882 forum posts
It had to come - it always does - That oops moment.
Although the basic wing is now complete it still needs a fair amount of work to finish. The net job is to fit the nacelles and here is a beautifully cut recess in the lower sheeting.
ONLY THAT IT IS IN THE WRONG PLACE!!!
For the failure to double check before cutting, the recess is between R5 and R6 rather than R4 and R5. What to do?
Well I could pretend that I did it on purpose so that I could fit much bigger props if I wanted. Not going to work as the nacelles wouldn't fit due to the wing taper. No one would believe me anyway.
Start again. I was so annoyed with myself I could easily have done something terminal to the whole wing. Luckily the red mist turned to a lighter shade of pink and some rationality returned.
I did swear but that's as far as I go on this forum.
Turning to more practical thoughts I reckoned that I could replace the length of sheeting. This time though before reaching for the scalpel I did wonder whether this was going to be possible without making things worse. Luckily the brain shouted compromise and realising that worse things happen on the flying field I settled on patching it and cutting the recess in the right place. This time around I would have a nice visual reference of where not to cut.
I thought it would be easier to do it in two pieces. I think it probably was.
The little strips were spot glued on to stop the insert from falling through and to get good alignment with the adjacent sheeting.
Final piece going in. Of course the grain would never match up so I would never get the opportunity to disown the whole affair but I did try to match the hardness and bendability to help it blend as much as possible.
Finally in and sanded. I can't help my eye being drawn to it every time I pick up the wing but I am living the hope that this will be therapeutic. I have promised myself that when the wing is covered I will forget all about and wait nervously for the next one!
It came quick enough. Those paper tubes that I prepared so carefully - well I forgot to put them in during the excitement of joining the wing.
My teacher was right all those years ago in Class 3B
|Peter Miller||05/04/2018 19:07:51|
10513 forum posts
I know that ot ios a lot of extra work but I do like fitting butt straps under any leading edeg sheet joins. Trickwer I know trying to cut away a 1/16" from the edge of a covered rib or one can cut the sheet a little ffurther out and go into the next rib bay out.
However, just to make you feel a little better.
I am going back to the 60s and building a Veron Deacon free flight model. The plan shows the wings super imposed on each other with just the tip and root clear.
Happily built both wings and went into the workshop planning to join them
Oh dear, Two RIGHT wings. First time that I have ever done that!!!
Luckily I just had to break out all the ribs, cut a new set and build it the right (or rather the left) way round and there is no sheet on the wings
882 forum posts
If this was a single engine aircraft we would be thinking about covering and finishing but this wing will keep me busy a while yet.
Now on to fix the leading edge strips. I should say this was done before joining the wings so I have crept out of chronological order. My apologies.
No particular difficulties here but it does pay to take out any minor waviness in the leading edge by dressing the false leading edge first. This can be made nice and straight so when the time comes to fit the proper leading edge it only has to be profiled and that makes things a whole lot easier.
Out with the clothes pegs and in with the rubber bands. These are kept in an old chocolate tin to keep out the light and so far have lasted quite a long time. It also helps to only have them stretched for the minimum amount of time for the glue to set stable otherwise they go limp or mine do anyway.
I have some small ones (mainly used on the fuselage jig) and these larger ones. To get the right tension they are simply knotted off as a suitable place and again unknotted as soon as practical.
The leading edge is going to be sanded so it doesn't matter if the bands bruise the balsa a little bit but I do want to protect the trailing edge. The alloy tube works well as it is easy to roll the bands up and down the wing.
This is a good place to see the recess on the right of the picture. This is to take the semi-split flap that has a wider chord than the ailerons.
The cap strips are on such as they are. The underside will be fully sheeted to just outboard of the nacelles.
882 forum posts
The main difference with my nacelles are that they will be dismountable. This was a decision not wholly backed up by logic but I suppose it will make covering marginally easier when the time comes. This meant of course that the nacelles have to be bolted to something and the main spar and the false leading edge are ideal.
Other changes mean that I am using less plywood, the nacelle can be tapered in two direction and the main one, I don't have to sand any plywood to a profile which I hate doing.
Here the port nacelle is hooked into the wing for a trial fit. The plywood sides are a sliding fit between the front sections of R4 and R5. The plywood sides are short and only extend a short way behind the main spar. This is enough to create a slot that picks up on the top and bottom spars which controls the height of the thrust-line and ensures that it is parallel to the datum ie No down-thrust.
