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PSS Tornado F.3

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Andy Blackburn24/12/2014 13:23:30
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Around about September/October 2014 I had quite a long discussion with Phil Cooke about Andy Conway's Tornado F.3 design. I built one of these as my first ever PSS model back around 1995 :

original-f3.jpg

...now, obviously, there are things that I wish I'd done differently, not least of which was to use 5 large cans of Halfords grey primer to fill the weave of the Solartex covering. It weighed something enormous, I think it was about 37-38 oz when new, and an ounce or two more after the inevitable repair.

I'd also changed the wing section to Eppler 205 with a view to improving the light-lift performance but this was probably a mistake as the wing was just a little too narrow in chord to allow the section to work properly; things did improve when the tips were turbulated, however.

Anyway, I'd always planned to build another F3 and had even acquired a moulded canopy, so Phil's blandishments and general encouragement to build another one fell on fertile ground and within a few days I had committed to building one "over the Christmas break"; I don't know how this is going to pan out, but I'll try and work on it every day for the next couple of weeks or so, and we'll see where we get to.

Naturally, I'm going a bit off menu with the plan and build, and will be making a few minor changes to the outlines. I have one of the early CAD plans and - this was years ago, remember - was fortunate enough to have access to an overhead projector, so I was able to copy a 1/72 scale drawing onto acetate, tape the plan to the dining-room wall (when The Boss was out, obvs) and then draw over the projected drawing outline directly onto the plan.

Scott Edwards 224/12/2014 17:38:15
218 forum posts
97 photos

Looking forward to the first build photos ! Crack on Sir !

Andy Blackburn24/12/2014 18:58:29
515 forum posts
487 photos
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I had a lengthy discussion with Phil about the wing section; I used E205 on my original effort which didn't work that well (it's not really designed for Reynolds numbers of less than 150,000, which in practice equates to about a 9 inch wing chord) and required quite a lot of stabilator angle and a bit of reflex on the ailerons to balance the pitching moment.

There's not a lot wrong with using the original E374 (although it tends to have similar problems to E205 at very low speed), but SD6060 is generally better than E374 all-round except for a small area in the top-left of the drag polar where one is scratching around in light lift, and it reacts well to turbulation if the low speed behavior needs a bit of tweaking.

I've re-drawn the wing planform, increasing the sweepback to a more scale value, added a bit of tip chord, reduced the span to about 44" and added 1.5 degrees of washout, which produces a wing area of about 298 square inches - if the weight can be kept down to about 35 oz, it'll have about the same wing loading as my original. Wing cores are from foamwings.co.uk with epoxy adhesive, glass cloth reinforced trailing edges and installed + sanded leading edge and weigh a tad less than 4 oz each - perhaps a little bit heavier than normal, but they should not delaminate with age.

So here's progress up to this lunchtime, just to show willing; tips made from 1/16" play core + thick balsa:

tips1.jpg

tips2.jpg

Wing marked out for cutting-out the aileron:

wing-marked-out.jpg

I've assumed 3/16" balsa for the aileron spars. Don't really know how much time at the building board I'm going to get on Christmas day, but we shall see...

Edited By Andy Blackburn on 24/12/2014 19:21:40

Phil Cooke24/12/2014 19:14:53
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Nice one Andy, great to see another PSS Tornado build thread on here - will be watching closely, there should be some good progress if you are having a daily run at this over the festive period!! thumbs up

Andy Blackburn24/12/2014 19:21:11
515 forum posts
487 photos
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Well, you say this, but I'm unlikely to attain the McLarenesque heights of 6+ hours a day at the building board, particularly over Christmas... smiley

Andy Blackburn25/12/2014 17:18:43
515 forum posts
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Managed an hour or two before dinner, in between peeling the potatoes and carving the turkey; tips are on and razor-planed to approximate shape:

wings1.jpg

tips3.jpg

Andy Blackburn27/12/2014 21:18:02
515 forum posts
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Thought it was about time I posted something - there has been *some* progress but I've been watching too much TV - but I think it's OK to watch classics like A Shot in the Dark ...

So, the ailerons were cut and faced:

aileron-facing-2.jpg

...which actually took quite a bit of effort because the skins are epoxied on and there's some lightweight glass cloth under the veneer where the ailerons go. It's also a bit heavier than expected but importantly, it's very rigid and - so far - the pieces cut off (e.g. ailerons) have stayed completely straight.

The area where the torque rods go needs some internal reinforcement, the pictures show how I chose to do it:

aileron-reinforcement-1.jpg

 

aileron-reinforcement-3.jpg

 

aileron-reinforcement-4.jpg

...then all the ends were faced with hard 1/16" sheet.

Luckily, this time I remembered to a) angle the torque rods backwards a bit so that the clevis holes are in the right place, and b) equalise the torque rod height before installation:

matching-torque-rods.jpg

This is the bit that I keep putting off because there's always an imagined risk of accidentally epoxying the torque rod rigid so that nothing moves; it hasn't happened yet, of course, but it might...

torque-rod-fitting-1.jpg

...but it seems I've got away with it this time - everything twiddles as it should:

torque-rod-installation.jpg

The aileron is fitted:

the-aileron-fits.jpg

Maybe the control surface gaps are a tiny bit too small - we'll see. All that remains to be done on the starboard wing is the aileron leading-edge chamfer, hinges, the aileron servo bay and final sanding - that's the first order of business tomorrow, then the port wing.

