Jet Provost 1.5metre Andy Blackburn PSS Plan

[Peter Garsden]

That's the one Andy, though with the tailplane it was Plan/Carbon Paper/Cardboard, then cut out cardboard and draw round onto wood. I did that because the plan would have been impossible to line up with the wood.

[Peter Garsden]

This is a link for the florist cellophane plan covering -**LINK**

[Peter Garsden]

I glued the 2mm bottom wing sheets together with aliphatic and let them dry overnight, then took the masking tape off first thing before work. To mark out the position of the spar and ribs on the bottom sheet, the easiest way is to extend the lines beyond the leading and trailing edges as I always cut the wood slightly oversize to allow trimming afterwards.

I took the sheet off the board to chamfer the trailing edge with the sanding disc. Makes it so much easier having different lengths of steel ruler

I find V5 roller ball pens the best for marking. Using pencils they get blunt too quickly.

I then too the laser cut ribs off the sheet and did a dry run fitting. Very accurate cutting - needed very little easing. Very impressed.

I notice that R7 to R10 are short, we will have to make up some dummy ribs for the ailerons, also make up the 3/16 leading edge and sub spars from scrap - should not be a problem.

Edited By Peter Garsden on 29/08/2019 09:17:44

[Bob Jennings 1]

Hi Pete, I use a trusty red BIC and lightly pass it over the wood so as not to damage the grain at the rib position. Just a thought. Well done for getting this started. It's already looking familiar. Not sure when I'll get around to making my 'Big brother JP'. Hope you decide to install the twin lights in the nose.

 

Edited By Bob Jennings 1 on 29/08/2019 10:30:31

[Piers Bowlan]

Nice scheme Bob .

[Peter Garsden]

And that was a competition winner if I am not wrong Mr Bob? I just wish I had the patience.

[Peter Garsden]

Bob's JP was indeed a competition winner for best static display. To reminisce I looked up the old article on the Mass Build and noticed it was penned by Matt Jones - that chap we used to see but sadly we bump into very rarely. - this is the link - **LINK**

Anyway back to the build. Just as well, I read the plan carefully as BEFORE PUTTING THE WING TOGETHER ONE HAS TO JOIN THE SPARS WITH THE NEW DIHEDRAL BRACES - BEWARE - in the old version the brace slid in after making each wing.

It is done over the plan. It is important to get this accurate of course as it dictates the line up of the wings etc.

Andy's attention to detail is immense - the words are quite clear, though I did read it several times when I was just about to glue up the ribs and spar.

[Peter Garsden]

Just as well I had 2 copies of each of the plan because whilst one is pinned to the table you cannot read the various helpful instructions or refer to other parts of the plan. This was invaluable because I needed to look at what was below the wing folded underneath and use my 2nd copy of the plan on my main bench.

I still have the old write up in Electric Flight on Andy's original JP if anyone wants a copy. I have it in pdf format. It is a bit different to the new model but still helpful. So PM me if you want a version as the magazine is no longer in print.

Edited By Peter Garsden on 30/08/2019 08:16:24

[Peter Garsden]

So once the spar had dried (I use Aliphatic), I assembled the wing using Super Phatic. What great glue it is. Cyano dries too quickly for me before you get the chance to position parts properly.

That sticky outee spar might be tempting fate. Let's see if I can avoid snapping it.

Those Graupner Pins are just ace - don't know how I ever managed without them. And coupled with the layer of cork tiles on the bench it avoids sore fingers as you try to push them in.

[Peter Garsden]

Finally, one take the wing off the bench to cyano (yes it is just right for this job) the bottom sheet up to the underneath of the ribs. I use activator spray so it will hold properly.

[Harry Twist]

Hi Pete, great progress already and looking good. Wouldn't mind a pdf pdf of the original JP article - I've pm'd you. Not sure when I'll start my large JP, but probably after the Sabre mass build. Keep on truckin!

[Peter Garsden]

Will email you Harry when I get home.

Another mistake I have made - to avoid.

R1A is a reinforcing rib which attaches to R1. It is 3/16" and lines the hole for the front wing dowel. DON'T glue it in until you have attached the bottom sheet to the front of the ribs. I couldn't understand why it didn't line up with R1 until I removed the wing from the board and realised that it had pushed the bottom sheet out of line. Doh!

I am sure we can cover that schoolboy error, but that is why I am ploughing the furrow for you all as I usually do.

[Andy Blackburn]

Pete,

In addition to not fitting R1A until you've attached the bottom skin to R1, both R1 and R1A are at the dihedral break and are at an angle (unlike all the other ribs) so need to be angled/chamfered at the edges to fit nicely.

Andy

[Peter Garsden]

Thanks Andy I have indeed angled R1.

I am now onto the ailerons which have been fashioned from scrap 2mm and 6mm balsa.

Note the use of .8mm ply as spacers and the masking tape to stop the plane damaging the ribs. I remember this being a problem with the smaller JP when I omitted to use the masking tape. One splits the ailerons later

I used a pin to make holes in the bottom sheeting so as to show the line of the ailerons when cutting out after the top sheet goes on.

