Marty d's CH-701 build log

[rick morawski]

He is in Tasmania...... gotta the workplace warm, or you get to inclined to stay out of it.

Put another aircraft build log on the fire

 

 

[Head in the clouds]

Sorry I haven't commented earlier but life's been getting in the way and I've only just found time to read through this thread.

 

I'm very impressed Marty, you're doing a fantastic job!

 

Your metalwork is exemplary, an absolute delight to look at. You demonstrate true craftsmanship, do you have a background in metalwork?

 

And - as others have said, it's a huge undertaking to build from scratch. I'm often just slightly amused by those who say 'I built it' when they actually have assembled it from a very complete, and often mostly pre-assembled kit. But that's not to take away anything from those who have gone that way. In my mind that puts them streets ahead of those who just bought a complete aircraft - I'm talking specifically in terms of their resultant knowledge of the airframe and systems - but it's a far cry from really having 'built it' as you are doing. I'm really looking forward to seeing the rest of it coming together, so thank for posting your log here.

 

Regarding paint protecting the edges and laps, and preventing moisture getting between sheets, it's absolutely essential that you don't think of paint that way, primarily because most paints are not adhesives, and are also quite brittle. When the skins are first painted it may look like the paint has formed some degree of sealing but with the constant movement of the airframe and the vibration, the paint always cracks along the junctions between sheets. The cracks can be so fine that they're not visible to the naked eye but moisture makes its way in very readily. In fact the finer the crack, the more powerful the capillary action is ...

 

As far as I know, there is only one coating that won't crack, and which will provide a good seal, and that's a flexible (rubberised) epoxy coating - the type which is used for sealing the inside of water tanks. I've used that several times, and with remarkably successful results that last decades ... on aluminium and steel boats. Unfortunatley it has several drawbacks which usually makes it unsuitable for planes, except perhaps for floats and floating hulls. It has to be applied thick so it's heavy, it must be applied direct to the clean scuffed metal i.e. no primer or undercoat, and it oxidises with UV exposure and gets a chalky surface, so it needs regular attention with wax polish to keep it glossy.

 

If you really need to seal the laps and butts that epoxy is a good way to go but the downsides listed above would usually preclude using it. Instead it's better to make a really good job of priming and undercoating the edges of each sheet (I've found White Knight etch primer to be among the best in a spray can that's readily available if you want to avoid the Alodine or Zinc Chromate process) before final assembly. Then, after the plane has been painted, liberally apply one of the aviation anti-corrosion thin film treatments, ACF-50, Corrosion X, Fluid-Film or similar, or work lanolin into the joint, or work 3-in-1 white lithium grease into the joint, and then polish the surfaces and joints with a hard bees-wax polish. Repeat the wax polish after 50 or so flight hours once the first paint cracks will have formed, and thereafter at least once a year. If you do the cleaning and waxing well and keep an eye on potentially suspect (ponding) areas, I'd defy corrosion to set in.

 

BTW - folk were talking about polishing the aluminium. Some planes are built using Alclad 2024T3 and others using non-clad 6061T6. The Alclad has a thin coating of pure aluminium on the surface which polishes to a mirror finish and is very resistant to corrosion. The Ryan pictured above is a good example of that. 6061T6 (and other marine grades) can be polished but it takes a fair bit of effort and there is a downside. 6061T6 is formulated to be left unpainted if desired but should only be polished if it will then be kept coated with a wax (or similar) polish. The reason is that the 6061T6 protects itself by oxidising on the surface (which gives it a dull patina), and if you polish that oxide away it's not protected anymore so it oxidises again and then you polish it ... quite soon it's all oxidised away altogether. With 6061T6 you're best to either abrade it when new with Scotchbrite or similar - or leave it to weather for a few months - then paint it with a thin coat of epoxy-based primer (for good adhesion) followed by a top-coat of polyurethane for colour and a hard and durable non-chalking surface. Just my opinion based on previous ...

 

Keep up the great work!

 

 

[rmorton]

Some great advice from Head in the clouds, thank you. I am hoping to get the Savannah kit and is an assembly type build, but I simply dont have the time skills or space to go from scratch with an Ali plane. I know however that the day I finish the kit (if I ever finish) the urge to build will be stronger than ever so a second project will have to be started.

