Jet Provost 1.5metre Andy Blackburn PSS Plan

[Peter Garsden]

So - not been a good day as I should have glued F18 (cut out of 3/16" from the plan as the part in the short kit is the wrong size, as it was not enlarged from the 39" version - see Phil's addendum above) before I added F1 and drew the fuselage sides in.

There are 4 x F18 pieces which form the curved shape of the sides.

I managed to squeeze them in afterwards and push out the sides into more of a curve as can be seen in the photo.

F11 and F12 are not in the short kit but can easily be cut out from scrap off cuts of the 3/32" wing sheeting. The are there to act as formers for the shape of the top and bottom of the fuselage.

[Andy Blackburn]

Parts files for F6 and F7 are now updated.

However, in a rare victory I should point out that the wing bolt plate hole is (or should be) correct because a) not all spiked nuts project into the hole, and b) some people prefer to invert the T-nut on top of the wing bolt plate and fix it with a good helping of epoxy; this has the advantage that - for an accurately made T-nut - the wing bolt will then be properly square to the wing bolt plate.

[Peter Garsden]

Andy is right about the wing bolt mea culpa

This shows the clamping of the rear fuselage. I noticed that there was quite a twist to the fuselage so it was important to pin down the fuselage to the work top over the top view of the plan. I used T pins as it was under quite a lot of pressure. Difficult to know how to avoid this.

I used some ammonia to ease the sides, but now realise one should put saw cuts in the 1 inch triangular near the bend at F5 and F6. The plan will be amended to show this, but it is the same theory for any bent triangular stock.

The recommendation is that one reinforces as many joints as possible with triangular stock for strength, so one can see the wing bolt plate which will have to endure much torque.

One can see the saw cuts I made to the triangular stock after the event to ease the bending stress.

Edited By Peter Garsden on 01/10/2019 21:18:57

[Andy Blackburn]

Posted by Peter Garsden on 01/10/2019 21:17:32:

...I noticed that there was quite a twist to the fuselage so it was important to pin down the fuselage to the work top over the top view of the plan. I used T pins as it was under quite a lot of pressure. Difficult to know how to avoid this.

Pete, I think this must be happening when the fuselage sides are glued to the battery box assembly - if they're not straight and square at that point (sight along the fuselage from the jet pipe forwards) then they'll twist when the ends are drawn together.

If the fuselage sides weren't square when glued to the battery box and the glue has already set, you'll have to live with it and try to carve/sand out most of the misalignment, but if you catch it before the glue sets then - with care - you can usually twist everything straight and nobody will be any wiser.

I'll add an extra clause to the fuselage instructions on the plan.

If its any consolation, most of my models end up with a small amount of fuselage twist, to the accompaniment of some bad language...

[Peter Garsden]

Thanks Andy - good advice - you are right, that is exactly when the twist happened - gluing up the sides to the battery box (not easy to get right). I panicked because I hadn't done a dry run and my clamps were too small for the width of the fuselage - lesson learned. I have, however eliminated most of the twist, and will build it out when I line up the fin and tailplane.

Incidentally, have you any idea what the wing area is in square feet to save me working it out?

Am now on with the fuselage apace

Top Decking

I remember that this was planked in the smaller version, then I read your piece in Silent and Electric Flight which said that the original design was for a piece of curved 1/8" balsa. You said that you curved it round a bottle of Wolf Blass (only the best as long as it was Red?!) having wetted it, but that it turned out a Horlicks so you scrapped it and went for planking.

Now, being addicted to the smell of Ammonia, I soaked both sides of the balsa and bent it round a bottle of Prosecco - not my favourite - my wife's tipple obviously - but it did not bend enough, so I forced it over the formers, which took the shape perfectly and pinned it with lots of pins wet.

I let it dry with the middle piece absent - this I added the next morning when it was dry, and re-glued everything with Aliphatic. It is worth turning it over to line up the sheet sides, and hold them with a pin across the join.

I also chamfered the bottom edges to line up with the fuselage sides - easy with a Permagrit file.

Error to avoid

Do not fit F11 or F12 (bottom of the nose between F1 and F2) until you have attached the bottom and top sheeting because they catch and split as you are turning and clamping the fuselage - I have repaired mine with cyano about 5 times!!!

[Andy Blackburn]

Posted by Peter Garsden on 02/10/2019 17:26:28:

...

Incidentally, have you any idea what the wing area is in square feet to save me working it out?

Yes, it's 3.80 square feet including the optional <ahem> high-performance plug-in rounded wing tips.

[Peter Garsden]

Thanks Andy - the fuselage seems to weigh quite a lot and I haven't attached the tail sheeting yet, but as is obvious we lose a lot of balsa in the rounding exercise. Will be interesting to compare oz per square foot with the smaller version. The beauty of the JP is that it flies in light winds, so hopefully that reputation will extend to the larger version.

