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PSS A-10 Thunderbolt II - build blog

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Phil Cooke07/11/2012 23:51:05
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With the end of the 2012 flying season upon us I thought it was about time I started a thread on an ongoing PSS build, one which will see me through the Winter for sure, and no doubt well beyond before this is finished and ready for the slope.

I actually started the build well over a year ago now, and I'd say im about half way through - but with work and life as it is, combined with other commitments in the hobby (like flying and event going) it has been very much a stop/start affair so far... there is no rush, no promises or deadlines, it will be done when it's done... so the first few instalments of this blog will be written retrospectively, but we will no doubt catch up with progress soon and then proceed 'real-time' with the ongoing build.  Oh, and as this is my first build blog, please go easy.

So, for anyone not familiar, let me introduce you to the Fairchild A-10 Thunderbolt II - the 'Tankbuster'!

A-10 low level.jpg

Yes, this is a real one - but this is the sort of image we are trying to reproduce - a scale looking A-10 Thunderbolt II thundering low level across the slope and looking every inch like the full-size. Thats the idea, anyway.

The A-10 has been proven from the slope before, but not at large scale as far as I know. Other than the twin engine pods, its considered quite a good design for PSS, in the air at least (I am worried about knocking the fins off each time I belly land, as they protrude lower then the fuselage - but more on that later!) Generally, it has a well proportioned layout with an unswept wing of decent area and ample moment arm between wing and tail.

I'm building the model to 1/6th scale, converted to PSS from an old I/C Ducted Fan plan (twin 0.91!) which will give it a wing span of 110" and a targeted AUW in slope configuration of 30lbs.

The plans were originally drawn way back in the early 90's by Josh Harel, the model was flown successfully (all built up, lightly!) with the twin I/C Ducted Fans, and later it was converted into a fibre glass fus and foam wing kit by Dean Lassek. Here is an example of the Lassek kit version, giving you an idea of the size of the model we are building here...

a-10 Josh Harrel.jpg

This is Danish modeller Stig Anderson, seen with his Lassek version just before a successful maiden flight, the model here fitted with twin turbines and weighing in over twice what my glider version will weigh (hopefully!)

Edited By Phil Cooke on 07/11/2012 23:56:01

Phil Cooke08/11/2012 00:08:21
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So the plans are detailed for sure, 4 huge drawing sheets covering everything you need to build a fantastic scale model - right down to a sheet of detailed cockpit and weapon pylon drawings... heres 2 of the sheets pinned up in my spare room - they are way too big for my work bench! Thats a king size bed to give you some scale! surprise

a-10 plans.jpg

For PSS, Ive made a number of changes to the design as drawn - some fundamental changes like wing section and tailplane incidence (both the full-size and I/C powered model both had a huge amount of positive incidence on the tail combatted by a similarly huge amount of down thrust on the engines - I guess to give the full size its slow speed cruise and manoeuvrability) - anyway this would not suit an unpowered glider version so we have gone for a far more conventional layup with the tail.

For transportation reasons I intend to build a 2 piece wing and a fuselage that splits just ahead of the wing, with removable engine pods, tailplane and fins.

Construction wise we are changing the plans here too, and veneered foam will be used for the majority of the build.  Certainly the forward fuselage, the fins, tailplane and wing panels will all be veneered white foam.  For stiffness, Im thinking the rear fuselage (which, even at this scale gets pretty skinny towards the back end - but still has to carry that big tailplane) should be conventionally built up in ply and balsa.  My intention is to glass all this prior to paint to give a scale, weathered finish.

Edited By Phil Cooke on 08/11/2012 00:13:33

Phil Cooke08/11/2012 00:46:07
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So, with that introduction - let's get started with the build!

