64mm EDF Jet Trainer - The Falcata

[telnar1236]

For the past year, I've mostly been focused on going fast, though I've had two LW-PLA side projects I've built which are both on the slower end. With those faster designs, I've learned a lot about how to improve my construction techniques, how to reduce drag, how to reduce unintended turbulence, and how to optimize inlets for high thrust throughout the speed range. With the design of the Super Duper Sabre basically done, it's time to take everything I've learned and start applying it to an easier to fly more accessible plane. In some ways, this could also be considered a follow-on to my 50mm jet trainer with the goal of building a plane with more thrust/aerobatic potential and capable of flying off grass that also retains the same very gentle stall characteristics and good slow speed handling. Finally, this can be seen as a sister plane to the Rapier (capable of 133 mph), and my laminar flow wing sport jet (capable of 105 mph). All three will use the same power system meaning that it will be possible to go from the Falcata, to the sport jet, to the Rapier learning how to build and fly increasingly high-performance EDFs. The end goal is to do a formal release of all of them around the same time which will give a sequence of EDFs that can all be built for under $100 using the same filaments (airframe, servos, EDF, and ESC, not including battery or receiver).

The Falcata is a pretty simple 5-channel design with straight wings and a T-tail. The combination of a high wing with flaps and a T-Tail is intended to make this plane grass-capable since a lot of people don't have access to a paved runway. It should also hand launch well, but personally I feel much more comfortable with ROG takeoffs, so I want that to be an option too. In order to take off from rough fields, there will be optional bush tires and lengthened nose gear strut (long nose gear strut isn't designed yet). The suspension is also improved and uses rubber bands to handle the larger bumps it's expected to run into.

Another area of improvement over the 50mm design is the inlets. They should allow the 64mm to get near its 1200g thrust when not in a duct and give better airflow at a wide range of angle of attacks. The 50mm trainer was fully aerobatic and quite maneuverable, but in terms of vertical maneuvers couldn't do much more than loops or Cuban 8s. Having more thrust on tap should let the Falcata do a wider range of things.

In terms of construction, it uses my standard techniques with ABS and fully modeled internals. This remains the lightest way I've found to build a plane and keeps it from getting damaged by hot weather.

I'm guessing this is still a few months out since I need to finish building the Super Duper Sabre and then go through the process of fixing any issues I find - plus I need to release my 50mm F-106 and MiG 15 at some point.

 

[telnar1236]

Got the Falcata built and flying - for a change nothing broke or didn't work right and it flies pretty much exactly as I wanted it to. Only minor issue is that the landing gear is a bit bouncy but that can be tuned by removing a rubber band to decrease the stiffness with no design changes and is really a matter of preference - I may actually leave it as is because it's not actually a problem on pavement and I suspect it will need the stiffness on grass.

Flying the Falcata is a bit weird after flying fast planes like the Super Duper Sabre and Rapier - it can't fly faster than maybe 60-70 mph so I was constantly worried about stalling and was flying it with far more throttle than it needed. This fairly liberal approach to the throttle gave me 3:20 of time on throttle so about 3:30-4:00 of flight time on a 2600 mAh or 3000 mAh 4s battery, but just cruising it should be able to get closer to 5:00 and it should be possible to fly it on up to a 4000 mAh pack for even longer flight times (though I doubt it could lift a 4000 mAh pack off grass). On the other side of the coin, it should still get over 3 minutes time on throttle with a 2200 mAh pack which a lot more people have - I haven't tried flying it on that light of a pack yet, but it definitely does balance with one pushed most of the way forwards and I suspect the reduced weight will make it even more agile.

Takeoff runs are very short, especially with full flaps - I was able to take off from one of the taxi ways going across the runway despite having a bit of a tailwind. It could do with a bit more thrust to have true STOL performance but it's still pretty good. Once it's in the air it's fairly stable although not quite as rock-solid as something like my F-106 due to its lighter wing loading. However, the light wing loading makes it very nimble and lets it slow down quite well. It can turn very tightly and is fully aerobatic. Thrust to weight ratio is noticeably less than 1 so it likes a bit of a run-up to vertical maneuvers - you can just about loop by hitting full throttle and pulling up from cruising at half throttle but it's a lot prettier if you let it build up some speed first. Inverted flight requires a bit of down pressure and is best above half throttle. It also has a really neat trick that I've only ever seen thrust vectoring or dedicated 3D flying designs do before. The rudder is very effective and by cross controlling with the ailerons you can hit more than 45 degrees side slip. The plane won't really keep flying if you do this, but it recovers very quickly if you just release the sticks - I'll probably tone down the recommended rates in the final release but for more experience pilots, it's very fun having such a conventional looking jet able to pull maneuvers like that. Stall is a non-event. You can pin the elevator full back, and it just sits there and slowly glides down. With a more aggressive CG, it will likely drop a wing eventually or even deep stall but the CG I'm flying it with right now gives plenty of maneuverability so I don't see why you would want to shift it back further. Landings are also easy - I'm used to having to land nose high but with how effective the flaps are, this airplane lands well with a quite flat attitude. My first couple landings, I landed at a higher angle of attack, and they were a bit bouncier but also very slow - probably better for grass but on a runway I prefer the flatter landings.

Overall, it's a very conventional and fairly simple plane that takes the best of what I've learned with my speed designs and combines it with the best of what I learned from my modular designs and other projects. There isn't anything new particularly new going on with this plane's aerodynamics - it's more a bit of a grab bag of what has worked the best in the past.

No video yet because I forgot my camera but should have some video soon.