Spacewalker half scale 168" electric

[Andy Boylett]

Ask Phil Clark to show you the S/Steel plate joiner system, much lighter and they put the loads and stresses back where they belong, i.e. on the spars.

Mark, thanks for the comments. I am sure we are both understanding it, just takes a a while to write in words. ....your "Forth Bridge" comment just happens be pretty much what my inspector (Phil) said. .....It isn't going to break! However, I would like to be able to do one lighter next time.

The German wing tubes I have (from Phil ) look absolutley superb - nice gold anodising. I haven't seen the other joiner type you ahve mentioned, they sound interesting, I'll ask Phil.

Cheers, Andy

[Andy Boylett]

As I am just an ordinary mortal, with ordinary concepts, I am totally bewildered as to why someone would deliberately weaken what is possibly the most important structural part of an aircraft in order to save an absolutely ignsignificant
amount of weight which would not make a hap'orth of difference to the wing loading on an aircraft of this size, but a very significant difference to the strength of the structure. I am referring of course to the wing joiner/main spar, call it what you will, and also the wing ribs which look to have had an awful amount of material removed. Please enlighten me someone.

Tony,
sorry if some of the stuff got very technical. If anyone is interested in checking out their designs I am happy to help with calcs. There is an excellent engineers site that lists most of the formulae that we use (as we cant remember them all )... http://www.engineersedge.com/beam_calc_menu.shtml ......the only problem is that you really need to understand the stress patterns in oorder to assess a design and decied how to go about applying the appropriate formula - this is where the engineering training comes in and you need to ask an engineer (aeronautic, structural, or mechanical engineer etc)....there are quite a few in the LMA.

I would still find it more useful to have a library of wing spar designs successfully used in large models. They would just need span, model weight and wing shape to be able to use them in other designs.
Regards, Andy

[Andy Boylett]

I have now made the ailerons for the left wing. I am using 2 receivers,with one controling one half of each aileron. Hence the aileron is split into 2 parts that will move in unison using 2 different servos. I am thinking of possibly even coving over the small gap in the finished model, once the servos have been synchronised.

Here is the inside of the aileron....

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There are wood blocks set in for the hinges and a small cyparis spar...

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And the finished aileron...

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[Andy Boylett]

And now for the hinges and servo mountings. I have made up 12 hinge mounting blocks that need trimming into a curve to fit the aileron edge..

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And here they are with 6 of them fitted to the left wing panel - the dowel is what I use to make sure they are all lined up...

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The servos are supplied by HobbyKing and are Turnigy, high voltage, titanium geared and 33Kg torque - so pack quite a punch. I do not like mounting these with screws into wood and prefer to bolt them. Proprietry mountings can be bought, but I prefer to make some up myself from 40mm x 10mm aluminium angle from B&Q...

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[Andy Boylett]

Having made the servo holders I have now fitted them to the wing...

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Where the outer wing panel joins to the centre section I like to create a small box to hold the servo wires, trianngular in this case. You can alos see the paper tube running from the servos to the box...

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[Andy Boylett]

Now I have added the concave piece of wood that makes up the wing side of the aileron hinge line. This took every peg off the washing line....

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I have also been doing the wing sheeting on one side of the panel. On one of these threads somewhere I read a post by Phil Clarke that suggests joining together sheeting flat on the bench before applying to the wing. It works well and here is a VERY big sheet of balsa, some 5 feet long!!!

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And here it is being persuaded to stay glued to the wing...

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[Andy Boylett]

Next is the wing retaining brackets. These are copied off photos of one Phil Clarke sent me...

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Next I have started on the wing tips. These are 26 inches wide and I was thinking of making them in glassfibre. To do this I would have to make a foam tip, them fill and sand it, then make a mould, then use the mould to make the tip. Then, as both tips are different, I would have to do the whole thing again. So, I have decided to make them in balsa.

I drew some profiles in Autocad and used these to make up this...

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Then, lots of sheeting, lots of carving and I got to this...

