Spacewalker half scale 168" electric

[John Greenfield]

Andy

It is best to talk to your paint supplier about placticisers as the type and quantity do depend on what paint you are using.

My best results when spraying over a combination of solid and open structurers is to use coloured dopes as per the full size. a full range of colours are available from companies such as Skycraft and of course it is totally compatable with the underlying dope layers and will bond to them very well so there is no chance of the finish chipping off. totally flexible as well...which is why it is used on the full size.

John

[Andy Boylett]

Andy

It is best to talk to your paint supplier about placticisers as the type and quantity do depend on what paint you are using.

My best results when spraying over a combination of solid and open structurers is to use coloured dopes as per the full size. a full range of colours are available from companies such as Skycraft and of course it is totally compatable with the underlying dope layers and will bond to them very well so there is no chance of the finish chipping off. totally flexible as well...which is why it is used on the full size.

John

Thanks john.

[Andy Boylett]

Lovely weather here today so got outside with the spray gun.....

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My spraying looks really nice and I have got a lovely smooth, flat finish. The thing that lets it down is the lack of filler and sanding earlier on!

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Especially when viewed at a low angle in the light.

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At least when I get the red paint on it should hide some of that!

[John Rickett]

Andy,
It invariably happens that once you've sprayed, or brushed, the nice flat surface shows up all the inperfections. Its not too late though, now is the ideal time to fill all those low spots and pin holes with something like P38 filler or 3M putty. Rub down and then put on another coat of primer. Don't worry about how much primer you're putting on, you will be removing most of it during the rubbing down process. This is the only way to get a good surface to apply the finishing coats to, if you start spraying gloss coats before filling the holes, the result will look worse than it does now, so don't leave out this important step!

[stuart cotgrove]

Andy,
It invariably happens that once you've sprayed, or brushed, the nice flat surface shows up all the inperfections. Its not too late though, now is the ideal time to fill all those low spots and pin holes with something like P38 filler or 3M putty. Rub down and then put on another coat of primer. Don't worry about how much primer you're putting on, you will be removing most of it during the rubbing down process. This is the only way to get a good surface to apply the finishing coats to, if you start spraying gloss coats before filling the holes, the result will look worse than it does now, so don't leave out this important step!

I agree with John. Get rid of those imperfections now, otherwise you will forever be looking at these every time you get the model to the field. And Red will make it look worse not better....

[Andy Boylett]

Thanks John and Stuart,
back to the sanding board then! I think the problem I had was that it is really difficult for me to lean over and sand a large surface (my back hurts ), so I rushed sanding a little. I just ordered some more filler......I think it is about time my pilot son Sam did some sanding .
Cheers, Andy

[Andy Boylett]

Guys, I forgot to ask about sanding. The last time I did P38 filling it was on a Mini with registration TRA 499M ....1974 that one was born!. When sanding I assume it is like for the car and I use wet and dry paper and do it wet to stop clogging? I then need to ensure it is really dry before any more painting as well?
Cheers, Andy

[Phil Clark]

Andy

The depth of imprefection will determin the type of filler to be used.......from your photos, you look to have some fairly major issues where sheeting has been joined. If the defect is any deeper than about 0.5mm, you really need to use a hard filler such as P-38...issue here is unless you use 80-120 grade paper (as you say, used dry) for the initial cut back, you'll be there forever feathering it all in with fine paper. 2nd issue is unless you are VERY careful you will end up cutting into the fabric surrounding the defect and end up with fluffy raised fibres that will need sealing and flatting themselves.........only way round it is to protect the surrounding areas as much as possible with tape whilst you sand. With filled areas, they will obviously loose their fabric weave........the overall surface will end up looking a little odd with some smooth patches amongst a mainly fabric model.......so I suggest you maybe consider loading the paint on a bit to flood the weave to achieve an all over smooth finish (it's not like you are short on wing area or power to carry an extra lb or two!!)

For shallow imperfections and pinholes, I find 3M's 'Acryl Red' to be the best going........fast drying and wet sand really well. Only down side is it does shrink V slightly as it cures hence why you can only use it for shallow imperfections.

Phil

[Andy Boylett]

Thanks Phil,
looks like they are going to be tricky then! I have just been looking at how deep are the imperfections and they are not too big, well under 1mm ....I took that photo deliberately with the sun shining at a low angle along the wing. Also, the weave is pretty much completely filled in already as I was following your doping guide - which filled it in most of it. As soon as I sprayed I got a pretty good surface finish.
I will have ago at one underneath first .
Regards, Andy

[Andy Boylett]

Phil,
following your warning about the risk of sanding through into the fabric I had an idea. When I used to do drafting using a pencil and tracing paper on a large board I had a special little device to aid with rubbing out the pencil. It was (well still really is as I still have it) a thin metal shim with various holes cut in it that could be used as a mask when using the rubber on the film, so that only the bit you wnat to rub out gets rubbed.

It just happens that I have some big sheets of shim steel 150mm wide by 450mm long. If I cut a big hole in the centre of a sheet I could then tape this over the area to be sanded -so protecting the surrounding. It might even be posisble to make a 'mask' just like the small one I have, with different sized/shaped holes.

