John's retrospective Jet Provost build thread

[John A H]

As the RedBaron has got the ball rolling with his Jet Provost build I thought I'd post up some photo's that I took while constructing my specimen. This is the model that appeared at this summers PSSA meetings with a few people having a stir of the sticks.

For those who purchased Andy B's plan from Traplet you probably also received a copy of the article that Andy did for the magazine. That alone gives very good details of the build sequence and method.

[John A H]

I had to cut out my own formers as the wood pack is only available now due to Phil C. encouraging Traplet to produce it.

A battery box (tube) is built ..... check your chosen receiver battery fits in. A 4.8v 2000mAh Envelope fits when the box is built as to plan. The front fuselage formers are then glued on square to this and the cypris/spruce longeron is added. This needs to be accurate as the rear fulselage formers F5 and F6 fit onto this (note the balsa quadrant used to increase the area for glueing on the fuselage sides.

The soft balsa quadrant is then glued to the fuselage sides (with saw cuts to help curve it round the nose section and jsut behind the wing. Use glue that sands well for this (yellow Aliphatic resin or balsa cement is what I used) as you will be sanding a lot of this off to get the get the fuselage shape and you get raised lines that are hard to smooth out if the glue does not sand well.

Fuselage components layed out upside down

[Tony Bennett]

watching this as i can see one turning up in my hanger later this year.

[Phil Cooke]

Hope it 'turns up' in time for you to join us on the Orme in June Tony!!!

John - great to see your retrospective build, will be watching with interest as the PSSA builds begin very soon now, 1st Feb!

[John A H]

Forgot to say above that you mark the rear former positions onto the inside of the fuselage sides before glueing the quadrant on (you can see them on picture above, also make sure you make a left and right had side.

Fuselage sides glued onto nose section and rear formers F5, F6 and F7 added. I photocopied the plan and stuck it to the building jig so that I could keep it all straight (I marked centre line on all the formers to match them up with the plan)

Even with the cuts in the quadrant it takes a bit of persuading to encourage it to form a curve (not helped by my rather heavy wood selection). At this point a wicked some super Aliphatic into the cuts in the quadrant as it penetrates better but later I found that this did not sand too well and it was quite an effort to get a smooth shape - I should have just rubbed normal Aliphatic Resin into the cuts.

The upper fuselage behind the cockpit is sheeted with 1/16th balsa so I dampened a sheet and left it to dry wrapped around my spaghetti container. It makes it easier to get it to follow a nice curve when attached without risking it splitting.

Fuselage top, bottom, decking and rear nose blocking added. Not a very pretty site at this stage (in fact quite embarassing to show a picture of it in this state - it had been lying around in the workshop for a month and had suffered enough hangar rash to already sport some filler. Why is there always a knife or pile of pins lying just where you "place" your unfinished airframe !!

Again use a glue that sands well for the nose block.

Starting to attack the nose with the razor plane.

Looking a bit more presentable after sanding.

Fuselage shaped using razor plane and then sanding block. Rear tail pipe area opened up with dremel. Also shows elevator control cable apearing out of the back of F7 (added before top sheeting).

[John A H]

Phil, I wasn't sure how soon to post the pictures as didn't want to jump the gun with you guys starting in February but as RedBaron started his first it I thought I was safe

[John A H]

Front nose block added and shaped and trial fit of the fin, tailplane and canopy. I'm never quite sure when to stop sanding, you come back to it the next day and there always seems to be a curve that in not quite right and needs a bit of "furtling". Take a bit off onbe side then decide it doesn't match the otherside - It's quite easy to go too far. It helps to use the join lines in the blocks to match the sides up. I also reffered to the pictures on the JETPROVOST HEAVEN website to see how the nose is shaped (and also had a visit to Elvington where they have a static JP and also a cockpit section that you can have a sit in).

I forgot to mention that when I put the rear fuselage top deking I jammed a sheet of scrap in between the two halves to make sure the fin and fin fairing was a tight fit.

Now looking a lot more like an aeroplane than a box made of tatty balsa sheets.

[Wiltshire Flyer]

Coming along nicely

[John A H]

I didn't take many pictures towards the end of the build.

