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Failure Point
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rexjan(at)bigpond.com
Guest

Posted: Thu Nov 30, 2006 9:08 pm Post subject: Failure Point

Where did it  fail ?

The carry throguh tube would be one of the weakest links.

Rod ends  would be the next weakest link I think.  If you look at the Avids 

they  do not use rod ends.

                                              Dave

  

 Dave,

             I'm  only going on memory here so please no one take it for gospel but I seem to  remember the weakest link is the rod end but also here in Australia anyway we  have Skyfox's that are rough copies of Kitfox's. These are apparently failing at  the carry through tube and there is an AD out for that. I understand they have a  weaker tube, maybe wall thickness not sure !

   Also  took my interest to read the Avid does not use rod ends. What do they do ? I  assume just a bolt ! Is it in shear ?

   I think  that loading the wing to failure point is on a video copied by Grant Fluent on  this list. I guess anyone that wants a copy could first check with Grant that  this is on the Video then buy a copy from him. I remember his price was  extremely reasonable and there was a lot of interesting stuff on the DVD copy  like loops and rolls in a Kitfox.

                                                                                                                     Rex.

 



   [quote][b]

dave

Joined: 22 Sep 2006
Posts: 1382

Posted: Fri Dec 01, 2006 3:23 am Post subject: Failure Point

Hi Rex, 

  

 I have a Model IV  with rods ends,    I have seen earlier Kitfox models without rod ends and the end of strut just  like the avid strut.   I would guess that the rod end was used to make  accommodate for wing adjustment to allow to a less precision wing build  ?

  

 I found this on the carry through tube issue on the  Skyfox    http://www.auf.asn.au/airworthiness/an956issue3x.doc

  

 I have yet to see the same on Kitfoxes.  Has  there been any reported rod end or carry through failures ?

  

  

  

 Dave

  

  

 [quote]   ---

_________________
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wliles(at)bayou.com
Guest

Posted: Sat Dec 02, 2006 11:29 am Post subject: Failure Point

Avid's, at least from the B model on, use one large size rod end on the 

rear strut of the left wing to allow trimming. No other rod ends are 

used in the wing or tail struts.  Bolts in shear take the loads.  Kitfox 

had some problems with rod ends failing in tail struts and finally went 

to beefier rod ends or simple struts for the tail.  Using straight 

struts in the Avid left little room for error but resulted in a stronger 

wing and tail. 



Jerry Liles



Rex Shaw wrote:



 	  Quote: 	
		   Where did it fail ?

 The carry throguh tube would be one of the weakest links.

 Rod ends would be the next weakest link I think.  If you look at the 

 Avids

 they do not use rod ends.

                                              Dave

  

 Dave,

             I'm only going on memory here so please no one take it for 

 gospel but I seem to remember the weakest link is the rod end but also 

 here in Australia anyway we have Skyfox's that are rough copies of 

 Kitfox's. These are apparently failing at the carry through tube and 

 there is an AD out for that. I understand they have a weaker tube, 

 maybe wall thickness not sure !

   Also took my interest to read the Avid does not use rod ends. What 

 do they do ? I assume just a bolt ! Is it in shear ?

   I think that loading the wing to failure point is on a video copied 

 by Grant Fluent on this list. I guess anyone that wants a copy could 

 first check with Grant that this is on the Video then buy a copy from 

 him. I remember his price was extremely reasonable and there was a lot 

 of interesting stuff on the DVD copy like loops and rolls in a Kitfox.

                                                                                                                    

 Rex.

lcfitt(at)sbcglobal.net
Guest

Posted: Sat Dec 02, 2006 2:34 pm Post subject: Failure Point

Jerry,



Interesting.



I still have the 3/16 rod ends on the foreward horizontal stab strut and it 

is part of my preflight check.



Regarding stronger wings.  I wonder if this is a plus, as the Kifox design 

with more "room for error" is a proven design as there have been no 

structural failures.  If after about 15 years of uneventful use, would there 

be a reason to change the design?



Lowell

---

dave

Joined: 22 Sep 2006
Posts: 1382

Posted: Sat Dec 02, 2006 2:48 pm Post subject: Failure Point

Lowell,



I agree on the horiz stab rod ends being ok.    I think alot of the problem 

might have been from the pilot  pulling on it rather than the grab handle ?



As far as the wings,  I agree they seem strong but the idea for 2 rod ends 

on the strut if probably to make up for builing errors if any as well as 

adjustment. .  I have not heard of them coming apart but I have broken them 

on other applications.  They are tiny compared to GA aircraft.  That being 

said, has ther ever been an in flight breakup of a Kitfox ?

