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Dec 02, 2012, 06:16 AM
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Build Log

F-16 Fighting Falcon - Starmax 90mm - Build Log

The Starmax 90mm F-16 PNF is a beautiful model!! More so if you like F-16's!!
I think they just have this almost classic look to them - a bit of this or that in them, but also a unique end result.

The paint finish of the kit is fantastic - whether in the all-grey camo version, or the blue-grey camo version. I chose the blue-grey, but I like either really!

It comes with AIR retracts, and with so many electric retract options these days, that is a far nicer system to have. Slower operation - not a "SNAP" and they are in, or out!
But as it turned out, setting up a good retract/oleo system was a pretty big task!! (more later of course).

I did a number of "improvements" to the base design - as I always do. To ensure proper operation, flying, and reliability of the plane. I try to cover ALL possibilities BEFORE they are ever going to happen! So I am yet to have a "Oh dear, this thing broke (or whatever) and it crashed.....". LOL

I also had about ZERO faith in the Starmax EDF unit, so even before I bought it I had intentions of going to a CS12 90mm fan unit. Though along the way some issues with those units have turned up (they can EXPLODE! LOL) so I am yet to finalise exactly what will be in the first test flight version! It will be a CS12, but I had a Turnigy 3025-1500kv motor installed in a 'early' CS12 unit, which may, or may not, be safe to use!
I also have a 1600kv 'new stronger' CS12 unit allocated for this F-16.... but I am tossing up on the odds of my 'early' CS12 being fine, because the flawed ones are beleived to have been from later batches than that one.
Eeeny, meeeny, miny, mo !!!

So next I will look at the F-16 and what it 'needs' done to it.....
Last edited by PeterVRC; Sep 12, 2013 at 08:42 AM.
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Jan 18, 2013, 10:07 PM
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Joining the front and rear fuselage portions

The fuselage comes joined top and bottoms, but is also in two pieces for front and rear. So you need to join those. They are a simplistic interlocking joint, so that does not look too good a way to join them just face to face. I put in 4 carbon fibre rods - two along the out edging, and two more around the upper fuselage circumference.
I use Epoxy for almost all foam joints - or pretty well ALL gluing really. Sometimes some foam glue, or CA, but only in 'appropriate' places for their use.

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.

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

Jan 18, 2013, 10:22 PM
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Main gear retract changes

To make the rear landing gear able to use slightly shorter leg lengths, and still have the F-16 at the right height, I made alloy plates to go 'over' the plastic retract mount, so the retract is more forwards. This means the landing gear leg can be shorter, and still fit into the wheel bay area.
This is so that it sits with a slightly positive AoA stance.... which still looks 'right' and assists take-offs too.
You do need to set up the nose wheel to the right height also, for the total result desired. More on that later.

This does nothing to really strengthen the main gear retract mounts. But I did do stuff for that later on.....

Last edited by PeterVRC; Mar 19, 2013 at 08:03 PM.
Jan 18, 2013, 10:38 PM
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Rear servos and elevators

I replaced the rear servos with metal gear ones. D-MG16 from HobbyKing ($9 ea). I also mounted a 2.5mm plywood 'face plate' onto the fuselage so that the elevator's plywood 'face plate' runs against that. This makes the elevator a very solid device, rather than if it is "Just a 3mm rod coming out of a pivot block". The face to face contact means it can't 'flex or rock' in any direction. The friction is minimal (unimportant).

I also ground flats onto the elevator pivot rod. Note that the pic of the elevator pivot is before removing the collar totally, as it is not needed with the plywood 'face to face' plates.

The pushrod system is replaced with a 2mm threaded rod that uses a nylon clevis at one end, and an adjustable alloy clevis at the other. This all forms a very solid and strong assembly, and has zero freeplay too.
So combined with the face-plates the entire elevator system is strong, rock solid, and highly accurate with zero freeplay!

Jan 18, 2013, 10:46 PM
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Nose gear - re-done

After having had previously 'improved' the landing gear on the F-16, it was still nowhere near strong enough for real long term survival! So this time I got SERIOUS on it all !!

