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Contra Rotating Propeller Drive for f3a 2m Pattern Planes

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Old 09-16-2010, 09:53 AM
  #76
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

No, ours is the same as Seba's. Each prop can run at a different speed. What's common between the props is the torque multiplied by the rpm of the prop, which is a proxy for power. Each prop absorbs the same amount of power, so if one prop is wider than the other prop (for instance...) the torque into the prop will be increased, and the rpm will be decreased. Also, we don't have any belts. We use gears.
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Old 09-16-2010, 11:36 AM
  #77
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

I certainly agree that there are opportunities for new plane designs to take advantage of the Contra Drive. In fact, after campaigning my Contra since before the USA Nationals I have noticed at least two things that I think will be useful:

1/.. The first thing is that fuselages don't have to have right thrust molded into the nose any more. This has been problematic for many plane designs because lots of people used them for both glow and electric, and since electric planes use larger props, more right thrust is generally needed than for planes that use glow engines. This means that the fuselage can be correct for either glow or electric, but not both. I know that with my Integral I resorted to mixing rudder with throttle in order to increase the effect of the right thrust that was molded into the fuselage. In fact, I think trimming a plane to account for assymetric motor torque is one of the harder things for new flyers to do, and with a Contra Drive, all of this effort is now no longer needed. This has the potential to help new pattern flyers quite a bit I think.

2/.. Contra powered planes exhibit a "constant speed" characteristic, which I think is because Contra Drives are more efficient than single props when the prop is flying at advance ratios that are lower than the prop's design point, and the braking effect of the props is double that of single prop setups when Contra Drives are flying at advance ratios higher than the prop's design point. This results in the plane seeming to fly at the same speed regardless of the power applied, or the orientation of the plane. What this means for plane design is that planes don't have to have huge draggy fuselages anymore in order to match the speed on the uplines and the downlines. Now fuselages can be slimmer, and they don't have to be as tall. This reduces aerodynamic interactions between the fuselage and the wings and tail, and reduces the power draw from the battery packs. This last effect means that smaller, lighter packs, or same weight packs with higher C ratings, can be used. (I'm going for the new 45C packs ...)
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Old 09-16-2010, 12:35 PM
  #78
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Quote:
ORIGINAL: Brenner

No, ours is the same as Seba's. Each prop can run at a different speed. What's common between the props is the torque multiplied by the rpm of the prop, which is a proxy for power. Each prop absorbs the same amount of power, so if one prop is wider than the other prop (for instance...) the torque into the prop will be increased, and the rpm will be decreased. Also, we don't have any belts. We use gears.
Ok, so you can restrain one prop, then turn the motor and the other prop alone will move. This would be at twice the RPM than if both were moving ??.
I was not suggesting you used belts, it was another contra unit in Austria.

Can this unit be re-engineered to run on an outrunner or direct drive innrunner (210/230 kv)
This would increase the market size.

Brian
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Old 09-16-2010, 08:09 PM
  #79
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Hey Brian,

Yes, both props can move independently of the other. If you restrained one prop, the gear ratio for the remaining prop would be half what it is when both props spin free. It wouldn't spin twice as fast though because there wouldn't be enough power available from the motor to spin it that fast, but if you were able to rotate the pinion gear at the same speed, then the single prop would rotate twice as fast.

We could develop a Contra Drive that would work with an outrunner, but I don't think it would be practical for pattern because the resulting weight would very heavy. This is because outrunners don't have an existing gearbox that I can replace with my Contra Drive gearbox.

The best configuration is the Contra Drive coupled with an inrunner motor. Currently we plan to support the Hacker C50-14XL Competition motor, and the Neu f3a motor.
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Old 09-20-2010, 08:28 AM
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

I was able to see this fly a lot this weekend. Brenner has made some changes and it is definitely faster than it was earlier in the year. Was very impressive. I would've loved to have flown it on Sunday, but with a 10 hour drive looming, I headed out early.

