Lessons Learnt: Changing a Kitfox Tail Spring

[Jono]

Hopefully this post will help somebody else further down the track and will answer any questions or make their life just that little bit easier.

Background:
Basically my Dad was cool (some say crazy) enough to build a Kitfox Mk4 while I was growing up so that we could both enjoy flying around the sky. He is even kind enough to let me fly the Kitfox whenever I wish. What an awesome Dad!
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I did the daily inspection, pre-flighted the aircraft and everything appeared to be OK and as expected. I signed off the aircraft and Dad and I jumped in and started taxing towards the grass strip. As we taxied there was a loud bang, the attitude changed slightly and the aircraft came to a rather abrupt stop.

We shut down and got out to have a look at a suspected tail spring failure.... Yep... broken tail spring.... (otherwise minimal damage)
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After clearing the runway with rather red faces, and a high level of disappointment we jumped onto the internet and started to google “Kitfox tail spring failures”. It seemed to be a somewhat common topic...

So we immediately sent an email to John and Debra McBean (who were great to meet at Oshkosh last year) asking for some help in organizing replacement springs.

We got a response rocketing back overnight from John, who suggested that we replace the 2 leaf spring with the new and improved 3 leaf spring and we may also want to look at investing in a pneumatic tail wheel to assist with the shock absorption.

We ordered the new spring set straight away and Debra was fantastic in getting the replacement shipped to Australia, complete with tracking!.

About a week latter we had the new springs in hand:
A few observations:

• They are the same width
• Same thickness
• Have a slightly more relaxed curve to them (no big deal.. just an observation)
• The middle spring has a larger mounting hole for the tail-wheel (by design)
• They are unpainted (which makes sense, what color is your aircraft?..)
• The third spring added 400grams to the weight at the tail, leaving the C of G minimally impacted (well within limits)

OK.. so now the trial fit, we needed slightly longer bolts (2 x AN3-16 I think) and spacers for the rear of the springs and a longer bolt (1 x AN7-16 I think) to attach the Matco tail-wheel.
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While looking at the tail-wheel assembly at the kitchen table (where else would you do it?) I noticed that the teardrop rudder linkages were quite worn.... I almost had a heart attack!
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So we replaced the linkages, chains and inspected the whole assembly for wear (I recommend you do so too, if not already).

After lots of taxi testing, etc we were back in the air once again! I must say, that the support that we as Kitfox owners have from Kitfox LLC is fantastic and a huge "Thank You" must go out to John and Debra for continuing the Kitfox support! Without them, our only option for tail springs would have been to drive to Mt Beauty and steal “Rosslr's” springs!

For those of you wondering:
The tail spring failed at about 250hrs (600 landings), when the spring broke, the bottom of the rudder made slight contact with the runway (thankfully just cosmetic damage due to the grass runway)

[rosslr]

Very funny Johnno! For others here, Johnno does visit our project while gliding in Mt Beauty - we have to frisk him every time he leaves!

Good to see you posting here Johnno and look forward to Kitfox coming over to visit!

[P Morel]

I had the same happen to me and I would like to add one additional thing. I had little damage to the rudder that I could see, but upon inspecting the rudder end rod connections, I found 2 completely broken, 1 bent and 1 with no apparent damage. I found these weeks later. Boy, did I break out in a cold sweat. So please, do yourself a favor and take a careful look to ensure that everything is just as it should be. After all, you did take a good size crunch when the spring failed.

[Jono]

G'day P Morel,

Thanks mate, we did have a very good look at the whole rudder assembly, as I agree it must have taken some sort of a "crunch". After a good inspection nothing could be found, except for some wear in the fabric at the bottom of the rudder.

If I understand correctly, you have a slightly different rudder connection to us. We have the "older system" effectively just welded tube with a pin. Is this a different system to what you are referring to?
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Cheers

Jono

[P Morel]

Yes, your system on the rudder is different than mine. The inspection is much easier to be made on the system you have. Who would ever think these thick metal springs would break?