[WIP] Flying Brick

[whale2]

Hi.

I've been working on it for a year or bit more. I think I'm on the finish

line now as most problems I could think of are more or less solved.

It started in that way - one of a rainy weekend we played with my son with

some Lego and it turned to be a half-done airplane of mixed color.

A few days after my son came up with 'Dad, will it fly?'. I answered "No, of course. It's too heavy

and too weak for flying", but this idea literally stuck in my mind so I

started to think about it from time to time. I started to evaluate things

from different points of view. It was obvious that I should give up using

Lego powertrain, there were no match for 0.8 - 1.2 KW required power.

Other two main problems were weight and strength. Problem of weight could be

moved away with enough power and enough speed. To cope with strength

issue I decided to move on with glue. There was also no chance of

controlling such a thing with IR stuff, so controls also should be

implemented using standard RC 2.4 GHz equipment. This left me with

only the airframe made of Lego, but nevertheless I'm pretty happy with it (Purists may

stop reading here :))). However, the model could stand on a shelf (and this

shelf have to be rather big :) without any glue, operate landing gear and may be

even control surfaces using only Lego parts. This means there are no cheats

like 'just glue this piece to that'. All connections are at first usual Lego

connections, glue just added for stiffness.

But to flying. First, I had to implement airfoil using Lego pieces. I did not choose

Carsten Swendsen's way of making only wireframe with Technic axles and using some kind

of monokote to cover it and instead decided to use System parts to make the wings and fuse.

I managed to implement Kline-Fogelman airfoil using 93606 and some plates with stud inversion.

May be this is not the best airfoil, but I think it weighs less than, for

instance, flat bottom airfoil with some curved slopes on the trailing edge.

Wings implemented that way have many space inside and could accomodate LiPos

and motor controller.

My first version of wing have following layout:

Speed controller on the root part of wing, then nacelle with landing gear,

doors and retraction mechanism, then batteries in configuration of 2 cells one

above another and one another cell next to them.

My chosen configuration was 2700 KV 590W motor and 3x2200 mAh batteries in each wing.

(With covering removed)

(Speed controller inside wing root)

Landing gear was implemented using single 9.5L shock absorber with double

springs and spacer made from modified 4624 wheel hub. Single 9.5L shock with

extra hard spring compresses fully at 1.2kg and I had no chances making the plane

lighter then 4 - 4.5 kg and any design with some kind of levers would weigh

more and take more space.

(And a bit boring video:)

My evaluations showed that take-off speed with flaps deployed will be about 40

kph, so landing gear must be able to sustain this speed for at least 30

seconds. There were some doubts how much load could be handled by Technic

axle rotating in shock socket at speed of 7000 RPM. I did some experiments

with it. Now I know that axle will be damaged if used without grease

handling load of 1 kg at ~ 5000 RPM, but could live with this load for 30-35

seconds if greased. This made me move away from that simple landing gear

design, it was also rather weak and any non-ideal (or may be even

ideal?) landing could break the strut or move it away from extended position

- the locking was not good.

(I'll post pictures of damaged axle and video of experiment a bit later)

At the same time I was thinking of other ways to reduce weight and came up

with idea to reduce weight by cutting flight time. I was targeting for 10

minutes before, but now I think that even 3-4 minutes will be enough to

prove the idea of flying Lego airframe :) I found another motor/prop/battery

configuration and combined it with new landing gear with 4 wheels per strut and more reliable

locking. New layout is using 4x950 mAh batteries, 1200 KV 530 W motor and smaller

speed controller and potentially could fit in root part of the wing at whole.

However, root part have to be lengthened. This is going to enlarge wing area

(which is good) but also probably will load root spars more (which is not so good).

On the other hand, heavy batteries are moved from outer wing section into

root section (and their weight is reduced; with lighter ESC saving is 90 g per wing)

First version of wing also featured front spar for almost all wing length.

In second version I decided to end front spar soon after engine nacelle.

After gluing wing v1 it was obvious, that front spar of that length is not

needed - wing is rigid enough. Also, when making wing v1 I had some

mess with covering root section - it was 10st length and there is no 10x8

tile to cover it. Wing v2 have root part of 18st and could be covered easier.

(Unfinished nacelle v2)

To make control surfaces I used micro-motor directly connected to axle,

holding the surface (except of flaps - flaps are connected by worm

gear. On ailerons other side of surface is attached to

potentiometer, connected to PCB of standard RC servo. Micro-motor is

connected to PCB via H-bridge. RC servo operates at 5 V and this is very low

voltage for Lego motor. With help of H-bridge, micro-motor is being fed by full

battery voltage (11.1V or 14.4V) and moves with reasonable speed.

