# DooMaw - build log

Discussion in 'Member Project Logs' started by Head in the clouds, Jan 13, 2015.

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1. Jan 13, 2015

### Head in the clouds

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Here we go again ...

I ran into a mental block with AussieMozzie. Among other things I had one problem after another with perceived engine cooling issues. The external plumbing for the liquid cooled heads on the R912 creates a real headache for making plenums or ducting to get air to flow reliably around the fins on the barrels. Not so much of a problem on a tractor configuration but a real nightmare for a pusher installation.

I also came to dislike the control system, I'd underestimated the size of torque-tubes for the aileron and elevator actuation so both of them are too springy and might be prone to propagate control surface flutter - and it'd be very difficult to increase their size without a series of major modifications because they're so embedded within structural members or passing each other with minute clearances. And - while my plan of installing the joystick and associated linkages in the central structural tunnel seemed like a good idea at the time because it kept the controls free of the risk of foreign object interference, it also made them very difficult to inspect and service. They're all good lessons learned for next time but in my case have probably cured me of pusher aircraft for good.

Then I lost more friends over the last two years, they were highly experienced and in crashes that could have been survivable if they hadn't been in spam cans that collapsed on them - and the Moz is worse than most in that regard, being a rear-engine spam can. For some time SVSUSteve's constant preaching about crash-worthiness had been nagging away at me and I guess this was one of the last straws.

I've also have had so little spare time lately which has meant that the Moz build took much longer than intended and in the meantime my requirement of aircraft type has changed ...

Much as I hate not completing a project I have decided to move on and build something entirely different. For many years I have had a hankering to build a really rugged trailerable bush-plane with 'extreme' STOL capability. Something that could take me to some of the places I used to be able to get to back in the grand old days when I had helicopters. If it was to be very docile at low speed, with no tendency to bite by dropping a wing when stalled or at minumum controllable speed, then there'd probably also be a market for such a beast on the cattle stations.

My first insight into the real possibilities came about when I saw this video of the Just Aircraft Highlander SuperSTOL.

.

I think what they've done in making the craft controllable and docile while operating well behind the power/drag curve, is remarkable - and the plane is clearly capable of getting into the confined spaces in remote areas that I have in mind. Consequently, whilst being my own original design, mine does have a fair few similarities to the Highlander. I hope they won't be too peeved - after all, imitation is the sincerest form of flattery.

As far as steel sizing and structural calcs are concerned I've had the enormously time-saving advantage of having Bill Whitney, one of Australia's most regarded aeronautical engineers, give me permission to use plansets of two of his similar-sized designs, so I have been able to lift a lot of his sizing and adopt some of his clever design concepts for the tubing structure. Bill isn't known for the lightest possible structures but they are very strong, several of them are FAR23 certificated, and designed for limited aerobatics. Consequently mine won't be as incredibly light as the SuperSTOL but it will be stronger, and it's certainly still a lightweight - the combined steel structures of fuselage, landing gear, fin, HS, elevators and rudder all come to just 64kg/141lbs.

This will have slats or slots, I've not decided whether to make them fixed or auto-deploying yet, or they could start out fixed and be changed later perhaps. Also large slotted flaps and long travel highly damped suspension with medium sized tundra tyres. I've incorporated as many as possible of the other smart design concepts as I have come across over the last 2-3yrs. It will have my version of Daffyd Llewellyn's (another of Oz's respected aero engineers) Airflow Kit which he developed for the Seabird Seeker, and which allows that aircraft to be flown fully unco-ordinated with full back-stick, or to be thrown into a hard turn at marginally low speed and stalled whilst doing so, and still not drop a wing. It's a very clever concept, the description of which can be found in the Do vortex generators really work. thread on the Australian Recflying forum.

I've kept all the flail clearances at least as large as were demonstrated to be necessary for the FAR23 certification of Whitney's Boomerang, as determined in actual impact testing. There is a large amount of stroke available under the seats without any hard structure to hit. The steel fuselage floor structure under the seats is double layered by having the gear mounting truss below the tubular fuselage floor structure, and the forward part of the lower gear structure forms an angle to the bottom edge of the firewall helping to prevent the firewall digging in and causing a sudden stop in event of a bad arrival. The engine mounting structure continues that angle forward, further improving the 'bounce off', rather than 'dig in' situation.

