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GTC by Levanter


Levanter
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Like the 1 metre yacht rigs in the background. Mine are in a box tucked away in the workshop and the Graham Bantock designed Rhythm I built some years ago hasn't seen either water or even daylight for some years.

Your organised and tidy working area (as well as the building itself) puts me to shame!

Geoff

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Geoff
​I would like boxes for mine but haven't got around to making any. Mine is a Topico and in dry dock as well at the moment. Might try and get back in commission for the summer.

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Mine is the red one, hard pressed with the medium rig. This was a regatta in Andratx harbour and the local club kindly let me join in informally before I got my registration, Just had to take the old sail numbers off. You should get yours back out on the water and have some fun. I will if you will!!

​Levanter

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You're very brave sailing in salt water. I always sailed on lakes and ponds with fresh water and it was impossible to keep things dry inside the hull, especially in a bit of a blow as in your picture. Most of us sailed using 27Mhz 2 channel systems and had to keep a stock of crystals to avoid clashes.

I'm guessing Andratx is the one in the SW corner of Mallorca? I first visited riding our tandem solo because my wife was tired after our flight. We were staying in a small hotel in the next bay to the east (can't recall the name) and I had a short ride solo over the hill into Andatx. It was a long time ago when I was both young and as fit as a butcher's cat

Geoff

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Now to put the fuselage jig to work.

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Here the nose is in the jig and it is quite a tight bend between F1 and F2. There was a bit of creaking going on so I put some razor saw cuts in the longerons while gently moving the clamps closer together. This stopped the protesting and we managed to get the sides touching F1 without a mishap. To help take the strain of the join onto F1 you can see two strips of balsa glued to the top and bottom edges. The bottom one was kept in place until most of the bottom sheeting was in place. The top had to be removed before starting planking but by then there was very little strain.

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​Another view of the jig in use with loads of rubber bands to hold the tops of the clamps together. In a way this is quite useful as you can adjust the amount of pressure by adding bands until the joints are fully closed. Incidentally the rubber bands are kept in an old chocolate tin. This keeps the light out which is enemy number one for rubber. The bands are now in their fourth year and all perfect except those that I gave an unfair amount of stretching.

​The sides of the fuselage behind F5 are basically a straight taper that needs very little force to close. The only thing is to be careful to keep the sides equally spaced and here, the centrelines left on the formers can be projected down onto the printed centreline to ensure all is how it should be. This is where I would have liked the printed lines to be finer for example.

Levanter

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Hi Geoff
​You are spot on and I reckon the place you stayed at was probably Camp de Mar or possibly Paguera. Either way I know those hills so yes, you must have been seriously fit. My cycling exploits are confined to the flat track between Port D'Andratx and the town of Andratx.
​Yes, the salt water did require some aftercare but the waves are fun along with the full sized stuff and of course the ducks!

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Going back to the centreline fixing points on the jig they serve two very useful functions. Firstly they can provide a positive stop to locate the fuselage longitudinally. If I now want to take the model off the jig for any reason I can put is back knowing that it is relocating in exactly the right place.

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​This is actually a picture of the tail end of Toot Sweet. Another Peter Miller design and a the most recent completion. At the far right of the picture you can see a temporary post. Later this will be removed to make way for the post of the fin. The temporary post is chamfered evenly and this chamfer locate in the slot of the SLEC clamps. It is made from the same stock as the fin post to ensure compatibility.


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As can just be seen on the extreme right of the above photo. This makes it very easy to make sure the rear sides of the fuselage are brought together exactly on the centreline but additionally it makes sure that the tail and hence the slot for the fin is truly vertical.

​I can now be sure that the fuselage is not twisted and that the fin will slot into place without needing any further adjustment.

​This is also a convenient time to make sure the tailplane seat is level. My favourite method here is to put a straight edge across the seat. The straight edge should be at least as wide as the jig board for best accuracy and then the measurements from the straight edge to the board should be the same both sides. Any minor discrepancy can be sanded out but more often that not, no trimming is necessary provided the previous steps are kept nice and tidy. I don't use a spirit level ever since finding out my table top was not that flat.

Levanter

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More work on the fuselage to prepare it for the planking over the nose and the rolled sheet decking. I have made the decking a bit higher than shown on the plan so F5b is correspondingly taller. The angle of the former is slightly arbitrary but I suppose a taper is necessary so that the wing releases itself if the bolts get sheared in an angry moment. If the former remained vertical I imagine the wing would jam causing damage to itself and perhaps the fuselage as well.

