Spacewalker half scale 168" electric

[Andy Boylett]

I have now finished the undercarriage design and will be making it from SS tube, TIG welded together as a faithful copy of the full size. For the wheels I noticed that TNT sell alloy 8" wheels but 2 problems with these. Firstly they are not scale and secondly would cost over $400. Hence now started making my own. I found that on Ebay you can buy a set of 4 8" wheels for just £20.....

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Each wheel weighs 998grams. The hub however is 568grams.

Once taken apart I have got inner tubes and tyres ready for some alloy hubs....

8" tyres

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The alloy hubs will be 2 piece, screwed together with small grub screws. The axels are 15mm SS tube (scale) with 21mm OD bearings. So far I have machined one hub, but not yet parted it into its 2 pieces, so it is curtrently 3mm (parting tool thickness) wider than it will be when finished. I have left it whole for now because I want to drill and tap the small holes first.....

alloy hub 1

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You can just see the flange of the outer hub inside the bore below. that flange will be parted off with the outer half of the hub.

alloy hub 2

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Current weight of the hub is 356grams, but this will be lower when parted off and with the addition of some large holes drilled through the centre.

[Ross Bathie]

Hi there Andy I made my own tyres from laminations of kids crash matt with custom cnc machined hubs very cheap and pretty light.

[Andy Boylett]

Hi Ross,
I like that idea and can probably use on it on another model of mine. This build is staying very scale so has pneumatic tyres with ineertube etc.
Thanks, Andy

[Andy Boylett]

Progress has been a little slow as my back was bad and kept me flat for 5 days, then just as I started to saw a piece of 6" aluminium bar to make another wheel hub, the motor on my 1960's power saw gave in. Hence as well as the 6" bar, you can also see a nice new motor below.....

Power Saw

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Anyway, managed to finish the wheels now. Split rim ally hubs with 20mm od, 15mm id bearings at either end. I was going to add a ring of 5 holes to lighten the hubs further but the total weight assembled, with inner tubes and tyres is only 880grams anyway.....

Wheel

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Wheels

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Today all of the cut wood arrived. This has all been provided by SLEC (Ian Hull) and is fantastically cut. This lot is from 6mm ply, 3mm ply, 6mm Lite ply and 3mm Lite ply. It has been cut using SLEC's CNC miller and is superb. The finish is excellent and accuracy is spot on. Just look at all those little pieces....all I need now is a bigger dinning room so that everything would fit ! Oh, and that is my son Sam's new Eurofighter in the background - it is currently being converted to 12 cell EDF with a 5Kw motor....what else are dining rooms for?

Cut wood 1

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And here is a wing rib (on top of an 8" wheel). The wing will use a main spar that is a built up box the same as its big brother. There will aso be two 50mm wing tubes.

Wing rib

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[John Greenfield]

Nice workmanship but a small question. What is going to tie the joiner tubes to the wing structure. The rear tube seems to be in the middle of nowhere and the front tube does not connect to the wing spar ?

Nice machining on the wheel hubs.

John

[Andy Boylett]

Hi John,
I am new to this size of plane so open to any suggestions. The wing is 3 piece, with the centre section just under 4' span. This is because there is quite a dehidral and I am not able to have the wing tubes travel across the centre line. Hence the large ply dihidral braces you can see in the picture. The front wing phenolic tube is attached to the main spar by a ply doubler alongside the ribs, that butts up against the main spar. These can be seen in the dining room picture "cut wood 1" - if you count 6 ribs in from the right and then go down the doublers are there. Also, lower down on same pic you can see lots of 'circles' in lite ply. these are also doublers that go around the phenolic tubes. Also, in the centre section, the most inner and most outer rib are 6mm ply. The frist rib in outer wing sections is also 6mm ply.

At 50mm I think the front wing tube is strong enough to take all wing loads. The second tube is additional, both for extra stregnth and to make the assembly nice and simple. The idea is that the wings will simpy slide on nicly aligned with the centre section. The rear tube is supported in the centre section just by the inner/outer 6mm ply ribs and circular doublers.

I haven't thought about how to hold the wing panel in place yet so any suggections from anyone most welcome.

Cheers, Andy

[Dave Collis 2296]

Andy, on my 1/2 size, I used a single 2" tube, and held the outer panel to the c/section by using the wing joiners that were originally supplied with the Sig 1/3 scale, ( aluminum blade into a piece of aluminum channel and a couple of small set screws.) This has worked flawlessly for the past seven years. On my new build (1/2 scale Gee Bee "Y") I am using two 1 1/2" tubes and the same wing joiner set up.

Cheers,
Dave.

PS.....sorry for using imperial measurements as that is what I was brought up with, never really did get my head around metric!

[John Greenfield]

Andy

The doublers to tie the tube into the front spar are a good idea but I was more concerned with the rear tube. If you look again at your wing ribs and all the lightening holes that have been cut out you will see that the tube hole has very little wood around it and not very much to transfer the loads to the spars. Even 6mm ply is not that strong as only nominally 1/2 the laminations are running in the correct direction to provide strength. It is a bit late now but it would have been much better to have used a smaller rear tube and not been so adventurous with the lightening holes in the ribs that carry the tube. With a smaller tube you could have set it back closer to the rear spar where load transfer would have been easier.

