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horiz stab cables

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Herbgh(at)nctc.com
Guest

Posted: Tue Jul 07, 2015 6:38 am Post subject: horiz stab cables

Just soliciting opinions... and I know the danger in that!!! 



    I can see that using two aluminum tubes to brace the top of the 

horizontal stab as is done with the two Mini Maxes that I have owned 

would be easily done...and would not require the contortion  that is 

necessary to install the tension cables underneath the horiz stab... 

Just two tubes on top in compression and tension......that could be 

removed by pulling the clevis pins... would necessitate the installation 

of two brackets on each side...



    Herb ...should have been flying the Firefly by now..!!!

byoungplumbing(at)gmail.c
Guest

Posted: Tue Jul 07, 2015 7:47 am Post subject: horiz stab cables

As I remember the contortions were not that bad...  the top only braces, how big are they?  Weight and drag?    Is there a length maximum?   If a tube got bent In flight,, (bird strike)  would that lock up your elevator so it would not move? Have you put together a list of pros and cons..  maybe that is what you are doing now.   

Kis.   Keep it simple 

Boyd

  On Jul 7, 2015 8:40 AM, "Herb" <Herbgh(at)nctc.com (Herbgh(at)nctc.com)> wrote:[quote]--> Kolb-List message posted by: Herb <Herbgh(at)nctc.com (Herbgh(at)nctc.com)>

 

 

 Just soliciting opinions... and I know the danger in that!!! 

 

    I can see that using two aluminum tubes to brace the top of the horizontal stab as is done with the two Mini Maxes that I have owned would be easily done...and would not require the contortion  that is necessary to install the tension cables underneath the horiz stab... Just two tubes on top in compression and tension......that could be removed by pulling the clevis pins... would necessitate the installation of two brackets on each side...

 

 

 

    Herb ...should have been flying the Firefly by now..!!!

 

 

 

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 [b]

Leland.Lam

Joined: 19 Nov 2014
Posts: 20
Location: Phoenix, AZ

Posted: Tue Jul 07, 2015 9:01 am Post subject: Re: horiz stab cables

I just remade my Cable Tabs for the Horizontal Stab. I considered a few option as I don't need to fold my tail, but in the end I figured Mr. Kolb had a reason for the cables so I stayed with them. I did change the cable tabs due to the failures that have occurred. Attached is the print I made and a picture of the finished tabs.

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Herbgh(at)nctc.com
Guest

Posted: Tue Jul 07, 2015 9:22 am Post subject: horiz stab cables

Just thinking out loud...the top tube in tension and compression     certainly works...for Wayne Ison...(UL hall of fame member, likely     along with Homer?)  designed his beefiest plane, the V Max that way,     and others..

     

     The difference is that the Horizontal stab on the Max does not     hinge...is in one part...and therefore stronger to start with... 

     

       this modification would be more simple...than fitting the 4     cables...with adjustable fitting on one or both ends...and could be     made from Cro Molly if necessary... Herb 

     

     On 07/07/2015 10:47 AM, B Young wrote:

     

     [quote]       

As I remember the contortions were not that bad...          the top only braces, how big are they?  Weight and drag?    Is         there a length maximum?   If a tube got bent In flight,, (bird         strike)  would that lock up your elevator so it would not move?         Have you put together a list of pros and cons..  maybe that is         what you are doing now.         

Kis.   Keep it simple       

Boyd

              On Jul 7, 2015 8:40 AM, "Herb" <Herbgh(at)nctc.com (Herbgh(at)nctc.com)>         wrote:          	  Quote: 	
		  -->           Kolb-List message posted by: Herb <Herbgh(at)nctc.com (Herbgh(at)nctc.com)>

           

           

           Just soliciting opinions... and I know the danger in that!!!           

           

              I can see that using two aluminum tubes to brace the top of           the horizontal stab as is done with the two Mini Maxes that I           have owned would be easily done...and would not require the           contortion  that is necessary to install the tension cables           underneath the horiz stab... Just two tubes on top in           compression and tension......that could be removed by pulling           the clevis pins... would necessitate the installation of two           brackets on each side...

