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Feb 22, 2018, 08:32 AM
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Build Log

Mig-29 Fulcrum - FlyFly Twin 90mm EDF jet No.2 (Rating: End Result 8/10)

Another FlyFly Mig-29 Fulcrum kit?? When the first one is not even completed!!??
Well Hobbyking had some on sale and.....

I decided - at that time - that I would make one as 'full house' - the original No.1 one. And then this second one as a simple Taileron only hand/bungee launcher. Mainly because operating off a grass field makes it much harder to ROG, plus very punishing on landing gear.
So for this one, it is Tailerons only..... but I will add landing gear also(!!), to only be used for LANDING. Take-offs will be bungee or hand-launch, depending on the final AUW. I will use a FRsky S8R Flight-Controller RX to allow TX/hands free launching too, and thus I will be able to do two handed launches to assure it is a good and fast/strong launch!

For the Landing Gear, it will be the Freewing Su-35 nose gear, which has a trailing link suspension action, and some Hobbyking trailing link main gear oleo/wheels.... which are all very useful on grass. It will only need the 'Medium' sized Retract units, with 4mm on all oleos. Mediums are fine for hard runways too, but you really want the Large size retracts, with 5mm pins, if operating from grass. Which will be what the No.1 Mig-29 gets.

I will add a wing spar (of course!).
I MIGHT even WBPU/Glass it. That can be the last thing done... or not done... once I know the AUW region it is headed for. I want to keep it under 3.0Kg.

It will use my Ex-Su-35 HET2W30 (2200kv) driven Wemo Evo's, on 7S as per the Su-35 used. But those are also 8S capable too... for just 100g of more battery weight with 5000mAH's.

I began work on it right away, seeing I THOUGHT I could do it quite quickly... but no... there is a LOT to do to make a FlyFly kit/aircraft end up truly airworthy and fit for purpose! But I will focus on it until it is DONE !! Maybe two weeks?

Oh... and it seems that the HobbyKing 'special batch' of FlyFly kits don't have EDF units of landing gear in them!! I didn't get those, and a few people have posted they didn't get any either. Not that any of those bits are much use really....
Last edited by PeterVRC; Sep 06, 2019 at 02:20 AM.
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Feb 22, 2018, 08:36 AM
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Enlarged Canopy/Hatch opening.

As per Mig-29 No.1 I have cut a larger opening at the canopy region, to form a much bigger hatch that has the canopy on it. This is to give far greater access into the nose area, for battery placement and RC stuff etc.

I also added the Rear battery Hatch/region, again as per on Mig-29 No.1, for the second battery to go into.
It will fly from either 7S via a 4S and 3S 5000mAH, or 8S via 2x 4S 5000mAH.

The pics are all of similar work like in the Build Log of Mig-29 No.1. I used it as a guide to get it much the same.

Feb 22, 2018, 08:41 AM
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EDF covers and exhausts

I also did the EDF covers like Mig-29 No.1 as that seems the best/nicest way to have them.

For the 70mm fan setup, they will have mounts that place them centrally in the 90mm bays and allow 'blow past' of any excess airflow coming down the inlets. In effect the EDF's will be in ;free air', much like on a test bench setup, so they should run at 100% of their capability - no inlet/exhaust restrictions.
I don't need exhaust narrowing to gain Efflux Speed, as it will be fast enough anyway and having maximum THRUST is of more use.

The EDF mounts will be a part of the fuselage rear 'side rails' plywood laminations for strength. Those plywood plates will also be the mounts for the Taileron Pivots, and the Taileron servos. Thus the whole rear end will be a very strong 'sub-frame' sort of end result. Of course I will cover this in its own post once I do that.

Feb 22, 2018, 08:58 AM
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Forwards hatch tray and nose gear mount - Forwards folding nose gear

Yes, I like things to be STRONG!! So that they LAST, and continue to allow reliable operation of aircraft! A bit like the Russians themselves do in their aircraft designs!! hehe

The FlyFly stock front hatch battery tray is a JOKE!! So weak - 'special number one Chinese plywood' !! I wouldn't rely on it to hold a 3S 2200mAH battery even!

