Contra-rotating rotors as plan B Update of the Humming Man Project

Dear All,

As we are now have finished the belt drive design as you can see, we are now in the making of it. Once we have tested one unit we can see how it functions, (acceleration, control, stress, vibrations, etc..). But yes always there is to be 

a plan B. And good to advance in that direction too. That craft would be configured just like the original see earlier blog. But at each end iso one e motor with belt, there would be two motors:  one up one down (just like in some quadrocopters). This would be a compact alternative with more redundancy. 

The motors would be controlled separately and we can vary the top and bottom speed. 

We see at first investigation that contra rotating props can have some higher efficiency as 2 seperate ones. We also understand that the prop pitch of the lower prop needs to be higher as the down wind it receives from the top one can then better be used.  

Now the issue is: does any one of you have experience or rules of thumb or simple first effect formulas to tackle the issue? Would think that with the some of the drones this issue must have been studied?

Hope to hear, Best Regards, Winfried team

Views: 1424

Comment by Jerry Giant on November 14, 2014 at 4:07pm

it seems a nice question, but where's the efficiency come from.

the purpose of a WWII war bird use contra design to put more props on its nose, as i know is to put more power within the same radius and rpm...

i think you guys could learn more from basics of engineering rather than following the forms. empirical knowledge is not always a good design. maybe you could learn how to fly a man by himself on a giant quad, or volocopter.

Comment by Phill Scott on November 14, 2014 at 5:25pm

To be honest, this isn't hard to calculate using blade element momentum theory. 

Here's an intro....;

Comment by Andrew Rabbitt on November 14, 2014 at 11:13pm

I must admit, I'd like to see the whirling things somewhat above my head if I was going to fly it...

Comment by Bart Theys on November 15, 2014 at 4:03am

Coaxial counter rotating propellers will never be more effecient than two separate propellers since the disk area stays small. However, at very high disk loadings ( thrust per disk area of the propeller ) , coaxial propellers become interesting and with a good design, the efficiency can be a little bit higher than 1 single propeller. 

Comment by F. C. Bearsch on November 15, 2014 at 5:36am
I have seen really great efficiency from planetary ivt drive systems, look at the Nuvinci by Fallbrook tech. The assembly is easily modified to reverse only, at the same time the varied speed capability will give some other benifit
Comment by Winfried Rijssenbeek on November 16, 2014 at 12:06pm

Thanks Phill, will have a check on this, but hoped that there would be practical rules of thumb: eg the pitch of the propellor below should be twice that at the top... Any there are many quadrocopters with such design of contra rotating props, thus.. 

Comment by Phill Scott on November 16, 2014 at 12:38pm

I'm not sure that there are such things as general rules for this.  The interactions have a lot of variables involved from design to atmospheric conditions so it's going to be a case of designing for a range of conditions.  You want to know this is going to work before trying it out, so you'll have to do the calcs anyway.

The other way to go would be to design an experimental rig with two props that you can vary the root angle of in a controlled manner, and then record results (mass balance, audio, vibrations observed, power consumption and anything else) so that you can try to optimise a configuration empirically.

Comment by Winfried Rijssenbeek on November 16, 2014 at 12:46pm

Yes, you are right. We will have to get into it again! But software can help... 

Thanks Winfried

Comment by Ed Kirk on November 16, 2014 at 4:52pm

I have designed and built quite a few multirotors with coaxial counter rotating motors including several which I modified existing single motors into coaxial setups.  The results have been great, nothing special, both props are the same diameter and pitch.  Just don't get the props too close to each other, the result is noisy and reduced lift, that's all. 

The video is one of my first copters, a tricopter with some parts from MultiWiiCopter, actually my second attempt into multicopters.  I designed the rotating tail assembly and used this platform to test the concept of a rotating boom and counter rotating motors.  MultiWiiCopter uses this rotating tail design in his equipment.

Comment by Ed Kirk on November 16, 2014 at 5:06pm

Another video of the tricopter above with the GoPro camera attached under the rear set of motors.  I did this to study the rotating boom in flight.  There was no vibration dampening with the attached camera, simply strapped it on with tie straps.  Pretty smooth setup considering I didn't take any special procedure other then balance the props.


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