I have been fitting the wing to the fuselage so I can find out how far out my twisted tail is. Whilst the bottom sheeting was absent, I lined up the wing and marked a hole for the wing dowel from the other side of the former - if you get it wrong and put the dowel under tension it can snap it - the Hurricane has this problem.

I then used my trusty method of cutting the head off a spare 6mm plastic bolt and sharpening the other end then screwing it in to mark the position of the hole. Good tip. My bolt is only just long enough

Having clamped the wing in place I reckon it is about 3mm out. So I plan to cut down one side of the tail seat on one side. First, however I will cut out the hole to get rid of some of the wood.

[Bob Jennings 1]

Can't wait to see the physical comparison to mine when you have this done Pete. Brave pioneering!

[Andy Blackburn]

> ...the fuselage seems to weigh quite a lot...

To be honest, I wouldn't worry about it; it's a much bigger model than the 1/12 scale version, the wing is operating in a much better regime as far as Dr Reynolds in concerned, and people used to fly ~60" Warbirds (Brian Taylor Tempest, P-47, etc.) that weighed 6 or 7 lb off the slope and they flew really well. So the chances are that it'll be fine.

Of course, if your wood selection has been a little, shall we say, "conservative" (the plan has something to say about this as well) then it'll be a bit more advantaged in the momentum department than one might have expected. However, that's not necessarily a bad thing.

(BTW, one of the updated notes on the latest version of the plan (which you have) talks about filling-in the area underneath the wing bolt plate with hard balsa so that in a crash, the wing bolt is persuaded to snap/shear cleanly and allow the wing to come off properly rather than just bend, which would damage the wing.

You might get away with another piece of 1/8" ply or very hard balsa positioned flush with the bottom of F14. It's not mandatory (depends how often you crash!) and you can always do it afterwards.)

[Andy Meade]

That's a good point actually on the nylon bolts bending rather than shearing due to longer projected lengths. My big Spit has had some issues in this department - I might add a plate to encourage it snip the bolts rather than pulling the bolt plate out (again).

[Peter Garsden]

Good point Andies (is that the plural of Andy?) or a type of hand tissue? Because I forgot the hard balsa inside the wing, I added a piece of 1/64 ply, then carbon bandage and resin, then the covering piece of 1/16 as on the plan - probably should have put the ply on first! - so I think I probably have enough of an edge to snap on a heavy landing?

Have had a merry time with lots of dust from cutting the hole in the tail seat to aid weight saving. I have also used the lightest balsa at the tail for the fin, the tailplane, and upper and lower sheeting (I actually weighed all the pieces and chose the lightest!). So I am probably worrying unduly about weight (could do with losing about 2.5 stone myself!). I used my handy Proxxon tool with the round circular Permagrit cutter - didn't have that when I made the previous version - don't know how I managed.

[Peter Garsden]

The fin needs 5 pieces of 4" wide 3/8 balsa, which I laid over the plan. Important to get the grain going the right way.

ERROR WARNING

Sorry chaps if you have already bought your wood, but I have overestimated the sheets of 3/8 balsa needed above on page. I think you can probably get away with 5 sheets. I didn't realise that some pieces could be sourced from the same piece of balsa - correction to my wood list on page 1 or 2 of this blog.

[Peter Garsden]

Next job is the nose. I do remember that in the first version, Phil suggested that you make some nose formers to help with carving the correct shape, and I adopted his good idea. I have done the same here, which unfortunately means that you have to layer 4 pieces of sheet per layer of nose if that makes sense. This is very handy to use off cuts from the many pieces of scrap sheet there are lying around

The cut out is for the battery to stick out furtther forward

[Andy Blackburn]

Posted by Peter Garsden on 06/10/2019 13:42:58:

Good point Andies (is that the plural of Andy?) or a type of hand tissue? Because I forgot the hard balsa inside the wing, I added a piece of 1/64 ply, then carbon bandage and resin, then the covering piece of 1/16 as on the plan - probably should have put the ply on first! - so I think I probably have enough of an edge to snap on a heavy landing?

It's not so much an edge that you need, it's as short a length of unsupported bolt as possible. Hence the filling-in below the bolt plate...

[Peter Garsden]

Well - to the air intakes which have to be carved to shape and fitted to the fuselage - tips and knack needed here, which I got from Andy's initial blog and this helped a lot - **LINK**. They are traced, or carbon paper templated onto cardboard as I did them from the plan

You will need 2 pieces of 4 inch width 3/4" balsa then a little bit added at the bottom - I used scrap from the blocking up process at the front of the fuselage. I have left them to dry as I used Aliphatic Resin.

