Jab under cart

[jabiruken]

The landing gear on my sp/Lsa are getting a bit soft, even after lifting wing they no longer kick the wheels back under. Any ideas on how to stiffin them up? Or has any one got a set they wish to sell. I've not contacted jabiru as yet so I'm not even sure that they would be still available. I have replaced the u/c bolts a year or so back and no issues were found, hot days, age and at mtow appaers to be taking its toll. Thanks Russell

 

 

[jetjr]

Look hard for cracks or delamination

 

I replaced outer flat rubber plates, they had compressed to nothing, helped a fair bit

 

From memory these legs are quite expensive

 

 

[Bruce Tuncks]

I agree with jetjr. Fibreglass does not go soft unless it has some damage. There would be some temperature at which load would cause a permanent distortion, but this would be well above any reasonable ambient temperature.

 

 

[Yenn]

Why wouldn't Jabiru have replacements?

 

Do you really think that they don't have Jab owners interests in their sights.

 

Give them a ring and you will most likely find they are a stock spare parts item.

 

 

[jetjr]

Some older models had different legs and Jabiru may not use or have them anymore

 

There's plenty of parts even from just 10 years ago Jabiru can't supply anymore

 

 

[geoffreywh]

there are at least 2 types. some have a tapered "block" at the wheel end (for adjusting toe in?) some are plain flat ended . So it may not be fit and forget?...

 

 

[jabiruken]

My old girl is a 1999 kit finished 2001. When looking front on to a/c you can see the bow just above axles to around three parts up the legs, both sides are identical with no sight of delamination. A thought was to wrap that area with Kevlar

 

 

[Bruce Tuncks]

My kit was 1998 and I reckon the legs might be the same. They are fairly square in cross-section, although the wrapping rounds them off just where the flat-sided bracket fits. Following a tip, I used flock on the legs at these points to make them a better fit for the bracket. Is there fore and aft movement in yours?

 

I wouldn't use kevlar for extra wrapping, it doesn't wet out so easy and it is quite flexible. I would use glass and LC 360.

 

 

[seb7701]

Having only around 15hrs in my SP, I always had the opinion that it was behaving badly on touchdown. Upon analysis of the camber and toe-in of the wheels which was waaaaaaay out, I came to the realisation that to shim the wheels would mean around 5 gazillion shims.

 

I then turned my attention to the legs themselves, which were looking a little 'bowy' in the centre of the main section, particularly one side. Upon sitting in the aircraft and watching the leg on the left, it was really much squishier than desirable which drew me to the conclusion that it's life was over and that the camber, which was really the direct opposite of what was required, was caused by the legs having lost their mojo.

 

It was also evident in the fact that they ended up either wide or narrower in track depending on whether you pulled the plane forward or aft.

 

Following a call to Jab, it was confirmed that they do in some cases deteriorate over time. As such, just like 'Lieutenant Dan', I have new legs!! Hope to get them on this week and we'll see.

 

 

[jabiruken]

Glad to hear that they are still available, are they exspensive? After a closer look today I found no cracks showing but have concluded that internally they have delaminated as I was able to deflect heal toe by hand about 10 mm... so my legs are not only flexing but twisting same time

 

 

[Oscar]

Seb, be careful when you fit the new legs.

 

The early Jabs. - mine is one - had the 'first' legs: basically rectangular in cross-section, and straight from the outer end of the outer 'saddle' down to the axle bit; the 470 usually had the same legs, I think. Mine was for almost all of its life, a training aircraft, and following an accident, had the legs - all three - replaced with what Jabiru describes as 'heavy-duty': basically the same shape bit with several extra layers of cloth in them, to increase the cross-section. All good BUT: they are an extremely tight fit in the outer saddle, to the point where the vertical edges of the saddle chopped into the legs. The edges of the saddle had not been chamfered to relieve this ( and they were installed by an L2, just one of many seriously bad jobs done on this poor little bugger).