Seeing I am using that same tray as the mount for the nose gear, it needed two levels of extra strengthening, and also to be longer.
So on its lower side (downwards) it has a medium sized extra bass-balsa plywood plate added.
On it top side a BIG new bass-balsa plywood plate is added. This is the whole length of the original plate, but also another 50mm more rearwards because the steering servo will have a mount added on that, rearwards of the retract.

Once the three plates were all laminated into place with epoxy, they form an extremely strong platform. But the rear end, where the retract goes, is also strongly supported by hefty foam areas of the UPPER fuselage - which is where forces will try to head from the nose gear.
Basically it is all a VERY strong assembly in the nose now!

I considered mounting the retract to store the nose wheel rearwards, as per the full scale actually does(!), but the Freewing twin wheel nose gear from the Su-35 is too WIDE, by just a few millimetres, to fit in between the inlet ducting. And in practical terms, the way FlyFly set up the gear storage directions makes a more useful longer wheelbase, and also virtually no change in CofG for gear down or up.
And it is also too hard to alter the main gear to operate in the proper full scale's direction, so no great use in getting just the nose gear 'right' anyway.

Last edited by PeterVRC; Mar 25, 2018 at 05:11 PM.
Feb 25, 2018, 06:26 PM
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Main gear

The stock FlyFly gear mounting blocks are a bit of a joke!! Pretty well only the size of the retract itself, and they will rip out very easily on any landing that is harder than a greaser! And wont last even one flight from a grass flying field!
You want an aircraft to be 'fit for purpose', so that it CONTINUES to operate reliably when it is used within acceptable limits. This means that for grass use the landing gear setup needs to be notably stronger - but even from a hard runway the FlyFly setup is not going to last.

It is a fairly simple fix. It just needs a lot more surface area for the mounts, so instead of the two small 33mm long strips they supply, I made up 115mm long plates. These just need a bit of modding to the foam area, to fit them. But I also wanted the mount to be some amount more forwards of the retract too, so that meant I needed to cut off a small bit of the Ducting 'half' of the fuselage, to move onto the main fuselage area - which the retract mount would be over. That is a very simple cut and glue bit to do.

On grass, Trailing Link suspension type oleos are WAY better than plain 'straight' ones, but there is an issue that their wheels being 'offset' from vertical means they either store more outwards, or inwards, of the fuselage - this depends on which way they fold into the fuselage, for or aft. In this case they go DEEPER into the fuselage, but it does not have any room for that! This then means you need the oleo itself to NOT get to 'horizontal' but be inclined still outwards of the fuselage, and that means when it is extended by the retract 90deg it will not be vertical. To achieve this, from a 'flat' retract mount, you just need to incline the retract itself using spacers.
You just need to decide if you want the benefits of Trailing Links versus Straight oleos, and accept that need for an 'angle' in the oleo if you use Trailing Link types. If you use Straight oleos then it can all operate with 'flat' mounted retract units.

I set it up for the Trailing Link type, but the looks do irk me.... so I am tossing up on whether I use Straight oleos instead.
For now I am only intending to LAND on the landing gear, so the benefits of Trailing Link type are not that important. They give much more benefit on take-off runs. But, maybe I will take-off from grass too.....
I will think it over as I go.... and it is an easy change to use either type.

Feb 25, 2018, 06:40 PM
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The stock FlyFly Taileron mounting system is pretty weak, though would work with reasonable reliability just as it comes.
There is a weakness in the rear fuselage foam 'side rails' that the pivot blocks mount into, but as long as no undue stress was ever encounters they would probably hold up fine. But they would be far more RELIABLE if made stronger... so.....

This is an easy mod/upgrade. You can use the stock mount/pivot just as supplied, but you add a plywood plate over the foam rail area to give it far more strength. This plywood plate can then ALSO be the servo mount and then it forms one 'unit' which is the Taileron pivot AND the servo mount.... keeping them physically interconnected as a 'sub-frame'.
The pivot blocks also get the plywood plates screwed onto them, so that it is not just foam holding them in!

I changed the Taileron 3mm stock pivot system to a 4mm setup. 3mm is just to small a diameter and allows a lot of slop and freeplay. The larger the diameter you use, the smaller the ratio so any slop/freeplay from tolerances are. I used 4mm piano wire, so that I could use the "L" setup method to mount it into the Taileron, but I would have preferred to use 5mm carbon fiber ROD.... except I don't have any. And I decided the 4mm piano wire way would work totally fine anyway. Once the pivot blocks were redrilled to 4mm the 'axles' ran snugly in them with no freeplay at all and it all feels very solid.

