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GTC by Levanter

Been on my list for a while now.

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Ron Gray11/03/2018 12:59:21
851 forum posts
213 photos

@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.

Levanter12/03/2018 10:05:01
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721 forum posts
351 photos

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

p1040842.jpg

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

Ace12/03/2018 10:51:43
181 forum posts
14 photos

Great demonstration of a skillful builder sharing tips - very much appreciated thumbs up

Following and stealing borrowing ideas for my GTC build.

Levanter12/03/2018 14:22:44
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721 forum posts
351 photos

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

McG 696912/03/2018 19:38:55
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2076 forum posts
887 photos

Very neat build, young man.

I really like the way you're approaching 'possible future' issues. yes

... or is it 'future possible'... No lo sé... indecision

Cheers

Chris

Edited By McG 6969 on 12/03/2018 19:41:40

Levanter12/03/2018 20:30:45
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721 forum posts
351 photos

Chris
​Possible future please. Firstly we hope the issues are only possible and secondly they are in the future so I might get chance to head them off.

Saves!

​Levanter

Levanter13/03/2018 21:26:08
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721 forum posts
351 photos

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.
p1050247.jpg

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.

p1050008.jpg

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

Levanter25/03/2018 11:29:37
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721 forum posts
351 photos

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.

p1050005.jpg

​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

Ron Gray25/03/2018 11:43:14
851 forum posts
213 photos

Do you ever use wing seat tape?

Levanter25/03/2018 11:54:10
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721 forum posts
351 photos

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

Levanter25/03/2018 12:37:27
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721 forum posts
351 photos

This being my first twin build, the nacelles have given me a lot of food for thought. In my first few posts I looked at fitting retracts and possibly going for a trike undercarriage but there were problems positioning the gear in relation to the CG and generally a lack of space. The latter was not helped by choosing to use 4 strokes which are quite a bit longer than the 2 strokes on the prototype. This meant moving N1 back a bit and the cowl is longer. Hopefully the CG will still come out roughly on the money and if we are slightly nose heavy I could always fit a tail wheel instead of the skid as drawn.

​In the end I have made some fairly drastic changes to the design of the nacelles with the main reasons being to try to save weight, streamlining, ease of fitting to wing section and finally I wanted then dismountable although I am still not entirely sure why! Rather than go into detail of the changes here, I hope they will be better explained as we progress through the build.

p1050148.jpg

​The first major change was to hang the nacelle from the false leading edge as well as the main spars. This allowed me to think of the forward section going up into the wing between the ribs and the rear section being fitted up against the sheeting which in this area is virtually flat. This should make it easier but time will tell.
​By supporting the nacelle in this way it is no longer structural behind the spar so a lot of it can be in balsa to save weight.

​The only change to N1 was to move the hole for the tank and fuel tubes to bring the middle of the tank closer to the centreline of the carburettor. It also make the holes completely clear of the engine mounts.
​As far as the ply sides are concerned these are much shorter and the front section now has a slot for false leading edge. Although I calculated the position of this slot taking the wing taper into consideration it did need quite a lot of adjustment later on so in hindsight I should have left the slot for later. A much more serious mistake happened later to which I will confess in due course.
​The ply sides have my usual lightening treatment making the cut-outs by chain drilling and then cleaning up with a Dremel.

p1050149.jpg

Due to the wing taper the nacelle sides are slightly different inboard to outboard. Here the cut-outs have been cleaned up and the paper templates (previously stuck on with Pritt Stick) are being removed by damping with water. I am too lay to get up to get clean water so provided my glue brush water is not too glue like it works just as well. I have found that if you get the paper quite wet and don't rush, most of the Pritt Stick comes off the paper. I have also recently found that the Pritt Stick copies are slightly better in this respect as they don't stick quite so well in the first place.

​N1 is now ready for fitting the captive nuts for the engine mount.

p1050150.jpg

​The nacelle side were made as matched pairs (inboard and outboard) and held together for working on with 3M spray mount. I have not tried copies for fear of them being permanently stuck together. With 3M they separate easily and if necessary, any residue can be cleaned off easily with acetone.

