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Dec 08, 2012, 07:33 PM
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Build Log

Su-35 Freewing - 1500mm Thrust Vector EDF Jet (Crashed/Destroyed)


This blog will cover mods and setup that I have done to the Freewing Su-35.
It is a very nice plane just as it comes, though as with all PNF's there are some shortfalls. But not many in this case. It probably could be flown just as it comes, with a pretty high chance of success/reliability... though it is really safer/smarter to always go over PNF's to make sure it is really airworthy/safe/ reliable, or else there will be a big bang at some stage!! And confetti foam everywhere.....

Because this plane was actually done many months ago, the order of mods etc could be amiss. For most of them that is not important anyway. And maybe I will forget some that I did.... but even if so, I will try to add them later when I do remember!

So for a start, if you like Sukhoi's or Migs, then this is a great option!! I think it looks awesome (like a Mig-29 does too) and Freewing has used some of the latest innovations of making modelling easier for users.
I think it is a 10/10 plane!! But none ever some truly perfect, and thus why there are always things to do that can improve them, and make them more reliable and last longer!

....

My list of 'good to do' mods: Start with the ARF !!!
1) Plywood sub-frame - full length from nose gear bay to rear end
2) Heavier Alloy main gear struts - alloy hub wheels (stock can split hubs)
3) Lander alloy retracts - slower operation and 'all metal'
4) Wemo EVO, DrMad 2200kv, on 7S with 60/70Amp HK SS Series ESC (otherwise 100A HV to enable 8S 4000Watts)
5) All servos digital MG (HK15178B and HK17148B)
6) Larger battery hatch - side wings and lengthwise
7) Elevator fuselage mount plates/bolts for strength
8) Vertical Fin carbon fiber rods and fuselage mounting system for strength

Options:
Nose gear fuselage shock absorber.
Leading Edge Flaps (more academic than a necessity).
Backbone AirBrake - this actual Su model did not really have that.

....
Last edited by PeterVRC; Oct 03, 2018 at 07:34 PM.
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Dec 08, 2012, 07:36 PM
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I bought the PNF Su-35. If I did it again I would buy the ARF.. and that way I could add all the parts I wanted to use. Not so much because the Freewing stuff is rubbish - it is mostly ok or good really - but seeing I changed to CS10's that means a lot of the expensive bits they give you were not used.
I also changed the elevator servos, so I may as well have done all the servos myself too.

So the first thing I actually did was assemble it totally just as it came, to see if MAYBE it was totally fine just as it came!!
It was all very nice and really it was all very well done too! Just a few small issues, but it was very close to 'fly it just as it comes'.... close......

So then the first things I found to do.....
Last edited by PeterVRC; Apr 28, 2014 at 07:31 AM.
Dec 08, 2012, 07:39 PM
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Elevator servos:
Replaced with D-MG16 18g digital metal gear servos. This is because the stock ones 'stepped' in steps that were too large, and thus fine control of the TX sticks still had the elevators 'jump' in steps - as per the servos movement manner.
This was unacceptable, thus the were replaced.

Elevator pivots:
The elevator pivots were quite stiff when installed. Too stiff... too much resistance for a servo. So I used a fine grade Wet and Dry paper, wrapped around them like a tube, to sand them down bit by bit until they were a 'perfect' snug, but free moving, fit.

Underside Cover Plates:
Freewing has used a few thin platic cover plates for otherwise open areas under the Su. They glue those on.
I drilled them for 'washer head' self tapping screws. They just screw into the foam, which they hold fine if you are CAREFUL when doing them up! One day I will Vaseline the screws, and put epoxy into the holes and do them up... to form a more solid screw hold in the foam - the Vaseline stops the screws being glued in!