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Anyway the angle was taken from the plan using this adjustable bevel / protractor.


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​And transferred to a scrap of balsa used as a jig to give the angled former something to lean on while the glue dries.

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​The jig was tacked to the lower part of F5 with two tiny spots of glue and stayed in place until the angled former F5b was securely glued.

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After which is as snapped off hardly leaving a mark.

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F1 was fitted with a 5mm doubler (not on the plan). This was for two reasons:
​First it secures the ends of the fuselage sides which are only glued to the edge of a 2.5mm former.
​Second, it provides a wider bearing surface for the forward end of the planks. F3 at the rear end of the planking is shown with a doubler. Here you can clearly see the saw cuts in the longerons to help them negotiate the curve immediately behind the spinner,

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THis was also a good time to bore the holes for the snakes and fitting them before closing the fuselage with the rolled sheeting. The cross grained lower sheeting was already in place as this does help keep the fuselage in good shape.

​Levanter​

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No to the planking of the nose. I stuck to Peter's 1/4" planks (6mm for me) but the top of the fuselage side has quite a pronounced curve which I did not want to have to follow for the whole planking process. In a similar way to the garboard plank on a boat which is generally wider than the others and a strange shape.

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This the first plank in place and is wide at both ends and narrow in the middle. This allows me to use more regular shaped planks for the remainder of the job. Because the plank is wider than normal the back was hollowed out slightly with my curved Permagrit to sit tightly on the curve of the formers. As the remaining planks are quite narrow is not really essential to hollow the backs so I didn't. The shape can be seen quite clearly on the plank lying on the towel.

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More planks in place working from the top on boat sides simultaneously. The risk of distortion using balsa planks that require little force to bring them into place is very low. In boatbuilding with harder planks it is important. Anyway it is good practice. The masking tape was useful to hold the planks in good edge contact while the glue was drying.

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Another view where you can see that each plank is tapered so that each one takes a share in forming the compound curve. It may help to think about the construction of a wooden barrel where each stave is tapered at both ends. The stave are also bevelled so that the edges of the planks have a nice uniform joint. The actual geometry is slightly more complicated because the tapers are not straight lines but slightly curved. In practice this is not too hard to do at this scale by eye. In larger scale and full size the curves would be plotted and marked out.
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​Nearly done and this is the closing plank and very satisfying to fit. The tapers and the slight curve are evident.
​In planking terms the shape of Grumpy's nose is not extreme and it was very easy to make all the planks run full length. There are no inserts or wedges. Again it helps to think of a barrel which being "barrel" shaped of course is wider in the middle than at the ends. Therefor the circumference is longer in the middle than at the ends. It follows that if all the staves (planks) are continuous the planks have to be narrower at the ends as they have less distance to make up. The analogy is very close and very useful.

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Planking complete. There are no gaps and therefore no filler required. Also the glue lines are as thin as possible so sanding is easy. The shape is quite uniform so a minimum of sanding is necessary to get a completely smooth surface.

Levanter

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Thanks you for the commentaries above and before.

​Are you fitting four strokes Ron or are you scaling up with two strokes. I have seen mixed reports whether it is wise to invert four strokes and there are many doomsayers who would say a twin IC aircraft is asking for trouble. I am taking Peters reassurance from Peter that all will be fine.

I like inverted because of the clean lines but I have always checked to make sure the cylinder head will not be the first point of contact in a nose over. It was marginal on Oodalally so I am fitting slightly larger wheels to get more clearance.

​I like planking Chris and this is a small job. On bigger jobs that can take days it pays to have a diversionary task because it can become a bit tedious. There are only 17 planks on Grumpy. As it happens I have a particular liking for doing caps strips, good food, good wine and good company.

Levanter

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Planking can be quite satisfying but this is the only model I've had to do a lot of:

veronica hull 6.jpg

It's my 45" Thames sailing barge hull. Most of it is flat sided but the bow and stern needed a bit of planking. Being an aeromodeller it's mostly glassed 3mm balsa. The hull is more or less complete but it's been stalled for a couple of years whilst I get the courage to do the rigging and 5 sails!

