Flight using Lego

[Heppeng]

Can't start building anything until tomorrow.

[1974]

No offense but all i see is talk...someone actually try building something?

Nope, it's not gonna work

But that doesn't mean I'm not gonna give my very best suggestions anyway

Spoilsport? Sure, but then again I have a very intimate relationship with reality

Edit : Those of you who are trying to make this work are _clearly_ not into RC planes/choppers or are pilots or have any decent education into basic avionics/physics. Sorry, but that's .. err .. reality. You deal with it

How about making something _else_ awsome with LEGO/Technics instead of chasing this phantom?

Most of you have much better Technic chops than me anyway

Edited June 26, 2014 by 1974

[anton1678]

Well, I don't have rotors or motors suitable for building

How about someone builds an airship first, just to show we tried?

I could do that maybe...

If you don't have helium, use methane, natural gas, still floats, doesn't leak

There is natural gas in Denmark... maybe even in Billund...

Edited June 27, 2014 by anton1678

[Heppeng]

Nope, it's not gonna work

Those of you who are trying to make this work are _clearly_ not into RC planes/choppers or are pilots or have any decent education into basic avionics/physics. Sorry, but that's .. err .. reality. You deal with it

Dangerous assumption to make, you clearly do not know my background at all, and are making wild guesses!!!

[Kelkschiz]

It's great to dream big dreams, or to have a constructive critical conversation. However one should always keep in mind to play the ball, not the man. Please don't make negative personal remarks towards other forum members.

[OzShan]

Bring it into this century of aviation, design some nice jet engines with these:

Much better thrust to weight ratio :)

[Tommy Styrvoky]

Bring it into this century of aviation, design some nice jet engines with these:

Much better thrust to weight ratio :)

would it generate enough thrust ? ( its only like 3 studs in diameter, a larger version would be required)

you could stack them and offset them for more thrust.

[camaudio]

you would have to rotate that 3000 rpm before even feeling air flow from it

[Zerobricks]

More like millions of rpm because its a sticker

[OzShan]

More like millions of rpm because its a sticker

Correct.

I apologise in advance if I upset anybody. It was meant to be a light hearted stab at the futility of using inappropriate materials for a given application.

[anton1678]

Whoever has helium or methane or hydrogen can make 2 balloons and attach PF with 2 propellers (any will do) and a reciever.

We will have 'flown Lego', at least kind of our original goal

don't look at me I have no helium

[Moz]

Trouble with helium or hot air is that Lego containers are usually not airtight and their walls are very heavy. You'd probably need to buy all the sails and glue them together to make a full size hot air balloon before it would float, just because of the wall thickness. And you could fuel it with the burning wrath of all the Lego sail fans :)

[anton1678]

Trouble with helium or hot air is that Lego containers are usually not airtight and their walls are very heavy. You'd probably need to buy all the sails and glue them together to make a full size hot air balloon before it would float, just because of the wall thickness. And you could fuel it with the burning wrath of all the Lego sail fans :)

:wall: Does it have to be a Lego container?

I said BALLOON not a Lego house filled with helium

[Heppeng]

Ok, back to the world of heavier than air flight with lego. Wings have passed proof of concept. They are buildable, provide loads of lift, but may be a bit marginal on strength. I think its possible to resolve that so its not a show stopper. These wings have been optimised to get the greatest lift/weight ratio with lego I think that is technically possible. You could make the wings smaller, but as the thickness of the lego remains the same whatever size you build, the lift/weight ratio is degraded. Make them (even) bigger and they will be too thin for their size, too flexible and require extra strengthening which will add to the weight and probably be detrimental.

Why did I say even bigger? Well having a wing that works, or at least can be made to work, further research was required and I thought that looking at existing electric powered model aircraft would be a good place to start. This is where things start to get a little scary! - an aircraft with this wing would fit in the IMAA category of 'giant electric aircraft' !!!!

It is also noteable that the general design requirement is big motor + small battery. If I have a set up that takes any longer than ten minutes for the battery to go from fully charged to flat, then I am carrying excessive battery weight. Indeed due to the experimental nature of this project I would say its necessary for the battery to go from fully charged to flat in under five minutes - it just needs to last long enough to provide proof of flight, any more is a waste. This of course requires the battery to supply a very high current for a short time, possibly to the detriment of the battery.

Now this wing is designed to fly slowly, simply to try and give lego electric motors a chance of being able to power it. the idea being that hopefully the drag, which goes up with the square of the speed, might be something lego motors could cope with.

So what about motor requirements? Well its a little tricky as there are many variables. Unfortunately Model aircraft seem to use a non-standard measure of power which I am not sure how it translates in to Watts. An airplane may have a motor of say 200kv fitted. Now clearly this is not a 200,000V motor, so the normal meaning of Kilovolts applied to this abbrieviation is not right. I suspect however that this might not be too far away from 200 watts. Why they can't just use watts I don't know...