The overhead structure to the spar attach points has crossed bracing rather than a single brace preventing the spar attach points intruding into the cabin space in event of impact by one wing or the other, avoiding what has been a fatal flaw in some Cub crashes.

I'm using the BD4/Tailwind style of square windshield/firewall front end purely for simplicity in construction and jigging, and it certainly doesn't seem to disadvantage those particular designs. That shape also provides more foot and leg-room which has allowed me to reduce the overall fuselage width to just 36"/915mm and the extra shoulder room that will be needed as a result will be provided by bubble doors. That also enhances downward visibility which is an advantage for a plane designed for ground-related activities.

A further difference which sets this design a little apart from anything else that I am aware of, is the wing and tail folding mechanism. Early last year I came across a plane called "The Mistress" that was for sale in Oz. It was designed by a gifted German toolmaker and has a wing folding feature that makes the folded plane into a more compact package than any I have seen before. With the benefit of CAD I have been able to enhance his concept a little and devise a system which will allow the wings and tail to fold in a genuine 'less than 2 mins', as well as having complied with Autoreply's insistence about the need for the controls to attach and detach automatically to avoid any possibility of the control connections being neglected while assembling the plane prior to flight. This will also address the situation where non maintenance-approved pilots might be expected to have an engineer to sign off the plane after each fold/unfold.

The difference between this wing folding and others, apart from its almost 'press-button' simplicity to operate, is that the wings and HS end up folded flat against the side of the fuselage while still being supported by the struts (see pics of the Mistress below - notice the picture of it in the trailer, the wings are lying flat against the side of the fuselage). This means that the widest part of the folded package is the wheels and they can easily be kept within the maximum width for standard trailers on the road. Other folding systems where the struts are not removed generally result in the wings simply rotating back around the lower strut attach point and the rear spar - the Kitfox/Skyfox being good examples (see pics following) - but that method imposes a restriction on the wing chord if trailerable width is a consideration. With the wings folded flat against the fuselage there is no chord restriction, but admittedly there is a fair bit more hardware required to achieve the folding geometry.

Amidst the 'real work' I have to do on weekdays, when I finally get this finished I'm hoping it's a plane that'll allow me to do more than other types might, so I call it DooMaw.

Since folks can't comment on the build log I've started a discussion thread as well - DooMaw discussion thread

The images below show -

The CAD model of DooMaw
The Mistress - showing wings and HS folding against fuselage sides
Kitfox wings folded

Last edited by a moderator: Mar 20, 2019
2. Jan 13, 2015

### Head in the clouds

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In August last year we moved home and now have much more room. We have an acre of garden so the plane trailer and shipping container of tools is easily accommodated and our 'new' house is an old traditional Queenslander (airy timber house with steel roof and verandahs all around), elevated on poles so there is a ton of room under the house for storage and parking, and a reasonably sized workshop separate from the house. My wife's car parks under the house but unfortunately mine is too high so it will have to share the workshop with the plane-building until I get a new shed built.

That meant the first thing I had to do was to build a workbench which can be easily moved to the side of the shop after use so that I can park my car under cover. At least I now also have a large amount of room to store tools and materials under the house.

The mobile bench design was straightforward enough but I found I couldn't work in the shop to build it after midday. It's a very hot summer here at the moment and the sun would stream in the open front door and rapidly took the internal temperature over 40C/104F, so I had to build a roll-up awning first. That made all the difference and it stops any rain blowing in too.

Below are a series of images which show the progress -

Our new home
The shed awning
CAD model of the bench
Bench under construction using self-levelling laser and chains with turnbuckles to keep it all straight
Addition of the wheels and lever-lift for moving it about
Adjustable feet to take account of the uneven floor
By placing it on the same marks each time the bench is flat and level to within 1mm/0.040" over the whole surface

3. Jan 13, 2015

### Head in the clouds

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Next I added the bench tops and cut them to shape for the fuselage whether on it's side or upright - the wider end has four outriggers added to the steel structure to support the timber overhang.

