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Mar 18, 2013, 04:44 PM
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Build Log

Mig-15 800mm - HobbyKing 64mm 3S


After writing off my Mini Mig-15 many weeks ago, I was missing my 'cold war era fighter' so I decided to get another one. At $69 it is a great little plane, but for $74 I could get its slightly bigger brother that is 64mm..... so I grabbed one of those instead.

Hmmmm, not sure about that idea now.....

The Mig's never have much equipment room, seeing they have their 'barrel fuselage of ducting' design, so all stuff needs to stay up above that - and there is not much room above that! The Mini Mig squeezed in everything just perfectly right! This 800mm Mig is also probably 'just right' for a 3S setup, of low capacity battery though - but not suited to doing almost anything else, unless you set off on a major project!

It is about a 2006 era design.... the early days of electric EDF foamies, where things were lack lustre and not as well designed or made as today. It is still quite a good plane, though a bit rough around the edges - mouldings, foam type, tailplane and pushrod flimsiness (0.5mm wire pushrods!).
After a first looking over it seemed unlikely to be much use trying to make it anything other than a 64mm 3S based jet, hand-launched.
After some more thinking about it, I might be able to get it to use 4S and a 70mm CS10/12.... for decent flight speed, and great sound then! So that will be the aim....

Another option is a 4S based 64mm alloy 10 blade, which Cyclone Power and Lander make (same units). But that is fairly costly versus a CS10/12 and L2855-2800kv outrunner combo - which run well and keeps costs way down!

Next I will look over the Mig-15 with pics.....

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Mar 18, 2013, 04:53 PM
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First look and Overview


The overall scale/shape of the jet is quite nice. In the air it would look totally fine. Up closer the foam moulding finish is a bit rough with 'edges' and moulding marks here or there. To fix those you would need to do some sanding and filling, and then would really need to repaint the whole plane. But then the stickers would cause a problem - needing to be removed, if possible, and possibly replaced. So I will not do that in the first build and test flight sequence, and will think about that later on.

The fuselage and wings are strongly made. Though the wing joining spar is only a small 3mm carbon fibre rod. Probably totally adequate for 32S slow flying use, but a bit small if you get it moving fast! The wings are also screwed on with a simple, and weak, lug system. Quite well done, but probably not suited to high stresses either. I will test and think about those.....

The Canopy is OK, but it mounts via the black plastic underside whish was horizontal tabs that you bend to near vertical to get them into the htach area and then they expand back out... a very poor hatch holding method. But again, probably fine for slower 3S speeds. But not for faster flight, so that will need to be improved.

The battery goes in vertically, down the middle of the Mig-15 ducting 'separator'. To keep that thinner, there is no foam to the left and right fuselage sides of that and the battery forms the separator ducting wall then! It will also only fit about a 1600mAH 3S, unless you modify the canopy to allow a longer 2200mAH to go up into that - which some people have done. So if I ran 3S I would do it that way too.

The elevator pushrods are THIN!!! 0.5mm steel rod. Probably unacceptable really.
The tailplane/elevators themselves have a good shape and thickness, but are made from 'coffee cup' foam, sort of. Quite weak. Again, probably fine for slower 3S flight, but not for high speeds! I will almost certainly replace them with balsa wood ones, made to shape.

The rear ducting has a rolled depron 'thrust tube', so for a 70mm fan you would remove that.
Some aspects of the plane's design are quite ingenious really.... just not adequate for a more powerful 70mm setup - or even decent 64mm setup.

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Last edited by PeterVRC; Mar 19, 2013 at 07:21 AM.
Mar 19, 2013, 02:29 AM
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Wings


The wings are not too bad. Quite ruggedly made. Some nice detail of having plastic strakes fitted.
They plug in and are screwed to lock them on, which is a pretty neat idea though a bit weak really. The wings can be wobbled a bit, which is not ideal but probably passable on the slower stock 3S setup.
I will be adding a larger 4mm spar, so with that in there maybe the extra rigidty of it will allow the stock mounting screws to be adequate then - because then they won't be supplying any strength at all, just stopping the wings sliding outwards and off.

