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Simon Bennett / DC12-44H | |
| Douglas DC12-44H Aviation Tractor Introduction I’m conscious that I may have a reputation for talking the talk but not creating the creation, well... This MOC came about in response to a number of challenges, both overt and self-imposed, in .technic and .modelteam. Steve Lane revealed his Rotinoff and made a towing challenge and I posted to the effect that I enjoyed looking at other’s MOCs but couldn’t produce anything like the quality of Dennis Bosman or Jennifer Clark’s stuff. I decided to take up Steve’s gauntlet and I thought a good place to start would be with a vehicle that is used to pull serious tonnage in real life. Now I like unusual vehicles (which is why my car is 30 years old) and one of the most specialised classes of vehicles is airport ground support so I decided on one of the weird flat trucks used to tow planes. Just at the time I made the decision I happened to take a flight to Edinburgh from Luton where you have to cross the tarmac to board and I got close enough to the ground support vehicles to discover they were all made by a company called Douglas. So I sought them out with Google and was surprised to find that they are based in Cheltenham. Since Douglas are so close I wrote to them asking for information on their range and they were good enough to reply. 
The letter from Douglas – which model to model? Stephen Cohen, Douglas’ sales manager, wrote back enclosing specification sheets with various photographs of their Aviation Tractors (which is what an airport tug truck is called). This revealed one very interesting feature of their DC12 range: the entire cab lifts by 610mm on hydraulics to enable the driver to see out of the rear. (It is also possible to specify a version with two cabs but since these seem to be rare I decided not to model one of those.) I thought this could lend itself to being done with pneumatics which would up the ‘technic-ness’ of the MOC, which was nice. 
As the DC12 is the biggest of their standard tractors (they also have a range of ‘Towbarless’ ones which lock onto the wheel of the plane, without lifting it which are really weird but less well-recognised so maybe another time...) it was obviously the one to do. 
Another cool feature is that the Tractors have four wheel steering which can be set to ‘front wheel’, ‘four wheel’ or ‘crab’. In order to model this in a powered MOC I therefore needed to use either the 8880 or 8465 steering elements. Preparation My first decision was the scale for the MOC. The best visual match for the wheels was those from the 8880 so they dictated the scale. I photocopied the spec sheet drawings of the tractor, enlarging them so the wheels matched the 8880 wheels. These drawings fitted onto two sheets of A3 so I stuck them together and used them as templates for the MOC. The 8880 steering/drive elements when combined have a set minimum width equivalent to 24 studs. This caused me to have to apply a tiny bit of selective compression which resulted in a MOC 58 studs long by 24 studs wide by 9 bricks high (round about an 8880 wheel plus a brick). General Views 
Building Took forever, or so it seemed. The cab had to be completely broken down and restarted many times: to get the angles as right as possible, to sort out the windows and many failed attempts at fitting the pneumatics. Part of the delay was due to not having the parts and the LLW Red Letter Day came in really rather handy there. Significant problems came when I finally put the built up chassis on a flat surface, the significant overhang of the cab at the front and the relative weakness of the grey suspension elements meant that the front of the model grounded. Rebuilding the suspension (Grrr, had to more or less take the whole thing apart to do this) with the stronger yellow pistons from the Silver Champion solved this problem. 
Unfortunately due to the need to use the new differential I had to cut down two crown gears to drive them. 
Parts used Element suppliers to the project, apart from my 8880, my parted out collection and a blue tub were:
Crisis – Technic Compo or Modelteam? It gradually became clear that if the MOC was a close representation of the DC12 it would never haul enough to be a contender. As Stephen Cohen had said that Douglas would be interested in seeing pictures of the finished MOC I didn’t wish to disappoint them so I decided that I would build it as a decent modelteam style MOC. On completion it has turned out to be a bit of a disappointment, it’s so heavy that it needs a push to overcome its inertia, I tried all the different types of motor and the 9v geared ones are best but still can’t quite move it. I have decided to post it up anyway and see if anyone has any advice on how to improve performance, I suspect removing the dual-differential would help as a lot of torque is probably lost driving such a long geartrain. I intend to rebuild it but I just can’t yet face tearing it all down once more. Features Drive: The MOC is driven by two 9v geared motors through a dual differential. A model V6 engine is also driven. 
Transmission: There is no transmission because I decided that I didn’t want to have to keep visiting the MOC to change gear. One day I’ll come up with a motorised transmission (I know Steve Lane already has) but I doubt I’ll modify this MOC to include it. Steering: A separate micromotor drives the steering of each axle as that’s the simplest way of achieving all the different steering possibilities. As there were only four studs of width between the rods which connect to the ball joints they had to be underslung below the rack, I also had to build a little tongue to enable the rack to slide in a slot left in the box around the differentials. 
Suspension: The rear uses the blue double wishbones from the 8880 and the original small grey pistons, the front is identical except the stronger yellow pistons from the 8458 Silver Champion are used. 
Pneumatics: The cab lifts by 10mm on two small pneumatic cylinders, slightly less than it ought to for the scale but I couldn’t get a longer throw as there is not enough space for a large cylinder. The cylinders are fed by a compressor running off a 9v geared motor. A switch hidden behind one of the access panels changes the direction of the cab movement. 
Music While building this MOC I listened to Tubular Bells II, particularly ‘The Bell’; Tribute for the Masses, the Depeche Mode covers album; Tori Amos’ Strange Little Girls and Under Rug Swept by Alanis Morrisette. Improvements Obviously the power issue needs sorting. There are a few bricks I couldn’t get hold of. I balked at buying an Island Hopper just to get four red wedges and I still need two white 1x4x3 train windows and the trans yellow 2x2 plate and tile for the warning light. Once money allows I will be buying one of John Barnes’ RC units since the four separate motorised features of the MOC are a perfect match for the four outputs of the RC unit. Other Views 
Special thanks go to Tom Pitt-Chambers for taking the photos and assisting with putting this page together. |
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