Edited By Andy Blackburn on 27/12/2014 21:19:44

Phil Cooke28/12/2014 08:00:56
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Like the idea to 'fill' the end of the hollowed out ailerons with balsa stock - that is very neat! thumbs up

Steve McLaren28/12/2014 20:53:11
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It looks like you're achieving a lot more building time than I am this holiday Andy!

I'm glad you've started on the wings. I wanted to see someone else cut into them before I dared to do it myself! Between you and Phil we should have a full set of 'instructions' very soon!

Did you cut the wing skins with just a knife, or is something more powerful required?

Keep up the good work!

Andy Blackburn29/12/2014 16:32:58
515 forum posts
487 photos
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> It looks like you're achieving a lot more building time than I am this holiday Andy!

I'm making up for it today, though - it's been a day of reading, playing games and watching DVDs smiley

The wing skins aren't a problem, it's just that you need many careful cuts - half a dozen or so - with a new knife blade using a long straight edge, maybe with a bit of blu-tack or double-sided sellotape under the ruler to discourage it from moving. I find it's also best to angle the cuts very slightly into the (in my case) 3/8" scrap area so that the foam on the wings and ailerons can be sanded flat afterwards (i.e. no voids when you glue the balsa facing on).

I've also tapered the ailerons slightly because I think it looks better, and because it should reduce the tendency to tip-stall if you give it a handful of aileron when it's flying close to the stall.

WRT the aileron infill, I'm glad it meet with approval, it seemed to be the obvious way to do it. However, should you decide to do it this way I should perhaps mention that a) you do need the masking tape, b) I think quick-drying PVA is best for this and c) it's probably best clamped something like this:

aileron-reinforcement-2.jpg

...to prevent distortion whilst it dries.

Edited By Andy Blackburn on 29/12/2014 16:33:57

Andy Blackburn01/01/2015 11:27:57
515 forum posts
487 photos
1 articles

Still finishing off the port wing, I would post some pictures but they look just like the starboard wing, only reversed

Should have the ailerons hinged and the wing joined today, so by tomorrow I should be able to work out where to put it - it's going to need moving forward from its original position for aesthetic reasons, partly because of the extra sweep, so I need to be able to position the joined wing on the plan-view drawing and move it around until it looks right when compared to a scale top view.

I've also been considering the finish and colour scheme; on balance, I think it's going to be lightweight glass cloth and acrylic varnish (Deluxe Materials Eze-coat) and either enamels or acrylic paint - I'm going to have a go with Hannants enamls/acrylics.

On the colour scheme, still not 100% sure but I'm leaning towards a reprise of 11 squadron's DH/ZE764 because it has that big black fin - there were a couple of occasions with the original where the camouflage did its job against a grey sky and all you could see was the black fin and spine.

Speaking of RAF Tornado F3 camouflage, I found some camouflage and markings on the Tornado SIG pages, and after a bit of scrabbling around with the IPMS Colour Cross-reference Guide have found the FS 595 equivalents:

  • Upper surfaces: Camouflage Grey (BSC381C:626) - FS26314 (satin)
  • Undersides: Light Grey (BSC381C:627) - FS26440 (satin)
  • Radome: Medium Sea Grey (BSC381C:637) - FS36270 (matt)

I *think* that's about right but as with all things colour-related, other people's mileage may vary, as they say...

P.S. Happy new year!

Edited By Andy Blackburn on 01/01/2015 11:31:55

Andy Blackburn02/01/2015 22:17:59
515 forum posts
487 photos
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After a few minor nistakes (managed to reinforce the fixed part of the TE rather than the aileron - that's what comes of listening to something interesting on the radio whilst building on autopilot), managed to get the wings joined, this is the top view:

wing-joined.jpg

In this condition they weigh a tad less than 8 1/4 oz which is really good, although one of the wings had a bit more washout than the other so the root had to be offset slightly.

The next problem is going to be where to put them; they have more sweep than Andy's original ones and are very much larger than the scale wings (on the order of 130% of the scale size) so I don't want to just drop them in the original position because there will then be a lot of wing towards the rear of the aircraft and the top view will just look odd. IMHO, anyway.

So, here are some experiments to determine where the wings should go.

Firstly, here's a representative scale top view:

f3-top-view.jpg

The feature that my eye is drawn to is the gap of very approximately half a wing chord between the stabiliser root and the wing trailing edge; I suspect that if that gap reduces significantly, it'll look as though the wing is squashed back towards the tail.

So, armed with the new wing, the original plan (annotated) and a couple of card stabiliser shapes, the wing can be positioned so that it's touching F4, which is about as far forward as it will reasonably go:

wing-aligned-at-f4.jpg

Even though everything is in about the right place (the root is nearly 30mm forward of the plan position but it looks about the same because of the extra sweepback), I think it looks wrong because the wing/stabiliser gap just looks too small. I should add that the stabilisers are nearly to scale size and a bit bigger at the root than the originals.

