Climbing Out of the Huon: How Kenworth’s T909 and AIR-CTI Keep Loggers Moving

When fully loaded B-doubles crawl out of Tasmania’s unforgiving Southern Forests, every ounce of traction counts. We sent Roadtrains.com.au’s Technical Editor, Howard Shanks, deep into the Huon Valley to ride shotgun with veteran logger Peter Madden and discover how AIR-CTI’s central tyre inflation system (CTI) is helping loggers conquer steep inclines, save tyres, and keep the wheels of one of Australia’s most demanding industries turning.

The Derwent River glistened in the mid-morning sun as Muskett’s Kenworth T909 wound its way up the southern outlet out of Hobart. It was a brilliant day in Tasmania, even the chilling winds had subsided. The smooth run on the bitumen would take us as far as Huonville, roughly 40 kilometres away. From here, we’d head right, where the narrow bitumen quickly gives way to a well-used gravel road that winds its way up into the mountains.

Peter has lived in the area all his life and has been logging for most of it. This is his second Kenworth, and with a little over 12 months bush work under its belt, Peter admits he’s more than happy with the T909’s performance, ride and reliability.

The heart of this Kenworth T909 is a Cummins ‘Signature’ rated at 580 horsepower coupled to an Eaton (2050lb) 18-speed transmission that drives Meritor RT46-160 with full DCDL rear axles riding on a Kenworth Air-Glide 460 rear suspension.

“The B-Double trailer set is a locally made Elphinstone Easy Loader that comes standard with easy weigh scales and automatic strap tensioners,” Peter explained. “It takes roughly 90 seconds to unload the back trailer at the log landing and stretch it out.

Inside the cabin, the ride was smooth and quiet with only the gentle hum of the Cummins out under the hood audible, which made for pleasant conversation.

Peter’s local knowledge is one of pride that encompasses his community, his job and its sustainability. He told us that logging in the Huon area commenced as early as the 1800s, along with whaling, where the workers would set up temporary camps.

Now well up into the mountains, deep corrugations in the road below were really putting the Airliner suspension to work. Apart from the occasional rattle from the trailers on the back, there was nothing inside the cab to suggest the road had deteriorated.

Air-glide 460

The Air-glide 460 was certainly getting a workout.  These Air-Glide 460 suspensions utilise a unique, compact parallelogram geometry that maintains constant axle alignment, driveline angle and tyre contact as the road surface changes – even during extreme cross-articulation – like this run today.

Kenworth claims that these unique characteristics of their Air-glide 460 improve traction, add roll resistance, stability, and ride comfort while significantly reducing stress on universal joints, linkages, and driveline components. They also assert that they contain substantially fewer parts for increased reliability, and they are virtually maintenance-free, with no periodic adjustments or lubrication required.

“It is really well put together, truck,” Peter volunteered. “I’ve been impressed with its overall performance, and so far I haven’t had any problems with any of it, including the engine, which I cannot fault either.”

The ride inside the Kenworth T909 was exceptional. Peter noted that the handling of this truck is the best he’s ever had. Observing his steady hand on the wheel from the rider’s seat and the seemingly effortless ease with which Peter guided the T909 around the winding track, its road manners were equally impressive.

Around another corner, and the countryside changed once more; tall trees lined either side of the road. “They’re what they call swamp gums”, Peter enlightened. “They are one of the softer hardwoods and are mostly used for producing veneer panelling.”

“You can see here in this clearing where they have logged this small coupe and are ready to replant it,” Peter explained, pointing out the windscreen a few corners further on. “The next logging coupe is left for several years, which leaves habitat for the animals and from a scenic point of view, the mountainside isn’t barren. A little further down the track, you’ll see where timber was harvested five or so years ago, and then, around a bit further, there is a patch that was harvested ten years ago. As you can see, it only takes a few years of growth, and it is very hard to tell where the harvesting has taken place.”

Fast-Growing Eucalypt Trees

The gums planted here are fast-growing eucalypt trees developed by forestry specifically for the industry. It is not a scene of destruction but a renewable resource we have here,” Peter emphasised.

Like many loggers in the area, Peter gets a little annoyed when reports mislead the community about how logging is destroying the forests. He also has little time for small-minded, misinformed individuals who block logging coupes and vandalise machinery, claiming everything as the last tall stand of timber.

