DooMaw - building a STOL

[Head in the clouds]

these guys do the whole aircraft tubing kits, works out about US$2500-$3000 more expensive than just the materialhttp://vr3.ca/refdocs.html

 

have a look at the fuselage links at the bottom of the page, it has detailed part descriptions

Hmmm - at that price I'll just stick with the wrap templates, there's probably only about 20hrs total in templating and cutting the notches by hand with a 1mm disc and shaped 6mm grinding disc in a pair of angle grinders. That doesn't justify a AU$4K materials cost price increase unfortunately. I'm pretty sure I came across a different mob that were quoting about US$1500 and buying the tubing direct from US would save about that amount compared with buying it here, even allowing for the freight. I'll see if I can find the link again.

 

https://fbcdn-video-b-a.akamaihd.net/hvideo-ak-xtp1/v/t42.1790-2/11721705_954854061227322_1170893149_n.mp4?efg=eyJybHIiOjYyNCwicmxhIjo1MTJ9&rl=624&vabr=347&oh=280f7c0284085068bc7b33220edd6492&oe=55BB2342&__gda__=1438331377_e387fc9283b40ed1795e5164c124b85d

This link should work

Yes, nice - it's a technique called 'walking the cup' and produces very consistent welds. It works well when butt welding two tubes well prepped with a chamfer to their edges, or for a fillet weld, or for a lap joint. You can even use it to produce a fillet down the middle of a flat sheet by clamping a guide to the sheet. The point being that you need one or two edges as a guide to walk the cup along.

 

For those who don't TIG, the cup is the ceramic cup that acts as a nozzle for the Argon shielding gas. What is actually happening to produce such a regular weld is that as you swing the torch from side to side you are producing a zig-zig ladder in effect, and stepping the cup up the ladder as you progress. You just have to match the dipping of the filler rod with each swing of the torch. It takes a bit of practice but isn't as difficult as it might at first appear. I managed a reasonable weld the first time I tried it on a test piece but haven't had a need to use it on a real job yet. The hardest part is feeding the filler rod along in your hand as it gets used up, and I guess even harder would be changing for a new rod on very long welds like that one shown in the video.

 

Progress on DooMaw since the last update -

 

Wednesday and Thursday I got 7.5 hrs in after work all spent notching and fitting up the tubes for both sides of the aft fuselage.

 

I spent an hour and a half on Friday evening and got one side of one side tacked, a bit slow as I had some dramas with the welder which I later discovered was power brownouts in the area, electronic welders don't appreciate that very much!

 

On Saturday I tacked the first side of the second side, labelled and removed all the wood-blocks, tacked the second sides of both sides and fully welded out the first side. Today I welded out the second side, so as Mark predicted the aft sides are done by this weekend.

 

As I suspected the very thin tubes were quite demanding but with the welder turned right down and the pulse function disabled, and using the foot pedal to modulate it off and on as you might with a MIG, I was able to make quite reasonable welds though a bit tiring on the ankles. Unfortunately being a cheapie welder it doesn't go to really low settings like a Miller does and at the lowest setting the background current when using the pulse function is just way too high for very thin material. No complaints though, it got the job done and one day I'll invest in a Miller.

 

A few pictures show the aft fuselage tubes in the jig during tacking, one frame tacked and the second in the jig, the portable welding trolley that I set-up a couple of weeks ago, the jig blocks removed for welding out the frames, some of the welds on the thin tubing, the last one shows the tiny 1/4" (6.4mm) tube right at the rear -

 

 

 

 

 

That's another 25hrs in the project log making a total of 210hrs so far.

 

Next I was going to join the rear sides to the front sides but I've changed my mind, for easier manhandling and rotating it all for welding the internals of the clusters, I'm going to jig and join the two front sides with all the front cross-members and vertical and horizontal bracings. That will produce a very rigid cabin assembly and it will be much easier to join the aft fuselage into it once it's fully welded out.