The ailerons are separate pieces held on by tape! The angled face, to allow pivoting, comes down from the top so the bottom edge is the pivot point. The tape on the lower flat face is fine enough, but the tape on the upper angled face lifts off easily. So they are really poor fittings.
I will take those off and hinge them properly.

The ailerons use very cheap 5g servos, which have notable slop. So that is another unacceptable part that needs to be replaced. I will use 9g HobbyKing 15178 servos, which are really great little servos!

The wing spar is a 3mm carbon fibre rod.... not totally useless, but not really adequate. It goes right across the fuselage, so that is fine, just in front of the EDF. It will probably be best to add another carbon fibre one (4mm?) further up front in the wing. I have to investigate the best idea for that.

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Last edited by PeterVRC; Mar 19, 2013 at 07:21 AM.
Mar 19, 2013, 03:03 AM
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Tailplane and Canopy


The tailplane is a nice shape, but it is very weak because it is made of ??? flimsy Depron? So whilst it looks fine on the plane, it is not really a good idea to keep it just like that. Once again, if used on the stock slow 3S it would probably be ok. JUST.
The tailplane halves are joined by a 3mm plastic rod, like the wing, but it does not go far into the tailplane so it doesn't help enough to make them adequate.

The canopy is not a bad shape and framework detail, so it looks quite nice.
The inner plastic section uses 'tabs' at the front and the rear that you bend downwards to go inside the hatch area for them to flex back out and hold the canopy on..... ummmm..... It works, but not with any real canopy holding pressure of much use.

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Last edited by PeterVRC; Mar 19, 2013 at 07:20 AM.
Mar 19, 2013, 03:06 AM
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Landing gear


The landing gear is quite nice looking - for 'cheap rubbish'. They would actually probably work totally fine really! And they have surprisingly good detail to look their part too. But they are fixed down, and you could never really install any form of useful retract. So you either keep permanently down landing gear (in flight), or leave them off and hand-launch it - like I will.

The nose wheel assembly has a steering servo built onto it all.

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Mar 19, 2013, 03:10 AM
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Pieced together to have a look


Once all pieced together it actually looks quite good. Not up to current foamie standards, but still nice enough.
Too bad it isn't structurally good enough really - unless flown in its stock, slow, 3S form. And even then, it would be an accident waiting to happen!

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Last edited by PeterVRC; Mar 19, 2013 at 07:20 AM.
Mar 19, 2013, 03:18 AM
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Inlet ducting and stock EDF/Motor/ESC


As per all the Mig-1x series the 'cigar fuselage ducting/engine' unit is nice for good airflow - in and out of the plane! The nose and the central divider were all designed and made well.
As mentioned earlier... the big issue with the design is how there is NO SPACE for much else!

The motor and EDF supplied are again 'old technology' and low specs....
I have had this motor/fan combo in another old series jet and it flew terrible - underpowered - and fried when I tried it on 4S without proper testing! Oooops.
But anyway, there is no way I would use what is in it!! If it fried you probably could land OK, but you also might be just in some position where things turn to crap! So it is better not to even waste the time with it.

After I got it out... hmmmm..... they used heatshrink to join the ESC onto the rear of the motor. Covering the heatsink of the motor!! And trapping the ESC inside the heatshrink with almost no airflow too!
Maybe the low power of it all would make that not matter, too much.... but it can;t be a good idea!!!

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Last edited by PeterVRC; Mar 19, 2013 at 07:20 AM.
Mar 19, 2013, 03:21 AM
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Fuselage Separation


After some reading up on the Mig-15 I found that the fuselage can be separated into a front and rear half!! This is done at the same lug assembly as hold the wings on. INGENIOUS design really!! "Old era' foamie??? Wow, this foamie has some innovative ideas in it really..... I must apologise to the manufacturer! hehe
It is still an underpower cheapie... but has some engineering ingenuity in it too!

When separated, there is the EDF unit, ready to slide out!
It has a thrust tube of depron rolled and taped onto it, so it all comes out as one unit. It is actually not a bad 6 blade fan unit. But I know the motor is cheap and sub-standard, and the way the ESC is attached to it is also a bit dodgy!! Mind you that fan/motor/esc portion is a HobbyKing addition (their stuff), so the actual manufacturer didn't come up with that lacking idea!