 

The bending point at the saddle is a high-stress area, for two reasons: the first is that it introduces a discontinuity in the line of force being carried by the composite matrix ( note that the later Jabs. have a curved frontal projection, so that where they pass through the 'saddle' they are far closer to straight. The second is, that when they 'rock' under load in the saddle, the square (or flat) shape of the saddle introduces a leverage aspect. This additional leverage as the material flexes adds a very considerable amount of stress to the leg material: exactly that problem beset Citabrias and continued with P92 Echos, to make main leg failure quite common. The cure for that is simple: put a small amount of radius on the bottom face of the saddle and chamfer the edges.

 

Jabiru did a fair job of combating that leverage aspect by adding a polyurethane strip (around 90 durometer, I think from memory) to the top and bottom sides of the 'saddle'; hopefully your new legs will come with new strips for installation. You can buy the sheet from suspension bush manufacturers but honestly, it's cheaper to just get them from Jabiru. I had to replace ONE front-leg donut - because (again) the L2 installation of a new heavy-duty front leg had been done badly - and in another aspect, very, very dangerously, but that is another story..

 

If the new legs Jab. have supplied are the 'heavy duty' specification, you will need new bolts for the saddles and for the inner ends - about 1 additional dash length. On my aircraft, the replacement was done with (obviously) whatever bolts the L2 had around, and there were up to six washers under one. AND: make sure that you use new, proper-grade, nylocs for final installation: I have to say (with regret) that I am aware of Jabiru sending out good bolts with lousy-spec. nylocs: get yours from Skyshop, or SunCoast Airparts, or your local engineering supply shop - but NOT Bunnings et. al.

 

It's worth a look at the 'drop test' video on the Jab. web-site (well, on the older one, anyway!) to see just how far the main legs distort on hard landing, to appreciate just how much movement there is at the 'saddle'.

 

The recommended toe-in for Jab main wheels is about 3/4 degree, for an unladen aircraft. You achieve that by adding washers as necessary to the front or rear of the axle and THEN install the axle with 'flock' - LC3600 with glue-powder additive - to take the axle load out into the leg. CG Composites: HOME : CGComposites are epoxy resin suppliers and offer composite material information can supply LC3600 in small quantities and glue powder ( e.g WEST 403 or equivalent), and are absolutely GREAT to deal with - 100% recommended.

 

The Jabiru recommended method to set toe-in, is, for my money, lousy - because it uses the side of the tyre as a reference. The damn tyres are NOTHING like accurate ( lift a leg and rotate the tyre with a dial-gauge against the sidewall to see how bad it is); at the least, you need to build a rig that references off the wheel rims. If you only use grass, that doesn't matter, but if you use bitumen, it will make the aircraft twitchy on ground roll.

 

 

[seb7701]

Thanks Oscar. Always careful, but it will hopefully be fairly prominent, should the clamp plate (the saddle your referring too?) have been chewing into the leg, as there should be around 13yrs of indication! There's no difference in specification for the legs these days, only the type 1 and type 2 (curved ones).

 

Given that I'd be goose not to replace all fittings when the legs are off, I have all new hardware, including the new red poly bushes and packers, which, like the nose wheel donuts, are superior to the old black rubber items. The packers only go between the leg and the fuse it would seem though.

 

I have seen the drop test plenty of times, but that's the type 2 gear, so probably not a lot of relevance to me in behaviour.

 

Looking forward to getting them on and see how it behaves, so watch this space!

 

 

[Oscar]

Seb: you are entirely correct in that the red poly sheet packers go between the leg and the fuselage. There is simply not enough room for a 2.5mm (from memory) thick packer between the 'second series' Type 1 legs and the sides of the clamp ( or 'saddle').

 

IF your old legs were the early - thinner - Type 1, you may not see any abrasion from the saddle edges. I don't have any early Type 1 legs to comment upon; but the 'Heavy Duty' Type 1's that were installed on my aircraft have notches in the edges from abrasion with the unrelieved edges of the clamp, after around 350 hours maximum flight time according to our log book.