For the plywood Fuselage 'rails' (plates) I decided to make them standalone from being combined with the EDF mounts, to save wood. Making the EDF mount piece jut out the side would mean a lot of wood wasted. I can epoxy other separate pieces across to the rails to form that 'link' anwyay.

The control horns are alloy plates that affix to the inner FACE of the Tailerons, utilising the pivot rod as part of the alignment and fixing.
With ball joints at both the servo and control horn ends.

Last edited by PeterVRC; Mar 10, 2018 at 08:58 AM.
Mar 04, 2018, 11:29 PM
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EDFs and their mounts

Seeing I am using 70mm EDFs the mounts need to be a narrower 'gap' and span within the 90mm EDF bays.
I made up some 2.5mm Plywood 5 Ply of 2 layers, for a 5.0mm 10 ply total. The centre single mount bridging right across from the left to right EDF.
The outer mounts are also epoxied to the Taileron/Fuselage rails.

Last edited by PeterVRC; Mar 08, 2018 at 05:05 PM.
Mar 08, 2018, 05:29 PM
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I wanted to mount the ESCs with their heatsinks facing into the inlet ducting, but to do that was going to be a very messy task! After more thought I decided to just mount them into the centre body, seeing there is a full length large channel down the middle of the Mig. If they were in the inlet ducts they would get cooling whenever the motors ran, and a lot of it! In the centre body they will only be cooled if the Mig is moving, which in most cases of EDF use it will be - it will just not be as good as inside the ducting for most situations. eg take-off where it is max power being used but a slow speed, whilst the inlet ducting the airspeed is always linked directly to the power being used.
On my other (first, and unfinished) Mig-29 I have made cutouts for them go into the ducting but had not been able to work out HOW to mount the ESCs in some good way yet.

I made a pair of 2.5mm 5 ply 'rails' to run below the surface level of the centre body so that the cases of the Turnigy ESCs could be screwed onto those. You can remove the ESC and heatsink assembly by four screws, then screw the case only down, and then replace the ESC and heatsink assembly. This was easiest done by running the two ESCs in line, one after the other. I could also have mounted them vertically 'sideways', back to back, with a mounting system for that, but then they are very close and cramped so the cooling would not be as good as the way I have done it now.
The heatsink surfaces are flush to the underside, which includes the ESC Capacitors also seeing they 'jut out' the ends of each ESC.

I will make one long 'cover strip' to go over the ESC section of the centre body so that it is all flush and tidy, with slots in it for the ESC airflow of course, and that can be painted to match the Mig underside.

Mar 10, 2018, 09:15 AM
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EDF and ESC wiring

With the EDFs and the ESCs mounted, it was on to the wiring stage.
This needed a bit of thought, and some foam hacking/cutting, so that it would all be tidy AND maintenance capable.
Because the cases of the ESCs are screwed down first, and they then block wiring path access, I had to work out the best way to make it all accessible and also easy to remove/refit etc.
I decided the only way to do this well was to use 4mm bullets for the ESC to Battery leads and those pairs of 12AWG Pos and Neg then feed into the single 10AWG leads. At this connection junction I also tap off the source for the SBEC, which goes to a JST connector to allow disconnection of that source so that you can use a small Lipo to power the RC system (SBEC) without a need to put in the flight batteries. Or to even just use a small 2S or 3S Lipo as the SBEC power source for flights.

When I was testing/checking the CofG capability, via battery movements, I discovered that BOTH batteries need to go well forwards. I had originally intended to put the rear battery in the long rear hatch I made up, but it needs to go much more forwards than that! This was no problem as it just means the RC stuff goes under that rear hatch instead, plus the rear battery is pushed in from that rear hatch, forwards into the main battery tray. It makes putting the batteries ion very easy... and easy taking them out off the velcro, due to that ability to get to the rear battery from both hatches (one hand coming in each end).
I had to extend the battery tray further also, to give a large range of CofG adjustment. I made it the full length of the underside nose piece, as that is all you can have on that and be able to assemble it. Once that underside nose portion and the main fuselage is all glued together I will probably add another 20mm or so of battery tray, to allow even more CofG range adjustment.