The CRMO tubing all arrived in one tightly wrapped package so I had to cut it open to check the contents against the delivery note. To prevent any rust getting hold of it before I cut it all up I resealed all the different sizes in individual plastic sleeves and store them under the house.

Then it was back to CAD work and produce some printed drawings for the forward fuselage section and main landing gear legs so that I could lay them out on a grid on the bench and install wooden blocking to hold all the members in position for tack welding.

The latest thing I have done is to print and cut out the paper wrap templates for the gear legs. I'll start with the gear legs as they are thicker walled tubing and will be more forgiving while I get up to speed with TIG/GTAW welding again, it's been a while.

More pics show -

The CRMO tubing in plastic sleeves
Printed drawings laid out for positioning the blocking
The blocking added and paper stripped away.

Approximate time spent on the project so far - apart from the year and a half of spare time designing it - is about 24hrs to make the bench and about 6hrs for the blocking.

4. Jan 23, 2015

### Head in the clouds

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Re: DooMaw - building the gear legs

Landing gear legs

Last weekend I made a reasonable start on the chromoly tubing work but didn't have time to write up the log. The main issue with doing that is the amount of time spent by having to upload the photos one by one as the uploader hasn't been working properly for over a year now. Do others still have this problem or is it just me? I used to be able to upload about a dozen photos at once but for a long while only the 'basic uploader' has been working for me.

First I opened up the appropriate plastic tubes that I had sealed the tubing into and then cut pieces of steel tubing to length for all the parts for the gear legs, then put the rest back and taped up their covers. Have to be very rust conscious here ...

Next I held each piece of tubing central in a vice and wrapped each end of it with its wrap template, held in place with a rubber band, and gave it a squirt of auto paint to mark out the notches. It was a very quick process and easy to judge the indexing alignment of each end by eye just by keeping the split in the template at the top (Pics 1-3 below). Four of the tubes were too short to be able to hold them in their centre and still have enough room to wrap the template on each end without moving the tube so I made an indexing line along the tube by scraping a sharp blade along it while holding it in the vice. I used an old electric planer blade which was easy to hold horizontal while running it along the tubing so it made a line that was true and didn't spiral around the tube.

Once the notches were marked and the paint dry I cut the bulk away with a thin cutting disc in a 4" grinder and shaped up the curves to the paint line with a 1/4" thick disc dressed to a rounded edge with a diamond wheel dresser. As long as I didn't try and grind too aggressively the paint stood up to the heat well and provided a good reference for accurate notching (Pic 4).

I laid the parts in the jig and they fitted perfectly which was very satisfying, it's always good to find that computers do know their stuff (Pics 5-8). I did have one small problem though. I had a software glitch that prevented me notching a tube end for more than one other interfering tube so where a longeron/chord, and two web members all came together the wrap template only showed the notch for the longeron and not the other web member, so I had to cut them by eye. Three turned out fine but one had a gap of about 1/16" so I had to remake that one (Pics 9 & 10). Later I sorted out the software glitch so it won't be a problem again.

The last pic shows the completed members for the port gear leg in the jig and starboard leg stacked above.

Back to work for the week - during the week I visited the welding supplies place nearby and brought home a large bottle of Argon - I'd returned the last one before moving house - tracked down the welding rods and wire I need, and I ordered online what looked like a nifty little device that mounts a small angle grinder, turning it into a mini drop-saw to make it quicker and easier to lop my tubing lengths.

The drop-saw attachment arrived today (Friday) and predictably it's amongst the worst of Chinese crap but it's a starting point for making something useful - perhaps ... (Pic 12)

A couple of 6 hour days, bringing the total so far to 42hrs.

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5. Jan 31, 2015

### Head in the clouds

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Catching up on last week's log again -

I did manage to make something useful out of the drop-saw frame basics.

I bought a new grinder, a 5 inch, which was a better fit in the frame and also allowed a deeper cut. Not that I want to use it to cut anything larger than 1"/25mm diameter as I already have a hot-saw and a cold-saw for heavy materials.

I had to pretty much re-make/engineer all of the frame components as it was sloppy as hell and nothing was straight or square. The worst part was the hinge which allowed the blade to move 1/8" laterally and rotate angularly by 5* each way. Luckily they had used a 15mm shaft so I was able to ream all parts out to 5/8"/15.88mm and I had some precision ground s/s shafting of that size. I then made up shim washers to take the lateral play out and we were up and running.

