Dumfries A4

[Malcolm Baird]

15th May 2016 – A4 Skyhawk Build progress.

Thought it was about time I reported on progress. The fuselage is coming along quite well (Pic 1), after converting a considerable quantity of balsa wood into dust. This latter op can only be done either at the far end of the garden (weather permitting), or while Mrs B is out.

<how does one get a picture in here?>

Edited By Malcolm Baird on 28/05/2016 23:46:27

[Malcolm Baird]

[Malcolm Baird]

I cut a set of templates (Pic 2) to check the external profile as I went along.

[Malcolm Baird]

A couple of unexpected problems occurred as the upper surface approached its designated shape.

Just forward of F4, (Pic3), and just forward of F7, (Pic4), a couple of holes appeared in the upper decking. I may have made the fuselage sides a tad too high, so that sanding back to my cross section template has resulted in overthinning.

[Malcolm Baird]

Problem resolved by inserting a spare bit of balsa inside (Pic 5).

...and sanding outside......

[Malcolm Baird]

(I just noticed Phil had had a similar problem at **LINK** (15/05/2016 21:36:57))

Contrary to almost everyone else’s grain direction on the upper and lower fuselage, mine goes spanwise. I’ve always built this way, ever since Keilkraft, Veron, Frog, and Mercury kits top deck sheeting must have conditioned me…

A small bit of surgical reconstruction to the fin, as I’d already assembled the laser cut components, has now produced the more visually pleasing layout, (well worth the effort!)

28/05/2016

Tailplane built and sanded, elevator ditto, and about to fit elevator servo before I start on the wing.

[Andy Meade]

Well done Malcolm, looking great

[Mark Kettle 1]

Nice to see a new name on the PSS A4 build - good work Malcolm. Are your outer templates working well?

[Malcolm Baird]

Thanks for the positive feedback guys.

My templates are as close to the plan outline as I can manage, and they generally highlight bits where further sanding is needed. Or alternatively where a bit of filler .... oops!

I've now got the wing plan laid out, and starting to check the fit of parts. I found that the R1 doubler needed extending, and also the slots for spars only match the plan on one side of each rib (due to NC laser cutter probably not being able to cut a 32 degree slot), so a bit of filing and filling is called for there. I've noticed the dialogue on gussets too, so will bear that in mind.

[Phil Cooke]

Evening Malcolm, good to see you making further progress...

Yes its understood the spar slots in the ribs need a little 'fettling' to enable the spars to pass through the ribs with the required sweep - this is impossible to achieve with 'conventional' 2D laser cutting - the costs of a 3D laser cutting machine would most likely be beyond the means of any model kit manufacturer.

I would like to learn a little more about your findings with the Rib 1 doubler - you say its 'short' - no one else has reported that yet? Any chance of a picture?

Keep up the good work!

[Malcolm Baird]

Hi Phil,

Sorry for the delay in replying. Hopefully the following photo will show what I meant in noting that R1A is approx 5/16" short by the time it's been fitted.

R1 has the slot for the upper and lower 1/8" square wing spars in the correct position at the wing centre line.

R1A is cut to the same outline, such that its length is the same as from the leading edge of R1, back to the front edge of the upper spar at the wing centre line. But by the time the upper wing spar has been fitted, its forward edge is about 1/16" rear of this on the other (outer) side of R1, and an additional 1/16" back from rear of the outer side of R1A. It would be neater if R1A was a bit longer (approx 5/16", and could then have its rear edge chamfered to fit snugly to the 1/16" sheet webbing between the spars. Purely my preference, and not a showstopper by any means.

Your build blog is a delight to follow - I don't know where you find the time!

thanks

[Malcolm Baird]

Wing halves joined this evening. Have decided to cover with woven 25g/sq m glass cloth from EasyComposites, with a pigment added.

As a complete novice in glass coating models, would appreciate any comments on how much 25g cloth (sq m) I might need, will one layer of cloth do?

Should I be using a heavier cloth? Or just apply extra layer(s) at key points, like the wing centre line?

Here are a few pictures of my wing build so far....

I decided to add the sheeting seperately, rather than build onto it, mainly because aftrer reading other posts, it seemed that cutting the slot for the wing joiner slot/ dihedral brace might spoil the sheeting. The intermediate open structure was a bit flimsy, but it has kept its shape OK.

