Mirus Build Blog

[Stuphedd]

just a quickie on props, I am no expert but the 10 " pitch on the prop basically means that the prop will be stalled when there is no forward speed , angle of attack and all that is to great, bit like a wing at too great er angle of incidence and it would be acting more like a paddle than a prop , its not until the forward air flow is "fast " enough does the prop bite, and then its OFF !!!

Thats why your 10x6 is OK for the slower sports plane where the 9x7 is better for the faster aerobatic plane .

I am sure the aerodynamisists amongst us can explain it better , , but its why most pure jet engines have flow straightener struts in front of the compressor to stop the pre-rotation of the airflow .

cheers

[Mannyroad]

Ok, it must be something like sailing, where the wind direction appears to shift forwards of true win direction once the boat is moving and creates 'apparent wind' direction, such that the 'apparent wind' direction increasingly swings round forward as the boat gets faster. Cheers Pete.

[Mannyroad]

Right, well the wing has now been glassed, really only to strengthen the wing halves joint rather than using a bandage like the last Mirus I built. on that one the bandage was still fairly visible even after trying to blend it in with filler. Having read a few thoughts from others about glassing the joint I thought I'd do that this time. Others describe their technique as laying up some kind of diamond pattern, though whilst I think I follow, I'm not quite sure how that would work on the Mirus wing shape.

So what I ended up doing was laying a 75mm strip down the wing joint itself, this being the width of the fuselage. Once dry, which is very quick, I lightly feathered the edge of the cloth with 320 grit and then applied a second strip/layer that was 200mm wide. Again once dry I feathered the edge and then glassed the whole wing. So I end up with 3 layers of cloth, top and bottom, over the wing joint and it doesn't show.

For glassing I've always used a product that Falcon Aviation used to make about 10 years ago, called Skin-Crylic, an acrylic based white solution that dries very quickly. I'm not sure they make it anymore but I still have a big bottle left. I suspect it might be similar to Poly C, which I've never used. Anyway, I just need to apply a couple of coats to fill the weave and lightly sand with 600 grit till smooth, after trimming up.

Hit a slight snag with the servo boxes. I'd realised early on that the 3mm ply lids were going to be too thick and would leave insufficient room for the servos, so I made new ones out of 1.5mm ply, using the ones supplied by Cloud Models as templates. Unfortunately, after strengthening the upper veneer with 0.8 ply, I found that the 9g MG servos, at 11.5mm thick were too deep -just!! So I had to change my plans and use a couple of 10mm deep thin wing servos I had. These just fit once stuck to the underside of the lids.

There isn't a lot of room in the servo boxes for the bigger thin wing servos, which use more space than the 9g servo, so it was a bit of a squeeze accommodating the servo leads. Not being much room I had to cut off the rear servo mount lug, but it isn't needed anyway. Ended up heat shrink wrapping the leads and glueing them to the lid. Also, the servo duct in the wing is round and too small to pass the 300mm extension lead plug through, so I have had to cut the other end off, so I can 'fish' it through once the wing is covered. After that i can re-solder the plug back on. In the meantime, to keep things tidy I've heatshrunk the extension lead connector to the servo lead connector and cyano-ed it to the servo (space really is at a premium). Tidy enough.

So, I'm at the point of needing to get things covered now. Drew up vinyls in CAD and these are all now cut, so I'm eager to move on with covering as soon as. If I get the wing sanded tonight I could get a good bit of the covering knocked off tomorrow, hopefully. That would be good

By the way guys, if anyone fancies having a go at this model but needs the plan, message me as i might be able to point you in the right direction for one

 

Edited By Mannyroad on 18/02/2017 19:13:27

Edited By Mannyroad on 18/02/2017 19:14:59

[Ace]

If you lift the small tabs on the male plug you can pull the three pins out, pass them through and then re-insert them into the plug.

[Mannyroad]

Ace, cheers for that, haha! Do you know what, I actully knew that but forgot. A brain fade moment i guess. already snipped the damn leads now. never mind eh, good soldering practice for me.

[Alan Pennington]

Hi Mannyroad,

I have read that something like Ronseal is ok for glassing as well. Never tried it though it's one of will do soon, as there is nothing so far you I have found here in France. But I keep looking.

