Mirus Build Blog

[Mannyroad]

Ok, so I've now cut out the rear fus top sheet and glued on the balsa strips each side that will help support the fin when glued in. I've also installed the servo tray, made from some scrap oak strip and installed the elevator and throttle snakes. Had to drill through the engine mount for the latter.

 

I 'm sure some of you are now thinking that the front end looks a tad wonky, but that's intentional. The firewall has been set to give 2 degrees right and down thrust and the engine mount has been set off centre the right amount so that when the engine is fitted the prop driver lies on the centreline of the fuselage, which will keep the front end symmetrical after I've finished the nose and balsa bashed it. Other plans often show the mount central but once side thrust is introduced I've often found that the spinner is off centre and the nose is never quite symmetrical. Rightly or wrongly this worked fine on the last Mirus I built so I've stuck to it. And the fuel tank still fits just fine.

Next job is to sheet the bottom of the fuselage, well, thats the bit I wanted to do tonight at least. The weights are just there to stop it moving around when I'm sticking pins in and to keep it nice and flat on the board while the aliphatic dries.

You've no doubt spotted my 'poor man's Permagrit'. That block of wood with 180 grit glued one side and 80 grit the other has stood me proud for many years now, although its looking pretty tired now and has already been replaced. i've all sorts of shaped pieces with two grades of grit on each. You may also have spotted those multi-coloured glass beaded pins. Avoid them like the plague. I thought I'd spotted a bargin on that well know auction site and duly ordered a load, only to find all the glass beads come off. I now have the T pins; much much better.  By the way, in case there is anyone watching who is totally new to building, the reason the pins are all stuck in at opposing angles is that it keeps the balsa securely held down, like skew nailing.  hope that wasn't too basic.

 

 

 

Edited By Mannyroad on 13/02/2017 21:23:45

Edited By Mannyroad on 13/02/2017 21:31:04

[Mark Kettle 1]

It's coming on quickly MannyRoad.

[Jimbo565]

Mr manny

If I knew where you lived I would pop around for dinner one night,your kitchen cupboard is better stocked than mine.

Mirus is looking good.

Stay with it.

Edited By Jim Carss on 13/02/2017 21:35:27

[Mannyroad]

Haha! Cheers guys. As you'll know Mark, these birds are a fast build.

[Alan Pennington]

Hi Mannyroad

How is the build going?

[Mannyroad]

Hi Alan, done a wee bit more tonight.

I need to sort fixing the ply nose ring and liked how Peter Miller approached this with one of his recent projects, so am copying his technique. So I've fitted a prop and JP Accessories 2 1/4" spinner (perfect profile for thie Mirus nose) to the SC32 and measured how far, behind the face of the prop driver, the back edge of the spinner sits. Its a couple of millimetres. So, I've knocked up a ply plate, recessed on the back face by 3mm with a forstner bit, and fitted it to the engine. The rear face of the thick ply ring now represents a face 1mm aft of the back of the spinner.  To this I've masking taped the 3mm thick ply nose ring. Later I will drill the engine mount, fit the engine and see how the land lies, so to speak. Hopefully with the engine mounted in the best place, allowing for pipework to come through the firewall, the ring will sit nicely on the front of the fus cheeks, ready for glueing up.

 

In the meantime, I've glued up the rear upper fus sheeting and the balsa triplers for the wing seat. All simple stuff really.

Edited By Mannyroad on 14/02/2017 22:51:31

Edited By Mannyroad on 14/02/2017 22:53:23

[Alan Pennington]

Just bringing it back to the top again.

[Mannyroad]

Nice one Alan.

Ok ,well, slacking a bit tonight as all I've got around to doing is cutting the ailerons and fixing the wing TE's. The centre section of TE, over the width of the fuselage is removed and a balsa infill piece is added, whic I have radiussed the edges so they will blend into the rads that I will form on the fus corner edges later. Need to radius it now because I will be glassclothing the wing joint, so it won't be possible to rad it after that. Last Mirus I built I used wing bandage but reading forum threads suggests that glassclothing is better as it is less visible on the finished model.

