Jet Provost Build by RedBaron

[RedBaron]

29/01/2014 More Stuff. I am really glad that I decided to play with dihedral at this stage, I kept thinking about it all through lunch, this did not help the Brownie Points situation with the Lady of the house! Here are some observations on setting the dihedral:

 

• I still recommend building the wings to this stage on the joined lower wings skins, but now is the time to carefully separate them.
• The instructions suggest skinning and then letting the ply joiner into the wing through top and bottom skins. There is nothing wrong with this but I doubted my own ability to do this neatly as a last step.
• Having separated the wing halves I checked the angle of the root ribs and did a trial assembly without the dihedral brace and found a really minor imperfection stopped me from achieving the correct dihedral. This was easily fixed using a big Perma-Grit sanding block and some very careful sanding of both root ribs.
• Thank you Traplet for including the dihedral jigs in the Cut-kit, but I do recommend adding some simple balsa feet (else they with drive you crazy with their falling over, and clearly mark the front edge of each jig.

 

 

• Next I decided to cut down through R1, R2 and R3 to trial insert the dihedral brace and found that the brace as supplied is only tall enough to fit between the wing skins not through them. I think that this is good, so Traplet please do not change a thing.
• It isn't easy to cut thin slots in structures. A search in the tool box found an old broken hacksaw blade that gave exactly the right width of cut. Using a piece of thick ply as a guide it was the work of moments to cut the required vertical slots down through the ribs.
• This made up my mind to join the wings now and skin the tops in a following action. Doing this means that the top and bottom skins will need not cutting or making good or further sanding after wing brace fitting.
• The next step was to glue some 3/32 in square section scrap balsa onto the lower wing skin next to the wing web. This means that the wing web the dihedral brace and the 3/32 square top spar and bottom scrap make a nice dihedral / spar box.
• I think that now that I have full access for gluing I will use PVA for maximum working time. Here is a picture of the whole wing jigged and clamped up ready to glue:

Edited By RedBaron on 29/01/2014 16:01:44

[RedBaron]

30/01/2014 - Wing and fuselage progress. Today the wings were joined as discussed above and are now awaiting their top skins. The block balsa for the forward section of the fuselage will be complete by the end of the day. Then after some rough planing, I plan to use my disk sander to "square-up" the fuselage to the horizontal and vertical profile.

Because I am not much of a freehand carver I will be making templates to help complete the job. Firstly a set of "Octagonal" templates to get the bulk of the shape right and then a set of templates as per plan sections to get the final shape. The octagonal templates will be easy to make from the sections on the plan by drawing 45 degree lines just touching the section proper.

I will do some photographs of the blocked up fuselage and octagonal templates tomorrow.

[Phil Cooke]

Well done RB - great progress - watching with interest as I'm sure many others are too - just about to start their build this weekend!

[Tony F]

Pardon my ignorance mate....I was in the RAF in the 80's and saw many JP's flying circuits....which version is this (3,5?) and where can i find more info ? Love the JP but a Bucc comes first....always will

Tony

[RedBaron]

Thank you for your comments Techy111 - I am with you on the Bucc (with all the interesting optional armaments)

My JP is going to be XN595 (because I can buy a decal set) If I like how it flies (don't tell anyone else this) but I have in mind a twice size one with flaps and all the working bits and perhaps a different colour scheme. But perhaps I had better finish my big B52 first....

I think XN595 is a JP T3A for more information see http://www.jetprovostheaven.com/index2.html and http://www.abpic.co.uk/photo/1124057/

[RedBaron]

31/01/2014 - More on Octagonals. With the forward block work complete, I squared everything up to the horizontal and vertical plan profiles by planing and by using the disk sander. Thinking further I decided that there was no need for octagonal templates. I marked up centre and datum lines on the forward fuselage. I drew 45 degree lines on the profiles on the plan and transferred the measurements to the fuselage and joined the dots. Careful work with the balsa plane and disk sander should give me a nice eight sided front fuselage as the next step to finished curves.