 

So as spare time allows, it's back to the CAD work again, produce more wrap templates, cut more tubes, sand off the mill scale, paint them with primer, mark them for notching, notch them, make a wood-block jig for the fuselage sides, laser level them to be sure they're level and square, fit up the cross-members and diagonals ... rinse and repeat.

 

 

 

 

 

 

[Kyle Communications]

Very nice

 

 

[Kyle Communications]

You can see where the expense comes in..its not the tube or the notching its the man hours involved in the hand welding of all the joints that you are paying for in a premade fuselage that is made like this. It would be nice to have it CNC tig'd if it could be done.

 

 

[Soleair]

Beautiful welding, HIC.

 

Do you have to normalize or otherwise heat treat the material after welding? ISTR if you heat steel above its Upper Critical Temperature the grain reorganizes itself, which may affect ductility, etc? Or is it not necessary?

 

Which model welder do you have?

 

Bruce

 

 

[Head in the clouds]

You can see where the expense comes in..its not the tube or the notching its the man hours involved in the hand welding of all the joints that you are paying for in a premade fuselage that is made like this. It would be nice to have it CNC tig'd if it could be done.

I expect it could be done by CNC TIG but I don't think the production volume would justify the set-up costs. I haven't seen one in action and the ones shown on Youtube don't seem to have a provision for adding filler material, they seem to just meld the edges together. I'd imagine there'd have to be some that do add filler though, probably from a reel a bit like a MIG machine I guess.

 

Beautiful welding, HIC.Do you have to normalize or otherwise heat treat the material after welding? ISTR if you heat steel above its Upper Critical Temperature the grain reorganizes itself, which may affect ductility, etc? Or is it not necessary?

 

Which model welder do you have?

 

Bruce

You can bring the completed fuselage back to the N (normalised) condition by having it heat treated but of course it requires a large oven and special care due to the thin material. As far as I know it's not generally done even on earlier steel tube production airframes like the Taylorcraft, Piper Cubs/Pacers or the Austers. They were all welded using OA (oxy/acetylene) process and the technique there is to bathe the HAZ (heat affected zone - the edge of the weld which shows the colour) with the flame after completing the weld, and slowly moving the flame further away to provide a degree of stress relief to the weld.

 

The TIG process allows a good operator to complete the weld with a lot less heat than the OA process and so the stress relief is less important. Naturally not all welds go as well as you might like so if one does end up having been heated more than you're comfortable with you can go back and locally stress relieve it later with a propane torch. When doing that you just heat it gently and evenly around the area until the blue colour disappears and is replaced with a straw colour, the same as used for letting back (tempering) heat-treatable steel (which CRMO is) after hardening it. Some folks have thought this would leave it annealed (in its softest state) but that's not so, it's still harder than the N condition (as the tubing is supplied - hence the 4130N designation for CRMO tubing) and the N condition is harder than the fully annealed condition.

 

The really important thing when welding CRMO is to avoid there being any drafts in the workshop because the moving air cools the welded area too quickly and that can leave it brittle and more prone to cracking in service. My shop/garage has slatted walls so when it's windy I have to place shields around the area I'm working on.

 

My welder isn't a branded one, it has a stupid name "Super-200P" and was sold on ebay by a mob who called themselves Proweld industries and they promptly disappeared after selling a dozen or so of them. There are lots of similar ones on ebay, they have different cases and the switches and knobs in different places but they all have the same or similar electronics inside. They are so generic that mine even has some of the knobs labelled wrong which caused me quite some confusion at first, my "AC Balance" knob actually controls the Pulse Duty ratio ... and the "Clean Width" is actually the AC Balance, I eventually worked that out because most machines have either Clean Width or AC Balance controls but not both. It was a bit of a learning curve because the previous TIGs I've used were transformer types not inverters, so didn't have any of the fancy features.

 

These are really cheap, mine was about $800 delivered but if anyone considers buying one of these it's worth checking what features it does have (or doesn't). Mine claimed to have AC Frequency control but it doesn't, and that would be useful for fine welds on Aly. Mine also has a knob for initial slope but it doesn't do anything and the manual says it doesn't have it. The problem with all this is that the people selling them generally know nothing about them or about welding, they just buy and sell them.