           

           

           

              Herb ...should have been flying the Firefly by now..!!!

           

           

           

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     [b]

Herbgh(at)nctc.com
Guest

Posted: Tue Jul 07, 2015 9:23 am Post subject: horiz stab cables

Looking at the picture...what kind of bends did you make...The look 

rather sharp ?  Herb



On 07/07/2015 12:01 PM, Leland.Lam wrote:

 	  Quote: 	
		   



 I just remade my Cable Tabs for the Horizontal Stab. I considered a few option as I don't need to fold my tail, but in the end I figured Mr. Kolb had a reason for the cables so I stayed with them. I did change the cable tabs due to the failures that have occurred. Attached is the print I made and a picture of the finished tabs.





 Read this topic online here:



 http://forums.matronics.com/viewtopic.php?p=444517#444517





 Attachments:



 http://forums.matronics.com//files/horizontal_tabs_210.jpg

 http://forums.matronics.com//files/horizontal_tab_print_985.jpg

Richard Pike

Joined: 09 Jan 2006
Posts: 1671
Location: Blountville, Tennessee

Posted: Tue Jul 07, 2015 10:25 am Post subject: Re: horiz stab cables

Just thinking here - With the cable method, the strongest point of everything in the 4 cable system is the lower 7/8" chromemoly tube that ties into the tail wheel support and is welded to the aft boom ring. This provides the primary anchor for the whole system, which is kept at a high tension. Therefore, the cables not only hold the horizontal tail in place, they also hold the vertical tail in place.



If you tied every thing into the upper vertical fin instead, now your primary anchor point becomes a 1" .058 aluminum tube with the tie in point several feet above the boom tube where the horizontal tail can exert substantial leverage should it choose to wiggle or shake. You have removed the lower cables that keep the upper vertical tube from being able to move from side to side. The design relies on the cables to keep things rigid, now all it has to keep from bending from side to side is whatever strength is in the tube itself.



Check out this diagram listed as Page 20 in the construction manual and you'll see what I mean.  Picture removing the 2 lower cables and replacing the upper cables with rigid tubing. http://oh2fly.net/oldpoops/Lexan%20rear%20enclosure.html



I am not an engineer, but your idea strikes me as being not nearly as strong, and not a good idea at all. You have completely redesigned all the inherent strength out of the tail assembly. I encourage you to at least get this idea looked at by more than one competent engineer before going ahead with it.

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

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

Last edited by Richard Pike on Tue Jul 07, 2015 10:30 am; edited 1 time in total

Leland.Lam

Joined: 19 Nov 2014
Posts: 20
Location: Phoenix, AZ

Posted: Tue Jul 07, 2015 10:30 am Post subject: Re: horiz stab cables

"Looking at the picture...what kind of bends did you make...The look 

rather sharp ? Herb "

Herb, 



Thank you for pointing that out. I too was somewhat concerned when I made these.



The bends were made in a Mill by bringing the Z axis Knee up into a pseudo forming die. There is a substantial radius on the far side surface. I was somewhat concerned about the 70 degree bend and the effect it would have on the overall strength, so I made an extra tab.  I then made a test fixture cable using (7/7) 3/32" galvanized cable.  I secured a thimble in place and clamped the assembly together using my Nico press and two copper sleeves.



I placed this system in tension until failure occurred. The cable broke and the steel remained unchanged. I then used a hardened steel bolt through the .193 and the .250 holes and placed this in tension until it failed using a 20 ton hydraulic press. The .193 hole failed not the bend.

I did not perform any test on the 20 or 45 degree tabs.



I realize these test are not completely scientific, but I do feel comfortable knowing the cable failed long before the tab.



A rough conservative guesstimate since I do not have a strain gauge at my disposal is the tab failed around 4000 Lbs of force

Leland

Herbgh(at)nctc.com
Guest

Posted: Tue Jul 07, 2015 11:58 am Post subject: horiz stab cables

Too...your stainless brackets are much thicker than normal for these 

attach points..



