  >


	


Paul -



Rubber U-Joint?  



I've not heard of this design feature.  (It's not on the M-3 Classic.)

Is this unique to the Kolbra?  Why would the designers want to "soften"

the control transmissions between the control stick and the ailerons? 



Dennis Kirby

jstewart(at)inebraska.com
Guest

Posted: Wed Jul 18, 2007 6:54 am Post subject: Mushy control stick

Maybe take Kimberly's advice and reflex the ailerons a bit.  That might help

a lot with the control forces.



J.D. 



 

 	  Quote: 	
		   My titan tornado, for example, has vastly more control, but 

 the stick is a lot heavier in comparison, even with the 

 spades on the ailerons.....

JetPilot

Joined: 10 Jan 2006
Posts: 1246

Posted: Wed Jul 18, 2007 7:32 am Post subject: Re: Mushy control stick

Richard,



I have thought quite a bit about the wingtip vorticies affecting spades on the tips, and I have come to concusion that I have no idea    I think the only way I will ever know is to try it.  I will bolt the spades onto the counterweights so that I can take them off if I dont like the results.  Threre is a possibility of the ailerons going hard over if the spades are to big or the vorticies are a big probelm, so I will start out with small ones to see how they act and make them bigger until the releive enough of ths stick pressure.  I will also flight test it by flying a foot off the runway and progressively faster speeds to get an idea of what they will do.



Lucien,



The aileron forces on the MK III Xtra are very heavy, much heavier than on a Cessna 172.  I could live with even normal forces, but not the very heavy forces needed to make a turn.  The Kolb is not designed to roll fast, and I dont want it to, but I do want to be able to turn the plane without a huge amount of effort.   I have thought about wing twist and fatigue of the panels, and I plan to fly the plane within its limits, I just want it to be pleasant and easy to fly.   Durring the building phase, I got some good advice from John Hauck and streingthened the wing structure with angle aluminum along the ribs, before and behind the spar.  This should make my MK III much more resistant to any fatigue and twisting from aileron forces.  Attached is a picture of the wing before covering.



Reflexing the ailerons might reduce the aileron forces some, but it is a horrible way to do it.  The proper term for reflexed ailerons is "Spoilerons", meaning the ailerons are also acting as spoilers.  It may make it a bit easier to roll, but relfexing the ailerons also kills lift, increases stall speed, and makes the wing less efficient.  I dont want any of these bad side effects in my plane.  



Michael Bigelow

UltralightMikeKolbBuildPictures073.JPG

Description:

MK III Wing Reinforcement

Filesize:

347.8 KB

Viewed:

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_________________
"NO FEAR" - If you have no fear you did not go as fast as you could have !!!

Kolb MK-III Xtra, 912-S

Richard Pike

Joined: 09 Jan 2006
Posts: 1670
Location: Blountville, Tennessee

Posted: Wed Jul 18, 2007 8:25 am Post subject: Mushy control stick

Find an excuse to get to NE Tennessee & stop by Indian Springs airport and 

I'll let you fly mine. Light ailerons and all.

Richard Pike

MKIII N420P (420ldPoops)



---

_________________
Richard Pike
Kolb MKIII N420P (420ldPoops)
Kingsport, TN 3TN0

Forgiving is tough, being forgiven is wonderful, and God's grace really is amazing.

Paul Petty

Joined: 11 Jan 2006
Posts: 226
Location: Mississippi

Posted: Wed Jul 18, 2007 8:54 am Post subject: Re: Mushy control stick

Dennis,

I guess the rubber u-joint is a Kolbra only design. It is needed to make the bend in the control rod.



do not archive

_________________
Paul Petty
Kolbra #12
Ms Dixie
912 UL 70" warp

John Hauck

Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)

Posted: Wed Jul 18, 2007 9:01 am Post subject: Mushy control stick

Mike:



The weakest, most flexible part of the Kolb  wing is the bow tip.  You 

plan on turning the aileron counterbalance weight into a spade at the 

weakest, most flexible point, outboard of the wing tip.  Might want to 

think on that a bit.  Also, the counterbalance weight attachment was 

not designed nor intended to have increased torsional loads.



Remember, every time you change one thing, it will affect several more 

in the chain.



If it were me, I would look at the geometry of the aileron control 

from stick to aileron.  To get a little more, or a lot more mechanical 

advantage, it is pretty simple to change the arm length of a bell 

crank or horn to more effect with less effort.



All Kolbs inherently load up the ailerons at speeds over 50 to 60 mph. 

You ain't gonna change that unless you cut the cord of the aileron in 

half.  Then you lose low speed aileron authority which, to me, is 

extremely important.   Much more important than light stick force at 

higher speeds.  At lower speeds it is easy to move the stick from stop 

to stop, when it is really needed should you get caught in violent 

winds and want to be on the ground more than in the air.



At higher speeds one does not have to deflect the aileron but a tad to 

make the aircraft roll.  A little rudder input helps.  Also a little 

patience.  Like has been said, you ain't flying a Pitts Special.



