whale2

Then I'll opt for making it so ugly, the earth will start repelling it. But seriously, power should get me more speed and more speed means more lift even with not so much of an efficient wing. Also, I did a crude test with sticking ton of short threads and blowing into the wing. Don't have a video, but the flow behavior seemed reasonable - re-attaching after that step, separation on higher angle of attack as expected and such.

Indeed, weight is the issue. The idea is to overcome it with sheer raw power and speed. It is overweight by about 2 kg compared to normal RC models with similar wingspan, definitely will have greater stall speed. About 5.4 kg Anyway, tested motors parameters with watt-meter. I was able to get 48 A on the test stand before, but now I'm getting only 42 with 7x4x3 prop (and obviously less thrust). Tried all possible combinations of whatever possible (batteries, pull-push swap, etc). Managed to get 50+A with 7x4.5x3 prop, but I've got only one of such.

Quickly checked the thrust of both motors... So far results are not particularly satisfactory. Based on my test rig results I expected 50% more value... Will test tomorrow with the watt-meter in attempt to figure out the reason.

Installled second motor/ESC/battery wiring, mated wings, made the wingbox

Measured the thrust once again, but in pusher configuration and got expected 18N of thrust @ 48A. Seems like in the puller config the propwash was pushing the scale plate really hard giving the wrong numbers (those were the rookie numbers!) Installed the motor, controller and wiring. Tight fit, but seems all right.

My point was that even cambered plate has somewhat elevated Cl. The actual wing is resembling Kline-Fogleman airfoil (https://en.wikipedia.org/wiki/Kline–Fogleman_airfoil) . While not very efficient, this one is quite doable with Lego. My hope is despite of high drag, this wing (with flaps) could reduce stall speed to a manageable value. Of course, this is a speculation, we'll see how it go. Also hoping to force through the drag with raw kilowatt-plus levels of power. Tried my prop test rig, so far not very exciting - got max 9N of thrust pulling almost 70A @ 14V. Going to re-check if I'm doing it right... (Late thought was the rig really should be horizontal, not vertical...)

Thanks :)

This paper suggest pretty high Cl for cambered flat plate, though, mostly talks about smaller Reynolds numbers. https://arc.aiaa.org/doi/pdf/10.2514/1.C034415 Having a flat plate still gets me a little bit less then twice the speed. Some other factors like WIG effect may play, but anyway, I'm ready to accept the error here and fully prepared for the total fault :) You bet That's the backup plan

Flap, old and new ailerons:

Sorry, I never stated that here gonna be LEGO motors for providing thrust. I have a bunch of 400-600 W RC motors with set of 6-7" propellers with target thrust about 12-14 N from each. Crude simulations I was able to get show that stall speed is about 40 km/h and wing drag is about 10N at this point. Wing placement was checked for proper CG location before finalizing its position.

This is a continuation of this project, which seemed to be quite thoroughly shelved, but recently got some new traction. Well, it's been a while... Since then I've changed few jobs, moved to another country and managed to bring the whole thing with me not losing any significant bits, except, maybe, LiPo charger. A lot of information is given in original post, but the short recap - this is an attempt to make a flying machine with 99% LEGO airframe. The powertrain and control system are, of course, totally non-LEGO, but, you know, the goal justifies the means... Though actual flying is not very likely, I did everything in my power to make it as close to the real flying thing as possible. At least, it should spectacularly burst into bricks :) Anyway, people call me crazy for this, but I don't mind. Let's have fun together :) Ah, yes, in order to keep the bricks together, almost everything is glued, except various fairings, access hatches and so on. Wing, tail fin, nose are also detachable. Since the restart, I reworked the flaps and literally a week ago I've found those Lego-compatible servo motors (like those used in this nice walking robot) Before that I planned to use micro motors with separate potentiometer, standard servo controller and H-bridge for higher Lego motor voltage. This even worked, but the torque of the micro motor is really tiny (about 1.5 N*cm) and that bothered me. New servos are sporting more comfortable 5 N*cm and also making the whole contraption a little simpler, also allowing for bigger ailerons. Anyway, the flaps are still operated by pair of micro motors with the same setup - potentiometer, servo controller, H-bridge. They drive the linear actuator via simple reduction gear and flap position should be read directly from the flap. Also, the Lego-compatible servo comes with the short axle and doesn't really fit. Would be much better if they make a axle hole instead... Next thing that got love and attention was the pneumatic system for the landing gear. While it is not complete, the pipes were installed and valves tested. Later it should be controlled by Arduino with few pressure sensors and more H-bridges, just because of complexity and small space available. Thing that I personally like and proud of is that all the machinery is hidden under the floor :) Few more shots of the wings - Next big thing will be finalizing the motor/propeller combo. I've made a thrust measuring rig fir this :) To actually start selecting the motors and propellers I need the battery charger instead of the one that was lost, so, now I'm waiting for it to arrive as well as for some electronic components for Arduino and another Lego-compatible servo, this time with 20 N*cm torque which will control the elevator. Having such big servo also allows making a bigger elevator which seems rather important. I've made a great progress during the Christmas holidays, I had a two week vacation and with the city in the lockdown it was really enjoyable way to spend the time. Now the holidays are over and despite the missing pieces, parts and components are about to arrive, I expect the building pace to slow down. Expect few videos of working components. Thanks for your attention and keep calling me crazy :)

(wrong post, sorry) Could mods please take it down?

This is not enough.

This is kind of final look (excluding the cat). I was moving the wing along the fuselage and now it seems almost in place - the plane is standing still on it's own wheels. Almost loaded with everything - motors, batteries and all structure parts. Weighs 4500 g now. Wires, hoses and electronics will add about 300 more.