Jump to content

Israeli Air Force A4 Skyhawk - Shalom


Recommended Posts

I may have spent time on a kibbutz when I was 18 years old but I have always held respect for the pugnacious behaviour of the Israeli armed forces, and their industrious attitude to life, so no better reason to build an A4 Israeli Jet.

Actually it is just that I like the colours. The previous paragraph was a load of tosh.

Link to comment
Share on other sites

As everyone else has started with the fuselage, I thought I would do the wing first. First job was to open the cnc cut parts and my parcel from the balsa cabin. First deliberate error - all the balsa sheet was meant to be 4" but I have bought 3" sheets - what a numpty.

I taped together the sheets to make the first bottom sheet of the wing then applied Aliphatic Resin. I have recently bought some Graupner pins. They are so easy to apply, even if they are a ridiculous price.

Link to comment
Share on other sites

Woke at silly o'clock again this morning (is it my age?) so did a bit.

  1. I made some marks outside the edge of the sheet balsa so I could draw marks for where the ribs, spar, and leading and trailing edge go because once the plan is flat on the board, one cannot see through the wood - tip picked up from the JP.
  2. I am using floral cellophane to cover the plan and it works very well.
  3. I used the hold the sheet together tightly with masking tape method, apply glue to the join then fold back routine, and now have nice tight joins. Good tip.
  4. I decided to try out super phatic glue I have had for a while but not used. It is a cross between super glue and aliphatic as the name suggests. It is brilliant because unlike cryano one can position the part first.
  5. I have invested silly money in some Graupner pins which Tim Hooper uses and they are worth their weight in gold. You won't regret it. The big ends allow you to really press hard and apply pressure. Even went through the spruce spars.
  6. I have left everything slightly proud to trim back later. I should have made two bottom sheets at once but didn't do so.

You can see the overlaid marks on the plan, I made with pencil so if you like it can be rubbed off.

I also have laid in the ribs and spars using my handy plastic rib aligner. The super phatic dries in about 10 minutes which is ideal.

I have also shown the rib template aligner for R1 which I couldn't find at first. It is made of ply. I found the ribs very accurately cut which was excellent. One has to dress them to angle them in position. I used my handy Permagrit smooth small file which is invaluable if you can stretch to one.

Link to comment
Share on other sites

Good to see a wing under construction Pete - thanks for starting with this bit not the fus!

Lorenz - the wing halves are joined with a little dihedral so considering that and the washout needed in each wingtip it would not be ideal building the wing with a single piece bottom skin.

Link to comment
Share on other sites

Yes Phil I agree re one piece wing. I had the same thought then discounted the idea for the same reason. One has to work with each half separately for many reasons.

McG, thank you. I sometimes think I am explaining too basic stuff. Glad it helps.

Anyway, this morning, with flying yesterday (the Jart once again soared supremely up Bosley Cloud), I have done a bit.

Having separated the two wing halves, which I did build side by side, so, yes Lorenz this is possible as long as you don't glue them together, it was work on the wing joiner.

I made a Horlicks of it, so don't you do the same - several school boy errors, all mine, but with a mite of mitigation.

  1. I was confused about how the 1/4 inch gussets worked. At first I thought they were triangular, but not so. One uses scrap balsa in between ribs R1 and 2.
  2. First job, however (Phil this is not on the plan as far as I could see), but mentioned in the RC Model World Article Part 2 - I am building back to front - are the fitting of pieces of 1/8" balsa webbing in between R1 and R2, effectively glued to the back of the existing 1//16". This makes sense as it gives strength to the join. I didn't do this and simply glued the 1/4 gusset to the rear of the 1/8 hardwood spar. Error 1.
  3. One then MUST saw a slice of balsa out of R1 and 2 to take the dihedral spar, not as I did, which was glue a large triangle of balsa gusset with a view to then cutting a slice out of it, which is a lot more difficult. Error 2

  1. As Phil says in his article, one cuts the slice first, then attaches a further piece of scrap balsa gusset to the rear WITHOUT APPLYING ANY GLUE as you have then to slide out the ply dihedral brace.
  2. I do think an amendment to the plan to show the 1/8" extra webbing would be prudent, as without it the wing join will be weaker. I had to fit an odd shaped piece of webbing to the gap left by the 2 gussets and it was very difficult and unnecessary - so beware

You can see in this picture that there is only 1 1/16" web and no 1/8" web behind it.