I disposed of the clamping/vise system altogether as it was worse than useless and I didn't need it anyway since I can hold the material by hand against the aly angle I fitted as material guides/supports. Then it was a case of some woodwork and drilling the blade of a tape-measure and Robert's your mother's brother so to speak. An engineer's clamp serves well as a stop for repetitive cuts.

In a short interlude during the week I unpacked the TIG/GTAW machine and had fun getting it in place under the bench. I had to lift the bench over it as it wouldn't fit in sideways between the angle bracing. Once it was under the end of the bench I 'just' had to lift it over one of the wheels while handling it from outside. No hernia but it was probably a close thing ...

The pictures show the rest.

During the week I eventually managed to find some quality 6mm/1/4" id hose that was priced just a little less than its weight in gold and bought 10 metres of it so that I can have the Argon bottle on one side of the shop and the welder installed under the mobile bench and run the gas hose through the rafters so I won't be tripping over it all the time.

Today's Saturday again and once more it's over 100 degrees in the water bag so for once I'm going to spend the afternoon in the hammock or on the deck having a splash in the little pool. Or go to the beach? Tomorrow's another day.

Another 6hrs for that lot making a total of 48hrs so far.

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6. Feb 15, 2015

### Head in the clouds

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A bit of an enforced break to keep up with 'real' work and the domestic/garden necessities then I was able to get a bit done on the more interesting stuff.

Before diving into the welding of the landing gear legs I thought it might be wise to run a few lines of dimes on some scrap sheet metal just to be sure I hadn't lost the knack. Actually my welds got to be respectable enough when I was doing a fair bit of it but I can't claim they ever resembled the lines of dimes that some fellas produce.

Anyway, welding's just like riding a bike isn't it, you never really lose it do you? Well I was a bit dismayed to keep falling off the bike and the dimes didn't even look as good as the proverbial bird excrement for the first half hour or so. Admittedly it's been a lot of years since I did any volume of TIGing but I did start to get a bit despondent, I must have contaminated the tungsten ten times in the first ten minutes. OK, I thought, time for a refresher course so I watched a few tutorial videos on Youtube and went back to the shed with renewed enthusiasm.

All went much better after that and the welds started to look promising again. But - I discovered that my welder has decided to take a holiday from pulsing which is a real blow because the pulse facility is what makes welding really thin material much easier as it helps you to control the heat. I spent a few hours playing with the various settings and pulled the electronics out and stared at quite a number of the boards with what I felt was a mildly threatening expression but it was all to no avail, she definitely has no pulse even though she's not completely dead ...

I installed an extra resistor in the foot controller which has brought the lower end of the current range down further so that after the HF start I can maintain a stable arc right down to about 10-12 amps with a fine tungsten and that's given me enough heat control even without the pulsing and I was able to make some quite acceptable test pieces. Over the next while I'll try and source a replacement control board for the welder but I'm not holding out much hope as it's a Chinese generic copy, but you never know, I might find another one being sold for parts where something else has died. There are lots of them around selling new for about $800-$1000 on ebay, all with different cases/brands but they're all the same inside.

For now it'll be OK so the next thing was to exactly position the main members in the landing gear jig (post#4, second last pic) and to do that I needed to have the bosses installed. The bosses being the pieces at the top of each of the main gear members which the bolts will go through to attach the legs to the fuselage. Naturally those bosses need to be in exact alignment with each other to allow the legs to hinge up and down without binding. I've had trouble with keeping them aligned in similar situations before, if they're not very firmly held in place they tend to pull out of alignment during the welding. Consequently I spent today machining up those bosses and making a spacer bar the ends of which I bored and tapped so that I could bolt the bosses to them until the welding is completed.

The pics tell the rest of the story - another seven hours approximately, a total of 55hrs so far.

7. Feb 18, 2015

### Head in the clouds

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She's alive! My TIG has a pulse again.

Actually she probably always did have but I had a wrong setting which was holding the Peak Power below the Background Power so the pulses weren't manifesting. It's one of the problems with having a TIG machine which is capable of having both/either a foot controller and/or a power controller on the hand-piece of the torch.