This makes the fan upgrading MUCH easier!! So the power system area is now a quite easy area to tackle.....

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Last edited by PeterVRC; Mar 19, 2013 at 07:19 AM.
Mar 19, 2013, 07:15 AM
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CS10 Installation


The fuselage separation meant it only needed a bit of dremel drum sander use to fit a CS10 housing into it. Maybe 1mm of radius expansion.
I cut the mounting flanges off the CS10 housing as it just need to slide in as a cylinder. the front fuselage portion has a ridge against the fan housing and the provide the 'face' to stop the fan being able to move forwards under thrust.
Again.... INGENIUS design!!

Because of the larger housing diameter I can't use their thrust tube now. Down the rear end are longitudal ribs for strength, so it is not a clean 'tube' but I don't think it will bother the EDF system much at all. The stock thrust tube stops about 60mm from the exhaust end, and is all solid foam then so that will need to be opened right up to match the area ahead of it.
Also, seeing the CS10 will run lowish.mid power anyway, it won't need as large a FSA area to work fine anyway. eg normally 60mm/61mm... this can probably be 58mm or even less.

I tried my 64mm alloy housing, which was really 68mm as it turned out.... it fits, but its permanent inlet lip doesn't work with the fuselage mounting system plastics that are there. That is fine, I want to save some weight anyway so a CS10 plastic housing is totally fine!

Above the fan area, and bridging from front to rear half, there is some space for wiring. It is big enough to modify it to fit a 60A ESC whch will then have its heatsink face in the ducting airflow. That IS the 'wiring' really, so that is fine to do that there.... BUT I will be using rear mounted servos, which will need their wiring coming down the backbone also. That will fit in there fine too.

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Mar 19, 2013, 07:34 AM
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Batteries and WHERE???


It is not much fun looking at the hatch and 'battery' area!! Small... limiting.... difficult....

I removed the elevator servo, as I will mount one or two down the rear end. This gives back a BIT of space.
The RX can go into the battery hole, or a gap that goes down to where the nose wheel and servo would go.

The battery - whatever I can work out to fit - will go horizontally right up the top, right under the canopy. I want to use a 2650mAH in 4S if possible, otherwise 3S.
I will cut out part of the top deck, continuing after the canopy, to get the required total of rectangle area for the battery. That will work fine, but the main issue is DEPTH. 3S can be done for sure..... 4S will be very marginal!
It is likely it would have to infringe INTO the ducting area - which there is plenty of area excess anyway. But then it would need a 'floor' made..... if I have to, I have to..... sigh.
And I really do need, and want, to use 4S !!

Being a smaller plane than typical 70mm jets, and it is after all just a 64mm jet, if not a bit smaller than they are typically too(!).... that means it is not about being "70mm" but just about the thrust required. For a 70mm fan it will be running low output. Maybe 600W? 800g to 1000g of thrust. I have to test out what I want and will need.

3S... 11.1V.... 600/11.1 = 55Amps Eeek! This is just no good for battery ease and wear, or capacity for flight time.
4S... 14.8v.... 600/14.8 = 41 Amps NICE and easy to do!
And 4S would even allow a bit more power if you wanted/needed to set up for that.
So it really needs to be 4S....
41Amps... 2650mAH, otherwise maybe 2200mAH.... 30C would be good for that.

CS10 with 2300kv???? Should be in the area....
And now that I checked.... I have L2855-2300kv tests on 4S which gave, HANDY(!!), 42Amps for 600W and 1000g thrust!! (Two different tests done). So that is a PERFECT combo for this to be a quite fast little jet!

What will it WEIGH all up??? It should come in at about 750g to 800g area.
That should also work out to be a very good flying weight for scale flight and inertias behaviour too.

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Last edited by PeterVRC; Apr 04, 2013 at 02:29 AM.
Apr 04, 2013, 02:23 AM
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Fuselage work


After a little rest period to regroup thoughts...... it was back to work on the Mig !!

Major surgery up front, to make a USEFUL battery/RC area!
I checked the inlet side ducting and relative to the very front end inlet area, the inner fuselage area is a lot larger - thus quite a lot of leeway to 'steal' some of it for the battery area!

