I beg to differ. A plane can fall on you from a serious height, and hit you e.g. in the eye. I think it's hard to even compare it to a car that can at best scratch your shoe.

Not to mention that the plane would be probably destroyed.

Edited June 20, 201410 yr by Sariel

I'd rather get hit by my Hotshot (=proper RC car) in the foot than a 150km/h RC propeller plane in the head

Only thing that might be worse than that would be standing in the path of that supersonic hamster

***

So, where's that flying LEGO plane then?

Come on sports, it's just me that's a Debbie Downer. It's doable, you know it is!

Let's see that mighty 5292 prove me wrong

You guys forgot about how much damage Lego guns that shoot bricks can do. I have build a few of them and they are very powerful when reinforced with technic beams and lots of rubber bands are used.

How does that influence the safety of a Lego plane?

Okay guys as stated I made a fyling tandem helicopter, but its very unstable because the RC motors are not totally the same and one is there for more powerull.

Edited June 20, 201410 yr by Zblj

Very nice try, Zblj!

My opinion (sorry): It will never ever fly because: 1. It doesn`t really take off at the lightest version 2. Making it more stable means to add weight 3. The rotors are not efficient enough 4. The power units are too weak. A helicopter, tricopter or quadrocopter, airplane ore UFO or whatever wouldn`t take off because it has to carry the batteries too! Making an independent flying object with Lego pieces only (!) is IMPOSSIBLE and will stay a dream for a while, I guess ;-) ! But I like the approach making the impossible possible one day. I would vote for new stronger and lighter RC units to be released by TLG!!

Okay guys as stated I made a fyling tandem helicopter, but its very unstable because the RC motors are not totally the same and one is there for more powerull.

Did the "dangerous" helicopter hit your eye? :D

I'd rather get hit by my Hotshot (=proper RC car) in the foot than a 150km/h RC propeller plane in the head

And they are made from 100% lego?, or have you somehow missed that what we are talking about here is a lego plane (or car) on a lego forum, that isn't going to be in any way comparable to your hotshot or 150km/h propeller plane?

I promised myself I wasn't to get involved in this discussion again, but my name keeps coming up so here goes .....

I'm sure an aerospace engineer could do the math, but I sincerely doubt that you can achieve the necessary HP to weight ratio necessary to achieve heavier than air flight with LEGO motors with an entirely LEGO airframe and unmodified LEGO battery pack(s).

It's very easy (if you have the chops and I think Blakbird allready did) to calculate the mechanical power output of a given motor versus weight versus rpm versus blade lift versus etc to see if it's even remotely possbile to achive flight

Indeed I have already done the calculations! Here is what I posted 2 years ago when asked what it would take to make the 9396 heli fly:

In order to use a lift equation you would need to know the lift coefficient (CL) of the rotor airfoil. Obviously there is no test data to generate any such information because these rotors are not actually intended to produce lift. You could use a lift coefficient for a generic symmetric airfoil like an old NACA 2412 as a starting point and assume a certain angle of attack (alpha), maybe 10 degrees. Then you need the overall wetted area (S) which is the projected area of all the rotors put together. Then you need the dynamic pressure (q) which is a function of speed. This is harder for a helicopter than for an airplane because the speed changes as a function of diameter.

However, you can save yourself the trouble. Although there IS an angular velocity (omega) that you could mathematically calculate which would make the rotor lift the helicopter, the LEGO parts would structurally fail and/or melt LONG before you ever got such a velocity. And even if, by some miracle, you really could generate the required lift, 9396 has no gryo for directional stability, no pitch on the anti-torque rotor, and no cyclic to control heading and balance the suspended weight, so it would immediately fly into the nearest solid object, possibly your head, and smash.

It would be an interesting thought exercise to at least calculate the number and just see how ridiculous it is, but big computers with really complex calculus are used to calculate this kind of thing. Let's do it the easy way.

A Blade 300 heli has about the same rotor size as 9396, so let's use it for comparison. It uses a 4500kV brushless motor, a 3S Li-Po battery, and weighs about a pound. This means that the motor spins at about 50,000 rpm. The main spur drive has a 15.5:1 gear ratio so that means the rotor spins at ~3200 rpm at full power. Let's assume it only needs half power to take off and lift the 1 pound weight. 9396 has twice as many rotor blades (4) and the Blade 300 (2), but they are also not really designed for lift so let's assume those two things cancel out. That means we need 1600 rpm/pound of weight to lift off. 9396 weighs about 2 pounds (without PF) so let's assume it would be 3 pounds and therefore would need to rotate the blades at 1600 * 3 = 4800 rpm. The linear speed of each blade at the tip would be about 292 mph (469 kph). Assuming you were using a 3S lithium battery at 11.2 volts, you'd need a massive 6750kV brushless motor producing about 700W of power and drawing 60 Amps. Considering that the largest Lego motor, the XL, is only about 16kV and produces 7W of power at this voltage, you're going to need about 100 XL motors in parallel. The PF battery pack is also limited to 1 Amp, so you are going to need 60 battery packs. Of course, all of this gear weighs much more than the entire helicopter and you're also going to have to lift all that which means you need even more power, and the weight is going up faster than you can add motors and battery packs. Now suppose you just use real R/C components instead of PF to power it. Well, the power system is going to cost you about $1000 including motor, speed controller, and batteries. Now once you install them you'll be generating a 100x more torque than an XL motor. Since an XL motor can already destroy a plastic axle, you'll quickly vaporize your entire model.

