main wheels alignment

[Bruce Tuncks]

My tyres wear out too fast. I operate mainly from Gawler, with asphalt taxyways.

 

The wheels were set up with 2 degrees toe-in, because I thought this was right at the time. Now I'm having second thoughts, since the legs are swept forward, maybe I should set it up with toe-OUT?

 

The tyres actually wear out more on one side, which I think is a sign that they are scrubbing.

 

Here's a pic of how I measured the alignment...straight bits of timber clamped to the wheels and tape-measures at the wheel and well in front.

 

 

[turboplanner]

If there’s another Jab getting good tyre life you could check the angle on that.

 

 

[Bruce Tuncks]

Yep turbs, that's the info I am looking for. There is a lot of good technical advice on this site, for example my prop looks as good as new now after fixing it according to advice from here.

 

 

[SSCBD]

Why not ring the factory - its a Jab right/ That's the first call I would make to get the correct information..

 

 

[jetjr]

Be careful, as the legs are kind of elastic, they are sensitive to toe adjustments.

 

One of mine was set at almost zero and at certain speeds would occilate until weight came on. Pretty violent shudder just on landing.

 

Also I think the toe changes as the leg takes weight of aircraft

 

 

[turboplanner]

Yes, I would sit there and take a very close look at where that wheel might articulate for any given weight, or thump on to the runway, and compare that to the wear pattern; you might be lucky enough to pick the problem point where an adjustment might work. (However as SSCBD said, don't forget the factory first because they may have dealt with multiple examples and have the answer.)

 

 

[PKnight]

I don't think that the wear on the outside edge of the tyre is caused by scrubbing while taxying as a result of toe-in. The Jab is a bit pigeon toed and when in the air the main undercarriage bends inwards as the weight has been removed. As a result on landing the first part of the tyre to impact on the runway is the outside edge. I think that this is the cause of the wear as it is a very aggressive event and will certainly cause tyre wear particularly on tarmac runways. I find that my tyres are good for about 100 - 150 landings before I think that the wear is getting excessive. If I wanted to economise I could simply rotate the tyres round so that the worn part was now on the outside edge but I have tended to avoid doing that as I felt that it could be a false economy. If my conclusion that the wear is caused by the landing impact then changing the toe in would have no effect and I would recommend staying with the factory recommendations.

 

Peter

 

G-PHYZ J430 1105 hours,

 

 

[Bruce Tuncks]

Thanks for the comments guys. I will ask the factory but don't expect too much from them.

 

Here's a pic I took today of the tyre which is about to go in the bin. But see how the outside has worn away badly.

 

The worst wear is where you wouldn't even think the tyre was touching the runway, well this must be wrong and I must be doing something wrong to get this result.

 

 

 

[Camel]

I used a lower pressure than recommend on the main for a smoother ride on a grass strip but when on bitumen got excessive wear on one side, now on recommend pressure and much better wear on mains but ride is not as nice ! Just my observation.

 

 

[Downunder]

Not sure if this is related but my outside left tyre wears the most.

 

I'm thinking it is from scrubbing on take off with the engine trying to pull to the left and I'm feeding in right rudder/steering.

 

Not a jab aircraft or engine I will add.

 

 

[turboplanner]

Not sure if this is related but my outside left tyre wears the most.I'm thinking it is from scrubbing on take off with the engine trying to pull to the left and I'm feeding in right rudder/steering.

Not a jab aircraft or engine I will add.

If you’re getting it right though, and the aircraft heading is straight down the runway the rear wheels should be in alignment.

 

 

[seb7701]

The manual states a smidge of toe is is recommended. Is it tracking straight and true? I only ask as I had ridiculously accelerated tyre wear, but also some interesting behaviours on roll out etc. which turned out to be worn gear legs. New ones transformed it and not with any great attention to alignment.

 

 

[kasper]

Thanks for the comments guys. I will ask the factory but don't expect too much from them.Here's a pic I took today of the tyre which is about to go in the bin. But see how the outside has worn away badly.

The worst wear is where you wouldn't even think the tyre was touching the runway, well this must be wrong and I must be doing something wrong to get this result.

Seems from the pic to be combination of under inflation and alignment as you’ve excessive wear on both edges compared to tire centre. I’d try just inflating more on one set of tires and see if it is ok - you’d be amazed how much excess scrubbing can be added from just excess softness on a tire.

 

 

[Bruce Tuncks]

Seb, the gear legs appear to be ok but it does take some skill to keep tracking straight. Last time I let another guy try a take-off, he lost directional control on the ground and I had to take over. The J170 he was used to is a lot better behaved.

 

Do you have a suggestion, short of buying new legs, to check this possibility out?

 

It may be that I have not noticed a gradual deterioration, but the legs don't appear floppy at all.

 

 

[Bruce Tuncks]

Thanks kasper, thats an easy thing to try... I'll go to 40 psi and see if that helps... the glider has 45 psi on its one wheel with no springy legs so 40 should be safe on the Jabiru.