 

You raised some interesting points about sealing joints and laps, The Savannah is a 6061 aluminium and they provide a protective paint for all metal to metal joints, which I assumed was for corrosion protection and sealing. That said if the aluminium protects itself with a layer of oxide doesn't that protect the joint? I am beginning to think that a preparation and epoxy primer are the easiest way to go. I bought some Prekote and Ekoprime to try but for areas prone to fuel spillage I will go for an epoxy primer. Hopefully for internal areas dont require more than that.

 

Th polished look is my favourite however unless I can find a protective clear coating such as the ever shield (not easy to get here) I dont fancy the republish every year that you describe.

 

Really looking forward to more Marty on the subject of painting and even more on the fitting out engine installation etc. Good luck and keep up the good work

 

 

[Head in the clouds]

..... - then paint it with a thin coat of epoxy-based primer (for good adhesion) followed by a top-coat of polyurethane for colour and a hard and durable non-chalking surface. Just my opinion based on previous ...

CORRECTION - I mustn't have been concentrating when I wrote the last line, it should have read "..... - then paint it with a thin coat of 2 part epoxy for good adhesion (i.e. not epoxy-based primer - the epoxy is self-priming so it doesn't require a primer) followed by a top-coat of ACRYLIC (i.e. not polyurethane) for colour and a hard and durable non-chalking surface. Just my opinion based on previous ..."

 

If you've used the epoxy for adhesion you will find that many slipways happily use a quality acrylic exterior paint (like Wattyl Solagard or Dulux Weathershield) over the top of it to protect the surface of the epoxy. These types of exterior paints generally come with a 15 year guarantee on the outside of houses with full weather exposure, so they're flexible and tough, and have good UV stabilisers. They also stick well to the epoxy surface, I've painted several boats that live afloat in harsh marine environments, that way with excellent results, and those exterior paints are about 20% of the price you have to pay for specialised aviation or marine coatings.

 

 

[eightyknots]

CORRECTION - I mustn't have been concentrating when I wrote the last line, it should have read "..... - then paint it with a thin coat of 2 part epoxy for good adhesion (i.e. not epoxy-based primer - the epoxy is self-priming so it doesn't require a primer) followed by a top-coat of ACRYLIC (i.e. not polyurethane) for colour and a hard and durable non-chalking surface. Just my opinion based on previous ..."If you've used the epoxy for adhesion you will find that many slipways happily use a quality acrylic exterior paint (like Wattyl Solagard or Dulux Weathershield) over the top of it to protect the surface of the epoxy. These types of exterior paints generally come with a 15 year guarantee on the outside of houses with full weather exposure, so they're flexible and tough, and have good UV stabilisers. They also stick well to the epoxy surface, I've painted several boats that live afloat in harsh marine environments, that way with excellent results, and those exterior paints are about 20% of the price you have to pay for specialised aviation or marine coatings.

Solagard is an amazing product. Where I work we used to use "road paint" to mark the car park stripes. This lasts about 5-6 years in full sun. The problem is that the road paint is expensive and has some pretty bad fumes coming off it. We tried Wattyll Solagard and this is pretty much fume-free and it seems to be just a durable for car tyre wear and sun exposure as the road paint which is four times the price. "What'll they think of next?"

 

It had never occurred to me to use Solagard as an aviation paint: it is a pretty tough product, once it has had a week of hardening, and remains somewhat flexible as HIC pointed out, a real plus.

 

I wonder if Solagard can be applied to aircraft aluminium with a non-epoxy undercoat? (I am thinking of lightness)

 

 

[Marty_d]

Sorry I haven't commented earlier but life's been getting in the way and I've only just found time to read through this thread.I'm very impressed Marty, you're doing a fantastic job!

 

Your metalwork is exemplary, an absolute delight to look at. You demonstrate true craftsmanship, do you have a background in metalwork?

Thanks HITC, I'm truly humbled to get praise from you!

 

No, I have absolutely zilch previous background in metalwork. Oh, I think I folded up a letter holder for my parents in grade 7.

 

All credit goes to the designers of this aircraft, who have thought through the process of building this plane very intelligently. For example, the rear fuselage and wing skins all fit from standard 4' x 12' sheets of 0.016". If your ribs are bashed out pretty square and the holes in the skins are drilled according to plan, then the wings will go together without twist. The plans and photo guides are comprehensive and so far I've found no areas of confusion.