I can't say the revival made everything perfect in an instant but some aspects got a lot better, others a bit more tricky. At least now it's just a case of lots and lots more practice to get my hand in again and there's plenty of that to be had as I've organised the progress so that the easier and thicker parts get welded first and the trickiest bits should be near the end.

Real work is a bit slow this week so I was able to take most of yesterday off and strike the first arc on the job instead of on practice pieces. It took me an hour to tack up the first side of the first gear leg and then I had the pleasure of lifting it from the jig, half an hour to tack the other side. At that rate I'll have this plane finished around 2025 but it WILL get quicker as I get more comfortable with the welding again.

I spent the next hour final-fitting the parts of the second gear leg into the jig and then went back to the first one and welded it out. That took a couple of hours so I am speeding up already.

Then I tacked up the second leg and removed it from the jig also, and was able to then label the jig blocks and their positions on the benchtop, remove them and put them in storage just in case I ever want or need(!) to build another.

The pictures show the first gear leg out of the jig and the parts of the second fitted into it, and an Alfoil Argon gas dam method I used during welding out the first leg clusters.

About six hours again, so 61hrs altogether so far.

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8. Jun 13, 2015

### Head in the clouds

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Sometimes life just gets in the way of the important things ...

Trips overseas, a ruptured water tank outside at home, improvements around the house and some interesting new work projects - and four months slips away with nothing done on the plane.

My wife and I did have a wonderful time in South Africa, some of it spent with fellow HBA member Kierie Pieterse and his lovely wife Janette in Pretoria and Kruger Park, a luxury rail journey and then touring around the Cape for a while brought back some fabulous memories of my upbringing in southern Africa. So much has changed of course but a hell of a lot remains the same, and the people are more engaging than ever.

More of that later - I got to have a personal tour of the works where they're building the AHRLAC, I mentioned previously that Kierie's grandson is one of the Engineers engaged on the project. Sadly no photos were allowed as they were stripping it down for inspection after phase one of the flight trials, but that did give me the privilege of having a close look at some of the cleverest design concepts I've seen. That aircraft has a big future ahead of it, IMHO.

Anyway, back to the build now, as time allows and looking forward to trying out my new TIG torch. I've had one that's been too large to get into some of the clusters easily, and it's a bit heavier than ideal, so I decided to get a really small one since most of the work is at very low amperage. However - typically I could buy the torch in Oz but none of the fittings to kit it up. In the end I just bought the lot from China, complete with a gas lens kit. I've not used a gas lens before so am also looking forward to seeing the difference that might make. It has a flexible head which should prove useful as well.

First I had to replace the Argon and electric fittings because the standard ones were too small for connecting to the welder but it's ready to go now, hopefully I'll have some time on it tomorrow.

Pic below showing the old and the new -

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9. Jun 14, 2015

### Head in the clouds

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Well - I've always enjoyed welding but today was the best day's welding I've ever had.

The small torch is just fantastic to use, so light and the flexible head is an incredible advantage, just twist the thing into shape instead of trying to twist your arm into crazy angles.

Also, the gas lens is just something else ... I can safely say I'll never want to weld without one again. No more bits of silver foil to make argon dams, the lens just keeps the welding smothered in gas leaving a bright clean weld every time. AND I was using 30% less gas pressure, so saving a heap of money on argon which is ludicrously expensive here ($190/fill). The whole torch and gas lens kit and a box of tungsten electrodes cost just$112 including the 3 day courier from China, so the gas saved will pay for it several times over on one airframe build.

Talking of electrodes - since I was ordering a new small torch I'd decided I'd try using the smallest tungstens it could accommodate and the lens kit came with collets for 1mm electrodes, about 5/8 the size of the smallest I'd used previously which were 1/16". As I said I couldn't get any kit for the small torch here so I wanted to be sure to get the right ones in the order from China.

I've recently lost a friend from cancer, he was an RAAF welder for about 20yrs and because of the locations of his cancers he had a reasonable suspicion that the thoriated electrodes he'd used for so long may have been responsible for his condition. Thoriated tungsten does come with plenty of warnings about possible risks as they are mildly radioactive and the frequent sharpening that amateur welders like me have to do, and without the correct vaccuum/ventilation equipment, gave me a high enough level of concern to look at, and change to, an alternative.