Great work though Brenner,

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Old 09-23-2010, 10:33 PM
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Uhhhh Brenner one very good question. I will use your system on an KRILL SPARK EVO plane and if the nose is similar to the SPARK that is out now, the diameter is only 63 mm and the length only allowed to be 45 mm! is this possible?
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Old 09-24-2010, 06:25 AM
  #82
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

I saw one of Andrew Jesky's Sparks last weekend, and the spinner on that plane was way too small to fit a Contra Drive into it. However, I've been toild that there is a new Spark coming that has a much larger spinner size. Are these dimensions for this new Spark, or the old Spark. If they are for the new Spar, then we are still out of luck.
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Old 09-24-2010, 09:18 AM
  #83
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

The new spark will have a spinner of 70mm but not sure how long it will be. Hopefully this info will help for you guys.

Andrew
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Old 09-24-2010, 10:57 AM
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Have You been testing the new EVO Andrew?
I will ask Ivo for the spinner size , I intend to use this on the new EVO
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Old 09-24-2010, 11:14 AM
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Thanks for the info Andrew.

70 mm diameter is still small. The problem is that the gearbox is integrated into the back of the spinner, and it needs almost a 70 mm opening in the front of the plane in order to have the necessary clearance for the soft mount.

If we opened up the hole in the nose as close to the 70 mm diameter as possible, it might work if the fuselage behind the nose widens enough to make room for the motor mount. Currently I need 68 mm minimum clearance for the gearbox portion of the drive. This leaves only 1 mm per side for fuselage wall thickness, but we probably wouldn't have to worry too much about weakening the fuse by opening it up this far, because we have to put a second carbon fiber reinforcing ring about 20 mm back of the nose to mount the drive to anyway.

Does anyone have details about how wide the new Spark fuselage gets behind the spinner? I need measurements of the narrowest width as a function of distance back from the nose.

Another thing I need is the maximum allowable length for a new Spark spinner. If I don't have enough length to fit two props in, then it's a no-go regardless.
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Old 09-24-2010, 11:23 AM
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

From Mr Krill himself.
The EVO I. have diam spinner 80 mm, I am trying to get the maximum length, rest will be very difficult in this moment, I will pick my 3 pcs EVO on Nov 1st
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Old 09-26-2010, 09:38 AM
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

When you get them can you post the required spinner dimensions for me? (Diameter X Length, etc ...)
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Old 09-26-2010, 10:15 AM
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Here are some pictures showing Dave Snow's new Wind S Pro. (Dave's in the pictures as well ...) Dave is trying out the Contra with his Wind S Pro. He is using the Neu f3a motor, and 25C 5000 mah f3aUnlimited Packs. He is drawing 80 plus amps with this motor, and pulling about 4000 mah out of his pack for the AMA Masters Sequence, (This is 21 maneuvers, excluding takeoff and landing ...) and Dave tells me that he is currently not using the brake in his ESC. He is relying on the braking effect from both props to slow the plane down on downlines.

Dave has about ten flights so far with this setup, and it sounds very quiet in the air. I saw if fly at Hoffman Estates in Chicago USA, and if there was another plane in the air, it was very hard to hear Dave's plane. Dave tells me that during the previous ten flights he has removed many of the mixes that he had put in to counter motor torque effects when he was running a single prop setup. He's also running with zero degrees of right thrust, and a small amount of downthrust. He's still optimizing the downthrust to get his vertical uplines absolutely perfect.

Dave and I actually flew together in Chicago. He had his Wind S Pro, and I had my Integral. It was real cool to see two Contra setups side by side on the flight line. (I should have taken a picture, but I was having too much fun flying ...)
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Old 10-11-2010, 08:17 AM
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

I saw (and heard) this WindS fly yesterday while at Shoe Factory Rd.....
The sound was quite distinctive! I was simply amazed at how slow and constant the plane's speed was...neat!
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Old 10-12-2010, 10:37 PM
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Hello Brian / Serious Power

Did I read correctly? Did you suggest that you've seen a belt-drive contra-rotator?
Details, please!

Best Regards,
Dean Pappas
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Old 10-12-2010, 11:03 PM
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Hi Dean,
Akiba had a reduction belt drive based on a Hacker C-50 at the Japanese Championships. Not a contra but it may have been confused for one. Follow the link for photos and details. http://www.rcuniverse.com/forum/m_9992444/tm.htm

Verne Koester


Quote:
ORIGINAL: Dean Pappas

Hello Brian / Serious Power

Did I read correctly? Did you suggest that you've seen a belt-drive contra-rotator?
Details, please!