Herb



On 07/07/2015 01:30 PM, Leland.Lam wrote:

 	  Quote: 	
		   



 "Looking at the picture...what kind of bends did you make...The look

 rather sharp ? Herb "

 Herb,



 Thank you for pointing that out. I too was somewhat concerned when I made these.



 The bends were made in a Mill by bringing the Z axis Knee up into a pseudo forming die. There is a substantial radius on the far side surface. I was somewhat concerned about the 70 degree bend and the effect it would have on the overall strength, so I made an extra tab.  I then made a test fixture cable using (7/7) 3/32" galvanized cable.  I secured a thimble in place and clamped the assembly together using my Nico press and two copper sleeves.



 I placed this system in tension until failure occurred. The cable broke and the steel remained unchanged. I then used a hardened steel bolt through the .193 and the .250 holes and placed this in tension until it failed using a 20 ton hydraulic press. The .193 hole failed not the bend.

 I did not perform any test on the 20 or 45 degree tabs.



 I realize these test are not completely scientific, but I do feel comfortable knowing the cable failed long before the tab.



 A rough conservative guesstimate since I do not have a strain gauge at my disposal is the tab failed around 4000 Lbs of force

 Leland





 Read this topic online here:



 http://forums.matronics.com/viewtopic.php?p=444526#444526

Herbgh(at)nctc.com
Guest

Posted: Tue Jul 07, 2015 12:01 pm Post subject: horiz stab cables

Richard



    That is why I posted in the first place....Your observations appear 

to be on the money...so I will certainly give more thought to the whole 

idea...and it was an idea to start...Not going to jump into a 

modification without a lot of input...and thought...Herb



On 07/07/2015 01:25 PM, Richard Pike wrote:

 	  Quote: 	
		   



 Just thinking here - With the cable method, the strongest point of everything in the 4 cable system is the lower 7/8" chromemoly tube that ties into the tail wheel support and is welded to the aft boom ring. This provides the primary anchor for the whole system, which is kept at a high tension. Therefore, the cables not only hold the horizontal tail in place, they also hold the vertical tail in place.



 If you tied every thing into the upper vertical fin instead, now your primary anchor point becomes a 1" .058 aluminum tube with the tie in point several feet above the boom tube where the horizontal tail can exert substantial leverage should it choose to wiggle or shake.



 Check out this diagram listed as Page 20 in the construction manual and you'll see what I mean.  http://oh2fly.net/oldpoops/Lexan%20rear%20enclosure.html



 I am not an engineer, but your idea strikes me as being not nearly as strong. Frankly, I think this is not a good idea at all. You have completely redesigned all the inherent strength out of the tail assembly. I encourage you to at least get this idea looked at by more than one competent engineer before going ahead with it.



 --------

 Richard Pike

 Kolb MKIII N420P (420ldPoops)

 Kingsport, TN 3TN0

 There are two kinds of people: those who say to God, 'Thy will be done,' and those to whom God says, 'All right, then, have it your way.'





 Read this topic online here:



 http://forums.matronics.com/viewtopic.php?p=444525#444525

John Hauck

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

Posted: Tue Jul 07, 2015 1:38 pm Post subject: horiz stab cables

I probably see things a little different than most folks.  I

apologize for that.



Never had a problem with tail wires and tail post on the

Ultrastar or Firestar, but the MKIII configured the way mine

is is a different story.  During the last 3,000+ hours I've

had the tail post fail 4 or 5 times, usually at the welds on

the lower tail boom ring or the tube separate just below

those welds.  The reason it failed was all the side loads

from the tail wheel during taxi are concentrated at this

point.



Most folks refer to the tail wires at "tail wire bracing".

To me they are actually spacers that keep the vertical and

horizontal stabilizers located where they belong. Not much

bracing power to them, except for those welds at the tail

post ring that harden the tube and assist in failure. 