Mr Google provided plenty of information on the subject and all anecdotal evidence seemed to point in the one direction - lanthaniated electrodes are considered by many folks to be the best all-rounder. The main concerns for someone playing in the arena I'm in i.e. running the thinnest possible electrode and welding heat treatable steel alloy, is how well the electrode can stand up to heat and how well (gently) it starts the arc on HF - as well as how stable and controllable the arc will remain during the welding.

Sky blue 2% lanthaniated seemed to tick/check all the boxes, though to be honest I'd never heard of them before. The long and short of it is, I am absolutely delighted with them. They sharpen easily, start the weld without any harsh arcing which can cause hard and brittle areas in/near the weld, they handle the heat exceptionally well when you do have to give them a burst - welding heavy bosses to light tubing for example - the arc is beautifully stable and predictable and an added bonus is that when you do inadvertently contaminate the tungsten it doesn't all go to hell all of a sudden, you can usually finish the run without any dramas.

So - today I welded out the second gear leg and also went back to the first one and tidied up a couple of the welds that weren't quite as pretty as I'd have liked them to be. I also made a few components for a bit of the project down the track and prepared the bench for the next stage, getting the forward fuselage sides in the jig.

Next I want to complete machining the bosses that carry the axles so that I can weld them into the gear legs and that'll allow me to sandblast and paint them before they start to rust in this very corrosive coastal environment.

Another 6hrs for the log, 67hrs so far.

10. Jun 22, 2015

### Head in the clouds

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I had a quiet day during last week so I used the little cut-off saw I built in January (see post #5) and cut all the tubing for the forward fuselage sides. It worked a treat, very quick and accurate and much nicer cutting with the thin 1mm discs than with the 3mm discs on the hot-saw, glad I persevered and got it made.

On Saturday I just got an hour in and continued yesterday with cleaning up all that cut tubing, getting rid of the mill scale ready for painting. I discussed the method in the DooMaw discussion thread. I adopted PTAirco's excellent suggestion of using the lathe and wrapping sandpaper around the tube to remove the bulk of the scale. I found that NoFil paper was best, the kind that doesn't clog and is generally used for removing paint. I used 120 grit first then followed that with 180 grit. Then on to the wire-wheel on the bench grinder.

So most of those tubes are nice and shiny now, with a slightly abraded surface, all of which should be perfect for paint adhesion I hope. I also managed to find a supply of quality Zinc Phosphate Primer. I had to get it from an industrial source, the hardware stores here don't stock it, instead offering a very inferior metal primer that doesn't contain any zinc phosphate at all.

I also serviced the ancient miniature spray gun that my old mate Baz gave me many years ago, so we're ready to go with the painting when I've finished cleaning the last few tubes.

After I've painted them I'll clean the paint off again, from the areas which will be welded.

Here are a few pics of the tubing before and after - the one where the same piece of tubing is half clean and half still scaled shows its condition straight after sanding on the lathe but before wire brushing.

Another ten hours for last week, bringing the total to 77hrs.

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11. Jun 22, 2015

### Head in the clouds

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More good progress today.

Finished de-scaling the last few tubes, strung a rope to hang the tubes from for painting, gave them a last wipe down with mineral turpentine and painted them.

The old spray gun was the perfect tool for the job with a spray pattern ideally suited to that relatively small work.

A few pictures -

Another 4hrs for the log - 81hrs so far

12. Jun 28, 2015

### Head in the clouds

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Late last week I had a few hours to spare so I went back to the gear legs and manually descaled them with sandpaper and wire brushes on an angle grinder. That was a great reminder of how much better it is to descale the new tubing prior to welding it into a frame. It was back-aching work and cost a fair bit of skin off the fingers. Finally I had them looking bright and silvery.

I had the axle tubes prepared and a neighbour with a heavy lathe kindly broached keyways into them. A key in the 5/8" bolt which serves as the axle locates into the axle tube on the bottom of the gear leg as well as into the brake caliper, so that the key prevents the axle bolt spinning when the brakes are applied.

