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Old Feb 03, 2012, 11:20 PM
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Build Log
Starmax F-16 90mm EDF jet - Build log

I have decided to add my own build log of the Starmax F-16 for a few reasons. Though I do wonder how many are left to be bought and built, and whether it is an ongoing model by Starmax still (or not). But the main reason is because it is a fantastic model that I can't praise enough so far! The design, the build quality, the finish, are all excellent and equal to the best of any foam aircraft I have seen. Lately some great planes are coming out from Starmax, Durafly, FMS, Art-Tech to name a few I know of. I mean with inteliigent design, great fits, great finishes.... pretty well everything you would HOPE you could get in some company's foam aircraft. Meanwhile some of the other high profile name company's are still producing what I consider "Sub-standard" aircraft. As if they do not have very good designers, and/or production ability, and/or finishing ability. Really poor when compared to the good ones mentioned above.

I am not saying the Starmax F-16 is perfect by any means, but it is easy to make it 'perfect'. And as a starting base it a plane that is alreeady 90% of the way there, and also the parts that are 'perfect' already are things you would not want to have to alter (eg paint finish, which is hard and messy to do). So the efforts to make the completed great aircraft are not that difficult or costly to do.

So anyway, after a month of construction (bits done here and there over time), I have decided the 'awsomeness' of this plane warrants that it gets some exposure, and also the things I have done to (hopefully) improve it - which a lot of others deserve the thanks for either coming up with or sharing to everyone. I used many of those, and extended some, or created some of my own.
I will show pics when it is useful (often I guess), but not to show stuff that has been already posted around the place 50 times (eg unboxing etc). And seeing I have gone a fair way into the build already, I will show and/or "un-do" sections to show what and how I did it, and in an order that is not impossible for someone to be building the plane right from its start also.

Here we go..... (well, at least bit by bit over time)....
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Old Feb 03, 2012, 11:41 PM
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I bought the F-16 from Hobby King (Australia). At $290 incl. shipping, this is a pretty great bargain for an aircraft supplied PNF. Meaning everything it needs to go, bar your RX and battery. Mind you, to make it that more 'perfect' aircraft you wuill need to spend more money. But it will still come in well under a typical cost of such a 90mm sized EDF jet, and it will be a fantastic 90mm EDF jet!

This pic (half useless) shows the fuselage join, of the back end joined to the front end. The HK version comes with the upper and lower fuselage halves arelady joined - maybe all Version 2's do now (?).
I used 4 x 4mm carbon fibre spars to strengthen this join. 1 each side of the body 'edge', as shown in the pic. The other two are high in the upper fuselage, about 40mm from the centreline - I actually forget the measurement, but when you look at it all you will easily see the best place to put those in.
I just use some 3mm piano wire to "drill" the hole into one fuselage half, then use short 'pointy' skewers just sticking a bit out of those holes, to 'prick' and mark the rear fuselage half points for then 'drilling' the piano wire for the rear half. So none are 'external, in slots', they are all 'inside' the body foam (eg half way from inside to outside surfaces).
It only takes a bit of care and checking alignments to ensure all 8 holes are parallel to the centrline of the aicraft so that the CF rods will run through all 4 joins aligned well. A bit of error is ok as the foam will "give" a bit when you assemble it.

Oh, a side note:
I use epoxy for pretty well everything! I keep reading that it is not good for this foam, or that, but I am yet to have a single issue using it for anything! Certainly no more than CA is half pathetic a 'glue' anyway.