I decided to begin with the nose section, and this was cut from white foam block using the plan formers as reference guide. In anticipation of this project, I had already been 'gathering' a number of important parts, not least a 1/6th scale 'Desert Storm' A-10 jet jockey, sourced and tailored for me by Phil Clark at FighterAces. I wanted to recreate a full depth cockpit to make the most of this figure. The nose section would also house a nose release unit (for PSS aerotow) and its operating servo and actuation run. It would also be fitted with a hardwood 'spine' running along the underside of the nose section in an attempt to keep the assembly rigid.

cockpit layout.jpg

I began by laying these items out on the plan, and once I was happy with the general arrangement and positioning, I marked up the foam sections for various cavities to be cut.

nose foam 1.jpg

The foam was then carefully removed to form the required cavities in each half of the nose section to create the required voids for hardware fitting. The foam panels were then ready for veneering.

nose foam 2.jpg

chris edwards 308/11/2012 07:12:35
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221 forum posts
64 photos

fliping heck thats huge, you could almost sit in it and fly from there!!

Matt Jones08/11/2012 09:15:12
1186 forum posts
1 photos

If this is anything like your other builds Phil the finished article will look superb! I'll be watching this closely.

David Gilder08/11/2012 14:17:56
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1825 forum posts
619 photos

WOW Phil... Thats going to make Matts Lightning look like a toy and mine look like Micro PSS!!!!

Your going to need a bigger car or even a van!!!

Watching this carefully!!!

wink

Phil Cooke08/11/2012 16:44:41
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1901 forum posts
1270 photos

Yes, it's big. But Dave, no new car or van will be required! In fact I've split the fus at a point that leaves the longer (rear) section just right for my VW Passat with the back seat down - its been tailored to suit! The wings split into 2 at just over 50" per panel, so smaller than many of my current models - there's just 2 of them, and yes, the car will be filled with the other bits, especially the engine pods which are quite volumous... but we will manage yes

In actual fact, at 110" span and 30lbs AUW it will be very similar in size and stature to the BAC Canberra, built by Matt and currently flown by Simon Cocker which you saw in action this season - I just hope the A-10 flies with as much authoritative grace as that does!!

Phil Cooke08/11/2012 20:12:25
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1901 forum posts
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I've not done much veneering before, but I've found the process fairly straight forward so far. I'm using some lovely quality 0.8mm obechi veneer procured from Cloud Models. I cut the panels to (over)size and lightly coated them with latex contact adhesive, applied with a small foam roller. I did the same to the foam halves and left them overnight to dry.

Once ready, I roughly positioned the foam block towards one edge of the oversize panel, and using the bench I simply 'rolled' the foam panel around its own shape onto the veneer. I found this method produced a nice, smooth finish with minimal risk of air traps.

veneer nose 1.jpg

Once both foam blocks were veneered it was easy to trim the overhangs with scissors and a sharp scalpel to finish the parts around their edges and around the cockpit recess. A quick bit of bench flying for the A-10 jockey - his first look inside his new office - still without furniture!

veneer nose 2.jpg

Before the 2 halves could be joined there was still a bit of work to do regarding the nose release actuation run and servo mount,

Bucksboy08/11/2012 20:20:23
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508 forum posts
101 photos

Fantastic blog, I'm sat here in awe.

Phil Cooke08/11/2012 21:06:23
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1901 forum posts
1270 photos

Hi Bucksboy, thanks for watching in! A long way to go yet, so I hope you are sat comfy!

As stated earlier, it is my intention to fly the A-10 from flat fields occasionally as we have had great success with the larger PSS models in the past via Aerotow - this enables another fun dimension to the model throughout it's normal slope based life, all for a little planning and work up front now. I've used a good quality, 1/3rd scale glider type of nose release, simple and sturdy. To mount that securely into a foam nose I needed a good quality 1/4" ply nose spine, keyed into a similar ply nose former - to take the loads - onto which cosmetic foam 'cheeks' could be mounted and later, sanded to shape.

