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Jun 18, 2021, 11:46 AM
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Freewing F104 Starfighter scale approx 1:12


Rationale

Pic FX65TAM78 Wild


After having clocked 1200 flying hours on the mythical F104 Starfighter during the seventies, I was eager to also have one in my model collection. Knowing how tricky the real one was to land, I kept a 2018 model of the Freewing 1:12 scale 70mm EDF PNP Deluxe kit in the attic during years. After having flown my Freewing T33 in Belgian Viet-Nam colors I wasnít afraid anymore of applying such a color scheme to the diminutive F104 (only 66cm wingspan). The choice of a particular scheme then was a no-brainer, I opted for the FX65 that I had the privilege of flying exclusively during the 3 month training and actual NATO Tactical Air Meet 1978 at Wildenrath (RAFG). It was a rare opportunity during which BAF F104ís wore the name of the pilot and crew chiefs below the cockpit during the competition week (not during the tactical week).

Pic pa at starfighter


[U]Analysis/U]

The early EPS kit was light and its parts needed minimal time to assemble to obtain a USAF model of dubious flat colors (the tan looked much too brown) with glossy decals all over it. It was still preferable to the silver kit version because rubbing that off created even more of a mess in house. Although the fuselage measures 140cm long, the wingspan is a diminutive 66cm and calculates to only 7,03dm≤ wing area (compared to 25cm≤ for the T33), keeping the model light seemed paramount. As with the rest of their models, Freewing (labeled FNRC on the box) delivers good quality scale-like foam kits but equipped with landings gears that seriously deviate from scale. Their F104 being no exception, sporting gear legs almost twice the scale length. Shortening the main gear legs would also reduced the already narrow track. As I intend to (one day...) fly it from grass Iíll initially keep the gear as in the box, hoping they can survive flying it only when the grass had been manicured very well. Adding pylon tanks could hide those long legs a bit.

After unboxing I first tested all the servoís before removing their link actuators. Contrary to many foamies this one has proper nylon hinges to augment the weak foam connection and mind you, both were essential because of the spongy EPS foam I first made the error to cut through the foam only to find out the factory foam glue around the nylon hinges wasnít sufficiently rigid to keep the aileron tightly in place and I feared possible flutter or loosing that aileron during high speed flying. I corrected the problem by applying expanding glue into the hinge cavities and refrained from cutting through the other foam hinges. The nylon hinges for the flaps were attached differently and were rigid but allowed the flaps to move up beyond the up position. I corrected that by gluing 0,8mm ply strips against the aft part of the wing. Thanks to the use of a reverse servo for the starboard flap, single channels for flap and aileron operation are sufficient. Port and starboard wings had been constructed differently, one wing having the servoís glued unpainted in the foam, the other with servoís held in place by plastic plates held with 2 screws in a custom frame! The glued in servoís prevented changing the arm angles to obtain mechanical differential when using a single channel for aileron movements.

Pic5578cr


A panel below the EDF unit can be unscrewed to access the fan assembly and the Hobbywing 80Amp ESC with 5v5Amp Bec. The ESC wrapping had been cut away where possible to augment cooling capacity and was held in place rather loose in front of the fan by two nylon straps. The 3065-2100kv inrunner motor and 12blade-fan are encased in a strong metal housing. The panel covering all of that has two large cheater holes to augment the air-intake volume and help cool the ESC on all sides. That also allowed the air intakes to remain scale, but they augmented the volume by seriously downsizing the intake cones. Cheating with the paint will help hide that later.

On videoís the model can be seen landing at high (wing) angles of attack, especially considering the 70į of flaps that some use. Real Starfighters needed blown air over the flaps (BLC system) to help the airstream curve the 45į full-flap angle. Contrary to the real one that had a symmetrical ultra thin wing with sharpened leading edges, the model has an entirely flat intrados and seriously curved thick extrados. That is only obvious to attentive scrutinizers, doesnít detract the scale aspect, but changes the behavior completely versus the tricky one of the full-size F104.

Pic 5576cr


Modifications and assembly

Trying to delicately remove the decals proved impossible even using quality strong adhesive tape, as with the T33 I had to use aceton on a rag. Be very careful doing that because aceton eats EPS foam, so carefully rub the decals to dissolve them without aceton penetrating below the paint. That locally contaminated the factory-paint but as the Humbrol paint covers both bare foam and painted surfaces equally well, I first removed all transfers from the model. Note to kit-manufacturers: please provide a SEPARATE decal-sheet so users can apply or replace/combine with custom artwork, or sell us cheaper so-called white-models without any paint nor art-work. Motion RC Europe showed new decal sheets in their spare part offers so I ordered that because of the excellent nomenclature on it. I also ordered an extra pair of tiptanks to later modify as pylon tanks (as a strike unit we often flew with tips and pylon tanks). A lighter 6S3300 30c battery was also ordered because it also is suitable for my 500 series scale helicopters. A spare 12-blade fan completed the order.

