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Re-covering HDO's fuselage with Oratex printer friendly version
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Bob Grimstead
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Posted Saturday, January 14, 2017 @ 11:18 AM  

Poor old HDO's fuselage paintwork, like that of so many other RF3s & 4s, was flaking and cracking after 48 years of sunshine and flying. The structure is fine, even the underlying madapolam cotton fabric is intact, it's just the many layers of paint on top of one another over the years that cause the flaking.

First, Oratex's documentation says the lighweight (and slightly cheaper) Oratex 500UL is approved for all supported surfaces, ie all wood-skinned fuselages like all production Fourniers.

Next, some people think you need to separate the fuselage from the wing to re-cover either, but with Oratex you don't. Separating a Fournier's fuselage and wing is both time-consuming and risky, with the major potential of causing serious damage to both fuselage and wing, and also the potential of minor damage, particularly from the protruding metal rear spar fittings, during re-assembly. There is also the issue of that awful 'haemhorroid fitting' in the casting at the base if the control column.

Because only the paint on the upper surfaces of HDO's fuselage was badly cracked, I decided only to re-cover it above the blue-painted belly. A two-inch (5cm) overlap of existing fabric is recommended, so I planned to make the transition at the bottom of the blue cheat-line. I masked either side of this with fourteen-day masking tape which, confusingly, happens also to be blue.

Pretty obviously, it is extremely important, while cleanly cutting through the existing paint and fabric, not to score the plywood, because doing that and then bending it is how you break it along a clean line. With a digital vernier caliper I measured the thickness of the existing fabric plus many layers of paint as approximately 0.5mm.

I could probably have rigged up a depth-gauge holder for a snap-blade Olfa knife, but I experimented with a cheap old rotary-blade paper-cutter I had. This routinely cuts through five sheets of normal-thickness paper, which seemed about right, but it was worn and wobbly, and so suffered from variable depth cutting — fine for paper, but not acceptable for this. I tried to buy a replacement, but the only available types had the cutter arm fixed to its board in some way or another. However, Officeworks stocked this neat ceramic knife/cutter.

According to the same digital caliper, its tiny blade is 0.7mm long and the depth of its cut can be varied precisely by changing the angle of its body to the cut surface.

By building up three layers of masking tape 2mm apart, either side of my intended cut I could ensure that I didn't cut too deeply. If my cut was too shallow, I merely removed a layer of masking tape.

Then, starting at the tail, and with my Steinel digital heat gun (which you will already have if you're using Oratex) set to intially 180, then 200, and finally 230°C, I heated and peeled back the old paint and fabric.

I tried using an ordinary Black & Decker heat gun, but that kept causing the removed cotton fabric to char, smoke, and burst into flames, so I strongly suggest not doing that.
Increasing the heat gun's temp above 240-250°C again resulted in occasional charring and smoking from the old fabric (but not the paint) which did not seem a good idea in an OAT of 37°C and a Total Fire Ban in the heat of an Australian summer, so I kept it at 230°. If I happened to knock the control back up to 250° that would quickly generate a smouldering fragment. It's interesting to think that the VW's red-line CHT is also 230°C. No wonder there are alloy protection plates either side of the fuselage by the engine cooling air outlets.

[Edit by Bob Grimstead on Saturday, February 4, 2017 @ 11:22 AM]

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Flying and displaying Fournier RF4Ds VH-HDO and G-AWGN, building replica RF6B G-RFGB and custodian of RF6B prototype F-BPXV

Jorgen
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Posted Sunday, January 15, 2017 @ 06:51 PM  

Go fb Bob go!

Incidently I know of a fuselage partly bare to the wood and I've been contemplating what process would be best, fabric/no fabric etc. I will follow your progress with interest and hope you will share your experience, pictures, foul language and all!

May the 4's be with you/ Jörgen

Bob Grimstead
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Posted Sunday, January 15, 2017 @ 08:26 PM  

Hi Jorgen and Sofi,

I am pleased to say that although it is slow progress, stripping the fabric has revealed a spotlessly clean, undamaged airframe.
Some people advocate covering the fuselage with fibreglass, although I'm not really sure why, and I can see three immediate disadvantages: It must be painted afterwards. It must be heavier than fabric. I think it would be extremely difficult to get it off again in the future.