Dave

---

Lynn Matteson

Joined: 10 Jan 2006
Posts: 2778
Location: Grass Lake, Michigan

Posted: Sat Dec 02, 2006 2:58 pm Post subject: Failure Point

I bought the 1/4" threaded stud inserts to fit those forward hort. stab 

struts, and welded them in, fitted the 1/4" rod ends and have had no 

problems in over 200 hrs of flight, and like Lowell, check them prior 

to, and after each day of flying.



Lynn

On Saturday, December 2, 2006, at 05:33  PM, Lowell Fitt wrote:



[quote] 



 Jerry,



 Interesting.



 I still have the 3/16 rod ends on the foreward horizontal stab strut 

 and it is part of my preflight check.



 Regarding stronger wings.  I wonder if this is a plus, as the Kifox 

 design with more "room for error" is a proven design as there have 

 been no structural failures.  If after about 15 years of uneventful 

 use, would there be a reason to change the design?



 Lowell

 ---

_________________
Lynn
Kitfox IV-Jabiru 2200
N369LM

pwmac(at)sisna.com
Guest

Posted: Sat Dec 02, 2006 4:30 pm Post subject: Failure Point

Yes there have been failure on teh horizontal strut. Don't know how 

many but the archives had the info.

The construction Skystar used was a #10x32 socket head cap screw 

welded in the end of the 3/8"x0.020" tube. Not an aircraft method but 

a short cut to avoid buying the correct AN490(?) tube end 

fitting.  As shocking as it is surprisingly only a few failed. 

probably due to excess heat on the hardened cap screw.

BTW, there is no way improper handling could break a #10x30 cap screw 

-For sure.

Most of us that did the mod to the AN part used 1/4x28 AN part and 

plug welded it as well as seam welded it to the end of the tube. The 

cost to do the upgrade is minimal - just the AN tube end and the 

appropriate rod end. My welder charged me $10 after I prepped the 

parts. Shortening the rod is required to get the same length as before.

Its very wise to keep checking for the failure.

Regards, Paul

================



At 02:33 PM 12/2/2006, you wrote:

[quote]



Jerry,



Interesting.



I still have the 3/16 rod ends on the foreward horizontal stab strut 

and it is part of my preflight check.



Regarding stronger wings.  I wonder if this is a plus, as the Kifox 

design with more "room for error" is a proven design as there have 

been no structural failures.  If after about 15 years of uneventful 

use, would there be a reason to change the design?



Lowell

---

jimcarriere

Joined: 27 Aug 2006
Posts: 22

Posted: Sat Dec 02, 2006 4:31 pm Post subject: Re: Failure Point

My 7 uses 3/8" rod ends at each end of the wing struts.  That is, the long threaded part of the rod is 3/8x24 (UNF), that attaches to the strut.  The ball has a 1/4" hole, a 1/4" bolt attaches that to a bracket (and the bracket is attached to the wing spar).



Those rod ends are pretty substantial...

Jim in NW FL

Series 7 in progress

_________________
Jim in NW FL
Kitfox Series 7 in progress
Rotec R2800

dosmythe(at)cox.net
Guest

Posted: Sat Dec 02, 2006 4:59 pm Post subject: Failure Point

Just a thought, once the horizontal stabilizers are adjusted for proper 

flight why not replace the horizontal  struts with "fixed" units.  That is, 

replace with tubing with crimped ends and no rod ends to break.



Don Smythe

---

dave

Joined: 22 Sep 2006
Posts: 1382

Posted: Sat Dec 02, 2006 5:09 pm Post subject: Failure Point

Don,  You would have to get the hole drilled perfect in that case.



I  drop the front of my horiz. stab when floats go on and have to adjust a 

few timesto get hands free flights.

Same thing going back to wheels in fall.  Ski season approaching soon.  



BTW Don I saw your Fox on Barnstormers.  Looks great !!  Surprising how 

these Kitfox sell so cheap and at a fraction of a new Kit.  Yours only has 

150 hours?  Good deal for some one.

If anyone looking fora 582 Amphib fox there is one there as well on Aerocet 

floats for 25k .  Flaots worth about 8k alone. Great deal

Dave

---

lcfitt(at)sbcglobal.net
Guest

Posted: Sat Dec 02, 2006 5:29 pm Post subject: Failure Point

Never!



And the horizontal strut faillures were discovered post flight.



I dare say that if we went through the design we could find lots of stuff 

that just doesn't "look" right.  I think of the Rans with their construction 

methods, a take off from the ultralight design.  Lots of brackets and bolts 

holding things together and their new stamped aluminum wing ribs - flimsy 

compared to the Kitfox design.  Maybe the Kitfox is overdesigned and heavy 

as a reslult, but I like the history.  I have been in some pretty heavy 

stuff, once in a flight of six flying over the Sawtooth Mountains of Idaho 

on our way to Smiley Creek - elev 7200 ft. - we did a quick 180 because we 

got tired of our heads banging on the skylight. Once in the middle of Nevada 

one of the guys inadvertently flew through a dust devil - no visible dust - 

and had a real ride, but other than having his headset knocked off his head 

and a good case of the shakes, no harm done.