It was a fairly major project....
I cut off a length of the fuselage forward underbelly, almost to the main retract starting point - slicing down the glue joint, then across the fuselage.

I cut a LARGE rectangular area out from the inside, for a retract mounting plate to be put in - using a 3mm plywood plate. This is made to extend longer past the ends of the required retract and wheel bay area, so that external plates can be used to bolt into the internal main plate to make an extemely strong total strength - by "clamping" via the EPO foam. Mind you the main plate is epoxied in strongly too - but that would fracture and fail over time if only that was done.

This large plate area allowed mounting the retract the 'proper' way (off its top instead of from its bottom side) for a pushrod steering system to be implemented optimally.
The foam in this area is 'destroyed' from numerous retract breaking out cases etc, but I will fix it all up to be just the bare minimum opening area required later on. The external "clamping" plates will be filled over and painted too.

The steering servo, I changed to a MG one and laid it sidewards so that it is down and out of view now.

For re-assembly I inserted three carbon fibre rods longitudally to the rear end of the "front cut-off", so that it gets a lot of its attachment strength back via those rods, not just the UHU POR used to glue it back on with. The rods are expoxied into the front portion, but just slide fit into the rear. This still allows slicing off the glue joint again if ever required.

"Stress testing" shows this assembly is as strong as the plane!! It spreads the forces over a very large area and if it breaks out ever then you have had some serious crash!! LOL
Anything you ever 'strengthen' needs to have the right balance of "what fails first, and under what situation". Such as, it should ALL survive any situation up to X amount above typical, eg survive quite heavy landings with no aircraft detriment at all.... and if you go over that X amount, then you have encountered a situation where there is more to worry about than just some cracked out landing gear bay!!
Another good "stress balances" test/result of retracts is that the RETRACT PIN should be what BENDS under "Above average landing stress", NOT have the mounts or retract itself break.

Jan 18, 2013, 10:48 PM
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Main gear - re-done

For the mains, I had already put an alloy plate over the stock plastic retract 'bay' - not for strength, but to allow repositioning of the retract a bit more forwards, whilst also bringing the retract unit outwards of the fuselage just a bit. This was just so I could set up the required oleo leg length, and final wheel bay storage and a desired positive static AoA stance of the F-16.

For strengthening - seeing one of the main retracts tore out on a grass landing too!! - I drilled a 3mm hole through the retract plastic 'bay' to allow another form of "clamping plate" to be put inside the fuselage/ducting and thus add many many times the strength to the retract bay fixture. By default the bay relies just on CA/foam-glue to hold it in, and that just tears out of the foam easily anyway!
Ideally the internal plate should have been quite a bit larger, but also CURVED to suit the ducting wall shape, but that is much too hard to do on the F-16 with the underbelly already glued on. Otherwise I would have done that and used dimensions double in each direction to give FOUR times the area of "clamping plate". That would give a result as strong as the nose area.... but this current method will still be very good, and probably adequate anyway.
By NOT having that larger plate, it lowers the level of stress (incident) that could tear the whole clamping plate out of the underbelly!! But I think even this area size it has will not have that occur unless you encountered that "more to worry about than retracts" situation!

Note that the internal mounting plate can STILL compress into the foam a bit, and thus end up with a bit of play in the main gear mount! It would have been good to have an open fuselage to do it all properly inside there!
I am investigating fibreglassing, with epoxy resin, that whole main gear area!! To make it a truly adequate structure for all 'normal' landing sisutations (eg grass etc) and last long term then too!

Jan 18, 2013, 11:13 PM
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New Oleos and Wheels

After using them on a few other planes, I am changing to these HobbyKing oleos for all aircraft now! They are very well made, smooth acting and robust!
For the case of the F-16 I used the 100mm version for the main gear legs, and the 75mm version for the nose gear leg.
BUT... you need to modify the nose leg to be even shorter!

To do this you disassemble it and drill and tap a new 3mm pin position for the locating pin. I did that after installing the main gear and checking what nose gear length was needed to look right, and have the desired slight positive AoA stance. I think it was about a 7mm shift of the pin.