Here is the starboard wing ready for it's top sheeting. Spars have shear webbing across the full span (as mentioned in BEB's Dawn Patrol build).

A set of standard aileron torque rods from SLEC fitted fine. I threaded the aileron outer tubes onto thin ply plates then slot it into the top of the ribs and glue the plates to the ribs.

I bent and cut the Aileron end of the torque rod to the size on Andy's plan and when I pushed the aileron on the end popped out of the surface of the aileron - oops, had to shorten them slightly and fill hole. The yellow staining on the front of the ribs and leading edge is the super Aliphatic that I used for that area. The bottom of the ribs curve up so with the wing pinned down you can jack up the bottom sheeting at the front and then wick the aliphatic in.

Don't forget to put in the balsa blocks to give the aileron hinges something to slot into and also the infill to block out where the wing bolt goes.

You then pin the wing back to the building board with the wash out "wedge" under the trailing edge from rib 6 out to the tip. You can now attach the upper 1/16th sheet and when you un pin it from the board the next morining it should retain its shape with the washout.

[John A H]

I've no pictures of joining the wings. The scarey bit is cutting into your newly created wing to create the slot for the ply wing brace. At these points in the build I normally spend at least an hour hovering over it with the knife trying to pluck up the courage to slice into it. Before joining the wing I marked the surface where the spar was and then used a a knofe to cut the top sheet and ensure I had "hit" the right spot. I used a razor saw (if that is right name) to then continue the slot through the two inner ribs - the blade thickness just about opens it up to the correct width for the ply brace to slot through (the slot is also through the bottom wing skin as well).

Picture below shows finished fuselage sat on wings. The engine intake blocks are taped in place and are taken off to shape. The jet pipe at the back had been shaped - I found that sand paper glued round the cardboard tube that profilm comes wrapped around was jsut the right size to sand a nice round jet pipe shape. As you can see you end up removing a lot of material from the back end - don't go too far. It looks fragile but once the tailplane is glued on it is strong enough.

On the picture above you can see I had to do some remedial with filler on the wings. When I glued the top sheeting on I put some flat weight on it to hold it down - I ended up with a flat spot on the port wing so had to reprofile it with some light weight filler. I also squashed the inner trailing edge on the starboard wing. Both show as white areas in the photo. It was careles of me but I thought I would own up to it to show anyone that is worried that they are too cack handed to join in the build can see that most situations can be rescued.

Below picture shows close up of "raw" jet intakes before shaping and also the cockpit area - the canopy is used to decide where to cut the cockpit sides. You can also see the position of the ply wing brace

[John A H]

Here are the tip tanks, one in "raw" state before shaping and the other shaped (few dints need filling in).

For the inner laminations I cut out the wing profile and slotted them onto the wing to check the fit before glueing. I then wrapped cling film round the wing tip, and glued the laminations together then pushed them onto the wing tip to get it lined up. Again try to use glue that sands easy as there is a lot of shaping needed.

I cut all the blanks to the same size but from seeing Phil's pictures of the Traplet cut parts I think they are tapered so you'll need to get them in the right order.

This is another of those "should I stop sanding before I go too far" moments. Once the tanks were finished I again wrapped the wing tip in cling film and the slapped a mix of epoxy resin and microballoons in the tip tank recess (just the sides not where it butts up against the wing tip end) and pushed them onto the wing tip and wiped away any that squeezed out. Next morning they were pulled off (cling film did it's job they came away cleanly) and I had a nice tight fit.

[John A H]

At this point my picture record is a bit lacking so it jumps straight to the finished airframe ready for painting/covering.

This is where I attempt to cover up my shoddy building skills by putting quite a bit of effort into preparing the airframe for the final finish.

The wings tailplane and tip tanks were to be covered in profilm. I decided it was easier to paint the fuselage than try to cover it with film (especially those jet intakes - I think Andy covered the jet intakes seperately and then glued them to the fuselage once complete).

A mixture of 50% non shrinking dope and 50% thinners was brushed onto the fuselage and the sanded back.
The same mixture was then used to apply a layer of light weight tissue (as can be seen on the photo I had some yellow lying around.