Note the line of holes

[Peter Garsden]

Next the aileron servo mounts - now at this point I did some headscratching because there is no rib profile view. Andy is making one and adding it to the plan, or we may be able to publish it here.

The point is that the aileron servo attaches to the bottom sheeting and the horn pokes out underneath.Andy advises cutting the aileron horn down so it doesn't foul on landing. There is much dihedral so not a problem I am sure.

I made the mistake of gluing the 1.5mm ply bottom skin in place first - I now realise that was a mistake. The order of events should be:-

1. Mark out the hole for the servo tray.
2. Remove the surround and place the 1/16" ply outer servo plate on the bottom skin and make sure it overlaps equally all round by about 3mm then draw round it.
3. Cut out the larger hole in the balsa.
4. Mark out a piece of 2mm balsa to fit the hole in the ply servo tray.
5. Glue in place the 4 ply triangles in the corners. Wipe any excess glue away.
6. The tray on which the servo rests had 2 layers - an outer 1/16 ply, and a smaller balsa tray on which the servo sits.
7. I am going to glue the servo to the tray with finishing resin and microballoons mixture as we do in F3F

[Peter Garsden]

Next the aileron servo mounts - now at this point I did some headscratching because there is no rib profile view. Andy is making one and adding it to the plan, or we may be able to publish it here.

The point is that the aileron servo attaches to the bottom sheeting and the horn pokes out underneath.Andy advises cutting the aileron horn down so it doesn't foul on landing. There is much dihedral so not a problem I am sure.

I made the mistake of gluing the 1.5mm ply bottom skin in place first - I now realise that was a mistake. The order of events should be:-

1. Mark out the hole for the servo tray.
2. Remove the surround and place the 1/16" ply outer servo plate on the bottom skin and make sure it overlaps equally all round by about 3mm then draw round it.
3. Cut out the larger hole in the balsa.
4. Mark out a piece of 2mm balsa to fit the hole in the ply servo tray.
5. Glue in place the 4 ply triangles in the corners. Wipe any excess glue away.
6. The tray on which the servo rests had 2 layers - an outer 1/16 ply, and a smaller balsa tray on which the servo sits.
7. I am going to glue the servo to the tray with finishing resin and microballoons mixture as we do in F3F

[Peter Garsden]

Questions Andy

1. Does one put the top skin on wing 1 before starting wing 2, or continue with the bottom skin of wing 2 then top skin both wings?
2. Not quite clear how to lay out the wing to get the wash out right. As I understand it one puts 2 10p pieces with 2 layers of masking tape under the main spar at R1. Presumably you also pin down the trailing edge of the wing at R1?
3. There are then 2 cradles made out of 1.5mm ply to hold the wing tips. Presumably one glues them together to make 1 3mm support or is it one support for each wing tip? I was going to attach the support to a piece of 2mm balsa with triangular to support it, so it is free standing?
4. One then pins the wing tip to the support cradle whilst the glue dries.

Could you clarify please as both Phil and I were a bit unclear.

EXTRA WOOD FOR WOODPACK

4 sheets x 48" x 4" balsa sheet for fuselage sides.

[Andy Blackburn]

> Does one put the top skin on wing 1 before starting wing 2, or continue with the bottom skin of wing 2 then top skin both wings?

- doesn't matter, really. Personally, I'd finish both bottom skins (making sure that all the wiring, etc. is in place) and then add the top skins one after the other.

> Not quite clear how to lay out the wing to get the wash out right. As I understand it one puts 2 10p pieces with 2 layers of masking tape under the main spar at R1. Presumably you also pin down the trailing edge of the wing at R1?

Yes, add the packing under the mainspar to increase the incidence at the root (which has the same effect as decreasing the incidence at the tip), make sure the trailing edge is flat on the building board all the way along, and the tip rib should also be flat on the board; weight it or pin it, if you pin it you'll have to take the pins out before glueing the top skin on. You can then add the top skin and as long as the TE and tip rib is still flat when you've done it and the 10p packing is still in place, the washout will be correct.

> There are then 2 cradles made out of 1.5mm ply to hold the wing tips. Presumably one glues them together...

Nope - there's one for each wing tip. You can add some scrap balsa to the bottom as a support if you want.

> One then pins the wing tip to the support cradle whilst the glue dries.

Well, you don't really need it for the wing because the dihedral is set by the one-piece manin spar and the washout is set by all the shenanigans you did with the 2 x 10p pieces and two layers of masking tape. However, they might be quite useful for supporting the wing during assembly/setting-up the tail surfaces. You don't have to use them...

A.

[Phil Cooke]

Hiya Pete - making good progress on the wings! Impressive!

I've made a start on the fuselage here - in an attempt to have the canopy plug manufactured as soon as possible.

Regarding the fuselage sides in medium 3/16" stock - yes you WILL need a 48" length per side if you want it to run from nose to tail one piece - but I can confirm you don't need 4 sheets - gluing a standard 36" length on top of the 48" length sheet gives you plenty of area to cut out the required shape of the sides... (to the grey triangles on the plan)

[Phil Cooke]

I've cut my fuselage sides out and have also made up the fuselage doublers F15/F16 which don't come as part of the woodpack - simple shapes using the offcuts from the fuselage sides. Triangular section has been cut to length and tonight all this will be glued together making up a L and R handed pair.

