Andy's Partly-Retrospective PSS Jet Provost Build

[Andy Blackburn]

I'm painfully aware that it's only a few weeks to the big day, but the JP structure is nearly finished and I have a few days off so I think I can still get it to a flyable state by the end of May. The big triumph this weekend was finding the carefully-hoarded roll of fluorescent orange Profilm that had been left in a dark corner of the loft, so I think that bodes well for the covering.

Continuing with the radio fitment; this is the switch that's actuated by a small piece of 20 swg piano wire running in a bit of snake inner:

...after which, the rudder servo can be added:

...and the elevator servo mount with a couple of velcro mounts for the spektrum Rx:

I did briefly consider soldering the elevator joiner, but TBH I don't think it's necessary - the original had an epoxied tailplane joiner and it survived several sudden arrivals with barely a scratch. This is the two halves of the joiner cyano'd together and wrapped with carbon tows:

...epoxied:

...and then finished off with a flattened brass tube and a 1/16" hole:

I did spend a large part of the weekend sanding bits of wood to shape, applying filler and so on - I'd forgotten just how much dust can be produced by balsa filler and was reminded of the hazards inherent in sanding outside when the minister for home affairs has the washing out on the line...

Still to do: tail surfaces, hinges, minor details (tail bumper, etc - although I could probably put that off till later as it's a non-essential part) and photographs of the assembled structure. With a following wind, should have everything ready in two or three days.

Edited By Andy Blackburn on 11/05/2014 20:41:28

[Andy Blackburn]

Was just about to start on the tail surfaces so thought it might be a good idea to just check the decelage before anything irrevocable was done; after a bit of fiddling with an incidence meter and checking the result with a straight edge, ruler and calculator, it transpired that the tailplane had more incidence than the wing! The black line shows the intended tailplane incidence:

This has probably happened because a) I've reduced the wing incidence on this particular model, b) I had to elongate the wing peg hole to get everything to fit, reducing the incidence further and c) the tailplane has already been fitted and required a fair bit of sanding to square it up with the fuselage, and I've obviously over-done it. Rats.

The easiest fix was to sand some 1/16" sheet to a taper and use that as a shim:

I did have the bright idea of making this sanding jig from scrap 3/32" and 1/4" sheet ti get the right jet-pipe profile:

Here's the fin and rudder, hinged and ready to fit. Haven't decided what to do about the rudder horn yet, other than to recognise that the rudder snake exit is at least 1/2" too close to the rudder; some novel solution might be required, but I'll deal with that later.

Here's the tailplane hinged and elevators fitted:

...and with fuselage fairings fitted, as well as inset reinforcing strips at the tips because they (the tips) have turned out to be very vulnerable to workshop damage.

And finally, the last bit of woodwork is the fixed part of the tailplane that sits between the elevators; this is it being marked for final shaping, the idea is that it will be permanently fixed to the fuselage before part-way through covering, before the tailplane is fitted. At least, that's the plan...

So, that must be ready to start covering, then ...

(I take pride in the fact that my lawn is obviously in a worse condition than Phil Cooke's)

Total weight in this state is 15.9 oz, which is OK. There are four servos to fit as well as more snakes and connectors than the original had, but I'm still hoping for a total weight of about 26 or 27 oz.

Here's a view with the (ahem) high performance wing tips replacing the tip tanks:

My word, those wings are small...

I think I have enough time to finish it before the big day (I have some holiday planned), although it might be missing some of the minor scale details and it will probably have to have its first flight at the Orme...

[Andy Blackburn]

I haven't made a huge amount of progress this week, partly because I'm having to re-learn how to cover with Profilm/Oracover again; this has been a voyage of bad language and burned fingers - I think Solarfilm would have been easier (and less painful!) but although both colours (silver and dayglo orange) are available in Solarfilm, I've been hoarding several rolls of Profilm and for some time and it seemed a shame not to use them.