So you put a thin flm of epoxy on the 4 rods and feed them into one half - or two into one half and two into the other. Then coat the parts sticking out and also the main join overlaps of the fuselage halves, and make the full join.
Coat both sides of the joins with a thin film applied over every mm of the joining surfaces. Missing a bit here or there is fine. Best is to use 15min epoxy.
Join it up and use you hands pressure to align it perfectly, and sit and watch TV while you hold it long enough for it to set well, whilst making sure it is all perfectly aligned that whole way. Don't worry, the time and effort involved is not that hard to do it like this! lol

Another side note:
Have 5min and 15min epoxy on hand, for the various tasks you will encounter.
And a HobbyKing plug (LOL).... they have great value epoxy, in bottles, which makes it very easy and clean to use. The 'Dual Syringe' types are terrible... or tubes not so great either. Once you have used it in bottles with nozzles you will never want to use it any other way again!
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Old Feb 04, 2012, 12:50 AM
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Ok, this is the rear retract.
The F-16 comes with air retracts now. I say "YUK" to air retracts! lol
No scale speed of motion.... a need to fill the reservoir..... so electrics are the way to go! Well for me anyway....

So strip out all the air retract stuff, and the rear mounts are pretty well ready to go for electric servoless retracts just as they are. Easy.
The total weights of all the air stuff, versus servoless retracts, is very close to equal.

The retract unit is the HobbyKing HKD-312 (which is probably a clone, or like many anyway). They are excellent for 1.5kg to 3.0kg sorts of aircraft. For steerable fronts, and fixed or rotating rears. They only cost approx $7 each (so about $22 for the three required). The rest of the original landing gear stuff is used with these.
I disassembled mine and drilled out the trunion to take 4mm (it was 3mm). This is easy enough to do.
They have two threaded 'clamping' bushes, so I used a 3mm grub screw on each side to clamp the 4mm leg in. It is also good to grind flats onto the leg on each side so the grubs screws can lock it all into place solidly, from each side.

To get the right landing gear leg 'splay' (angles) I am placing a 4mm plywood strip under the outer edge of the retract. For any retract, even the original air ones, you would still need to do this. The resulting angle gives near vertical tires, and closer to realistic spread between the landing gear, albeit with a narrower stance meaning trickier landings - well, you just need to get better at them! LOL.

I will also replace the short 4mm leg with piano wire, because the original wires are a bit soft. And also test with two coils in that.
I am intending to make up "realistic strut covers", to form some more shapes as per real landing gear. eg CF tube of various diameters - or plastic tubes from stuff here or there. To show shock absorber sorts of stuff etc.
And even to add just the leading support system they have - sort of like a runner that runs forward into the fuselage, forming somewhat of an A-frame. That would actually be fairly easy to do mechinically, so watch for that option somewhere down the track.
The secondary vertical landing gear support stuff they really have, would be possible to add also but at the cost of structural integrity of the fuselage down the middle, so I am not going to even try that.
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Old Feb 04, 2012, 01:05 AM
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For the front retract.... that is a bit more work. The hard part is working it out. Doing it after knowing what to do - which is what this build log is also aimed to help!! - is much easier!

So first you 'hack out' the front retract area. Using a Demel and auger bit - well I made that 'auger bit' description up, because I don't know what it is called. The bit that works like a router bit, sort of.
The pic shows the shape to make it match, and the depth down the middle (where the retract body goes) needs to go right down to about 2mm from going right through! That depth is fine and doesn't bother the inner duct, or strength, at all really.

The existing steering servo remains in place to be used. Note a partial channel cut on the servo side for the steering pushrod.
A pushrod... no crappy pull-pull wires here!!
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Old Feb 04, 2012, 01:43 AM
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The nose gear....

For those who don't know how to set up these retracts for steering:

1) Instead of using the two side screws to clamp the landing gear leg, you use them to feed into a 'circular slot' that you dremel into the top end of the leg. A 1.5mm ring, like a circlip would use, and thus the grub screws go into this ring, but are not done up tight enough to clamp the leg. So now the leg can rotate, but not fall out of the retract. Use locktite (as you should everywhere anyway) and set the grubs screws for that ice fit, that doesn't bind when turning the nose leg.

2) Put on a steering arm, that is long enough to extend out past the side of the retract body (any type will do that anyway really), and on that arm you have a long bolt that heads down towards the retract side bush - which is the retracts pivot point. Down that end of the bolt you fit a small arm so you can fit the pushrod into that.
Check the pics for better details on all of this.