 

Your clamps may have been set-up for the later, thicker legs: I suggest you compare the new leg dimensions at the clamp point with the ones you are replacing. I THINK - but am not sure - that the '470' designation relates to the MTOW - my aircraft has a 430 MTOW - so it may well have had the thicker legs installed as standard, with the appropriate clamp..

 

.

 

 

[seb7701]

Yep, 470 does relate to the MTOW...

 

 

[jabiruken]

Installed new under cart today,

 

handles like new. I thought the sloppy x wind take offs and landings was due to my aging, But today the old girl proved it was in fact those flexing legs as she tracked true and predictable in x wind.

 

 

[Oscar]

EGGsealant!.

 

 

[Bruce Tuncks]

Congratulations jabiruken, were the new legs dimensionally the same as the old ones? Do they look to be made the same?

 

Is there a chance of cutting the old ones open to look for internal damage?

 

 

[facthunter]

I wonder if something like the Skyranger U/C of Aluminium could be used. Nev

 

 

[Oscar]

The standard Jab. U/C has been pretty robust over the size of the fleet. There are two potential problems with 'glass legs: a QC issue in the resin mix resulting in lower strength / stiffness, and if the aircraft has been tied down on a bitumen strip in the extreme Australian summer, the lower area glass reaching softening temperature (around 90C) from reflected heat off the bitumen and being subject to high(ish) loadings while in that condition.

 

 

[jabiruken]

Congratulations jabiruken, were the new legs dimensionally the same as the old ones? Do they look to be made the same?Is there a chance of cutting the old ones open to look for internal damage?

Yes the legs were the same in every aspect, i only had to use flap disk on sides of legs to allow fitting of saddles (they were not squared). i added 1.1/2 deg negative camber and 1/2 to 1 deg toe in. Good idea about cutting legs, will do that next time at hangar and post photo if interested.

 

 

[seb7701]

Ken - that was quick, but is great news. I was starting to think that I had lost the plot with some of my landings and was reluctant to 'blame my tools', but was my plane was/is behaving similar to what you have touched on.

 

I am hoping to get to mine on the weekend or early next week. Can I ask how you went about adding the camber and toe-in? Was that shimming with washers or did you hit it with the flap disk little?

 

Definitely interested in any tips before I tackle it. Was sounding quick and simple until I read that I needed to flock the saddles and wait 24hrs for them to dry!!! Doh!!

 

 

[jabiruken]

Ken - that was quick, but is great news. I was starting to think that I had lost the plot with some of my landings and was reluctant to 'blame my tools', but was my plane was/is behaving similar to what you have touched on.I am hoping to get to mine on the weekend or early next week. Can I ask how you went about adding the camber and toe-in? Was that shimming with washers or did you hit it with the flap disk little?

Definitely interested in any tips before I tackle it. Was sounding quick and simple until I read that I needed to flock the saddles and wait 24hrs for them to dry!!! Doh!!

The original builder machined a stainless washer marked with 0deg over one hole 1/2 over next 1 and 1 1/2 last hole, the washer looks like a slice of cheese if you get my meaning. I did not flock it as I see no reason to. The idea of just rotating the shim to alter the camber proved simple yet effective. One wonders why jab didn't come up with the idea

 

 

[seb7701]

Thanks Ken. That sure does sound very handy in terms of adjustment and yes, a perfect addition from the factory you would think. If you happen to have the camera lying around....

 

I did wonder about the flock...not sure what it is in aid of...

 

 

[jabiruken]

 

 

 

 

 

[jabiruken]

Thanks Ken. That sure does sound very handy in terms of adjustment and yes, a perfect addition from the factory you would think. If you happen to have the camera lying around....I did wonder about the flock...not sure what it is in aid of...

The way I understand it, some use masking tape plied up to get the desired setting, you then lightly flock the stub axle in place. The alloy shim can be quickly fashioned and won't require flocking in my view.