Lowell

---

dave

Joined: 22 Sep 2006
Posts: 1382

Posted: Sat Dec 02, 2006 6:23 pm Post subject: Failure Point

Good to know Lowell.  I too like the design of the Kitfox and have found it 

a easy adaptable airplane to fly.

What happened on the horiz stab issue ?  Were they broken from tugging on 

them ?



As far as heavy , I think that any plane can get heavy in a hurry from all 

the add on as well as engine choices.



In my opinion the Kitfox is one of the best on the market if not the best. 

Not to mention best bang for the buck  on the used market.  I am lost to 

understand whatd folks like about Challenger, Beavers and Chinnook planes 

but they are very popular and some really hold the mkt value for some reason 

that I will never understand.



I think if a guy bought up 1 mil $ worth of used Kitfoxes that he could see 

at least  50% return over the next few years and if not he would have a nice 

collection of toys.



Dave

---

wliles(at)bayou.com
Guest

Posted: Sat Dec 02, 2006 6:27 pm Post subject: Failure Point

While it never caused a crash that I'm aware of there were just too many 

incidents of failure of the horizontal stab rod ends to call it ok.  I 

recall one incident a few years ago related by a member of the Kitfox 

list of having to wrestle his airplane back home as it suddenly wanted 

to descend and turn and he could not figure out why until someone on the 

list suggested he inspect the horizontal stab.  If the forces had been a 

bit greater the stab might have twisted or fluttered and made the plane 

uncontrollable or stressed the rear rod end to failure.  That might have 

hurt.  As for the rod ends on the wings they seem to be trouble free and 

adequately strong and  make it easier to correct any minor 

misalignments, certainly more so than on an Avid, though I had no 

problem with mine.



dave wrote:



[quote] 



 Lowell,



 I agree on the horiz stab rod ends being ok.    I think alot of the 

 problem might have been from the pilot  pulling on it rather than the 

 grab handle ?



 As far as the wings,  I agree they seem strong but the idea for 2 rod 

 ends on the strut if probably to make up for builing errors if any as 

 well as adjustment. .  I have not heard of them coming apart but I 

 have broken them on other applications.  They are tiny compared to GA 

 aircraft.  That being said, has ther ever been an in flight breakup of 

 a Kitfox ?

 Dave

 ---

Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Sat Dec 02, 2006 8:10 pm Post subject: Failure Point

Dave:



Not hard to see the interest in the Challenger and its clones.  Lots of

unobstructed view and a very light engine.  Capable on floats.  Very fast to

build.  Just watch their video on low and slow flying.... You can do the

same in the 'Fox but they won't tell  you that. The easily removable doors

are great for aerial photography.  



I looked at the Challenger quite closely.  What I liked was above.  What I

didn't like was the blind riveted cluster fish plate joints.  I don't think

they even used Cherry max rivets on them.  (I could be wrong as those joints

are made at the factory)  I feel safer with 4130 in the frame than extruded

aluminium where I can easily see it.   I also didn't like the idea of being

stuck with tricycle only landing gear.  In the kitfox there is still the

tricycle option.



The real selling point for me was the wing folding feature of the Kitfox.

I can unfold mine in less time than it takes to tell you how to do it.  The

plane goes back into my garage after every flight.  I fly floats so I like

the idea of the bologna slicer being out front as far away from the spray as

possible.  I also like the idea of a 4130 welded frame!  Side by side

seating to me is another plus but I also liked flying the Super Cub that has

tandem seating.  I find pre-flight and post-flight inspections are easy to

do on the Kitfox as the whole front cowl is quickly removed and access even

to the back of the instrument panel is easy.



Weather here is rarely hot so I installed a gas shock on my door to hold it

up during flight.....effect is fabulas.  Landing on floats with the door

open is at this stage beyond my ability to adequately describe.  That one

you will have to try for your self.  It's a bit like your first solo.

The end result is personal preference.  Both are good planes (the Challenger

by reputation).  I think the Kitfox and Avid (which one is the clone?) are

stronger and better in the harsh environment I live.  If there is a fault

with the Kitfox it has to be I get nervous when someone who has never been

around a plane before offers me help launching or retrieving the plane.  It

would be much worse with the Challenger.



Noel



[quote] --

_________________
Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

dosmythe(at)cox.net
Guest

Posted: Sun Dec 03, 2006 4:29 am Post subject: Failure Point

I have this mod on my list of things to do.  Just remove one rod (with rod 

end) at a time.  pre-drill the fuselage end and attach new rod.  Put a tick 

mark down through the hole in the stab where you want the new rod drilled. 

I think that should be as close as you need it.