Nose gear:
The Freewing retracts are quite sloppy, thus the landing gear legs can wobble around - side to side, for and aft. On the front gear this is almost a good thing! The fact it can move fore and aft some amount, means the resultant motion in the 'leg support ram' can be fed into a shock absorber so that fore-aft shocks can be absorbed very well then!! I used an old small oleo leg, in a 'box housing' in the belly, for that 'leg support ram' to feed into.
Fairly elaborate... you don't need to do it this well, but it is well worth doing something of this nature to absorb shocks that will otherwise eventually damage the retract or mounts.

...
Last edited by PeterVRC; Dec 09, 2012 at 06:36 AM.
Dec 08, 2012, 07:39 PM
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Thrust Vector alignment:
To align the Thrust Vector nozzles, measure from the facing lip of the nozzle (fuselage end) to the fuselage.... at the top, bottom and both sides. To get them dead neutral.
They do have some marks on the nozzles balls, but that is pretty useless to use as the error margin, if you use something like that, is large! Using the nozzle faces is far more accurate.

CS10's:
I pulled out the stock 6-Blade fans and replaced them with 10 blade CS10's. But you can't use the stock motor in these. 2300kv and the 'medium' level of build of the motor is not going to cope with the power level they would then try to run at!
I used L2855-2100kv motors, but as it turned out even at a lower 2100kv, which runs them at about 1100w to 1200w area, still fries them easily!!
You also need higher Amp ESC's to cope with the higher current it will all run at, so I chaged the stock ESC's out to 70Amp ones.
I THINK the CS10's sounded a BIT better than the stock fans. But nowhere near as good as I expected they should sound.
The stock fans are very efficient for their power output, so you only really want to go to CS10's if you also go to 'very good' motors, and then run a higher power system in total too. Certainly not a 'must do' thing at all !
Last edited by PeterVRC; Dec 09, 2012 at 06:47 AM.
Dec 08, 2012, 07:40 PM
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CS10's with HET 2W30 2200kv:

After frying the CS10's on the L2855-2100kv motor/s, I switched up to HET 2W30-2200kv motors. These are inrunners and of a much higher capability than 'cheaper', or 'average' motors.
If fed with an adequate battery they can do 2.0Kg thrust on the bench... 1450Watts!!... but at 70 Amps! And getting a battery that can power TWO of those is not easy!
Almost impossible really... any will be under high duress at those levels. That is at WOT.... so you have to be careful with that WOT use! But really, you only need 1000W each side to fly well - normal, fast level flight.
The full power would (should) only be called on for 3D manouevers that need huge power amounts.

This meant changing the ESC's to 90Amp each. And redoing wiring to suit also.
They have been fine so far, but I have not used a low IR battery that gets the most out of them so far. So they have been "totally fine", but untested at their true peak abilities!
Last edited by PeterVRC; Dec 09, 2012 at 06:46 AM.
Dec 08, 2012, 07:41 PM
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Going to "Full house"... 11 channels plus:
To use all the possible control surface motions the Su could give you, you need to use more TX/RX channels!!
I have used 13 Channels !!
This needs rewiring of the stock "Y" connections used here and their (eg Ailerons) so that you have one channel for every servo.

So the list of channels is:
1) Aileron - Left
2) Aileron - Right
3) Elevator - Left
4) Elevator - Right
5) Throttle - Left
6) Throttle - Right
7) Rudder - Left
8) Rudder - Right
9) Gear
10) TV - Left
11) TV - Right
12) TV - Yaw
13) Steering (Mixed from the Rudder)

So in my Turnigy 9X, with ER9X Firmware reflashed, it was 286 bytes of model memory later..... (typical aircraft are 100)
To run the 9-Channel T9X - which is really only 8 Channels of use! - with more channels you need (which everyone should use anyway!) ER9X Firmware, which allows taking another 8 Channels out through the Trainer Port and you feed those into another TX module!
Thus you end up with 16 Channels... and you use TWO Receivers, one for each TX module, to bring those 16 Channels into the plane. I also use two BEC's - one for each RX. Thus the current loads on each RX are only its share of the servos it controls. And by thinking intelligently about all the control surfaces, you can actually set the plane up so that even if one RX fails, the remaining one (no matter which) has enough Pitch, Roll, Yaw and Throttle controls to still fly the plane to an emergency landing!