If you are interested in doing snap rolls and aileron rolls then you 

might need a whole buncha aileron at higher speeds.



Kolbs are not to be compared with Cessna 172's, Piper Warriors, 

Challengers, Titan Tornados, ect.  They have very little in common. 

Kolbs do things differently than most airplanes.  Yet, they are very 

easy to fly and very forgiving, if you don't turn into a design 

engineer and screw it up.



john h

mkIII

_________________
John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama

possums(at)bellsouth.net
Guest

Posted: Wed Jul 18, 2007 9:11 am Post subject: Mushy control stick

At 11:32 AM 7/18/2007, you wrote:

 	  Quote: 	
		  



Richard,



I have thought quite a bit about the wingtip vorticies affecting 

spades on the tips, and I have come to concusion that I have no idea 


	




One of the guys we used to fly with put spades on a Firestar, but he 

put them in the middle

of the ailerons ( I think). John H might remember.

John Hauck

Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)

Posted: Wed Jul 18, 2007 9:26 am Post subject: Mushy control stick

| I guess the rubber u-joint is a Kolbra only design. It is needed to 

make the bend in the control rod.

|

| do not archive

|

| --------

| Paul Petty

Paul P:



Prior to using the very expensive aircraft universal joint in the 

aileron torque tube, an inhouse designed and fabricated square tube 

4130 universal joint was used.  This ujoint was not successful.  When 

TNK bought out Old Kolb, TNK upgraded to the aircraft universal.



I don't know that it is a rubber ujoint.  Never looked inside one. 

However, I do know they work much  better than the old square tube and 

bolt ujoint, and doubt very seriously they are rubber.



This ujoint is utilized in all FSII and Kolbra.  Don't know if it is 

in the FF or not.



Personally, before I started chasing something different to change to 

correct your problem, I would correct the first change you made to 

your system.



You have two serious problems that I could see when I looked at your 

airplane:



8" more or less of unsupported aileron torque tube on the aft end.



An incorrectly fabricated sleeve that is cut 90 degrees, rather than 

45 degrees or less.



Either of the above can lead to a catastrophic failure of the aileron 

torque tube.  A condition that Kolbs will not successfully fly in.



If it were my airplane, as I pointed out to you Sunday at Laurel, MS, 

I would support the aileron torque tube at the aft end.  Sorry I did 

not point out the bad sleeve joint.



john h

mkIII

_________________
John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama

Paul Petty

Joined: 11 Jan 2006
Posts: 226
Location: Mississippi

Posted: Wed Jul 18, 2007 10:15 am Post subject: Re: Mushy control stick

John,

What sleeve are you talking about?

do not archive

_________________
Paul Petty
Kolbra #12
Ms Dixie
912 UL 70" warp

Paul Petty

Joined: 11 Jan 2006
Posts: 226
Location: Mississippi

Posted: Wed Jul 18, 2007 10:23 am Post subject: Re: Mushy control stick

here is the U-Joint.

P1210049.JPG

Description:

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Viewed:

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_________________
Paul Petty
Kolbra #12
Ms Dixie
912 UL 70" warp

Thom Riddle

Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)

Posted: Wed Jul 18, 2007 10:43 am Post subject: Re: Mushy control stick

The photo of that "rubber u-joint" looks to me like a regular u-joint with a rubber dust/dirt cover. I'll give you good odds that the connection is NOT rubber. 



Some 25 or so years ago when I was doing machine design work, we would sometimes use a "rubber" flexible coupling but they were not designed to correct for an angular mis-alignment like this one is obviously doing. The rubber flexible coupling was intended to compensate for very slight axial mis-alignment and prevent transmission of source vibrations throughout the system.

_________________
Thom Riddle
Buffalo, NY (9G0)

Don't worry about old age... it doesn't last very long.
- Anonymous

Paul Petty

Joined: 11 Jan 2006
Posts: 226
Location: Mississippi

Posted: Wed Jul 18, 2007 10:57 am Post subject: Re: Mushy control stick

Thom,



I never really thought about it nor looked at it that much. What you say makes sence tho thanks!

do not archive

_________________
Paul Petty
Kolbra #12
Ms Dixie
912 UL 70" warp

Paul Petty

Joined: 11 Jan 2006
Posts: 226
Location: Mississippi

Posted: Wed Jul 18, 2007 11:02 am Post subject: Re: Mushy control stick

wow! never knew there was a tiny U-Joint in there. Looked them up in AC spruce.

http://www.aircraftspruce.com/catalog/appages/ujoints.php

do not archive

_________________
Paul Petty
Kolbra #12
Ms Dixie
912 UL 70" warp

John Hauck

Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)

Posted: Wed Jul 18, 2007 11:11 am Post subject: Mushy control stick

| here is the U-Joint.

| 

| --------

| Paul Petty

 



That is a rubber dust cover, not a rubber universal joint.



john h

mkIII

_________________
John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama

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