Don Smythe.

dave

Joined: 22 Sep 2006
Posts: 1382

Posted: Sun Dec 03, 2006 5:17 am Post subject: Failure Point

Don, I would like it keep the option for adjustment and the Rod ends seem to 

serve  well.

Would your modification be considered a airframe modification?



Dave

---

dosmythe(at)cox.net
Guest

Posted: Sun Dec 03, 2006 6:11 am Post subject: Failure Point

I would think that once they are set to length, they should not ever need 

changing.  However, I believe you mention changing to floats and this might 

require a seasonal change??  If I remember correctly, the rod ends on the 

stabs are 3/16" where every other rod end on my Fox is 1/4" or bigger.  I 

also seem to remember that Fox's sold overseas required the stab rod ends to 

be upgraded to 1/4".  There has been a couple cases where the rod ends were 

found broken after a flight.  Regardless whether they broke due to flight or 

rough ground handling, I think a good field fix might be in order.

    I don't know if this type mod would be considered an airframe mod or not 

but probably would.  So, that is another question.  I'd say, you can do the 

mod, log it and forget it???  If you have a case where winter/summer lengths 

are different, make two sets.  This is probably not a major concern but is 

always on my preflight check list to wiggle all four rods.  I've had my 

plane moved many times by other hanger mates and you never know what they 

might do in moving your plane.



Don Smythe

---

lcfitt(at)sbcglobal.net
Guest

Posted: Sun Dec 03, 2006 9:32 am Post subject: Failure Point

Jerry,



Apples and oranges here.  The failure with wrestle had to do with the jack 

screw in the larger models that trimmed the horizontal stabilizer.  That is 

what failed.  It had nothing to do with the struts, though it is agreed that 

the larger models the struts had been beefed up and possibly with the use of 

accepted AN fittings.



I remember two - maybe more of the rod ends - rather the stud going into the 

rod ends - failing and it was discovered on the ground after a flight.  I 

don't recall if there was a "feeling" in flight, but it definitely was not a 

wrestle.  There was an upgrade offered, but I couldn't find a Service Letter 

or Bulletin on the issue.



Lowell

---

pwmac(at)sisna.com
Guest

Posted: Sun Dec 03, 2006 4:48 pm Post subject: Failure Point

Testing my memory but didn't they offer the aero tubing and 1/4x28 

rod ends. The

up grade was very expensive.

Paul

===============

At 09:29 AM 12/3/2006, you wrote:

[quote]



Jerry,



Apples and oranges here.  The failure with wrestle had to do with 

the jack screw in the larger models that trimmed the horizontal 

stabilizer.  That is what failed.  It had nothing to do with the 

struts, though it is agreed that the larger models the struts had 

been beefed up and possibly with the use of accepted AN fittings.



I remember two - maybe more of the rod ends - rather the stud going 

into the rod ends - failing and it was discovered on the ground 

after a flight.  I don't recall if there was a "feeling" in flight, 

but it definitely was not a wrestle.  There was an upgrade offered, 

but I couldn't find a Service Letter or Bulletin on the issue.



Lowell

---

wliles(at)bayou.com
Guest

Posted: Sun Dec 03, 2006 5:01 pm Post subject: Failure Point

Lowell



There was an incident of tail strut failure in flight with difficulty 

maintaining steady level flight that was reported to this list. This was 

a Model 4, not a Model 5 with the jackscrew trim system.  The 

correspondent couldn't figure out what had happened until someone (might 

have been me) asked him to inspect the tail lift struts.  My point is 

failures have occurred for whatever reason and may well occur again.  

This is a type of failure that is survivable but is potentially 

disasterous.  Kitfox (Skystar) finally upgraded the struts to larger 

rodend fittings.  My feeling is the small rod end fittings on Model 4 

are a known point of failure,whether from improper ground handling, 

improper assembly, or stress of flight, with potential for disaster and 

I would replace them. 

Back then the list manager had a reguarly updated message called "Kitfox 

Safe" where all the problems and potential problems and how to handle 

them were listed.   Unfortunately I have a relatively new computer and I 

do not have a copy of Kitfox Safe.  Perhaps someone else saved a copy?



Jerry Liles

Lowell Fitt wrote:



[quote] 



 Jerry,



 Apples and oranges here.  The failure with wrestle had to do with the 

 jack screw in the larger models that trimmed the horizontal 

 stabilizer.  That is what failed.  It had nothing to do with the 

 struts, though it is agreed that the larger models the struts had been 

 beefed up and possibly with the use of accepted AN fittings.



 I remember two - maybe more of the rod ends - rather the stud going 

 into the rod ends - failing and it was discovered on the ground after 

 a flight.  I don't recall if there was a "feeling" in flight, but it 

 definitely was not a wrestle.  There was an upgrade offered, but I 

 couldn't find a Service Letter or Bulletin on the issue.



 Lowell

 ---

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