Spacewalker half scale 168" electric

[Andy Boylett]

I have been working on this project for a few months now and am just about to start building - the design is 95% complete, just the landing gear to do.

My 1/4 scale electric Spacewalker 2 was flying in 4 of the LMA shows this year (my son Sam was flying it). We like it so much we have decided to build a half scale one.

The full size is currently built by Serenity Aviation (http://serenityaviation.com/home/) and supplied as a kit.....so if anyone fancies building a full scale we will have the full set! Serenity were very helpful and sent me their drawings so I could get the scale spot on. The full size drawings were my starting point and once I had loaded them into autocad it took 10 seconds to scale them and then start desinging.

Myself and Sam have been flying electric for 2 years now and have been using LiPo's from the start. We have developed loads of experience with them and fly everything from indoor 1 cell to 12 cell 4.5Kw aerobatics. We eventually homed in Turnigy equipment as being one of the best made money can buy. Now I know there are lots of stories from people who can tell you they had a "such and such" and it was rubbish, but usually we find when we ask for full design/operating details the reason something was "rubbish" was because the owner broke it. There is quite alearning curve and most users new to elec will have failures as they abuse various items.

Siince we use Turnigy pretty much exclusively now, I started discussions about this plane with HobbyKing many months ago to see whether they would be interested in sponsoring an electric 38" single prop plane. Yes was the answer, so I now I can design around using 12cell Turnigy batteries.

I'll put design specs and drawings on when I can work out how to do photos.

[Dave Parry]

When you post, you will find under the Save, Preview and Submit buttons two tags Options and Upload attachments

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Click on the Upload attachments tab and add your picture the max size is 600x400

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then just click on Place inline, job done.

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Hope this help you on your way with your posting.

[Andy Boylett]

Here is the design data:

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[Andy Boylett]

Now that I have fully designed the model in autocad I have prepared all the shete materials ready for laser cutting. Ian Hull at SLEC is providing all th ewood and doing the laser cutting for me. After a quick lesson from him in how to format the drawings so that his laser cutter will work with them I have got them sorted. Here are a couple of examples:

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Spacewalker 2-Drg 3.jpg (25.81 KiB) Viewed 28125 times

[Dave Collis 2296]

Hi Andy.
I have been flying a 1/2 scale Spacewalker 1 for 7 yrs. now. 156" span weighs 70lbs. 3W 200.
I have just returned fron Monsterplanes USA in Florida, a seven day trip each way for me! There are a couple of photos on RC Universe, in the "warbirds" forum under "Monsterplanes"
This is a great aircraft to fly, so easy and forgiving. Can't wait to see some pictures.

Cheers,
Dave.

[Andy Boylett]

Thanks Dave, did you build it? I would be interested in some of the desing details as I have started from scratch and have never built a half scale before!

[Andy Boylett]

While waiting for wood and glue to arrive I have been looking at linkages and hinges. My over 20kg inspector says commercial hinges are not up to the job so I need to do them some other way. I can see a few photos here and there on this forum of different ways people have been making hinges. Which is the best way? Let me know please.

This is what I have made as a trial for the hinges on this plane. I will not have access from the wing end to slot a rod in and I am also planning to do the ailerons as 2 completely seperate surfaces on each wing ie 4 of them, so I can nicely split the control between receivers. The following is a Protech 3mm heavy duty clevis, which slots perfectly into 6mm (0.5mm wall) brass tube, which will then be glued into the wing hinge mounting blocks. The control surface side is a piece of 3mm aluminium plate with a 6mm sealed bearing fitted. This will be glued in place and 'pegged' through the end. The hole you can see in the ally strip is just how it was mounted whilst in the milling machine. The control surface can now be fitted (and un-fitted) by the 3mm cap head screws.

The hinge parts

IMG_2499.JPG (20.35 KiB) Viewed 28046 times

assembled plan view

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assembled elevation

IMG_2501.JPG (21.85 KiB) Viewed 28046 times

Anyone used hinges with bearings? Did they work? Were there any problems?

[Dave Collis 2296]

Andy,
This was my first "BIG" model, so I was going into uncharted territory. I took the Sig 1/3 scale plans and had the blown up to half scale. I basically followed the 1/3 size as far as construction goes, with suitably sized wood where required. As for hinges, I used Du-Bro giant scale hinges for all the surfaces, I used lots, not just 3 or 4, and used a length of piano wire for the pin. My wing tips are removeable, so the aileron hinge pin can be removed if nec. I have had ZERO problems with the hingeing system. I have also flown this on floats. I covered it with Stits fabric and auto urethane paint.