 

This one also does stick welding and plasma cutting up to 16mm plate but I don't use those features although it does come with all the necessary accessories to do so.

 

--------------------------------

 

In gaps in real work I've been preparing the next stage of the build, printed the wrap templates for all the members that go between the two sides of the fuselage front and will form the cabin. There are a lot more members than at first meets the eye, more than 50 members which is nearly as many as the total I've done so far in building the front and aft sides, here's the Marking Plan -

 

 

 

[Head in the clouds]

Not much interesting stuff to report on but plenty of hours have been put in to get nearer to the next stage.

 

With the time spent on CAD and creating the templates described above (13hrs), correcting them to reduce the fit-up time later, cutting them out and then cutting the tubes to length (8hrs), descaling the tubes in the lathe, and descaling the larger tubes (spar and strut carry-throughs) by hand, then washing, masking and painting them and begin the wrap template stencilling (14hrs) has made for a busy week with another 35hrs on the project on top of normal work.

 

So the total hours on the project so far are 245hrs.

 

The pictures show the tubes during preparation -

 

 

Not too far off until I have the stencilling finished and the notching done, then I can start to jig the two fuselage sides together.

 

 

 

[Head in the clouds]

Nice progress this week, starting the assembly of the two sides.

 

It's good to see the shape coming together but the welding gets a lot harder, getting access to the insides of the frame to tack it all together when you can't rotate it into position is hard on the ageing back but probably good for personal mobility in the long run, certainly a lot better than sitting at a desk a lot of the time like my 'real' job.

 

The rest of the stencilling took a couple more hours then 15 hours to notch all the ends.

 

Next I had to make a very accurate jig for the top frame so that the carry-through members that the wings connect to are perfectly aligned each side. It involved a bit of machining, clamping, welding and gladly turned out very well. That allowed me to assemble and fully weld the top frame with its cross-bracing in the jig so that ensures that the wing rigging will be accurate and was also a lot easier way to weld it than as part of the main cabin frame.

 

Following that I checked and re-adjusted the levelling of the bench - the earth around here moves a fair bit according to moisture content and the laser showed it had moved 3mm across the feet of the bench which is magnified to 6mm across the full length of the bench. Easy to adjust with the threaded feet on the bench, then I could start to mark the positions for the wood blocking that holds the bottom of the side frames parallel.

 

Installed the blocks and packers to keep the bottom rails off the timber so that the larger cross-members could fit under them and then had to devise a means of holding the side frames vertical. I used small chains and turnbuckles a bit like rigging a yacht mast and had to add some chains under the bench as well to balance the load on the top edges of the bench.

 

With that in place I could set the laser up on top of the bench and set the side frames level and vertical, now it was nice and easy to adjust with the turnbuckles opposing each other.

 

Then I could drop the top frame on and was delighted to see it fitted almost perfectly, a light touch of the grinder and it dropped into place with barely a visible gap anywhere. That meant I could then remove the external jigging frame and add the side fore and aft members. None of those are welded in yet, I need to get all the vertical bracing in place before doing that.

 

With the top frame sorted I could turn to the front and rear cross-members, final fitted them and tacked them in and then added the vertical bracing. I used a couple of extra chains and turnbuckles to fine adjust the alignments where the complete welding of the sides had pulled them out of flat by a few millimetres.

 

Then I added the front horizontal bracing behind the instrument panel and the whole assembly is locked up and rigid so I could move the bench aside to put the car away for the night.

 

There was 41 hours in that lot, so the log shows 286 hours so far. Some pics -

 

[ATTACH]37355[/ATTACH] [ATTACH]37356[/ATTACH] [ATTACH]37357[/ATTACH] [ATTACH]37358[/ATTACH] [ATTACH]37359[/ATTACH] [ATTACH]37360[/ATTACH] [ATTACH]37361[/ATTACH]

 

 

[Head in the clouds]

Nice progress this week, starting the assembly of the two sides.