I should note here that unless you are going in for a scale competition, symmetry and a pleasing shape reasonably close to that required will be quite satisfactory for happy flying. If anyone wants to measure your JP with a micrometre just draw their attention to the lovely finish. The following photograph shows what it looks like at this stage:

[RedBaron]

If you are new to this particular thread don't forget that my real NoteBook on the JP build is kept on SkyDrive.

You can view it and see all the details by using this link:

**LINK**

On your first visit to the NoteBook, if you bookmark that page in your browser it will save me keep putting the link in multiple places here. Also it will be quicker for you to check the shopping list therein or any other sections.

Manythanks

RedBaron

[David Tweddle]

Hi RB with you on this one and bookmarked thanks.

David

[RedBaron]

Thank you David for commenting, it is much appreciated.

01/02/2014 - The fuselage progresses. The part over the wing bay is now covered. When I looked in detail at the curve (it is not a simple curve) I doubted my ability to sheet the area from one piece, so I planked it carefully. In the photograph below I have not done any sanding yet.

The balsa plane has been working hard and the fuselage forward section is now eight sided. Follow Andy's advice and be bold with the plane (but only if you have marked all the guide lines for cutting). For the first time I can really believe that some elegant curves are hiding inside the balsa. I have now marked up the fuselage ready to make it a sixteen sided shape. If you do this use a coloured pen different from that used for the eight sided lines. I also made a 22.5 degree wedge to mark up the sections on the plan to aid transferring measurements to the model. Here is what it looks like at this stage:

The top wing skins are ready to be cut roughly to shape and then be applied to the wings, however before that we must face the matter of the "Weenie Washout Wedge". This is going to get it's own section in my NoteBook. Not bad for such an apparently insignificant thing. I know most of this will be well known to most of you, but as a full size glider pilot I feel that there is still more to say on this subject. This section coming soon. There will also be a short test when you come to fly your Jet Provost

Edited By RedBaron on 01/02/2014 11:44:25

[RedBaron]

01/02/2014 - I did not fancy trying for 32 and 64 sides, so a change of approach is needed now. I felt it really was worth the trouble to make up some cardboard templates illustrated below. The fuselage will have to thread into the templates as far as the required station. I decided to do a bit of final shaping around the nose and F1 as a trial and it looks pretty straightforward given the accurate roughing out already done. The plane has been put away and I used two small sanding blocks medium and fine to remove the edges and a builders flexible sanding pad, rough one side and medium the other. This is best done in a strong slanting light to show up irregularities (lucky the sun came out for an hour). It may be worth drawing your attention to the black stuff on the building board. This is a sort of fine rubber mesh, I purchased it some while ago from a wood workers tools and supplies business, it is a soft anti-slip mat to go on the bench to stop materials sliding around. Just the job when handling soft balsa parts such as planing and sanding this fuselage.

 

Edited By RedBaron on 01/02/2014 15:19:17

[RedBaron]

01/02/2014 - More stuff:

Here are some practical suggestions for the WWW for those who want to skip my theoretical observations these being completely optional:

• I decided that my wedge will run effectively at the position of the torque tube ending as per plan at the outboard end of the aileron cutout.
• Now cutting a wedge 18 inches long tapering from .8mm to nothing is clearly possible. However measuring .8mm accurately would need a lot of care. Measuring a length of 1mm is a bit more attractive and if the wedge is 22.5 inches long we get the same angle and can use any 18inch section of it.
• The next stage of my thinking was to cut a 22.5 inch long wedge tapering from 1mm to 2mm this will do the same job but avoiding the possibility of runout of the knife as one approaches the end. This worked just fine

Laying out my plan on my really flat building table, I covered it with transparent kitchen paper. Starting with the port wing, I pinned the outboard thick end of the WWW in the correct place, positioned the inboard end and tacked it to the paper with a small drop of Cyano.