Like you, each side of the plane has its own rx, batts,switch etc. (spectrum AR7000) JR9303 tx, 2x 2400 nimh and the system has beem bullet proof....so far!
I am using 2x Hitec 705 on each ail., 1 on each ele., and two for the rudder, probably overkill, but again I didn't really know how much servo power would be req'd.

I am sure I could have made it lighter, but for me, treading into the world of BIG planes I wasn't sure where and how to cut the weight and not loose structural integrity...all water under the bridge now.

The 3W 200 is adequate power for the style of flying I do, slow and reasonably low, no aerobatics as of yet, though I am sure it would do them just fine.

Now on to the next project...1/2 scale Gee Bee "Y" with a Moki 400, 15' wing, hopefully under our 77lb. (35kg) Canadian weight limit....not sure if I will be able to get this out of the workshop

If I can assist you in any way, please ask.

Cheers,
Dave.

[Andy Boylett]

Thanks Dave,
I am sure I will have some questions as I get going on this. The 1/4 scale Spacewalker I already have was made from a SIG kit.

For the servo loadings I did calcs from first principals looking at mechanical loadings and then used some shareware for calculating the aerodynamic loads. The software gave lower loadings as below (and I did use rather an extreme max speed):

Servo loadings

ab2010-10-10 servo loadings.jpg (17.84 KiB) Viewed 28028 times

The rudder comes out at 33Kg.cm
I am thinking of using the new Turnigy 33kg.cm HV servos. These are a compact servo, only slightly larger than standard, with titanium grears, an all alloy servo body and work directly on 2 cell LiPos, which keeps the current lower. These have been extensively tested in 1/5 scale off-road buggies as the steering servos and have faired excellently. As I am splitting the ailerons in half this is fine with 2 each side. Two will be great on the rudder. I could get away load wise with one on each elevator half, but the large model inspectors over here don't like 'standard size' servos used on thier own so I will either have to use 2 on each elevator half or a bigger 150gram size servo.

[Mike Booth]

Andy, Dubro make metal hinges, which will do the job fine if you use the correct amount on each surface.
Have a chat with Phil Clark at Fighteraces I am sure he carries them.
Mike.

[Dave Collis 2296]

Andy, Dubro make metal hinges, which will do the job fine if you use the correct amount on each surface.
Have a chat with Phil Clark at Fighteraces I am sure he carries them.
Mike.

Mike, I just looked at both the Du-Bro catalogue and Fighter aces and don't see metal hinges. Phil does have some excellent parts I didn't know existed

[Phil Clark]

Andy, Dubro make metal hinges, which will do the job fine if you use the correct amount on each surface.
Have a chat with Phil Clark at Fighteraces I am sure he carries them.
Mike.

Hi Mike

Funnily enough....I'm Andy's over 20kg inspector on this one and we've already had a lengthly workshop session going over various details. The hinges you mention are made by Sierra not Du-Bro and I had left over from my projects examples of their 'HUGE' and 'QUITE BIG' hinges for Andy to look at......

Being a 'I want to make them' sort of guy, Andy has opted for the method shown above......my only suggestion after seeing them is if the Protech part is to remain 'removable', then the tube it's secured into should be from thin walled steel (stainless?) rather than brass as this is relatively soft and once subjected to vibration and flight loads, I can see the rear end of the tube swaging slightly and play working it's way into the system.

Phil (...that bloke at Fighteraces!!)

[Mike Booth]

Good one Phil, needs to be as good as the real thing.
It is almost an ultralite UAV.
Mike.

[Phil Clark]

I coudn't agree more Mike...hence why (in my opinion) 'plastic' hinges have no place on 1/2 scale models.

Phil

[Dave Collis 2296]

I coudn't agree more Mike...hence why (in my opinion) 'plastic' hinges have no place on 1/2 scale models.

Phil

When I built my 1/2 scale( 2003-4) there weren't any metal hinges, but I used enough of the dubro giant scale ones as to almost be a full length piano hinge.
Glued and pinned...non have loosened or broken to this point in time.