Best Regards,
Dean Pappas

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Old 10-12-2010, 11:30 PM
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Maybe it was this. I believe on the Delro stand at the EC. It is half belt driven but is of course a fixed ratio drive to each prop with no differential gearing.

Brian
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Old 10-13-2010, 05:38 AM
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Hi Dean/Brian,
Yes thats the one and yes on the Delro stand.
I do not have any pics,, ,or more detail sorry.
Akiba was not in Austria.

Brian
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Old 10-13-2010, 10:18 PM
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Thank you, Gentlemen ...
What a shame: no torque sharing and gear maintenance.
Back to the drawing board.

Dean P.
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Old 10-14-2010, 05:30 PM
  #95
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

From what I can see in the pictures it looks like the belt and the exposed gears don't provide any gear reduction. They just take the output from the motor gearbox and split it into a counterclockwise, and a clockwise rotation for the front and rear props.

This means that the weight of the belt and exposed gears is in addition to the weight of a planetary gearbox, which is looks like it's located directly behind the exposed gears, and in front of the motor, so you are probably looking at a fairly significant increase in weight over a single prop setup, maybe up to 300g or so.

However, this might be a good solution for a glow engine like the DZ170. Maybe you could use it to get the DZ to spin a pair of 22X20 props, and make a DZ powered plane fly similar to an electric. I wonder if the guys from YS are looking at this.
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Old 11-21-2010, 11:58 PM
  #96
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Well, our version two Contra Drive design is finished, and Mike and Andy have all the drawings and specs. Attached are two profile views showing a Hacker C50 installation, and a Neu f3a Motor installation. I'm also showing a performance chart that shows predicted performance with various props, and gear sets.

For now the numbers are relative, because I haven't had the chance to corrolate the numbers with actual flight test data, but the relative differences should be a pretty good indicator of how performance changes with each setup. Our current thinking is that the speed is selected by choosing the appropriate prop, and then battery/power consumption is fine tuned for each setup by selecting the appropriate gear set.
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Old 11-22-2010, 09:18 AM
  #97
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Thes is a very interesting system.
When will it be available and where?
What is the cost??
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Old 11-22-2010, 05:38 PM
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes


Quote:
ORIGINAL: Brenner

Well, our version two Contra Drive design is finished, and Mike and Andy have all the drawings and specs. Attached are two profile views showing a Hacker C50 installation, and a Neu f3a Motor installation. I'm also showing a performance chart that shows predicted performance with various props, and gear sets.

For now the numbers are relative, because I haven't had the chance to corrolate the numbers with actual flight test data, but the relative differences should be a pretty good indicator of how performance changes with each setup. Our current thinking is that the speed is selected by choosing the appropriate prop, and then battery/power consumption is fine tuned for each setup by selecting the appropriate gear set.
Is it designed so the user can exchange gear sets or does one need another complete assembly to change gear ratios?

Jim
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Old 11-22-2010, 09:01 PM
  #99
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Answering Chester's question first:

Currently we are planning to make a small batch of version two units for the end of January. The distribution of these units have already been accounted for, but we hope to be able to follow this with a larger batch of units that will be available probably sometime in April. This date is tentative right now because it depends on what changes or modifications we need to do after the first batch. (However, our expectation is that no changes will be required ....)

Pricing is still not completely firm, but I think it will be in the following range:

Drive: $1,000
Sets of two Props: $200
Gear Sets: $200

Now to Jim's question:

Currently the design is setup so that gear sets are modular, and can be changed at the field without removing the motor from the plane. After you remove the props you can remove six bolts and take the spinner off, revealing the inside of the gearcase. The gear set can then be swapped out and the spinner and props can be bolted back on.

Our thinking here is that with a Contra Rotating System the trim of the plane isn't affected when you change props like it is when you change props with a single prop setup, so it's much more feasible to consider changing prop setups betweem rounds to take advantage of changing weather conditions, (Calm vs windy for instance ...) or maybe to have different setups for f3aP and f3aF, and even if a pilot doesn't want to do this, the option to swap out gear sets makes it easier to more closely match the power delivered to the prop versus the power drawn from the battery pack for a given setup and a given pattern schedule. (Advanced vs masters for instance ...)

Brenner ...
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Old 11-22-2010, 10:31 PM
  #100
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Sounds good. What's the time table on the second batch?

Jim
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