Rear suspension bolts on SK & SP

[hfrensch]

I assume everybody knows about the Jabiru recommendation to upgrade the bolt size from 5/16" to 3/8" on the early Jabiru SK & SP models. I heard about it early last year but was slow to react due to what I thought were logical reasons.

 

When I heard about the bolt size upgrade I removed the rear bolts on my SP 6cyl which had 95 hours on the airframe and inspected them. They were straight and had no stress marks. I also buildt a SK Jab (2nd Jab kit sold) completed May 97, which is now owned by brother . This aircraft had 1500hours on the airframe all with the 5/16" bolts. With this information I decided not to change the bolts. WRONG!!!

 

Late last year I decided to fly to a friends place for some socialising, as he has his own strip and works from home repairing aircraft. When I was in the circuit at his place I noticed the hanger open people and other aircraft. With the wind direction it meant I would be landing in front of and near the hanger, so I thought I better make this a good landing as fellow aviators like to judge and make comments.

 

My landing was a greaser and my friend commented to the other people "thats how you land a Jabiru". After the wheels touched I heard a crack as if a krock had hit the left hand wheel spat. As the plane slowed down I noticed the left hand wing slowly getting lower and just before the plane stopped the wing touched the ground. I immediately knew what had happened, the suspension bolt had brocken.

 

Because the leg was bent right back I had to climb out of the right hand side not easy for a fat old block, especially when it could have been avoided if I had upgraded the bolts.

 

The damage to the aircraft was minimal. A 2" scratch on the left hand wing tip, small scratch on the underside of the elevator, demolished wheel spat and brocken/bent suspension bolts.

 

We lifted the wing on to the roof af a station wagon my friend had some new bolts which we fitted. With the help of my Level 2 friend we thoroughly inspected the Aircraft but found nothing wrong structurally wrong.

 

I threw all the brocken fibre glass bits in the back had a coup of coffee and flew home . The following week I ordered 2 sets of 3/8" bolts from Jabiru and replaced the bolts in my brothers SK as well.

 

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[Yenn]

A friend of mine just replaced the bolts in his Jab and found that the bolts were OK but there was some elongation to the holes.

 

I didn't see it so cannot give any more info than that.

 

 

[Ross]

Hi hfrensch

 

My J160 is yet to fly.

 

I changed my bolts in my J160 #14 kit from 5/16" to 3/8" which was flagged as an optional mod and "only done by Jabiru on the J160 by the factory to try to increase the common spares over their model range".

 

Paul Middleton even wrote a piece on it in the magazine before the recommendation came out explaining that at that time the UC and the seat belts shared the same bolts which would not do you much good if the bolts did not fail in a crash.

 

So as Paul pointed out the seat belts were on the same bolt as the UC so it was designed to fail in a crash.

 

So if you put in 3/8" bolts for the UC which could tear a hole in the cabin floor in a crash the seat belt anchor need to be moved away from the UC bolts otherwise your lower half could be dragged through the botton of the cabin near the seat together with the UC in the case of a crash that removed the landing gear.

 

Hence the modified arrangement of the seat belt anchors that was eventually put out by Jabiru to go with the larger UC bolts.

 

My kit for the J160 came with or I was eventually sent the extra pieces necessary to mount the seat belt anchor bolts on separate bolts away from the UC mounting bolts. It caused me some confusion at the time because of the many changes done in the early J160 kits. So I had mods to do while building the kit.

 

I think it would be sensible to do regular checks of the UC system to make sure that there is not excessive play in the system otherwise shock loads will be magnified increasing stress on the components the fibreglass and the bolts. This would involve removing the cover plate below the UC to get access to the bolts but might also involve adding extra washers under the nuts inside the cabin behind and under the back of the seats. This area is fairly difficult to access once you have installed the windows in a J160. I don't know about other models.

 

The same kind of remarks apply to a number of the oil pump modifications for the early 4 cylinder motors including mine but mandatory for early 6 cylinder motors I think because the failing of older style oil coolers.

 

I think it would be prudent to do the oil pump changes as well but the original oil cooler was made of aluminium which in my opinion would probably not like multi-millions of rapid reversing loads from the oil pump no matter how small. I don't know what the later model oil cooler that I was supplied with in the kit is made of but it is a different colour.

 

I know of at least one early J400 series that without warning except for not being able to see through the windscreen lost its oil on the way to Natfly a few years ago about the time the first J160 kits were being ordered. Much of the oil ended up across the wind shield.

 

They did a dead stick landing in a paddock, disconnected the oil cooler, filled up with diesel engine oil from a local farm and flew it a very few miles to an airfield with a rapidly rising oil temp and waited there for another oil cooler. They arrived a day late. I think on his way home his manifold bolts came loose or maybe that was another trip but the same plane.

 

Regards

 

 

[hfrensch]

Hi Ross, The suspension bolts on the SK&SP I Buildt are not used to locate the seat belts. The bolts I changed on the SK after 1500+ hours and over 2000 landings had bent bolts on rear of each leg.

 

The oil pump rework is a must on the 6cyl as my freind had a oil cooler split on his SP on the way to narramine 2 years ago. The rework does drop the oil pressure a bit but stops the extreem pulsing. I have not reworked my brothers 2200 and this engine has now done 1000 hours and is about ready for a top end overhaul.

 

I am sure when you get your J160 flying you will get an imense amount of pleasure from flying it as I have from my Jabiru's over the past 10 years.

 

Cheers Helmut.