This stripping is slow, meticulous, laborious work, even after you've got the knack. Fairly obviously, if you try to rush it, you'll cause the sort of damage South East Aircraft Services inflicted on my poor British Fournier.
After a while and some experimentation, I found the best method was to heat an edge, ease the rounded tip of an ordinary table knife under it to lift a bit about a centimetre square, and then grip this with long-nosed pliers and slowly, gently peel it off in a long strip, moving ahead of it with the heat gun to melt the old adhesive (clear dope) at the constantly-moving separation point.

Yours, Bob

[Edit by Bob Grimstead on Friday, January 27, 2017 @ 10:52 PM]

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Flying and displaying Fournier RF4Ds VH-HDO and G-AWGN, building replica RF6B G-RFGB and custodian of RF6B prototype F-BPXV

Donald
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Posted Monday, January 16, 2017 @ 07:20 AM  

Good to see you back on here Bob with some informative stuff.

Regarding the cracked paintwork at the start, having had to make a repair to my own wing last year I have an opinion on this, no surprise there.

Aside from a crack in my leading edge D box plywood I also had some cracks in the paint (dope). Scraping down through revealed some old coloured finish clearly indicating that not all of the fabric had been renewed and that residue of coloured paint/dope gave rise to some incompatibility between old and new finishes, hence the cracks.
Were I ever to recover my Fournier I would therefore ensure it was stripped to the wood, so your post here about stripping is good.
I'd also be seriously tempted to look at Oratex purely to avoid the spray part of the process.

Bob Grimstead
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Posted Monday, January 16, 2017 @ 10:00 PM  

My thoughts entirely Donald.

I am convinced that most of the paint cracking on older Fourniers is because somebody in the past has decided to re-spray over the existing paint, rather than do the job properly.

And yes, the lack of a need to paint it afterwards is my prime motivator for using Oratex.

The weight saving is merely a nice additional benefit.

Yours, Bob

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Flying and displaying Fournier RF4Ds VH-HDO and G-AWGN, building replica RF6B G-RFGB and custodian of RF6B prototype F-BPXV

Bob Grimstead
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Posted Sunday, January 22, 2017 @ 05:34 AM  

When peeling off the long strips as described above you need to use surgical care, otherwise they just snap off.
On some areas it was just impossible to do this and the old stuff had to scraped off laboriously, centimetre by centimetre. It was very frustrating and time-consuming. For reasons I shall never understand, and believe me I have thought about this a lot, the area on the left side of the fuselage between the canopy latch and the static port was by far the most difficult of all.

Time taken so far:
Measuring, marking, masking, cutting 3:00.
Disconnecting tail controls, removing fin fillet and inspection panels, tail surfaces, canopy, hinges, cowlings, exhausts & protective side plates (including making a couple of specialised tools) 4:30

Removing old fabric. As far as I could measure accurately, I expended a total of 53 hours scraping off the old fabric and paint (over eight days of working). That's only from three-quarters of the fuselage's circumference of course. The blue bottom area will be done another day.

The good news is that throughout the airframe the plywood looked like new, with no damage or oil soakage, and only the tiniest bit of staining at the eight screw holes holding on the front protective exhaust shields. There was also visual evidence of disolved dirt having soaked through many tiny cracks in the surface paint around the fuel tank filler, but these mostly wiped away with MEK.


[Edit by Bob Grimstead on Friday, January 27, 2017 @ 10:27 PM]

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Flying and displaying Fournier RF4Ds VH-HDO and G-AWGN, building replica RF6B G-RFGB and custodian of RF6B prototype F-BPXV

Bob Grimstead
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Posted Saturday, January 28, 2017 @ 10:51 AM  

Once all the preparation had been completed, the actual application of the fabric was comparatively rapid. I had previously measured the circumference of the fuselage from the lower blue line on one side of the cockpit to the other as being six feet (the width of the fabric) just ahead of the rear corner of the cockpit cut-out in the fuselage. So I planned to use one continuous piece of fabric from the stern-post to this point, and then overlap it with another single piece of fabric working from the firewall backwards. Because it was important that the new fabric exactly abutted the edge of my pre-existing paintwork, I decided once again to ignore the direction of the very fine warp and the weft in the fabric and simply place the beautifully finished edge of the new fabric directly against the lower left line on my fuselage.