Here you can see my Dremmel Scroll Saw which with all the thick sheet to cut up was worth its weight in gold then finished off with my sanding disc and belt sander combined which I bought from Axminster Tools for £75 which I thought was a bargain - now £84.95 - https://www.axminster.co.uk/axminster-craft-ac125bds-mini-belt-disc-sander-105113

Edited By Peter Garsden on 07/10/2019 17:44:11

[Peter Garsden]

Well there is a lot of planing and sanding to do to reduce this heavily padded fuselage down to size. Andy suggests in his Quiet and Electric Flight article that you mark off on the fuselage with pencil lines how far to sand to - eg at F6 the curve of the fuselage is 30mm down the side and the triangular stock is exposed to 10mm. This proved a brilliant tip and stops the anxiety of exposing too much.

[Phil Cooke]

Great progress Pete!! You should have this all finished and awaiting the canopy before we start the Sabre builds on 1st November! Impressive!

I'm at a not too dissimilar position with my fuselage - It's effectively all built up and squared off. I need to do some shaping now with the razor plane and the sanding blocks and then I can get to work on the canopy plug as promised! Photo shows it next to her smaller cousin aligned at the back for a sense of scale.

[Peter Garsden]

OMG so much balsa to remove with the plane. I filled a bin full of shavings. And I take it all back, the fuselage feels so much lighter as well. I have ordered some pilots and am going to do a deeper cockpit than on the small one as there is much more space.

Note the handy curved sanding tool, which Andy describes on his Canberra blog and which was made for the --Canberra. It is basically 2 pieces of cardboard bent over the fuselage and contact glued together then lined both sides with sandpaper - easier with a constant radius fus like the Canberra of course but still very useful.

If you have puzzled how the tailpipe is meant to be shaped, then this is it. Needs a bit more sanding of course

[Peter Garsden]

Back to the air intakes - again see Andy's blog which goes into much detail and is the one to follow. Here are the intakes carved and sanded to shape

They fit on the side of the fuselage above the wing and have to be fitted to the gradient of the wing dihedral. Underneath the fuselage is needed a filler to fit the contour of the curve - so how to do that - again, Andy has the answer

This is underneath the fuselage showing the gap to fill

Block of 3/4 inch balsa - long enough to cover the width of the intake and a piece of coarse sandpaper attached to the fuselage, then rub away until the underneath meets the piece of scrap balsa.

A gauge is rubbed away which can be trimmed in depth to cover the gap to be filled - clever tip and trick from the Blackburn stable...again.

[Peter Garsden]

This shows the filler bottom piece sanded down to fit the fuselage side with the air intake overlaid. Andy suggests making these intakes detachable for covering but attached to the fuselage side temporarily with bamboo sticks. Great idea!

It is suggested that you start with a pin hole from the inside of the fuselage followed by enlargement with a 1/8" drill, then filling with 2 stubs of bamboo, then fitting to the fuselage.

The fuselage is lined with cling film to stop the air intake sticking to the fuselage sides. I am now going to trim down the filler pieces and line up with the fuselage contours before starting the other side.

[Peter Garsden]

I have taken advice, listened to it, and followed it. Here is an extra piece of 1/8 ply on the underside of the wing not seen which will encourage the plastic bolt to snap instead of pulling out the bottom of the fuselage at least that is the theory. This is an addition to the plan.

[Bob Jennings 1]

Good move. Keep at it Pete, this is really useful and interesting.

Cheers

[Andy Blackburn]

If the ply plate is fixed to the wing, then if one wingtip hits first and the wing bolt snaps, the wing will pivot in the horizontal plane and the ply reinforcement will remove part of the wing seat on its way out.

What you could do to try and manage this is to add a chamfer to the edge of the ply plate to try and persuade the wing to move downwards as well as sideways during the crash.

Edited By Andy Blackburn on 11/10/2019 18:54:32

[Peter Garsden]

OK will do Andy - chamfering next job. I will use my handy Proxxon mini sander - great tool.

Anyway - following on from Andy' advice on his blog, I have used carbon tows and cyano to bind the wires together instead of fuse wire - works really well, but the brass tube I bought is too small so will swop it for a bigger size.

[Peter Garsden]

Have also been busy making decals from the very helpful photos sent to me by the Newcastle shared Jet Provost that I am copying based at Durham Airport - **LINK**. I emailed them and they were incredibly helpful. They have photographed all the decals close up for me. They also offered me a flight if I pay for the fuel. Couldn't be more obliging. They are also going to take a photo of hte cockpit for me.

I used my Vinyl Cutter to not only cut letters using their software but also print and cut on white vinyl. Worked reasonably well. I uploaded the images then put it through my printer then cut out the scrap. I had to do this for the airforce logos as they were to intricate to cut with a scalpel. The square ones I will simply score with a knife on white printable vinyl with a sticky backing, then the third sheet is clear sticky printable, which will show up against a white background of the top of the fuselage and the grey wing.

Some of the images I made with Adobe Fireworks - the stripey no step stickers on the right as I couldn't find an internet image. The black squares showing the fuel inlets I made with Microsoft Word

Edited By Peter Garsden on 13/10/2019 18:42:56