Edited By Peter Garsden on 24/04/2016 14:26:49

Link to comment
Share on other sites

So to "dressing". I always thought I did enough of that at night and morning, but then I am no engineer?

I have always had trouble trimming the height of trailing edges. It is easy to catch the ribs and break them, so I use a David Plane from front to back. I have seen people tape masking tape over the part of the plane you don't want to catch the ribs with. Although Phil specifies 1/4 x 3/16 in his parts list one has to pair down quite a lot to meet the top of the ribs, and the sheeting bridges both rib and t/e.

The sub l/e also has to be paired down, again I did this with a plane, but from inside to outside to avoid catching the ribs. If you finish off with a sanding block again be careful not to catch the ribs.

Link to comment
Share on other sites

Do as I say not as I do and make the sheets larger than you need. You can see in the R/C Model World that this is what Phil does. It is impossible to line up all 4 sides accurately. I have ended up with a few cracks and gaps, but hey what is filler for - if everyone was a good carpenter, then filler manufacturers would go out of business?

I use a mixture of x-acto blade, a balsa saw and a topless saw - you know what I mean to trim.

Link to comment
Share on other sites

I thought I would show you the technique I use for making the sheets. It is so easy and effective. First you cut the sheets- obviously - then tape each end together - same way you do silicone hinges

Then apply masking tape along the join.

Then I use the metal syringe nozzle of the Super Phatic to apply a steady stream of glue to the join, then pin down the finished sheet and allow to dry - otherwise it will probably warp out of shape.

Anyway, more to do - cant stay here gossiping to you lot.

Link to comment
Share on other sites

Question here - I managed to fit the dihedral brace between the top and bottom skin, but the instructions in the mag say cut through the top skin. I haven't done that and think the join will be stronger..

Also one can see the sliver of balsa used for the wash out support, which tapers from 3mm to nothing. At first, when it says make it out of 6mm balsa I thought it meant sand it down to 3mm when that is not the intention ie cut a slice out of 6mm balsa starting at 3mm and tapering to nothing.

 I used Aliphatic resin to glue the leading edge on as I always do because you can spread it better and ensure a good join as well as taping the joint tight with masking tape.

Edited By Peter Garsden on 24/04/2016 22:06:24

Link to comment
Share on other sites

Next job is to plane down the balsa leading edge to profile. Problem again is to get it close enough to the join with the top sheeting, but avoid nicking the sheeting with your plane. Again, a tip from the JP build, line the join with masking tape to prevent any damage. You can see in this photo where I have nicked the tape slightly, but leaving the balsa underneath intact.

After removing the tape one has to finish off with the sandpaper to finish off the join.

Link to comment
Share on other sites

I bent the torque rods to shape this time making sure that each end was at right angles to each other unlike the JP. The mechanical effect of a rod not at right angles is to give the ailerons differential. This was used before the days of computer digital adjustment.

I experimented with the Permagrit needle file in the dremmel which worked really well. Beware however, there is very little depth to play with, and I am dreading the gluing of the rods in place because there is so little surface area to glue to. I am planning to use Aliphatic Resin in the hope that it will be less likely to stick to the moving parts.

I also used the conical shaped permagrit tool to make the hole for the clevis screwed rod.

Link to comment
Share on other sites

I needn't have worried.I coated the torque rods in a thin coat of Vaseline to stop the glue sticking then applied a thin coat of Super Phatic glue which does not ooze like epoxy resin, and pinned down the trailing edge - much easier with a flat bottomed wing, and left to dry for about 15 minutes - stuck fast and the torque rods moved easily. I then glued the tips together which are a sandwich of 1/32 balsa, 1/2 and 3/8 balsa.

Link to comment
Share on other sites

I hope this thread will not go the same way as Ken Livingstone today. You never know.

Steve - what happened to your Tornado. Didn't know you had a crash??