I also cut all springs a bit shorter, as tested and required to have an appropriate level of suspension strength for the aircraft's weight.

On the main gear legs, the axle (4mm that comes with the oleo) was bent to give the required angle that an F-16 needs the axle/wheel to be at.

They work very very well ! So this final landing gear setup is how it should all be! But note the nose gear pic.. the retract to oleo pin is BENT! It is best to change thos pins to be Motor Shafts, which are hardened and won;'t bend. Those will shear off in a big crash, because they are brittle, but will survive through all normal landings, including on grass and rougher landings.

Jan 18, 2013, 11:22 PM
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Motor/Fan combo and cheaters

I didn't like the Starmax EDF unit at all... far too flimsy and cheap!
I replaced it with a CS12 fan and the Turnigy 3025-1500kv "heli motor", which tests have shown it to be a good low cost motor to use.
I took off the motors end plate cover (just screwed on) to allow airflow through it.

I kept the stock ESC, which is "100Amp" and my peak current is almost that. But for the most you would fly from 80A to 90A areas.

The thrust in-plane was well down on the bench test reuslts, so I cut out a pair of rectangular cheaters on either side of the underbelly just ahead of the fan unit. That helped get more power capability back, but it is certainly not a 'high power' setup.
I have a 1650kv motor to change into it eventually.
I also want to test the stock Starmax motor in a CS12.... I forget the KV... probably too high for 6S use. (1700kv? 1770kv?)

Jan 21, 2013, 03:52 AM
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Nose gear retract parts and operation.

I had used the HobbyKing:
and that has a 4mm pin, but the oleo has a 5mm pin. So I used an alloy tube for a sleeve to bridge that gap.

The other thing I did was grind down the 4mm pin's "top flange" that keeps it in the trunion, because to ever take out the pin (eg to straighten it if it bends) you then have to remove the retract and disassemble it! So I make it into a plain pin and then grind a 'ring groove' near the end so that you can then use the two 'leg clamping screws', that go into the sides of the metal trunion, as 'locking guide pins' to then keep the pin in the trunion whilst still allowing it to rotate for steering. You just use some blue loctite so those two 3mm grub screws will stay at the point you adjust them to, so they are in that pin groove but not tightly so as to lock the pin from turning.
Easy to do, and then it means you can remove the whole oloeo and pin easily at any time - without removing the retract at all.


F 16 Retract & Steering operation (0 min 32 sec)
Last edited by PeterVRC; May 16, 2013 at 08:04 AM.
Jun 03, 2013, 08:53 AM
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Landing Gear redone

After a few flights, and more landing gear damage than flying (!!) - due to my useless flying field with its runway inadequate for larger aircraft - seeing the LG was damaged the last time out I decided to re-do the main landing gear mounting setup so that it is 'very robust'.
Plus because now I do have a 'large' hard runway 'airfield' - a 4 lane roadway of over 600metres!

I pulled out all the stock plastic mounts and made much larger 5mm plywood plates to epoxy into the fuselage, from the outside. This is because that is far easier to do on a fully assembled plane. If I had a KIT then I would also do stuff from internal, to give greater fixture strength. Having to do it externally means I will need to use some fibreglassing to reach that same total strength level.

Basically you want/need a "one piece" landing gear assembly, if you could - from mains to nose gear. Joined via a sub-frame type assembly. Otherwsie two very strong separate sections - nose gear, and adjoined main gear units.
Thus why I will fibreglass right across the belly from side to side to have the left and right main gear adjoined then.

I also moved the main gear approx 40mm more forwards - to be where the real F-16 has it. This is to assist rotation on take-off, by being closer to the CofG. In the stock form it is WAY behind CofG.

I made up and put in the main gear mounts and the main gear, and made sure they were equal/symmetrical. I also cut out the required extra foam from the fuselage, for the more forwards gear storage, but I also filled in all the unecessary 'open' areas around the stored main gear.

