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Nov 22, 2019, 11:27 AM
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Taft Viper Jet - 90

End 2017 I acquired a brand new (never flown) secondhand relatively cheap Taft Viperjet for its electronic components. With still to be assembled FlyFly kits of a Hawker Hunter and an F100D Super Sabre in the attic, I was in need of quality high-blade good 90mm EDF assemblies and that Viper happened to have been upgraded with a E-Jet EJ90-9 nine-blade 90mm fan on a HET700/60/1865 motor with a Phoenix edge HV120 12S EDF and Savox SH0255MG servoís. That factory-balanced EDF set is advertised as producing 2030W with 91Amps at 22,3V: 3,1kg thrust! With the withdrawal of my FlyFly MB339 EDF trainer I decided to fly the Viper for a season before cannibalizing it.

Although the seller told me I just had to install a receiver to get it flyable, I spent more than a week getting it ready during fall 2019. The ESC had been screwed to a plywood plaque that had been glued within the fuselage, no way to unscrew it anymore in those confines. Since that ESC had no battery connectors I had to solder my EC5 plug within the fuselage, not an easy task considering the very thick wires and required heat within that foam environment. The wires also still had to be connected to the motor, necessitating the opening of the taped-over access hatch. That revealed that the fan-housing had been mounted with only two small screws, I upgraded that to six.

After mounting the receiver I discovered that none of the flight controls deflected properly. The previous builder/owner did cut the standard too delicate foam connections through and replaced them by proper nylon hinges, but used an expanding gorilla-type glue that had been so liberally applied that all 15 hinges were completely engulfed by foam and glue, and thus mechanically totally frozen.

The quality strong (3,9kgcm) Savox SH0225MG servos pushed and pulled those control surfaces a little bit in the good direction by bending the entire foam control surfaces, already causing cracks in the process. It took me two entire days to pry the glue away and again obtain free flight control movements. That must have been the reason why the builder sold that model for a moderate price, but I would have preferred he had told me the truth at that time. The Castle CC10 BEC was then reprogrammed to 6 Volts and all the wiring tidied up. Here is a picture showing the damage done to the areas around the hinges during the freeing surgery of the tail section. I also reinforced the top of the flimsy rudder top with a carbon strip.

The nose wheel steers by a plastic geared CYS S0009 analog 1,5 kgcm servo, I wonder if it will cope with grass surfaces. Given the fact he had handed me all the uninstalled large geardoors in a bag and hadnít installed the servos to operate them, plus I intended to try operate the model from grass as well as from tarmac, I decided to make cutouts in the doors before fixing them locked in closed position. That is a system I use on many of my models. It allows the gears to still be retractable, but without the complicated and delicate door mechanisms, and takes care of partially reducing the sometimes large wheel-well openings (and associated drag).

All those jobs with the cutter-knife had caused serious damage to the factory stick-on decoration, which I corrected by brushing paint here and there. Weight and balance was then performed and extra wood glued front and back of the Gens-Ace 6S 4400 45C LiPo battery to avoid accidental CG shifts. The rubber under the batteries was opened up to allow the intended cooling air through. Parallel next to that engine battery I tighten a 2S2100 LiFe flight battery that still can be adjusted front and back to shift the CG without having to use lead, but it will also be blocked after test flying. Forward of that is plenty of room to accommodate my FAS100 Volt and Amp sensor (allowing me to display Cnsp or consumed Mah, on my Tx), as well as the BEC and a FrSky X8R receiver.

Now for some pre-maiden figures: Ready for flight with a Taft recommended 100mm CG balance, the model weighs 3500grams. Wingspan is 1450mm for a length of 1274mm. I calculated the wing area to be about 25dm≤ resulting in a wing load of 140gr/dm≤, that will be a stable ship allowing me to handle crosswind operations. As for the power, a quick glance at my telemetry with the motor running on a half-loaded 6S battery showed 1200W and 74 Amps. Even the present moderate power provides 450W/kg, more than sufficient for a trainer. Probably a fully loaded battery and correctly programmed ESC will increase those values but this already will do for test-flying on tarmac. Awaiting warmer spring weather I stocked the Viper and the Stampe completely assembled on a new rack. Both models require extensive labor to separate the wings from the fuselage but are small enough to be transported in one piece.

Stay tuned and come back for the flight report to be published end of spring 2020.
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