The SBEC and RX will now go on the 'floor' of that rear hatch area. There is a LOT of room in there to have those plus any possible wiring paths and amounts you could ever need.

This new arrangement was also great to make the power wiring EASY to connect and store any excess leads in that rear hatch area. So all in all I was happen with this new layout!
For 7S 5000 (1x 4S 5000 and 1x 3S 5000) the 4S battery needs to go up the front end.

Another side benefit of this new layout is that a Wing Spar can be positioned to cross that area almost anywhere it would be best to have it. Not just have to be to the rear end of that hatch length.

Mar 11, 2018, 10:46 AM
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Landing gear "reversed"

I just didn't like the way the main gear had to be set up to work and the best way to improve this was going to be to reverse its direction of storage, to match the full scale. So then I decided to investigate the nose gear to see if that could be reversed also.
After some pondering and calculating I worked out I could reverse both the main gear and the nose gear quite easily. AND also gain some good benefits from each of those having done that too!

For the main gear all I needed to do was turn the retract unit around to face the other way, making new 'locator key' holes for the PZ retracts, and then opening out the retract motor end and oleo channel. Most of the finishing aspect of that I would do AFTER fitting the Wings.

For the Nose gear, I made a 10mm mounting block and moved the retract forwards about 50mm and turned it around the other way. The 10mm block was because now the trailing link nose wheel needs more clearance 'above' (down from) the battery tray underside. But test fitting had showed this was going to all work out just right.
One issue is that the width of the Freewing Su-35 nose gear I am using is a FRACTION too wide due to the two wheels and flange/nuts out each hub side. A shallow channel can be made into the inner intake sides but there will be zero tolerance for the wheel getting into its bay if it is turned, or the retract pin is bent. I will make up a 'straightener guide' that forces the leg/wheel to be dead straight as it folds in. It is not too likely it will ever encounter a bent SIDEWAYS retract pin and that is the other case that would cause trouble to not hitting the ducting sides.

Last edited by PeterVRC; Mar 11, 2018 at 11:35 AM.
Mar 11, 2018, 10:54 AM
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Wing Spar

Luckily I had left the Wing Spar to 'later', so that now with the main gear retracting the opposite direction I could put the Wing Spar right after the retract unit, and sort of close to between the half chord point and the CofG point. This is also a nice thick portion of the wing.
The 750mm x 8mm carbon fiber tube runs out close to 150mm into each wing - plenty.
I ran it through the fuselage, tested to get it squared and level horizontally and then epoxied that in. I was test fitting the wings as I went also, to be sure they were going to be square and level.

For the Wing spar hole I used screwdrivers of larger and larger size to form the hole - which reached about 6mm diameter and 80mm depth - then onto an 8mm threaded rod to 'drill' out fully to the 150mm. This ate a hole a bit larger than 8mm really, but that was fine as I aimed to use PU glue for the Wing Spar into the wing. This will expand to fully surround the Spar in the Wing section.

Last edited by PeterVRC; Mar 11, 2018 at 11:37 AM.
Mar 11, 2018, 11:01 AM
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Fuselage completed

Seeing I had done all that I needed to do with the Fuselage in pieces, I glued in the Nose Underside Fuselage piece and then the Inlet Ducting pieces. Thus the Mig became a "full fuselage".
I had added a 10mm thick piece of balsa wood to complete a bulkhead that is just under/ahead of the canopy. This position has the battery tray front end under it and without that being "solid" - like a full bulkhead - there is not that much support above the battery tray, which is also the Nose Gear mounting plate and thus it could push upwards on a harsh landing. Mind you, making it 'strong' means that the NEXT thing in line to break on a very harsh landing is the whole NOSE snapping off! That is a Freewing Su-35 weak point....
But, you are not supposed to do such a harsh landing - just as the full scale would be in big trouble if the same was done to it! lol.

Unfortunately right after joining all those pieces I realised I had forgotten to do the main gear retract wiring! I had started it before the Wing Spar, but then forgot to put it all into place before finishing the Fuselage pieces! It won't really be a problem to do it later but it would have been easier and better to do them FIRST!

