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Author Topic: PZL Wilga for .5cc diesel  (Read 8259 times)
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Squirrelnet
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« Reply #50 on: December 03, 2018, 05:38:40 PM »

Just wondering if or how slats work at these scale sizes?

I’m not sure how effective they will be as slats for delaying the stall but in a model I think the key thing will be to keep both sides the same. I built a Bowden Meteorite which has similar slats but in the tips only . Its a good stable flyer even in a breeze but trimming it made me realise how critical the slot gap is. Any small difference resulted in an unwanted turn , I’m expecting the same from this one.

The experience of trimming the Meteorite lead me to think that if the gap is too small the slats merely add extra drag as air slows trying to get through the gap ,the turn was always towards the side with the narrower gap. It could well be that on a model all they do is add extra drag ? .... The Bowden Meteorite is rock steady though
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Squirrelnet
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« Reply #51 on: December 08, 2018, 01:27:05 PM »

Time to tackle the cowling   Grin.

I spent most of the day at work  Undecided so workshop time was a bit limited today but some progress was made

For those that are interested I stuck a long 6mm coach bolt through the centre line of the planked balsa cowling/pen holder and bolted it up tight with some large 2" washers so I could put the whole thing in a drill.

Some coarse 80 grit oxide paper was taped to the bench and the outside edge gently sanded down to the rear edge dimensions, I wore a dust mask for this.

With the rear edge at the right size I then used some good old 'boy scout' whittling with a snap knife to get the rough shape and then more sanding with the drill.

The result needs a bit more fine sanding work but looking the right shape at least
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Squirrelnet
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« Reply #52 on: December 09, 2018, 01:12:33 PM »

Some more work on the cowling today.

First thing, I made a dummy grill for the cowl from 1mm ply. I will cut this up later into inner and outer rings and add the grill slats from 1/64 ply but for now it finds the centre for where the engine needs to poke out. First problem was that the original AP plan has the thrust line slightly too high !!!  Undecided Hmmm.. great time to find out.

My original plan was to fit 1/8" Ali plates to mount the engine so I lowered the engine bearers to fit to the thrust line on the plan. OK you're probably ahead of me now, anyway the solution was to use 18swg Mild Steel for the engine plates instead, which with the rough guess of 3 deg downthrust and 3 degs right thrust I was able to make up some plates so the prop driver pokes out in the right place.

I'll sort some suitable length bolts for the engine, I'm not cutting those down as long 10BA bolts seem to be hard to find. The engine plates nuts are epoxied to the engine bearers to make them captive so I can permanently fix the cowling on and still have access to remove the engine...and possibly make up different engine plates with different thrust angles if needed.

I couldn't resist another tape together assembly of the bits, this kind of thing keeps the momentum in the build for me.  Interestingly it balances on the main spar as is, I just need to make the covering and paint weigh the same as putting a prop on the engine... does anyone make lead propellers ?  Cool

The cowling has been given a coat of resin and I have added a strip of carbon tissue to the inside to help give it some strength. I did a small test piece on some scrap 1/16" balsa so it'll be interesting to see how much stronger this makes it. I used Ezy-Kote which I have not used before and I have to say is funny stuff. It has no tack what so ever, unlike all the other resins I have used it makes it quite tricky to use. The tissue has to fit well as the resin is not going to stick it down as would be the case with epoxy finishing resin. Water clean up though is a huge bonus




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Squirrelnet
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« Reply #53 on: December 16, 2018, 12:13:31 PM »

Last week I did a small test piece with carbon tissue and Ezy-Kote resin and the first thing that's apparent now it's dried is I should have stuck to the instructions.

They said to coat the piece with Ezy-Kote first and let it dry, I didn't and I can see why now. The resin is water based so as it dries on the balsa the balsa shrinks, the carbon tissue doesn't so you are left with wrinkles in the covering. I did two layers of tissue on the 1/32 sheet and a non scientific break test seemed to show little increase in strength over the untreated side. Bit surprised by that I expected a bit more from it.

Anyway didn't stop me putting another layer on the inside of the cowling and another coat of resin.

I've added a front to the cowling from 1/64 ply, I think the original had opening slats to control the engine temp so hopefully this looks a bit like having them half open.

Some carbon rod has been added around the front of the cockpit which will hopefully some strength to what still looks like a weak spot to me.

OK stupid question time....

I'm planning to spray the model with enamel paint thinned with cellulose thinners.

Is enamel paint diesel fuel proof ?

I'll give the engine bay a coat of Aero-Kote anyway but it would be good not to have to do the whole aircraft.

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vtdiy
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« Reply #54 on: December 16, 2018, 12:48:25 PM »

Amazing model!