 

I think your DooMaw is an entirely higher level, given you are not only designing the whole thing from scratch but also welding the frame (welding is a mystery to me, up there with astrophysics and feminine thought processes).

 

I used to design and build my own R/C aircraft, which I guess taught me a fair bit, but it's a whole different level of care when my butt (and others) will be actually in the aircraft.

 

 

[rmorton]

Just a quick question but do you "press" the ribs to shape them or are they just riveted ? I ask because ICP explained that they re-temper the aluminium by reheating and cooling to fairly precise temperatures when it has been folded or pressed.

 

 

[Marty_d]

Just a quick question but do you "press" the ribs to shape them or are they just riveted ? I ask because ICP explained that they re-temper the aluminium by reheating and cooling to fairly precise temperatures when it has been folded or pressed.

All the alloy in the 701 is 6061-T6, which has already been tempered. To manufacture the ribs you cut out two wooden form blocks from wood, which include channels around the edge for relief bends. The rib blanks are screwed between the blocks, placed in a vice and belted with a rubber mallet to fold over the edges at 90 degrees to the rib. To stop crinkling in the bent over bit, you use various diameter rods/tubes (from screwdriver shank to 20mm) to whack in the relief bends, which then straightens out the bits between the reliefs nicely.

 

Finally the lightening holes are done with a fly cutter, placed between flanging dies and pressed with a car jack. Works like a charm but gets a bit wearing when you have multiples of the same part.

 

 

[eightyknots]

All the alloy in the 701 is 6061-T6, which has already been tempered. To manufacture the ribs you cut out two wooden form blocks from wood, which include channels around the edge for relief bends. The rib blanks are screwed between the blocks, placed in a vice and belted with a rubber mallet to fold over the edges at 90 degrees to the rib. To stop crinkling in the bent over bit, you use various diameter rods/tubes (from screwdriver shank to 20mm) to whack in the relief bends, which then straightens out the bits between the reliefs nicely.Finally the lightening holes are done with a fly cutter, placed between flanging dies and pressed with a car jack. Works like a charm but gets a bit wearing when you have multiples of the same part.

If, or rather when, I am going to build a plane it will be an assembly of parts rather than what you have been doing.

 

Marty, I have great admiration for what you are achieving. Do you have any pictures of the process you have described above?

 

 

[rmorton]

Thank goodness your doing a biplane! That is indeed an impressive amount of work for each rib and no doubt sub-assembly. When I visited the ICP factory much of the "clever machinery and testing was linked to the bending and re-tempering of the ali (which is also a 6061. The difference I think is that they need speed so they soften the metal first press and bend it then temper back to specification. I would love to see the finished ribs and assembly of your plane though.

 

 

[Marty_d]

If, or rather when, I am going to build a plane it will be an assembly of parts rather than what you have been doing.Marty, I have great admiration for what you are achieving. Do you have any pictures of the process you have described above?

Thanks 80kts. Just been looking through some old photos and although I don't have pics of me wielding the rubber mallet, here's a couple:

 

1. Laying out the bits:

 

 

2. Wooden forms for wing rear ribs - see relief indentations. All formwork has a 3mm radius routed into it to prevent stress at the bend.

 

 

3. Formed rib (stabilizer)

 

 

4. Equipment to flange the lightening holes - borrowed from a fellow builder here in Tas - thanks James!

 

 

 

[Marty_d]

Status update: historical pics

 

 

Looking through the old photos, I thought I'd post some to show various parts.

 

1. Rudder skeleton & skins. This was the first assembly, you can imagine the stress (on me, not the part!)

 

 

2. Finished rudder.

 

 

3. Stabilizer skeleton. The little fellow on my back is Harry - he's 6 now!

 

 

4. Stabilizer complete.

 

 

5. Stabilizer and elevator joined. Testing trim tab deflection.

 

 

6. Close up of stab/elevator centre hinge point.

 

 

7. Close up of stab/elevator outer hinge point.

 

 

8. Formed wing rear ribs and nose blanks (sitting on spar web).

 

 

9. Bending nose skin over using ratchet straps.

 

 

10. Wing tip installation.

 

 

11. Installing the Savannah wing tank.

 

 

 

[rmorton]

Brilliant

 

 

[eightyknots]

Status update: historical pics

 

Looking through the old photos, I thought I'd post some to show various parts.

