Jabiru nose wheel suspension bush (yellow type)

[Wayne T Mathews]

Good post Ian, any post that may possibly save someone from potential grief, has to be a good one in my eyes.I'm sure you will get responses from others after they've checked their aircraft.

Kind Regards

 

Planey

Hear hear... What Planey said.

 

 

[biggles]

BobThe motor was in poor condition when i bought it using around 200mls/hr (stuck rings in Pistons). It had a top end rebuild at 580 hrs.

 

I then suffered a no.2 exhaust valve head separation from the valve stem at around 650 hrs. This was mainly due to finding out afterwards that it was running too hot and too lean on a few cylinders. My factory temp gauge on no.6 always showed good temps. I then carried out a full rebuilt including new fine finned heads, Nickasil coated standard barrels (experiment), stainless valves, Full Egt and Cht monitoring of engine fitted etc etc and by around 750 hrs found excessive blowby . This was due to the valve guides being worn/oversize and the nickasil coating coming off the barrells (experiment didn't work). So at 750 hrs i again fully stripped the motor, New Pistons, New Barrels, new K liner inserts fitted to the heads, Ceramic coating etc. I sorted out heating issues and carby issues and now all temps are excellent. CHT's around 110 - 120 C down the hole in the head between the plugs. EGT's around 680 - 700 F at cruise and 620 - 650 F full power. I have now done 1008 hrs total time on airframe with 258 hrs on the latest rebuild and all signs are looking good. No oil usage between service intervals and 72 - 76 / 80 at the 1000hr service done 2 weeks ago.

 

Cheers

 

Andrew

G'Day Andrew ,

 

Thanks for that comprehensive reply . You certainly have done some work to it , and good to hear that all appears to be well now . Do you monitor all the cylinders or just the back two ?. My temps on 3 & 4 rarely go above 230 oF which is similar to yours. I have heard about people using that centre hole for temp monitoring and it sounds like a better way than under the spark plug , which is a bit of a pain when checking the plugs and re-torqueing . What do you use to keep the T/C wire in place ? . I spent a month in Bundy last year and had the through bolt nuts replaced . Always intended to check out 'aeroplane beach' but never seemed to get around to it . Will be back this year and will try again . Would'nt like to be there right now though !

 

Bob

 

 

[Ian Burdon]

Hear hear... What Planey said.

[Ian Burdon]

Hear hear... What Planey said.

Thanks for that Wayne. Don't want other pilots to c.t.g. if it can be avoided. Learn from others mistakes. It's far less painful. cheers. Ian.

[MAB123]

Its called pre flight check or did your instructer forget to tell you it is your life in the seat and to check everything thing because the is MURPHY waiting for the time

 

 

[rogerpl88]

No heavy landings this end.Ac has done just over 200hrs and ALWAYS hangared.

What year were these defect rubbers installed and why wern't pilots in Australia as well informed as those in the UK? The procedure you describe would be difficult to perform unless you had another pair of eyes behind the nose wheel to inspect for cracking.

 

The other pilot that I know of had just performed a 100 hourly and had checked this area thoroughly.

 

When he heard of my problem he inspected again and saw some very small cracks. When proded lightly the rubber failed.

 

Where did you find out about the preflight procedure for the nose leg?

 

You seem to be quite knowledgable on this subject. Thanks for the reply Roger. Ian.

Ian, I dont know how to post a picture on this forum but if you send me your email address to [email protected] (re-insert @) I will send you one showing a new rubber that failed soon after it was installed on the aircraft.

 

What year were these defect rubbers installed and why wern't pilots in Australia as well informed as those in the UK? ..........Not sure exactly but must have been around 2007. I cannot say why you are not informed but once the problem was known in the UK the yelllow rubbers were changed for the red type.

 

Where did you find out about the preflight procedure for the nose leg?.........Over time you make your own procedures so that you are know that the aircraft condition is to your satisfaction. Heavy nose wheel landings were a common occurrence when the Jabiru was introduced in the UK. It was due to a combination of poor rigging and pilot technique. As Inspectors, we quickly recognised the signs of a heavy landing with crushed rubber being one of them. For a preflight, I put my foot on the front tyre and pull the nose of the aircraft down - it checks the tyre pressure and also the 'give' in the suspension. After a while, you dont even have to see the rubber - you can feel the amount of 'give'. For the pilots with fairings - you have to make the choice of your aircraft looking good over a proper pre-flight check. Personally, I like to eyeball all critical areas so any fairing that cover these areas are not fitted.