I could not get the wheels to go completely into the fuselage, as you would need 105deg retracts to achieve that - or maybe ones with a lot of rotation of the wheel as it goes in. That would be nice, but too difficult and/or costly.

I did make one BOO-BOO......
I did not check the HEIGHT of the landing gear, and I had decided to give it a bit more wheel track - wider spacing - which of course meant some of the oleo leg length went into 'width' instead of 'height'. So I lost 10mm of height or more!
The rear is a bit too low for my liking now. By about 10mm or so.
I will think about solutions for that, but it will be passable as it is for now.
It just gives too much Positive AoA stance and just looks to angled. And also means the rear underside dorsal fins will very likely hit the ground on any roation over about 20 degrees - which I guess I don't really want to do anyway, but could be a hard task to assure you don't do!

At this point I have not done the underside fibreglassing, as I will assess the whole thing a bit more before committing to that - there will be no changing of anything after doing that fibreglassing!

Jun 03, 2013, 08:56 AM
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Missile mountings

I cut off the wing tip missiles, and made screw on mounts for those and also the inner mid-wing missiles. A few 2.5mm plywood plates, on the wing and also 'in' the missiles, so they can be easily removed or re-fitted.

The missiles are a bit vulnerable to damage, so it is better to have them off for transporting - plus you might want to have none for some flights.

Jun 29, 2013, 08:50 AM
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Landing damage....

A tip: NEVER have an offset nosewheel setup!! LOL
eg the wheel being off to the side of the oleo leg - make sure it is central to the oleo, whether via a "dog-leg" (like a P-51 main gear has) bit at the bottom of the oleo, or a "stirrup" (U) assembly.

On one landing - not that many after doing the nose gear - the stress that an offset wheel causes just dragged the oleo off the filed flat, and to a 30deg or so new angle... and sent the F-16 off into the road-side gutter, which it did not like that much!
The nose leg bent a bit... one main gear retract mounting plate was torn out, in half, so that whole main leg came out. Luckily a gutter is the change from road to... whatever.... grass in this case. So the rest of the plane shot over that gutter jump and onto grass, so it wasn't damaged in any other way.

So.... time for a PROPER nose leg setup!!

I picked a set of metal retract landng gear - they are actually Lander.
Turnigy Full Metal Servoless Retracts with Oleo Legs (Tricycle, Habu type)

This is the only set with a nose leg anywhere near correct for the F-16. As it turned out it was excellent and just right!! The main gear retracts I left as per what I had, but the metal retracts are much slower to operate - about half the speed - and that looks much better! So I will have to change the main gear retracts eventually too - so that they also look good!

I also repaired the main gear mounting plate, and made an alloy "bridge" that conjoins the two main gear mounting areas, and forms a very strong chassis for the main gear. It was all calculated to be well suited to last long term under normal uses, and in a bad crash it will pull out the main gear as one assembly (hopefully never!).

After a few flights today..... EXCELLENT. The F-16 now tracks perfectly, and ground handling is just perfect! Between the main gear rubber tires.... their oleos... and the nose gear oleo and centred wheel.... landings are just a perfect energy absorbed, no bounce, smooth process! And it goes straight... or where you want it! So now it is a JOY to land.. and even to take-off!!

As for the flying..... it flies well, but is just a bit underpowered for my liking. But I do fly it around at 60% throttle to protect the Turnigy 1500kv heli motor, which is not really up to the task.
I set my timer for 3.0mins and if I land right away then, it typically is 4100mA sort of area recharge. So that is not good as far as increasing the power would go! eg a higher KV motor. The flight time would be even shorter!
But maybe a better motor, of higher KV, might run under less stress and be moire efficient too!
Otherwise a 7S or 8S solution would be needed.
I like my Turnigy Fandrive 3968-1500kV CS12 on 7S setup (not in any plane yet) so that looks a good candidate for this (and many 90mm jets!). I have to check the 7S battery fit.... for that I use a 7S 5800mAH.

Jun 29, 2013, 07:50 PM
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F-16 down!

I didn't really like that Turnigy 1500kv heli motor!!