I have the axle tube bored to 3/4" with a 5/8":3/4" sleeve on the axle bolt, this will allow me to upgrade the hubs to ones with 3/4" bearings and hence allow the use of 3/4" axles should the current 5/8" ones that I already have left over from the AussieMozzie project, prove to be a bit light. This landing gear is designed to be very rugged throughout as it is expected to take quite a pounding during the 'smack-down' landings which the aircraft should be capable of.

I set up a very simple jig to hold the axle tubes at the correct angles, tacked and welded them in to the base of the gear legs. Some tricky corners to get into during the welding, made much easier with the new small torch, and the appearance of the welds continues to improve as I get more current again.

Then I printed out paper templates for the oleo strut connection, cut them out and used magnets to hold them to some CRMO sheet while I gave them a spurt of paint as a guide for cutting them out. I welded some washers onto the cheeks of the cleats to provide more bearing surface for the oleo connection bolts - and welded the cleats into place on the gear legs.

Once I'd welded a cap plate to each of the combined step and jacking points the legs were ready for painting.

In the last hour of the weekend I notched the forward fuselage tubes that I had already marked out a couple of weeks ago and descaled them.

A few pictures tell the rest of the story -

Another 21 hours in that lot, bringing the total to 102 hours so far.

13. Jun 29, 2015

### Head in the clouds

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Primer adhesion failure - again!

Not happy today!

I had a couple of spare hours so I pulled out all the painted tubes to mark their ends with the wrap templates ready for notching.

To align the templates correctly end for end I place a small piece of sheet metal over two adjacent tubes and run it along the tube so it makes a light line which is indexed the same at each end. Since the tubes are now painted I didn't want to scratch the paint off so I ran it along very gently and was very peeved to see it completely remove a line of paint all the way to the bare shiny metal.

I then used my thumbnail to scrape off in a couple of seconds what is shown in the picture below. The zinc phosphate primer hasn't adhered at all.

An hour on the phone to the paint manufacturer and a while spent on the net and it appears that I should probably have used an etch primer even though it's ferrous steel. On the net I did find a couple of mentions of using a phosphoric acid based 'conversion coating' which converts to a zinc phosphate crystalline layer which chemically bonds to and passivates the metal so that corrosion is inhibited and, more importantly from my point of view, it provides a suitable foundation for the adhesion of the zinc phosphate primer ...

Also - the paint people think that the preparation I did on the metal was probably 'too good' in that the end result was too shiny a surface. I might have been better off to leave the surface sanded rather than wire brushed.

Anyway I have an appointment with the paint company's industrial coatings chemist in the morning so I'll take along some samples and see what they suggest.

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14. Jul 5, 2015

### Head in the clouds

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Back where I was two weeks ago ...

The paint people were very helpful - as described in the DooMaw discussion thread - the tubes were left too shiny, and I used the wrong primer. Although I did abrade the tubes well, I then made them too smooth again by using sandpaper that was too fine (180 grit) and then finishing them on the wire-wheel on the bench grinder. Microscopically you could see that the wire wheel had polished the abrasions out of the steel again and removed all the keying that the paint needs to grip onto.

Also, I should have used a self-etch primer which contains hydrofluoric and phosphoric acids as well as free zinc. Apparently the hydrofluoric etches the steel and the phosphoric passivates the surface and combines with the free zinc to make zinc phosphate which can then bond molecularly to the changed surface chemistry as well as having a good mechanical binding to the keyed and etched surface.

So - I removed all the original zinc phosphate primer by sanding in the lathe again, this time I only used 80 grit and ran it back and forth rapidly to create a criss-cross pattern of abrasions for good keying. As the surface was quite rough I couldn't clean the tubes satisfactorily with a rag and thinners without being likely to leave a fair bit of lint on the surface (thanks Jay) so I built a wash bath out of PVC stormwater pipe and washed them in it with thinners and a nylon brush - it did a good job.

This time I masked off the areas which will be welded and today I re-painted the tubes with self-etch primer. Sixteen hours of work later and we're back to where we were a fortnight ago, albeit in better shape.

It was noticeable that the primer was adhering better the longer it was left, and the gear legs weren't polished on the wire-wheel so I will be leaving them as they are until I'm ready to paint the top-coat, which will be months away, and the non-etch primer may have adhered a lot better by then and save me the effort of having to clean it all off manually. It the meantime they're in storage under the house and the present primer will keep them from rusting, which was the current objective anyway.

