Mirus Build Blog

[Denis Watkins]

Very smart Manny ditto Jim, anyway, looking back through the thread on props

My OS 40 just about flew a 10 x 6 prop so 10 x 8 could be tricky in my view.

So the .36, like you say 9 x 6 ideally with others on standby

This is an excellent build Manny

[ron evans]

Smoke on MR....

[Nigel R]

That was fast!

Much like the model, I imagine, it looks quick standing still.

I like the colour scheme too.

[Anthony Pattison 1]

Hi Mannyman

Mirus looks great, how heavy is it?

Do you have a vinyl cutting machine for the PC or is the cutting done on a Pro machine?

Tony

[Mannyroad]

Well, what can I say, but thank you very much for all your gracious comments, I'm somewhat bowled over.

Just got home and weighed it, ready to fly at 56oz. Wing area is 460 sq. in. which is 3.2 sq. ft, so the wing loading, by my figures is 17.5oz/ft2. Ok I reckon, even though i possibly build a tad heavier than some.

As for the vinyl cutter, I use a Sillhouette Portrait, coupled to my computer. I draw my vinyls up in AutoCAD and import it into the cutter software where I then scale it to the right size, though if you haven't got a CAD drawing package its possible to draw in the portrait's own software, or import a picture and trace it. The roundels are referenced overlays, though I had an accident and lost the referencing, so resorted to applying soapy water to the white part of the roundels and overlaying the blue, moving it about till it aligns, much the same way we use Solartrim and the likes. The RAF font was drawn in CAD.

As for fast build, I'm not sure. After all, its an easy build and I certainly know one guy (you know who I mean pal) who can knock spots off me for fast building

Anyway, guys, hope you enjoyed the build, I certainly did, and thanks again for looking in and leaving comments, all much appreciated.

Edited By Mannyroad on 22/02/2017 18:49:11

[Alan Pennington]

Hi Mannyroad,

As everyone has said a job well done. When is the maiden flight?

Cheers Alan

[Mannyroad]

Thanks Alan,

Not quite sure yet. Weather's a bit unpredictable and I fly off the beach so have to get the tides right too.

I've a couple of other new builds I haven't flown yet, so must get down the beach soon.

If you build a Mirus, kepp me posted.

[Alan Pennington]

Will do Mannyroad. But not for a while, got to much to do on the house over here. Still trying to finish a model called the Pacer but to much is getting in the way.

Cheers for now Alan

[David Foley]

Well done, wish I could build that fast. Colours look realy well.

Dave

[Mannyroad]

Hi guys,

Well, weather's been up to its usual tricks and, as I fly off the beach, this and the tides have to work with each other to be able to fly. So no maiden yet of the Mirus.

Anyway, to stave off boredom I've been busy re-drawing the plan of the fuselage for an electric version. its pretty much sorted now, based on using a particular HK motor. my problem is that I'm not very experienced with electric setups and though I've read back issues of the RCME to try and get a better handle on this subject I'd still very much appreciate the view of any of you guys who are big into electric.

The Mirus (i.c. version) has come in at 1600gms / 3.5lb all in, ready to fly. I gather that for a fast flying model I need around 200w per lb., so 700-750w should be about right, which is roughly equivalent to a 0.40 i.c I gather. Now, I want the electric version to go really fast, kind of like a pylon racer I guess, but I'm not sure if 200w / lb would give me this.

I have based the plan on a HK Aerodrive SK3 4240 - 740kv motor which runs on 4-5s lipo, has max. output of c.870w and max. current of 50A. My problem is that I'm not confident that I'm on the right track and I don't want to go and buy the motor and battery if its not going to give me the results I'm looking for. The same motor also comes in a 620 & 530kv version with slightly lower power and amp specs but I have made the assumption that I'll need the 740kv motor to get the prop spinning fast enough for fast flight.

I plan on using a 5s lipo to keep the amps down so I get a decent flight time. I already have a 60A & a 70A esc which i think will be ok.

As for the prop, I was expecting to be needing one of high pitch, like a 10 x 8. One review tested the motor, with the following results:

tested on brand new TGY 5S 3000mah 30C (fully charged):
1. 11x6 Cam Carbon (Aeronaut) 2780g Thrust, 38Amps, 770W
2. TGS e 11x10 2830g Thrust, 48Amps, 930W

Can anyone reassure me my thinking, setup-wise (motor esc,battery,prop), or suggest any alternative, before I buy the wrong gear?

 

Edited By Mannyroad on 12/03/2017 20:34:28

Edited By Mannyroad on 12/03/2017 20:37:08

[Alan Pennington]

Hi Manny,

Did you have to make much changes to the front end to covert it to electric?

[Mannyroad]

Only tweeks really. Kept the wing seating/retention the same.

Am hoping someone can help me with my electric setup query above. tweeked the plan for the HK Aerodrive motor and also did an option for the HK Donkey ST4010-820 too. But I need advice.

[Anthony Pattison 1]

Hi Manny

Well the electric details you give all look very workable to me. The static thrust figures for the weight should be enough (!) and with a horse power (740W) on tap it will be fast that's for sure! From my experience with an OS32 on full chat (about 1hp) you will need a fair bit of downthrust so do make provision to adjust this if you can....

Tony

[Mannyroad]

Thanks for your comments Tony. Are you suggesting that maybe I'm over-cooking it?

By the way, yes, I've built in 2 degrees of down and right thrust and that works very well on my older Mirus.

[Anthony Pattison 1]

Hi Manny

I don't think you are over-cooking it if you like very fast. Great thing about electric is you can easily adjust performance to suit what you want. With your setup I think you have bags of performance and by reducing cells or smaller prop you can reduce power if you want a bit less performance and longer duration... Post some pictures of new build? I now have 3 Mirus-us-us-es to sort but 1972 Triumph MOT tomorrow and still trying to sort workshop to take new lathe.... Not sure when planes come back to top of list!