13 Channels is just the Channel count of course. You then have MIXES underlying how the TX input controls (Sticks, Switches, Pots) form the output streams for the aircraft controls - and even some mixes feed into other mixes to form new ones! So it is a very complex grand total, and you need a very capable TX to be able to program all the required stuff!!

I set up:
1) Flaperons - running off Pot 1
2) Spoilerons - Running off Pot 2
3) Rudder Air Brakes - Running off the 'spare' Rudder DR switch (could mix that in to Spoilerons too?)
4) Tailerons - mixed off the Ailerons of course
5) Elevons - or what do you call synchronised Elevator and Aileron? - Ailerons mixed off the Elevators
6) Nose gear steering only active on gear down position. Mixed from the Rudder source.
7) TV's Active only for ID2
8) Of course every servo connected as an individual channel unit to allow all those combinations and their indivdual end points and trimming.

ID0 (flight mode 1): Just plain typical Su-35 control surface operation
ID1 : All the interactive surface mixes added in.
ID2: TV's are online also
Last edited by PeterVRC; Dec 09, 2012 at 07:14 AM.
Dec 08, 2012, 07:45 PM
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New main gear setup and AoA stance improvement:

This all started after being very annoyed with the Su's "Very long take-off runout process".
Basically the Su has a reasonable amount of "trouble" taking off. It needs a long runout and whilst it can take-off somewhat fine from a hard runway, it really sttruggles off grass. A large part of the grass struggle is how it is impeded by the resistance of grass and then will need a much longer run to get to as high a take-off speed as on a hard runway.

In either case that take-off is still 'abnormal' - it will leap into the air. This is because of its resistance to even take-off, because it won't rotate easily/nicely which then needs a pilot to inject an elevator and/or TV "jolt" to make it rotate. And that is overly hard to do in a fully controlled manner, so you end up with a sharp rotation - to maybe something like 30deg to 40deg (or more) - that is fast and thus a 'leap' occurs. And if you are good enough and quick enough, you can tidy that up into a nice climb-out, but the fact will always remain that it leapt into the air at first.
I decided this was predominantly due to a terribel "AoA stance".... it is pretty well at negative AoA when on its landing gear. By a fair amount.
It LOOKS pretty level, but if you look properly at the wing and elevator incidences on the ground, they are down.

The first way to improve this, and done by a fair few people, is to block up the nose gear so that the nose goes higher. You can do up to 10mmm without any retracting issues. But even at 10mm it is still not level AoA! Thoug it helps a lot.

The second way came about because I bent a main gear oleo. They are pretty cheap and weak!! Barely adequate for the job, but would survive fine if you operate of a hard runway and never "bang it in" by mistake ever!
So I replaced the whole main retract/oleo/wheel setup, and gave that about 6mm reduced height at the main gear point. To keep the wheels position suited to the stock wheel-bay I kept oleo to axle lengths as standard, but used smaller diameter wheels.
One other addition I have is WEIGHT. I run at 3.4Kg so far, which is a fair amount over typical flying weights. But ALL my aircraft have that, to improve 'inertia realism' - you can't replicate a real plane's motions if you don't have appropriate weight and inertias for the plane's size and how it acts in the air. So this plane needs somewhere heading towards 4.0Kg to achieve that, but you usually have to compromise at some point as a foam plane won't like that large a weight increase above stock weight, and survive the stresses etc. I will go to about 3.6Kg eventually. And one benefit MASS gives is int he take-off process. Lifting more weight, and also via the need to alter larger inertia force vectors, changes the whole motions a plane can do.... so a take-off becomes far more realistic, because it can't "leap" anymore even if it wanted to. But more weight with NEGATIVE AoA Stance makes an ever worse case..... so that AoA Stance must be fixed up too!!