The starboard side offered up for a trial fit and to check it is parallel to its partner.
A short section of birch ply is glued to the inside of the false leading edge. There is a gap at each end that accepts the side plate of the nacelle. Captive nuts are in place in a direction that allows access to the fastenings from within the tank space.
The second piece of ply was drilled at the same time as the piece fixed to the leading edge to make sure of good alignment. This second piece then gets glued to the nacelle itself.
In this photo the nacelle is accurately located by the slot and the loose piece of plywood lightly bolted to the fixed piece on the leading edge. This is a dry fit at the moment. It would be all to easy to get some glue in the wrong place which would certainly spoil my day in terms of them being removable.
To get a decent gluing area corner fillets are added. These were made from rock hard balsa as they were joining plywood and glued in place using aliphatic taking care to keep it where wanted. When the second fillet was fitted an the glue set, the loose piece was firmly attached to the sides of the nacelle.
The pin is not actually pinning the joint but was used as a handle.
So I could get the glue on and also to hold it in place for a few seconds for the glue to "grab". Aliphatic is good in this respect of getting quite a rapid initial bond.
N2 was then fitted in a similar way with the bolts going between the spars after the space had been packed out with some medium hard balsa.
When the glue had set overnight, the nacelles were unbolted and carefully slid out of their recesses. I then went over all the joints with cyano which would of course have been madness to do in situ.
882 forum posts
Next job is the sheeting on the underside of the wing. This will extend just outboard of the nacelles for maximum strength and torsional resistance. The rest of the wing will be open structure to save a bit of weight. The section is very nearly flat aft of the spar so there will be negligible sagging of the covering between the ribs.
In preparation for the sheeting, strips of 2mm birch ply have been recessed into the ribs and these will be the framework for the servo holders that will also double up as hatches.
You can also see the backing plate with the captive nuts that connect to N2 when the nacelles are in place. Having forgotten to put the paper tubes in before joining the wings I have put a thin strip through all the ribs. The servo leads will be cable tied to these strips in a few places to stop them flapping about.
A section of sheeting about to go in with the glue painted on in readiness. The cut-out is for a flap servo and the slots take the ends of the nacelle that locate on the aft side of the spars.
With the sheeting in place the nacelles can be finished.
With the structural sections of the nacelles temporarily back in place, the side pieces can now be finished. These are made from 3mm medium balsa which is easy to sand to match the section on the underside of the wing.
Here being clamped in place.
And here nearly ready to go into the fuselage jig.
The side pieces of the cowl were built 6mm (3mm each side) wider than the ply so when these balsa sides are fitted, the outside becomes flush. The aft end is just rough cut for the moment and will be trimmed to bring them inside the line of the flap hinges.
Time also to fit the holder for the throttle servos. These glue onto the aft side of N2 and the end grain gluing of the Liteply is helped with some small triangular fillets.
882 forum posts
It is a bit like making three fuselages for one aircraft. Perhaps this is the reason there don't seem to be that many twins around.
Back into the SLEC jig to finish the sheeting of the nacelles. The side pieces have been rounded off more or less like the plan but I am also squeezing them in. I can do this because the side pieces sit on top of the wing sheeting and don't have to be glued to the wing ribs which are of course parallel.
Damping the sides with clean water they were gradually teased into place. Because the nacelles are relatively short I could get them both on the jig at the same time making it easier to make them the same.
Sheeting going on and the very end has a solid block that will be drilled to take a small fastening.
This view is the top side of the nacelle that is lying on the underside of the wing. It is sheeted between the side pieces and this gives the whole assembly a lot of stability. The hold is lined with an aluminium tube to take an M3 nylon bolt. This will screw into the trailing edge of the wing where a suitable block has already been fitted. This bolt is not structural but just helps to keep the long overhang on the nacelle in the right place.
This just leaves the hatch to do before we move onto the wing fixings and the cockpit.
882 forum posts
I forgot to mention the throttle servo being mounted at an angle. Here is the photo again.
This was to make sure the servo bracket did not foul the sides of the nacelles when they were pulled in.
Now on to the hatches. These are shown as 1/32" ply but I wanted to make mine a bit thicker so I could put a radius on the corner.
These hatches are two laminations of 0.6mm ply topped off with 3mm balsa laid cross grain.