“This is the third time this area has been logged,” Peter pointed out. “There has been a real evolution in the way timber is harvested and forests managed over the last four to five decades. You can walk around some parts of the coupe and see this evolution from the old tall stumps where the fellers would cut the shoe holes for their planks to the shorter stumps cut with the chainsaw.

“Some of them can’t see the wood for the trees,” Peter mused, referring to the extremist minority.

A call on the UHF radio broke the conversation. It was the bush crew checking his arrival time. “I’ll start heading down to the landing,” came the reply after Peter informed them of his position. “Just coming in around spur three”. Sure enough, around a few more corners, dust rose from the ridge as the excavator made its way down to the large stacks of logs neatly sorted on the side of the bank.

Peter eased off the throttle and nosed the Kenworth T909 into a small clearing, waited for the dust to clear, then selected reverse and backed alongside the log stacks. There were a couple of chains on the Elphoinstone Easy Loader that needed to be undone; then it slowly rolled off. Peter selected low, eased out the clutch and stretched out the trailers.

Elphinstone Onboard Scales

There was time for a quick chat with the excavator driver, then the machine’s large arm with its mechanical beak began clasping logs and gently placing them between the poles of the trailer. Like most log trucks down this way, Peter’s truck is fitted with Elphinstone onboard scales, and the truck can be loaded accurately to the maximum weight.

Interestingly enough, how accurately they load the logs is crucial, as the load is nearing completion. Peter monitors his handheld readout and signals the excavator driver on how much weight is over each axle group. The excavator driver can then move the log either forward or backward to achieve the correct axle grouping. The loading time is approximately half an hour from when the truck arrives till it is chained up and ready to leave.

Peter admits that the logging industry is very good, although he notes it can be tough at times.

A whoosh of air exhausting from the spring parking brakes signalled it was time to leave, then as the big bore Cummins under the hood bit hard and the tyres gnawed through the dust searching for traction in the soft powdery dirt track, Lester, his Kenworth T909 and 40 tonne of logs slowly moved out of the landing.

A few kilometres from the landing, there is a steep climb, so steep in fact that two concrete strips have been laid to help the trucks maintain traction on the climb. However, Peter freely admits that without the AIT-CTI, they would not be able to get out. “Only trucks fitted with the AIR-CTI cart out of here,” Peter says.

It would be another four hours before Peter would reach the mill, a journey that would take him right to the heart of Hobart and up the middle of the state, but that’s another story.

AIR CTI – How it works.

Kevin Muskett from Muskett’s Transport told us that a fully laden log truck, tandem drive, on the highway needs 92 psi only in its drive tyres. “This is actually the required hot tyre pressure,” Kevin explained. “This would relate to an 80-psi cold pressure, which is exactly what Michelin, and most other tyre manufacturers recommend, for 16.5 tonne on eight 11R22.5 tyres that you will see on the Muskett log truck.”

“On gravel roads, this loaded truck should run 60 psi,” he said. “In really poor traction areas, he can drop to 30 psi for maximum traction, inflating back to 60 once the road improves.”

An empty prime mover with Elphinstone Easy Load trailers towed behind only requires 40 psi on the highway.  The eight tyres will support a maximum of six or seven tonnes.  On the empty run back to the log landing, the driver would drop his tyre pressure to 30 psi on the gravel.

“To get a reasonable idea of optimum tyre pressures on the highways, look at the flat spot on the steer tyres where they meet the road,” Kevin explained.  “That flat spot should be six or seven inches long, 150 to 190mm long.  Then look at the drive tyres.  What length is the flat spot where the tyre meets the road? Is it similar, or is it totally round?  It should be identical for highway work. This provides the best traction, ride, tyre life, and safety.

“If anyone argues, just point back to the front tyres,” Kevin smiled.

“Sure, we get so many comments from people who say you can’t run pressures that low. But do the math, an empty semi-trailer on 12 wheels may only be supporting four tonnes or less per tyre. Conversely, an empty tandem drive prime mover will have four tonnes on eight tyres.  Consider the family Falcon car with two passengers for a moment; it weighs two tonnes on four tyres. It’s the same load, but you don’t run 100 psi in your Falcon tyres…”

Howard Shanks is one of Australia’s most respected transport journalists and photographers, renowned for his in-depth features and technical insights into heavy vehicles and road transport. This story was first published on www.roadtrains.com.au on 16 October 2016.