Jab under cart

[seb7701]

Thanks Ken -will take a look at the bolts sent and cross my fingers....

 

The left leg is worse than the right. We did manage to tighten the left up a little a while back, thinking that may have been the issue, but no....

 

My main concern will be the camber when I stick the wheels straight back on. Will be interesting to see whether simple shamming with washers can achieve the desired result.

 

 

[jabiruken]

Thanks Ken -will take a look at the bolts sent and cross my fingers....The left leg is worse than the right. We did manage to tighten the left up a little a while back, thinking that may have been the issue, but no....

My main concern will be the camber when I stick the wheels straight back on. Will be interesting to see whether simple shamming with washers can achieve the desired result.

I think the camber will be ok if axles where bolted straight up, the toe can be achieved at the saddle area. by flocking them in place to set toe - or +. Mine is set "toe in" a little too far for my likening, but will monitor tyre wear, when my spacers were fitted the builder placed 80 kg on each seat and used a skate board under axles to observe the flex in legs. Personally I don't think this area is that critical, as there are many variants in aviation ie: bounce and goes, solo flights. Everything is just a compromise and jab would have well covered this area in design.

 

 

[Oscar]

jk - I think you mean, the toe-in can be set by flocking at the axle (that is what Jabiru recommends, btw). You'd not want to reduce the strength of the leg by shaving anything off at the saddle clamp, it's a high-stress point on the leg, and it's (normally) a very tight fit anyway.

 

I made up this device for setting toe-in: uses a laser level (which I have calibrated to be pretty damn accurate at 10 metres, within the laser-dot margin of error):

 

 

It clamps onto the machined centre of the wheel (the bearing housing area) using the spat extension tube, and clears the tyre so it's reproducing accurately the machined surfaces of the actual wheel (the centre bolt floats on the spat extension so it pulls the thing down hard onto the wheel). I checked it in my lathe for accuracy and the laser-dot on the wall about 16 feet away, was again within the size of the dot circle for each end when rotated 180 degrees. I am quite sure I won't be able to get the aircraft lined up on a centre-line to anything like that accuracy, BUT, the mains will end up as a pair, with the combined toe-in equal either side and at the Jab. recommended toe-in - just the aircraft may taxi slightly crab-wise.. but that's going to be the same result for any other method, I believe

 

If you have access to a lathe and can weld, it's dead easy to make up..

 

 

[jabiruken]

jk - I think you mean, the toe-in can be set by flocking at the axle (that is what Jabiru recommends, btw). You'd not want to reduce the strength of the leg by shaving anything off at the saddle clamp, it's a high-stress point on the leg, and it's (normally) a very tight fit anyway.I made up this device for setting toe-in: uses a laser level (which I have calibrated to be pretty damn accurate at 10 metres, within the laser-dot margin of error):

 

[ATTACH=full]47064[/ATTACH]

 

It clamps onto the machined centre of the wheel (the bearing housing area) using the spat extension tube, and clears the tyre so it's reproducing accurately the machined surfaces of the actual wheel (the centre bolt floats on the spat extension so it pulls the thing down hard onto the wheel). I checked it in my lathe for accuracy and the laser-dot on the wall about 16 feet away, was again within the size of the dot circle for each end when rotated 180 degrees. I am quite sure I won't be able to get the aircraft lined up on a centre-line to anything like that accuracy, BUT, the mains will end up as a pair, with the combined toe-in equal either side and at the Jab. recommended toe-in - just the aircraft may taxi slightly crab-wise.. but that's going to be the same result for any other method, I believe

 

If you have access to a lathe and can weld, it's dead easy to make up..

Yes I wondered about the crabbing issue, to align the nose wheel to the mains would be hard as the nose leg flex some what. Yes you should not shave legs, But. The legs are to wide to fit in saddle,they where flap discked on edges to fit. The leg is still somewhat rounded and do not seat well in saddle. Bolts loosened you can pull legs 2 or mm forward and aft. I believe 2 mm up there would equate to a large moment of toe at axle, flocking saddle in will square bottom of leg and set leg so for and aft movement doesn't occur in saddle.

 

 

[Oscar]

jk - obviously, there are considerable manufacturing tolerances at play here!. My 'heavy duty' type-1 legs are tighter than a fish's between the bolts of the saddle, I radiused the vertical (and horizontal) edges of the saddle to stop it biting into the glass.

 

If you flock the saddle for forward-and- aft movement, make sure the flock doesn't go onto the bottom of the saddle. The 'flat' edges of the legs flex and change shape with deflection, and if the saddle width is anything more than necessary, that introduces a leverage effect that raises the stress at the clamp point by a heap. Citabria legs and P 92 Echo legs fail for that exact reason: if the bottom surface of the saddle is not changed to a slightly convex shape, the stress rise breaks the leg. Jab legs have a bit more tolerance, but better not to ask of them more than reasonable!.

 

 

[seb7701]

In a nutshell - the flocking of the clamping plate (saddle?) to the leg is simply to ensure a good fit between the two, as the legs are far from 'geometrically perfect'!! It is basically performing the same function as what the poly packer does between the leg and the lower surface of the fuse.

 

 

[seb7701]

Well, first flight today since replacement of legs and, as per Ken's experience, it was like a new plane!!! Tracked straight and true on take-off and landing, but most noticeable was the ability to land and have the plane simply track straight down the strip like it was on rails, compared to the weaving and legs fighting each other. Brilliant!!

 

 

[jabiruken]

Well, first flight today since replacement of legs and, as per Ken's experience, it was like a new plane!!! Tracked straight and true on take-off and landing, but most noticeable was the ability to land and have the plane simply track straight down the strip like it was on rails, compared to the weaving and legs fighting each other. Brilliant!!

It's a Nice feeling knowing that it's not just us getting old and unserviceable, How did you go with bolt length and camber etc?

 

 

[seb7701]

You're right about that Ken - I thought I had suddenly forgotten how to land!!!

 

In terms of bolts, I ended up grabbing the next size up for each, so basically popped the rear bolts in the front and getting new rears. I originally went with the standard flocking process and TWO poly packers on top, however it left large gaps between the clamping plate and the leg, so we actually now have used a cut down packer under the leg, epoxied to the plate. All very nice fit now. The camber looked mickey mouse, but once we got it outside onto the tarmac, the trusty iPhone clinometer said there was actually 0 degrees both sides, so will run with it for the moment, otherwise can see if some more neg camber is needed. Currently nothing in terms of shimming etc.

 

The main bit is the fact that it now just tracks straight as a die, not only because of the lack of camber, but these legs have WAY less flex in them!!!