As the basic airframe has been completed the next task to tackle was the undercarriage.
The plans show a set of Robart retracts and so I contacted them to find a price. They stated that they had only produced a few sets and would a produce a set for the trivial sum of $4000 (£2500 plus a likely £500 vat at customs) wanting half this up front. Blimey I thought if they can make them so cheaply then perhaps I could make them myself!
So disappearing to the shed and using shedology's main rule to keep it simple, I scoured my workshop for bits. Finding oleos that came from a b17 that crashed 12 years ago ,a set of off the shelf retracts and a vague idea of a plan the work commenced.
I ganged up the 3 retracts , this helped provide the torque to lift the oleo and 4 wheeled bogey and also spread the load of the weight of the model.
The biggest problem was getting the bogey to fit into the nacelle. With the oleo the correct length I couldn't get the bogey to fit, then after a eureka moment I moved the hinge point of the bogey 5 cm and it fits. I've yet to fit a air ram to rotate the bogey, it's being shipped, it will use the the retracts air supply.
Once the retracts were built they were handed to my son for testing, so far so good.
As I'm now waiting for the air rams to be delivered to finish the mains off my attention focused on the front leg. Unlike the mains where at least I had a vague idea of a plan I had no real ideas about the front leg. I originally thought of using two long hobbyking oleos welded together as per the hornet , these have served me well, but I needed a steering mechanism, preferably with a servo directly attached with a push rod.
Working on the mains I had noticed a free set of oleos that had come with a set of the retracts. These were still in their wrapping and after mulling over an idea when out running a new plan was formed. The oleos connected together with a steering mechanism are a perfect fit. Until the model is finished I'm unsure how much weight will be on the front so I may strengthen the bottom leg.
It may not be super scale but the undercarriage goes up, it goes down and it rolls along the ground. At a cost of less than a 10th of what robart wanted it's another victory for shedology.
The main wheels are now finished having fitted the air cylinder that rotates the wheel bogey on retraction. It all works well, the added air cylinder also acts as an extra oleo/shock absorber. I've posted a eight second on video on you tube of it operating-
I've also shown a picture of the four z38's, the engine/firewall/tank/throttle servo are all attached, each engine being a modular unit that slides into the nacelles.
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The idea for the removable engines I stole from Steve Vodrey's B25, with the nacelles so slim it made sense on the bear.
The retract system is fully installed, it has two systems one front,one mains, thus no joiners so the system can be activated when the model is apart.
The sharp eyed amongst you may have noticed the unscale split in the rudder. For redundancy two receivers are fitted, so it makes sense to me to have redundancy with the rudder as well.
I thing we will have to lengthen the runway Karl . Her are some pics of the field after mowing yesterday and a pic of our old field, shame after all the work john has put into it over the years. Can't make it today, have a good day flying.
Unable to make the field today as the van is being repaired, however I don't think the bear will have any problems, she should be a floater. The field is looking great we just need to covertly trim the trees on the west side.
As the pictures show I've managed to balance the bear today.
I used a 20mm metal bar held in position by tabs on the c of g, then balanced this on my wooden triangle through the bomb bay. Amazingly it was nose heavy, requiring a pound of lead in the tail.
I don't have much experience with swept wings and just hope the marked c of g is correct, the two Don Smith plans I've done so far have been cock on.
The model is complete, final inspection then test flights.
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Having balanced the bear I finished off the wooden cowls and started the engines. She sounds awesome. I just have to finish off the hatch covers.
After finishing the model the next step was to work out how to move it. After flirting with the idea of a giant roofbox for the centre section ( just too heavy) then deciding on a trailer (poo -poo'd by Mrs m after requiring half the garden to park it) I discovered I'm able to squeeze it in the rear of my T5, I can't close the rear doors fully however I can cope with this.
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