I added some 1/4" blocks for Kavan aileron hinges. I slotted them once both upper and lower sheets were fitted. The upper surface is still unsanded here - best done once the bottom sheet is fitted.

Fitting lower sheet, after previously sanding the underside gently, especially the sub leading edge.

Bits of spare sheet below the TE are to set washout -1/8" at tip, 3/32", 1/16", 1/32", equal spaced along to R3. I did try cutting the long thin wedge shown on plan, but after several attempts decided this way is more predictable. various heavy objects hold it down for the night. Glued in two phases - aft of spar, including spar itself first, then when that's dry, roll the forward ribs onto the sheeting and tack them with CA, ensuring the sheet is fixed to sub LE and not my fingers.

[Malcolm Baird]

Wings cemented together, clamped overnight

Ailerons need a bit of trimming

Excellent clamps from Screwfix!

I'll cut the centre out of the Servo box, and fit a couple of 1/4" beech servo supports once it's dried.

[Andy Blackburn]

Posted by Malcolm Baird on 04/07/2016 23:47:48:

Wing halves joined this evening. Have decided to cover with woven 25g/sq m glass cloth from EasyComposites, with a pigment added.

As a complete novice in glass coating models, would appreciate any comments on how much 25g cloth (sq m) I might need, will one layer of cloth do?

Should I be using a heavier cloth? Or just apply extra layer(s) at key points, like the wing centre line?

 

25g/sq m cloth is what I usually use, or possibly even a bit lighter. But 25 g/sq m will be fine; an extra layer at the wing centreline (like a thin wing bandage) is a good idea if you're paranoid (nothing wrong with a healthy dose of parnoia!), although I think there's a wing brace so it's not really necessary.

Personally, I'd buy a couple of square meters of cloth, not least because it's easier to find a large bit for the for the bigger components when you've already cut some parts out.

If you've not glassed before (I assume it's epoxy resin), here are a few random thoughts:

• Glass cloth blunts knives and scissors really quickly; I recommend the purchase of new scissors
• Vinyl gloves will protect your hands, latex ones - AFAIK - won't
• Most of the weight (75%+) is in the first coat of resin because it soaks into the wood straight away and it's very easy to put too much on; for this reason, I usually seal the surface with sanding sealer or acrylic varnish first, but I'm paranoid about weight.
• One way of persuading the cloth to stick down to the surface is a very short spray of Spray Mount into the air a couple of feet above the component, step back smartly and wait for the droplets to settle. The cloth will then snug down to the surface and it doesn't seem to affect the cloth/epoxy adhesion to any appreciable degree.
• The wife's credit card makes a very good resin scraper

 

Edited By Andy Blackburn on 05/07/2016 08:35:18

[Malcolm Baird]

Thanks Andy - that's encouraged me that I'm on the right track. Haven't heard the Spray Mount one before - will give it a go. OH has some already, plus a credit card, so we're almost there!!

[Malcolm Baird]

Making progress, and deadline now starting to look achievable! Have completed fibreglass 25g covering.

In hindsight, I made a couple of errors which slowed the process down.

1) I used slow hardener in my resin, which doesn't harden for 30-40 hours, and allows P L E N T Y of time for dust to collect. Next time I'll use quick set.

2) My second resin coat included a colour pigment - this slowed the preparation time a bit, wasn't as effective as I'd hoped, and I still needed to spray with final colour to get an even coat. So probably won't use that approach again.

Final spray is Halfords Ford Polar Grey, with decals from Pyramid models. One flaw in the decal set - the red bar is missing from one side of the USAF emblem on two of the decals. Has anyone else had this?

Another question - Is anyone else still using 35 MHz on 11th Sept, and if so what channel(s)?

Here's the current state of my efforts - canopy and wing tips still with masking tape in place. I still have a bit of work to do on the canopy to get it to fit, and the cockpit interior and pilot await decoration.

and some fuselage details too

[Malcolm Baird]

Well - I'm almost there!

• Painted, radio in and control throws setup,
• added 2.5oz lead to balance, CG about right,
• a few cosmetic issues, nothing to do with Liz Earle though.
• Flying weight is approx 2lb 10oz.
• Maiden flight will be off the Orme on 11th!! Fingers crossed!
• I have a PG03 gyro in the roll axis, at least until I've had a few flights to get the feel of it.