So, onto the mod.....
Last edited by PeterVRC; Dec 08, 2012 at 08:00 PM.
Dec 08, 2012, 08:04 PM
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I chose the HobbyKing 100mm straight oleo for the job. That is too long, but these oleo series can be modified a reasonable amount for various lengths etc.

First, just a comparison of the Su stock leg and the new oleo. The new one is much larger, more approriate size - for the job and to scale (sort of) - and operates much smoother. Partly as a larger diameter piston can be made with better tolerances, but also because it IS a better quality item.

$13 for two:
https://www.hobbyking.com/hobbyking/s...Class_1pc.html

In this pic below I have already modified them to be shorter and match the stock Su oleo. I will explain the whole process...

...
Dec 08, 2012, 08:23 PM
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Here you can see the first modded oleo next to the new oleo as it comes. You can see an empty 'locating pin' hgole - to shorten the oleo I move the locating pin down the leg more and cut off the piston by that same length.
To work out the modification length required, disassemble to oleo and remove the spring, then slide the piston back in and compate the oleo to the stock one - slide the piston to get that required total length (going by the matching AXLE lines!) and mark where the locating pin now needs to be. It was approx 11mm on these (but do the check yourself!!).

Seeing I had already done one, I have one extra step required.... to make them identical. So by putting them both onto on axle I don't need to use measurements, but use a "just do them the same" manner.

I normally use a drill press to dril the new locating pin hole, but I did this one freehand with an electric hand drill. You can do that as long as you are CAREFUL and ACCURATE! Centre punch the drilling point, use a 2mm drill to make a very small start, check that, and 'angle drill/adjust' little bits, and check and check and check, till you can see for sure that you are going to drill dead centre of the piston leg. Then do the full hole, checking often to make sure you are straight in all dimensions.
Even the SLIGHTEST error means the locating will not match the outer oleo casing's pin slot - but you can fix up slight errors. Best is to have as close to zero error as possible!
My second one came out something like 0.0001mm error!! As best as you could ever do really!

The re-drill to 2.5mm, ready for a 3mm tap. I drill right through the leg becuse tapping a 'blind' hole is much harder, and it isn't any issue to go right through and then tap it right through. I only use the 'starter tap' as the pin does not really go right through, and the starter tap will leave the thread not quite fully done, so the thread tightens up as the pin gos deper into the hole/thread. (not critical to do at all).
Clean up the hole with a larger drill afterwads (6.5mm here). Then cut off the piston leg to match the required length.

...
Dec 08, 2012, 08:36 PM
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Test the inner leg into the outer casing, with the pin done up, and check the aligment and freedom to slide. You will pretty surely need to clean up the pin slot edges. Camfer them a bit, as required, inner edges and outer edges, Once the piston slides totally freely that is done, and you can 'adjust' the spring strength by cutting it off X amount.
At full length it is too strong for the Su-35.. even at my heavier weight. But getting the strength right is a trial and error thing. You could leave it until the final assembly, re-test operation on the pane, then disassemble and re-cut later.
I took off about 6mm right away, and it is still too strong.
Cutting the nice 'flat end' off leave a corkscrew spiral, but that is fine - put that end to be against the pistion face.

Clean everything up well (all shaving etc gone!) and assemble the oleo with Silcine Grease (as per it came).... done....

I have a bunch of wheel types that could be suitable. First requirement is a smaller diameter than the stock 65mm. So the first wheels pic has 63mm, 60mm, 55mm (too small really). I decided on the 60mm plastic hubbed wheels. For now....

The oleo can also have to top end of it cut of to almost 10mm if need be. Losing the first grub screw set. But you don't have to have those anyway - they are somewhat overkill strength to have 4 in total.
Thus another 10mm approx can be reduced if need be later - just by an easy "cut and clean up" process.
I would do that if I use the 63mm alloy hub wheels.