We experimented many times with welded gussets, splices,

etc., to find a remedy for my tail post failures, but it was

Dan Horton, a local builder, that came up with the idea of

an external tail post brace that we welded from the tail

boom ring to the bottom of the tail post.  Amazing how much

this stiffened the lateral movement of the tail post.  I can

grab the top of the upper vertical stabilizer, shake it

laterally, and there is no give.  Try that with your Kolb

and see the results.  Since this fix, no more tail post

failures.



Several others have borrowed our fix.  Most use aluminum

strap, bolting to the tail boom ring and the attachment bolt

for the tail wheel strut.  No welding and fabric replacement

required.



I remember one year, back in the early 1990's at Oshkosh

while flying passengers in the Kolb Aircraft Company MKIII,

breaking the tail post as I turned onto the ultralight strip

to take off.  This MKIII had very low hours, not nearly what

my MKIII has. 



Another time my tail post broke within an hour of returning

from my last flight to Alaska in 2004.  That would have

certainly put me in a bind had it happened a week or so

earlier.



I would not modify and fly with rigid braces on the tail

section on a Kolb.



I found some photos of my tail post and one of Gary Haley's

fix with aluminum strip and a couple bolts.  It works.



john h

Rock House, OR





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

Herbgh(at)nctc.com
Guest

Posted: Tue Jul 07, 2015 2:23 pm Post subject: horiz stab cables

thanks for the refresher on your failures...been here long enough to 

recall one or two of the incidents...



   Side loads and hitting the rudder to get the break away tail wheel to 

caster are the likely culprits.   Probably cable stretch 

contributed..?   I think  that replacing the cables top with and bottom 

with tubing would stiffen the assy just as well as the additional 

bracing... penalty would be a bit more drag... Then again...not what I 

want to do....so....I shall go with a bit heavier cable and check/adjust 

tension as part of pre flight.. secondly , I shall install a safety 

strap in case of a failure of the tensioning bolt.. That little bolt has 

worried me for years!! same with the top one ... Likely never been a 

failure...however.... Herb



On 07/07/2015 04:38 PM, John Hauck wrote:

[quote] I probably see things a little different than most folks.  I

 apologize for that.



 Never had a problem with tail wires and tail post on the

 Ultrastar or Firestar, but the MKIII configured the way mine

 is is a different story.  During the last 3,000+ hours I've

 had the tail post fail 4 or 5 times, usually at the welds on

 the lower tail boom ring or the tube separate just below

 those welds.  The reason it failed was all the side loads

 from the tail wheel during taxi are concentrated at this

 point.



 Most folks refer to the tail wires at "tail wire bracing".

 To me they are actually spacers that keep the vertical and

 horizontal stabilizers located where they belong. Not much

 bracing power to them, except for those welds at the tail

 post ring that harden the tube and assist in failure.



 We experimented many times with welded gussets, splices,

 etc., to find a remedy for my tail post failures, but it was

 Dan Horton, a local builder, that came up with the idea of

 an external tail post brace that we welded from the tail

 boom ring to the bottom of the tail post.  Amazing how much

 this stiffened the lateral movement of the tail post.  I can

 grab the top of the upper vertical stabilizer, shake it

 laterally, and there is no give.  Try that with your Kolb

 and see the results.  Since this fix, no more tail post

 failures.



 Several others have borrowed our fix.  Most use aluminum

 strap, bolting to the tail boom ring and the attachment bolt

 for the tail wheel strut.  No welding and fabric replacement

 required.



 I remember one year, back in the early 1990's at Oshkosh

 while flying passengers in the Kolb Aircraft Company MKIII,

 breaking the tail post as I turned onto the ultralight strip

 to take off.  This MKIII had very low hours, not nearly what

 my MKIII has.



 Another time my tail post broke within an hour of returning

 from my last flight to Alaska in 2004.  That would have

 certainly put me in a bind had it happened a week or so

 earlier.



 I would not modify and fly with rigid braces on the tail

 section on a Kolb.