I used lightweight filler to close all the gaps between the servoís and around the wires plus most of the all too deep panel lines except on panels that were often opened on the real one. As I read that many guys had problems with the nosecone separating from the fuselage upon (not so smooth) landings I added 3 extra magnet pairs to reinforce. I also glued scrap foam in the all too large openings around the servo arms in wings and tail. As I hated those thick square trailing edges on all the control surfaces I I used a long wide raspy file to thin the trailing edges both at the intrados and extrados so they end in an ultra-thin edge, using a bit of PU wood-blue to reinforce where needed. The EPS allows material to be filed straight, EPO is much more difficult in that respect because it would have ended with unequal cell heights. While sanding I took care to also eliminate all mould stars along the entire model and after some more touching up all the separate parts were ready for painting.

Pic5579


As the camouflage lines of the real BAF 104ís didnít match the ones to the model and
passed along many sub assemblies I had no other choice than to assemble the model before painting it. Instead of using the kitís epoxy I preferred my expanding PU glue and therefore used the knife to make cuts all over the surfaces to be glued (for better and deeper bonding). I started by gluing the wooden lower fin into the belly, that was nicely snug. When dry-fitting the vertical stabilizer into the tail section it immediately became clear that it was much too loose and wouldnít provide
sufficient lateral support to dry square to the fuselage. I used strips of 0,8mm ply in the gap on both sides to obtain a proper tight fit before taking everything out and apply glue on both sides. When that was sufficiently dry I used the same procedure to join the entire tail to the fuselage but fumbling to get the tail servo wires and connectors to lay flush in the gutter was a messy affair with the glue interfering, and not mentioned at all in the instruction manual. I used pins to line everything up and after using a servo tester to ensure electrical continuity of the wiring between receiver and tail servoís, the assembly was allowed to dry overnight, standing on the tailpipe to keep the joints tightly together.

Pic5580c


The painting was done using the many pictures I had collected in my albums during that decade of flying the rocket with wings. The ordered spare decal sheet did not come through, they sent sheets for a silver model instead. Although the correct decals sheets were still advertised by Motion RC as available, somebody messed up the SKU numbers and the sheets I needed were out of stock forever both in the USA and in Europe and was promised a refund. I thus was forced to use a combination of the Caligrafics artwork with some nomenclature by Freewing and hand painting more details to decorate my model. Next I tried to connect the servo linkages to the control horns again, using a servo tester to to setup the mechanical throws. Thatís when I discovered that using the kitís linkages and nylon kwiklinks didnít work on the control surfacesí outer holes of the control horns. That hole was much too wide and for precise control and eventually could be the cause of flutter. As anything but the outer holes would result in too large throws and my metal 2,5mm kwik links weigh too much and couldnít be connected properly to the thin pushrods needed in the servo arms, I resolved the problem by gluing shut these outer holes a redrill them to proper 1,5mm diameter. I then lowered the gear and mounted the horizontal tail to the vertical one. As it is solidly fixed by two screws and once inserted, the vertical carbon tube prevents the horizontal tailplane to be slid out again, I didnít apply any glue to the carbon tube and just slid it into position (possible later removal for maintenance). After some more touching-up I used a coat of relatively flat varnish over the entire model to get a uniform finish and better fix the decals and stickers.

Pic5592cr


Pic5593cr


I took the model to a friend, removed the nosecone to put it vertically on a scale and measured figures for both batteries. Although I initially favored the 6S3300 it didnít prove sufficiently heavy to balance the model so all the figures you see on the technical recap entry are for the 6S4000 60S battery. That motor is very powerful and our model has a thrust to weight ratio close to one, but with only 7dm≤ wing area wingload is an astronomical 286gr/dm≤. I also calculated the wing cube loading but that also amounted to an astonishing 108, more than four times the value of my other EDF models. That made me decide to postpone the maiden till my flying abilities and confidence reach better levels.

This build-log will eventually include flight data and pictures but I cannot foresee a date soon for that.
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Jun 18, 2021, 11:47 AM
The sky is the limit
BAF23's Avatar
Thread OP

Flight behavior


to be published later
Jun 18, 2021, 11:48 AM
The sky is the limit
BAF23's Avatar
Thread OP

Technical recap figures


Dimensions: length:140,3cm, span:65,6cm, height:35cm, wing area:7,03dm≤.
Loads: Wing load 286gr/dm≤. Wing load cube: 108 !!
Power load at battery: 1786W. Effective output motor: 589W. Power load model: 293W/kg.
Weights: Total empty: 1390gr. Takeoff weight: 2011gr (6S4000)
Thrust to weight ratio: 0,94
Batteries: motor: 6S4000 Rx:no separate bat
CG: initial: 2,8cm. Final: 3,2cm?
My final throws: Ail: +- 10mm, Ele: +15 mm- mm , Rud: mm L&R, flaps: 0-30-40mm (up to 75į! is ok)
Motor:inrunner 3065-2100kv 1500W 66A 2,3-2,5kg? Fan:70mm 12blade. Measured thrust: 1,9kg
ESC: Hobbywing 80A with 5v5A BEC
Servos: all 9gr plastic except ELEV: 9gr metal gear. Retracts: .
Expos: aileron: 35%. Elevator: 35%. Rudder: 35%
Mixes: throttle to rudder: %. Aileron to rudder: .. Flap to Elevator: +4mm, +6mm
Paint:Humbrol DK GR 116, TAN94, LT GR 105, Belly 28, varnish v33 mat


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