Before I glue the TE's I have to cut off the section that forms the ailerons; these will be tack glued to the false TE with 3 spots of cyano so I can sand them in to the false TE's later, once the TE's are glued on. Once the ailerons/TE's are all sanded up to blend with the wing profile I can add the 12mm med balsa wing tips and sand those in, before glassclothing the whole wing.

Ailerons and TE's glued up, weights to keep everything flat on the underside and T-towels to prevent marks to the obechi veneer

 

 

 

 

Edited By Mannyroad on 16/02/2017 00:01:13

Edited By Mannyroad on 16/02/2017 00:02:44

[Alan Pennington]

On the top again.

Looking good Mannyroad

[Mannyroad]

Ok, so today I've done a bit more. Sanded the ailerons & TEs, so I thought I'd do a bit on the nose of the fus, but spotted I'd not quite got that right. Turned out that once I'd decided that the furthest aft position for the mounting of the engine, to give some room for the fuel pipes to come through the firewall, was just a bit too far forward for the ply nose ring to sit on the front of the fus cheeks, so had to add a couple of bits of scrap balsa to make up the shortfall. Once sorted it needs two short pieces of 9.5mm balsa fillets to glue the ring to the cheeks. Once they are dry I will add infill fillets top and bottom and infill between the cheeks at the base of the engine bay with some 9mm balsa, before completing the bottom sheeting of the fus through to the front. This will give me plenty of balsa to carve away to blend into the nose ring smoothly.

The F clamp just squeezes the cheeks in abit to get a bit more glue area for the nose ring. It doesn't matter that the balsa isn't protected from the F clamp as a lot of this will be planed off.

On my version of the Mirus i didn't want 3 bolt fixing for the wing, drilled down the centre of the wing. I'm having an 8mm dowel fixing up front and just th one wing bolt aft. So I marked up the F2 position and knocked off another 7.5mm for the 6mm hard balsa and 1.5mm ply laminate that will help strengthen the wing joint. The cut out width was widened to fus width plus 4mm to allow for 1.5mm linings to the sides of the wing pocket.

In my excitement to crack on I forgot to add the 1.5mm lining to the front of the balsa before drilling, but no matter I'll add it later. Before drilling the wing for the dowel I stuck some foam tape onto the wing seats to set the wing close to the right height for when I put wing seating tape on the wing seats.

[Mannyroad]

So, here is the front of the wing, with 30mm x 8mm dowel epoxied in and all ready for glassing. 1.5mm ply now added too.

[Mannyroad]

Bump. Did this because I've put an explanation re the Mirus plan on my other thread, below in the list.

[Mannyroad]

Bench ran the new SC32 this aft. Prop lightly brushed my finger, at full chat, whilst adjusting the main needle. Close.

[Alan Pennington]

One nill to the prop.

[Mannyroad]

Just weighing up the tank bay top sheeting, which is 9mm, and realised that this will get really thin close to F2, thickening up quickly further forward. So have added a bit of scrap balsa to the front of F2/2A.

Also glued in the engine bay bottom sheet too and decided there isn't room for the 9mm fillet pieces I was going to add around the nose ring; not needed anyhow. Oops, photo missed that bit. So, ready for fuel proofing tank bay, fitting top sheet and then balsa bashing the nose.

[Mannyroad]

Bump.

[Alan Pennington]

.

[David Foley]

Great build. Remember this model from my youth. Looking foward to your finished model and test Flight.

Dave

Edited By David Foley on 17/02/2017 02:01:12

[Mannyroad]

Thanks David. Nice to have you on-board. I'll be adding more later, after I've skinned the wing today.

[ron evans]

Hi Mannyroad

Watching with interest too. Just got to love that wing shape....it's doing 90 sat on the building board

Ron

[Anthony Pattison 1]

My first trainer was Cambrian Instructor around 1982. Second model was 36 inch mirus with OS 20. Model wasn't too fast and very stable. Visibility wasn't that great as it was camouflaged but my eyesight was better then! Built a one piece version of it about 2002 with wing in middle of fuz and along engine thrust line. Was overpowered with OS32... Fantastic machine and I'm building an electric one at the moment.