 

Incidentally, the 'foot on the tyre' check can also be done on the main tyres. Gently move the aircraft back and forth by the strut while looking and listening. There should be NO movement where the leg is bolted to the fuselage. If you have a fairing fitted, you should be able to hear the movement.

 

 

[Ian Burdon]

Ian, I dont know how to post a picture on this forum but if you send me your email address to [email protected] (re-insert @) I will send you one showing a new rubber that failed soon after it was installed on the aircraft.What year were these defect rubbers installed and why wern't pilots in Australia as well informed as those in the UK? ..........Not sure exactly but must have been around 2007. I cannot say why you are not informed but once the problem was known in the UK the yelllow rubbers were changed for the red type.

 

Where did you find out about the preflight procedure for the nose leg?.........Over time you make your own procedures so that you are know that the aircraft condition is to your satisfaction. Heavy nose wheel landings were a common occurrence when the Jabiru was introduced in the UK. It was due to a combination of poor rigging and pilot technique. As Inspectors, we quickly recognised the signs of a heavy landing with crushed rubber being one of them. For a preflight, I put my foot on the front tyre and pull the nose of the aircraft down - it checks the tyre pressure and also the 'give' in the suspension. After a while, you dont even have to see the rubber - you can feel the amount of 'give'. For the pilots with fairings - you have to make the choice of your aircraft looking good over a proper pre-flight check. Personally, I like to eyeball all critical areas so any fairing that cover these areas are not fitted.

 

Incidentally, the 'foot on the tyre' check can also be done on the main tyres. Gently move the aircraft back and forth by the strut while looking and listening. There should be NO movement where the leg is bolted to the fuselage. If you have a fairing fitted, you should be able to hear the movement.

Thanks Roger. I have a removable shroud that I made up to stop rats and mice from entering the engine bay via the nose leg (this worked very well during the recent mouse plague). This sits just above the suspension bush so on removal I am looking straight at the suspension. From now on I will be doing the foot on the tyre check as well. Have been doing the main gear check. It seems as if you learn more about your aircraft from these forums than you do from the manufacturer. I would still like to know why Jabiru or RA-Aus have neglected to inform Australian pilots. If they had I would not be sitting at a keyboard writing this!!!!

[JabSP6]

Bob

 

I don't want to change the topic of this thread. I will PM you.

 

Cheers

 

Andrew

 

JabSP6

 

 

[G-OMER]

will check mine at the w/end for sure as they are yellow ones

 

 

[Bruce Tuncks]

Thanks guys for the warning about the yellow bushes. I changed to the new red ones yesterday. The old yellow ones ( replacing the original black ones) showed no signs of cracking and they had been there for 9 years and 1 month, and about 350 hours of flying.

 

I remember when I put the yellow ones on, I cut off one or 2 segments because I thought the deformations required to fit the whole thing were too much, with about 15% deformation being right to have what I reckoned to be the right preload. The new red ones have had the same treatment. I cut off 2 segments and it all feels real tight, if anything I reckon the nose leg doesn't move enough when I load it up.

 

I really like my plane and it hasn't missed a beat for more than 10 years , but I have to say only 400 hours.

 

cheers, Bruce

 

 

[Ian Burdon]

Thanks guys for the warning about the yellow bushes. I changed to the new red ones yesterday. The old yellow ones ( replacing the original black ones) showed no signs of cracking and they had been there for 9 years and 1 month, and about 350 hours of flying.I remember when I put the yellow ones on, I cut off one or 2 segments because I thought the deformations required to fit the whole thing were too much, with about 15% deformation being right to have what I reckoned to be the right preload. The new red ones have had the same treatment. I cut off 2 segments and it all feels real tight, if anything I reckon the nose leg doesn't move enough when I load it up.

I really like my plane and it hasn't missed a beat for more than 10 years , but I have to say only 400 hours.

 

cheers, Bruce

[Jaba-who]

Bruce tunks said

 

"I remember when I put the yellow ones on, I cut off one or 2 segments because I thought the deformations required to fit the whole thing were too much, with about 15% deformation being right to have what I reckoned to be the right preload. The new red ones have had the same treatment. I cut off 2 segments and it all feels real tight, if anything I reckon the nose leg doesn't move enough when I load it up."

 

Excuse my response but that sounds a bizarre thing to do. Jabiru did a huge amount of testing on the bushes which included compression testing to define the amount of compression (and thus the closeness the prop tip gets to the ground when you drop the nose say from a high flare). So when you chop segments off the bush the force needed to compress or extend the wheel height changes.