Interestingly, I wonder if something like this would also be a useful tool when sanding sanding balsa when it is one of those situations where you do not want to oversand the surrounding area - such as on flexible areas.
Cheers, Andy

[Phil Clark]

Andy

I know the little 'steel' rubbing masks....I have a set that belonged to old mans when he worked in a drawing office circa late 60's!!!

Larger versions may work, though sound like a lot of work to make.....I generally use PVC insulating tape in such situations as it's very durable and doesn't break up like brown parcel or masking tape does.

The key to all this though is in the early stages of the build. When sheeting large areas, don't try and join the sheets on the model and correct any slight misalignment once the sheeting is bonded in place.....make up an overside sheet on a flat bench and sand both sides prior to attaching it to the airframe, this way, no sanding will be required once the sheeting is in place, so sanding on 'flexible' areas such as between ribs is avoided.

Phil

[stewart clifford]

just a thought Andy, if at this stage you're not happy with whats underneath the covering showing through then consider time, cost, end result and take the covering off and sort out the imperfections and then recover. Sometimes I think what may seem worst case scenario is much better, like I said just a thought.

[Andy Boylett]

Andy

I know the little 'steel' rubbing masks....I have a set that belonged to old mans when he worked in a drawing office circa late 60's!!!

Larger versions may work, though sound like a lot of work to make.....I generally use PVC insulating tape in such situations as it's very durable and doesn't break up like brown parcel or masking tape does.

The key to all this though is in the early stages of the build. When sheeting large areas, don't try and join the sheets on the model and correct any slight misalignment once the sheeting is bonded in place.....make up an overside sheet on a flat bench and sand both sides prior to attaching it to the airframe, this way, no sanding will be required once the sheeting is in place, so sanding on 'flexible' areas such as between ribs is avoided.

Phil

Ha, ha,
I still did a set of planning application drawings on a board in 2001 and I still have the A0 drawing board if anyone is interested!...free to a good home.
I'll try the PVC tape first then.
One wing looks pretty good - I am guessing that will be the one where I joined up all the balsa sheets flat on the bench first. The problme I found with this though was that it was such a large piece it became imossible to handle without damaging it....so I went back to 'single sheeting'.
Regards, Andy

[Andy Boylett]

just a thought Andy, if at this stage you're not happy with whats underneath the covering showing through then consider time, cost, end result and take the covering off and sort out the imperfections and then recover. Sometimes I think what may seem worst case scenario is much better, like I said just a thought, oh and I have been to the pub tonight

Thanks Stewart,
The low points are really not too bad. I deliberately took a photo with the light at a very low angle. If I ever did/do need to take the covering off, is there a way to do this? Mine is glued on round the edges with cement and the all doped.
Cheers, Andy

[John Rickett]

Andy,
The covering adhesive can be softened by using neat, whatever thinner was used in the first place. Assuming you used dope thinned with cellulose thinners, then liberally brush cellulose thinners where the fabric is attached. It will require a few coats to soak through and can be a tedious job, but it works.
The same trick can be applied to dope runs and pools - hold the surface upside down if necessary and soak the area with thinners and the runs or pools will disperse. This is much better than attempting to sand them out and risking cutting through the fabric.

[Andy Boylett]

Andy,
The covering adhesive can be softened by using neat, whatever thinner was used in the first place. Assuming you used dope thinned with cellulose thinners, then liberally brush cellulose thinners where the fabric is attached. It will require a few coats to soak through and can be a tedious job, but it works.
The same trick can be applied to dope runs and pools - hold the surface upside down if necessary and soak the area with thinners and the runs or pools will disperse. This is much better than attempting to sand them out and risking cutting through the fabric.

Thanks John, I think that will definately be useful for the part where I have put my finger through the balsa and need to do a little repair!
Cheers, Andy

[Mike Booth]

If it were me as a dyed in the wool pattern maker, I wouldnt go anywhere near P38 or the airborne one either.
You are going to cause yourself a staggering amount of work rubbing down the granite compond when it has gone off.
Go on line and buy yourself a tin of pattern makers filler from Amber Composites.
Its the same two pack stuff but easy sand, farrrrrrr easier.
I have always got five litres kicking around and use it all the time.
We used to have a saying in motor racing, 'what you put on will have to rubbed off', so take it easy , all filling will always need two applications to achieve a finish.

One last thought is that I would be surprized if that Dracon covering will take too kindly to much wet and dry burnishing, if its a finish for paint that you are after.

[Tony Collins 1073]

Go on line and buy yourself a tin of pattern makers filler from Amber Composites.
Its the same two pack stuff but easy sand, farrrrrrr easier.

Mike, are you referring to Minfill, or fillite filler as I am in need of something like that myself?

Cheers Tony

[Andy Boylett]

Thanks Mike......
and if you use fillite or minfill, which resin do you add it to to make up a filler?
Cheers, Andy

[Mike Booth]

No guys dont use that, IVe never used that and I wouldnt be inclined to mix resins in, as you can guarantee that they will be like granite when they have gone off.
The thing about filling is you want to know you can cut back to a finish easily, without eroding the area outside the fill to any extent.
Use pattern makers filler from Amber Composites, they will mail you a tin next day and its not that dear. OR>>>>>>

You can go direct to Axson who make it ,AXSON Ltd, Unit 15, Studlands Park Ind Est, Newmarket, Suffolk, CB8 7AU
Ask for sales. A 3.5 litre tin will last you for several projects and the odd window sill repair!!

01638 660062.