I cut the parts to the form on the plan and spent some time weight reducing the ply whilst still maintaining its strength and stiffness. A dry fit of the parts proved everything was sound and ready for some epoxy... The white plastic tube you can see runs from here to the cavity in the foam at the back of the nose section, this is for the release actuation rod to run in safely back to the servo bay.

nose ply 2.jpg

The area of ply spine below the double red lines still needs to be removed, this is where the A-10s nose mounted canon will be sat... more on that soon! smile d

Edited By Phil Cooke on 08/11/2012 21:09:46

Phil Cooke08/11/2012 21:26:26
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With the nose spine further fettled to accept the Gatling canon, the ply assembly process can begin. First, I glued the nose release unit into the ply spine using a strong, slow setting epoxy with micro balloons to get the best possible bond between the metal cylinder and the ply. Some care needed here to make sure you don't glue any of the moving parts!!

Next, I glued the ply spine to the ply former, ensuring a 90deg true alignment. Finally, again using a slow drying epoxy, I secured the finished ply assembly to the veneered foam nose section. With the large surface area of bond, we will be good to hang this 30lb model from the nose release no problem once this is fully cured.

Time for a cheeky glass of Rioja whilst its drying...beer

nose ply 3.jpg

I made a control rod out of 6mm carbon tube and fitted a sturdy 3mm clevis. This has to be good for the life of the model, as what you see here will be soon encapsulated in foam - never to be seen again!!

Edited By Phil Cooke on 08/11/2012 21:35:42

GrahamC08/11/2012 22:48:05
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1221 forum posts
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Oh I do like a nice build log. I'm watching this with interest!

Phil Cooke08/11/2012 23:03:44
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1901 forum posts
1270 photos

With my decision to split the fuselage at a point tailored to suit the length of my car boot, the forward fuselage section needed to incorporate a further 7" of fuselage to the rear of the canopy, and a repeat exercise was performed with foam cutting and veneer to produce the required section using templates from the plan.

This was epoxied square to the back of the forward fuselage section before a 1/4" ply mounting former was attached to the rear face - as this would act as the mating surface between the fore and aft sections it needed to be robust as it will take knocks every time it is assembled in the field.

rear nose 2.jpg

The rear cavity in foam shows the plastic tube to accept the nose release carbon pushrod and the cavity which will house the actuation servo and later, the fuselage mounting brackets - so it needs to be big enough to get your hands in!

rear nose 1.jpg

The 3 key slots in the ply former are for the ramin fuselage spine (bottom) and doublers to be fitted to reinforce the bond between these 2 fuselage sub-sections.

rear nose 3.jpg

So here's the basic forward fuselage complete, still awaiting its foam nose and a good sand down before the nose release servo is fitted along with the 7-barrel canon/housing and cockpit - all to follow soon! wink

Edited By Phil Cooke on 08/11/2012 23:09:49

Foamie Dave09/11/2012 12:50:23
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Subscribed !!! smile p

Olly P09/11/2012 14:10:31
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3215 forum posts
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Nice Phil.

Can I suggest Vaseline or another petrolium jelly? Coat the mechanicals in it before gluins and the epoxy wont stick, then wipe off with some washing up liquid and water!

Olly

Matt Jones09/11/2012 14:13:57
1186 forum posts
1 photos

I vaseline the knuckle on the Robart hinges I use, works a treat to stop them getting glued up. A quick waft over a lighter and the vaseline wicks into the joint fully thumbs up

Phil Cooke10/11/2012 10:35:37
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1901 forum posts
1270 photos

Thanks for the Vaseline tips gents, will remember to use that next time! I've got some Robart hinges to fit myself a bit later on!!