What seems to take the time is going around the edges first, particularly when there are more edges because of the more scale hinge lines, and there's an extra hinge line for the rudder:

Granted, you have to do the same with Solarfilm, but it's a more flexible and stretchy film that will easily go around right-angle corners, and it can be stretched with less effort so there's less risk of crushing the balsa.

Anyway; here's the tailplane covered and hinged:

(Yes, I know there are blemishes. I'm out of practice!)

Fin:

(Also did the ailerons but its a boring picture)

The intakes are turning out to be a bit of a pain (I've done one, the other will have to wait 'til tomorrow morning) - from memory, it can be quite difficult to retain a good edge to the corners of intakes, so they were covered separately:

...followed by the back end and the intake face:

And then finally, after a considerable amount of pulling, stretching and burned fingers, the (almost) finished article:

So tomorrow morning I'll start with the other intake, then I'll move onto the fuselage and painting the cockpit furniture - I did have half a mind to detail the cockpit properly with more scale ejector seats and so on, but there just isn't time.

Edited By Andy Blackburn on 23/05/2014 21:47:17

[Phil Cooke]

Looks really good Andy - well done with the Pro-Film, I agree the material does need a lot more work (and a much higher temperature I found) but you will be rewarded with a finish that never sags or wrinkles in the sun and will require far less maintenance than Solarfilm...

It will be very interesting to compare the two finishes between your model and that of Matt Jones, same scheme, different materials...

Edited By Phil Cooke on 23/05/2014 22:15:02

[Matt Jones]

Phil, I've got the Profilm equivalents here, the orange is a bit less flourescent so probably more scale. Profilm is generally my preference but used Solafilm for this as it's lighter.

[Andy Blackburn]

Here's where I've got to with the fuselage covering, as of lunchtime on bank holiday Monday:

...and I have to say that Profilm isn't as easy to use as I remembered! There are a number of areas that I'm not very happy with (small bubbles and creases, that kind of thing) but most of it looks OK.

Plan for the rest of today is to do the fluorescent orange areas on the nose and rear fuselage - not looking forward to the nose area, but I think it might be OK with four pieces (one to each quadrant) pulled and stretched into place - or maybe three if I can get away with it.

Having had a good look at what's left to do and how long it's likely to take, I have taken a sensible pill and I have to report that this model will NOT be ready for next Saturday (31st May); there's just too much to do and I don't like rushing things - and in any case, it seems that I'm just not capable of building quickly even if I cut corners!

However, I have managed to negotiate the loan of my original JP from Scott Edwards, so I'll bring that to the Orme instead.

[Andy Blackburn]

Marking out the rear dayglo panel took longer than expected - measure twice, cut once and all that. Since the rear fuselage is basically a straight taper, it can be covered using one panel of film each side, with a pattern made from drafting film:

This took a lot longer than it should have done because I initially didn't believe the angle of the colour demarcation, eventually (after checking against photographs) realised that it was an optical illusion caused by the angle of the silver film off-cut, which can *just* be seen through the drafting filmin the picture above.

After that, cutting to the pattern and ironing-on with a very cool iron (circa 70 degrees) was pretty straightforward...

But I'm quite upset with myself for not checking the dayglo Profilm before using it - the bl**dy stuff is slightly translucent! This means that the silver film overlap shows up through the dayglo orange film. Schoolboy error, I suppose. But I'm still quite narked at myself.

It's now clear that the nose area will require some special treatment to minimise the effect of that translucency. Drat.

Edited By Andy Blackburn on 27/05/2014 16:53:48

[Phil Cooke]

I had exactly the same problem with my Orange solarfilm, I only used one colour thankfully but where it DOES overlap it becomes a more solid colour - so the joints become very visible - and where its not overlapped you can see all my wood joints through it...

I think Rez's tissue and dope finished with spray paint method is the best way to achieve a true scale finish and Ive already promised myself I'll do it that way on my next PSS build...

[Andy Blackburn]

Yeah, I think tissue/dope/paint or acrylic/glasscloth/paint is probably the best finish for future projects, and - given how long I've spent getting the wrinkles out of this one - will probably be quicker. I'm really quite hacked off with it, actually.