And here are the calculations I did to figure out how fast the AN-140 would have to fly to get off the ground:

The weight was 4,15 kg last time I weighed it. That is not counting any batteries and (servo)motors. I assume maximum 5 kg

Wingspan is 155 cm

chord lenght at fuselage: 19cm

chord lenght at tip: 11 cm

OK, so your approximate wing area based on average chord is S = [(11+19)/2]*155 = 2325 cm^2. We need this in square meters so that's S = 0.2325 m^2.

For calculation purposes, I'm going to assume that you have an airfoil equivalent to NACA 2415. In order to by able to fly with a reasonable amount of drag, we'll assume that you need to be able to take off with an angle of attack of alpha = 10 degrees (which is very generous). Based on the lift coefficient charts, your lift coefficient is CL = 1.0. This is really good and your actual airfoil will probably be less efficient than this.

For the density of air, we'll assume standard sea level conditions. rho = 0.0023769 slug/ft^3 or 1.2012 kg/m^3.

Lift is equal to weight which is 5 kg (this is actually a mass).

Now we can get the velocity V for takeoff (no climb) using V = SQRT [2L/(CL*rho*S)] = 5.98 m/s or

21.5 km/hr

This is not a scale speed, this is actual speed. To actually be able to climb and maneuver you'll need a lot more speed than this and you really don't want to be flying at an alpha of 10 degrees, so you'll want your top speed to be about 3 times this or 60 kph. The drag forces on your plane at 60 kph are going to be very high, so you will need very high power to achieve this speed. I would plan for at least 2.5 kg of thrust.

Structurally, you'll need to make sure that your plane can be lifted by the wings with a factor for gusts. I would lift it up by the wings at about 1/2 span and shake it up and down and make sure they stay on. If they don't they will break off in the air.

Plan your center of gravity to be at about the 1/4 chord point of the wing.

As you can see, the technical challenges are enormous. And by enormous, I mean impossible. I'm not saying impossible to discourage anyone or stop discussion or start an argument. It is simply a calculable fact that LEGO parts don't have the power/weight necessary for heavier than air flight. Furthermore, as has been pointed out, TLG would not make such parts available to children.

But you are trying to get that hamster into orbit, aren't you?

Blakbird never said we could't do that, right?

I also fly rockets and would have no trouble launching a hamster, though it surely violates the safety code.

Okay guys as stated I made a fyling tandem helicopter, but its very unstable because the RC motors are not totally the same and one is there for more powerull.

This is a really cool demonstration! Good work! This is actually useful to make my point. Even using the most powerful motors and the most efficient propeller, the LEGO contraption cannot quite even lift the weight of motors with NO structure and NO power supply. The battery box alone is as heavy as the rest of the device, and this is why self-powered flight won't work. To lift the weight of the battery box you need more power, and to get more power you need another battery box which you also need to lift, etc. This cycle never converges with LEGO. The same cycle exists for rockets, especially those leaving orbit, and that's why the Saturn V needed to have such a massive amount of fuel to lift the Apollo capsule. 90% of the fuel was just to lift the other fuel.

I'd rather get hit by my Hotshot (=proper RC car) in the foot than a 150km/h RC propeller plane in the head

As it turns out, I've been hit by an R/C car, plane, and helicopter! The car hurt the worst, but only because of the weight. The helicopter was a tiny 2 ounce quad. Didn't even feel it. The plane was a foam BN-2 Islander. Mild discomfort. The car was a 1/8 scale truck weighing 8 pounds and traveling about 30 mph when it hit me in the shin. That hurt a lot. I've never been hit by a rocket but that would be bad.

Well guess what guys I'm not giving up that easy I will use new batteries and gonna try to mechanically synchronise both motors...should be fun if nothing else...About sunglasses yeah I dont really trust bricks too much getting something in the eye at the speed those rotors are turning...no thank you.

@blakbird:

Please build a rocket out of 100% Lego pieces, powered by non-Lego fuel ;-)!! And don`t forget to hide under a bunker, the pieces flying around will hit you! Will get many many YT clicks for sure!

LOL

Was I writing in invisible ink when I said rubber bands? Make one of these out of lego and you will stand at least half a chance of making it fly:

Edited June 20, 201410 yr by Heppeng

I also fly rockets and would have no trouble launching a hamster, though it surely violates the safety code.