[Andy Boylett]

[quote="Phil Clark"...my only suggestion after seeing them is if the Protech part is to remain 'removable', then the tube it's secured into should be from thin walled steel (stainless?) rather than brass as this is relatively soft and once subjected to vibration and flight loads, I can see the rear end of the tube swaging slightly and play working it's way into the system.
)[/quote]

Yes, SS sounds good but probably have to drill/ream to get the 5mm bore. The brass just happened to be 6mm with 0.5mm wall so fitted perfectly I cant find thin wall SS with 5mm bore.

Also, I need to source thinwall SS tube for the landing gear. I need 300mm legnths in OD of 18mm, 15mm and 13mm (to be scale) for the main parts, anyone know a good place to get small lengths?

.....then I need to fix my TIG welder which has broken!....electronic faults always seem invisible !*?!**???

[Phil Clark]

When I built my 1/2 scale( 2003-4) there weren't any metal hinges, but I used enough of the dubro giant scale ones as to almost be a full length piano hinge.
Glued and pinned...non have loosened or broken to this point in time.

You obviously did a very competent job in the installation Dave as my concern with a large number of hinges of this type on 1 surface is accurate alignment so as not to end up with binding hinges, plus drilling a large number of holes in a false TE and LE of a control surface so as to almost make a piano hinge also rings alarm bells for me. 3 - 4 very robust hinges per surface in preferable in my mind. (Just my 2p's worth....yours has obviously proved itself, so that fine)

Phil

[Phil Clark]

Yes, SS sounds good but probably have to drill/ream to get the 5mm bore. The brass just happened to be 6mm with 0.5mm wall so fitted perfectly I cant find thin wall SS with 5mm bore.

Also, I need to source thinwall SS tube for the landing gear. I need 300mm legnths in OD of 18mm, 15mm and 13mm (to be scale) for the main parts, anyone know a good place to get small lengths?

.....then I need to fix my TIG welder which has broken!....electronic faults always seem invisible !*?!**???

Andy

I have a supplier with 4, 5 and 6mm tube with a 0.3mm wall.....and 12mm x 0.3, 15mm x 0.4 and 18mm x 0.5, all in 1m lengths. Also 'seamless' in 10, 12, 13 & 14mm x 0.5 in 400mm lenghts (if thats of any help).

Phil

[Andy Boylett]

The rudder and elevator on this build are very large curves. The stab is approx 1400mm across. To make the curves for the rudder and elevators I have been using the laminating technique. I have done loads of laminating before, but these ones are bigger than anything done previously. I am looking for an 18mm finished width trailing edge, which will vary in thickness from 12mm to 6mm. There are lots of ways of bending balsa using water or NH3 (amonia), but the one I prefer is to use no liquid and start with wood that is thin enough to bend anyway. Althought this means more layers it does not take that long done like this below.....

This picture shows my strips cut ready. This time 1/32" balsa and 18mm wide so I have spare to sand off later. I need 21 layers but need lots more strips as the curve is longer than the wood and need joins.

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Now I have cut all the strips to length and formed a stack of 21 layers, with all the joins in different locations. I am just starting to put on a layer of glue to the first strip here. I do the lamination by completely glueing the whole stack first, then picking it up and bending it round the former.

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I am using water proof white glue and I make sure that there is a nice uniform thin layer. On this picture you can see how the left half has been carefully 'scraped' to leave just a thin layer, the right half is before.

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Next the completed straight stack is picked up and placed onto my template. The thing I find now is that the glue on thin strip makes them very bendy, just like they had been soaked in water. The template has been cut 20mm smalled than the finished outline. The edge has been covered in plastic and then it is screwed to a base, also covered in plastic.

Laminate 4.JPG (36.85 KiB) Viewed 27932 times

I clamp the stack tightly by using L shaped brackets screwed to the template. There is a technique when putting the screws in of pushing the screw tightly against the far side of the hole in the bracket to start with, then as the screw starts to go in it pulls the bracket half a screw width tighter.

Laminate 5.JPG (35.52 KiB) Viewed 27932 times

I cant seem to add more pictures, so continued in next post................

[Andy Boylett]

Continued.....

Here it is half clamped.

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And fully clamped, before being left in a warm place for 2 days.

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And here is the finished laminate (with a newly home-made indoor foamy in the background.

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