I'm going to sleep on it and then decide what to do next; leading option at this point is to remove the dayglo film and cut back the overlap to a much smaller amount (maybe 3-4 mm), then re-do the covering. The wings shouldn't be so much of a problem as the dayglo film can go on first, but the dayglo orange overlaps might show up. Maybe a few tests might be a good idea...

Edited By Andy Blackburn on 27/05/2014 19:54:19

[Phil Cooke]

agree with your 'leading option' - but I'd leave 1/4" of your dayglow orange on as opposed to removing it all - thus saving all your hard work to get the edges positioned accurately - cut through both orange and silver film, then you just have to 'fill in' with orange upto this 1/4" double thick area... that will be the quickest and neatest solution I think...

On the wings, like you've already said, do the orange first and put the silver on top - that will solve the problem completely...

Edited By Phil Cooke on 27/05/2014 19:59:05

[Andy Blackburn]

Good idea, but I don't need to do that - I've retained the cutting pattern for the dayglo area, so all I need to do is to mark the edges of the piece with masking tape before taking the old piece off; the new piece will just drop into the same place.

After having considered the matter at some length, I think I have a workaround solution:

1. Cover all the other dayglo areas as originally planned over the top of the silver with a very minimal overlap - something like 1/8", or less if I can get away with it.
2. Take a view on whether the whole thing is an acceptable representation - am I prepared to accept the appearance of the film overlaps.
3. If it's not deemed to be good enough, mask off all the silver areas with tape that abuts the edge of the dayglo film (which is why it had to go on top of the silver), scrub up the exposed dayglo film with wire wool and then over-spray it a thin coat of Humbrol Fluorescent Flame Red, which will be a bit translucent but should hopefully be enough to make it look just solid enough.

In other news, I've nicked my old Jet Provost back from Scotty and (after cleaning itup a bit) am planning to roll up with that at the Great Orme on Sunday.

[Peter Garsden]

Been reading all this Andy - I wish I had your patience and obvious better finish with Solarfilm.

I am doing the same finish as you but all in Solarfilm. Their dayglo orange is not see through because it has a white backing/glue which makes it opaque.

I do know what Phil means though because I covered my Alpha Jet in their Red which is slightly see through. Because I am not so meticulous, I just put up with it, It was however next to white which made it slight see through mark but not as bad as your overlap with silver.

The Solarfilm colours obviously vary

Will probably see you on Sunday.

Am hoping that after my 2am go to bed last night I won't fall asleep on the A55!

I was making the lighter tip tanks as the wind forecast is light - didn't line the tips with an extra layer of ply and it needs it as the balsa is too soft to plug into. It is also a shoddy job as it was done between 1.30 and 2am!

[Andy Blackburn]

> I am doing the same finish as you but all in Solarfilm. Their dayglo orange isnot see through because it has a white backing/glue which makes it opaque.

Yeah, the Profilm dayglo also has a white backing, obviously not opaque enough though. I suspect that Solarfilm is possibly quite a bit easier to use and certainly requires less of a pull to stretch it, and operates at a lower temperature so the inevitable (for me, anyway) burnt fingers will not hurt quite as much.

I've got over my temporary strop with the covering and am pressing on with fixing the issue; first order of business was to assess how the dayglo orange overlaps looked, so I had a go at the tip tanks; managed to cover one of them in two pieces after much pulling and tugging of film at 300 F (~150 C) and 350 F (~175 C)

It doesn't show up in this picture, but I've noticed that the film tends to de-laminate a bit when it goes around tight corners (e.g. tank leading edge), maybe Solarfilm would have been easier.

I discovered that it's actually a bit easier if the iron is held between one's knees, holding the tank in one hand and the film in the other. This can lead to mildly singed fingers if there isn't quite enough film to grab hold of, though.