The next step on the forward fuselage section was to add 2 huge foam 'cheeks' to the nose to form the correct rounded shape around the 1/4" ply spine. I made these from pink insulating foam, ideal for fine sanding and forming. This comes from Homebase in 2" thick panels so needed to be laminated to create the thickness needed towards the rear. I shaped them roughly correct in 2D profile before they were attached to the fuselage. Cavities were cut on the inside faces to ensure the aerotow mechanism and pushrod was left clear of both foam and glue.

foam nose 1.jpg

Once happy with the fit and clearances they were glued in place against the ply spine and front former using 5 minute epoxy. Once dry the sanding could commence!  I refined the 2D profile first, sanding them down to the ply spine, which was the correct shape to the plan.

foam nose 2.jpg

It was then a case of cutting the corners off with a bread knife, then rasp, file, before sanding blocks with coarse, then fine papers were used.  The material works well with all these abrasives and other than getting covered with statically charged foam dust it is a pleasure to use.  I had a plastic model A-10 for reference in an attempt to get the nose shape just right... it is not just a simple dome so needed some attention in plan view profile - and the top face of the nose is quite flat, almost planar - where the air refuelling door is sited. Heres the end result, after a good sanding/checking/sanding/checking session with the palstic model proving invaluable as reference.

foam nose 3.jpg

You can see the aerotow fitting now flush with the very front of the nose.  Job done bar any final adjustments... next job the A-10s most well known feature - the 7 barrell Gatling canon!

Edited By Phil Cooke on 10/11/2012 10:40:33

Phil Cooke10/11/2012 13:03:07
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1901 forum posts
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So with the basic structure of the forward fuselage complete, I decided to turn to a bit of detail modelling to break-up the workload.

The full size A-10 is built around its most versatile weapon, the GAU-8 ‘Avenger’ Gatling cannon. It’s huge, over 4-metres long, and its 7 rotating barrels can deliver 70 x 30mm armour piercing rounds per second onto the target. The cannon is such a prominent feature of the A-10 the model would not be characteristic without it, and at this scale it needed to look convincing.

canon closeup.jpg

Phil Cooke10/11/2012 14:14:00
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1901 forum posts
1270 photos

So I set about trying to recreate the cannon in a manner that would be sufficiently robust and not too heavy. I was conscious that any nose down landings will see this feature strike the ground first, so its make up and mounting needed to be fairly strong to avoid losing it on the first such arrival. I found some plastic piping at my local hardware store that was just the right diameter for the rotating barrel sleeve, and a mating section which was just right for the outer fuselage shroud.

I carefully marked up the holes on the inner pipe and machined this with my Dremel taking care to get the spacing and angles as good as I could by hand. These holes were finished off with a little wet and dry.

plastic canon 1.jpg

Next, I used some 5mm aluminium tubing procured from my LHS to form the seven barrels at 1/6th scale. I glued these vertically into a 1/8th ply disc machined with 7 equally spaced holes at its outer diameter. This was a little fiddly, but the assembly was made more rigid and better aligned when another end cap was added to aid the gluing with epoxy. Once dry I wacked a lot more epoxy on the base of this structure to pot the ends of the tubes solid.

plastic canon 2.jpg

This assembly was slid into the plastic tube with the correct orientation relative to the holes and glued from the rear. The basic cannon assembly was completed with the addition of a 1mm thick plasticard end plate.

plastic canon 3.jpg

Once sanded flush with the tube using a fine paper, the hole assembly was painted with Humbrol 'Gun Metal' and polished back a little to give a spot of wear and weathering. All it needed now was the central fixing bolt head and the cannon was good to go.

plastic canon 4.jpg

Edited By Phil Cooke on 10/11/2012 14:29:37

Phil Cooke10/11/2012 16:19:44
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1901 forum posts
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With the cannon completed, it needed a housing and the pink foam nose was drilled out to accept the outer plastic shroud - this would sit flush up along the length of the 1/4" ply nose spline and engage into the ply nose former giving it a mount with the required strength. It proved a little tricky to remove the foam accurately and a little too much material was removed above the shroud which would later need filling, but we got there in the end.

With the shroud fitted the cannon could be slid into place and cut to length.

cannon housing 1.jpg

cannon housing 2.jpg

Once happy with the cannon itself a fuselage fairing and air scoop was made to replicate the full size. Again with landings in mind, this was made solid with ply formers and light ply faces. This would later allow the corners to be rounded off akin to the full size fairing when I was happy with the fit.

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