Blue foam twin-boom build and maiden

[Tom Wright 2]

View of wing with booms removed for transport.

 

[Tom Wright 2]

View of booms removed for transport.

 

[Tom Wright 2]

[Tom Wright 2]

View of the recess cut out under the front fus to accommodate the RX and lead outs.

 

Just draw the outline 8ins x1in and use a sharp modeling knife to cut down about 3/4" then make multiple cuts 1" across spaced at about 1/4" and dig out with a chisel or flat blade screw driver with a sharpened edge.

Or a simple hot wire profile could be used ,in a trigger type soldering iron .Don't worry if the bottom of the recess comes out a bit rough ,just tack a 1/16" balsa sheet in the bottom to tidy things up.

The 3/32" balsa sheet hatch can be retained by magnets or simply use masking tape as it sticks well to foam.

 

 

 

I am sure you can make a neater job than my hurried effort.  .

 

 

 

Edited By tom wright 2 on 17/05/2011 15:32:44

[fly boy3]

Nice one Tom. Whats that saying, about one picture better than 1000 words. Cheers FB3

[Tom Wright 2]

Just done a trial on 3M Scotch -Weld Universal Contact Adhesive 10 , it can be brushed on or sprayed ideal for sheeting foam or producing strong foam to foam joints ,its very quick to use and the bond strength is amazing .

It comes in a 1LTR Tin which is far more economical than little tubes of stuff,This product appears to be the ultimate answer to bonding blue foam.

 

Tom.

Edited By tom wright 2 on 17/05/2011 16:10:52

Edited By tom wright 2 on 17/05/2011 16:15:36

Edited By tom wright 2 on 17/05/2011 16:23:32

[Tom Wright 2]

Closer view of the motor mount ,i am sure you could do a better job !

 

Note the folding prop.

 

Edited By tom wright 2 on 17/05/2011 16:45:51

[Tom Wright 2]

[Tom Wright 2]

Photo of quick sample bond ,Will leave it a week or two in high UV to check for degrade or interaction with the foam. For butt or small surface joints i found 2 -3Min's OK before pressing together ,haven't tried large surface areas yet but will do as time allows.

 

Data sheets are on the 3M site haven't checked them yet ,but it may be necessary to stir before use in case there is a solvent accumulation at the top after standing.

 

The join junction sands very nicely,and no pick up occurred,will do more samples.

 

[Tom Wright 2]

If your landing area is a bit rough it might be an idea to add some tip skids,the ones I've used are HK but all sorts are available ,for a really good anchor a thin py plate is glued into place first.

 

[Tom Wright 2]

During STOL take offs the underside of the fins can strike the ground ,this can be clearly heard in the video, i just sand the affected area now and then ,but you may want to add some protection.photo after a quick sanding .

 

[Tom Wright 2]

Have been taking a closer look at adhesives for use with blue foam.

 

This one is very good and handy for small to medium surface joints the bond strength seems to be as good as the 1 Ltr universal 3M ,but you do need to wait a bit longer before the two parts are pressed together.

Its good on foam to foam and foam to balsa or ply joints,and does not eat into the foam ,and is very convenient to use .but not very economical on larger areas that need sheeting.But at between £1.99 to £ 2.99 for a 40 ml tube its a good contender.

 

 

 

 

Edited By tom wright 2 on 17/05/2011 20:36:43

[Tom Wright 2]

This one is an interesting find ,and well worth looking at for bonding large areas ,such as balsa sheet to foam ,surprisingly it does not seem to effect the foam,and its very quick and easy to use ,a 500ml spray tin is widely available at well under £5.As with all products do check the instructions and data sheets ,none of the fumes etc , bother me ,but could be dangerous to some one else!

This spray adhesive seems to be the best bet for sheeting and very economical .

On reflection the one below and the UHU are the two i personally would use the1ltr3M

universal is a bit expensive and not as convenient to use on the typical model build ,although i will do some more work with it .

 

Edited By tom wright 2 on 17/05/2011 21:26:40

[Tom Wright 2]

The 3M 77 spray is much more expensive ,but i found it very good for sheeting foam,however Timbo recons they have changed the formula and its no longer foam friendly ,so check the data sheets before useing .

Have you found any othe product that works well on blue foam ? if so let us know .

