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View Full Version : Do counter-rotating blades give more lift?


phupper
05-05-2007, 04:04 AM
The guy at the hobby store told me that electric heli's like the Blade CP did not have enough lift to carry a wireless camera. I'm just a noob, but I'm pretty sure he's wrong. I saw a Dragon RC that comes with a camera pre-installed.

He also said that the dual bladed counter-rotating models provide less lift than a comperable single bladed model. Variable pitch on the single could make him right on this one.

But tell me guys, am I going to have trouble lifting a wireless 2.4GH Eyecam with any of these size models?

Thanks!

Brutal E
05-05-2007, 11:15 PM
If you tie your camera into the lipo then you have no problems with weight if you have to add a battery then the CX2 is going to have problems. The CP Pro will be sluggish. Go brushless and the CP Pro can lift a good amount. Stock CP is going to be too little lift me thinks. Without extra battery will probably still struggle.

Spencer J
05-06-2007, 08:24 AM
Regular 9v batteries probally won't work on the cam, even with brushless....

phupper
05-06-2007, 07:37 PM
Well, the weight of the camera and transmitter is 9 grams (when it arrives in the mail). So I taped a small Bic lighter (11 grams) and a standard 9v battery (46 grams) to the underside of my CX2. To my amazement it lifted right off! It's sluggish and uses about 75% of the throttle to hover, but it's very flyable. I kept flight times to under 30 seconds because I don't have heat sinks yet. If I use LiPo instead of the 9v batt I may be able to lighten the load even more.
I'm surprized these models don't have a max-load rating like real helicopters.

vortex05
07-03-2007, 02:30 AM
I've measured the blade CP it seems to lift good up to 100g it does become sluggish at that point. This is stock with a lipo and 9T motor.

it might lift more than 100g but I'd be careful at that point.

IMO 100g is plenty of lifting power. (use the stock woodies flat bottom for the added lift)

Flyingace451
07-08-2007, 08:02 PM
The cheaper beginner helis with counter rotating blades barely have enough lift to carry themselves let alone a camera. And no, the dual blades do not give more lift, they provide extra stability by countering each others torque and any negative ground effect. But like I said most of them hover at 3/4 throttle giving very little climb rate, and little climb rate means little thrust, little thrust means it can't carry much or anything at all.

You would need a powerful heli in order to lift anything, and most 3D birds will have that. The Blade CP or even the CP Pro are not 3D birds...they are mildly aerobatic but that's it. You will need something that can rocket upward or hover a couple of clicks above or below half throttle upright or inverted. Power power power!

vortex05
07-08-2007, 09:07 PM
Lol did someone say TRex?

Flyingace451
07-08-2007, 09:35 PM
Nope, but I thought about it! They actually sell Trex/video camera combos somewhere...forgot where though.:)

Sentertainment
07-09-2007, 03:41 AM
I should have taped my a vid of my Blade CX (not even CX2) using stock motors and running a 7.4v 2200mah LiPo...
I got much better torque with the motors using the better battery, but my climb was much slower...anyways, point is is flew and I could get it to climb just fine to fly it.

(yet again, I did have the carbon boom kit installed...that does give the heli a better lift)

HX3D014
07-13-2007, 08:30 AM
The guy at the hobby store told me that electric heli's like the Blade CP did not have enough lift to carry a wireless camera. I'm just a noob, but I'm pretty sure he's wrong. I saw a Dragon RC that comes with a camera pre-installed.

HE probably didn't know the weight of the Wireless system (boy have they come down in weight recently) seems you proved him wrong there. hehe.

He also said that the dual bladed counter-rotating models provide less lift than a comperable single bladed model. Variable pitch on the single could make him right on this one.
A counter rotating blade system will invariable have more lift.
especialy due to the Foil design of the blades.
However. the current polithera of Micro indore CX heli may have dificulty lifting even the current light weight Wireless systems, Especialy concidering they have a hard time outside as they are.

