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Semi-scale ASH25

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Jolly Roger
Posts: 306
Joined: 30 May 2015, 20:35
Location: Sutton Bank, North Yorkshire

Semi-scale ASH25

Post by Jolly Roger »

Well it had to happen. After 20 years of joyous flying in all conditions in every corner of the country, I stupidly stuffed my 4m ASH25 into the ground last August. Nasty turbulence at Leek turned a fast pass at +3m height into a sudden stop at -25cm. A photo in RCM&E shows the carnage.

The bits (and there were many) have been in the workshop long enough. Looking over them last week, I decided it's worth fixing as the wings are virtually unscathed. So all I need to do is make a new fus.

I'll change a few things just to add interest, the main one being to mold the fus using the lost foam technique. I made some fuselages like this decades ago but they were pretty primitive. Hopefully I can refine my technique. I'm inspired by Roo, and how believably fast he makes his fuselages. I'm also determined to do a better paint job than my usual satin finish - I want GLEAMING! And I'm going to vac-form a canopy too - I always meant to do one for the ASH25 but had so much fun flying it I never bothered.

First question - I'm planning to make the fuselage plug from XPS (extruded polystyrene) foam, the kind available in 6mm - 30mm thick sheets for electric underfloor heating. Is this the best stuff to use? I like its small-cell texture and it shouldn't break off in lumps like EPS (expanded polystyrene).

Second question - can you hot-wire cut XPS for foam wing cores? If so I'll buy plenty for future foam-veneered wing projects.

Meantime I've drawn up a new fuselage plan and practiced some composite layups. I plan to use 2 layers of 200gsm twill glass cloth either side of 175gsm Diolen - an aramid cloth similar to Kevlar but cheaper. First samples seem great. Light and stiff but with an extra resilience due to the Diolen. The Diolen cloth is a nightmare to cut (it just fluffs up!) but it wets out OK and seems to bond well to the glass. It cuts better after the epoxy has set.

I'm a dead slow builder as I overthink stuff and have very little spare time but I hope to make a start on the foam plug before new year.

Rog
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Chris Bowles
Posts: 69
Joined: 18 Mar 2015, 16:12
Location: South Devon

Re: Semi-scale ASH25

Post by Chris Bowles »

Good luck with your project Roger, I used EPS on my 17 fuz, wouldn't use it again to flexible, had to stiffen the plug with carbon to keep it straight. have been using XPS for foam wings for years, first in green then blue, they have stopped making blue now, grey is the new colour, it cuts much better than EPS but does require a bit more heat in the wire, it also carves and sands better than EPS, you could bring the model to Eden next year, no pressure then
Chris

Jolly Roger
Posts: 306
Joined: 30 May 2015, 20:35
Location: Sutton Bank, North Yorkshire

Re: Semi-scale ASH25

Post by Jolly Roger »

Chris Bowles wrote:
24 Dec 2019, 09:12
... you could bring the model to Eden next year, no pressure then
Chris
I'll do my best!

roo Hawkins
Posts: 794
Joined: 18 Mar 2015, 20:12
Location: Northamptonshire

Re: Semi-scale ASH25

Post by roo Hawkins »

Hi roger glad you are inspired by my builds and I hope l can help if possible. I have used blue foam on my 1/4 models it is easier to carve but really hard to remove. I remove it by hand so it was really hard to remove and did not melt very much with chemicals like petrol ect. My bigger models are Wight polystyrene foam it is harder to carve right but is easyer to remove it will melt with petrol. So I will now only use white foam now.plus it is cheaper. Blue foam is getting really hard to find you can still get it but it is now gray in colour. The last time I asked it was £250 order . Wight foam will have more flexibility so it will need a jig and I layed carbon tape along the tail boom then let it set first. I then add 4 layers of glass cloth of about 200gm plane weave. You will lose some weight when you sand but you can add inside more glass or carbon if needs be. I whould consider not using kelver. Best of luck Roo

Jolly Roger
Posts: 306
Joined: 30 May 2015, 20:35
Location: Sutton Bank, North Yorkshire

Re: Semi-scale ASH25

Post by Jolly Roger »

Thanks for those tips Roo.

