Help me make a flying helicopter!

[Zerobricks]

While it looks good on paper, you are forgetting that the torque will cause the axles to bend, so the rotors will never be fully horizontal. Thanks for input anyway. i think getting getting a stable quad might be easiser than a tandem.

[Brickthus]

Instead of the white fan blades, try Unimog door panels. These are available in both hands, to make mirrored rotors. Definitely the broad blades. The thinner ones don't work very well, as I tried a 12-bladed fan with those.

I have run a counter-rotating twin-rotor (not intermeshing) experiment with 1 5292 motor per rotor and 4 door panel blades on each one. It achieved 200g of lift on a 270g model at 9.1 Volts (equivalent to fresh batteries) and took about 2.5 Amps. The motors won't last long at that power level. I am using a bench power supply because batteries run out too quickly, but I would move to the light LiPo battery once I have a datum point for the motors and frame leaving the scale pan!

The 5292 motor is definitely the right one - fast and powerful. An XL motor is just too slow, and a pair of M-motors geared up 5:1 doesn't do as well as a single 5292. A pair of L-motors geared up 5:1 is a possibility. I did try this with 6 9396 blades angled at 22.5 degrees on a single rotor but those blades are not designed for creating actual lift and the model didn't make much of a down-draught.

Another key is to widen the radius. I kept extending the radii of my Unimog door panel rotors. A key with this is to make sure they can't fly off, so I use 8M axles with bezel end and also 16M axles with multiple half bushes to keep them attached. If a single half bush flies off then you just have time to shut down before a blade follows it! I use a piece of Lexan sheet to avoid injury!

For maximum thrust, wide radius and high speed are needed. Maximise swept area per second. Also get a good blade angle so that the air flows over both surfaces. It's not just a paddle! Too steep an angle and it will be like a stalled wing and create turbulence rather than thrust.

Best wishes for take-off!

Mark

[SkyrateShadowStorm]

Here is a good list of test results from all or most of the LEGO Motors. From it you can choose the best motor based on Torque, RPM, and Mechanical Power.

From my research of real world Helicopters, most use a constant, low RPM.

H-13 Sioux runs at 333 rpm(source).

AH-64 Apache runs at 292 rpm(source).

UH-60 Blackhawk runs at 258 rpm(source).

CH-47 Chinook runs at 225 rpm(source).

Mil Mi-26 runs at 132 rpm(source).

Note that on each helicopter, the rotor diameter is lengthened and the rpm required is lessened.

If these multi-ton machines can achieve flight at low RPMs, surely a few KG of LEGOs can.

Here is another thing to take into consideration.

I'm not saying RPM isn't required. But one thing I've noticed in every LEGO flying attempt I've seen (and I've seen a lot) is that they have very high RPM, but the body is either too bulky or the blades have no airfoil design.

Here is an interesting thing from NASA on airfoil designs.

You need RPM, but you need controlled RPM. If you have a few hundred RPM and good torque you can work on designing good blades. The Mil Mi-26 has a 105 ft diameter, if you figure one stud ~= 1 foot then that's a 105 stud diameter, or 52.5 stud radius. Roughly a 50 stud blade. The other helicopters I listed barely have 60 ft of diameter(most have less). You can see why the Mil Mi-26 is such a heavy lifter, nearly twice the blade length.

The Model RC helicopters I've seen operate at 900-18,000 RPM. They also usually have shorter, thinner, blades and only 2 or 4 of them. They also usually don't have pitch control, thus their altitude is based on RPM, not Pitch like a real helicopter. Many also run on gas engines.

We may be looking at acquiring our lift the wrong way. Just something to consider.

I look forward to more tests.

[camaudio]

@CamAudio, You have to have the pitch of the rotor blades be correct. Just reversing one motor would causing it to pull the craft down instead of up.

@ZBLJ, Quad may still work, you just may have to use different speeds. I.E. X at 75%, Y at 80%.

I've done a fair bit with rotor and gear testing with technic and know what you mean. The 5292 is not hospitable to gearing due to its high rpm but very low torque. I think XLs may be able to drive the driveshaft and then be upgeared or vice-versa. Using round gears you can get a 1:3 ratio with one assembly, using normal(or as I say, 'hard') gears, you can get 1:5. The XL spins at around 146-214 depending on your voltage. That could get 438-642 or 730-1,070 rpm, with decent torque(easily enough for those blades).