 

It's good to see the shape coming together but the welding gets a lot harder, getting access to the insides of the frame to tack it all together when you can't rotate it into position is hard on the ageing back but probably good for personal mobility in the long run, certainly a lot better than sitting at a desk a lot of the time like my 'real' job.

 

The rest of the stencilling took a couple more hours then 15 hours to notch all the ends.

 

Next I had to make a very accurate jig for the top frame so that the carry-through members that the wings connect to are perfectly aligned each side. It involved a bit of machining, clamping, welding and gladly turned out very well. That allowed me to assemble and fully weld the top frame with its cross-bracing in the jig so that ensures that the wing rigging will be accurate and was also a lot easier way to weld it than as part of the main cabin frame.

 

Following that I checked and re-adjusted the levelling of the bench - the earth around here moves a fair bit according to moisture content and the laser showed it had moved 3mm across the feet of the bench which is magnified to 6mm across the full length of the bench. Easy to adjust with the threaded feet on the bench, then I could start to mark the positions for the wood blocking that holds the bottom of the side frames parallel.

 

Installed the blocks and packers to keep the bottom rails off the timber so that the larger cross-members could fit under them and then had to devise a means of holding the side frames vertical. I used small chains and turnbuckles a bit like rigging a yacht mast and had to add some chains under the bench as well to balance the load on the top edges of the bench.

 

With that in place I could set the laser up on top of the bench and set the side frames level and vertical, now it was nice and easy to adjust with the turnbuckles opposing each other.

 

Then I could drop the top frame on and was delighted to see it fitted almost perfectly, a light touch of the grinder and it dropped into place with barely a visible gap anywhere. That meant I could then remove the external jigging frame and add the side fore and aft members. None of those are welded in yet, I need to get all the vertical bracing in place before doing that.

 

With the top frame sorted I could turn to the front and rear cross-members, final fitted them and tacked them in and then added the vertical bracing. I used a couple of extra chains and turnbuckles to fine adjust the alignments where the complete welding of the sides had pulled them out of flat by a few millimetres.

 

Then I added the front horizontal bracing behind the instrument panel and the whole assembly is locked up and rigid so I could move the bench aside to put the car away for the night.

 

There was 41 hours in that lot, so the log shows 286 hours so far. Some pics -

 

 

 

 

 

 

 

 

 

[Kyle Communications]

Looking F.A.B Alan :)

 

The thunderbirds are go

 

There is a lot of work in that chrome moly tubing for sure. But probably a lot stronger than any alu bent metal framing

 

Mark

 

 

[Kyle Communications]

Looking F.A.B Alan :)

 

The thunderbirds are go

 

There is a lot of work in that chrome moly tubing for sure. But probably a lot stronger than any alu bent metal framing

 

Mark

 

 

[Head in the clouds]

Once some of the cross-members, the vertical and some of the horizontal bracing was in place I could release the chains which had been holding everything in position on the bench and roll the structure over to add the lower cross-members and bracing which form the floor of the cabin.

 

All those parts had to be fitted and tacked as well of course, so it was a couple more days before I could start the welding out. It was a good feeling to get past the constant fit-ups which I find rather tiresome after a while.

 

Since then it's been a case of welding, welding, welding. Some of the very tight clusters where several members come together in a a cone shape were quite difficult and required moving the whole frame several times, gaining just ten or fifteen millimetres of weld each time. In fact setting up for each weld is what takes the majority of the time, each setup can take 10-20 minutes and the weld is then completed in a minute or two.

 

It was a long week burning the candle at both ends with a fair bit of new 'real work' coming in again and working early and late to keep the plane build progressing.

 

I haven't quite finished welding it out yet, there's still another day to go, and then I have to add the lower chord and web members that form the truss behind the instrument panel that resolves the landing loads. Then there's also the underfloor members that support the top of the gear legs. So it'll be another week at least before I get to start attaching the rear fuselage but plenty to look forward to.

 

So, another 39hrs in the build log this week, a total of 325hrs.

 

The pics show the frame off the bench and the rest of the cross-members and bracing added, and the welding underway. The last pic is how I have to wrap it up every night, otherwise with our coastal weather it'd be covered in rust by the next morning. Covering it, and the primer paint I did earlier is doing it's job well so far and it won't be long before I can prime all the welded areas too.