John

[Andy Boylett]

Thanks John,
The rear tube is not carrying anything like the load of the front one (which could take the whole load on its own). There is more wood than you think around the rear tube as well. I have a spare 1/4 inch ply rib and have just been testing it with a tube through the rear hole and leaning on it while supported at the spar points - it is strong! Also the rear tube has stregnthening around the holes. In the photo I posted you can also see the rings of plywood. these are for further support around the tubes to spread the load and provide lateral stabillity ie stop the rib trying to twist. However, I note your points and just to be sure I will test the structure further when I have built one of the centre sections. If needed it would relatively straight forward to put some more stregnthening in.
Cheers, Andy

[Andy Boylett]

Slow progress, bad back and too much other stuff to do! However, managed to make one elevator now.

Elevator

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That is a mix of ply, lite ply, cyparis, hard balsa and medium balsa....phew.

[Andy Boylett]

And now for something really tricky. I am mounting 2, 7Kw electric motors on a single shaft. I have removed the shaft from one and designed a combined shaft as below. The outrunner casing on the rear motor will be pinned to the shaft using the middle 4 'flats'and 'pin drive'.
I am not used to mounting props with this amount of power turning them so I do not have details of a multi-bolt prop driving system. Has anyone got details they could let me have so I can machine one up to fit the front electric motor? Thanks.

Motor shaft

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[Andy Boylett]

All of the remaining wood for this model arrived from SLEC today. Ian Hull has done a fantastic job supplying all of this. All the different items have been individually labelled as per my cutting list. I will take some photos once a I can walk again - I am on crutches for now after yesterdays knee surgery and it is pretty dodgey trying to get out to my garage in the snow....2 weeks before stitches come out

[Andy Boylett]

So here is the wood, 4 large boxes from SLEC. That's all the remianing wood for the Spacewalker and the Genesis.

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Yesterday i managed 80m on crutches to get across 80m of garden with a foot of snow in it, to my garage. Having got there finished the elevators and stab.....

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[Andy Boylett]

Another long hop to the workshop....and finished the fin and rudder.

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I have also started to make the fuselage join as Phil Clark (my inspector) suggested. This consists of L shaped brackets made from SS shim plate. Each bracket is screwed into the longeron with 8 small screws to spread the load out. The end of each strap then wraps around the fus former at the join point. Four longerons, eight straps, 64 screws. The straps are wider than the longeron (15mm for stregnth) and hence are 'handed' and off-set drilled to suit the 9mm wood.

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Loosly asembled below....

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[Andy Boylett]

At our local club meeting last night Harry Harland said when's this going to be finished, so I am trying harder, hopping across the garden more often!!

I completed the twin motor mount today. This is the most complicated electric motor mount I have made to date. It has 2 motors mounted on a single shaft, but each motor is still mounted using its rear aluminium mount. This menas that the rear motor has to slide in through the front motor mount. Anyway, here it is. I have put in a single motor (the other is in pieces as I took the shaft out). The motor shown is attached to F1 (the firewall in I.C. models) and the mounting woodwork continues through to F2. It is just resting on a couple of blocks to hold the front up......

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This last one is looking in from the top. Anyone noticed the very holey firewall? We have found with large electric models that it is much better to have a forced air-flow from the prop, through the cowling and into the fus for speed controller (and sometimes battery) cooling. We also leave a very non-scale large opening in the underside of the fus near the rear, to let the air out.

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[Andy Boylett]

I also continued with buiding the fus sides, up to the join point. The fus is built in 2 pieces, each about 1.5m long.

Here is a close-up of the fus joiner metalwork attahced to a longeron.

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I have desinged the fus to look excatly like the full size, which is a steel space-frame. The longerons match the steel in the full-size. I have also set up a row of block packers that build-in a complex curve (15mm lower at F1 than the middle and 34mm lower at F6).

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Here is the fus side after the glue dried.

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[DAVE JOHNSON]

Andy---keep hopping to that workshop---a very interesting build DAVE

[Andy Boylett]

Thanks for the encouragement Dave.

Fus front half now together. here it is all jigged up with epoxy drying. The only problem with freezing temp was the epoxy took forever to set!

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And the the next few pics show the top half of the fus being worked and prepped ready for sheeting. I have also made the front pilot hole....must be a tight fit in the full size!!

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The sheeting around the pilot seat is a laminate I make of 3mm balsa with 0.4mm ply attached. It makes a really nice lightweight strong material for large areas.

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[Andy Boylett]

I have just been weighing everything and could do with a little help from those of you that have built big before.

I have weighed everything built so far, all the remianing wood to build the wing and fus and then all the motors, servos, esc's, batteries etc. Total weight 35kg.

However, this does not include the covering. I have calculated 8.5 yards of the 60" wide Diatex 1000. Does anyone have an idea of what weight this will add when doped and painted?

My initial target weight was between 30kg and 45kg (a wide range because I did not have any good idea of what it would be), so it looks like I am somewhere within this range.

Andy

[Dave Collis 2296]

Mine weighed 70 lbs.(32kg). I'm sure I could have made it lighter by 10lbs. Sounds like you're in the ball park weight wise.
I covered mine in Stitts uncertified full scale glider polyester fabric, and auto. paint....(heavy!)

Cheers,

Dave.