 I found some photos of my tail post and one of Gary Haley's

 fix with aluminum strip and a couple bolts.  It works.



 john h

 Rock House, OR





 --

zeprep251(at)aol.com
Guest

Posted: Tue Jul 07, 2015 3:02 pm Post subject: horiz stab cables

Just take a half hour and install flat strap braces on the tail from the ring to the tail rod through bolt. Just do it. 



Sent from my iPhone



[quote] On Jul 7, 2015, at 6:23 PM, Herb <Herbgh(at)nctc.com> wrote:

 

 

 

 thanks for the refresher on your failures...been here long enough to recall one or two of the incidents...

 

  Side loads and hitting the rudder to get the break away tail wheel to caster are the likely culprits.   Probably cable stretch contributed..?   I think  that replacing the cables top with and bottom with tubing would stiffen the assy just as well as the additional bracing... penalty would be a bit more drag... Then again...not what I want to do....so....I shall go with a bit heavier cable and check/adjust tension as part of pre flight.. secondly , I shall install a safety strap in case of a failure of the tensioning bolt.. That little bolt has worried me for years!! same with the top one ... Likely never been a failure...however.... Herb

 

> On 07/07/2015 04:38 PM, John Hauck wrote:

> I probably see things a little different than most folks.  I

> apologize for that.

> 

> Never had a problem with tail wires and tail post on the

> Ultrastar or Firestar, but the MKIII configured the way mine

> is is a different story.  During the last 3,000+ hours I've

> had the tail post fail 4 or 5 times, usually at the welds on

> the lower tail boom ring or the tube separate just below

> those welds.  The reason it failed was all the side loads

> from the tail wheel during taxi are concentrated at this

> point.

> 

> Most folks refer to the tail wires at "tail wire bracing".

> To me they are actually spacers that keep the vertical and

> horizontal stabilizers located where they belong. Not much

> bracing power to them, except for those welds at the tail

> post ring that harden the tube and assist in failure.

> 

> We experimented many times with welded gussets, splices,

> etc., to find a remedy for my tail post failures, but it was

> Dan Horton, a local builder, that came up with the idea of

> an external tail post brace that we welded from the tail

> boom ring to the bottom of the tail post.  Amazing how much

> this stiffened the lateral movement of the tail post.  I can

> grab the top of the upper vertical stabilizer, shake it

> laterally, and there is no give.  Try that with your Kolb

> and see the results.  Since this fix, no more tail post

> failures.

> 

> Several others have borrowed our fix.  Most use aluminum

> strap, bolting to the tail boom ring and the attachment bolt

> for the tail wheel strut.  No welding and fabric replacement

> required.

> 

> I remember one year, back in the early 1990's at Oshkosh

> while flying passengers in the Kolb Aircraft Company MKIII,

> breaking the tail post as I turned onto the ultralight strip

> to take off.  This MKIII had very low hours, not nearly what

> my MKIII has.

> 

> Another time my tail post broke within an hour of returning

> from my last flight to Alaska in 2004.  That would have

> certainly put me in a bind had it happened a week or so

> earlier.

> 

> I would not modify and fly with rigid braces on the tail

> section on a Kolb.

> 

> I found some photos of my tail post and one of Gary Haley's

> fix with aluminum strip and a couple bolts.  It works.

> 

> john h

> Rock House, OR

> 

> 

> 

> 

> --

John Hauck

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

Posted: Tue Jul 07, 2015 3:35 pm Post subject: horiz stab cables

That sounds like good advice, but I doubt some will hear it.





john h

Rock House



--

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

Herbgh(at)nctc.com
Guest

Posted: Tue Jul 07, 2015 4:45 pm Post subject: horiz stab cables

anyone ever talk to Bryan about fixing this?  It is certainly a 

problem...I know that Bryan is not "net Worthy"...   Herb



On 07/07/2015 06:34 PM, John Hauck wrote:

[quote] 



 That sounds like good advice, but I doubt some will hear it.

 



 john h

 Rock House



 --

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