 

 

 

 

 

 

[Oscar]

Very, very nice....

 

 

[Kyle Communications]

Excellent work as always...really starting to take shape now

 

 

[rick morawski]

That looks like one helluva strong cabin frame! I would feel safe in that!

 

 

[Head in the clouds]

24-30 Sept 2015.

 

Another busy week. Last post I mentioned there was still another day of welding to weld out the cabin frame, it seemed like it was almost done and I thought I had completed all the most difficulty clusters. Actually it took another 14 hours to finish off that part.

 

Next I added the parts that form the truss behind the instrument panel and which stiffens up that zone which has to resolve the forces from the landing gear oleo struts. It's just a few small members and easy to get at for the welding on the inside i.e. from the side where the crew will sit, but very hard to reach from the other side i.e. the foot-well side. I ended up trying to weld while curled up in a ball, all entangled in the frame members. And of course every time I thought I was ready to weld I'd find that I had forgotten a glove or filler rod or something and have to extricate myself and start all over again. All part of the rich tapestry and all that, but those few members took another 7 hours to fit and weld.

 

Following that I went back to the CAD work to check the actual dimensions that the frame would be when it is on its wheels. I needed to know this because when I add the rear fuselage the frame will become too heavy to easily manhandle on and off the bench every day, to make room to put the car away overnight. The plan was to get the frame onto its wheels as soon as possible so that I could wheel it into one of the parking bays under the house for storage when it wasn't being worked on. I can't put the car under the house instead because the car is just a little too high.

 

Typically when I measured it the plane would be about 100mm too high also, and that is even if I put some small wheels on, with the real wheels and tundra tyres it would be way too high. I thought about using really tiny wheels, maybe just solid plastic wheels 100mm or so in diameter but then discovered the track is also too wide so I realised I would just have to make another set of gear legs much shorter than the real ones. I bought some cheap 20x1.6SHS and fabricated a set of temporary legs using a pair of barrow wheels that I've had lying around.

 

I stencilled and cut out the bracket hardware for the gear leg attachment points and jigged them up onto the central gear support member using the real gear legs to set everything up in alignment on the bench. Tacked then welded those brackets and re-assembled it all to make sure it hadn't pulled out of shape while welding and that the legs still hinged freely throughout the whole suspension motion.

 

Before the weekend was over again I then just had time to tack enough of the gear support members to the cabin to be able to install the wheels and move it all under the house.

 

A busy few weeks of real work ahead means I won't have so much time to spend on the plane, but the next stage will be adding the rest of the gear support members then welding them out before being able to start on attaching the rear fuselage.

 

Another 39 hours in the build log, a total of 364 hours, some more pics tell the story so far -

 

 

 

 

 

 

 

 

 

 

[Head in the clouds]

I haven't had a lot of spare time for the build during the last three weeks, just a few hours here and there, but today I did get the cabin welding finished and, except for the strut attachment points, wire-brushed and painted all the welded areas with primer.

 

That means the next stage will be to fit and attach the rear fuselage sides and then the rear fuselage cross-members and bracing.

 

Another 28hrs for the build log, making 392hrs in total, and here are a couple of pics. If it looks a bit odd that's because it's sitting on its tail i.e. the firewall is 'up' -

 

 

 

 

[Head in the clouds]

Another busy work week so only the weekend to get a bit done on DooMaw.

 

As mentioned last post it was time to get the rear fuselage sides attached to the cabin.

 

First I had to solidly lock the cabin frame to the workbench with it level and central on the bench so that I could use the flat bench and a central chalk-line as points-of reference. A number of steel blocks, shims, wood-blocks, pieces of plywood, lots of screws, a few bolts and three hours later the cabin frame was set up and totally rigid so I could be confident nothing would move later.

 

Next I checked the CAD model to determine the height that the tail sections of the fuselage sides needed to be above the bench and built a support frame from scrap steel and bolted it through the bench frame.