​In the background you can see one of my favourites, my dusting brush. You can see that the stainless steel ferrule is wrapped with masking tape. The edges of the ferrule are sharp and if you have a beautiful surface already prepared, they are the ideal scratching tool. Taped up you can brush with complete abandon. This was one of the first tips given to me when I first started in a GRP moulding shop and all my dusting brushes are taped up.

Levanter

McG 696925/03/2018 14:53:10
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2076 forum posts
887 photos

Hi Levanter,

Still following this great build blog. yes

In fact, you're not building a Grumpy TC. To me it seems more like you are 'designing' your first twin engined craft... wink

Keep on the nice work, young man.

Cheers

Chris

Levanter25/03/2018 19:10:07
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721 forum posts
351 photos

Thank you Chris.

​It will certainly have all the Grumpy looks with the only external change being the raised aft deck. Most of the changes are internal and maybe even with home made tin fuel tanks. I have boxed myself into a corner and the 4oz Kavan tanks won't fit due to making the nacelles dismountable. In another thread I asked if it was possible to 3D print fuel tanks as that could be ideal. Before that though there may be some off the shelf squarish type tanks in the helicopter world or in boats. I have a feeling some acrobatic tanks are fairly square and maybe someone will come up with some ideas. I would rather practice on much smaller units.

​Back on the job then and there are some nacelle parts to stick together.

p1050152.jpg

​Here N1 is being glued to one of the sides. After a job in a shipyard I managed to squirrel away a length of extruded aluminium alloy angle. I checked it out and it was perfectly square and the internal corner was sharp. Ideal then for jigging bits together at 90 degrees.

​The former N1 now has the captive nuts which are pressed in using a small vice. This ensures that I can press them in dead square and have quite a tight fit. No need for glue with these and eventually the fuel proofer will seal them nicely.
​The small hole is for the throttle rod and is in a different position than shown on the plan to suit my 4 strokes.

p1050154.jpg

Here the other side is being stuck in place and immediately the corner blocks to provide extra strength ultimately for the engine support but importantly in the meantime for handling strength.
​The corner blocks are home-made from some rock hard sheet balsa I spotted at Leroy Merlin (B&Q esque) while on domestic duties. These sheets are reserved for spars, triangle stock and other tough applications. Good stuff and straight as a die.

p1050155.jpg

Time for a bit of belt and braces. Generally speaking I am happy with glued joints but I am hanging a heavier engine further out that the plan so here I am beefing up the joint where the edge-ply is glued to the face ply. The holes are 3mm diameter and the ply is 6mm thick so marking out needs to be quite accurate. The dowel are cane skewers which just happen to be a gentle tap fit.


p1050156.jpg

Here are the dowels sanded flush making a very strong joint.


p1050151.jpg

The engine mounts are Radio Active Size 19 - 30 and are a perfect fit for the OS FS 30 Surpass engines. The bearer arms however suffer from shrinkage making them hollow and slightly twisted. This shows up very clearly on the right hand mount which is not yet finished.
​The left hand mount has been sanded using the Permagrit and as can been seen is now flat and parallel. Now when the engine is bolted up it is fully supported and there are no twisting forces on the crankcase. Small details but I think they are important.

p1050157.jpg

These are the throttle servo mounts. They are a strange shape for reasons that will become clear later on. Eventually they will be glued to the back of former N2 but as N2 will be fitted when the nacelle is offer up to the wing they are both set aside for the moment.

​The cowl however can be completed as it only has to reference to N1 and the engine.
p1050158.jpg

Here the nose rings are glued to temporary formers that are bolted to the prop drivers. There are three spacers at 1.5mm thick which will give the required clearance between the spinner and the nose ring. The spacers are soft balsa which is easily cut through when the temporary former has to come off. Note the centrelines and the little pop marks so that the lines don't get lost.


p1050159.jpg

​Here is a better view of the nose ring. This nose ring method follows Peter Millers ideas and instructions as does the built up cowl which is to follow.