As regards engines, I don't think there's a great problem using 4 strokes inverted provided you get the fuel tank height right to avoid fuel syphoning. However with a twin it would be electric all the way for me I'm afraid. Especially one this size. Never the less, with your fine building there shouldn't be a problem however you choose to go.

Geoff

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Some more work on the fuselage which turns to the rolled sheet decking at the rear. First job was to fix the small extra former F8a on the fore side of F8 to locate the spine. The spine is then securely held at the without interfering with the slot that will later take the vertical fin.

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​Here I do it the other way round from the instructions by starting at the top. The reason for this is the curve is most severe at the top so making this the closing joint has proved difficult to make neat on previous builds.
​Here the starboard side is being fixed to the spine with plenty of spare material to trim back against the slanting F5a (Yes I have made that mistake before!).
​The centreline was marked on the top of the spine and the port side masked with a run of tape. This makes it much easier to get the glue on quickly on the working side of the spine. Later the port side will need to be glued to the other side of the spine and it is unhelpful for the wood to be already smeared with glue or have blobs where the glue has squeezed out.
​The pins at the front and rear are simply to make a quick register to stop the sheeting sliding around and taking more than its fair share of the spine. The strip of wood is packing to stop the clamps digging into the decking surface.
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Here is a similar view without the clutter of the clamps. The glue line for the port sheeting is nice and clean.
​The wing clamping plate does not have blind nuts. The plate is made from high quality ply with many thin layers and on the underside doublers can just be seen to give a generous length of thread. The ply itself is drilled and tapped and the threads then hardened with cyano. The tap was then run through again to take out any furry bits and to true up the thread form. This will produce ample strength for the nylon wing bolts.

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​The tight curve at the top of the decking shows up very clearly. Here the port side has nearly been cajoled into place. The masking tape is used to induce the curve while the dampened balsa creeps around. It probably took three or four stages to get the curve fully developed but this was one by damping the sheeting with water. No ammonia was used and I have never needed to. The trick is to only damp the balsa in narrow strips where the bend is required. If the whole sheet is damp is becomes floppy and it will not wrap where wanted.
​The decking blanks were cut leaving a small trimming allowance so sand off at the joins with the existing fuselage sides.

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Back to the fore end and the sheeting conforms closely to the former F5a but in particular the top is nice and fair.

​Also in this photo is the packing block fitted to the wing plate and the holes line with thin walled aluminium tube. This prevents the edges of holes being "drawn" by the flexible nylon bolts if the wing tips get caught. The tube also acts as a sheer point so that in the event of hard impact the bolts will be encouraged to break cleanly at this point rather than stretch and pull causing unwanted damage to the woodwork.

Levanter



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@Levanter - 4 strokes for me but sidewinders not inverted. I’m sure that the majority of running problems with engines are down to poor tuning, wrong tank positions and incorrect or cheap glow plugs. Having said that, my first hand experience of glow 4 strokes has been with Lasers so I’m spoilt but I have helped fellow club members with their Saitos or ASP or SCs and whilst I’m no expert, problem solving has usually centred around the above.

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Just a few more details to add to the fuselage which is nearing completion as a structure.

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Here is the tailplane seat again marked with the centreline. The two strips of balsa are spot glued to the top surface to act as a jig. They stop the seat from going too far down into the fuselage because the glue grabs quickly. It is easy to push down slightly but hard to pull up to make any adjustments.

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​Here is the seat in place and held tightly together with masking tape.

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Here is the finished tail end with the slot for the post of the fin and at F8, the slot to locate the forward end of the fin.

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This is a repeat photo to show the importance of having the fuselage square and true before drawing together. This has ensured that the tailplane seat (located by the temporary balsa strips) is exactly level and no sanding or adjustment is necessary.

Levanter

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Thank you ace. I a enjoying every minute of it. Not all plain sailing though as a couple of bloopers will be revealed in due course!

​The fuselage is about to be put to one side but a couple things still to do.

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​Here is the nose block dutifully hollowed out according to Peter's instructions. Notice the arrow pointing down but actually should be pointing up! The slot is to allow fine lead shot to be poured into the block at a later date if required. I don't know whether any nose weight will be required as the four stroke engines weigh a bit more than the SC 15s on the original. They are also mounted a bit further forward having to make room for the rear mounted carburettor. If the tail ends up light I will fit a steerable tail wheel instead of the skid. Anyway I want to glue the nose piece in place and not take it off again to add weight.
​The nose block is slightly shorter than drawn because I added a doubler on the front face of F1 as I described earlier.

