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Valdez Stol Record breaker build blog

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Levanter20/03/2019 13:44:55
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436 photos

Peter

Absolutely on my build list so looking forward to the magazine. When you know which issue, will you let us know.

Another one of your quirky designs you like so much.

If I can take off and land on my balcony I will be well chuffed wink

Levanter

Edited By Levanter on 20/03/2019 13:45:43

Peter Miller20/03/2019 18:13:38
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10253 forum posts
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It will probably be announced the month before and that couldbe the first I know but if I know before I will tell you.

It depends on the size of your balcony....surprise

Oh! And I have found another quirky design..

Tim C09/04/2019 13:23:48
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496 forum posts
259 photos

This will be a summarised build blog of Frank Knapps Li’l cub.

This will be the free plan in June’s RCM&E. Just to wet the appetite of aspiring builders, Peter had kindly sent me a copy of his original hand drawings, sketches and some build notes, and will be using those as a basis for the No 2 protoytype build.

The plan is for an electric powered 55in span model around 1:6.5 scale and 3 Lbs AUW. It’s and all wood build.

The Knapp original is a heavily modded Cub J3, stripped to bare essentials, lots of carbon fibre , new STOL wing with flaps and leading edge slats. In 2017 the aircraft set a new STOL world record at Valdez, with a take off in 13 feet 8 inches, and a landing in 10 feet 5 inches. A reputed top speed of 62mph with its large low pitch prop to maximise take off thrust.

I have made a few minor changes to the original that will hopefully work out and add a touch more scale fidelity. I will detail these in the build blog.

Tim C09/04/2019 14:01:12
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496 forum posts
259 photos

I made a start with the tail, elevators, rudder and fin. The tail has a 1/4 in balsa spar and laminated outlines from 3 x 1/16 balsa strips. I made the laminate mould from 6 mm depron. The balsa was soaked in my custom soaker, a length of old waste pipe sealed at the bottom with aluminium duct tape, fill with hot water, pop in the balsa, bung the end with a piece of foam, and 10 mins later you have pliable balsa ready for bending, I used Titebond and held the laminates in place with masking tape.

a0c0d35d-a37d-4fde-a856-18f9896cae3c.jpeg

Tim C09/04/2019 14:04:02
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496 forum posts
259 photos

Completed outlines, I left in the join on the elevators spar, which I will cut out once I put in the wire joiner, makes the job easier and keeps all nice and flat

cb43ccf8-9503-4d53-95d3-f7193254ed5d.jpeg

Peter Miller09/04/2019 14:04:32
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10253 forum posts
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10 articles

Hi Tim

Glad to see you here. Your mods and improvement will be very useful to others. I may comment on some of them.

Tim C09/04/2019 14:05:26
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496 forum posts
259 photos

Completed fin and rudderfd8c6dc4-4a4b-464d-9ab4-12e2b9ff4358.jpeg

Tim C09/04/2019 14:13:21
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496 forum posts
259 photos

I have opted to use polyspan (polyester tissue) for the covering. This is iron on using Balsaloc ( or In my case Impex Pva, which is in the gold bottles from any haberdashery or Hobbycraft store). It shrinks on like solarfilm, heat takes out the wrinkles, shrinks round corners really well, then 2 coats of dope to seal it. I have airbrushed Dulux tester pot yellow, mixed to Lockhaven yellow, the True cub yellow colour, the rudder has 2 coats on it probably needs a another coat

 

ea794045-495e-4872-92c1-543937799036.jpeg

Edited By Tim C on 09/04/2019 14:30:56

Tim C09/04/2019 14:14:53
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496 forum posts
259 photos

Covered fin in polyspan6f7ce2c4-7f82-490b-a1a4-85ecae7fc2ee.jpeg

Tim C09/04/2019 14:33:01
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496 forum posts
259 photos

I have opted for polyspan as the covering medium, for those not familiar, this is a polyester tissue, it’s lightweight, strong for it weight, but the strength is a bit unidirectional, in that it tears more easily on one direction than the other. It heat shrinks but needs a separate heat sensitive adhesive. I used Impex original hi tack all purpose glue, available from most haberdashers, it used by sewing and garment makers.