The job started by making a former out of a piece of 12mm hardish balsa. The curve was taken off the plan but made a fraction tighter to allow for spring-back of the lamination.
The ply was cut so that the more bendy direction would help wrap around the curve.
Resulting in this after resisting the temptation to take it off the former too early. Overnight was fine for the glue to have really set. Aliphatic spread thinly and smoothly.
The holes were marked on the plywood lamination to coincide with the hardwood blocks and in this case N1 and after using these as a guide to drilling the nacelle itself the holes were tapped M3. (Drill size used 2.5mm)
The threaded hole then has a dab of cyano to harden the thread and the tap run though again to clear out any whiskers. This makes a perfectly adequate thread for something that is not load bearing. In this case just the hatch as the fuel tank will be supported elsewhere.
The cross grained balsa has been applied and a typical bolt is now fitted. This is a good time to make sure all the bolts line up and I had to tease a couple of holes slightly with a needle file to get a good clearance. This removes a lot less material than simply drilling a bigger hole.
The bolt head will easily crush the balsa but underneath there is some nice hard ply. Here I have used a section of an old aerial that neatly fits over the head of the bolt. The balsa is drilled own to the ply and the bolt removed to hook out the balsa plug.
This leaves a nice neat counterbore for the head to sit in. Later when it come to covering I may make the counterbore a bit wider. I haven't decided yet but if I do I will put the original aerial section back in place and slide the next size aerial section over it and drill again. This will ensure it is concentric to the bolt head and remain neat looking.
The finished hatches.
|McG 6969||09/04/2018 10:40:45|
2909 forum posts
Excellent, neat and tidy work over there, Lev.
Looking forward to see it covered soon now.
882 forum posts
Thank you Chris. I feel as if I am some way away from covering and apart from the simple fact I have not decided on a colour scheme I am not sure how I am going to cover it.
I am toying with the idea of painting the fuselage. This will allow me to reinforce the planking at the nose with some tissue. This also means that I would reinforce and paint the fuselage section above the wing so it matches seeing as that is planked too.
I experimented on some painting on the fuselage of a Graupner "Topsy" kit I finished earlier in the year. This is a real cutie that I bought from a traditional model shop in Italy a couple of years back.
It was a lot of coats over the tissue but very little weight as most of the paint was sanded of ending up with 800 grit before the final top coat.
Getting back to GTC I may do the same on the nacelles but the wings and tail feathers will be film for sure.
Still more work on the wing and Peter suggests doing the fuselage and cockpit section on the wing with planking
I have built a shoulder wing aircraft before. It was the Super Sytky designed by Christian Moes and a free plan in RC Model World.
In this case there was virtually no twist in the sheeting, just a fairly tight wrap that was easily sorted out by damping the balsa with clean water and working it round. In Grumpy's case there is a lot of twist and I don't think this was caused by the higher decking so Peter's advice to plank was good.
That is coming next.
|McG 6969||10/04/2018 11:41:07|
2909 forum posts
... did I spot a 'Belgian crew' in your Topsy, Lev...
882 forum posts
Yep!! Co-pilot Smurf is checking the smurfs (chocks) have been smurfed (removed) before they smurf (fly) from North to South for a conference on taalstrijd.
In this foreign land of course they are called pitufos
|McG 6969||10/04/2018 13:22:39|
2909 forum posts
... regarding "Taalstrijd", it smurfs where in your lovely "foreign land", a bit up north close to Barcelona they smurf them 'barrufets'...
882 forum posts
Thank you for that diversion Chris and I am sure Gaston is much further up the evolutionary path.
Now back to the wing which needs to be in its finished position so that when the cockpit is built up everything lines up as it should.
This is a spare length of dowel sharpened to a point on a lathe. It can be almost as easily done in a drill and it is not too hard by hand.
The dowel is then slipped into the alloy tube in F3 so that when the wing is correctly positioned it can be pushed into the leading edge to make a small dimple. In this case quite easy because of the lightening hole above. In previous builds I have used two scalpels to grip the dowel from each to push it into the balsa to make the mark. That was not quite so easy.
Here is a good example where retaining all the centrelines was a great help. The wing was lined up with the lines and then checked with the string and pin method with no difference between the two. It does mean that if the wing has to move for any reason you can rely on the lines as a quick and easy reference to get back into position.
Next build however I am going to use a square plywood peg in a square hole. This will be much easier to adjust if the height is not quite right by putting a stagger on the peg thus avoiding anxious moments.
