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Old Dec 04, 2012, 02:50 PM
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Originally Posted by rimshotcopter View Post
Welcome kahloq and no, I do not mind at all. In fact, I am excite about the company.

Your last picture with the dual motors is very interesting and I also had considered that option. jy0933 made an argument that the second prop "either the lower prop cant get enough air or the top prop get dragging faster due to the demand of more air" which sounded very logical to me, so I set the idea aside. Too many other issues to address. I love how you have your motor support and that servo assemble is my dream!! Would love to purchase a pair of them.

Yes, Please join the party.
Actually, the suggestion that two props within the same prop disc moving in opposite directions would cause dragging problems and not enough air for one or the other prop is false.

Please keep in mind that there are several planes that have or do have counter-rotating props within the same prop disc and Im not meaning counter-rotating props on different motors at different locations on the airplane.

The Spitfire Mark XIX had what is called Contra-rotating props inline on the same axis with a planetary gear turning the 2nd propeller. In order to make the most effective use of this, you want the SAME pitch propellors, but, NOT the same blade count. However, it isnt required to use different blade count, but merely to eek out the last bit of efficiency.

Here's a basic explanation on how this works:

"When airspeed is low, the mass of the air flowing through the propeller disk (thrust) causes a significant amount of tangential or rotational air flow to be created by the spinning blades. The energy of this tangential air flow is wasted in a single-propeller design. To use this wasted effort the placement of a second propeller behind the first takes advantage of the disturbed airflow. The tangential air flow also causes handling problems at low speed as the air strikes the vertical stabilizer, causing the aircraft to yaw left or right, depending of the direction of propeller rotation."

This torque effect on the rudder is USED by quadcopters and up to move in whatever direction by altering the speed of various motors arranged around the frame without the need for any tilting action of the motors themselves.
However, on a tricopter or tri edf type setup, the rear motor/fan unit is normally tilted via a servo action to control yaw. As such, the torque effects of the main props has little bearing on how the vehicle flies. ALL the props can spin in the same direction and the vehicle will still fly, it will just take a bit more yaw servo movement of the rear prop/fan to compensate for the tangential direction of the airflow at all 3 corners. Normally, one motor is given a COUNTER rotating prop to combat that.

In the case of using counter-rotating props within the same duct work, the torque effects would be eliminated AND you can gain almost 20% more efficiency thru the same ducting.

Here's more explanation:
"If it is well designed, a contra-rotating propeller will have no rotational air flow, pushing a maximum amount of air uniformly through the propeller disk, resulting in high performance and low induced energy loss. It also serves to counter the asymmetrical torque effect of a conventional propeller (see P-factor). Some contra-rotating systems were designed to be used at take off for maximum power and efficiency under such conditions, and allowing one of the propellers to be disabled during cruise to extend flight time.

Contra-rotating propellers have been found to be between 6% and 16% more efficient than normal propellers.[1] However they can be very noisy, with increases in noise in the axial (forward and aft) direction of up to 30 dB, and tangentially 10 dB.[1] Most of this extra noise can be found in the higher frequencies. These substantial noise problems will limit commercial applications unless solutions can be found. One possibility is to enclose the contra-rotating propellers in a shroud. It is also helpful if the two propellers have a different number of blades (e.g. four blades on the forward propeller and five on the aft).

The efficiency of a contra-rotating prop is somewhat offset by its mechanical complexity. Nonetheless, coaxial contra-rotating propellers and rotors are moderately common in military aircraft
."

The above quoted sections come from an article on wiki explaining how Contra rotating setups increase efficiency. The full article can be read here:
http://en.wikipedia.org/wiki/Contra-rotating_propellers

In our case, there is no complexity added except mounting a 2nd motor as I illustrated in my prior post.

Also...we should see more then 16% thrust gain simply because we are using more then one motor to do the same thing as the article describes via ONE motor.
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Old Dec 04, 2012, 03:00 PM
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The Spitfire mark XIX wasnt the only plane to use this. The later variants of the Seafury used it as well as many others. The Russian TU-95 Bear had 8 prop blades on a contra-rotating turbo prop engine design. It was the most powerful piston powered plane EVER. The Russian The Antonov An-22 is the largest turboprop plane in existence and is still in use today. It also had contra-rotating propellors and was only surpassed in size by the US C-5 galaxy(jet powered) and the Russian AN-124(also jet powered).

There are several other examples including a contra-rotating prop P-51 racer and a General Motors P-75 to name but a fraction.
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Old Dec 04, 2012, 03:04 PM
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Interesting to say the absolute minimum!! I know a number of veteran guys here on RCG did a number of test with open air stacked dual rotors and off the top of my head, I believe the findings were the bottom prop system was 15% less efficient as the top rotor. I had wanted to use an arduino to control the motor speed of the top and bottom props to compensate, but never got around to it. What led me to the idea of using dual rotors in a duct was the compressor blades of a Jet engine. The bottom prop would accelerate the air faster however if the tip distant was at optimum, there seems a vacuum would exist.

