PSS A-4E 'Top Gun' Skyhawk

[Phil Cooke]

With a PSSA event run 11th/12th June and with Weston Park and Wings and Wheels both attended this weekend I've just had a fortnight off building - time flies! It's only 12 weeks now until the A-4 mass build event on 11th September so I've got to get going again...

Having tidied down the desk (I'd still not properly unpacked from the Orme event)  I've laid up the lower wing skins in 1/16th balsa prior to marking them up with the positions of spars, ribs, sub L/E and T/E. With all the ribs laser cut this should be a quick assembly job.

Edited By Phil Cooke on 20/06/2016 18:43:13

[Phil Cooke]

Wing panel assembly has begun with the T/E, lower spar, ribs and top spar all now glued up on one wing.

First job was to mark up the position of the ribs and the lower spar with a panel pinned down to the board, positioned accurately on the T/E. Note skins are overhanging at root, tip and L/E.

The 3/16" x 1/4" T/E is glued flush with the back edge first, to help keep this straight I used a length of 1/2" balsa as a guide when gluing and pinning. Worked well. This T/E then becomes your datum for all the ribs.

Having relieved the rib spar slots to allow for the spar sweep, I placed the bottom spar down gently with PVA but did not pin it - I let it 'float'. I then added Ribs 2 to 8 ensuring the rib T/E was tight up against the T/E stock - adding glue only to the spar slot and the rear half of the rib at this time. The rib 'drags' the spar into the exact position required from this T/E datum, taking out any errors in my rib slot adjustments.

Rib 1 was then added ensuring the dihedral angle was in place. Finally the top spar was dropped in between Ribs 1 to 7 and the assembly was left to dry overnight.

[Phil Cooke]

A bit more wing progress...

The 1/16th balsa webbing was added between the top and bottom spars between Ribs 1 and 7 (vertical grain) and an additional web of 1/8th balsa was added in between Ribs 1 and 3 - this sits ON the bottom spar and aids alignment of the wing joiner set up later...

With the wing still pinned down to the board behind the spar, the front lower sheet was raised and curved up along the bottom edge of the ribs, a length of aileron section was used as shown to vary and control the elevation of the sheeting before cyano was used to glue the front half of the ribs to the lower sheet.

The 1/8" sub L/E was then glued to the front face of the ribs 2-8 - there was a little mismatch with the rib fronts after I'd chamfered them to accept the swept L/E - the straight edge ensures its all kept true whilst the PVA sets overnight. This panel is ready to come off the board once dry.

[Phil Cooke]

The first wing panel progresses a little further...

It was removed from the board and the overhanging bottom skin was trimmed to size. At the T/E, balsa aileron section was used to 'block out' the rear part of rib bay 1-2, stiffening the area where the wing bolt will load up (this is not shown on the plan but the idea pinched from Steve Houghton's thread!) and two aileron hinge blocks were added.

Rear of the spar, the forward 1/4" balsa gussets were added at the root, top and bottom.

[Phil Cooke]

The 1/16" ply wing joiner is designed to sit in a groove or box formed by the 1/4" triangular gussets and some 1/4" strip which is mounted behind them leaving a 1/16" gap. I used some medium 1/4" x 1/2" strip which fell to hand in the workshop...

4 pieces are needed per wing panel - use offcuts of the 1/16" joiner ply supplied to ensure the gaps are sized and parallel.

A matching pair...

The wing joiner slot is complete once a saw is used to cut down through ribs 1 and 2 allowing the 1/16th ply joiner to slot fully home - it needs to protrude THROUGH both the top and bottom skins to be sanded flush with the outer skins once the wings are joined (the joiner supplied in the kit isn't sized sufficiently to allow this - its been sized to sit inside the skins )

Whilst that was all drying I made up the composite tips - each one a balsa/ply/balsa sandwich - a L and R handed pair are required as the balsa isn't the same thickness top and bottom.

 

Edited By Phil Cooke on 02/07/2016 15:35:58

[Phil Cooke]

Time to cut the wing joiner slots...there's the right tool for every job - he's not often used - it's time to bring out FAT MAX!

The saw is just under the 1/16" thickness required, but ideal with the wide chord blade running in the channel formed by the wing gussets...

The skins were cut to the required depth of 65mm, then cleaned up using a piece if the 1/16" ply that will eventually be used as the joiner -forming the perfect gap through Ribs 1 and 2 and the bottom skins.

[Phil Cooke]

A little work on the wing servo bearers tonight. I've gone for a 2 servo wing this time - allowing me to mix a little flap in for light lift conditions and dragerons on landing.

Hardwood bearers were dropped into notches, flush to the top surface of Ribs 1 and 2. I will sheet over half of their span later leaving just the servo visible. The bearers are notched to allow the rubber wiring 'grommet' to pass through before the servos are slid along away from the centreline ensuring adequate clearance from one another.