With a mark now on the leading edge of the wing, an aerial drill was used to make a hole for the alloy tube liner. Going back a few stages we put a slit at the required depth in bother F1a former. When the aerial drill met the slit the balsa plug just fell out avoiding any digging.
At the trailing edge of the keel the trusted pointy bolts were used to mark the correct positions.
The offcuts from two previously shortened wing bolts were given their points are screwed into the fuselage wing plate so the points are just proud. When the wing is lined up (pencil marks again) the wing is pressed onto the bolts making small impressions to guide the drill. I have found that nylon bolts are sufficiently hard to make a useable impression even in plywood. Grumpy's wing has thin ply plates top and bottom. Keeping the drilled hole a neat clearance fit ensures that the wing will come on and off, accurate aligned each time by the bolts.
I always enjoy this hurdle as at this point the two major components can be put together and held together. All of a sudden we have something that looks and feels like an aircraft.
882 forum posts
The wing needs do be securely in place to get the alignment correct for the formers.
The wing is bolted in place and the aft end of the cockpit is glued in place. The little triangular bracket stops me from knocking it off before the planks hold it in place.
There are layers of masking tape stuck to the canted former on the fuselage. This gives a bit clearance and so that the wing is not too tight after covering. I have allowed a bit more because later the former on the wing will be faced with very thin ply to give some resistance to dings on assembly.
This is the rear section ready for planking and the front of the cockpit is in place. This in not very high so I thought it didn't need support. The formers are thicker than shown on the plan. These are 5mm and give a greater gluing area and something to push pins into without splitting.
F3a is being prepared and has been hollowed out so that it fits neatly around the leading edge of the wing.
This gets the tape treatment as well to make sure there is sufficient clearance. I have been caught out before by making these sort of fits too tight.
F3a and F4a are now fixed so now ready for the planking.
|Rob Ashley||11/04/2018 20:39:11|
253 forum posts
Man you are catching me up quick.. Nice build too..
882 forum posts
Thank you Rob
First planks go onto the cockpit.
These go right at the front and have to cope with most of the twist.
They are glued along their bottom edges and left overnight. They are up for some serious torture later! These first planks reach almost to the thickest part of the wing. This means that all the remaining planks will have very little bend, virtually no twist and just need tapering.
Just made it. The wood was starting to pull away from itself so it was a close shave.
Next plank goes from front to back still with some twist but manageable.
Next plank at the rear doesn't have to go the full length as there is no point planking over the cockpit. Before getting too carried away with the rear planking we need to work out how the wing bolts are going to work. There is not much detail on the plan but on the photo of the original Grumpy Tigercat it is possible to see the holes were the bolts go but if there are just access holes in the planking I could see much time being wasted trying to fish them out of the cavity. Additionally the two holes need to be quite close to the edge and that would make part of the planking quite fragile. It was easier on Super Sytky because there is just one bolt on the centreline bt in this case I decided to use tubes.
The tubes were made from two laminations of well wetted 1.5mm balsa wrapped around a suitable piece of aluminium tube. The bore of the tube is just a fraction bigger than the head of the bolt.
The tubes will be fitted after the planking as it would be very difficult to plank around them neatly
To make sure they arrive in the right place later on thin strips of balsa were glued onto the wing plate and these will guide the ends of the tube into place when the time comes.
A dry run to make sure the theory works.
Planking complete including the front end and with the rough opening for the cockpit.
The holes are cut ready to take the tubes. At first a small opening was made with a scalpel and then this was gradually opened out with sandpaper wrapped around a dowel. For the final finishing some 400 grit was stuck to a made-up round piece of balsa just a bi smaller that the required hole and carefully dressed to size. It sounds tricky but it was surprisingly easy and quick.
The tubes were dropped in with plenty of glue and found the guides with no problem. Here they are trimmed and faired to the finished planking. Excess glue in the hole was mopped up with a cotton bud.
The bolts now drop down the tubes and through the holes in the wing plate. I may leave the holes open or perhaps hide them under a sticker or something. Suggestions very welcome.
|Tim Ballinger||12/04/2018 08:08:21|
676 forum posts
Good idea with the balsa tubes Levanter. I used paper tubes which I impregnated with thin cyano once in position. Comes out rigid and light . I then made the bolts captive by finishing with balsa cap with a hole just large enough for the right sized screw driver. You hardly notice the holes after it is covered so I never bothered with covering it over with tape even though that was my plan. Like your balsa tubes though , very neat 👍
|Peter Miller||12/04/2018 08:40:39|
10513 forum posts
Don't you just love that moment when you take the rough, uneven planking and a few minutes work turns it into a smooth, curved surface.