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Which looks pretty good on the end of the wing...

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[Dave Parry]

Hi Andy, motoring on very nicely, do you ever go to bed.

Have you abandoned your Genesis, I was just thinking it would be a nice article in the Journal, don’t think we have had a electric trainer done before, if we have I am sure someone will let me know, so how about it then, are you up for it.

[Andy Boylett]

Thanks Dave - I have a bad back and cant sleep much so do stuff when ever I can!! Sometimes I have to lie flat for days, other times I have to keep moving .

I have had my son Sam doing some of the Genesis build and with Christmas, exams, skiiing and whatever else teenagers do he has not been doing much. We will get back to it soon and are hoping to have it done for East Kirkby. So yes, we would be up for an article on it...in fact the covering I ordered has just arrived this morning, so now we need to get the structure done

I just need to get that Spacewalker thing off the bench now....

Cheers, Andy

[Andy Boylett]

Finished wing tips....

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And now cant even see the Genesis. It is in there somewhere....

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[Andy Boylett]

Undercarriage

I have made the undercarriage identical to the full size. All the parts below are made from the full size drawings reduced down. I use wallpaper paste to stick things to metal because adding a little water later makes it fall off easilly:

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After some time I had this lot cut out of sheet stainless steel...

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I found these sheet metal hole cutters/punches on Ebay and have bought the sizes I needed to custom make exactly the right sized 'washers' for the various parts of this construction:

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After teaching myself how to silver solder and how to cut different sized metal tubes so that they come together with no gaps, I arrived at completed undercarriage:

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[Andy Boylett]

Here are some more pictures of the undercarriage. It has not been cleaned up yet and have I not got the springs or the coreect length of bolts(on order). It is all set up temporarilly on a piece of wood. If you look carefully you can see the end brackets for the 2 springs that are not there at the moment:

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One of the attachment brackets. Each of the pivot points is just like the full size and has a bush inside the fixed tube of the 'legs'...these have a 3mm bolt inside a 4mm ss tube with .5mm wall, that acts as the bush and this is then inside a 5mm ss tube with .5mm wall that is fixed to the struts:

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And a wheel installed on its two 15mm ID bearings. Note I have now shaved the tread off the original cheap sack truck tyres:

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[Andy Boylett]

Back to completing the woodwork now....

I have made the wing centre section removable and it is mounted using 'hook over' brackets at the front and 8mm nylon bolts at the rear. This is the bracketry on the inside of the fuselage:

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There are 3 holes in the bracketry above, one either side and a double one in the middle. These holes fit perfectly the woodwork on the wing - there are 4 brackets, each assembled over the fron wing tube:

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And here is the wing slotted into its front supports:

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At the rear of the wing I now need to just add bolts through the in-built ply parts:

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Here is the fus stood on its nose on the bench, with the wing centre section now snuggly fitted:

[Andy Boylett]

Someone asked me about the mountings at the rear of the wing centre section. These are attached with small ply plates slotted in between the rear spars:

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[Andy Boylett]

In-Line Twin Motor

I have now completed making te extra long shaft for my in-line twin electric motor. This shaft allows me to assemble two 7Kw motors into a single unit but also allows me to use 2 seperate speed controllers. The shaft is quite complicated as it has to have the 2 groves for circlips and 8 flats for the drive areas.

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The reason I am running 2 seperate 7Kw motors on a single shaft is so that I can use 2 seperate speed controllers, one for each. By doing this I can double up on current without getting excessive, keeping cable sizes smaller and lossess lower. So I will be running 280amps continuous and peak up to 400amps. This is however split into 2 lots of 140amps continuous and 200amps peak. I am using esc's capable of 200amp continuous. Using 12 cell LiPo at 50 volts full charge gives 50x140=7000watts continuous and 50x200=10,000watts peak....alll of course doubled up to give 14,000watts (18.7hp) continuous and 20,000watts (26.7hp) peak.

Here they are now set up with the esc's all wired up and connected:

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I have only connected one 'bank' of batteries for the purpose of testing - that is 12 cell 5amp.hour.