And this is where it starts getting tricky. I think that the next stage would be to make a towed glider with this wing. The towline would need a spring balance to measure how much drag needs to be overcome. The glider would need weights adding to simulate batteries and motors. By progressively adding one motor and battery weight as required then measuring the additional drag required to get it to fly, a graph can be plotted. From ZBLJ experiments, knowing the weight of the RC motors we can get an approximate idea of how much thrust per motor we can get. We can then plot this on the graph, and see if the 'thrust available ' vs drag plots are diverging or converging. If diverging, then we know flight won't happen, if converging, we should be able to work out how many motors/batteries we need.

So this is where I am at. I am likely to need a number of RC motors. They are not cheap. I will also need expensive batteries that I am likely to ruin. It will also take a long time to do all this development work. Reliable Electric RC planes, with absolutely everything optimized only became practical comparitively recently, presumably to the development of the motors and batteries required becoming available. Lego components are no where near as advanced or efficient as these beasts, which is a huge disadvantage.

The problem is I can't take this project forward without spending lots of time and money on it which I cannot justify. Which is a pity because I would really like to prove that flight is possible. If someone else was mad enough to take it forward I can perhaps provide photographs of the wing as is - but it will need work!

[Zerobricks]

What about this parachute guys?

http://54.208.56.110/catalogItem.asp?G=4296983

Could be usefull?

[anton1678]

What about this parachute guys?

http://54.208.56.110...m.asp?G=4296983

Could be usefull?

Parachute provides air resistance, making it fall down slower, but also making it fly up slower.

No use at all

[OzShan]

What about this parachute guys?

http://54.208.56.110/catalogItem.asp?G=4296983

Could be usefull?

If it were more like a parasail than a chute it might be of some use.

Edited June 29, 2014 by OzShan

[_Cookie_]

Hello,

I'll just toss in my experience with normal RC planes (those three points are common):

- 3D or vertical flight: 200W/kg

- Average flight (trainer model): 150W/kg

- Glider (with good aerodynamic profile): 100W/kg (or less, if it is built really good)

I don't know the output of regular Lego Motors, but given that they can run hours (?) on simple AA batteries... shows that they won't deliver >10W.

And as Heppeng said, you'll need a strong battery (a lipo or lifepo4, cheap AA batteries won't even hold their voltage at >1A).

Oh, and about the KV: example 1000KV = 1000rpm/V (@idle !). At 10V it would have 10000rpm, now subtract ~20-30% (depends on propeller) loss and you're at 7000-8000rpm.

Greetings,

Cookie

[1974]

Buggymotor : 4,6-6,2W mechanical watts, 55gr

So you're not gonna hit that 200W/kg with batteries and frame/wings

Edited June 30, 2014 by 1974

[anton1678]

Hello,

I'll just toss in my experience with normal RC planes (those three points are common):

- 3D or vertical flight: 200W/kg

- Average flight (trainer model): 150W/kg

- Glider (with good aerodynamic profile): 100W/kg (or less, if it is built really good)

I don't know the output of regular Lego Motors, but given that they can run hours (?) on simple AA batteries... shows that they won't deliver >10W.

And as Heppeng said, you'll need a strong battery (a lipo or lifepo4, cheap AA batteries won't even hold their voltage at >1A).

Oh, and about the KV: example 1000KV = 1000rpm/V (@idle !). At 10V it would have 10000rpm, now subtract ~20-30% (depends on propeller) loss and you're at 7000-8000rpm.

Greetings,

Cookie

Sorry if this sounds like I'm being really annoying, but how we know this is true

Happy 100th post to myself

Edited June 30, 2014 by anton1678

[1974]

Who are 'we'? Has this been posted before? Do you dispute it?

If that's the basic power/weight ratio needed and LEGO parts don't come even near that how come this discussion with LEGO motors is still going?

I cannot run 100km/h. It does not matter what fancy shoes Nike comes up with, ain't gonna happen

[Sariel]

If that's the basic power/weight ratio needed and LEGO parts don't come even near that how come this discussion with LEGO motors is still going?

It's people believing in miracles. And in magic pieces, like this one ;)

[vmln8r]

What are you guys doing? Using logic, in this thread?

*shakes head*

(I'll be back again, this thread is somehow incredibly addicting)

[anton1678]

What are you guys doing? Using logic, in this thread?

*shakes head*

(I'll be back again, this thread is somehow incredibly addicting)

Yes, logic hasn't ever got anyone anywhere.

except for life-and-death logic

It's amazing how after 6 pages, people are still actively posting.

I've gone from new member to citizen since it started

Edited June 30, 2014 by anton1678

[Sariel]

I've gone from new member to citizen since it started

I'm starting to think this is the sole purpose of this thread.

Look, with all due respect: have you noticed how the most sceptical people here happen to be people with most experience with Lego and RC flight? Doesn't that tell you anything?

It's amazing how after 6 pages, people are still actively posting.

The same would happen if you built a really good MOC instead of sitting here wishing for the laws of physics to stop working.