882 forum posts
Tim. Maybe I will follow your idea and make some balsa plugs but not glue them in. I just know that if I make them captive I will break them! Another thought I had was to fill the tubes nearly to the top again with balsa and use longer bolts with the heads just below the surface. I will try the paper cyano trick sometime.
Peter. It is immensely satisfying. The ugly duckling transforms into the graceful swan. I am definitely going to try some of your curvy designs.
Grumpy's wing is starting to come together compelling me to think of a colour scheme. The net job after the planking was to sort out the cockpit.
Which looked like this after the planking.
Rounding off one side was easy. No particular shape to follow because here I have deviated from the plan.
One side done and now I have to make the other side the same. Here I took a paper template and marked it along the edge of the finished side a bit like doing a brass rubbing. The pencil was to make it visible and then I pricked the line through with a pin on the second side. This gave me a "do not cross" line to get the shape roughly right and then careful sanding by eye sorted out the rest.
To end up like this. The inside edge is still a bit wavy and I will sort that out later when I decided how I am going to finish the cockpit. I the meantime, to harden up the exposed edge a bit I put a couple of coats of sanding sealer which gives it a bit of protection.
Some other details of the wing. Both ends of the cockpit are face with 0.4mm ply. This will stop the ends getting bruised. The inclined F5b will get the same treatment. F3 doesn't need it as it is ply already.
This is the part of the nacelle that stays on the wing.
This is the underside of the very nearly finished wing. Ailerons and flaps still to do plus fitting the servos that I haven't got yet. In truth I am not sure what servos to use. There will be four of them so I want a good compromise between quality and cost.
The sheeting on the underside stops just outboard of the nacelles. The centre recess which Peter uses for his aileron servo driving rods and bell-cranks will be a handy place to join the extension leads and Y leads if I use them. If they could all be wired into one multi-pin plug that would be fantastic.
882 forum posts
The wing now only needs the ailerons and flaps sorting out but I have a few decisions to make before going ahead so I put it to one side to have a go at the canopy. Nothing in my box of spare canopies was anything near suitable so time to make my own.
Starting of with the profile cut from 10mm sheet.
Then building in successive layers, each one smaller than the previous to get the basic shape.
This technique known as "bread and butter" was quite popular with boat modellers.
Then attacked with a Davids plane. Likewise quite satisfying. The trick here is to develop the shape in sections. Don't try to round everything off too quickly. The corners of the layers act as a guide and turn into lines the nearer you get. When they are just still visible it is time to turn to sandpaper.
To end up like this. In previous incarnations I worked in a factory making architectural mouldings and sometimes the work entailed making shapes freehand. Here I learned a very useful trick. You have to be courageous roughing out first with coarse medium. The coarse side of a Permagrit will eat balsa and make quick work of even harder material. The coarse medium will cut and should be used to get as close as possible to the finished shape. Only then should a finer grit be used, perhaps 120 or 240 to do the final shaping. If you change to a finer grit too early the job will take much longer but more importantly you are more likely to be just smoothing off irregularities. The more you then try to correct the shape, the more likely the shape will wander from what you want. Only when you have the final shape should you to a finer grit and on balsa I rarely use anything finer than 400 and mainly to simply takeout the earlier sanding marks.
When sanding it pays to look at the job from many angles. If the part has a smooth convex then there shouldn't be any flats or hollows from whatever direction it is viewed. If you do find irregularities, mark them lightly with a pencil so you don't loose them and do a bit more work.
The job was to fit a hard 3mm plywood base which protects soft edges of the balsa. I did not do this when I made the plug for the Atom Special canopy and the shrinking force of the heated plastic bottle completely crushed the corners.
For moulding a canopy I have seen on this forum that getting a really smooth finish is not necessary. Having got this far however I may use this as a plug to make a mould. I can then make GRP canopies as often as I like or use parts of the mould to get compound shapes. For this reason I have painted the plug but also as soon as you paint something in a solid colour it will tell you if you have got your shaping right and give you a chance to make minor adjustments.
Now waiting to find a suitable bottle to shrink over it.