• Small balsa blocks were pinned to the board along the l/e, tip rib and t/e.
• The top skin was cut about 1mm oversize (aileron to be skinned separately).
• A small cut out was made for the aileron horn wire and the root end of the sheet lightly sanded slightly concave to fit exactly along the port R1
• The sheet in front of the spar was lightly misted with a water spray
• PVA was run over all the surfaces due for glue.
• The top skin was positioned along R1 and along the t/e and pinned at the t/e
• Using a ruler the skin was pressed down up to the main spar where it was pinned in a number of places and then moving forward gently pinned to the false l/e.
• Many weights were applied to ensure contact with all the ribs.

This all went pleasingly quickly. So time for a coffee whilst the PVA really sets to full strength.

There is more detail in the NoteBook on SkyDrive in the JP WWW (Weenie Washout Wedge) section. I have decided to leave my aerodynamic notes on washout and tip stalling (much better called "incipient spin") in the NoteBook and not put that stuff here.

 

Edited By RedBaron on 02/02/2014 00:00:39

[RedBaron]

02/02/2014 See JPWeenieWashoutWedge section of my NoteBook for details of top skin. Now that the top skins have been applied to the wings I felt that I had got to the stage where I wanted to perch all the parts together to get some indication of the finished model and here it is:

Lots still to do but at least the JP character is beginning to emerge. I think that I will now continue with the wings, installing the servos, making up the pushrods, fitting the l/e stub tips wing tanks etc.

[Phil Cooke]

Going great guns with this RB - keep up the good work!

Are your pilots from Vortex like mine? - the look very similar!

[RedBaron]

Thanks for your comments Phil, I was just thinking that at this rate your JP will maiden next week end

No on Vortex I just followed Andy's lead and got mine from Petes Pilots. Quite solid but I begin to feel that weight will not be of prime concern for this model.

[RedBaron]

04/02/2014 The aileron servo connectors: Again I was looking for a relatively simple solution with preferably no wire bending or soldering (not that I mind that stuff) but I felt that this approach might be useful for the less experienced builders. A search through my spares box yielded the stuff for my approach, shown in the picture below:

Starting at the left: servo horn and pushrod connector; standard 2mm threaded push rod (needs to be shortened); standard metal clevis, but with the pin part removed with a Dremel parting tool (leaving a one-legged clevis) and lastly another pushrod connector to be screwed to the vertical aileron horn and retain the one-legged clevis. I hope the idea is fairly clear despite the poor focus picture. This set up will translate the servo arm movement from one plane into the plane of the vertical aileron horn movement. This approach would need beefing up for bigger models but should be just fine for the JP size.

[RedBaron]

Here it is all connected up. Adjustment is possible everywhere to suit later.

If you have not yet applied the aft fuselage top sheeting it is advisable to check that none of the works here interfere with the wing bolt retaining plate. Now to do all the wing shaping, I think that three wing templates will be needed to get that nice wing section into shape.

Edited By RedBaron on 04/02/2014 19:32:58

Edited By RedBaron on 04/02/2014 19:33:37

[RedBaron]

05/02/2014 - Fitting the wing tanks. Here is a picture of the port wing tip:

The inboard half of the tank has been fitted to the wing tip stub, and hopefully you will be able to see the magnets for tank retention. Given the snug fit to the wing I felt that a pair of 6mm Neodymium magnets would do the job.

If your local model shop does not have any try: www.first4magnets.com for great service. The holes for the magnets were bored with a piece of sharpened aerial tube and the magnets retained with cyano, I did do a double check for correct polarity!

Well next I guess do the same for the starboard wing, join the tank halves and do a bit of carving. Then the wing and its works will be just about finished for this construction stage.

[Tony F]

Nice RB Silly question that may of been asked before , has anyone thought of upscaling this and adding an EDF ?

Tony

[Mark a]

I would be interested in a EDF JP build.

[RedBaron]

Thanks for your comment Mark, the thought did go through my mind as I already have several slopers with EDF installed and flat field flyable as well.