But this is great and Welcome again!
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Old Dec 04, 2012, 03:05 PM
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Originally Posted by kahloq View Post
The Spitfire mark XIX wasnt the only plane to use this. The later variants of the Seafury used it as well as many others. The Russian TU-95 Bear had 8 prop blades on a contra-rotating turbo prop engine design. It was the most powerful piston powered plane EVER. The Russian The Antonov An-22 is the largest turboprop plane in existence and is still in use today. It also had contra-rotating propellors and was only surpassed in size by the US C-5 galaxy(jet powered) and the Russian AN-124(also jet powered).

There are several other examples including a contra-rotating prop P-51 racer and a General Motors P-75 to name but a fraction.
Most of these if my memory is correct, were open air systems, not ducted.
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Old Dec 04, 2012, 03:59 PM
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That is true....but as the article suggests....a shrouded design maintains the direction of airflow and also was talking about within the same prop disc of backwards airflow(on a plane) making the thrust produced in the same space more efficient. I wouldnt doubt that the bottom rotor might be less efficient in energy usage, but the sum gained in thrust would be significantly more then what one motor can produce

And as you know...a jet engine has forward impellors that blow air backwards at a higher rate then what it came in the jet housing as and then is mixed with fuel and again blown out the back with another impellor. Of course, not the same as what we're talking about here since we arent combusting anything.

There IS a reason why a y-6 design works in order to lift more weight

Im in no way implying Im an expert and I wont know if I need to add the bottom motors till Im alot further along. Once the frame is done and i can test the entire unit, I can easily see whether adding the bottom motors helps enough(if needed to begin with).

But, as I also mentioned, since my craft will be quite large, I dont have to put the 2ndary motors in the ducts. I can mount them inside the wing areas hidden to get as much thrust effect as possible(if in fact it would be more then putting them in the outboard duct nacelles). In that case, they would be shrouded since the depth of the wing wouldnt be near as much as the 5 gal buckets. I'd like to avoid this though since it would be rather obvious when the vehicle is flying.

One last option in my case would be to mount 70 or 90mm actual ducted fans in the wings pointing down for additional lift. I could easily explain that away as manuevering thrusters and no one would know squat different

That last option is what Im expecting to do if the 3 ducts dont get it off the ground......... and if needed, could actually put as many in the wings as needed to get the craft to lift off and fly ok.

But....if simply using counter-rotating props/motors inside the same ducting as the main motors does the trick....well...that would solve everything for me and be a lot less power hungry.

I'm already planning on using TWO 6s 8000mah packs in parallel
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Old Dec 04, 2012, 04:05 PM
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I'm already planning on using TWO 6s 8000mah packs in parallel
Wow and I thought I was the over weight kid around here

I really want to see more.
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Old Dec 04, 2012, 05:23 PM
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Here is a pic I took a few weeks ago to show approx size width wise of the vehicle.
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Old Dec 04, 2012, 05:35 PM
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Here is a pic I took a few weeks ago to show approx size width wise of the vehicle.
Awe yea, she is going to be huge. One thing I opted for was to increase the Root and tip measurement verse length. Same area but True, more drag but at the speeds I am planning, should not be any harm.

Edited: My first experimental wing, I had some taper but that did not work out very well, so I just made the Root and Tip measurement the same. If this works, I will work on a newer verse with taper at the tip.
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Old Dec 04, 2012, 06:10 PM
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I dont have to worry about wing lift or shape of wing to optimise lift because my project doesnt fly on the wing at all.
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Old Dec 04, 2012, 06:12 PM
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Awe!! the two wood looking pieces I thought was the wing tips. Sorry
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Old Dec 04, 2012, 08:32 PM
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I believe it will just be a monster tri ??? no wing lift needed , other than the look ? right ? kahloq ?

Terry
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Old Dec 04, 2012, 09:34 PM
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Awe!! the two wood looking pieces I thought was the wing tips. Sorry
They will be the wingtips. The buckets will be fastened to the outside of those wingtips with the aluminum exoskeleton blocked servos. Those will then be anchored to a larger more robust wing leading into a central frame. All of that will need to be reinforced with aluminum tuning and whatever else I need to keep it strong.

Once I get the entire vehicle flyable, I'll then add the "scale" detail and overall shape of the HK's actual body shape.

While it will have wings and they could provide lift if the vehicle were flying fast enough in forward flight, I dont envision needing to make it fly that fast. It isnt really the point. I will have a camera gimble mounted inside a clear dome that will have my Drift Innovations Action cam mounted in or on it.
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Old Dec 04, 2012, 09:38 PM
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Originally Posted by KAMAX-T View Post
I believe it will just be a monster tri ??? no wing lift needed , other than the look ? right ? kahloq ?

Terry
Not exactly. It will look like a giant tri with shrouded/ducted rotors, however, all the rotors will be able to tilt in at least one axis...so usable tilt motors.

Also, it may not end up being a tri. Shape wise and visually yes, but if necessary, there may be 2 or even 4 additional edf fans imbedded in the wing.

So...it could end up being a 5 or 7 motor vehicle or it could end up being a really large complex y-6. We'll see once we I get to that point.
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Old Dec 05, 2012, 06:36 PM
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thanks kahloq ,....
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Old Dec 07, 2012, 02:20 PM
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Figured it would be a good idea to keep everyone up to date with some in process videos. This is the very first test with props on, no intentions of actually taking off. This test was solely to discover any problems, some were noted and soon to be corrected.

Mollie VTOL - Preflight Test01 (0 min 52 sec)
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