 

1. Rudder skeleton & skins. This was the first assembly, you can imagine the stress (on me, not the part!)

The designer (Chris Heintz) was a stress engineer for the Concorde and Robins in France as well as for De Havilland in Canada.

 

(as the designer, so the builder)

 

 

[Marty_d]

I knew he worked on the Concorde, didn't know what bit though.

 

 

[eightyknots]

I knew he worked on the Concorde, didn't know what bit though.

I understand he did the "higher order" stress calculations for the Concorde. I would have to re-find his bio (somewhere on line) which describes this some more.

 

 

[Head in the clouds]

.......Finally the lightening holes are done with a fly cutter, placed between flanging dies and pressed with a car jack. Works like a charm but gets a bit wearing when you have multiples of the same part.

 

.....4. Equipment to flange the lightening holes - borrowed from a fellow builder here in Tas - thanks James!

 

[ATTACH=full]46944[/ATTACH]

I can imagine winding the car jack up and down a hundred times or so would have been a bit wearing ...

 

I guess it's a bit frustratingly late to mention it for your current build, but it doesn't actually take much force to press the flange around the lightening hole, so next time you don't really need a jack or a powerful shop press. On mine I use forming dies that are virtually identical to your friend's, and I just bump them together using the quill of the drill press. It's pretty much effortless and each one takes about two seconds -

 

 

Terrific craftsmanship once again Marty, and another great set of scratch build photos, thanks for posting

 

 

 

[Marty_d]

Thanks HITC. I didn't know about the drill press trick - wish I had!!

 

Bit stalled at the moment as other projects have taken over. I'm champing at the bit to get started on the fuse.

 

 

[Marty_d]

Ok, bugger the other projects - I needed to build!

 

Started on the rear fuselage by marking and cutting out the bottom skin, then clecoed the two rear formers and the next two L angles.

 

Jeez it felt good.

 

 

 

 

[nomadpete]

It's raining too much to do any domestic infrastructure building. Glad to see you're off to a good aircraft start for the new year.

 

 

[Marty_d]

It's raining too much to do any domestic infrastructure building. Glad to see you're off to a good aircraft start for the new year.

Isn't it! Corner of Davey St and Sandy Bay Road is flooded apparently. Pelting down here - the tanks are full.

 

 

[Marty_d]

Over the last couple of weeks I've been doing endless marking out and cutting of the various bits and pieces needed for the fuselage.

 

Most of the stuff that needs to be bent up is too long for my little 750mm bending brake, so I'm getting everything ready for a visit to my friendly sheetmetal man. I think I'll need to book him for about 3 hours - there's a lot of stuff to do.

 

Will post photos when it's done - at the moment there's not much interesting about a bunch of flat strips with lines and scribbling on them!

 

 

[MartyG]

Hey Marty-d, Any idea what the cost difference is between building from scratch as you have and purchasing the complete kit tto assemble?. cheers

 

 

[Marty_d]

Hey Marty-d, Any idea what the cost difference is between building from scratch as you have and purchasing the complete kit tto assemble?. cheers

Hi Marty,

 

Well, the bare metal cost a bit over $5,000 freighted down from Sydney. I've probably spent another $2,000 or so on bits and pieces - picked up some Savannah fuel tanks, wheels, doors etc, and some stuff from Zenith in the US (gear/strut welded assemblies etc).

 

I don't know what the kit price is, but if you don't want to spend years producing what's in the kit, it's probably worth it!

 

Of course this doesn't include engine, FWF, instruments etc, but you don't get that in most kits either.

 

Personally if I was going to get something a bit cheaper than a kit or completed aircraft, I'd do what Mark (Kyle Communications) is currently doing - buy a damaged aircraft and do it up - http://www.recreationalflying.com/threads/my-savannah-s-model-rebuild-blog.156180/unread.

 

 

[Old Koreelah]

Hey Marty, just catching up on your log, I noticed one deficiency in your ergonomics.

 

While building a plane you often need the assistance of an extra set of hands.

 

Why not wear Harry's harness in front?