Webbit example build: Covering

[Richard Wood]

Hi All,

 

Covering a model is often one of those jobs people don't look

forward to or enjoy.

It covers up all that nice wooden structure & some film coverings

can be very tricky to use successfully.

I've tended to use Solartex recently, which is one of the easiest

iron-on coverings to use,but is a little too heavy for a Webbit.

I've decided to use standard Solarfilm for most of the model

but with perhaps Poly-C for the tail bits, but I've not decided yet!

 

The iron temperature is critical for applying Solarfilm - too cool

& it won't stick, too hot & it will wrinkle as soon as it goes near

the film, so I'll make sure I try & get that right!

 

Solarfilm doesn't stick too well to Ply (fuselage sides) without

a coat of balsaloc - so that's another thing to try out.

 

Poly-C is an excellent way of doing a traditional tissue job on

sheeted surfaces without the problems of cellulose (smell!)

It needs quite a few thin coats & then careful sanding to get

a perfectly smooth finish for painting, so it'll take a bit longer

to do than just applying film.

 

It'll be a few days (I'm not the quickest builder!) before any

covering starts, but any comments or suggestions or help

please chip in!

 

Cheers

Richard

 

 

 

 

Edited By Richard Wood on 01/04/2011 12:10:30

[Richard Wood]

Hi All,

The weather was great today so been in the garden sorting

out the mess from last winter.

My Webbit is taking shape though so time for a posting.

 

I've decided to use Poly-C and lightweight tissue on the tailplane

& fin just to illustrate it's use & because I quite enjoy using it.

This sort of finishing technique really comes into it's own on

for example, a fuselage with lots of compound curves where

film would be difficult to use.

 

The first job is to seal the wood with sanding sealer - Poly-C

is water based so it could warp or swell the untreated balsa.

Give it a light sand when it's dry - just a few minutes.

 

Cut the tissue with about 1" excess all round,lay it on the

part & apply the PC with a brush from the center outwards.

It's quite easy.

Any small wrinkles can be pulled out gently and smoothed out

with a finger, thumb or piece of tissue.

Don't worry about getting it on your fingers - it'll wash off easily.

 

This shows the tissue in place & the first coat of Poly-C.

The slits in the tissue help it around curved edges.

It takes 20 -30 minutes to dry & can then be trimmed with a

sharp blade or by running over the edge with sandpaper.

Any raggy edges can then be stuck down with a tissue

wetted with PC.

Incidentally the room needs to be quite warm for it to dry

in the 20 minutes stated in the instructions on the website.

 

 

 

 

Here they are both sides covered & trimmed ready for more coats -
up to 8 or so thinly applied with a brush.

 

So far 5 coats have been applied - 2 or 3 more & it will be time
for a bit of finish sanding with fine wet & dry to get a (hopefully)

perfectly smooth finish ready for priming & painting.

 

 

 

More tomorrow hopefully.

 

Cheers
Richard

 

[Richard Wood]

A quick post on covering control surfaces with Solarfilm.

 

Plane & sand the rudder & elevator to a tapered section.

Finish sand with something extra-fine. I use flexible

3M material - as shown in the pictures.

Any imperfections will show through the covering so

time spent here will be worthwhile.

 

The iron temp must be correct, so if your iron has no temp readout

calibrate it first with squares of film.

Set the iron to low (about 9 -10 O'clock if it has a rotary control).

This is 100'C.

Let the temp settle & place a square of film on the iron, adhesive

side up.It should bubble slightly.

This is the setting for applying the film.

Increase the temp to high (about 1 O'clock - 120'C).

Use another piece of film & it should bubble up more.

This is the shrinking setting.

It's best to do covering in a seperate room from building to escape

the dust!

Cut a piece of film with 1/2" - 1" extra all round & place on the

component.

With the iron on low work along & outwards with gentle pressure.

The idea is to stick down the film with no air trapped.

Seal down the edges with a rolling action & pull gently to remove

wrinkles if necessary.Don't iron down wrinkles.

Repeat for the other side, taking care not to mark the surface

with fingernails!

 

Set the iron to high & gently go over the surface again to shrink

the film & seal it down.

It's a good idea to use an iron sock or piece of tissue here

as the film surface is quite easily marked.

Any slight air bubbles will disappear when the film cools.

 

 

 

Same procedure for elevators & ailerons.

I wouldn't recommend using a heat gun for shrinking

on solid balsa as the film can bubble up too much.

 

I'm sure everybody knows all this stuff anyway.