 

 

[jetjr]

Jabiru have raised recommended pressures over time

 

 

[Camel]

Thanks kasper, thats an easy thing to try... I'll go to 40 psi and see if that helps... the glider has 45 psi on its one wheel with no springy legs so 40 should be safe on the Jabiru.

It will make a huge difference as I mentioned earlier ! The wear on the outside is in my opinion due to the low pressure, you will find it very different on the takeoff roll on rough ground,

 

 

[Roscoe]

Recommended pressures on my 170 is 45 for mains and 30 for nose.

 

I seem to get more wear on the LH Main in the middle for some reason?

 

 

[Bruce Tuncks]

The tyres I am using have a stamp " max pressure 250 kPa" which is 36psi. The previous pressure used was 25psi which Jabiru specified.

 

Increasing the pressures makes sense when you consider how the crown of the tyre is relatively unworn, so I have pumped them up to 35psi but haven't had a test flight yet on account of a thunderstorm today.

 

After the advice here, I am coming to the conclusion that it was a combination of too little pressure and too much toe-in.

 

 

[seb7701]

Bruce - I was amazed at the tyre wear I saw between a couple of photos of mine when I realised how little time was between when they were taken them.

 

Anyhow, my Jab took off and landed ok, but I just didn't seem as I would have expected and used to wander a little unexpectedly and at times deliver some interesting 'sideways' type behaviours too.

 

It seemed like the legs were fighting each other a little at times. Anyhow, Jab advised that the older straight gear legs do let go over time, although they hadn't see an actual failure.

 

The crux was when I looked at the camber opposite to what it should have been and realised that correction with shims etc would be absolutely impossible, as the legs themselves had too much curve in them. That when common sense told me the legs had gone floppy!!!

 

Replacement legs were around $600, upgraded to the bigger gear bolts while I was at it. Very straightforward job and totally transformed the takeoffs and landings - dead straight and that was without a wheel alignment or camber adjustment. Totally different!!! Here's the before shot when you can see the incorrect camber- I can take a snap of the 'after' if you need it...just cant find one atm...

 

 

 

[Bruce Tuncks]

Thanks Seb,

 

Yes I would like to know more. I can't see anything wrong with those legs on your plane in the photo, they just look like mine which is a bit of a worry.

 

Do the new legs look just like the old ones or have they been improved a bit?

 

Did you cut up the old legs looking for a failure? Where would you look? I imagine at the top of the leg where the bending load is greatest.

 

If there were a delamination, maybe an epoxy injection would fix it.

 

 

[lyle janke]

Thanks Seb,Yes I would like to know more. I can't see anything wrong with those legs on your plane in the photo, they just look like mine which is a bit of a worry.

Do the new legs look just like the old ones or have they been improved a bit?

 

Did you cut up the old legs looking for a failure? Where would you look? I imagine at the top of the leg where the bending load is greatest.

 

If there were a delamination, maybe an epoxy injection would fix it.

hi all

i have a j120 jabiru which used to wear the inside of tyre U/C would splay on landing LH would wear more than RH while using factory supplied tyres (chinese). can`t offer an explanation for outside wear .

 

rang the man at wagga tyres ( he has advertisements on forum sidelines at times easily found on google any way) he has a wealth of knowledge on jabiru`s & what does & doesn`t work tyre wise ,a change of tyre from chinese & problem solved negelible tyre wear / less punctures & to my susprise landed with a puncture & didn`t even know unlike chinese brand it would do all sorts of damage

 

worth phone call & chat you might solve problem with some new info

 

hope post helps you

 

lyle

 

 

[seb7701]

Bruce, here’s a shot from this morning where you will see a difference in the camber, although it’s prob not ideal even now, though works just fine. The legs just lose their stiffness it seems and sag a little. The indicator in last nights photo is when you look and imagine what kind of shimming would be required to get things right which is how I realised there was too much curve / sag in the middle section of the legs.

 

I wouldn’t look at trying to fix them when the replacement cost was pretty reasonable for something with 180 layers of glass in them. It sounds like you might be following in my footsteps - my originals were new in around 2002. Here’s the new pics. PM me if you like - happy to duck you my number and have a yarn

 

 

 

 

[jabiruken]

Thanks Seb,Yes I would like to know more. I can't see anything wrong with those legs on your plane in the photo, they just look like mine which is a bit of a worry.

Do the new legs look just like the old ones or have they been improved a bit?

 

Did you cut up the old legs looking for a failure? Where would you look? I imagine at the top of the leg where the bending load is greatest.

 

If there were a delamination, maybe an epoxy injection would fix it.

Bruce,

I found the legs had delaminated at the lower half. Once cut all you see is brownish discolouration in between the layer of glass here and their, they appeared to be totally sound other than for strange colouring in glass which I assumed was moisture related.

 

 

[Bruce Tuncks]

You would not need much delamination deep in the legs for the stiffness to become too little to function properly. The stiffness is proportional to the cube of the beam depth, so replacing one beam with 2 beams of half the depth sitting on top of each other might look the same but it only has 1/4 the stiffness. With 4 layers of 1/4 the depth, the stiffness is one sixteenth.

 

I wonder why this happened, and what if anything is different with the replacement legs to prevent the same thing happening again .