Here are the finished tanks:

The photos don't show it up, but the film overlaps seem to be quite acceptable. There is a tendency to expose the white backing film in some areas, but it should be possible to trim some of this off carefully with a scalpel. Or I guess I could just leave it as-is if everything looks OK from a range of several feet...

My conclusions from this are that a) Profilm can be quite challenging to use around sharp corners, and b) the dayglo orange overlaps look OK.

Edited By Andy Blackburn on 09/06/2014 13:51:26

[Andy Blackburn]

So, fixing the fuselage covering problems...

Here's the offending covering (as discussed above) with see-through dayglo Profilm:

It doesn't show up that well, but you can just see the (large) silver overlaps under the dayglo orange.

The edges of the dayglo area were marked with tape and then a 1/16" wide strip of masking tape cut and stuck around the edges, then both layers of film cut through and removed. It came off reasonably well, actually - if it was Solarfilm, there would have ben some colour residue:

Then the last bit of 1/16" tape was removed, along with the film, ready to be re-covered using pieces of film cut using the same template as before:

...and here's the finished article, which looks quire reasonable to me; the film is a little bit see-through, but the 1/16" wide silver film showing through at the edges isn't obtrusive at all.

Getting a reasonably representative colour demarcation on the nose will be done in a similar manner - 1/16" wide masking tape to denote the edge of the colour line, then another 1/16" strip of tape in front of it:

Then the film trimmed to the front strip of tape:

...and that strip removed to reveal a 1/16" wide film that can be overlapped:

As you can see, it was dark when I finished.

The plan tonight is to cut and stick some fairly narrow bits around the edges, then pull/shrink/stretch a compound-curved piece to fill in the gaps.

[Steve McLaren]

Very impressive Andy. That tail section looks so much better.

But I have a question! How do you cut away the already fitted film to an accurate line without risking cutting significantly into the balsa? When I have to do this I am always worried about weakening my structure, so I tend to peel first and then try to cut off the peeled bit. Doing this, I can't ever get an accurate shape. Do you have a clever method or is it just a case of taking great care with the blade over the depth of cut?

[Steve Houghton]

Andy,

I'm also as intrigued as Steve is to hear your methods for this process. I'm just about to start covering my wing tanks - they have a white stripe down the centre, blue above and red below. I anticipate a lot of re-trimming may be required, so your tips will be appreciated

Steve (H)

[Andy Blackburn]

Basically, it's a case of using a new scalpel blade, being gentle with it and trying not to cut any deeper than the film; if it doesn't go all the way through in a couple of areas, just pull the old film away from the balsa (the film doesn't have to be very hot to do this) and slice the recalcitrant bits carefully whilst pulling the film gently.

I don't think a shallow cut in the balsa will do any harm, or at least it hasn't up till now.

WRT the tanks, I found that holding the iron between my knees (as described on one of the other threads) worked best, which leaves two hands to hold the tank and the film. I also found that if you don't leave enough film around the edges (maybe 3 inches or so), you tend to burn your fingers on the iron.

The thing you have to watch with Profilm/Oracover is that if the adhesive gets warm enough (only slightly warm, actually) which tends to happen if the piece of film is a little small, is that it just kind of floats on the adhesive and you can't stretch it because all that happens is that the film moves. I'm having a lot of problems with the nose area, actually - pictures of the carnage will be posted this weekend.

On balance, I think (for me, anyway) Solarfilm is a lot easier to use. And it hurts less when you burn yourself.

I think that in future, it'll be dope & tissue (jap tissue works best for me) or glass & Ezecoat or other acrylic varnish.

Edited By Andy Blackburn on 13/06/2014 13:57:24

[Steve Houghton]

Andy,

Thanks for the hints. I have used the sharp scalpel method while starting to cover my tanks, where obviously there is no risk of wood damage as they are non-structural.

I have used Solarfilm fairly successfully and will post a few photos on my blog shortly.

[Andy Blackburn]

I've been working on the dayglo nose for so long that I'm losing the will to live (almost!), and it's been a traumatic experience because normally this stuff "just works" - but not this time...