Polyspan is applied glossyside up, the adhesive I thin very slightly, maybe mines thickened, as the bottle is over 4 years old! Brushing on a coating on the balsa surfaces and letting it dry, lay over the polyspan tacking down and pulling it tight, I use a slightly hotter iron than with regular covering circa 130c, once it’s covered, I ramp up the temp to 170c and shrink and seal up the edges. Repeat the adhesive on the reverse side and brush a coating on the overlap edges and repeat again,

What you end up with is a nice wrinkle free taught covering. Next off I used a coat of shrinking dope to seal the surface, but WBPU seems to work as well, though needs an additional cote. Already for top coat colour cote.

Tim C09/04/2019 14:34:55
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496 forum posts
259 photos

I have airbrushed a cote of Cub yellow on the rudder as a test of the paint and colour.

Just as Ferrari’s have to be red, Land Rovers Green ( despite my current one being blue!), Cubs need to be Cub Yellow. Cub yellow is a much disputed colour, but widely accepted that Lockhaven yellow is the correct colour. Using a colour chip found on the internet I converted the code to one that Homebase can use in there Dulux colour paint machines, £3 and I was in possession of a 250ml pot of Lockhaven yellow, well the Dulux equivalent .

For spraying I mixed up some paint with 10% of Floetrol and thinned with Lidl window cleaner to a consistency the would spray with my airbrush, I was pleased with the colour, which looks correct in my eyes, and it flowed and sprayed on well, it’s only one coat so far, it will probably need 3 thin coats to provide an opaque finish, no primer is used, I will finish of with a final coat of Matt clear WBPU to seal the surface.

 

Rudder hinges

 

Edited By Tim C on 09/04/2019 14:35:20

Tim C13/04/2019 09:11:04
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496 forum posts
259 photos

ceceb500-aa1b-4a53-b39a-f41abb2230a9.jpegNot a lot of progress this week due to major plumbing disaster, water coming up through kitchen tile floor due to burst pipe in the screed, eeek!

anyway manage to finish of the tail group and get it hinged ready for covering, I do like the mini hinges from Banggood

Edited By Tim C on 13/04/2019 09:13:36

Dwain Dibley.13/04/2019 13:47:07
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1269 forum posts
1265 photos

Hi Tim,

Great Blog........wink

What weight covering did you use, there are 15g, 25g and 35g per sq M available at free flight supplies.

Thinking of using this on my Cessna 120, so I can use a chrome paint ???

Cheers

D.D.

Tim C14/04/2019 11:32:34
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496 forum posts
259 photos

Covering in Polyspan. I use the 25gm version, I have trialled the heavier 35gm type, but concluded no real benefit, this version has a threads running one way as extra strength, this hinders shrinking as is more uni directional, and tear strength is only improved across the material, not much different the other way.

stage 1 is to cut out a piece of material, make sure shines side up, I use a circular cutter, easier than scissors.

tail cover 1.jpg

Tim C14/04/2019 11:34:24
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496 forum posts
259 photos

Next is to coat the balsa in glue, I use impex, brushed on slightly diluted and left to dry.

impex.jpg

Tim C14/04/2019 13:52:38
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496 forum posts
259 photos

Tacking with iron, then seal down all the edges, shrinks well around the curves

Cover with the polyspan, just place over the top shiny side up and tack withe iron, I use about 130c

cover.jpg

Tim C14/04/2019 13:54:48
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496 forum posts
259 photos

I then run to iron to seal the trimmed edges, and a quick run to shrink the covering, all ready for the top side covering.I use a double edge razor blade for trimming, just tape over 1 edge to protect the fingers

trim.jpg

Tim C03/05/2019 15:49:13
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496 forum posts
259 photos

I am getting behind with both building and posting on the blog. A plumbing disaster, bust hot water pipe in the solid floor in the kitchen and a holiday away caused work to stall.

I have nearly finished the wings, and have been working on the flaps and ailerons. I designed a flap hinge which I printed on my ANET A 8, this gives a slotted flap, it will be screwed and glued on final assembly. The pics show the trial version. I used a M2 hex bolt and nut for the pivot.

hinge1.jpg

Tim C03/05/2019 15:49:58
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496 forum posts
259 photos

More detail of the hingehinge2.jpg

Tim C03/05/2019 15:51:20
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496 forum posts
259 photos

Hinge in action

hinge3.jpg

hinge5.jpg

hinge4.jpg

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