Oh, so you think that if you took a hamster to the launch pad, hamster would be the one ending up in the rocket. That's cute. Let me answer with a GIF: http://0.static.upco...ijn-deel-is.gif

Edited June 20, 201410 yr by Sariel

Well guess what guys I'm not giving up that easy I will use new batteries and gonna try to mechanically synchronise both motors...should be fun if nothing else...About sunglasses yeah I dont really trust bricks too much getting something in the eye at the speed those rotors are turning...no thank you.

Glad you used sunnies, keep up the good work!

Okay guys as stated I made a fyling tandem helicopter, but its very unstable because the RC motors are not totally the same and one is there for more powerull.

That is a solid effort. How about separating out issues of stability and control for now and concentrating on outright lift? If you extended a (lightweight) pole about 20l underneath and held that loosely in tube you could limit all the tipping and falling.

If the contraption lifts up while being stabilized by the tube, you know you have enough lift and can start looking at stability. If not it's back to the drawing board.

First I will mechanically sync both rotors.

You guys forgot about how much damage Lego guns that shoot bricks can do. I have build a few of them and they are very powerful when reinforced with technic beams and lots of rubber bands are used.

I made a lego crossbow, proper mechanism, with plastic beams being bent to produce the power, and it broke my 11 hole technic beam when it fired

i don't really want to try that 'how much power can a lego crossbow make' experiment again, i'm pretty sure that could shoot straight through my leg if i sharpened the bullet

Was I writing in invisible ink when I said rubber bands? Make one of these out of lego and you will stand at least half a chance of making it fly:

those things in total weigh like 2 grams, no way you can fly like that with lego, just a friction pin would be like half that whole thing

Because I'm stubborn as **** I improved the tandem heli design, adding a synchronisating axle and I increased the main drive axle length. The model is now much more stable but still needs more juice:

SOON GUYS, SOON

Edited June 21, 201410 yr by Zblj

everyone, keep working, we can make this happen

Look, if you're so sure, then start building something. I see you only commenting so far. If Lego flight was possible, it would be done already, as many talented people attempted it.

Blakbird was kind enough to give you solid mathematical proofs that Lego won't fly. You can argue with us, but you can't argue with laws of physics.

Lastly, the "only the spark plug wouldn''t be lego, and the balloon casing, and the fuel" ideas miss the entire point. It's not a Lego flying apparatus if non-Lego elements are essential for it to work. If I put a Lego brick on my hamster, does it become a Lego hamster?

Edited June 21, 201410 yr by Sariel

Blakbird was kind enough to give you solid mathematical proofs that Lego won't fly.

No he did not, he was kind enough to provide solid mathematical proof that lego model number 9396 could not be made to fly, not that no lego could fly, which is no surprise because 9396 was never meant to fly anyway. A model that was specifically designed to fly from the outset would be completely different mathematically, and as ZBLJ has shown he is nearly there, albeit some way to go, but close enough that a good deal of stubborness and persistance may well pay off.

Edited June 21, 201410 yr by Heppeng

Some fresh LiFePo AAs can provide up to 9.6 volts and high current in an old style battery box... that would be max power without really cheating or going too far out of spec for the motors. And even then rpms may be not enougth and those propellers are completely useless

Well, what do we define as flight? A glider or a skeleton similar to zblj's which stay in the air for a few seconds (glider is actually stable) is probably as far as we can go. True flight is simply impossible with the array of parts/motors we currently have. Zblj gave a perfect example-when trying to make it more stable, it gained too much weight and couldnt create enough lift. Giving it more power would simply make it less stable again. And this is all with an external power source. What's more interesting is creating small non motorized flying contraptions that could actually have a good amount of stable flight, I think some examples were already mentioned. BUT, I don't discourage builders to try, because it would be interesting to see how long their project could hover uncontrollably before smashing into the ground

Look, if you're so sure, then start building something. I see you only commenting so far. If Lego flight was possible, it would be done already, as many talented people attempted it.

Blakbird was kind enough to give you solid mathematical proofs that Lego won't fly. You can argue with us, but you can't argue with laws of physics.

Lastly, the "only the spark plug wouldn''t be lego, and the balloon casing, and the fuel" ideas miss the entire point. It's not a Lego flying apparatus if non-Lego elements are essential for it to work. If I put a Lego brick on my hamster, does it become a Lego hamster?

Well, blakbird implied that flying would be with the batteries, zblj is experimenting with the batteries on the ground.

a lego brick on a hamster makes the hamster a part of the model, I only mean we could use a spark plug or fuel because lego doesn't provide those parts, like lego doesn't provide live hamsters as part of it's models. Anything is impossible if you don't try.

Edited June 22, 201410 yr by anton1678

After adding 2 more batteries in series the whole contraption flies, I recorded it badly tough, and one motor broke (comutator broke off)...So now I only have 1 Rc motor left for flight (I wont risk 2 new ones), so yeah....I got ti to fly, but at a big cost.. I'm so angry I didnt record it properly

So this is what I managed to record: