[WIP] The Flying Brick Restarted

[whale2]

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.
 

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Micro motor in the nacelle. Small aileron is visible. The blue piece is the flap position sender (potentiometer)

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.

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New servo motor with bigger aileron

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...

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Flap reduction gear, two micro motors and bunch of wires and pneumatic pipes. Motor nacelle cover removed.

 

The H-bridge. Was made for the old aileron setup, now has more pins that it needs to

 

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. 

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Nose removed, pneumatic cylinders for the front gear bay doors and the main gear cylinder visible. Behind the main cylinder one can spot the air pump.



View from the top

 

Thing that I personally like and proud of is that all the machinery is hidden under the floor :)

 

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Few more shots of the wings -

 

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At full span


 

With gear deployed

 

Next big thing will be finalizing the motor/propeller combo. I've made a thrust measuring rig fir this :)

 

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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 :)

[Sariel]

Nobody's calling you crazy. We're simply calling you a person who ignores explanation by a Boeing aerospace engineer who presented detailed calculations of how far LEGO motors are from being powerful enough to allow flight here a couple of years ago (hint: they're like at less than 5% of minimum required power if I remember correctly). Of course there's always the possibility of running the LEGO RC buggy motors from an external power source at a crazily high voltage and this has been proved to allow tethered flight, but your approach will, I'm afraid, only result in you ending up with a big, heavy brick of glued LEGO pieces that you can't use for anything else. Sorry to see such a waste. I sincerely wish that you put this kind of dedication and focus into something that's actually realistic, like making a 100% LEGO working submarine, which is totally doable and doesn't require glue. The sooner you abandon this project, the fewer pieces you will lose to glue and the smaller your frustration in the end. Honestly, just ask yourself a few basic questions: whats the weight of your project so far? How much thrust are you getting from the motors and props? How much aerodynamic drag and how much lift is there in your construction? Do you have any plan for controlling where the center of gravity is going to be? Sorry to sound so negative, but I just really hate to see a dedicated builder with an obvious talent wasting it on something that probably wouldn't even work with 10% of Earth's gravity. It's great that you keep going at it since 2014 despite people's negative opinions, but as the saying goes: if one person tells you you're drunk, and you feel fine, ignore them. If ten people tell you you're drunk, go and have a lie down. Nobody ever beat gravity and basic physics by perseverance alone.

Edited January 2, 2021 by Sariel

[domleg]

I hope you've seen this video, someone proved that no glue and no tether is necessary to make lego fly, just a more powerful power source:

 

 

[whale2]

6 minutes ago, Sariel said:

Nobody's calling you crazy. We're simply calling you a person who ignores explanation by a Boeing aerospace engineer who presented detailed calculations of how far LEGO motors are from being powerful enough to allow flight here a couple of years ago.

...

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.

[whale2]

Flap, old and new ailerons:

 

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Has some stutter, but it doesn't matter anymore

 

 

New aileron is more responsive (and bigger)

 

[Jurss]

8 hours ago, domleg said:

just a more powerful power source:

And it is not lego anymore. Anything can fly, if You kick it properly.

[howitzer]

8 hours ago, domleg said:

I hope you've seen this video, someone proved that no glue and no tether is necessary to make lego fly, just a more powerful power source:

<snip>

 

My immediate thought also. Yeah, it's not Lego in a purist sense but still pretty impressive achievement, considering the motors, propellers and frame is still Lego, even if the power source and control electronics are not.

---

I hope this thing will fly but it probably won't. For me it appears to be far too heavy and complicated to get off the ground and into a controlled flight.

[domleg]

1 hour ago, Jurss said:

And it is not lego anymore. Anything can fly, if You kick it properly.

If you put it that way ten any moc using Buwizz isn't lego either. It's just power and control electronics, literally every other component is lego, most crucially motors and propellers, as howitzer already mentioned. 

[Bartybum]

11 hours ago, whale2 said:

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.

How did you determine your lift coefficient curve? I'm quite interested in seeing your calculations That 40kph estimate should be at least doubled, if PeterSripol's flying Lego plane was anything to go by

Your approach seems really heavy, but I'm really interested in seeing how this progresses.

Edited January 3, 2021 by Bartybum

[Gray Gear]

20 minutes ago, Bartybum said:

Your approach seems really heavy

That's what I thought as well... Wouldn't it be easier so skip suff like retracting landing gear and keep the plane as small as compact as possible to keep things light?

[Bartybum]

59 minutes ago, Gray Gear said:

That's what I thought as well... Wouldn't it be easier so skip suff like retracting landing gear and keep the plane as small as compact as possible to keep things light?

Yeah, agreed. It'd be best to restrict yourself almost entirely to large flat tiles and baseplates, just to bring that weight down as far as possible and require lighter motors. Kinda like what PeterSripol did on YouTube:

Technically you can make a totally functioning RC plane that only has throttle and yaw control, so there's no need for ailerons or elevators, although I suppose the next challenge would be trying to figure out how to implement those. If I were doing this, I'd start from the point Peter left off, try straighten the main wing to make the connections more legal, and then look at adding more control surfaces.

Edited January 3, 2021 by Bartybum

[2GodBDGlory]

Whether or not you succeed, it looks like a very cool machine you are making!

[M_longer]

Please please please record its hard landing in slow motion :)

[Gray Gear]

On 1/4/2021 at 3:39 PM, M_longer said:

Please please please record its hard landing in slow motion :)

Hard landing? I highly doubt it'll leave the ground on its own power...

Edited January 12, 2021 by Gray Gear

[whale2]

On 1/3/2021 at 11:10 AM, Bartybum said:

How did you determine your lift coefficient curve? I'm quite interested in seeing your calculations That 40kph estimate should be at least doubled, if PeterSripol's flying Lego plane was anything to go by

Your approach seems really heavy, but I'm really interested in seeing how this progresses.

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 :) 

36 minutes ago, M_longer said:

Please please please record its hard landing in slow motion :)

You bet

On 1/3/2021 at 11:41 AM, Gray Gear said:

That's what I thought as well... Wouldn't it be easier so skip suff like retracting landing gear and keep the plane as small as compact as possible to keep things light?

That's the backup plan

Edited January 4, 2021 by whale2

[whale2]

19 hours ago, 2GodBDGlory said:

Whether or not you succeed, it looks like a very cool machine you are making!

Thanks :)

[Bartybum]

7 hours ago, whale2 said:

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

Oh man I wasn’t prepared for a full paper hahah. How close can you realistically get to a proper airfoil though? On top of that, while a cambered airfoil does produce more lift than a flat plate, you need to lug around a lot of extra weight in the internal structure :S Are you sure the tradeoff of C_L vs required lift is in favour of an airfoil?

[whale2]

2 hours ago, Bartybum said:

Oh man I wasn’t prepared for a full paper hahah. How close can you realistically get to a proper airfoil though? On top of that, while a cambered airfoil does produce more lift than a flat plate, you need to lug around a lot of extra weight in the internal structure :S Are you sure the tradeoff of C_L vs required lift is in favour of an airfoil?

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.

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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...)
 

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Edited January 5, 2021 by whale2

[Bartybum]

Well isn't that curious. I'm gonna watch this with a keen eye

[whale2]

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.

 

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Edited January 8, 2021 by whale2

[whale2]

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

 

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[Brickend]

This is utterly diabolical......please keep us updated! 

[whale2]

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.

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[Brickend]

How much does the mighty brick weigh now?

[Seasider]

As an aeronautical engineer by degree and an automotive engineer by career I’m very interested to see if this will ever fly.

Having built in the past a RC airplane I can remember how light they typically are and from your wing a fuselage construction all I can see is weight and more weight. So I’m very curious about how you are going to solve the thrust/drag & lift/weight issue.

All I ask is when you do finally get to attempting a first flight please do video it as personally I can’t see it having a successful flight.