The last pic shows them attached to the larger "Large sized" retract units, which is more what this size of plane should use, but it is too hard to alter those items in the plane mounts. I chose the left wheel, but I do like the right hand wheel, which is alloy hub and a 'proper' ribbed rubber tyre. So I might change to those later...

...
Dec 08, 2012, 08:57 PM
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Next is the retract....
The Freewing retract has nylon trunions and a reasonable amount of slop in them. I always change trunions to be alloy/metal ones, but you can't do that with the Freewings because they are a fractionally different design to the typical ones, so the aftermarket alloy trunions will not work properly in them. Which I only found out AFTER having changed them all over..... BAH!! (so pics show the Freewing retract modded).

That meant I had to change to using different retracts, which is a pain because Freewing also made theirs 'trigger' by opposite direction servo commands than typical too! This means you need to put a servo reverser unit in-line to the main gear retracts now - and all three Su retracts come off one soldered joint, so you have to re-do some wiring to get the servo reverser into that main gear retract line!!
Thus the project took a lot plonger than originally expected....

The new oleos use a 5mm leg pin. The "Medium sized" retracts use a 4mm pin. So you either have to sleeve the 4mm pin into the oleo, OR drill out the retract trunion to be a 5mm pin. I chose to go to the 5mmm pin....
So trunion into the drill press and drill that out to be 5mm. Which is fine as I need to open and change the retract trunion to the alloy one anyway, so the trunion was 'out' already.

Because the trunion is now all alloy, the thread for the pin clamping screws is all alloy too - not a brass bush that can actually pull out, like the nylon trunions have! But grub screws are always lack lustre compared to a bolt, so in this case I change to using a bolt (you don;t have to!) - which means they will stick out of the retract and thus the retract mount needs some dremelling to allow for the bolt to be there then. Easy enough to do....

The non-Freewing retract also has some lugs on the sides which then need extra Dremelling of the retract mount unit.

I did one side with 63mm alloy hubbed rubber tired wheel, to see how that looked... and it is a much nicer end result!!
The problem is that even with the 60mm wheel it is JUST at AoA Positive Stance, and I really want it a few degrees more positive! But I will try flying it with both to see wha

Both wheel types are wider than the stock wheels, so the wheel bays need a bit of widening on the outer sides - not much at all, as they were already much wider than the stock wheels anyway.

So that was that... all done for now...

...
Dec 08, 2012, 09:09 PM
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When I was checking the Su AoA Stance etc, I saw that the nose leg was bent sidewards at a bit of an angle! On checking, the whole foam "floor" in side the plane, where the retract mount system is, was fractured, bent, pretty well wrecked!! This must have happened on the second (of three) crashes where it came down 'pan-caked' onto its landing gear - but it had all seemed fine after repairing that! Obviously not truly all fine! Probably finished off, and brought to the forefront, in the last "crash" - which was just an "Inability to take off at all and hit a fence post" crash really.

Actually, the last flying day (and take-off crash) long run across grass probably finished off this damage.... collapsing the nose gear X amount "into" the plane more.... which then lowered AoA Stance to more negative, thus made that take-off impossible!! It all adds up now....

So anyway, seeing I have a full "plywood box frame front end" in the Su now, that means I have a way to make an extremely ridig/strong nose gear support system. By using the side plywood rails. So I made an alloy bracket to do that.
This allows my total nose gear "lift" to go to about 11mm now. I have some plywood spacer blocks under the retract also.

In the nose gear pic you can also see the "Oleo hydraulic ram" installed to absorb rearwards "flex/wobbulation" pressures that the slop in the stock retract allows!! They are very sloppy - which can be turned into GOOD USE, by using the fore/aft motion ability to be spring loaded!
You can also see my "Nylon strap oleo to plastic RAM bolted attachement system".... seeing the stock plastic 'loop' broke and disappeared one day....
This bolt idea is far more rigid and permanent! I cut the plastic ram pins off and drilled a 3mm hole through so I could use a bolt instead.