There is no prop driver yet as I need to machine one up, much bigger than the one supplied with a single motor. I have ordered the 54mm diamter aluminum bar needed for this and am waiting for it to arrive.

My plane is sponsored by HobbyKing as it will be one of the largest single prop electric planes world-wide. I have just received the HobbyKing Turnigy batteries - all 24 of them! So I know have 12 cell 30amp.hour or 12 cell 15a.hr for each motor. Since each motor also runs on 3 banks of batteries, each bank of batteries only has to supply 1/3 of the current, which will be 46amps continuous or 66amps peak. I already run these batteries on planes that take over 100amps continuous so I know these will be fine.

[Andy Boylett]

Today's bulding.....making a blue foam cowl ready for galssing. That is one big block of foam:

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[Andy Boylett]

The alumiium bar I ordered for making a prop adapter has arrived and I have spent ages machining it. Because I am putting 2 lots of motor power through one prop drive this needs to be much stronger than the original. Also, electric motors can exert much, much more torque than an ic engine and it is very easy to damage prop drives.

#### Technical note. Whereas an ic motor torque drops off with lower revs, the opposite happens for electric and the torque is maximum when at zero rpm. This is one of the reasons why an electric plane is so dangerous when the prop is not turning but the motor is 'armed'. As the prop starts to turn there is maximum torques and a hand in the way will not stop it. #####

My prop adapter is one complicated little beast. There are lots of fixings involved:
- The 6 bolt fixing for the prop.
- It is attached to the front of the front motor casing with 4 bolts. This takes the drive power from the front motor. These bolts are accessed through enlarged holes in the prop drive plate.
- There are studs down onto flats on the shaft. This helps to transfer the power from the rear motor through to the prop drive.

Here are 2 photos of the finished adapter...

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And here it is attached to the complete power unit..

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[DAVE JOHNSON]

Andy---this is looking superb,can we twist your arm to bring it to display at the Spring Seminar??

[Andy Boylett]

Andy---this is looking superb,can we twist your arm to bring it to display at the Spring Seminar??

Dave, yes I could. Sam is going to be with me for the seminar so he can help me with moving it. Now I just have the challenge of getting it more finished

[Andy Boylett]

Well I always knew that lining up my 2 motor mounts was going to be tricky, but this has been VERY tricky. I know that it can be done because a guy in the USA has put 3 of these motors on a single shaft to drive a go-kart. The only problem is that he has been able to accept an amount of vibration, whereas I cant.

I have had the front half of my fuselage sat vertically so that the motors are vertical and there is no induced bending of the shaft. Because there are 2 sets of ball-races in each motor it means that there is a significant ability to 'flex' one mount relative to the other as the play in the bearings allows it. The problem is that I needed to end up with both motor mounts tightly held, but with all 8 bolts and mounting points perfectly alligned. I put a clock gauge on the side of the prop mount and when I first did both mounts up there was 0.120mm (48 thou) run-out. This was sufficient vibration that when I turned on just one motor the fuselage leapt off the bench !!

Over the last 3 days I have had something like 25 assemblies and then taking apart again . Each time I managed to get the shaft a little straighter. Having finally got perfect allignment I then found that if I needed a slight axial differential in the mounts so that as I tightened the mounts they 'unloaded' the motor bearings a little. I did this by putting an additional 5 thou shim under each of the front mounts....see photo below....

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So here it is all assembled..

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You can see I have mounted the 2 speed controllers either side of the motor mounting box. They are mounted on ss mounting legs so they are held clear of the structure with no stress on the circuit board and really good air-flow around them. It all uses swg8 wiring. Here is another view -that shows all those shims under the motor mount!!.

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I have also drilled and balanced the trial prop I have. This is smaller than I need at 30" but is the largest that HobbyKing do. Does anyone have any experience of how good balance needs to be at these diameters? I have got this one balanced to within "2 small pieces of paper" - you can see them on the right side of the prop.

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