Height of torque rods - I think Phil recommends 20mm. I am planning to snip off the tops to the height of the screw metal threads which is exactly 20mm.

I have manged to break off both tips and had to reglue them - so don't use Aliphaatic resin - had trouble with it before I now remember. Have reglued with epoxy resin.

Link to comment
Share on other sites

I managed to glue the wings together with a mixture of epoxy and microballons

It says that the epoxy can be sanded afterwards.Here's hoping.I didn't need to cut a slot in the top skin, but I know that the magazine recommended it. I have a suspicion that the dihedral is a little more than recommended but I doubt it will be a problem. If anything it will assist the turns.

It is best to save the 1/4 balsa for the front of the wing until this stage rather than try and fit it whilst the wing is pinned to the board. i cut mine over size then planed and sanded it smooth. Over the front of this goes a piece of 1/8" ply. Again I am going to cut it over size, cut it again then sand it smooth; It is otherwise difficult to line up the dowel hole..

Here you can see how I did a pencil rubbing to establish the rough size of the piece of ply.

Link to comment
Share on other sites

Thanks Phil - did you see my comment earlier on about the 1/8" webbing not being on the plan? Also the query about cutting the balsa wing skin for the dihedral brace. If not it would be helpful to know what our lord and master designer thinks. Glad to see I'm not the only one up at this ungodly hour on a Saturday!

Just to make you happy, I am in Anglesey and am meeting Keith up the Orme today.Not sure about conditions as it is WNW which might be on the point? Will hopefully be flying the Jart as all my PSS Model Receivers have been sent off to Japan for a firmware upgrade. I have insisted they be returned by 21st May. Sadly I cannot come to the June event as I am going to a wedding. crying

Link to comment
Share on other sites

Thanks Pete, I did see your previous posts yes, I'd struggled to add a response with 100% confidence as on the prototype (to reduce build time) I built the fus and Matt actually assembled the wing in parallel. My original drawings left the wing joining method a little 'open to interpretation' and the resultant method (as explained in the magazine article) was devised by Matt during that first prototype assembly.

The additional 1/8" webbing aids to bridge the stagger between the top and bottom spars - helping us then to add 2 identical 1/4" triangular gussets top and bottom to enable a vertically orientated wing joiner. Its not there for strength - just joiner alignment. If you made the top and bottom 1/4" gussets slightly different sizes you could still achieve the same vertically aligned joiner. That's all the additional 1/8" webbing does. From memory it sat ON top of the bottom spar which was rearward of the upper spar.

Here's a couple of Matts photos during the first build, as used in the mag. They show the 1/8" balsa web on the bottom spar but mating with the rear face of original 1/16" webbing in between the 2 spars as per the rest of the span.

wing join 8th balsa 1.jpg

wing join 8th balsa 2.jpg

Its not easy to show this on the plan as the 1/8th balsa overlays the bottom spar - perhaps an isometric sketch of the assembly would aid the builder in future - all I can offer now is these photos and wording to outline the design intent - as per the write up and photos in RCMW.

As for the joiner breaking THROUGH the top and bottom skins - this is just the easiest way to ensure the join is good and the top and bottom skins are acting structurally regarding the wing join - the strength on these little skinned wings comes from the skins and its good practice to ensure the joiner is integrally joined to both to ensure max strength. Leaving the wing joiner proud through the skins and sanding back flush after the wing is joined is the easiest way of building absolute confidence in the joint.

Hope that helps others - Ill copy this post and add it to the general building guide thread too I think...

Edited By Phil Cooke on 30/04/2016 07:52:37

Link to comment
Share on other sites

Excellent explanation and so thorough as always Phil. I can see what the design thinking was now. I wish I hadn't bothered with the extra webbing now as it was a real phaf. I can also see the point of the cut through.

I notice you don't specify any wing bandage on this one. What do you think? I don't think I have made a soaring glider wing without it to date? I suppose it is a big chord and not really necessary? I was erring on the side of not bothering.If I did so it might be just a narrow strip covered in diluted PVA?

Edited By Peter Garsden on 30/04/2016 07:57:50

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...