I've chosen metal geared HS-65 for the job, ample for a single flying surface of this size. I made up the torque rods tonight too, sized as per the plan.

[Phil Cooke]

Top skins now added and tip washout set to 2 degrees...

I cut a washout 'former' from 1/4" sheet as per the plan - 3mm deep at R8 and running out to ZERO thickness at R3...for ease I cyano'd this to my building board.

Top skin was trimmed so it was just oversize and the hole was cut out for the servo bay - PVA was applied and the skins were pinned down working forward from the T/E. Balsa strip batons were used to aid constant curvature over the span. Further weights were placed on top along the spar and webs ensuring no 'lift' from the inner structure.

View on R8 shows the conforming upper skin and the resultant washout angle. Time for a beer whilst that sets.

Edited By Phil Cooke on 11/07/2016 22:44:18

[John H. Rood]

"... I've gone for a 2 servo wing this time - allowing me to mix a little flap in for light lift conditions and dragerons on landing.

Hardwood bearers were dropped into notches, flush to the top surface of Ribs 1 and 2..."

Phil, that blend of flight options sounds great! And I just so happen to have two of those HS-65MGs myself!

Ummm, for the digital-era novice (me!), can you be so kind as to explain here (or in a PM so I don't clog up your thread!) how that digital mixing is done?   Or I can sit tight and see how you rig your model for it here in this thread!

I'm so old, rusty, and "basic" that I've never used mixing or any of the post-1990 technology. I have only set up and flown models with either rudder + elevator, elevons (mechanical ---sliding the aileron servo fore and aft on rails), or ailerons + elevator.   Really I might be better off keeping things simple with just two servos, ailerons and elevator, as I am coming out from the dark ages and am so out of practice,  The Keep It Simple concept...

Lastly for now, what size hardwood do you recommend for the servo bearers?

Thanks in advance!

 

Edited By John_Rood on 12/07/2016 19:23:48

[Peter Garsden]

Simples John, you just select a model with a 2 servo wing and the transmitter should do the rest, at least that is what my transmitter does. No need to do individual mixing at all. What transmitter do you have? Mine is a Futaba 14SG. I think some of the older transmitters are more of a fiddle to set up so it depends.

To set up spoilerons, you select Butterfly on my transmitter then adjust the amount of movement you need for aileron 1 and 2 - same direction say 75% up with about 4mm down elevator, and set it to your Throttle stick. I fly with up stick to the top for neutral flap and down for up spoileron. Some people do it the other way round.

For thermal setting, I use Cambermix and set it to a switch which activates both ailerons to move down 5mm.

If you had flaps you would set them to move down about 70 degrees with 2/3 up aileron and again about 4mm down elevator or sometimes more depends. This would be crow braking as it is called. I don't use this to land my PSS models to be honest apart from the JP because it flies so bloody fast.

To be honest the Skyhawk flies slowly so you probably won't need spoilerons to slow it down for landing. You should just be able to feed in a bit of up elevator to get it near the stall to slow it down, or just dump it in the heather.

I do agree that some thermal flap setting might help in light wind, so I can imagine using that.

[John H. Rood]

Thanks for all that, Peter.

Golly, I might wanna actually read the instructions that came with my transmitter?

So I checked inside my Airtronics RD8000's manual **LINK** and gee mate --- what do ya know --- my radio DOES have that flaperons / dragerons capability!

"FLAPE" they call it. Brilliant!!!

(At this rate, I might well prove to be a candidate for The Darwin Awards!)

Edited By John_Rood on 12/07/2016 22:55:56

[Phil Cooke]

Hi John,

The servo bearer material I've used is 1/8" x 3/8" which gives plenty of area and thickness to self tap screw these little Hitec servos into...

[Steve Houghton]

Phil,

I like your use of batons to hold the wing sheets in place. I've never tried that - must remember for next time! There's always something to learn from the masters on these mass builds.

[Phil Cooke]

The wings have been removed from the board and the top skins trimmed and sanded to shape.

The Leading Edges were cut from medium 1/4" sheet and stuck on the front.

[Martian]

it's looking really good Phil lovely neat work

[Phil Cooke]

As Andy has mentioned on the A-4 build tips thread, he kindly presented me yesterday with the prototype refueling probe S-bend which he had modelled in 3D CAD from a sketch I had provided, before manufacturing the kit of parts on his 3D printer.

For ease, we had sized the plastic parts to slide onto McDonalds drinking straws, which were the right outer diameter for scale, and universally available to all meat eating modellers.

2 small square holes were machined in the side of my fus and the whole assembly just pushes on. Heres the initial dry fit.

Andy is happy to hear from anyone else who might want one of these plastic probes to fit to their A-4 - drop him a PM on here or PM me if you want his email address.