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The roughly blanked out nose piece is now glued on and ready for some profiling. The masking take (a best friend) protects the other surfaces while some aggressive sanding is done with the Permagrit.

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The nose block is now profiled but not finished sanded. There is a small allowance to sand off as well as rounding off the corners as I know the second it is finished sanded I will bash it on something so that might as well wait for later. The ends of the planks are now properly protected at least.

The doubler on F1 shows up well in this photo.

​Levanter

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Nearly ready to put the fuselage to one side. There is not a lot of detail on the plan concerning the undercarriage but people familiar with Peter's designs will know the ropes.

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​The bending is quite straight forward especially if you have a wire bender. Worth every penny. Here is one leg where the left hand end goes into the fuselage and the right hand is the wheel axle. It is not actually drooping like it appears and the illusion is because the gear is raked forward. Always work from one end of the wire and it is best to start with the fuselage end because that has to match with the woodwork. If there are any accumulating errors then it doesn't matter too much if the wheels don't end up in exactly the right spot (within reason) as long as the wire is the same shape from one side to the other. To help get this symmetry, do mark the bend positions on both wires at the same time and you wont be far out. Leave plenty of trimming allowance but here I have been a bit generous at the axle end. Better always to be a bit too long and trim than too short.
​There is a difference from the plan and that is the short vertical section inboard of the axle. I though I might fit spats and this will be where they are attached. If I change my mind it won't make any difference but I always have the option.
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This is its partner and now it is clear that the undercarriage wires cross the fuselage so the port wheel is anchored on the starboard side and visa versa. This gives the undercarriage some torsion suspension as well as its natural springiness. The bending is not accurate to the last fraction of a degree and some gentle tweaks will be done on final assembly to get the aircraft to sit right and to get the wheel pointing in the right direction staring the toe-in / toe-out discussion all over again. It is quite important to get the first bend accurate as this has to go up into the fuselage and also lie nicely across the fuselage bottom.
​Do not that where the wires cross under the fuselage one passes in front of the other. This seems obvious but important to take account of when fitting the supports inside the fuselage.
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​Here are the support blocks that will support the vertical sections in the fuselage. I find them much easier to fabricate than to drill a solid block. Here offcuts of the wire are used to make the correct gap between two birch ply block of the same thickness. This ply has to be hard and strong to take the reaction. The two blocks are glued to a thinner piece of ply as outright strength is not needed. In this case I have used Lite ply as it is much easier to sand. You will see that there is a wide block and a narrow block. This is to make sure that one wire is further forward than the other by the wire diameter so they can sit side by side under the fuselage.

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This photo shows the starboard block glued to the doubler, F3 and a ply base inserted in the lower cross grain sheeting. Very strong and provides accurate alignment.

Levanter

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  • 2 weeks later...

A week working away put a stop to the build and the blog but here we go again with a few more bits and pieces before moving on to the nacelles.

​Not shown on this plan but quite common on other of Peter's designs is a trebler on the inside of the wing seat. I like the idea of a trebler for two reasons. Firstly it creates a slightly wider seating area for the wing and is therefore slightly kinder on the wing sheeting. Secondly it gives a it more room for the covering to be securely stuck down.

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​Here the port side is being clamped in place and the starboard side is cut ready to go. I used 3mm medium soft balsa which gives me 6mm total thickness.

​On every build I have done so far, the wing seat has needed slight adjustment to get a really good fit to the wing section. A useful trick I found recently is to leave the top edge of the ply doubler around 1 - 1.5mm short of the wing seat line on the drawing. This means that when the seat needs to be sanded you are sanding the balsa only which is so much easier and quicker. I have also found it helps with getting good accuracy. If, when finished, there is a very slight groove above the ply it can be filled and smoothed off with light weight filler.

Levanter

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Hi Ron

​I have done in the past but find that it tends to creep and then invariably comes unstuck. What I tend to do now is try to obtain a really close fit so the load is evenly spread. To prevent the covering wearing through on the wing I use a strip of black gaffer type tape with the edge aligned with the outside of the fuselage. This gives me a quick visual reference that the wing is on straight. I haven't done a black covering yet so I get a good contrast but if I did I would probably use the grey coloured gaffer tape.

​Levanter

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