3) The exact position of this pushrod arm has to be fine tuned when in situ, so that the retract moving in and out, keeps that arm pivot point in the same place in space throughtout the motions. Thus the servo never has pressure on it, via the pushrod. This is an ingenius sytem!! Easy to do, and pushrods are far far better than pull-pull wires!

Note that in Pic04 my steering is a bit turned, so the pushrod arm is not very close to the retract pivot point. Even when in situ and working, the pushrod arm pivot point is NOT right over the retract pivot point, for it all to work correctly.
You can end up with little 'foibles' in various aircraft, such as the pushrod path making the steering turn a fraction as it retracts, or it turns a bit but then goes back to straight by the time it is fully retracted. So just test it and fine tune the pushrod length and the steering arm 'offset bolt' length, slight bends in the pushrod where necessary, so it works adequately. Sometimes having the steering arm a bit off 90deg when the retract is extended and the wheel is straight, can be beneficial.

At the servo end I use a linkage stopper, as that gives the best motions and adjustability for this setup.
In pic06 & 07 you can somewhat see the pushrod path/shape. It is kinked a bit so it allows the steering arm to come down into the fuselage and not hit against it. Plus there is the foam cutout to also allow that.
There are two 3mm washers between the retract unit and the steering arm, to keep it from catching on the edge of the retract body as it closes.

Also note how part of the retract mounting plate was cut off/away on one side to allow the steering to work. The retract is really held in only by the front two bolts, as rear bolts would do nothing at all for strength anyway. Pressure on the retract is "pivoting it rearwards", so the rear end only needs support under it - the original/existing plywood still runs down that left side in the pics. You can't have any one the right side (the real left side).
It is all very solid so I expect it will be fine as it is.... once again, it will definitely fine for people landing 'properly'. LOL.
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Old Feb 04, 2012, 01:54 AM
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The electric retracts have a new wiring harness made specifically for them, by cutting and soldering servo extensions, but to keep the joint count down.

So basically it is a Y at the rear retracts end - about 50mm for one Y side and 25mm for the other. Seeing the single lead then runs down one side of the internal fuselage wall, to the main upper wiring duct.

This, now single, lead splits again in the front RX area, to feed a connection down to the front retract, via the pre-existing path the steering servo takes already.
Thus all very easy to do once again.....

For setting up the steering....
Use a mix from Channel 4 (rudder) for the nose gear servo channel, and then you can use the gear switch to lock out the undesired steering ability when the gear is raised!!
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Old Feb 04, 2012, 02:51 AM
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Rear body "side-rail" support - and MG tail servos:
This has been shown in the past, but I found two reasons to have the plywood support at the rear side rails under-sides.

1) To strengthen the rear end - which I don't have personal experience showing it needs that, and it alls feels pretty strong to me anyway. But added strength is just a side benefit of another more useful reason for it.

2) To hold in the tail servos and the elevator pivot boxes. Which otherwise have no decent form of support to hold them in solidly!

So the plywood rails are 2.5mm (2.0mm would do anyway). But they are not to be glued down as per the other posted method!
Instead I will feed in and epoxy 5 or 6 plywood 'plates' that each have two captive 2mm nuts, horizontally in from the sides of the fuselage, halfway up those fuselage side rails. These will allow the bottom plywood support rails to be bolted into the plates with something like 10mm x 2mm allen bolts. They would be about 20mm 'aircraft lengthwise' and 20 to 25mm 'into' the aircraft, made of 2.5mm plywood.
This is to allow removal of the support rail for servo changing/repairing, if ever required. Plus no glue ever works 100% solidly on foam anyway, and to use glue you would have to clean off all the paint quite well, so "pulling together" two surfaces (the side rail to the internal plates) is a better way to fit these rails. The epoxied in plates will replace the foam cut out for them and be even stronger in there than the original foam was. The support rail (2.5mm ply) will not quite be as much a strength addition as per a glued on method, but I don't think it needs much extra support really anyway - thus that is not overly important.