Many thanks Andy, great job.

[Phil Cooke]

Time for some sanding...

Edited By Phil Cooke on 16/07/2016 15:44:45

[Phil Cooke]

Torque rods fitted and fixed T/E stock now attached firm with epoxy...hopefully no 'ooze' to bind the workings...

[Phil Cooke]

Wing tip laminates were added today, its really important to glue these on at the right angle so as not to undo the washout built into each panel and to enable a 'true' Trailing Edge line when viewed along the wing.

First, I cut a 1" length of aileron stock and temporarily pinned it to the wing flush with the tip rib. I pinned it at an angle so the underside surface of the wing ran smoothly to the centre of the extreme T/E - marked with the line in the photo. Some material will have to be sanded off the ailerons top and bottom but this works fine for positioning the tips.

The tip laminates mating face was sanded smooth and planar, I put some plastic tape over the end of the pinned T/E section to avoid gluing it to the tip then used 5 minute epoxy to glue the tips onto R8. Whilst drying, I ensured the central ply core of the tip laminate remained on the marks on the extreme TE centre and the same at the LE centre. A lot of material to come off here once the glue is cured, but its important the ply core runs to the extremes and doesn't drift above or below the required marks.

[Phil Cooke]

I took a little break from all the sanding and shaping and focussed a little on some other details like the pilot. With LCDR Rick "Jester" Heatherly being a well known film star I wanted to ensure my pilot figure was representative of the character, as such I needed to create a dark blue helmet with an array of small yellow stars.

Huge thanks to Tim and ModelMarkings for his work, he very quickly cut and supplied me with a sheet of tiny 2mm diameter stars, laser cut on a self adhesive vinyl. My hope was these would stick well enough onto the gloss painted helmet, although applying them was going to be a bit like watchmaking at 1/12th scale...

Anyway it went alright, despite the mocking I received from my wife - not her idea of a fab Saturday night apparently! They do stick fine, and I'll finish them off with a top coat of clear gloss to fully retain them - don't want them dropping off inside the cockpit during those 9G Aggressor S-turns!

So that's the pilot ready to taxi... back to the airframe and more sanding

[Shane Talbot]

" Jester" in the pilot seat, I like that.

[Phil Cooke]

Slow week on the blog other than messing around with the pilot - but I've been busy with the sanding block - wing L/E, T/E, tips etc - With each wing panel now fully sanded up it's time to join them using a 1/16" ply brace. The one supplied in the kit (top) isn't quite tall enough to break through top and bottom skins as per the design intent, so another was made to the same size and angle but with an additional 8mm on the top edge. I found rounding the corners and edges aids assembly as a dry fit.

For scale, each wingtip needs to be raised by 14mm. I made a couple of 14mm high jacks from balsa scrap and glued them onto the plan along Rib 8 - with the panels 'grounded' on the board along the centreline this guarantees the dihedral is correct. Using a 30 minute epoxy I joined the panels ensuring everything was square, butt-jointed and with the dihedral brace sticking a few mm out of the top, its height at the bottom is dictated by the lower skins being board mounted.

I even remembered to pre-line my board with glossy tape so I didn't glue it all to the desk!

I pinned the extreme T/E to the board to ensure accurate alignment at the back end. Once fully cured the join can be cleaned up and the dihedral brace sanded back flush to the skins.

[Peter Garsden]

I think I recognise Tom Cruise as the pilot - such a gay film that Top Gun or so Ant Jervis reckons - all parading around in their pants apparently. What do I know, and I couldn't possibly comment in the field I am in of course?

[Phil Cooke]

A little bit of metal work needed in preparing the elevator joiners. The M2 threaded rod ends are simply potted in epoxy and micro balloons within the 5mm brass tubing which is later crimped to form the elevator horn.

[Phil Cooke]

A few finishing jobs completed on the wing today, and for the first time I've married the wing to the fuselage and bolted it up. To achieve a good fit I had to relieve the fuselage wing saddle doublers a little all the way along, but especially at the front where the angled surface of the wings upper skin (R1 is taller than R2) was binding and stopping the wing seating fully.

Prior to that I sanded up the L/E dowel retaining plate - I've made a slight error here and used 5/16" balsa behind the 1/8" light ply front face, instead of 1/4" balsa as per the plan (late nights, tired eyes) which means my wing T/E now sits 1/16" further rear than it should... and I've had to relieve the fuselage sheeting to enable the wing to fit - I'm sure no one will notice

I've added a 1/8" light ply load spreader (I didn't use the one in the kit as I felt the hole machined in it was too large as supplied - and the one I've made is slightly longer) and the wing/body blend from 1/8" balsa is now fitted and all sanded to suite.

Bar the ailerons the wing is now ready for final surface prep prior to glassing, as is the fin and tailplane... I can't put the glass and resin task off much longer.