Do you know your target RPM?

Flip the blade around

nvm, i just realized that wont work

Edited January 10, 2013 by camaudio

[Burf2000]

I have also been trying to get something flying and as Zblj points out you need a lot of volts. I would love to see a better hovercraft made that can take a NXT.

[Zerobricks]

Wow. so much info i got here at once... Will try the panels, but i doubt they are as efficient as the white blades, so I'm affraid the motor prtoection will kick earlier. I will continue the project in few days, but tommorow I am getting a new set to build.

Any pics of how you used panels Mark, so that i dont have to reinvent warm water.

[DLuders]

@ Zblj: On Mark Bellis' Brickshelf webpage, it shows what he did with those old-style Lego Technic Panels to make fan blades. His prop_lift_info.txt file has lots of good information about his experiments.

[Sariel]

I'm no physicist, but shouldn't we favor long blades over wide blades? I mean, the longer the blade, the greater the angular speed of its tip, which has rather large impact on total thrust, right?

[legolijntje]

I'm no physicist, but shouldn't we favor long blades over wide blades? I mean, the longer the blade, the greater the angular speed of its tip, which has rather large impact on total thrust, right?

That would probably work in real life airplanes, but I think if you try to make longer blades with Lego and you're going to turn them very fast, they'll start wobbling. And that would make the whole creation a lot more unstable...

[allanp]

You mean like this?

http://www.youtube.com/watch?v=p4VLhnTZpb8

[SkyrateShadowStorm]

I'm no physicist, but shouldn't we favor long blades over wide blades? I mean, the longer the blade, the greater the angular speed of its tip, which has rather large impact on total thrust, right?

That would probably work in real life airplanes, but I think if you try to make longer blades with Lego and you're going to turn them very fast, they'll start wobbling. And that would make the whole creation a lot more unstable...

I don't think any of us are physicists, if we were we probably wouldn't be discussing this.

From my studies, yes, longer blades are more efficient. This is because they have less drag and create less turbulence. A wide blade, while moving more air, will have more drag and creates more turbulence in the air it passes.

A helicopter rotor is not designed to move air, it is designed to change the air pressure above and below it.

A fan is designed to move air, not to change air pressure.

Yes, Helicopters do make quite a downdraft of air, but that is not the intention nor how it stays in flight.

LEGO has the advantage that the stud system is very strong. Throw a few 4x8 plates together overlapping some and they aren't coming off unless your blade hits a solid object. The centrifugal forces are naturally pulling the studs together(sideways), not away. Granted, if the blades go haywire uppity downy then the blade could separate.

Another thing to consider about longer LEGO blades is this:

I forget which helicopter it is (I think it was the Mil Mi-26, heaviest lifter in the world), the blade tips are designed to not provide lift(or very little). This is because if they did they would wobble out of control, like legolijntje mentioned. The middle of those blades provide most of the lift. The Mil Mi-26 has 8 blades, each being about 50 ft(15m) long.

One thing we should keep in mind is that not all helicopters have the same number of blades. When most people hear the word 'helicopter' they picture a four bladed machine with a 4 bladed tail rotor.

Helicopters can have anywhere from 2 to 8 blades on one rotor. The Chinook uses two 3 bladed rotors, Mil Mi-26 uses one 8 bladed rotor, CH-53 Super Stallion uses one 7 bladed rotor. Most combat helicopters use one 4 or 5 bladed rotor.

Usually the more blades a helicopter has, the more weight it can lift. It may be worth us considering using 6 or 8 of those white blades on one rotor.

Something like that, perhaps?

[xxlrocka]

Something like that, perhaps?

I'm no expert on helicopters or Technic, but maybe that could work.

[AVCampos]

I Also thought about the issue of number of rotor blades. What other factors are to be taken into consideration when choosing the number? It mustn't be predefined, or else all helicopters would have the same number of blades...