For rudder, elevator and flaps I will have to add some gears to connect

potentiometer. I hope the play in gears could be compared to play in

servo-to-surface linkage of traditional RC setup.

I started some mock-ups of fuselage about the same time as wing v1. Seems

like I can fit all the required equipment (air compressor, front

landing gear, flap mechanism, pneumo-switches) under the floor (slightly

raised in nose section) and some other things (RC receiver, air tank) in

aft section. This makes realistic look for cabin, it can be fitted with

seats, crew and passengers :)

Fuselage, however, is a quite ugly being made from System pieces.

With one wing attached:

Some amusing details :)

Now I'm waiting for new powertrain and some missing pieces for nacelles.

After that, if this layout proves doable and reasonable, I'm going to glue

both wings, finish fuselage and rear control surfaces and attach wings so CG is in

the right place. I think I'll be almost done at that point.

However, there are some minor unsolved problems. Design of front landing

gear and bay doors make it impossible to close doors when landing gear is

down like in main struts. On the other hand, doors must open before extending

gear and close after. And there is no place for third pneumo-switch. My idea

is to make some kind of throttle to create delay in pneumo-cylinder

operation. Also, there is no place for mechanical sequencer, so I'm going to

make some simple microcontroller stuff for sequencing door-gear operations.

I don't see anything hard here.

And yes, there is still a bigger problem - will the whole thing work as

expected? :) Well, at least it will be fun to watch how it crash.

Sure I should have started with some simpler design - no retractable landing

gears, some simple fuselage, something like WWI era airplanes, but my

current design is so much fun to build, so I probably revert to simpler

construction only after I done with current one.

Hope you enjoyed this crazy thing.

[Alasdair Ryan]

This is definitely crazy all right....

At long last we might see a lego flying plane....

I hope you manage to finish this as I really want to see it get airborne.

[nicjasno]

You need to use the technic panels more and less bricks. Kee it as light as possible. As of right now, this thing looks awfully heavy already.

Panels, the liftarm frames and liftarms are your best friends in reducing weight.

[whale2]

Technic panels are very uneven and with lots of holes.

I'm targeting to 5000 - 5200 grams and this seams feasible.

[nicjasno]

The wings need to be as you did them, of course. I'm talking about the fuselage itself and the engine/landing gear housings.

[whale2]

I will consider that :)

[nicjasno]

The potential for saving weight is enormous. Any bricked structure will be both heavy and weak. Panels are tthe way to go, like in a real aircraft. :)

[whale2]

Can't argue with weight saving. But about weakness - I'm already cheating here, the left wing v1 is already glued and is very rigid, though I will have to scrap it.

[camaudio]

you wont have to scrap it, after it flies it will become part of lego history :)

[paul_delahaye]

I so want this to fly, but I'm sitting here and I can't but help picture in my mind those human powered flying machines where people launch them selves off a pier into the sea whilst trying to fly. I really have my fingers crossed for you. Roll on the first test flight.

[piterx]

i really hope it will fly :P

[Gee]

This is mental! Can't wait for test flight #1!

[Tamas Juhasz]

Cool project, very impressive. I'm curious for the test flight.

But something has to be cleared:

At long last we might see a lego flying plane....

I see, nowadays there are even less purist mocers, and this isn't good imho. A few years ago, when somebody used something non-Lego part in a moc, then most of the community didn't considered that as a Lego moc. Nowadays "every second moc" (note the "" signs) has non Lego parts. The whole technic moc building is turning slowly to a mixture of RC and Lego constructions. Years ago, the challange was, to make all with only Lego parts. This plane should be presented in the RC world, or here, as hybrid Lego construction. This is very far from flying Lego plane with tons of non Lego components. So we can't call it as a "flying Lego plane". Please.

I'm still with the opinion, only custom rubber bands (round shaped is better), strings and pneumatic hoses are "legal", which are non Lego parts. Because they mostly substitute the expensive original Lego ones (custom RC wheels are also ok, they appeared because of necessity).

I don't want to be against anything, we just have to clarify, this plane isn't a Lego moc, it's an RC moc.

Edited January 17, 2014 by Mbmc

[z3_2drive]

This looks awesome so far! But one thing is...the landing gear. As you said it's weak and I can only imagine the horror when it lands/takes off and the landing gear snaps, and the plane hits the ground... Some sort of reinforced triangle with a shock absorber attached would be bulky but actually survive. I know the routine of making something revolutionary but practical. At least on my cars a failure during testing won't risk complete destruction I wish you luck with this great build!

EDIT: Mbmc, I see where you're going but us builders who use some non lego parts usually set our own goals.

