Variable Pitch Propeller

[Sariel]

Just a simple concept, tested for thrust with the 9396 set's blades:

Reading and a full building instruction: http://sariel.pl/2013/11/variable-pitch-propeller/

[captainmib]

Nice creation.

Maybe we can use it in the upcoming cargo-plane.

So the conclusion is that lego is never gonna fly? Increasing the pitch didnt help at all, since the goal is to make the weight-counter lower...

[JM1971]

I've seen the mythbusters do this sort of stuff, they tested a cage full of birds sitting and then flying and it weighed the same, air is pushing the scales down too.

[DrJB]

Neat experiment. The video introduction covers helicopter rotors and that might be a bit misleading as those have both collective and cyclic. In your case, I think you're using only collective. Now, and as you do know, how sensitive is the thrust to blade angle depends really on the blade geometry. I wonder how the thrust depends on both the pitch and orientation of the blades from the energy add-on set. Lastly, possibly one contraption I'd like to build/see is with a mindstorms system. Such system would be suspended by 3-4 parallel wires as a pendulum, the blades would be assembled such that the thrust vector is horizontal. When the blades are on, they would pull the system (against gravity) to the side, and depending on how far the system moves, that would be the 'amount' of thrust the system would have developed ...

Nice creation.

Maybe we can use it in the upcoming cargo-plane.

So the conclusion is that lego is never gonna fly? Increasing the pitch didnt help at all, since the goal is to make the weight-counter lower...

I am not sure those blades generate enough thrust ... not only that, but they are so flimsy and most likely will have so much vibration that the 'thrust' vector would 'not' be constant ...

Edited November 9, 2013 by DrJB

[Sariel]

Just to remind you, we've had all this discussion on flying with Lego before:

http://www.eurobricks.com/forum/index.php?showtopic=77519

[captainmib]

Didn't think of the airflow pushing down to the scale.

I know of the discussion, but your test just refreshed the idea of flying in combination with lego ;-)

[VWcharger69]

Just an indication. As I like playing with toys, I own 2 RC planes and 1 RC helicoptere.

Just as comparaison my RC heli have the folowing specs:

- 2 main rotor: diameter 460mm each

- weight in flight order 410 grammes

- electric motor: 2 unit: power 400 watt each.

Here is a photo of blade use in RC:

http://www.hobbyking.com/hobbyking/store/catalog/074000013.jpg

All specs are far away, we can find in technic piece. Perhaps you should mix RC parts like blade and motor (thinking about a 1 kw motor) to make a RC technic heli.

[Sariel]

Yeah, I was curious how effective these blades can be. They seem to be the most realistic of all Lego blades so far.

[rm8]

Sound cool - like real helicopter.. Wuuuiiiiiiiiiiiiii...:)

Edited November 9, 2013 by rm8

[JM1971]

Superlight lego and turbo jet prop engines, might be able to make this :D

[VWcharger69]

Yeah, I was curious how effective these blades can be. They seem to be the most realistic of all Lego blades so far.

Most of these blade are made from very rigid polymer or composite. ABS fron the lego piec isn't rigid enough for this application (I'd made several tests on different materials as an engineer)

IN RC helicoter, Nylon is use for the blade of small helicopter (500 mm long, weight less than 600g).

For bigger blade are made of carbon fiber reinforced polymer (resin is alomst epoxy). With this type of blade, lenght can be over 600mm. Weight of the helicopter in flight order can approach 5 kg for the bigger.

As an indication look at this reference: Align T-Rex 450: http://shop.align.com.tw/product_info.php?products_id=5116

If you had any other question, like how to stabilise the heli... Electric motor use or battery technogy, I'll be happy to share my experience in RC.

Christophe

[Lakop]

You want to propel a car with it.

H

[Andy G]

I made something like this a year ago. The problem is the blades aren't very aerodynamically efficient. It does produce some thrust but not enough to be useful. I even geared my prop up using 4 medium motors and had that prop turning at a scary speed but still it wouldn't pull much load.

[Sariel]

OK, to clear out any confusion I made a simple comparison between thrust you can get from regular LEGO run at 9V, and between what AR 2 Parrot drone does:

Edited November 10, 2013 by Sariel

[Technyk32231]

I made something like this a year ago. The problem is the blades aren't very aerodynamically efficient. It does produce some thrust but not enough to be useful. I even geared my prop up using 4 medium motors and had that prop turning at a scary speed but still it wouldn't pull much load.

Very nice! In the video description, it says that the design uses a modified part. Which part would that be?

[trekman]

So the conclusion is that lego is never gonna fly? Increasing the pitch didnt help at all, since the goal is to make the weight-counter lower...

I noticed that the sound of the RC motor changed a lot with the variation of pitch. Did the motor actually run at the same RPM? and were the batteries fresh ones each time. These variables do make a difference when you are talking about such small changes in results.

I reckon that the motor was under more load in the later tests. You would really need to hook up to a more consistent AC - transformer supply, and also do a test with pitch variations, but just measure the load on the motor. You would need to maintain consistent RPM on all tests to give a fair reading on the scales. (I used to do some work in R&D /stress analysis for an aerospace firm)

[DrJB]

How about these Lego blades 89509? I wonder how much lift would they generate.

Edited November 11, 2013 by DrJB

[Junpei]

I think those are the closest you can get. How much does it depend on speed? e.g. Would a Lego airplane probably be able to fly if the rotors spun at 13000 RPM? I know some real helicopters' blades spin at less than 400.

[legomuppet9]

Just to remind you, we've had all this discussion on flying with Lego before:

http://www.eurobrick...showtopic=77519

How about these Lego blades 89509? I wonder how much lift would they generate.

These blades were used extensively in the topic above with no success

[Sariel]

I noticed that the sound of the RC motor changed a lot with the variation of pitch. Did the motor actually run at the same RPM?

Of course not, it was slowed down by large pitch. The batteries were fresh every time, you don't kill Eneloop batteries that easily.

[JM1971]

Of course not, it was slowed down by large pitch. The batteries were fresh every time, you don't kill Eneloop batteries that easily.

I have eneloop too, they seem to last forever with lego. :)