The best searches for XPS foam included underfloor insulation . The boards are usually 120cm x 60cm and from 6mm to 50mm thick. Unfortunately they are typically sold in packs of boards to cover a large area, and for my small project I only wanted a single 120cm x 60cm board of 50mm thickness. The cheapest place I could find that would sell a single board was ezheat on ebay. Prompt, free delivery, well packaged, all good.

One board cost £15 but if you buy more the unit cost goes down. It was blue by the way. For info, the new grey stuff contains graphite which will likely increase density - not a good thing if you're using it for foam wing cores.

In terms of lay-up, I'm pleased with the 200gsm twill glass / 200gsm Diolen / 200gsm twill glass test piece I made. The Diolen adds a lot of resilience to the lay-up. When I hit it with a hammer, like you do, the glass eventually splintered and tore but the layer of Diolen held it together. If the fuselage feels a bit too flexy I could always lay up another layer inside.

I'm back to work now so may not get much done for a few weeks....such is life.

Chris Bowles
Posts: 69
Joined: 18 Mar 2015, 16:12
Location: South Devon

Re: Semi-scale ASH25

Post by Chris Bowles »

Roo/ Roger, I have found that cellouse thinners will remove XPS foam, it dosen't dissolve it, but turns it into a thick paste, which is very small is size, compared to the plug, also insulationsuperstore, advertise XPS foam, Danosa Danopren, 1.25×60×5, 8 sheets for £41, we have a store near by, so will check it out, and let you know
Chris

Jolly Roger
Posts: 306
Joined: 30 May 2015, 20:35
Location: Sutton Bank, North Yorkshire

Re: Semi-scale ASH25

Post by Jolly Roger »

Thanks Chris - that is a great deal from Insulation Superstore, especially of you can collect locally. Please let us know what the quality is like.

I assume you wrap your foam plug in parcel tape before glassing to make it slightly easier to clean out the foam? Either way, it sounds messy!

Cheers,
Rog

Chris Bowles
Posts: 69
Joined: 18 Mar 2015, 16:12
Location: South Devon

Re: Semi-scale ASH25

Post by Chris Bowles »

Hi Roger, yes I normally wrap the foam plug in parcel tape, and give it a coat of release agent, makes it easier to remove in the boom area, where there is not a lot of room, it's not that messy, once the front end is clear, stand the fuz up on its tail, in a container, pour in some thinners and wait, best of luck

Chris Bowles
Posts: 69
Joined: 18 Mar 2015, 16:12
Location: South Devon

Re: Semi-scale ASH25

Post by Chris Bowles »

Hi Roger, took a trip to the superstore, more like a small building, no stock, to bulky to store, we can get it for you, carriage extra, quoted £55 for delivery, needs to be but on a pallet, so pallet charge, tried a few more firms, all the same, apart from one that wanted to charge £80 delivery, so your price looks reasonable
Chris

Jolly Roger
Posts: 306
Joined: 30 May 2015, 20:35
Location: Sutton Bank, North Yorkshire

Re: Semi-scale ASH25

Post by Jolly Roger »

Chris Bowles wrote:
11 Jan 2020, 18:28
Hi Roger, took a trip to the superstore, more like a small building, no stock, to bulky to store, we can get it for you, carriage extra, quoted £55 for delivery, needs to be but on a pallet, so pallet charge, tried a few more firms, all the same, apart from one that wanted to charge £80 delivery, so your price looks reasonable
Chris
That's useful to know, Chris.

It's a shame that although builder's often use materials that look very cheap to modellers, you need to buy a shed-load to get these savings!

In one of those lovely quirks of fate, I stumbled on a bunch of offcuts poking out of a skip outside the school's DT department this week. They are now in my workshop.

This is all the proof I need that god is an aeromodeller. ;)

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