Here are some pics -

Another sixteen hours brings the total to 118hrs so far.

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15. Jul 12, 2015

### Head in the clouds

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Progress again at last ...

More delays waiting for information on the day job has its benefits - a bit more time to spend on the fun project.

I was able to spend half of Friday and half of Saturday so I had enough time to template and notch all the ends of the tubing for both of the forward fuselage sides. Then I spent yesterday fitting up the first lot in the jig which I made in January. The unsupported edges of the plywood bench-top had warped a little due to the large humidity changes we've had recently so I added some timber bracing underneath which pulled it back to flat again.

The computer generated wrap templates were very accurate but all the tube members were a tight fit so I had to relieve all the ends just a little and now they all fit nicely without gaps.

I had that finished by mid afternoon so then spent a while retrieving an old wheeled steel cabinet from the back of my storage container. Next I am going to convert that into a welding trolley for the TIG machine and accessories as I'm not finding it as convenient as I'd imagined having it mounted under the project bench. Once that's done I'll tack this side of the fuselage, remove it from the jig and fit up the other side.

Just one pic this time -

Another 17hrs this time, for a total of 135hrs so far.

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16. Jul 19, 2015

### Head in the clouds

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12-19th July 2015

This week's progress -

In a few spare hours early in the week I made the accessories to convert the wheeled steel cabinet into a welding trolley, painted it, made some capped tubes to hold the various filler rods, removed the welder from under the bench and re-wired and plumbed it for the Argon. I also made a purpose-built miniature grinder from a shaded pole motor for dressing the 1mm tungsten electrodes. That all made the welding aspect much more user-friendly as I can now move the welder around easily and all the accessories are in one place.

On Friday afternoon I tacked the first forward fuselage side together, removed it from the jig and on Saturday fitted up all the parts for the second side, tacked that one, labelled and removed all the jig blocks and tacked the other side of both frames.

Today, Sunday, I completed the welding of one of the sides. The welds aren't too bad, but still improving -

I'm not including the hours for building the welding trolley in the log, so another 14hrs on the airframe this week making the total 149 hours.

17. Jul 26, 2015

### Head in the clouds

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20-26th July 2015

Quite a productive plane building week, especially as I had to fit it around a busy week of real work.

I completed the welding of the second fuselage side and really enjoyed doing it. The welds are getting neater and brighter as I get more practiced again.

Once I had the sides done I had to go back to the early part of the next stage so it was all a bit deja vu. Back to the CAD work and produce a dimensioned set-out for the aft fuselage sides, produce full-size templates of all the member junctions, transfer the full-size set-out to the project bench, attach the cluster templates ready for fitting the wood blocking that will hold the tubes in position, produce the CAD wrap templates for the tube member ends, cut the tube members to length and de-scale them in the lathe ready for painting. Then I cut the wood strips up for the blocking and that's where I'm up to now.

I couldn't get the painting done as I've run out of daylight and the damp evening is nigh so everything is under sheets of plastic waiting for the next spare time I have to paint them when it's sunny.

I did have an interesting moment while de-scaling the lengthy longeron members. Necessarily I had a long overhang at both ends and they decided to resonate and had the lathe jumping around the shop floor so I hung a bit of rope over each end with a couple of pounds of lead attached to act as a damper, worked a treat. A bit of graphite dust where the rope was rubbing made sure it didn't get hot from friction and catch alight ...

Pics show welds still getting better and the preparation for the aft fuselage sides -

18. Jul 29, 2015

### Head in the clouds

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Re: DooMaw - build log, 27/28th July 2015

Slow real work days on Monday and Tuesday gave me time to cut, drill and screw the woodblocks onto the table, positioned along the lines on the paper templates.

Then marked and bent the longerons by heating with a propane torch. And used the wrap templates and spray-paint to mark all the tube ends ready for notching -

I forgot to add the hours to the last post, they were 24 bringing the total then to 173hrs and another twelve hours for the work in this post brings us up to 185hrs.

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19. Aug 2, 2015

### Head in the clouds

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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.

20. Aug 5, 2015

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