I hacked out all the exsting foam area up top, to allow a large plywood plate (battery tray) to be added inside there. Down low enough so a good capacity and C rated battery would fit.
I put "walls" into the open slots they had left for a vertically mounted battery - using 1.5mm balsa sheet. This area will be the "hole" for the RX.

The hollow ducting "divider" the Mig has, will be well suited to allow wiring to run down inside that, so the battery has no interference up on its top tray.
I was able to JUST get enough area and depth up top to have a decent battery for the EDF combo! 4S 2300kv, using 4S 2650mAH 35C NanoTech batteries.

Once the plate was glued onto the top of the remaining "ducting divider" I put side wall pieces in to close off that battery area to the fuselage sides.
Looking into the ducting it is pretty clean, but not perfect. That will be fine as it has enough open area, and the battery tray "edges" seen in there will cause some nice airflow noise - white noise. I doubt it will bother the fan flow at all.

So the battery and RC area worked out very well !!

The ESC, which is hard wired to the fan/motor unit, feeds into the front fuselage portion and rests on the tray. This will have a balsa "cradle" affixed to it, to hold/align the ESC in position - so when you put the two fuselage portion together the ESC will just end up in its position.
The ESC battery wiring runs along under the battery tray - entering the ducting divider near the rear end, and exiting right near the front of the tray area. The way it just lays into that battery tray centreline slot means there is no issue with the separating/joining of the fuselage halves.

This layout does not allow the stock canopy assembly to work at all. But I will use just the upper canopy portion, with a new added front 'flange' thingy, so it will all fit on and be attachable nicely.
More on this part later on.

But everything was thought out in advance before taking this quite radical surgery path on the fuselage! hehe

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Last edited by PeterVRC; Apr 04, 2013 at 02:35 AM.
Apr 04, 2013, 02:28 AM
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Ailerons


Earlier I mentioned the lousy ailerons, and useless servos!! So out with the old servos, and in with some of the very nice 9g HK 15178 servos!
Then I cut off the ailerons and their rubbish tape hinging, and put 6mm balsa facing onto them - after cutting them squared off, instead of the 45deg sloped face they come with.
This is because squaring them off loses 6mm approx. There is no way you could reface them to be "normal" aileron face "points" without adding more material. And balsa makes them nice and strong too!

I used 3mm round pinned hinges - three per aileron - epoxied in.
So now the ailerons are robust quality devices!

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Feb 24, 2014, 06:21 PM
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Tailplanes


Flimsy Depron... nope.... in go the balsa replacements.
I think I used 3/16" and shaped that to an aerofoil shape.
Pinned hinges for the Elevators.
And a spar run across the fin and into the tailplanes, to join them strongly.

I have worked out the best elevator servo idea yet, but leading the idea bunch is to have one servo in the fin, driving both elevators. This idea allows room for a rudder servo too, which I want but have not decided on 100% yet.

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Feb 24, 2014, 06:26 PM
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New fan to be used


Because of CofG balance issues, I decided to mount the fan more rearwards.
I also wanted to permanently joint the fuselage and wings, so the split fuselage idea - which makes for easy fan installation - would not be viable anymore.
So I cut a more conventional fan hatch/cover, and mounted the fan in from the bottom.

I will use an XRP housing with a Turnigy L2855-2300kv motor in that for now. But I will likely change that up to a 2800kv later.
It will be a 4S jet - seeing it is quite small and not that heavy.(1000g region AUW)

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Last edited by PeterVRC; Jul 11, 2014 at 11:27 PM.
Feb 24, 2014, 06:31 PM
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New - AGAIN - battery area and hatch


Whilst thinking over fan and motor options, I decided that the very limited space for the 4S battery was not really acceptable! Plus the battery is way above the centreline and making it a bit top heavy.
So I decided to gut the whole front assembly, and make up a whole new 'module' down the guts of the ducting, that can hold a 4S 3300mAh easily, and even some smaller end 5S (3000mAH).

In the end the ducting flow around the pod was not really any worse than before. Either way it is a bit limited and will need a cheater for sure.

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