First I laid the fabric over the rear fuselage and taped it in place to cut it approximately to shape, marking with a 2B pencil the area on which to apply the adhesive.

Then I spread the cut fabric, shiny side down on my suitably masked five-metre work table (the right wing) and painted glue on it while Karen painted it all over the fuselage. As advised, we use foam 'brushes'. It is important to keep a wet edge and not get any runs or bubbles — as usual.

Then I ironed on the fabric (at 90°C) following up with Oratex's felt blade to hold it in place as it cooled, being sure a) to press hard — 3kg and b) not to push it off the Jerry can it was standing on to be at a useful height.

Then I popped the fin and canopy back in place to make it look more finished than it really was.
Total time taken from opening the hangar door to closing it again was just under four hours — not a bad day's work, all told.

More soon, Bob

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Flying and displaying Fournier RF4Ds VH-HDO and G-AWGN, building replica RF6B G-RFGB and custodian of RF6B prototype F-BPXV

Bob Grimstead
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Posted Sunday, January 29, 2017 @ 08:25 AM  

I have realised that I've missed out a step.

Oratex (and most other fabric manufacturers, I believe) recommend a 5cm (two inch) overlap of the new fabric over the old, so I peeled off the masking tape, re-masked two inches lower along the underside blue line with low tack tape so that I didn't pull off the old paint when I was done, and then used the heat gun & knife to remove the many layers of paint. That was easy and got off most of it. Acetone removed the remnants. Then I left it to dry.

When the remaining fabric & dope was thoroughly dry, I sanded a chamfer along the top edge. I was surprised at how straightforward this was, and also how very effective, with no fraying.

Leaving the lower masking tape in place, Karen painted on the adhesive and then we're back to the top of the last post.

[Edit by Bob Grimstead on Monday, February 6, 2017 @ 10:16 AM]

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Flying and displaying Fournier RF4Ds VH-HDO and G-AWGN, building replica RF6B G-RFGB and custodian of RF6B prototype F-BPXV

Bob Grimstead
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Posted Monday, February 6, 2017 @ 10:32 AM  

Today's achievement...

Laying out the forward fabric and cutting it roughly to shape.

By chance, I have used precisely five metres of fabric so far.

I have mostly ironed it in place today, but not completely finished. Fitting it around the fuel tank filler was a bit of a bugger, plus I kept getting inquisitive visitors, which seriously didn't help my concentration. Working with hot tools... well, I won't go on about the weather, but it did become a bit fatiguing. Anyway, each wrinkle has a name: They are Ed, Howard, Paul and Rick. There are a few small, unamed ones too!

One thing about Oratex. You're supposed to stretch it out flat with one hand, while ironing it with the other, over the silicone paper you hold in your third hand, while smoothing it down with the felt blade in your fourth hand. I find that all a bit tricky.

I'll try to provide a photo soon, but there is lots of other stuff happening right now.

Yours, Bob

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Flying and displaying Fournier RF4Ds VH-HDO and G-AWGN, building replica RF6B G-RFGB and custodian of RF6B prototype F-BPXV

Bob Grimstead
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Posted Sunday, February 12, 2017 @ 09:11 PM  

Glueing & covering that front part took 4hrs & 5 hrs, with the fiddly finishing & trimming around the lower edges and tucking the forward edges under the firewall taking another 4 hrs.

This whole job used exactly 5 metres (leaving me three spare) of fabric and 500ml (half a litre) of adhesive. Obviously, if you were covering an entire fuselage you would need more of both. Probably eight metres of fabric and a full litre of adhesive.

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Flying and displaying Fournier RF4Ds VH-HDO and G-AWGN, building replica RF6B G-RFGB and custodian of RF6B prototype F-BPXV

Bob Grimstead
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Posted Friday, February 17, 2017 @ 10:27 PM  

Pretty obviously, I didn't want to remove the firewall, because that would entail removing the whole engine with all the other work that goes with it. Also there's asbestos in there! But the outer firewall material is pretty soft aluminum, so I simply teased up the edge by perhaps thrity degrees to remove the final vestiges of the old paint & fabric.