The plates will be either side of the servo, either side of the tail box, and then one at the front and one at the rear end of the support rail. (6 needed ?). That is the current thing I am doing on the F-16 (amongst a few other things in parallel)
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Old Feb 04, 2012, 03:02 AM
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In the prior post you can also see the EDF cover in the second pic.
I have epoxied the plywood 'locking plates' on to the EDF cover. They could be left just 'free' and would still work fine, but I figured it must be better to have them fixed as part of the aircraft anyway. Plus they will work a fraction better if glued to one surface (rather than to none).
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Old Feb 04, 2012, 06:08 PM
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Thanks for the info. I have been wanting to pick one of these up for a long time.
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Old Feb 04, 2012, 09:52 PM
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There are plenty of people with comments on how it flies fine, so that part of the aircraft is not too hard to 'see' (tons on YouTube) and accept. The most annoying thing I find with model aircraft is when the actual model itself is sub-standard or flawed in design or materials - yet it still could fly totally fine. You can't see that part when it is flying, and people rarely mention much at all about the actual physical aircraft design and construction, or finish.
I mean in the intelligence of the design - foam thickness, bracing, how parts are joined, how landing gear can mount - or at least even what structure there is to make it solid even if you have to totally refit landing gear mounts etc yourself.
I don't mind fixing, or improving, issues, as long as the base you have to work on is not so lacking that it needs almost as much engineering thought to 'fix' it, than the original designers put into the whole thing anyway! (eg if they didn't apply much overly useful thought at all).

And as per my earlier post mentions, this plane ticks almost every box in the list that really matter to the base plane itself.
Other aspects, like the EDF fan is meant to be sub-standard - the housing too weak and flexes to much. Something like that is a negative still, but it is an item that can easily, and not overly costly, changed. Power system stuff can be changed easily (at a cost), but the base design of the whole aircraft often cannot.
Though there are people flying it just as it comes and not worried about it's 'problems', and are not having notable issues at all. Though I suspect they are not 'techo' flyers, and more likely just throw together anything and just fly it as it turns out. Whether good or bad really. LOL.

And there are probably not too many aircraft that were designed well enough to still NOT need some improving anyway.

Probably the best way to do this F-16 would be via just a basic airframe kit, so that the EDF and air retracts, servos etc, cost is not wasted - IF that could be aquired for a viable price. But you can't get one here (Aust) for any useful cost saving, so the HK one was the only way I could find to get it. Well, I tried a bit to do it that way, but maybe not hard enough, lol.
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Old Feb 04, 2012, 10:18 PM
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In Post #7, pic 1:
I forgot to mention the replaced tail servos. Some minor foam cutting to fit the slightly larger 18g HXT D-MG16 - from HobbyKing yet again.... $9 each (2 of).
And I have 2mm pushrods made up to replace the pathetically flimsy 1mm (1.5mm?) ones they provide with the plane. So this setup will keep things rock solid in the critical tailplane department!

For the all-moving tailplanes, I have added a 3mm collar to the pivot shaft, between the tailplane and the fuselage. This is so that there is a reasonable 'round face' for the tailplane to have for support that will give the pivot system rigidity and that is equal at all tailplane angles (because it is round). It also keeps the tailplanes' face off the fuselage and thus less friction at the otherwise plywood to platic/foam/paint meeting, which also varies the friction result as the tailpane 'face' surface area changes per angle of deflection. Though the real aircraft has them effectively running right on the fuselage, but they have far more room and proper mechanisms running everything.

I was looking at other ideas to give a much bigger 'face' to that tailplane/fuselage contact point - like a thin teflon or nylon plate fixed to the fuselage side of it, for low friction etc. But for now I will use the collar, until I can find that other better solution. The current collar does not really have a big enough outer diameter, which would give it even more surface area for better support and stability (though it is ok), plus it is too thick and moves the tailplane outwards too much, so I will find or make a more appropriate one.
But the real aim is to do the 'plate' idea, if I can dig up something flat, thin (1mm) and rigid enough.
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Old Feb 18, 2012, 02:33 AM
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Slow going... too many things to do!