Don't know about enamel mixed with cellulose thinners per se, but my one lung Lister type diesel engine generator is definitely painted with enamel and in service for 5 years. Rustoleum was the enamel. Not saying all brands and types of enamel would work, though -- just my experience with that one type and application.
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billdennis747
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« Reply #55 on: December 16, 2018, 01:17:11 PM »


Is enamel paint diesel fuel proof ?
I assume it's gloss, so yes.
My view on 'new' paints and glues is that if it doesn't smell dangerous or harmful, it's no good!
PS I'm sure you'll know this Chris - a white base coat under the yellow. I once did a yellow Jungmann without and even after 13 coats it wasn't right.
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Squirrelnet
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« Reply #56 on: December 16, 2018, 01:38:48 PM »

Thanks Vitdiy. Good point I guess a lot of pre war machinery was painted in enamel and has survived the ravages of time very well

Quote
I assume it's gloss, so yes

So Matt enamel isn't fuelproof ?

Quote
if it doesn't smell dangerous or harmful, it's no good!

Not impressed with Eze-Kote at all, the lack of tack in a finishing resin where you're trying to produce an even finish and attach the FG matt/tissue is a real problem. Their water based sanding sealer 'SandnSeal'  works very well though - as a sanding sealer ... and looks very similar to Eze-Kote. I wonder if Eze-Kote is the same stuff but more concentrated Huh
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billdennis747
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« Reply #57 on: December 16, 2018, 01:55:05 PM »


So Matt enamel isn't fuelproof ?
I think you would end up with grease spots, rather than the finish itself falling off, as it does with glow fuel. I have finished many models with matt enamel but always with Tufkote/Aerokote over it.
As Eric Coates described, you can get away with it on a colour dope finish if you mix your fuel with mineral oil (OK for a run-in Mills!) and clean down with ether, but why bother. I think he was concerned about cellulose repairs over a fuel proofer finish but I've never found a problem if careful.
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Monz
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« Reply #58 on: December 16, 2018, 02:03:55 PM »

Loving the Wilga so far Chris.

Re 'eze kote'... If you go into B&Q and buy the Ronseal Diamond Hard water based floor sealer - same thing... but half the price. Same with Poly-C. Most of these 'modelling products' are re-bottled and re-branded from things you can buy elsewhere at half the price. I'll bet their sanding sealer, epoxy, cyano etc are the same.

I've limited experience with composites, but I'd only use the carbon tish with a laminating resin. With the left over 'water based floor sealer' you have, 25g/m² glass cloth works well it, but I'd seal the balsa first with a coat or three of proper sanding sealer. The glass cloth and WBPU give a flexible but firmish finish. much less firm than if using epoxy.

The added bonus with the Ronseal is that it comes in matt, gloss and semi gloss/matt, I use it on the large depron models.
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Squirrelnet
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« Reply #59 on: December 24, 2018, 12:31:01 PM »

Ok so I think I now have a complete airframe  Grin

I've added a non scale trim tab to the rudder and elevator to make trimming easier. The elevator is banded on for trimming, once I've found a good setting I'll glue it down and use the trim tab for fine adjustment.

I toyed with the idea of adding the landing light to the LH wing tip but as the AM plan is not that faithful to the original it would be tricky to do so it looks right, so I think I'll leave it off... actually I think, looking at the pics it might be easier than I initially thought.. I have a plan

Just noticed I've still got the undercarriage fairing to do as well... I can start covering the rest though...apart from the left wing Undecided

..so almost a complete airframe  Wink

Happy Christmas





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billdennis747
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« Reply #60 on: December 24, 2018, 02:59:16 PM »


I toyed with the idea of adding the landing light to the LH wing tip but as the AM plan is not that faithful to the original it would be tricky to do so it looks right, so I think I'll leave it off... actually I think, looking at the pics it might be easier than I initially thought.. I have a plan
Do you mean a real LED landing light? That would be dead good/cool
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Squirrelnet
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« Reply #61 on: December 24, 2018, 03:36:47 PM »

..sadly not maybe I should have said Faux landing light... actually if I could work where to hide the battery so I can get to it....
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« Reply #62 on: December 26, 2018, 12:46:24 PM »

Today we went for nice Boxing Day walk to a hill in the fog Grin from the top you could see for yards !!! It's my usual slope site as well strangely no one was flying.

I did manage a bit in the workshop though when no one was looking and made a faux landing light hole in the wing and gave the fuselage a nice christmasy pair of flared trousers.

Landing light is not wonderfully accurate but looks better than not having one I think. A bit litho plate and an acetate cover and it should look vaguely right from a distance.

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« Reply #63 on: December 27, 2018, 12:42:14 PM »

I managed to find a bit of workshop time today, which I wasn't expecting so I set about making a quick dash for the Wilga.... in both senses

Some suitable sized holes where punched into some thin black plasticard and the instruments which by chance happen the about the right size in a pic downloaded from search where cut from a print out and stuck behind the holes. The fairing between dash and the bulkhead is white foam, from my airbrush compressor packaging, as are the other relief bits on the dash.  Hopefully it makes for a good passing resemblance through the large canopy as it whizzes past the judges head  Wink.