After applying the new fabric all over the foredeck, I carefully trimmed it to fit, and then pushed the front edge under the firewall's lip with my trusty Royal Australian Navy round-tipped table knife.

I then set the glue by playing the heat gun on the knife's blade, while pressing down on it, and it stuck down beautifully. The final step was to tap down the firewall's lip gently back into place with a light hammer.

Job done!

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Flying and displaying Fournier RF4Ds VH-HDO and G-AWGN, building replica RF6B G-RFGB and custodian of RF6B prototype F-BPXV

Bob Grimstead
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Posted Sunday, February 19, 2017 @ 11:45 AM  

When all seemed done, I was dissatisfied with the join along the bottom. There was a two-inch overlap of the new Oratex over the original madapolam, as required, but there was a definite difference in thickness at the lower butt-joint between the many layers of paint on the belly and the fag-paper thin Oratex above it. I was concerned that water, oil or possibly spilled fuel might run down the Oratex, and then seep behind the thick, multi-layered paint around the belly, perhaps softening it and allowing it to peel away from the underlying madapolam.
So I ran two lengths of masking tape along the joint, one a milimetre or so above the joint and the other a millimetre or so below. The plan was to run along a 2 to 3 mm pinstripe of white paint to seal the join.

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Flying and displaying Fournier RF4Ds VH-HDO and G-AWGN, building replica RF6B G-RFGB and custodian of RF6B prototype F-BPXV

Bob Grimstead
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Posted Monday, February 20, 2017 @ 03:02 PM  

I think that worked out quite well.
It is definitely sealed, and you can only see the thin line of white Hammerite Smooth paint if you look really closely.

The upper blue lines are temporary cheat lines made from blue masking tape, pending the arrival of specially ordered blue Hammerite.

[Edit by Bob Grimstead on Monday, February 20, 2017 @ 03:03 PM]

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Flying and displaying Fournier RF4Ds VH-HDO and G-AWGN, building replica RF6B G-RFGB and custodian of RF6B prototype F-BPXV

Bob Grimstead
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Posted Monday, February 27, 2017 @ 03:27 AM  

I pondered for a long time about how to seal around the fuel tank filler neck. A bit of research turned up this product: Dow Corning 730 solvent resistant sealant. It is expensive (more than $100 per tube) but it is the best thing I could find for the job.

I used a wooden lollipop stick to smooth off the surface once I had applied the sealant. While it is still damp, excess can be wiped away from the metal surfaces with a rag soaked in MEK. Oratex doesn't like MEK so it's better to use isopropyl alcohol on that
I haven't perhaps produced the best possible finish, but it is completely sealed so that fuel can't get under the new fabric.
Oh, and it is white, so it looks much better than the original black Sikaflex.

Happy Fournicating, Bob

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Flying and displaying Fournier RF4Ds VH-HDO and G-AWGN, building replica RF6B G-RFGB and custodian of RF6B prototype F-BPXV

Bob Grimstead
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Posted Wednesday, March 1, 2017 @ 02:53 AM  

Neither Oratex nor Hammerite make a light blue paint matching HDO's Plyfiber/Poly-Tone Bahama Blue, so Karen mixed their dark blue with white until she got the nearest possible colour for the side-stripe cheatlines. I traced the upper front curve by eye, but the more important lower, swoopy, aerofoil-shaped curve will have to wait until I bring out the template from England.

Here she is all masked up and painted. It's confusing, because the masking tape is blue too!

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Flying and displaying Fournier RF4Ds VH-HDO and G-AWGN, building replica RF6B G-RFGB and custodian of RF6B prototype F-BPXV

Bob Grimstead
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Posted Friday, March 3, 2017 @ 11:32 PM  

And here she is completed.

At last I got to fly her again yesterday. She doesn't fly any better, but she does look a lot nicer :-)

I shall leave the current cowlings white, but the new cowlings for the new engine will be painted blue in accordance with the original Fournier scheme.

Yours, Bob

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Flying and displaying Fournier RF4Ds VH-HDO and G-AWGN, building replica RF6B G-RFGB and custodian of RF6B prototype F-BPXV

Jorgen
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Posted Saturday, March 4, 2017 @ 02:03 PM  

Looks magnificent Bob,
well done!

May the 4's be with you/ Jörgen

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