 

Then cleaned up and notched the ends of the longerons and created the fish-mouths in the end of the cabin longerons where the rear longerons would splice into them.

 

Introduced the rear sides to the cabin frame and with a touch of a file here and there it all fitted together perfectly. I used the self-levelling laser for a double-check that everything was level and central, it was, but I wanted to be sure, there'd be nothing worse than a banana shaped fuselage and nothing could be done to put that right later, so it was good insurance to spend an hour to laser check it all.

 

Once I had it all balanced in position I could haul it tight with chains and turnbuckles and tack it up.

 

Next weekend it'll be the old deja vu same-old-drill thing again - I'll need to make all the rear fuselage cross-members and bracing so it's back to the CAD work to create more wrap templates, cut the material, sand the mill-scale off in the lathe, paint the tubes, mark the ends with the templates, notch the tubes, fit them up and tack them ... all before I can get to the stage of welding out the rest of the fuselage frame. Nonetheless it's coming along, some pics below show the progress.

 

Another 17hrs in the log, making a total of 409hrs so far -

 

 

 

 

 

 

 

 

[Head in the clouds]

How time flies - two months since the last report ...

 

It's my busiest time of the year for the day job so there hasn't been a lot of time to devote to DooMaw. Nonetheless scratching hours here and there and the odd full day has resulted in some continued progress, though much slower than it was. Work usually eases up for me over the Christmas and New year period so for a while things should speed up again then.

 

I cut all the cross-members and bracing then descaled, painted, notched, fitted and tacked them. By a couple of weeks ago I had welded out all I could get at without turning the airframe so it was time to unchain it from the jig and roll it this way and that on the bench. On Saturday I completed the last fuselage structural cluster weld. The contortions required to get at many of them far exceeded the hardest calisthenics work-out so I'm now reminded of several muscle sets that previously had been long-forgotten.

 

It's not shown in the photos, but I then wire-brushed all the welded areas back to bright metal and painted them, so the whole fuselage is now quite well protected from rusting in this rust-prone coastal environment, as long as I keep it covered with tarpaulins anytime it isn't actually being worked on. I can't get the final epoxy coat on until all the ancillary parts are also made and welded on.

 

Because of heir hard-to-get-at location I added the tailwheel oleo cleats before tacking that cross-member to the structure and I have also added the forward fin mount but there are still a lot of additional cleats for the control system and fixing the floors and baggage locker, the harness attachments, instrument panel anti-vibration mounts, engine mount hard points, windshield edge mountings and plates to fit at the wing-roots, but once all the parts are made welding them on is easy compared to the clusters.

 

Yesterday I went shopping for marine ply and coatings to make the floor panels, under-seat anti-intrusion/support panels and instrument panel and started cutting them out. I also found the timber batten material for the ventral and dorsal fuselage strakes which support the fabric covering and blend it's shape behind the central landing gear mounting points and ahead of the fin/HS fairing.

 

Another 59hrs in the log, making a total of 468hrs so far.

 

A few pics -

 

 

 

 

 

 

 

[Head in the clouds]

29th Nov - 22nd Dec, 2015

 

Another month has passed so I thought it's time I caught up on recording the progress.

 

Once the fuselage structural welding was completed it was time to start sketching out and making all the brackets that will hold the floor and ply panel under the seat that acts as an anti-intrusion panel in case of a hard arrival somewhere that has lots of debris or tree limbs perhaps, and that panel also supports the energy absorbing foam beneath the seats which is there to protect the spine from sudden deceleration in the worst event ... all part of the planned occupant protection in the crash-worthiness design. Not something you ever want to put to the test but nice to know it's there just in case.

 

I drew up the parts in CAD, templated them and cut them out with a 1mm cutting disc. I had intended to have all these small parts laser cut but I've got ahead of myself with the build and hadn't produced the cutting files in time, so instead of waiting a couple of weeks lead time with the laser people I decided to just get on and cut most of the hardware by hand. It doesn't take that long and saves a few dollars too. There are some very tedious plates I'll need later to fit the edges of the windshield and forward fuselage metal skins and I'll definitely have them laser cut, they're too fiddly.