The undercarriage fairing has been carved to shape . The top part of the fairing I think I'll do in paper so any undercarriage bending arrival results in crumpled paper rather than crumpled fuselage sides.

I even made a start on the covering  Grin
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Squirrelnet
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« Reply #64 on: December 28, 2018, 03:39:01 PM »

I got some covering done this morning. I love Mylar its so easy to use most other coverings see me struggling to get a decent wrinkle free finish

Inside the cockpit the dash gives hint of something the right shape without huge amounts of detail. I hope to try a similar trick with the pilot....
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Squirrelnet
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« Reply #65 on: December 31, 2018, 01:53:18 PM »

Yellow Esaki tissue over silvered mylar... I have a gold aeroplane  Grin

I added a 1mm carbon rod to the Aileron flap to add some stiffness as it looked a bit liable to warping , so just those and a the LE slats left to cover.

The fuselage will be painted . I was thinking of tissue covering it first but as its a complex shape it's probably easier to directly paint the balsa. It's had a couple of coats of sanding sealer already.



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« Reply #66 on: January 01, 2019, 02:00:49 AM »

Not wanting to teach granny but personally I would want to cover the fuselage.  Is there no way you can do it in sections, taking advantage of the panels lines etc?

Looking good though.  I covered my mini vintage Dinamite wing in silver Mylar and yellow jap and it looks quite eye catching.

Mike

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Squirrelnet
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« Reply #67 on: January 01, 2019, 12:39:56 PM »

Thanks Mike.

I had thought of covering with tissue following the panels lines but it would be fiddly job. For ease and speed I'm thinking some rattle can white primer and some 1200 wet and dry will give decent surface for the final paint. There are reinforcing mouldings on the original to add too making covering even trickier. The DH60 I built a few years ago uses the same method of painted balsa sheet and has proved fairly resilient and also it's fairly easy to repair - a very useful feature with FF :-)

I covered the flaps/ailerons today. The plan has them attached just at the end ribs but that looks like it could give variable gaps and maybe even allow flutter so I'll add some attachments along the TE in scale positions. Its similar with the LE Slats without the flutter issue so I'll add some spacers there too

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« Reply #68 on: January 01, 2019, 07:05:06 PM »

That is a wild gold finish on the wings and tail. You won't lose sight of that too quickly Smiley

Happy New Year

John
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Squirrelnet
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« Reply #69 on: January 03, 2019, 03:05:25 PM »

Thanks John Happy New Year to you too

I've added some reinforcing to the exterior of the fuselage before it gets primed so its looking quite Wilga like now.

Engine bay is painted and fuel proofed so the cowling has been permanently glued on.. and yes I can still get the engine in and out ;-)

The fin has been glued on too. Approaching the point where I'll have use my new Airbrush in anger  Undecided
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billdennis747
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« Reply #70 on: January 03, 2019, 03:10:33 PM »

I knew something was missing! Those strips transform it
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Squirrelnet
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« Reply #71 on: January 04, 2019, 01:19:17 PM »

Thanks Bill

 I've added more reinforcing and given a final coat of sanding sealer so next stage is paint !

I made a first attempt at the front cowling which hopefully with be a piece of 1/32" moulded balsa strengthened with epoxy and carbon tissue. First stage is some balsa steamed and taped over the nose and left to dry to get the shape. My hope is I can make whole top section, which is painted matt black on the original, removable and held on with some neodymium magnets



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« Reply #72 on: January 05, 2019, 06:00:42 AM »

The fuselage certainly looks stronger now SN. Smiley

John
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« Reply #73 on: January 05, 2019, 01:10:02 PM »

The fuselage certainly looks stronger now SN. Smiley

John

Thanks John. Hopefully not too much heavier as its already getting a bit porky  Undecided.... I have a Mills .75 on standby
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« Reply #74 on: January 13, 2019, 01:12:39 PM »

Well, the moulded 1/32" balsa cowling seems to have worked OK .

I gave the top side a coat of laminating epoxy and reattached it to the nose to dry in the right shape and then added a couple of layers of carbon tissue and laminating epoxy to the inside. Carbon tissue works much better with laminating epoxy than my earlier attempts with floor varnish/ Ezykote. I think that stuff is best left for floors or as a heavy duty sealer for engine bays, I can't say I'm that impressed with it.

The resulting 1/32' balsa carbon epoxy moulding seemed to have a useful amount of strength for a top hatch and after adding some structure to the inside so its sits right and locates in the engine bay it's looking like it will do the job. It fits very well using friction to hold it in but I'll probably add a couple of magnets for safety. The front of the cowling has a small opening so the engine has some cooling for those calm, hot summer days we will be flying in next year  Cool

Right I have no excuses left I'm going to have to paint it next ..... Shocked
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