 

What testing did you use to define that 15% deformation was about right?

 

 

[Ian Burdon]

Thanks guys for the warning about the yellow bushes. I changed to the new red ones yesterday. The old yellow ones ( replacing the original black ones) showed no signs of cracking and they had been there for 9 years and 1 month, and about 350 hours of flying.I remember when I put the yellow ones on, I cut off one or 2 segments because I thought the deformations required to fit the whole thing were too much, with about 15% deformation being right to have what I reckoned to be the right preload. The new red ones have had the same treatment. I cut off 2 segments and it all feels real tight, if anything I reckon the nose leg doesn't move enough when I load it up.

I really like my plane and it hasn't missed a beat for more than 10 years , but I have to say only 400 hours.

 

cheers, Bruce

G,day Bruce, Fitted the new suspension today. Removed two segments and it fitted nice and tight. I think over compression may have caused my yellow rubbers to fail. This may explain why yours showed no signs of cracking. Anyhow hope to be back in the air on Wednesday if all goes to plan. Cheers. Ian.

 

 

[Bruce Tuncks]

Hi Jaba-who, your response was fair and reasonable, so I'll try to explain a bit...

 

My first action with the new red suspension bush was to put it on a threaded rod and tighten the nuts to compress it to the amount required. I had read that if you compress it like this and then put it in a freezer then it will be easy to fit. Well I got nowhere near the required deformation and the forces were enormous and the red donuts were really deformed. So I did the trimming, and my testing (which you rightly question ) has consisted of lifting the nose up and banging it down as hard as I could. I got plenty of squashing on the tyre, but no movement of the red bushes that I could see.

 

Now I've done taxi-tests on tussocky ground, and I reckon its more than stiff enough. I have flown several times since, but I've not tried to land on the nosewheel and I hope to never do that. There would not be a nosewheel aircraft out there where this would be a good idea.

 

Now I have to say that mine is a 19 registered aircraft, so I am the "manufacturer" and therefore more free to do this sort of thing. But surely the right stiffness of the nosewheel can be felt by some bouncing and applying your weight.

 

And while I really like my plane, there is no way that Jabiru could have done a ten-year test to see what the best compression should be. Well Ian and I have a small sample of two on the old yellow bushes, but mine went 9 years with no prop strikes or cracking, and Ian's broke up unexpectedly.

 

So that's my case, but I really appreciate your comments.

 

regards, Bruce

 

 

[Jaba-who]

I do agree - It is hard to question the action when it is followed by 9 years of use without a problem - no matter how compelling the theoretic argument against it. So on that ground I don't have a problem.

 

I have the red version on my experimental class aircraft which I installed myself using a 6 or 7 foot rod as a lever and a couple of pillars that hold up the shed roof as pivot points, so I know what you mean by it being a pretty hard job.

 

I agree that a nose wheel landing would be beyond any nosewheel assembly but was more refering to the times when you flare nose up, maybe a little early, flare, flare flare, onto the mains wheels in fairly nose high attitude then the nose drops. Then you really don't want the bush to compress any more or you get a prop strike. For what was otherwise a non-event (though not pretty) landing and you end up having a bulk strip on the engine. Same for the times when the strip is tussocked or uneven and the nose bounces (either on take off or landing) or if you drop the nose wheel into a small hole while taxying and the drop allows "just that extra" compression and the prop hits.

 

Given that there seems to be no problems with the red ones from this collapsing problem, I would have thought if you were going to put in a red one anyway the safest thing would be the grunt factor and a long pinch bar and use the full red bush.

 

Just my $0.02 worth.

 

 

[Bruce Tuncks]

Hi Jaba-who, are you using a Jabiru noseleg on a different (experimental) aircraft?

 

When I was building my SK kit, I remember thinking that the noseleg was way too strong and heavy, and I wondered about getting an aluminium one made. But then I heard that this was noseleg design number 3 and the previous ones were not strong enough. So the only thing I've done is to use bigger washers on the fibreglass firewall fitting. I did buy the alloy fittings but found that they are not bolt-position compatible to make the change away from the fibreglass fitting easy.

 

I reckon that this fitting and its attachment to the firewall is the vulnerable part of the whole setup.

 

regards, Bruce

 

 

[Jaba-who]

I'm using the jabiru nose leg on a Jabiru 430.

 

Sadly, speaking from experience, i can advise that the weakest point is the upper single tube below the fittings you are concerned about.

 

At least it is the most vulnerable part if you have sideways force on the wheel.