Completing the Fuselage then allowed to move onto fitting the Wings....

Mar 11, 2018, 11:08 AM
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Wings fitted

I put a good amount of PU glue into the Wing Spar holes, and also coated the spar with it. Then roughened up and put epoxy onto the Wing Root to glue each Wing piece onto the Fuselage. As previously mentioned, the PU glue will expand and totally fill the Wing Spar hole and that will also make it all become 'spar' too.

Later I will add some plywood plates to the rear end of the Wing/Fuselage joint, plus some carbon 6mm x 1mm strips. This is to provide a second locating/attachment point to the rear end of the Wing - so it can never 'rotate around the spar'. Though that occurring is almost impossible now really anyway. Or even totally impossible. PU glue... Epoxy... so much to hold/lock each Wing piece all solidly in place. But a bit more can't hurt!

The Wings don't feel like they really need any long 6mm x 1mm carbon fiber strips slotted into them, to reach more outwards to the tip areas. I will most likely NOT add any. But maybe I will. They could also be easily added any time in the future anyway, if it seemed necessary for more rigidity in the Wings.

Mar 11, 2018, 11:18 AM
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Main Gear leg length

The Hobbyking Trailing Link landing gear set has quite short main gear.
The Freewing Su-35 Nose Gear set I am using is quite tall - perfectly suited to this Mig-29.
But this means the Main Gear lengths/heights are WAY to short. By about 20mm.
To 'fix' that I made up LONG Retract Pins but they will need 'sleeves' - much like alloy oleo portions - over them the "fill" that open area from the Retract Trunion to the Oleo. If that is not done then the long exposed retract pin section could bend far easier. I actually do not have anything to do this, but I will find something.....
At worst I will need to get some 10mm/12mm aluminium rod and drill that to be the sleeve(s).

You can see those long Retract Pins and how they are exposed for now, in a few of the pics posted so far.

The lengths I have it all set for means the Ducting Undersides are parallel to the ground. The Full Scale has a slight incline upwards to the REAR - which means even longer Main Gear required then. But for an RC model it is more use to have a bit more Positive AoA stance at rest. This means rotation/lift is much more assured and 'automatic', because basically the faster the jet moves (eg still on the runway) the greater ratio of lift it produces due to having that Positive AoA already. You can even just do nothing but accelerate down a runway and it will lift off without ever needing to MAKE it rotate! This allows very smooth, scale, lift offs instead of the more typical LEAPS of EDF jets.

Last edited by PeterVRC; Mar 11, 2018 at 11:40 AM.
Mar 11, 2018, 11:33 AM
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AUW so far

With all the main parts assembled now I did a AUW check.
3.10 Kg with the 7S 5000mAH 45C Turnigy Graphenes.
At 2600W total power the EDF's will be able to exceed that 3.10Kg easily. They should do about 3.5Kg region.
There is a bit more stuff to do and probably about 200g more in total weight to go, so maybe it will end up about 3.3Kg to 3.4Kg AUW.

In test bed setup the EDF's each do 2.0Kg of thrust on 7S. It will be interesting to see in this Mig-29 because the fans are 'free standing' just like in a test bed - seeing it has 90mm ducting. They could very well do the full 2.0Kg thrust each still !!
Allowing for a bit of Voltage 'Sag' under full load, maybe they will only do 1.8Kg or a bit less. So it should be able to do 3.5Kg of total thrust I would think. So that will mean it should remain over the 1:1 ratio of thrust to weight.

AND.... it can be run on 8S for 4000W also..... !!!
100g more weight for 8S over 7S.... bench tests are 2.65Kg thrust for 67Amps (for one fan), so for 140Amps (ouch!!) you can get 5.3Kg of thrust!!
The batteries would SAG with a pair of them running, and the 140Amps, so drop off some chunk and it would probably still come in at 4.5Kg region. For about 3.6Kg AUW.
The MOTORS are only "1500W continuous' rating so USING 4000W (or say 3500W with sag) has to be used with care! I have tested the motors on 8S for reasonable lengths of run time there, and they were not overly hot after 20 seconds. But it just not a good idea to use that much power except for rare/special cases and not for too long!
I am not actually aiming to use 8S, but I will test it out and see what I can do at least.

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