 

Below is a pic of the parts for the floor, the under-seat panel, and instrument panel attachment -

 

 

Small plates like those are very hard to hold in place while you tack them, especially with a TIG welder. With MIG you can hold the plate with one hand and tack it with the other hand because all of the welding is controlled with one hand. However with TIG welding you're using one hand for the torch, the other for the filler rod and also one foot to drive the power pedal, so you need other means of holding parts in place while you tack them.

 

Larger pieces that connect to something at both ends aren't too much of a problem because you can either clamp them or hold them in place with small chains and turnbuckles, wire, springs, bungee cord, weights and even rubber bands - I used all of those at one stage or the other - but small plates require a different strategy.

 

I cut a strip of copper from a 1/2" plumbing pipe and silver soldered a small steel plate on one end and screwed a small crocodile (alligator) clip on the other. Then I was able to attach the steel plate to a heavy steel block with a powerful magnet and bend the copper into any shape I wanted to get the crocodile clip to hold the plate in place. It was very fiddly and time consuming to get the plate sitting just right, but it worked.

 

Unfortunately you can't short-cut the process and just use a magnet to hold the plate in place because the magnetic field affects the arc, which goes all over the place, and you can't tack it. By using the copper strip, the copper isolates the magnetic field from the plate being held in the crocodile clip.

 

 

And here are all the floor and under-seat panel plates fitted and primed -

 

 

And the instrument panel plates -

 

 

That lot took longer than expected, the welding was quite demanding and it was easy to blow holes in the thin plate edges, and the fuselage had to be rolled over numerous times to get at them - another 21hrs for a total of 489hrs so far.

 

 

[fly_tornado]

is there a reason why don't you use magnets? When I worked in a welding shop they sold these magnets encased on steel plates.

 

 

[Head in the clouds]

is there a reason why don't you use magnets? When I worked in a welding shop they sold these magnets encased on steel plates.

 

Unfortunately you can't short-cut the process and just use a magnet to hold the plate in place because the magnetic field affects the arc, which goes all over the place, and you can't tack it. By using the copper strip, the copper isolates the magnetic field from the plate being held in the crocodile clip.

The welding magnets you describe are predominantly used for holding parts together for SMAW/MMAW (stick electrode) welding, where the magnetic field has a lesser effect on the arc. Even then you remove the magnets as soon as the parts are tacked or you will end up with a very messy weld. You can just about tack parts held with a magnet if you are GMAW (MIG) welding but it can be messy, and it's virtually impossible to tack or weld with GTAW (TIG) if you have a magnetic field emanating from the parts, the arc goes anywhere except where you want it to go.

 

29th Nov - 22nd Dec, 2015 contd ...

 

As the fuselage structural assembly nears completion I had to firm up the design of the control runs. I was a bit slack in that regard about a year ago, and a bit keen to get on with some practical work rather than spend more time at the computer, I'd already been working on the CAD side of this in spare time for close to two years, so having confirmed that I had the clearances to get the controls in place, the motions of the elevator and rudder were unhindered, and the wing-folding geometry didn't cause any clashes, I was pleased to get onto some time in the workshop.

 

I had already confirmed the shape and position of my elevator control horn which is tucked between the fin/tailpost and the HS rear mounting bracket and that it can just accommodate the required 50 degrees (25 degrees each way) of motion. I found I needed one bellcrank, one walking beam and three pushrods to connect it to the joystick. The screenshot below shows the development of the geometry -

 

 

I tried every bearing and engineering supplies shop within 100km or so to try and get suitable bronze bushings for the bellcrank and not only couldn't I get suitable ones, I couldn't get any at all. The best they could come up with was a 12" length of 1" diameter phosphor bronze and since I already had a couple of them I set to work and machined the bushings instead. It just shows the dreadful state of industry here these days, considering that bearings of all kinds are the backbone of engineering.