....
Dec 09, 2012, 02:37 AM
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LEF (Leading Edge Flap) modification:

After all the take-off issues, and the last crash and damaged winfg leading edge that it gave, I decided to waste some 'techinical fun' time on fitting Leading Edge Flaps (LEF). Which turned out to be a bigger project than I predicted....

First was cutting off the portion of leading edge to be the LEF. Tha tis pretty easy - just a nice ruler edge sharp knife cut, vertical when the wing is "flat" on a table.
The harder part is BEVELLING the fact of the LEF piece, to the 40deg approx aimed them to be able to move to. Or at least possible to go to 40deg - in real use it might be less than that.
So a lot of sanding, and careful checking of the face angle... more sanding.. etc etc
They came out very well really! So that was good. But you do need to be PATIENT and careful!

They are to be hinged with "Flat pinned hinges" run right at ALMOST the very top edge. You can make slots 'downwards' at 45deg into the foam, so it has a solid place to hold, but the pivot point needs to be dead on the 'surface level' of the wing surface. That way they will pivot down with a remaining near perfect top joint.

The 40deg Bevel means a large opening is there when the LEF is retracted, but that gets covered by a "Slide Strip" so that effectively the wing underside is always continuous, smooth and flush. (see pics).
In the test setup the Slide Strip is thick card, but the real version will use PET 3C plastic sheet. This will maintain its stiffness long term and also 'takes the curve' cleaner and more consistent, due to its high desire to return to flat always.

I did the damaged wing side first, as that only had about 2/3 of the leading edge usable, so if I mess that up I can just make a whole new one anyway. But it all worked out very well right away....


...
Last edited by PeterVRC; Dec 09, 2012 at 06:26 AM.
Dec 09, 2012, 06:14 AM
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The good wing side was a bit nicer to do....

When you cut off the LEF, it exposes a bit of the alloy tube of the spar. I ground that back on an angle grinder, to be flush to the 'new' flat front edge of the wing.

The LEF gets hinged by Flat Pinned Hinges, which about 9 or 12 will fit across its length! This is to give a very true and rigid pivot system to the LEF. Then the top joint is also covered by tape, so that it becomes almost as perfect a surface as the original plain wing surface was.

...
Dec 09, 2012, 06:24 AM
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The LEF closes/deploys fully at about 30deg to 40deg. At this point the two flat faces of the wing and LEF join flat against each other.

The LEF servo, in this case, is a MG 17g Freewing servo. I had taken the elevator ones out and replaved those, so I used those... for now. This is because their issues of poor stepping are not really important in the LEF case. Unlike the elevator the LEF will not move repeatedly and in fine degrees. It will have just three positions. Retracted, some mid point, and a full out point.
MAYBE I will set them up to act with flaperons, and thus be continually used across their entire range, but I will see....

The servo is set so it drives a control horn on the LEF at "Mid stress point"... which means more towards the inboard 'heavy' end. The aim being that it is the centre point of equal stress out in either direction of the LEF from there.

I used nylon control horns - which I use on ANYTHING I ever make a control horn for! Nylon is SUPER strong.... all but unbreakable. Whilst plastic is almost rubbish! I modded it for the shap required and embedded it into the LEF with epoxy.

The servo pushrod and clevises need to be RELIABLE... strong. So based around a 2.0mm wire pushrod, which over this distance is 100% rock solid, it has a nylon clevis at the servo end - because its pin is 1.5mm and the servo horn is drileld to 1.5mm. The other end uses an Alloy Clevis, which fits the 2mm pushrod, and also uses a 2mm hex bolt for the LEF Control Horn joint.
Thus all fittings are 100% fits = 0% tolerance = 0% freeplay. And rock solid.
The only shortfal then is the SERVO, and how accurate it is, or how much slop it has.

...


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