Here's the wing moved another 20mm forward:

wing-moved-20mm-fwd.jpg

...and that still looks a bit too far back to me. Let's try an additional 10 mm further forward (a total of 30mm forward of F4) with the extra stabiliser root chord (about 1/2" ) trimmed back:

wing-moved-30mm-fwd-te-in-scale-posn.jpg

That actually puts the wing trailing edge in the scale position, but I'm thinking that the wing is now probably a bit too far forward when compared with the scale drawing so I think the right position is to have the centreline of the wing 20mm forward of F4 (the leading edge will need trimming, of course)

One last check, lets try the wing 50 mm forward of F4:

wing-moved-50mm-fwd.jpg

Nope, that looks wrong to me - definitely too far forwards.

So in summary, I'm going to take enough off the "point" of the wing root leading edge to allow it to fit in the wing bay at the desired position, which is a total of 48mm further forward at the root to compensate for the additional wing sweepback and additional wing chord arising from the wing enlargement. The wing root fairing will still be OK because the intakes on the plan are actually about 3/4" forward of the scale position, so everything still fits.

Now I need to re-draw the fuselage plan... 

Edited By Andy Blackburn on 02/01/2015 22:22:02

Scott Edwards 203/01/2015 10:41:41
218 forum posts
97 photos
Very good looking wing. If all else were to fail, you have a nice Zagi there (apologies for the profanity there)

Looking at the scale photo, my (poor) eye is drawn to the wing root fairings. With wings fully extended these are a very noticeable part of the overall planform. On your wing position tests, these roots are not easily visible on the plan, and could possibly make a difference to the overall visual perception ?
Andy Blackburn03/01/2015 11:28:56
515 forum posts
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You're right, it might. Well spotted, that man.

I'll see if I can do another check picture this afternoon.

Mark Kettle 103/01/2015 11:33:58
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I like your build and layout process Andy, looking forward to the redrawn fuse with root fairings.

Phil Cooke03/01/2015 12:51:04
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Andy I have to ask as I cant replicate your 'stand back view point' of the plans you've done without getting either my feet or my beer gut in the shot... what are you using to elevate the camera to a height sufficient enough to get that shot indoors? The camera must be near the ceiling (unless you have a room with carpet on the walls!)

Andy Blackburn04/01/2015 17:06:26
515 forum posts
487 photos
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It's an iPhone held up at head height (arms outstretched) and the originals do of course include my feet; I then cheat by rotating and clipping the picture in Paintshop Pro .

Andy Blackburn05/01/2015 21:13:16
515 forum posts
487 photos
1 articles

Have just re-checked the wing position with due allowance for the wing root leading edge fairings and I think the final wing position (that is, virtual root LE 20mm forward of F4) is probably the best one, if there's a problem I can always go back to the scale stabiliser size.

I now need to re-draw the formers to match the new wing position and top fuselage shape (very slightly slimmed compared to the original plan). I think I can get away without having to re-draw the fuselage, although there are now so many pencil lines and red pen lines on the plan that it's getting difficult to tell which line is which...

Andy Blackburn11/01/2015 17:57:12
515 forum posts
487 photos
1 articles

After a mammoth re-drafting session (my plan is very old, dated 23/9/93) I've now got something that I can work with; the formers were re-drawn by sketching the new (slimmer) top view sizes onto the existing former drawings and the interpolating:

re-drawn-formers.jpg

Not sure how much you can see from this but most formers needed adjustment, some needed correction as they weren't quite symmetrical, and F1 needed a re-draw. I also took the opportunity to change the angle of the rear fuselage sheeting to 30 degrees - hope this works out OK...

The rear/outer fuselage sides were also re-drawn:

rear-outer-fuselage-sides.jpg

...the wing section was printed out to the right size using Compufoil and stuck to some thin card so that it would hold its shape when drawn around, and was set at an incidence of +1.0 degrees to (approximately) compensate for the 1.5 degrees washout. The stabiliser pivot point was moved up about 8mm to a more scale position (early plan, remember) and because of the sharp taper in plan view around the jet nozzle area, some 1/4 doublers were added on the inside of the fuselage sides so that the shape could be sanded in. Finally, the front of the drawing was extended by 1mm for a good fit on F4, allowing for the curve in the fuselage top view.

The front/inner fuselage wing cut-out was done similarly:

inner-fuselage-sides.jpg

...but I've basically guessed where the airfoil section should besmiley.

On my original, I don't think the inner fuselage sides made contact with the bottom wing surface and that, coupled with the basic flexibility of a bit of 1/8" sheet (plus some ply reinforcement) meant that the wing bolts never fractured in a crash - the inner fuselage sides broke.

What I've done is to work out - theoretically - where the wing section will sit on the front/inside fuselage side, allowing for the 3/16" anhedral, and I'll cut the wood so that there's enough gap for a bit of wing seat tape, or something similar. The plan is to use a strip of 1/8 ply and some local reinforcement and a normal spike nut instead of the SLEC wing bolts.

Wood cutting starts tomorrow.

Mark Kettle 111/01/2015 19:12:13
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Good work.

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