[Blakbird]

More blades means more lift per unit diameter, but it also means more torque required and more drag. That's why you see fast helicopters use 2 or 3 and heavy lift helicopters use 4 or 6. Military choppers often try to split the difference with 4. The CH-47 is heavy lift but since it has tandem rotors they can each have 3 blades. Also, at some point the blades become too close together and are fouled by the turbulent wake of the preceding blade, so 6 is about the max.

The previous which shows the white blades with very wide chords won't be very good. Not enough free space between the blades. Heli blades are always constant chord, not tapered, and if you were going to taper them they would be wider at the root, not the tip.

All of the suggested parts will act as flat plates rather than airfoils. This means they will produce lift, but at a tremendous drag and turbulence penalty.

[SkyrateShadowStorm]

@AVCampos, All depends on what you need to do. For LEGO tests, I would think our current main concern is weight thus we should probably consider mimicking a heavy lift helicopter. LEGO aircraft have to have certain weight(motors & technic pieces) so it would be better to try to design around that weight rather than just reducing the weight.

@Blakbird, The Fastest Helicopter ever made uses two 4 bladed rotors in a coaxial design.Turbulent air wake is only an issue when hovering, not during flight. During flight the leading half of the rotor is going through undisturbed air. 8 blades apparently doesn't cause too many problems otherwise the Mil Mi-26 wouldn't have 8. 8 may be a few too many for beginning LEGO flight though. 6, whether on one rotor or tandem is probably the best.

More blades do require more torque and induce more drag, which is why speed is not always the most important factor. More RPM will also make the turbulent air wake effect the helicopter more, another thing to consider with high RPM.

The white blades depicted are the ones ZBLJ has been using on previous tests. They are not ideal nor the most efficient airfoils but for testing they are a good start. I believe the best LEGO airfoil will have to be carefully designed and use plates.

Igor Sikorsky didn't build a successful helicopter in one day nor by himself. I highly doubt it was on the first day, either. As we talk and think about different aspects, concepts, and designs and test them we'll get closer and closer to success.

[piterx]

i know anyone is focused on helicopters...but i was wondering:

if that motor can lift itself, probably it could also drag a wheeled vehicle, so: what if this wheeled vehicle has wings that can generate portance :P?

i mean, to me a lego airplane could easily fly and bring with itself all the power functions that it needs....

that wouldn't be a matter of how much a motor can spin, it would only be a proportions problem to solve

[Zerobricks]

Was thinking the same. Plane looks easy now that a motor has enough lift to lift itself. You got idea how to make wings?

[DLuders]

Well, Grohl made this Lego Technic glider that could possibly be towed by a vehicle:

[piterx]

maybe:

the frame of the whole entire model should be made of axles and connectors, so it will light and solid, and you'd need to wrap the frame with some light plastic sheets....probably it could be good the plastic wrap that's used to store food

the main problem is getting the proportions right...

i was starting to build it when i first saw your post but then i had to fly to london to work :(

anyway, you should start with a small glider that can take off ....if it will, and it will :D, we could start thinking on how to add PF to make the plane roll and maybe land without crashing

if you give me some minutes im gonna draw what i mean :)

Well, Grohl made this Lego Technic glider that could possibly be towed by a vehicle:

Well, Grohl made this Lego Technic glider that could possibly be towed by a vehicle:

yeah that's not bad but im not sure about the wing's shape and the way he put plastic on it....

plastic should be wrapped really tight around frame

[captainmib]

Helicopters are very technical and difficult machines.

I was wondering, why not use wings to generate the lift that you need.

I was thinking of this airplane:

Maybe not that many engines, but if the wings are of good shape they will generate the needed lift...

I'm sure someone can calculate the weight/wingspan formula.

[piterx]

lol dude you came half an hour late :P

[Zerobricks]

Where is Blakbird when you need him

Edited January 13, 2013 by Zblj

[piterx]

here it is....i apologize for the quality of this drawing but im in a hotel room sit on the bed and i've drawn it with a wacom placed on my knees :D

anyway...

i think it's quite important having the plastic around it tightly firmed....it will give more strenght to the frame and will generate a better portance

[Blakbird]

Where is Blakbird when you need him

He is distracted by being in England right now.

[piterx]

this wing can lift over 100kg....with the right proportion yours will lift easily 3-400g :)

Edited January 13, 2013 by piterx