​Levanter



Peter Miller26/03/2018 11:13:47
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9065 forum posts
1042 photos
10 articles

Oh Dear. I have been missing out on this build blog and a few others. Don't know how that happened.

Looking great.

Levanter26/03/2018 19:10:41
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721 forum posts
351 photos

Just the cowls to be built now and because there is twice the number of a "normal" aircraft it is worthwhile setting up a bit to help with repeatability.

p1050160.jpg

​But first the engine has to be fitted temporarily. This holds the nose ring in the right place while construction is underway but it is also a good opportunity to check things like clearances and that the hole for the throttle control is in the right place.

​There are only two angles to make. The side pieces are the same angle front and back and the top piece has a slightly different angle but likewise the same front and back. Here we can thank Peter for designing many of his models without side thrust or down thrust making the nose ring and the firewall parallel.

p1050161.jpg

These are the two simple sanding jigs to cater for the two angles. The angles themselves can be lifted straight off the plan.

p1050162.jpg

This is how they are used. The jig is lined up just back from the edge to be sanded and lifts the piece to create the correct bevel by using a Permagrit on its side or some other square sanding block. To do the other end, the piece is reversed and turned upside down and sanded to the reference lines. The pieces need to be accurate in length to frequent offering up is the key to not taking away too much material. This method helps to keep the glue lines nice and tight which helps a lot with the strength but makes final sanding to shape a whole lot easier as well.

p1050163.jpg

​Here you can see the Permagrit on edge and one of the sanding jigs. The main point of this photo concerns the strip pinned to the end of the side piece. If the outside edge of the side piece was glued flush with edge of the firewall it would be impossible to avoid a hard line when fairing up without sanding into the firewall itself. The strip hold the side piece a set distance outside of the firewall so when it is sanded I can fair the curve tangentially and this results in a sweet fair curve. Here the amount outside the firewall is a bit more than usual as the firewall and plywood nacelle will be sheeted with balsa and this accounts for the thickness.

p1050166.jpg

​Here is one cowl all glued up and with internal triangle fitted to give extra thickness for when the outside is profiled. The engine is taking out at the earliest opportunity one the nose ring is stable and definitely no sanding beforehand.
p1050227.jpg

Finally we have two part-built nacelles with their rough shaped cowls. The holes are for a number of things including needle valve, slow running adjustment, choke rod and to access the screw on the throttle arm.

​We now have nacelles sufficiently far advanced to tackle the wing. In the instructions we have to adjust the positions of ribs 4 and 5 to be a neat fit for the nacelles. In my case this is doubly important as the nacelles will be fixed with screws and need to be a good sliding fit but without slop.

​On to the wings then.

Levanter

Levanter27/03/2018 19:37:37
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721 forum posts
351 photos

The wing is needed to finish the nacelles and of course being a shoulder wing aircraft some of the fuselage sits on top including the cockpit.

​As mentioned before I made a set of aluminium rib templates for my Oodallaly. All but one were the same and that is R1 which has the cut-out for the central servo on the bottom of the wing for Grumpy whereas it is on the top for the low wing Oodallaly.

p1050167.jpg

p1050173.jpg

​Cutting around the alloy is dead easy just remembering to keep the scalpel upright. Almost no sanding is then required and in no time at all you have a full set of these. This is the point where it clicked that R1 is different and this picture shows the wrong R1 before I threw it away to avoid getting mixed up.
The alloy templates have the positions of the spar slots scribed in but they are not cut out. This gives me the freedom to use different spar sizes and sections just using the rear scribe mark as a constant reference.

R1 has the slot for the wing dowel. It is not continuous because of the dihedral brace. I will be using individual servos for the flaps and ailerons but I have no idea what size of type to use if anyone would like to comment. Help please!
​The recess will instead be used to house the connectors for the various leads that will come to this point. I will be looking for advice on using a multi-pin connector for ease and neatness.