Here are a few pictures:

The battery retainer is just a 1/16" plywood 'lollipop stick' which holds a rolled up bit of flooring underlay (not shown) in the batttery box, to keep the battery down the forward end.

Radio

PG03 gyro on the left, and a tiny futaba Rx on the right.

The tailpipe is two layers of 1/32 balsa sheet approx 1.5" - 2" wide, spiral wound in opposite directions onto a 40mm plastic pipe used as a former. The pipe is first wrapped in clingfilm to stop it sticking, the balsa is boiled for 10 - 20 mins to soften it (ammonia didn't seem to work as well), then wrapped around the pipe, one layer clockwise, followed by a liberal coat of PVA, then the second layer of balsa is wrapped in the opposite direction. Finally a good tight winding of masking tape, and allow the assembly to dry overnight. Slide the balsa tube it off the plastic pipe, trim, and cut to length.

Here's my cockpit and pilot

I forgot the ejector seat handle before I glued the canopy on

Here's the 'scruffy' corner (above)

but overall, looking not bad!!

Might add refuelling hardware, and arrestor hook if I have time

[Mark Kettle 1]

"Another question - Is anyone else still using 35 MHz on 11th Sept, and if so what channel(s)?"

Malcolm Yes some do use 35 Mhz there will be a peg board in operation. Nice looking model by the way.

[Phil Cooke]

I like the cockpit detail with the extra depth Malcolm - where did you get the A-4 console picture from - are you able to share that? Congrats on finishing your model in good time ahead of the event, I look forward to seeing it in action next month!

[Malcolm Baird]

To get the cockpit instrument panel detail, I googled 'A4 Skyhawk cockpit Instrument Panel images', found a suitable candidate, took a screen snip which I edited with Windows 'Paint' to remove unwanted details such as a watermark. Probably not strictly copyright procedure... Then scaled the printer output onto glossy thin photo card. Cut out and stick on!

[Phil Cooke]

thanks Malcolm, I too had googled images for a console but couldn't find on square on and well lit suited to processing... this appears to be a rendered image not a photo - I must have missed this in my search - looks good at model scale!

Will you put a photo and a little description of your finished Skyhawk in the 'Completed Model' thread for us all please? Many thanks

**LINK**

[Steve Houghton]

Hi Malcolm,

It was nice to meet you at the Orme Yesterday. Sorry about the loss of your nose, but do remember that nose jobs are still very in vogue at the moment!
I mentioned that I had noted something from your blog, and I've remembered now that it was your lolly stick battery retainer. Having failed to complete my radio installation in time to fly yesterday, I may well use something similar when I complete mine over the next few days, after I catch up on some sleep first!

There's also a small matter of rebuilding my demolished Jet Provost wing - or binning it.

Regards, Steve.

[Malcolm Baird]

Hi Steve,

In spite of returning home with a truncated version of the original A4, I had a fantastic time at the Orme yesterday. My A4 performed much better (for its short performance) than I had anticipated, I only wish the same were true of my eyesight.

The damage is not as bad as it first seemed, - the wing is completely unscathed - and I'm anticipating a relaunch before too long. Maybe with a slightly lower Beaufort number.

I met a great bunch of guys, and look forward to getting along to future PSS events. Good luck with the JP rebuild too.

best wishes

Malcolm

[Chris Barlow]

The sun out in front wasn't ideal and was causing a few orientation problems so I wouldn't blame your eye sight that much Malcolm. Any photos of the damage and repair sequence?

Steve, sorry to hear about the JP. What happened to it?

[Malcolm Baird]

Here's an overview of the general mess, and my initial thoughts on the rebuild...

Most of the splinters are the battery box, which was pushed backwards into the main fuselage, impacting the elevator servo and F4. The tail servo mounting will need to be replaced, but apart from the battery, the electronics have all survived intact.

The impact appears to have been nose first, - apparently full bore straight into the clifftop. I will salvage most of the nose, cut some new formers, and rebuild from F3 forward, perhaps with a (temporary?) F3B.

Minor damage also to the spine/tail mounting which sheared off.

Almost all damage is forward of F3,

Engine intakes are OK, as are wings and tail set, and pilot. But I may invest in a new canopy...

Amazingly the canopy antenna survived, as I had some doubt on Saturday that it would even get as far as the Orme without me accidentally demolishing it.

Out with the scalpel!