Tony

[Mannyroad]

Excellent, I'll get the motor and batteries ordered up. Once I get going it won't take long but I've a couple of bikes too that need some attention for the Spring, and all the dreaded house jobs

Yep, will post a couple of pics but to be honest, apart from a lump of ally not sticking out of the front it won't look any different because I'm using the same livery scheme so i can just swap the wing over. Looking forward to trying the electric version though as I've not flown much electric stuff at all.

[Alan Pennington]

Hi Mannyroad,

Have you had the Mirus in the air yet?

Alan.

[Mannyroad]

Hi Alan,

 

No, not had much opportunity yet with hols and sorting out motorcycles for this season. Also, tides and weather haven't been pulling together for me to get down to the beach to maiden it. Might get a chance in two weeks when we are on neaps.  TBH I expect it to fly pretty much as well as the Mirus I already have and fly, but we shall see.

Finished the re-work of the fuselage plan for the electric conversion so am going to get cracking with an electric fus this week hopefully. If my calcs are right the battery will end up centred right at the CG point which is perfect. Will put a pic or two up on the forum when i've completed it, which might be just as the neaps arrive, so could have both versions ready to maiden.

Edited By Mannyroad on 17/04/2017 19:04:37

[Alan Pennington]

Hi Manny,

Do you race the bikes? Sounds good about the Mirus, photos will be good of the electric conversion and of the flying as well.

Cheers Alan.

[Mannyroad]

No, don't race them, just sports/leisure riding. Been building a custom bobber and that's consumed a fair amount of my time, but it's finiahed now, so have time to get back to flying/building stuff.

I'd love to video the flight of the Mirus but I'm not really well up on this stuff. I don't have a video camera and certainly nothing with enough zoom capability to show the Mirus in any other form than a dot in the sky. Will do my best though, when the time comes

[Mannyroad]

Hi Guys,

Well, been busy sorting out bikes and cars and stuff but eventually managed to find a bit of time to have a go at the electric version of the Mirus. I'm quite pleased with how it has come out, though i found myself making a number of changes to get it all sorted.

Below is the finished plane, alongside the fuselage of the IC Mirus I built in the blog. The wing is transferrable between fuselages, which might be good as it allows me to swap over to IC whilst the batteries for the electric version recharge. Well, thats the theory at least. Also put in a pic of my full squadron of mirus' too.

I managed to get a couple of vents up front by the 'firewall' which means i'll get some good cooling air right alongside the motor body, hopefully. was intending not to have these as i thought they might look a bit naff sticking out of the side, but I thought the motor might get a bit warm, batting along on full chat. I was going to use one of those vented spinners but, from what I've read, evidence would suggest they have marginal if any real cooling ability. so vents it was. Stuck a tail vent in to allow the air out. Will let you know how it performs after testing.

Just need to check the CG now, before testing.  I calculated the battery position, offsetting for the loss of the IC engine, tank, throttle servo & RX battery, against the substitute gear (elctric motor, esc & battery).  The calcs placed the battery pretty much central to the desired CG so that will be beneficial should I opt for alternative battery makes, with different weights, as the battery is the chief factor in the calc, being 620g!!

If anyone wants any photos showing the main changes made, let me know and i'll post up pics. I was working from a revised version of the IC plan but found I still needed to tweek that here and there; will now update my plan to reflect the changes.

Setup as installed is the HK SK3 4240 740kv motor (which if I recall will give me 870watts on a 5s lipo), 60 amp HK Plush esc, 5s 5000mah Lipo. I'll see how it performs with a 10x6 APC-E prop up front (haven't put the watt meter on it yet to see what it draws static). Will say this though, I don't fly much electric, being an IC man, but boy when I nudged the stick to half throttle the plane nearly pulled my arm off! Am well impressed so far; reckon it'll be quick, though having the 5s 5000 battery is causing a weight gain I'd rather not have.

One thing I'd like to ask you electric buffs: I've read a few articles/threads on lipo discharging in flight and it seems I shouldn't discharge below 80% of battery capacity, i.e 4000mah. Is this correct? I've always believed that the esc's low voltage cut-off prevented over discharging, hence it cutting power to the motor before battery over-discharge. Is this not correct? If it is, them why do I need to worry if the esc will handle this aspect for me? As I say, I've not dabbled much into electric, the Cartoon Cutlass and my Gonzales being the only two electrics I've flown. help on this welcomed please.

Edited By Mannyroad on 18/05/2017 14:36:33

Edited By Mannyroad on 18/05/2017 14:46:47

Edited By Mannyroad on 18/05/2017 15:00:22

[Jimbo565]

Very nice Mr. Manny,you will need your 20/20 vision to be on top form when that missile is in the air.

[Alan Pennington]

Hi Manny,

What is the weight differences? Looks great though.

Alan

[Mannyroad]

Hi Alan,

Just weighed it. It has come out at 2000g (4lb 6oz) dead, 400g more. The battery adds a lot of weight. Don't know enough about electric flight to know what capacity I can get away with for a 6-8 minute flight, especially given that you can only use 80% battery. The 5s 5000mah lipo is not far off 1.5lb!!

Some of the changes I made to the electric version added weight too, like adding 3mm ply for the fus bottom, with some small spruce strip around the battery hatch for strength during landings, given most of the bit that scrapes along the floor is hatch. Also there is a sizeable 3mm ply battery tray to carry the battery on bumpy landings, it being a brick.

Still, I was very surprised at the thrust it seems to generate, so it'll move fast enough to carry that extra weight; just wonder how fast its going to come in on landing. gulp.

[Alan Pennington]

Hi Manny,

Hope you get them flying soon.

Cheers Alan