RE: Bob Cat Copy Falcon 120 Jet
Hi, I bought the Falcon 120, a few weeks ago, she is built and ready to fly. I work away from home so will be a couple of weeks before she takes to the air.
I fitted my own built jet, similar to the KJ66 (arnt they all). The only part not home made is the compressor.
Due to this I limit the engine to a conservative 108,000 rpm, which gives me just over 12 1/4 lbs thrust. i wanted something lightly loaded, which will fly slowly and not have any nasty vises(tip stalling). Because my engine is home built, it weighs 3 pounds without accessories, so have been looking for a model like this for a while. some rough calculations show a wing loading 38.8 oz/foot squared at 18 lbs AUW. My dry weight complete with UAT full of fuel is 14lbs 14 oz. i have tried to keep weight down as much as poss. I have ordered a carbon main spar, which should save @ 35 grms. I weighed the individual parts when the kit arrived, for info here they are
Fuse - 1-045 kgs 2lbs 5 oz
Booms- 255 gms 9 oz (each)
wing - 575 gms 1 lb 4.25 oz (each)
Canopy - 75 gms 2.5 oz
Main spar 100gms 3.5 oz
front spar - 20 gms 3/4 oz
Tailplane - 115gms 4oz note my scales are only acurate to + or - 5 gms
U/c legs and blocks (fixed) 185 gms 6.5oz
optional retracts 455gms 1 lb
Fuel tank 1500ml 190gms 6.75oz
hanson UAT - 55 gms
Although I was trying to save as much weight as possible, I fitted the opt retracts (69 UK Pounds), which added 270 gms.
I used 225mg servos on rudders and flaps, but fitted one DS811 servo into the tailplane to save the weight of two servos and extra wiring. Ailerons are DS811
The Hanson UAT weighs more than I expected, the festo conection on the front is really heavy and has a really small hole in the center (1.8mm, if i remember correctly). I opened this up to 2.8mm and machined the hexagon down on the outside of the festo, this saved @ 10gms.
The canopy was a pain to fit. I steamed some 1/64 ply to the correct contour then bonded on a balsa sheet which I could not bend that much. I cut groves all along it and bonded to the ply, whist supported with pegs on the fuse. I then covered this and bonded it to the canopy to produce a deck. I wanted the canopy instantly removable. tried the normal peg in the front of the canopy and a hatch release pin on the rear, but the rear section of fuse around the canopy area is complex inside and didnt want to weaken it. I settled for two pegs in the rear canopy and a good quality spring hatch release on the front. Works a treat, but a lot of work. I like the velcro, and L shaped catches in the earlier video.
A note on the Dubro Fuel tank. The 1500 ml tank fits in niecly, but it actually holds @1800 ml. I have read about this before. i fitted my tank further back than the one shown in the video, as close the CG as possible. I removed the top web of one of the formers, and trimed the 2 formers rear of this one, so the tank slides in niecly. It is retained by 1 large tie wrap that fits around the front and rear spars beautifully. Niece and easy.
Engine is mounted on an ally angle section at front and a double curved ally plate at rear. I have fitted two failsafe lockwires at the rear until the double bent rear plate is tried and tested. 5 degs down thrust was incorported. With engine running, the tailplane is cool (also covered it in heat resistant tape), and with engine running, I can run my hand all over the rudder/fin and tailplane surfaces, no heat. Obviously the hottest period is at idle power staionary on ground.
I will post some more info shortly, might help new builds,
Kind regards Tim Ps many thanx for everyone who has posted.