Two or three springs ?

[egp8111]

I've just gotten my hanger find KFIV-1200(912ul) back in the air after it had been sitting for 10+ years. I installed a new tail spring from KF using only two of the three springs. I works well but I was wondering if maybe I should put the third spring on it. I've seen people doing it both ways any reason to put the third spring on it ?
Attachment 32507
I plan to change out the Maco tailwheel for a T-3 at some point if for not any other reason than to try and get a little more vis over the nose.
It has the Grove gear and 8in wheels with Nancos.

Thanks
Skip
NC

[jiott]

I have a Kitfox SS7, which is heavier than your model 4, and I started out initially with the 3-leaf spring. Over a period of a couple of years the spring gradually took a permanent set, making the spring flatter and messing up the tailwheel pivot geometry. This caused shimmy problems which seemed to get worse. I finally changed to the Grove single-piece tailwheel spring, a much stronger spring which solved the shimmy problems and has now been in use for over 8 years with no change in geometry.

The reason I say all this is I believe if you eliminate one leaf on your spring you will be asking for the same problems I had, even though your plane is somewhat lighter. If I were you, I would stay with the 3 leaf spring until you are ready to change to the T3.

[Delta Whisky]

Jim - at the risk of being accused of hijacking Skip's thread I have to ask more about the geometry change you observed. Reason - the frequency at which I'm getting a shimmy (and it is getting worse) has been increasing lately. I don't have any idea of how to tell if or how much my spring(s) have changed over the 450 landings I've made. (And, it goes without saying that they were perfect. ) Any ideas/suggestions would be appreciated.

[alexM]

Jim - at the risk of being accused of hijacking Skip's thread I have to ask more about the geometry change you observed. Reason - the frequency at which I'm getting a shimmy (and it is getting worse) has been increasing lately. I don't have any idea of how to tell if or how much my spring(s) have changed over the 450 landings I've made. (And, it goes without saying that they were perfect. ) Any ideas/suggestions would be appreciated.

Here you go. I went through this with my Citabria.
tws.jpg
I didn't have many options (read: zero) with my certified aircraft, so I replaced the springs with a stock set. It did solve the issue I was having with shimmy.

My project came with the Grove aluminum spring gear that jiott mentions, which does have the advantage of being single piece. I haven't heard anything nasty about them (in fact jiott's statement is encouraging), but when I was at Stick & Rudder they had T3s on both planes and the aluminum Grove was in a box under the counter. They didn't bad mouth them but I was left with the impression that "the cool kids are all running a T3".
Now that I've installed the T3 it seems a little floppy in the side to side direction. The Grove aluminum one did not, so I'm hanging on to it in case I change my mind.

[jiott]

Right on Alex. As time went on, my 3-leaf stock spring started slowly flattening out (less bend), which changed the geometry toward the No. 1 picture in your post-equals more tendency to shimmy.

I like the Grove because it eliminated all that. It is a very strong, tough tailwheel spring; however, that comes with a downside-less cushioning in hard landings or rough terrain. The T3 has just the opposite set of features-very good cushioning and shock absorption but somewhat less durability than the Grove (from what I have heard). Choose your poison; its hard to get both. Personally, I would rather live with less cushioning and have a bulletproof tailwheel. My off-airport landings are few and far between (no I don't have 31" bushwheels, just 8.50 Dessers 22").

[Delta Whisky]

Thanks for the comparison set up picture Alex. I attempted to take a picture that matched the angle of the example you supplied and it appears I have a good set up. Admittedly, this was taken with out any weight in the cockpit. I am suspect that with the variability in the gear position at landing, with loads in the cockpit, what is seen in the picture becomes neutral to negative and explains why is doesn't happen on every landing.

Tail wheel geometry.jpg

So - I took the recommendation for a Grove landing spring but can't locate one in their catalog - I'll give them a call tomorrow.

Until I get this solved, please keep your suggestions coming.

Thanks, Darrel

[airlina]

Lets face it the tailwheel takes a beating back there and I don't like a single point of failure especially in that area. On my Series 5 , my first tailspring was single aluminum spring that was an option with the kit from Skystar . I ran this trouble free for many years incident free until at a Kitfox flyin here in the Northeast , I ran into another Series 5 guy that adamantly told me I'd better replace that tailspring, because his and a few others had failed and the damage it caused with the failure was extensive (wrecked his rudder) . So once I heard that I switched to a 3 leaf spring gear for more redundancy . This has proved to be a good move , because last year on preflight I found one of my 3 leaf springs had cracked thru (after 500 hours of my landings!) but the other 2 springs made it a non event. Going to the hangar today will take some pics and post later today. Bruce N199CL

[efwd]

Darrel, Its hard to see in the pic but if you have the least amount of slack in your cable springs you will have problems with the Matco. I had left slack in the springs as you would with a Scott (now ABW) and learned the hardway. Nearly Groundlooped it as the shimmey happened to draw my focus away from my feet I guess. Before learning of my error, I already had ordered the T3 set up as I had planned anyhow. Just make sure you have tension on those springs with the Matco. Good Luck.

[jiott]

Regarding Airlina's comment about failed single-piece aluminum springs, I doubt very much that those springs were equivalent to the Grove aluminum springs being sold now. If it came with a Skystar kit, then that was way before Grove came out with the aluminum spring assembly being sold today. If anyone has heard of a failure with the newer Grove spring I would be very interested in hearing about it; I personally have not heard of any. However, I still respect Airlina's opinion about single point failures.

[airlina]

Here are the promised pic of my current 3 leaf tailspring versus the aluminum spring I ran for several years before guys started complaining about failures and the ensueing damage that they caused. And Jim you are right in that the manufacturer of this spring was unknown and circa late late 90's long before the grove one you guys are running. I liked the geometry of the aluminum spring and made a pattern of it for my current 3 leaf setup. And as you can see a failure of one spring in my 3 leaf setup will not cause a catastrophic failure (read rudder on ground) like the old aluminum single spring. The Skystar sales brochure was proven wrong over time, guess thats why we are in the experimental category.
Bruce N199CL