 

The walking beam has a similar amount of angular motion - around 50 degrees total - but the bushings are under very small load since both connections are on one side of the bearing rather than on opposite sides, so the bushings for the walking beam are mild steel drilled eccentric to provide clearance between the moving and stationary parts. The moving part will have an oiling hole for lubrication at each hundred hourly or annual inspection.

 

The pic below shows some of the bellcrank and walking beam hardware awaiting assembly -

 

 

Although I'm not concerned about the boxy shape of the fuselage front and rear I do want to provide reasonable airflow over the empennage so I have two fairing battens external to the structural steel, one on top which fairs the dorsal fin into the rear fuselage, and one below which eases the 'step' which would otherwise exist right behind the rear landing gear mount. Those battens are 20x10mm Tassie oak because it is less than half the weight of even a small 3/8"x0.035" CRMO tube. The battens are attached by 0.040" steel plates bent into an angle, and are infuriatingly tricky to get aligned properly because regardless of setting them up straight the welding pulls them all over the place. I got them right in the end. The forward bracket for the top batten doubles as an attach point for the forward end of the ventral fin.

 

 

I also added some bent steel tubes forward of the HS mounting to shape the fabric to meet a 'removable for inspections' GRP fairing at the HS/fin intersection that will cover the elevator pushrod and bellcrank.

 

 

I then added handles to the sides of the rear fuselage for ground-handling because otherwise the only thing you have to get hold of is the leading edge of the HS and that doesn't do the fabric any good over time -

 

 

Added the plates to the corners of the firewall which attach the engine mount -

 

 

Completed cutting out the floors and gave them a first coat of clear poly -

 

 

Roughed out and trial fitted the instrument panel, it attaches to the mounting plates via rubber anti-vibration mounts so the whole thing can move around slightly, and also makes it easy to remove for any work required behind it. It'll have chromed dome-nuts on the front side eventually.

 

 

Finally I started making the joystick hardware ready for assembly -

 

 

Reasonable progress for the month, another 39hrs in that lot, making 528 hrs on the project so far.

 

 

 

 

 

 

 

[Oscar]

HITC - just lovely work to look at, I tips me lid again ( as always).

 

Amen to your comments about the magnetic effect, particularly for tig, it's a hopeless pain trying to chase the arc when it's coming off the electrode at 60-degrees from where you want it...

 

 

[Head in the clouds]

Thanks for the kind words again Oscar.

 

As you know, building a plane is a long road - and building rather than being out flying is sometimes rather tedious, so the encouragement is much appreciated.

 

 

[Oscar]

A long road indeed if it's a scratch-build and you're the designer - because ( just to add to everything else), you will see (as you have) things that need to be done to satisfy yourself that it's been done to the standard you expect of yourself!. Your lifting handles out the back are, I reckon, a classic example of sitting there and looking at it and thinking: 'jeez, I ought to do that, it'll make life easier / better /safer..'

 

I've been watching and sometimes helping a family member build his own design tandem 'utility' style ( i.e. workhorse, intended to be airwork category), for something like 10 years at least. It has a tube cockpit, not at all dissimilar to yours except it wil;l have a moulded 'glass skin, a bulkhead monocoque structure alloy sheet tail cone and tail feathers, and 'glass wings. Abut six, maybe eight years ago, I built him a 35-tonne large-frame hydraulic press just to do the bulkhead and tailfeather rib pressings. Moulds for the glass work... moulds for the cockpit and cowlings... jigs for things like the FAA-compliant impact-absorbing pilot seat, it goes on - and that's before the actual building work can be done! Multiple hundreds of hours have gone into just those bits alone. Several complicated 'rotisseries' for welding tubular structures, for the airframe and the engine mount (which has been used for several other engine mounts along the way, to be fair, for other projects.) And it's still a long, long way off being actually built..

 

Do you sometimes go to bed with some detail problem niggling away in the back of your mind, and wake up in the early morning with 'the answer' suddenly hitting you? I damn well do, and sometimes it's 'the answer' to something that I hadn't registered as a problem. Maybe builders are subliminally obsessive by nature (aka 'weird').

 

 

[facthunter]

Confucious say "man who go to bed with problem on mind wake up with solution in hand" Nev