I've double checked all the CNC and laser cut fuselage parts against the plan and all seems absolutely spot on apart from the 4-off F8's which come supplied with the woodpack. These don't appear to have been scaled correctly in width - the SLEC parts have been cut correctly to the .dxf file but the definition as supplied needs tweaking (NB - Andy B has now already corrected this in the definition and future SLEC kits and plans will be altered) - but for the 12 kits already bought here's the simple fix...

The 4-off F8's are designed to seat up horizontally against the vertical face of the battery box - giving a sturdy curved profile against which the fuselage sides can be pulled in onto... as you can see the length and curvature are correct, but the formers aren't wide enough to meet the battery box.

In fact each F8 is 10mm too thin.

The parts are simple enough to recut - or modify by adding a 10mm width strip of 3/32" balsa before they are fitted - alternatively a 10mm block can be glued on the outside of the battery box between F1 and F2 against which the parts as supplied could then be accurately fitted. I think I'm going this way. Many ways to solve this.

 

Edited By Phil Cooke on 31/08/2019 19:46:59

[Phil Cooke]

All,

My fuselage build has identified another minor issue with the updated drawing - again already discussed with Andy B and we've agreed future drawings and woodpacks will be modified to clarify design intent.

For those first 12 plans/kits please note the following;

At the larger scale a pair of balsa fuselage doublers have been added top and bottom towards the front of the fuselage, namely F15 and F16. These were never part of the smaller build. Neither part is actually part of the woodpack, but they are defined on the drawing and need to be cut by hand from 3/16" medium balsa.

The lower doubler, F16, sits over the spruce longeron on the plan, and in dry fitting the assembly it was clear either F16 needed altering or the spruce longeron needed to be relieved locally to sit on top of the balsa doubler.

Discussion with Andy made it clear the design intent is for a full width curved spruce longeron which is glued to the fuselage side, so the balsa doubler F16 needed to be channelled and split into 2 - creating F16A and F16B.

The following photos should make perfect sense once builders have the new JP plan in front of them...

F16 cut to shape as per the plan. The dotted band is where the 3/16" spruce longeron will pass. We need to remove this section from the doubler to allow the spruce to be glued to the fuselage side material;

Removing the dotted section carefully produces a 2-part doubler, known from this day forward as F16A and (the rather fiddly) F16B

These are then glued to the lower forward fuselage side ensuring they are square to the datums and that the spruce doubler (offcut shown in place) is a nice fit - not too slack, not too tight - to aid assembly of the nose section in 3D later...

that's the fix done - all simple enough.

[Bob Jennings 1]

Gonna need more space to replicate this shot!

[Peter Garsden]

Have been sidetracked putting together a Mini Q flying wing - sorry, inappropriate on a PSS blog - but some of us do sin occasionally.

Thought I would show you some pictures of the servo installation. Incidentally I was wondering if the wing needed the beef of an HS85mg - I think you could get away with something lighter and metal geared as the drive length is short and the torque should not be enormous.

This shows how I have glued the servo to the plate using Finishing Resin mixed with microballoons to gloop it up - not epoxy glue in case you need to remove it again. This is the method favoured by F3F modellers and it makes a secure finish. I have tried wooden posts and they are problematic as they split.

The KST X08 would work but it is pricey at £38 - maybe a Ripmax SD150 or an Emax metall geared for £7!

This hole you cut out first from the ply template before sticking the inner ply liner with a smaller hole to it, then the triangles.

I used a plug and socket as opposed to soldering the extension lead as it was easier.

[Peter Garsden]

I have found this fabulous router type tool which makes a great countersink for my tiny plate screws.

It goes in the Proxxon Dremmel - what would I do without it?

Incidentally the biggest servo horn is only just big enough. You could ignore the 2mm balsa layer and just attach the servo to the ply plate, which would be just as good. I suspect that is the intention of the plan. Andy reminded me that it is the same system as the Canberra, but I can't remember now how it fitted.

Edited By Peter Garsden on 10/09/2019 08:42:34

[Peter Garsden]

Next top skins - I found that 3 sheets of 4 inch wide didn't quite reach, so a trim piece at the leading edge was needed. Also my medium 2mm balsa was a bit springy, so I decided to try out my recently purchase ammonia. I have previously use acetic acid - clear vinegar, however ammonia seems a lot better - this bottle is 5% but some types are 10% so you can use it from the bottle without dilution.

It worked a treat and bent the sheet over the leading edge straight away. I am using aliphatic resin. I have tried thick cyano and can't get it all in the right place quick enough, though Andy does recommend it. I like to fiddle and move it around a bit.

You can see in this picture that there are no pins in position and the leading edge of the top sheeting has just draped itself over the structure. I still used pins but there is was much less pressure on them.

You can see the hole for the wire which I initially cut with a piece of sharpened 6mm brass tube then opened it out to about 9mm with a conical shaped permagrit grit. Worked well. You can't drill balsa neatly as it is too soft.

Edited By Peter Garsden on 11/09/2019 11:35:25