 

[Tim Mackey]

Actually, all I said was that I have heard from some of the USA forums that the latest formulation eats foam ( the propellant no doubt ) - I havent experienced that myself

Seems they now use acetone in the mix

SEE HERE

Edited By Tim Mackey - Administrator on 17/05/2011 21:28:01

[Tom Wright 2]

 

Posted by Tim Mackey - Administrator on 17/05/2011 21:26:25:

Actually, all I said was that I have heard from some of the USA forums that the latest formulation eats foam ( the propellant no doubt ) - I havent experienced that myself

Seems they now use acetone in the mix

SEE HERE

Edited By Tim Mackey - Administrator on 17/05/2011 21:28:01

Sorry if i miss quoted your post Tim , Thanks for the info it looks like the Ever build spray is the best and cheapest for sheeting ,unless of course its the same as the 3m in a different can ,it just reinforces the advice check all adhesives on scrap foam before using ,and always read the heath and safety data.

 

Do check out Tims link it does provide lots of useful info on 3M adhesives.

 

Tom.

 

Edited By tom wright 2 on 17/05/2011 21:49:43

Edited By tom wright 2 on 17/05/2011 21:52:53

[Tom Wright 2]

Just done another test using the Ever build spray, i flooded a large area of foam way more than you would ever need ,left it to dry and it had not eaten the foam at all !

 

[Tim Mackey]

Sounds good Tom - I was chatting with a guy yesterday who says he found some foam safe carpet glue aerosols in B+Q for under £2 a tin.

Sounds a bargain?

THIS is the best I could find online

Edited By Tim Mackey - Administrator on 17/05/2011 23:25:57

[Tom Wright 2]

Thanks Tim got mine from the local hardware shop ,so carpet adhesive ,5 min / 30 min epoxy , and UHU por ,come out as the foam bonding stars,unless some one has a better solution? The BFM and twin boom were built with these and no problems have been found.

 

Tom.

[Tom Wright 2]

OK that should cover the adhesive side of things ,but if you are new to blue foam as a model building material the following may help.

Surface finish.

If the material is purchased in the 1" thickness suggested for the project it should be noted that the surface finish is harder than the cut edges , there is also a slight sheen .The reason for mentioning this is related to the final finish on exposed foam surfaces.

The trick is to not to sand the exposed foam except were needed to create a change in profile, do you best to keep the sanded lines following the strait lines and curves so that as they meet the unsanded foam a nice junction is achieved .

 

Forgotten to load the photo so its on the next post.

[Tom Wright 2]

Not a good photo but the dividing line between the sanded and not sanded can be seen avoid wavy junction lines and the finished job will not only look better but the none sanded exposed foam will be more durable.

Dont worry if this is not achieved at the first attempt the model will fly just as well.

 

The change in texture is not obvious in the photo but it does show for real.

 

Edited By tom wright 2 on 18/05/2011 01:59:02

[Tom Wright 2]

Sanding

Take sensible precautions as with all sanding jobs don't breath in the dust .

 

Where a significant depth of foam needs to be removed a good quality aluminium oxide cloth backed product will do a much better job than the cheaper sand papers.

Start with 50 grade practice on scrap foam and try coarser grades until maximum cutting is achieved without problems.p 50 is a good starting point,use light pressure and make strokes in one direction only otherwise random direction scratching occurs ,which will spoil the finish.

Using very fine grades can be more difficult again experiment to find the grades that suit your own technique.

Always use a block to support the abrasive,i use closed loop sanding belts and fashion a 3/4" thick piece of flat wood long enough so it has to be tapped into the loop or make a seperate small section and tap in between the end of the block and the inside of the abrasive, this keeps the abrasive surfaces taut.

This results in a good finish and a longer abrasive life ,tap or vacuum out embedded foam at frequent intervals.

 

Edited By tom wright 2 on 18/05/2011 02:49:18

[Tom Wright 2]

Again poor photo but it does illustrate the idea.

 

 

You wil find the first sanding strokes on the new surface is harder than than working on a sanded surface. 

 

 

Edited By tom wright 2 on 18/05/2011 02:47:57

[Tom Wright 2]

Just to say hello to the peeps that have done all this stuff before ,my apologies if when you look in its all a bit boring .

This thread is aimed at forum members who have little experience with the material ....foam type models...... or even EP.

The aim is to also encourage scratch building ,thoughts about basic design ,and to quickly produce a tidy model that performs well ,for a very low cost.

 

 

 

[Tom Wright 2]

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Edited By tom wright 2 on 18/05/2011 03:14:02

Edited By tom wright 2 on 18/05/2011 03:15:21