How's it going with the build?

[Alan Pennington]

Mannyroad forgot to ask what did you glue the wing servos in with.

Edited By Alan Pennington on 19/02/2017 17:50:14

[McG 6969]

@ Alan,

If you're looking for a Ronseal comparable water based/acryl varnish in France, look for the 'V33' brand.

Their 'Vernis dur pour parquet' or even better 'Vernis Marin' fills the bill perfectly.

Cheers

Chris

Edited By McG 6969 on 19/02/2017 18:22:12

[Alan Pennington]

Hi McG 6969,

Thanks for the information I will check out the DIY shops.

Cheers Alan

[Mannyroad]

Hi Alan, the servos come with double sided adhesive foam tape. Strong too, so i used that to stick them to the lids.  As for the use of Ronseal Diamond Hard Floor Varnish, yes, I've read that too.  Will do a test at some point in time, though until the Skin-Crylic runs out I'm more than happy.

Well, its been a busy day covering today, though I used up my 2m of Solarfilm Poyester and hadn't quite finished the fus. So its off to the shop tomorrow so i can complete the covering tomorrow night and hopefully get the vinyls on.

Hinged the ailerons and elevator too with cyano hinges and got them hooked up to the servos. I decided to double bevel the control surfaces because I never quite seem to get a perfect finish when i try to top hinge them, which is my preference. The thin light strip you see in the photo is just low tack masking tape for marking the hinge positions.

Also re-soldered the extension leads to the wing servos, after forgetting I could remove the pins. Thanks again for the reminder Ace. Anyway, all back together now and tested.

Edited By Mannyroad on 19/02/2017 20:44:59

Edited By Mannyroad on 19/02/2017 20:45:27

[Alan Pennington]

Hi Mannyroad,

Looking good. Learnt something new about the masking tape along the te of the wing.

[Anthony Pattison 1]

Hi

Is there a CAD version of the Mirus now available? I have an old original which is actually very simple so doing a CAD version should be pretty easy I would guess. Ken Stokes died about a year ago and the design stems from early '80s so I doubt there is a copyright issue really? Have you seen the Model Geeks videos of Mirus on YouTube - they look good but the proximity of their flying site to the road and houses would worry me!

Strangely enough I'm just about to return from a ski trip with my sons and on Friday saw a couple of old Mirus (Miri?) for sale on BMFA classifieds. I bought the pair (£60) and had them collected by a friend yesterday. Looks like I really do need to get around to getting a couple of them back in the air - electric and i.c. I think.

Will post some pictures.

Cheers. Tony

[Mannyroad]

Anthony,

Copyright lasts 70 years after the death of the author/originator of the work. So yes, it still applies. Even if one signifcantly adapts or varies the original work, to qualify for Derivative Work status, is still problematic as , technically, such adaptations require permission from the author of the original work.

Its true, the original plan by Ken is indeed quite simple in form but even such a simple plan form takes quite a lot of time and effort replicating the paper information into a digital format. I know, I have done my own CAD plan of this model and, whilst CADing it, took the opportunity to make numerous changes to bring it 'up to date'. Even with these changes I still cannot avoid the copyright issue.

Edited By Mannyroad on 20/02/2017 19:47:33

[Alan Pennington]

Hi Mannyroad,

When you covered the wings does the covering stick well to glass cloth or do you coat the glass cloth with something first.

[Anthony Pattison 1]

Bored with trying to post pictures on this website now. How do you all do it?

Anyone who wants PDF of Mirus plan in four A3 bits email me.

I'll send pics of my old mirus and maybe someone else can post them?

I recall someone was selling Mirus plans on ebay some time ago but I don't have details now.....

[email protected]

Tony

[Alan Pennington]

Hello Tony,

If you send me your photos I will post them for you

[Anthony Pattison 1]

Think I might have ability to post some pics now - thanks for information guys..

This Mirus dates from about 2007 and is a 36” version fitted with OS32. It was glass cloth covered which made it too heavy really and it was overpowered and needed more down-thrust

[Alan Pennington]

Looks good Tony. You didn't say if you still have it or did I miss reading that bit.