[Stuphedd]

I have just been reminded by an ex club member that he has the fastest Mirrus yet to be seen , It is powered by a piped Leo 37 ? and is propped 8x10 !!! He now flies with one of the Leicester clubs ( where I guess sound ? is not a problem !!)

It has no thrust whilst stationary hence it needs a tame javelin thrower to get it air born But it goes like the "wind "

you will love it ! so build 2 whilst you are at it !!

cheers

[Mannyroad]

Hi Ron, Anthony & Pete, nice to have you along.

Ron, yeah its a fab shape isn't it. I'm planning to finish it with a hint of the Red Arrows livery too; looks great on the computer. Already cut the vinyls in anticipation.

Anthony, I'm curious about your mid-wing version, sounds interesting. Have you a photo? My current Mirus is powered with an OS Max 32SX and that is a good size I think. I have a 9x7 prop on it so it goes well enough.

Pete, I really must gen up on props. I've never really quite got my head round why you might chose a 10x5 over a 9x6 for a .32 engine, the first for sports and the second aerobatic. You comment that the 8x10 has no thrust while static. i don't quite follw you as i would've thought that the 10 pitch would kick back a lot of thrust.

[Mannyroad]

So, what's new?

Well, I fuel proofed the tank bay and glued the top sheet on. Once dry I planed and sanded up the nose (note: the part of the sheet near the wing still needs a lot planing off, but I wanted to get the nose done), temporarily fitted the engine so i could mark the areas to be cut out for the exhaust and main needle. I also marked the rear exhaust allen bolt position on the port cheek, by sharpening a bit of 3mm piano wire and poking it back through the rear exhaust mount hole, continuing on to bore through the cheek. This marks the right spot to open the hole out to around 5mm. Without this hole one can't get the rear exhaust bolt in.

When I'd finished sanding up I wasn't quite happy with the final blending in around the nose ring so used epoxy with micro-balloons to add more material and re-sand up to get a better shape. Worked out ok in the end.

Fitting the engine showed me that, at full throttle, the throttle linkage would catch the balsa fillet behind the nose ring so I used the dremel to drum sand some away. Sorted.

In between I glued the 12mm sheet balsa wing tips on with 5 min epoxy, shaped them up, removed the ailerons which were still cyano tacked to the false LE and started on the wing servo boxes. Cloud Models, who did the wings, provided me with their standard wing servo box pack for their C2K Wasp (at my request). This comes with two templates, two lids in 3mm ply and a pack containing screws and short dowels, the latter going in each corner of the servo box to provide something to screw into.

I marked up the line of the servo lead groove, pre-cut inside the wing and marked a line across the wing from the start of the aileron, helping me position both boxes. The ply template (with 4 holes in) is fixed onto the wing skin and then one drills carefully through the veneer and foam, trying not to go too deep. Once through the veneer i recommend carefully removing the foam with the drill loose in the hand. this way you can feel when you reach through to the upper veneer, and stop.

Once done, the dowels are epoxied into each corner remembering to set them low to allow for the lid. Then cut out the veneer and hollow out the foam to make the servo box. I use an old soldering iron to tidy up areas of foam where a sharp knife won't quite reach. You can see the servo lead duct in the corner; my line was slightly off, thankfully. Sorry about poor photo.

The wing is quite thin in this location so its necessary to remove all the foam right through to the upper veneer. I strengthened this with 0.8mm ply once i'd removed all the foam off the wing veneer properly. With both boxes done and the wing tips now done, I can now strengthen the wing joint with glasscloth. Tomorrow's job.

(Wow, all those edits; really must learn to proof read my posts before posting, haha!)

Edited By Mannyroad on 18/02/2017 00:21:41

Edited By Mannyroad on 18/02/2017 00:22:57

Edited By Mannyroad on 18/02/2017 00:24:00

Edited By Mannyroad on 18/02/2017 00:24:56

Edited By Mannyroad on 18/02/2017 00:27:00

Edited By Mannyroad on 18/02/2017 00:29:28

Edited By Mannyroad on 18/02/2017 00:32:18

Edited By Mannyroad on 18/02/2017 00:32:55

[Anthony Pattison 1]

Hi

Currently away from home but will try to post some pics of old Mirus models when I get back next week.

Tony