So, The nose covering started out OK:

...the idea being to demarcate the edge of the daygo area with tape and then go around the edges:

...with shaped bits of tape to provide an edge, fill-in as much of the flattish bottom area as possible, and then cover the top with one piece of film. That last bit didn't go well:

...there were wrinkles everywhere. Still, we've got lots of Profilm, so strip it off and start again - maybe it might be better to use several vaguely-triangular-shaped smaller pieces:

...but unfortunately that didn't work for the reasons discussed above - very difficult to stretch smaller pieces of Profilm with a very hot iron because it loosens the adhesive and attempting to stretch the film then just pulls the film sideways, so there were wrinkles. And there were a lot of film overlaps.

I had several goes at this, with the same depressing result each time. And of course, an awful lot of Profilm has now been used:

So...

Obviously, take it all off (carefully) and have a think about what to do next:

- more on this grisly experience a bit later on this evening..

Edited By Andy Blackburn on 15/06/2014 19:05:08

[Andy Blackburn]

Having thought about it at length, there seem to be a number of issues;

• The "sliding film" effect mentioned above - maybe securely taping the film in place would work.
• The excessive number of wrinkles when trying to cover in one piece - it might be possible to pre-stretch the film in two directions and tape everything in place before actually shrinking, and going straight to a very high iron temperature might be a good idea.
• Cutting through the bottom layer of film when trimming to size causes unsightly blemishes when the film is shrunk - maybe covering just over the edge of some pre-applied masking tape and using that as a backing to cut the film might work.

So, the surrounding fuselage was wrapped in tape:

...and a large piece of film tacked at the bottom and then stretched to the top of the fuselage, then shrunk and pulled into place:

I've seen better covering attempts, but it didn't look *too* bad as it was shrunk down:

There were a few blemishes on it, maybe it should have been stretched more at the left and right fuselage sides; note that the film was not sealed onto the masking tape around the edges, although it did stick:

Having shrunk the film, there were still a few blemishes, but it didn't look too bad. The idea then was to apply some thin strips of tape as scalpel guides (the masking tape under the film is identifiable using a strong light) and then cut through the film and into the masking tape underneath, but hopefully not through it;

This is after the cut is made; looks promising:

Removing the masking tape from underneath the edge of the film seems to work best when pulling back on itself:

The edges were sealed, and it finished. There are blemishes, it's not perfect but (never thought I'd hear myself say this), it'll do.

I should probably tidy up a bit before attending to the cockpit furniture, cockpit and wings...

Edited By Andy Blackburn on 15/06/2014 20:24:54

[Mark Kettle 1]

..... ' theres nothing scuppering his endurance when a man covers his plane in orange enduring niceness ' .....

Keep going Andy it will be worth it.

Edited By Mark Kettle 1 on 15/06/2014 20:47:35

[Phil Cooke]

Looks like a good result to me Andy - nice that you have no join along the centreline of the nose - very smart. And with it being Profilm, now its shrunk and down like that, it should stay put too!!

[Andy Blackburn]

Kind words, chaps, but I do feel constrained to point out that a) there's a visible vertical crease almost on the centreline, and b) it took me about a week to do it.

I think on the next PSS model it'll either be sanding sealer and jap tissue or lightweight glass and Eze-Kote and then either sprayed with car paint spray or brush-painted with humbrol enamels.

Hopefully, that was the difficult bit...

Edited By Andy Blackburn on 16/06/2014 14:04:58

[Matt Jones]

Andy, stick with Solafilm. I did the section below the nose centreline in one piece, similar for the piece above. It was dead easy with the film having lots of stretch in it.

[Andy Blackburn]

I think you're probably right about Solarfilm, it's a lot easier to use and is a lot stretchier. The big advantage of a glass finish, of course, is that you're less likely to find an imprint of your jacket zip embossed in the wing centre section when you get to the top of the slope...

Edited By Andy Blackburn on 16/06/2014 20:17:33