I made some channels in the sidewalls of the fuselage rear duct for the motor to ESC wires, so they can come out of the motor and head 'straight' towards the rear edge of the fan housing and then be routed down that channel rearwards. This is so they can arc around and then into the original top channel to head forwards again. This allows for my Outrunner fan system, and the original fan system, (or any other I end up using) to both be able to run their wiring outside of the thrust tube (not yet made). So all the airstream gets is a short straight run of 3 motor wires heading to the, or a, side channel.

Next I tested the supplied motor/fan......
In my home-made MDF/pine engine test bench unit.

It needed some balancing, but once I got that done - via a somewhat haphazard static fan balance and then fan position rotation to reach the minimum vibration possible - I built up to maximum power without too much vibration of worry. Not that I know how much matters... preferably to have none. But I ran it up for quite long WOT runs a number of times (whilst a 19mm MDF board/shield was guarding it!!).
To me, it sounds like it is balanced enough to not self-destruct.
Hopefully!
But it does have a few minor harmonic points as you come up through the RPM.

Then I threw on the test bench's wheels (which run it at 90deg - EDF horizontal then).... and hooked it up for a thrust test.
I am not sure what I am doing truly counts......
It starts at 1600W and drops off to 1450W area for a long and fairly constant period then. The thrust measured was 1.4 Kg !!! That sounds a bit pathetic to me, for a 90mm that is eating up 1450 W !!
I have to do some reading to see if that is badly amiss, but I am pretty sure it is.
Surely the F-16 will weigh in the region of 2.0Kg to 2.5Kg AUW with battery?

I have two other 90mm motor/fans to try, so that will also give a clue as to whether or not the 'weak' thrust is truly occuring, or just a function of the testing method.

I will try to add some pics of all this later on.
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Old Feb 18, 2012, 02:43 AM
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Nice thread Peter

Keep us posted

Steve
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Old Feb 18, 2012, 05:18 AM
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As mentioned, this 'loopback channel' in the fuselage allows the ESC wiring to stay outside a thrust tube right to the rear edge of the fan housing. The wiring is too stiff, and a very sharp turn without such an arced path doesn't work well and would not be good for the wiring anyway.
To do this, the motor wires will be extended - not the ESC end.

I think for the stock inrunner (if I use that) I will use some plastic tube, just big enough inner diameter for the three wires, to get it from motor to fuselage sidewall in a streamlined manner - Not just the three wires flailing their way across the airflow.

I also re-routed the elevator and rudder wires away from the motor wires and of course they will go 'around' the thrust tube exterior - recessedinto the fuselage wall. I haven't decided if I will keep them in their own channel all the way past the ESC also, seeing my fuselage is already joined (as it came) and thus that makes it very hard to do new channelling all the way forward.
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Old Feb 18, 2012, 05:49 AM
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Here are some pics of the EDF test rig. The wheel system comes off so it can be stood with the EDF vertical, for balancing purposes. For that I mount the EDF facing the other way so it is fan upwards on the bench.

Static fan balancing is done with a typical prop balancer, suspended between two very strong rare earth magnets, so there is almost zero friction. Electrical tape tabs placed into the impeller hub inner walls to get it balanced out. But I might switch to using hot glue instead.
Dynamic balancing is done by rotating the impeller on the motor/adaptor shaft, to get the least imbalance - "measured", by sound and vibration of the test unit, and a bit of visual - but I have the "mobile phone balancer" system almost ready to go, to fine tune the EDF to a better final optimal balance. (hopefully). And I probably won't do static balancing first (at all) for that method.

I also filed two flats on the adaptor shaft so I can use a small shifter to hold the shaft while I tighten the main nut. You can just make that out in one of the pics here.

The stock fan ran up to full power for long periods, without exploding so far! LOL
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