 

[Biggles' Elder Brother - Moderator]

Great explainations Richard - really clear!

 

BEB

[Steve W-O]

Posted by Richard Wood on 03/04/2011 12:42:13:

 

I'm sure everybody knows all this stuff anyway.

 

 

 

 

No, forgotten about using one heat to stick and one to shrink!

 

As soon as I read it it clicked, but I have been doing it all on one heat, so all you have mentioned is worthwhile.

 

 

Prior to last year, I had always used a household iron!

[Biggles' Elder Brother - Moderator]

Just shows how useful these threads can be - even for experienced builders

 

BEB

[Richard Wood]

Cheers gents.

It's full steam ahead on the wings at the mo' - so I'll try & post

something on Solarfilming & Solartrimming them soon.

 

 

 

Edited By Richard Wood on 03/04/2011 20:06:56

[Big Bandit]

Fantastic Richard, your a star.

[Geoff Smith 1]

Posted by Richard Wood on 03/04/2011 20:06:07:

Cheers gents.

It's full steam ahead on the wings at the mo' - so I'll try & post

something on Solarfilming & Solartrimming them soon.

 

 

 

Edited By Richard Wood on 03/04/2011 20:06:56

Great post Richard, just what I need. Cheers

 

Webbiteer 20 AKA Geoff

[Richard Wood]

Hi All,

 

Hi Geoff - sorry to hear of the bother with your model mate.

The most important thing is that it's all straight & soundly stuck

together.

Don't worry about a fancy covering & finishing job - it won't make

the model fly any better.

 

Just a quick post on preparing the wings before film covering.

Before filming it's a good idea to spend time filling in cracks & blemishes

with lightweight filler & then sanding with fine paper.

The best way to remove small dings & dents is with a bit of spit to swell

the wood which can be sanded smooth when dry!

 

Good lighting helps.An adjustable desk lamp shining on the job at

particular angles will highlight any areas that need attention with filler

& sandpaper.Also cover up the building board with an old towel

or bubble wrap as any hard bits or dried glue spots on the brd will

give the model a rash & you can end up going round in circles

removing dents!

 

The TE section at the centre was about 1mm too thin to mate up

accurately so filler was used to blend in the joint in two stages.

Thick layers of filler take an age to dry.

Apply second layer of filler after 1st is dry & sanded.

Sanding the joint between LE & LE sheeting can be tricky if there's

a hard glue line to deal with.Go easy as the sheeting is quite thin.

 

Give the wing a final once over with the extra-fine & then it's time to

say enough! - remove all dust & it's time to cover.

 

 

 

Filler awaiting the sander.

More later all being well.

 

Cheers

Richard

 

 

 

[Biggles' Elder Brother - Moderator]

I'm pleased to see I'm not the only one that uses the "bit of spit" method for getting dings out of the balsa!

 

BEB

[Richard Wood]

Essential part of the toolbox BEB!

 

[Phil 9]

is it just me or does the front of the webbit look like a pig

[Geoff Smith 1]

Posted by Biggles' Elder Brother - Moderator on 05/04/2011 11:26:39:

I'm pleased to see I'm not the only one that uses the "bit of spit" method for getting dings out of the balsa!

 

BEB

Another worthy note in the memory bank. Keep 'em coming lads. Cheers

Geoff

[Biggles' Elder Brother - Moderator]

Posted by Phil B on 05/04/2011 13:00:02:

is it just me or does the front of the webbit look like a pig

 

 

You're not the first person to spot the ressemblance Phil!

 

BEB

[Phil 9]

now that one really does look like a pig

[Richard Wood]

Covering the wings uses a different technique from a sheet or solid

balsa surface.

 

An extra piece of balsa was added to the tips so there are no gaps to make

life difficult here.

Putting it on

The top & btm can be covered in one piece each as the wing is flat.

Start on the btm with a piece of film 1" wider all round (bit more at

the tip if desired).

 

With the iron low ,100'C, spot tack th efilm down at about 12 points

all around the perimeter up to the end rib & at the tip TE.

Seal down the film at the edges only by pulling over the TE & LE.

 

The film over the wing doesn't need to be taut - small loose wrinkles

will be shrunk out later.

The tip area will look like this at this stage:

To deal with the tip set the iron to high, 120'C.

 

Pull th efilm over the tip, apply the iron & the film will wrinkle

noticeably.Keep pulling the film & moving the iron slowly over

the area & it will shrink.

