FMS Alpha Jet

Introduction:

I had this kit for a long time now, but didn't want to build it yet because I didn't feel the need for something fast. Since that has now changed, I decided to build this out to see what it can do.

Components ($40):

• FMS alpha jet glider kit
• Emax 1806 2280kv motor
• 12amp esc
• 4 channel micro receiver
• 4g servo (ailerons) & 5g servo (elevator)
• Bamboo skewer (aileron and tail)
• Misc weights (for balancing CG)
• Magnets for canopy & fuselage
• 6050 propeller
• 3d printed & hand modified bonsai motor mount
• Push rods for aileron & elevator

Conclusion:

I initially wanted to use a 1306 motor, but after thinking it through, I decided on using something bigger since I wanted it to fly like a jet and not lack power in doing verticals. The 1806 was a compromise as I had wanted to go with a 30gram motor instead, but had trouble getting it to balance on the factory CG for the kit. Keeping the tail light and yet removable for adjustments was definitely a challenge. It came out heavier than expected since I had to use weights in the nose. The elevator servo position was also moved as far forward as possible to avoid too much nose weight. Powering it up in my hand, I can already feel a lot of torque roll from the motor, so I fear that hand launching this may be a challenge unless I can keep my hands on the roll control on the transmitter. Total weight is 160g w/o battery.

Update 1 (after maiden) - I took it out today for the maiden and on the whole things went pretty well. It took me a couple of tosses to learn how to best get it in the air due to the torque roll (which was expected). The key was to hold it on the belly an inch behind the COG and throw it hard at about a 30 degree angle (half throttle). If you throw it too gently, it will roll upside down. Too much throttle initially and it will also roll during launch. The roll rates are amazing, and it is pretty quick, but definitely not a rocket. I think a 3s battery will be needed for any kind of speed. Overall, I would say it is a success and I may end up using 3s to see how it performs.

Update 2 - I flew it a couple more times and broke it on the 2nd flight flying in a smaller field than where I usually fly. This thing is a little faster than I remember, but I think speed is inversely proportional to the size of the area you fly in. :) After I hot glued it, I flew it again the next day and I've come to the conclusion I have a lot of learning to do when it comes to flying jets.

Update 3 (conversion to 3s - 6/8/17) - After a couple of crashes on 2s, one of the nose weights was lost. Instead of trying to find the perfect replacement, I decided to remove the other nose weight as well and use another battery in the canopy instead. It was hard deciding the placement of the 3rd cell as the canopy was already tight on space. Overall, she is now a tad tail heavy, but not too bad (still perfectly flyable). With 3s, unlimited vertical is possible during the first minute or so of flight while the batteries are still fresh. I should note that with high discharge cells instead, she should be capable of much more than she is now. Overall, she flies much faster than on 2s (pretty much everything I envisioned when I set out on this project) - even with the low discharge lipos I currently use. In fact, she's a bit too fast for the field I currently fly in. With just half throttle, the only thing I can really do is circles around the field. If she's not always turning, she's be out of sight in no time. The only other thing to note is that the initial conversion to 3s didn't go so well because I didn't have enough elevator authority (control surface was too small). The elevators I had initially cut out were sufficient for 2s, but far from enough for 3s. I had to extend them out (double the size) before I got her to have enough bank for aerobatic maneuvers.

Overall, a ton of fun on 3s, but size is a limiting factor. She gets away from you a little too quickly. You'll need a larger field for her to fly in and due to her size, you'll have problems seeing her in the air. I'll need to order some higher discharger lipos and try to unleash her full potential. For now though, I consider myself done with modifications for this plane.