For example, I enjoy building vehicles where the construction is 100% Lego, motors and all, but unleash the performance potential and fun factor by increasing voltage and range with a third party receiver/transmitter and battery. I consider what I build to be true Lego MOCs, but not purist. I don't modify any of the pieces themselves either. I tell myself that if I want higher performance with hobby-grade motors, then I will just build my own metal frame/ buy a custom kit and use the electronics I already have, because if I am interested in top performance, I should leave Lego behind. But these hybrid builds are right smack in the middle of that gray area...

Edited January 17, 2014 by z3_2drive

[lukeandahalf]

Great moc! Looking forward to more progress:) sure came along way from that first picture! Purists remind me of my 87 year old grandfather, he grumbles about "those damn hot rods" whenever he sees a modified car... Maybe its not for everyone, but whale2 has a skill set that I'm very envious of...

And in terms of legal or not...let's not forget Lego is a toy...

Edited January 17, 2014 by lukeandahalf

[legomuppet9]

This'll be brilliant if it works :)

[aol000xw]

If the space shuttle did it, there is a good chance for this.

@mmbc: All this non purist thing is TLC fault. They fail year after year at meeting AFOL expectations on several fronts, hence people feel more inclined to look for solutions out of Lego inventory in order of meeting their goals. And I think it is good, Thinking outside the box is always good.

[Pedro Antunes]

The stress on those mini LA is making me cringe

[Tamas Juhasz]

I understand your viewpoints, maybe there is a better topic to discuss about Lego or non Lego moc.

The only thing I tried to explain: if you use some non-Lego parts in a moc (except few exceptions), then it's not a Lego moc, it's a hybrid. So simple. The ONLY problem is, I think, when something contains non Lego parts (exceptions are ok), and it's considered as a Lego moc. I hope nobody of you think, it's equal, when two cars have the same performance, but one is full Lego, the other not. Technic moc-ing will always have the real challenge to make your goal with the existing Lego parts. Imho thinking outside of the box isn't means the using of non Lego elements, it means the using of Lego parts in clever way. With non Lego parts everything can be solved easily (if you have skill in the non Lego theme, like RC technic).

And in terms of legal or not...let's not forget Lego is a toy...

I didn't wrote legal, I wrote "legal".

Sorry for off, I just had to clear the situation.

Edited January 17, 2014 by Mbmc

[whale2]

Thanks for all good words, guys :)

I don't want to put myself into any kind of holy war, therefore I call it 'plane with Lego airframe' and this is to certain extent close to truth :)

you wont have to scrap it, after it flies it will become part of lego history :)

I mean scrapping wing v1 in favor of wing v2. Just to save some pieces :)

This looks awesome so far! But one thing is...the landing gear. As you said it's weak and I can only imagine the horror when it lands/takes off and the landing gear snaps, and the plane hits the ground... Some sort of reinforced triangle with a shock absorber attached would be bulky but actually survive. I know the routine of making something revolutionary but practical. At least on my cars a failure during testing won't risk complete destruction I wish you luck with this great build!

Your advise is absolutely right. Landing gear of last version is not that weak, however, I understand that may be I will have to redesign it again and again. And that's that most funny thing of all of it :)

The stress on those mini LA is making me cringe

Yep, this part also need a rebuild. I just tested that micro-motor is able to operate pneumo-switch.

Next main step is to check layout with new powertrain and I expect those new thingies to arrive in two weeks.

I'm going to do some experiments meanwhile and share results.

[Lakop]

Something that started as a bit of fun has become a massive project. I know the feeling and I want to see you complete it. It will be heavy using the parts you have used. if you can, rebuild the main body with technic beams and panels. If you can't, or don't want to, then continue as you are and let us see the finished model. It looks huge and if you can get all your functions to work well then it will be worth it.

Good luck.

H

[lukeandahalf]

Agreed, not the right topic, agree to disagree Reading/Looking though this again, I am fascinated to see a Lego air-frame do 40 km/h, best of luck!

[kieran]

All the best on this, I hope it works

[Energo]

Are u crazy?))

Such a monster...very big scale, like it. Wish u luck and hope, this plane will be amazing/exciting/wonderful when it's finished)

[hysot]

Hey!

Well well....I really doubt this plane will fly....

1- The airfoil is really a bad one. I know it's tricky to build a good airfoil in Lego but this one won't give any result. This airfoil is used on model scale airplane built with foam. Way much lighter than your plane.

2- You're plane is waayyy too heavy and too complex for the experiment. You're like the Wright brother designing a boeing 737 as first plane of the history. If you want to build the first flying Lego plane, make it simplier. No retactable landing, no flaps (Btw I don't think flaps will be usefull on a such airfoil) no doors.Just think light and strong airframe.

Good luck!