Seal film down securely at the tip ends.

Go over the rest of the tip:

Make sure the film is now securely ironed down around all edges

of the wing.It will pull out when shrunk if it isn't.

Trim excess off with a sharp blade.

 

Shrinking

 

The Solarfilm instructions use a high iron to shrink the film,but I find

it a lot easier to use a heat gun here.

Mine is a bog standard Black & Decker one.

 

With the gun on a low setting, hold it about 4" or so from the wing.

Start at the edges & heat the film gently with the gun slowly moving

across & in towards the centre.

The film will wrinkle like this (or worse):

 

Keep slowly moving the gun & the film will shrink tight.

Don't keep it in one spot for long or it will burn the film

Go over the whole wing like this from the edges inwards - any air

underneath the covering at sheeted areas will be forced out towards

the centre.

All wrinkles will go & the job should end up taut.

 

Same for the top.
Next will be brightening up with Solartrim.

[Richard Wood]

Don't forget to install aileron servo extension leads before covering

the top.

Once forgotten - never repeated

 

[Big Bandit]

Richard, Wow your my hero, may start the mini or nano Webbitt this week end so I've plenty to practice on.

 

Cheers,

 

Chris.

[Richard Wood]

Cheers Chris, glad it's been of some use.

 

[Richard Wood]

Cracking weather today, so a quick update & then it's out

into the garden for cucumber sandwiches & a couple

of tinnies.

 

A couple more things worth noting on Solarfilming:

 

When covering the second side you'll find that the film

doesn't stick to itself on overlaps as well as it does to balsa.

Prymol can be used on overlaps to etch off the gloss to improve

adhesion, although I find the film will stick to itself well enough

with firm pressure & a slightly hotter iron temp than low.

 

I've found that using an iron sock when putting the film onto

sheet or solid balsa surfaces (as per earlier post) makes it

a lot easier - almost as easy as using Solartex.

Have the iron temp slightly higher - about 105'C or so.

It seems better to take it off for edge sealing though.

 

If you're using an ic engine it's a good idea to run a line of fuel

proofer over film joints.

 

Solartrim was used on the wing top to add a bit of colour in a

sort of Wotty - inspired scheme.

Solartrim is quite easy to use with the soapy water technique -

warm water & washing up liquid in a large dish.

It's harder to use 'dry' as it tends to grab immediately & is difficult

to reposition.

Check there's no dust or bits on the model as they will show up

through the trim!

 

Put soapy water on the model, cut out the trim & dip it into the water.

Place it on the model & pull & slide it around for correct location.

Use a tissue to remove air & water from the centre outwards.

Press down to satisfaction & leave to dry.

A low setting iron can be used to further seal down if necessary.

 

Because of it's high gloss, paint won't take to film well.

Use Prymol to etch it first.

The wing tips on mine could do with some red spray!

 

 

 

Cheers

 

RW

 

 

 

 

 

 

 

 

[BILL PETTIT]

Richard : Very educational I will try your technique when I get my kit Don't know when that will be Just ordered it today but it has to cross the pond to get to me in upstate New York.So I will be soaking in everyone's post for a smooth build. Should be a fast build.

Regards Bill

[David Gilder]

Bill, Please can you put a post with requested details in the Signing Up Thread,

Just helps us keep track of who is building the Webbit and Where!!

Thanks

Dave

[birdy]

That looks like classic wot 4 scheme to me.

 

[Richard Wood]

Slowish progress for me this week but here's a note on covering

the fuselage.

 

Solarfilm will not stick to the ply fuselage very well at low temps unless

higher iron pressure is used. This can mark & scratch the film.

Applying it with a high iron temp will make it wrinkle too much.

 

There are a couple of ways around this:

 

Balsaloc can be used as a priming coat before covering to improve

adhesion.

Apply it thinly with a brush or piece of plastic foam & let it dry for an hour

or so.

Experiments on scrap ply have shown that covering straight on top of

unsanded Balsaloc produces a poor finish, so sand a little before

covering.

 

As an alternative to Balsaloc, put the iron sock on & set the temp slightly

higher than low - to about 105'C or so.

The sock will allow you to press down hard onto the film to seal it to the

ply without marking it.

 

The technique illustrated earlier for covering control surfaces is used

over most of the fuselage.

The open structure method (wings) - where the film is sealed down at the

edges first & then shrunk will produce trapped air bubbles if used on a

sheeted surface.

 

 

Edited By Richard Wood on 14/04/2011 10:34:28