A number of times, over flights, it 'coughed' and sputtered at times, just for a second or so.... not very often. But every time I tested it stationary it ran non-stop and fine, even if pulsed off/on and varied acceleration etc.

This last flight, as I taxied it out and slowed to turn back 180deg for take-off, it didn't spin up after resuming some throttle. But another move to zero throttle and then up, had it all running again.... a bit of a worry!! But off we went anyway!

About 1.5mins into the flight it suddenly went 'quiet', and I instantly recognised it had lost power. A quick flick back through zero, to maybe 'reset' the ESC didn't help. It was only up at about 8 metres so I knew it was a very critical and narrow time frame to plan the response!
I was heading DOWN wind so I was going to have to turn back! Plus it was heading towards an outer bound fenceline, and continuing that way would be a long way away to see, plus hit the fence or something, so I needed to get it back into the nearby grass/field area. Turning back from down wind lost height FAST!! I did pretty good job really - it could have been a tip stall disaster really(!) - but it only made it to about 160deg of the turn and was out of height and pancaked into the field... then flipped when a wing tip caught the longish grass. DOH!

If not for that it would have probably been a zero damage event... but that catching force, and the flip, broke things....
It won't need a lot of repair... (aileron ripped off... wing tip torn off.... wing bent).

This time I will put in a decent motor and ESC!!
I can't even remember what ESC is in it.. maybe the stock one. The fault seems more ESC like than motor, in the way it acted, but I will have to test things to see.

I normally take photos of crash events (air crash investigation!!) but I totally forgot this time.....
Jul 06, 2013, 07:58 AM
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F-16 Power system failure

On investigation, one of the ESC input side capacitors 'blew up'... exploded... epanded and burst....
That is an interesting thing. The battery side wiring is fairly long.... maybe 30cm or so. So this MIGHT have been a factor in the capacitor dying.

The motor feels OK... more or less.
The windings are very dark... verging on black for some. But it spins freely.
I would say that it was under high duress.... over currented. After all it is just a "1300W" spec motor.... and running at 2000W or so for WOT.
So maybe the motor is not 100% OK, though I don't think it can cause an input side ESC capcitor to blow. I would think that is more due to inductance of long battery leads. ???

I am changing the whole fan unit, as the CS12 blades also scraped the housing! Maybe due to the motor "Stuttering around" at times.
So the F-16 will now get a "Lander 12 blade rotor, in a CS12 housing, with a DrMad Thrust (Lander) 1620kv 3674 inrunner".
A more decent motor for the job!!!

And also a HobbyKing SS Series 190/200Amp ESC.
Mind you the stock ESC was 100 Amps and is MUCH bigger.... almost double the volume in size! Though 100 Amps is cutting it close for a good 6S system on a CS12 or Lander12 fan.
The SS Series 190A is cheap, but seem to be very good. And they are also 7S capable (and even 8S, with a slight downside), which is the real aim for having that installed for the future.

The new motor/fan combo should give a bit of extra power/thrust for it......
But an aspect I don't like is that doing that on 6S means even higher current levels! I will see how it goes and then re-assess......

Jul 09, 2013, 08:44 AM
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Power System upgrade and more mods

I made up a CS12 with Lander 12 blade rotor, running a Dr Mad Thrust 1620kv 3674 motor. With an SS Series 190/200A ESC.

Then because running wires, and fitting the ESC, is all so cramped inside the assembled fuselage, I decided to cut off the whole bottom portion to make it a "bolt on removable sub-section". Thus giving total open access to the plane's interior.

I sliced it along the stock join line, until the point where that steps away higher - so I kept going in an almost linear horizontal path.
This removed lower section is the whole landing gear assembly portion too, so it will need to be attached to the upper half quite well. Probably with some "keying" and also probably some bolts.

I rewired the landing gear setup to run all servo wiring up through the very front hatch area. It also needs to be run in a manner that can come out if the lower section is removed again in the future.

Most of it is done. The main thing to do is decide on the exact "Keying and bolting" design/method.....


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