Alan

[Mannyroad]

Hi Alan,

No, I don't coat it with anything, it sticks fine.

Nice looking 'Mirus' Anthony. Unusual to see a mid-wing version. i see you've got full span ailerons too, though I've not found this necessary. As Alan says, have you still got it? And it looks like guys can now get a copy of the original plan too.

[Anthony Pattison 1]

Hi everyone.

Unfortunately I don't have the mid-wing Mirus anymore - sold on ebay when I had to reduce models prior to building a new house. I now have three mirus-es which need a bit of restoration and intend the first one to be a copy of this mid-winger but with electric power. Trouble is finding the time - just bought a 'new' lathe which needs some repairs plus 1972 Trident and 1975 Moto Guzzi both need services and MOTs. One day I'll retire and have some time for playing with the toys!

Tony

[Anthony Pattison 1]

Forgot to say about the ailerons. I don't think the model needs full span ailerons really but I have used them on mine as I find it a bit easier to make the wings like this. In the past I have had problems getting the torque rod system working freely and yet have a positive connection where rod connects into the aileron - alignment of tube with hinge line can be a problem sometimes.

Tony

[Mannyroad]

Hi Anthony, yes bikes can take up quite a bit of time. My two keep me busy too, services and MOT's due, for new season.

I changed the aileron set up by going to servos in the wings as you've seen in my blog. Works well I've found but you have to be a bit careful opening out the servo boxes.

So, been a busy time since my last report on progress. Got the extra covering and finished the whole plane now. Added the 1.5mm ply plate for the rear wing bolt and also the 3mm ply wing alignment plate below this.

Got the vinyl set on and am pleased with the outcome. having said this, the Union flag is actually done using Solarfilm polyester, but second time around i'd do it in vinyl, easier.

Forgot the rear wing mount plate, so got this epoxied in. I used 10mm balsa strips under triplers as restrainers for the plate which helps set it just below snake level. Wing was popped back on and hole drilled for T nut. Flight battery sits underneath this plate. The brown wing seating tape is actually foam door/window seal tape; works quite well.

Stabiliser could now be glued on, after trimming part of covering away top and bottom. Final connections made for ailerons and elevator and throttle snake linkage sorted up front ready for engine install.

Engine installation is a squeeze but looks fairly tidy i think. Hit a small snag in that I will need an extension for the exhaust as it is touching the fus and won't quite nip up. No problem, will get one from JE. My other Mirus didn't need one surprisingly. Guess its down to how you plane up the nose profile. I found the JP Accessories 2 1/4" spinner profile compliments the nose. I tend to use a different pipe for the fuel feed just so i know which is which.

My tank is a Slec 6oz/180cc jobbie. Its slightly wider than the tank i fit in my last Mirus, so I had to sand the opening in F2 a bit wider. Also, it sits quite low in the fus, which i haven't found to be a problem, fuelling-wise, during flight in my current Mirus, but to be on the safe side I decided to file away a bit of the top of the aperture on F2 to raise the tank, which I've sat on foam.

Finally, radio installed. The polystyrene block retains the tank and the other foam retains the flight pack and gives a soft base for the Rx (stuck down with double sided foam tape). Just need to set up the radio and control surfaces etc now, check the CG and get it maidened.  Oh yes, but not before I fit those keepers missing from the elevator clevises

 

 

 

 

 

 

Edited By Mannyroad on 22/02/2017 00:25:58

Edited By Mannyroad on 22/02/2017 00:29:35

[Mannyroad]

Ok, so, after a 9/10 day build here's what its all about:

So, what's next? Well, I've decided that I want an electric version of this plane, so i'm going to knock out a quick nose job detail for an electric conversion and build another fuselage that can be interchanged with the wing; same decal set on both. Will keep you posted on that one. I'm just waiting for some advice on what would be the best set up for electric, which is not my field. Mark Kettle's been helpful in this respect and I'm hoping the Model Geeks might be able to let me know what their electric Mirus set up is. Don't have much clue on electrics, so any help would be good please.

[Jimbo565]

Very smart Mr manny,that vinyl cutter works well,very impressed.

[Ace]

Looks fantastic.

First cut to vinyl decals in just 10 days - mine will take 10 weeks if I am lucky.