​R2 is also discontinuous as I decided to increase the length of the dihedral brace by one bay as I am hanging heavier engines than the two 15s specified. For some reason I forgot to make the hole for the servo leads but I did remember before gluing it in place. There are no other lightening holes because the flap servo will go between R2 and R3.

​R4 and R5 are Liteply to give me a bit more resistance to the nacelles coming on and off.

​R6 and R7 have solid sections aft of the spar as this is where the aileron servos will go.

​R8, 9 and 10 are standard but on a bit of a diet.

​There is not much of R11 as there just needs to be enough to glue it to the wingtip block in due course.

​The eagle eyed (of which there are many on this forum) will notice that the spar slots get shallower as we go outboard.

p1050170.jpg

​This is because the spars are tapered down to 2mm at the wing tip. The taper starts midway between R5 and R6 which is just outboard of the nacelles. The tapers were rough cut on the band saw and finished off with the Permagrit sanding in pairs to keep the edges parallel.

​The spars are probably Oregon Pine or Douglas Fir as they are too grainy to be Spruce. A surprising amount of weight was saved by tapering the spar and of course saving weight in the right place. I did wipe each spar with a clean rag soaked in alcohol before assembling but I have never had any problem gluing these material even is less than ideal environments. The tapered spars look really nice in situ and didn't take long to do.

​Levanter

Levanter28/03/2018 18:28:47
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721 forum posts
351 photos

The first major variation on the wings is that they will have flaps. The ailerons will still be the strip type but only extend from R6 to the wing tip. I am counting on them having sufficient authority and the trailing edge section that I have in stock is slightly wider in the chord so I will gain a bit of area.
​The flaps will be fitted between R2 and R6 but I want real barn door stuff and not just a personnel entrance so they are significantly wider in chord and recessed into the lower trailing edge capping.

p1050171.jpg

​Here is the lower trailing edge capping recessed to give me some more flap area.

p1050172.jpg

This close-up shows that the extremity of the recess is just supported by a rib and the aileron will take over from there.

​Incidentally seeing as it shows up well my standard building boards are 19mm multi-ply carefully selected for straightness. The surface is two layer of cork tiles which gives a decent thickness for the pins to grab. The joints in the tiles are staggered to keep them as flat as possible and given a quick dressing with the Permagrit to take of any nibs and ridges. My boards are clamped upright when in storage an as an example my favourite 1.2m board (4ft in old money) is flat and untwisted to less than 1mm in any direction. It is now three years old and although it has acquired a few interesting stains it is still doing fine. One day if it decides to go wonky I will cut it up in smaller sections for use with minor assemblies and tail feathers etc.

I have the plans copied so I don't have any guilt about cutting them up and take lots of A4 and sometimes A3 copies for specific details. Ordinary domestic cling film is then stretched over the plan and taped in place. If I ever get to build bigger then I will have to progress to catering sized cling film. It is so incredibly cheap and easy that I gave up saving the backing from covering films a long time ago.
​Oh and another thing. I have learned to be cautious if I ever use thin superglue. It can run down the pin and through the cling film and left me with a conundrum about which bit to break.

​Levanter.






Peter Miller28/03/2018 19:07:58
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9065 forum posts
1042 photos
10 articles

Really with strip ailerons most of their effect is out towards the tips anyway.

Levanter28/03/2018 20:00:37
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721 forum posts
351 photos

Peter
I suppose if the roll rate was a bit slow I could always mix (Ha Ha because I haven't got a clue how) the flaps individually to the ailerons in normal or max'd out flight and have them come down together in a different flight mode on a knob or a switch. Academic really I suppose but might be fun.

Peter Miller28/03/2018 20:13:11
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9065 forum posts
1042 photos
10 articles

That sounds horribly complicated. I wouldn't like totry it.

Just increase the throws would be my answer

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