Slight side note.
the increased weight will add stability (Depending on how much weight) but will have an effect on you airspeed due to the relativly low power system
Ever seen a chart that ilustrates the Forward and Upward componet of thrust required for forward Flight.

Not to much to worry about if you just want to go up. Theoreticaly. If you have enough thrust to get more than 2 rotor diamiters high. they you will keep going up. (Until Airpressure is low enough to cause you to stop climbing, but you will either be too high by then or taken away by some High altitude (100ft+) winds<Depending on the day>)

Get a vidio on You tube when you have it together. Would be interested in seeing how you go. (No need to go High. just Do what you wanted eh :) )

Lister
07-21-2007, 10:04 AM
For a given motor power and weight of the whole system a counter rotating blade system should be capable of giving more lift. One of the reasons is that with the single rotor and tail rotor countering the torque quite a lot of power is wasted to counter the spin. In the counter rotating one the torque of each rotor cancels that of the other one, with no extra power input needed.

However it does seem that counter rotating helis are usually the small and cheap models only, which probably explains why the dealer said that they have less lift.

I suspect that the very reason that the cheaper ones are almost all coaxial is precisely because it is easier to get enough lift without using powerful motors.

vortex05
07-22-2007, 10:51 PM
There's also another reason, to get the amount of performance that's required to match the more advanced models requires the counter rotating blades to also be CP and that would be a nightmare at this small scale. Just imagine a dual swash system with dual linkages I dunno there's too many points of failure in my mind.

The FP fact of the counter rotating models alone will limit it's carrying capacity.

HX3D014
07-26-2007, 11:46 AM
Not sure the FP part is the Limiter. Obviously the pitch is near CLmax and when a Blade is at CLmax it is esentialy at its maximum AoA before stall. So there is no more that could be added by useing a pitch change (As far as Colective is Concerned in relation to geting more lift)

Here it is

Lift = Cl x 1/2r x (V x V) x S

Cl is the foils ability to produce lift. this is variable in a CP heli and at max on a FP heli.

1/2r is Half the Air dencity

V squared is Velocity of wing area

and S is Size of wing area.

so how do you incrase the lift on a FP heli.

Cant change CL (it is Fixed)

Cant change 1/2r (well you can. by changing altitude of flight. IE Flying
sea level and flying high in the mountains will give different Lift abilitys)

Cant change the Size of the wing area. (Keeping the scale of a single
rotor system and a CX system the same in this area)

then there is one last thing to change....

RRPM (V x V)

THis is not to say that a CP CX heli would not be more adjustable to variations in load and thus more efficient for each load variation (Given it has a Similar foil shape a the RC FP CX heli do). just that a FP CX heli is set with its rotors at near maximum lift production Clmax.

Down side is that the Drag increases with increase in RRPM especialy when it is alredy at CLmax. IE CLmax is not just max lift, but max drag. which = Max power less efficient. but this could and would vary from one FP CX heli to another

So in short. the typical cheep CX heli with FP systems are good lifters for their power being used. but if you want better endurance for a lighter load. then a CP system would benifit in reducing drag, by way of reducing AoA.

another way a CP CX heli is better over a FP CX heli is that it has a better yaw controle and is faster with efficiency. and the way a FP CX heli is beter over a CP CX heli is its max lift ability.

the CX heli most people are buying are good lifters concidering their power used (At the Hub). but they are (As we all know) limited in Agility and Speed.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

He also said that the dual bladed counter-rotating models provide less lift than a comperable single bladed model. Variable pitch on the single could make him right on this one.
this statement from the Original Post is Out and Out wrong.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

phupper
07-26-2007, 09:56 PM
Wow. Unbelieveably, I kinda' understood everything you said except AoA. Is that Angle of Attack?

vortex05
07-26-2007, 11:36 PM
Interresting so the only thing that can be determined from being FP is your forward flight capability is greatly reduced compared to a FP heli.

I guess this is true, setting the heli up in idle up mode and allowing me to utilize full head speed usually I can observe better forward flight characteristics, this is probably due to less drag due to lower AoA (lowered pitch and higher RPM to achieve the same lift).