On the Flyers and Builders Forum (on Proboards) there is a build blog in progress now for a foam JP with brown paper covering (you do have to register on this forum to access even viewing)

http://furbirdsmc.freeforums.net/board/24/flying-related

Best wishes

RedBaron

[RedBaron]

Thanks also to Tony for your comment.

Not a silly question at all. I have in mind a x2 sloper but had not got as far as thinking EDF for that one as well hmmm.

Best wishes

RedBaron

[RedBaron]

09/02/2014 - Wing construction is now complete, except for a few minor things like do the under wing block work, fit the wing bolt ply plates, fit the little wedge at the inboard edge of the ailerons, adjust the working clearances for the ailerons and a final light sand.

 

Here is the wing at this stage:

 

 

And here is the wing actually bolted to the fuselage for the first time:

 

There are a number of points that I should make now:

1 The wing tanks - If you have not already glued together your wing tanks you might like to consider the following. I did leave out the central lamination to get the initial dimensions as close to the plan as possible. Now with the tanks carved and sanded to shape close examination will show that I have not been able to sand out all of the lamination lines. The reason is that without the central lamination the geometry of the remaining laminations does not quite work properly. This is no big deal, one might sand the tanks undersize to get rid of the lamination lines or fill and sand the small gaps which is what I will be doing. If you have not glued up the wing tanks do include the central lamination (as recommended by Andy) and just do a bit more shaping.

2 Bolting the wing to the fuselage - After inserting the dowel into the leading edge of the wing (unglued at this stage) I was surprised to find that I could not get the wing to seat properly. Not a major problem I just gently filed the lower arc of the dowel hole in F4 downwards (by just about half a dowel diameter) until the wing seated properly. I then made an appropriate hole in the rear of the wing for the wing bolt and as you see the wing is a very nice fit. Now having to ease a dowel hole is pretty normal but this kit has such a nice plan and such accurately cut parts I felt that I had to get to the bottom of this problem.

A cup of coffee was needed to encourage the two brain cells to come up with the answer, I think that this is the explanation: Very early on in the build one of my first jobs was to fit the triangular sections to the top and bottom of the fuselage sides. As we often find the triangular dimensions are rarely accurate. So when I came to fit the formers I had to adjust the diagonal edges. Lacking care here F4 ended up a little high relative to the sides, I remember having to sand the top and pack the bottom of F4. I did not think about the dowel hole at that stage!

So if you are still at an early stage do check that the dowel hole in F4 is correctly positioned relative to any chosen datum on the fuselage. If you do not get it quite right the solution is easy, but I did feel that I had let the designer down on this point.

Well I guess it is back to the fuselage next.

If you are new to this thread then please note that my complete NoteBook for this build is on SkyDrive, the link to it is given earlier in this thread.

Edited By RedBaron on 09/02/2014 22:35:34

Edited By RedBaron on 09/02/2014 22:35:59

Edited By RedBaron on 09/02/2014 22:37:04

Edited By RedBaron on 09/02/2014 22:50:53

[Andy Blackburn]

> ... but I did feel that I had let the designer down on this point.

I disagree!

I'm now wondering whether the hole is in the right place, because I had to do the same. But, as you say, it's easily fixed.

[RedBaron]

Thanks for your comments Andy.

I have just looked at the plan again and still can't work it out, I suspect that the dowel cutout in the R1s does not match the plan?? Plus the small effect of dihedral also plays a little part.

However no great problem and easily fixed.

So long as the top surface of the wings fits exactly to the correct place in the fuselage sides (and mine does) then the wing incidence should be just fine.

Thanks again

RedBaron

[Andy Blackburn]

Well, I made all the original parts by hand, but the CAD parts that I'm working to were sourced from the CAD files. I'm wondering if I've done something silly like positioning the hole in the former out by something obvious, like half a diameter? An easy mistake to make (he said, getting his defence in early, just in case). I'll have a look at it at the next opportunity (Wednesday) and report back, possibly wearing sackcloth and ashes...