Talcum powder was then mixed into the dope mixture and this was applied over the tissue and once dry this was sanded down. This process was repeated until the until I had the smoothest finish I could manage. It probably took 6 applications of talc/dope with sanding between.

The work went something like - Get out of bed apply coat of dope/thinners/talc, go off to work, come back home give it a good sanding, apply another layer of dope, go to bed. Next morning sand it back and apply another layer, off to work etc. etc. No lighting naked flames in the house

[John A H]

One thing I forgot to mention is that the ailerons were made using stock aileron material. The ailerons taper and when the shape is cut out the leding edge of the aileron material is a close match for the trailing edge of the wing. They were just oversized enough to allow the wing tip washout to be sanded into them.

[John A H]

Finally we come to the paint/covering.

The wings were covered in grey profilm. The tip tanks and tailplane were covered in Ferrari Red profilm. It did take me three attempts to cover the tip tanks to an acceptable standard - it took two nights of muttering and heat gun fried fingers.

All the paint was halfords spray cans. First a coat of primer filler was sprayed on and sanded back. Then two thin coats of white primer. Then a coat of Appliance White Gloss, this was left to dry for a few days. Then the nose was masked up and the black anti glare panel and cockpit inside. Finally the white areas were masked out (including the 46 on the nose, roundel area and "first aid" square) the it was sprayed with several thin layers of Vauxhall Flame Red (it is a fairly good match for the Ferrari red profilm).

Paint masks for the black registration numbers, rudder and engine cover outlines were cut out using a Cameo Sillouette vinyl cutter and then sprayed with halfords matt black. I photocopied the fin shape from the plan, copied it into the Vinyl cutters software and then I could draw and position the lines and numbers where I wanted them (it even allowed me to modifiy the "1" for the "1 FTS" to get the correct shape). I then cut out the mask and stuck the whole lot to the fin and sprayed it. The same process was used for the engine cover outline.

I couldn't decide on the right colour match for the blue so that was all cut out of vinyl. The markings on the wings were cut out of vinyl.

The paint and markings scheme is based on the old Linton-on-Ouse gate guardian XN589. I was lucky that the Elvington cockpit section also sports the yorkshire rose on the nose so I took a picture of that and lazer printed it onto white transfer paper - unlike inkjet prints it seems to be water proof without any treatment (no worried about requiring fuel proofing).

The sliding canopy effect is achieved by using two canopies so that the front section sits on top of (overlaps) the back section. Andy mentions it in his build article so I can't claim any credit for the idea. Vortex Vacform provided the canopies. The pilots were from Pete's pilots, they actually come as nearly full bodys but their lower halves were sacrifices to fit in. I also cut the head off one and repositioned it to look out of the canopy side rather than have them both staring straight forwards.

The one glaring omission is the two forward facing lights either side of the nose - I haven't decided how best to represent them yet. Ideally some functional lights in there would be best (like others have on their BAE Hawks) but I didn't have the nerve to drill into my smoothly sanded nose.

[John A H]

That's a whole Jet Provost build in one night.

Phil has some nice pictures of it flying at the August Lleyn PSS meeting including the one he used in the "introduction". I posted a short video of it flying in Andy Blackburn's "Design notes" thread which I won't repeat here.

Hopefully it has been some use or at least has encouraged everyone to get started. Later in the week I can take some photos of the radio installation if that helps - it is mostly as Andy describes in his article.

Due to poor wood selection, filling in dents and vast layers of dope and paint plus I rather over engineered radio switch installation operated by the antenna arial it is a bit of a bloater. Andy says his original was 24 oz where as my collection or hard balse, glue filler and paint comes in at 37oz. It not one to chuck off a slope in marginal conditions but in decent lift it has very good energy retention and penetrates well.

For reference I used a Hitec HS-85MG servo for the elevator attached to the fuselage side as on the plans, using the mounting lugs that come with them, and two Hitec HS-65MG for the ailerons, again installed as on the plans.

Finally, the tip tanks are such a tight push fit that when I caught a wing tip while landing instead of the tip tank coming off it broke the wing tip off with the tank still attached. It was a clean break so just needed glueing back on and the profilm ironing back down.