Not to get too off topic but has anyone found blades specifically designed to reduce responsiveness and increase stability for CP heli's like the blade? Just curious if there is such a thing, I know that there are a few for 450 size that are supposedly used in FAI.

Prehaps a set made from foam that will flex horribly will gain stability at the cost of movement.

HX3D014
07-30-2007, 02:15 AM
Wow. Unbelieveably, I kinda' understood everything you said except AoA. Is that Angle of Attack?
Correct. Angle of attack. AoA is different from Blade pitch angle. but, generally speaking, Changing the pitch angle changes the Angle of Attack.

You did good to Kinda Understand all that ;-)

HX3D014
07-30-2007, 02:25 AM
Not to get too off topic but has anyone found blades specifically designed to reduce responsiveness and increase stability for CP heli's like the blade? Just curious if there is such a thing, I know that there are a few for 450 size that are supposedly used in FAI.

You can get a similar effect by adding weight to the Fly Bar.


Prehaps a set made from foam that will flex horribly will gain stability at the cost of movement.
would be an interesting thing to try. The blades may fold. but ... I am intending to make a foam blade for my heli so my son can learn.. this should save the boom and posably the mast.

Useing the formula above. I intend to find out how much of an increase of the Blade Chord will result in what kind of reduction in Rotor RPM with same or slightly less lift... (That is when I pull my finger out.. been puting that one off for a while now)

anyone know how to formulate Disk size and Disk Solidity ??

HX3D014
08-14-2007, 07:40 AM
OK. Learnt how to calculate Disk size and Solitity. Though the rezultant #'s do little more than provide an Idea. how to incorperate them into the project is another thing.

So I can get Ideas of what is my heli like compared to others. Could I have peoples dimentions.

My Heli is 350 odd grams
Rotor Dimentions
Centre of Main shaft to Blade Bolt is 1.24cm
main bolt to thick part of blade chord is 3cm
Blade Length from start of thick chord to tip is 24.5
Blade chord is 2.5 cm
Blade listed length (Bolt hole to tip) is 25.5cm
Rotor listed Diamiter is 560mm
My Rotor RPM is 2600

Given these details
I get a tip speed of 270kph
my total disk area is 2375.9cm^2
My Solidity of Main chord area over total disk area is (IE after it turns to the 2.5cm area) 19.39:1
Solidity based off blade bolt to blade tip is 17.66
I also learnt how to calculate the extra effective weight load placed on a bolt (Lateraly) given an added weight at a given Distance from Axis and RPM.
IE If I placed 5g at the tip of my blade and span it to 2600 rpm. it comes out to over 10kg

Any one else have details they want Calculated ?

vortex05
08-15-2007, 07:17 AM
I would like to calculate the sheer load on the center spindle due to a blade strike, as not all energy is transfered into the spindle the majority of it goes into the blade itself.

HX3D014
08-15-2007, 11:40 AM
you got me thinking now...

I know what you mean about being absorbed into the blade. but not sure if it would be most. (unles the blade breaks)

I think (Not sure) but think that all the energy at the tip will be dicipated to the Point of contact (that is those over the contact area and those outside <shoul the strike have been not directly on the very end of the blade. and as the parts in from that are further from inpact point, their energy continues and that energy is balanced between the bolt and on and the impact point. Like I said. I am thinking about it now. and am not sure.

I am thinking how you have in effect changed the moment...


Nah. I just blew a fuse. Not sure how to come to an exact answer on that.

to many thing I dont know about moving a mass around an Axis and the Forces imposed at various points..
i might get to it one day. but for now. I am happy with the calculations I can do at the moment.


Shere powere would be based on length of moment and mass x V ?

Information ?
where is the contact point on the blade mm
what is the length of the blade mm
what is the weight of the blade g
where is the blade CG mm
what is the RRPM
what is the blade made of (Predy sure this is needed)
what is the object contacted made of. (Not sure if this is needed ? )