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Contra Rotating Propeller Drive for f3a 2m Pattern Planes

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Old 04-01-2012, 12:10 AM
  #701
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Hi Brenner,
Thanks for the suggestion.
I do not exactly know how it should look like, but think it looks OK.

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Old 04-01-2012, 06:15 AM
  #702
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Hans,

I am planing to use contra in the Gaudious. The Gadious comes with positive (up) motor thurst. It is more common to see a little negative (down) thurst. Just would like to know how you set up yours?

Thanks,

Vicente "Vince" Bortone
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Old 04-01-2012, 08:39 AM
  #703
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Hi Vince,
Have flown the Gaudius now for two years. This first thing two years agoI thought that this uphrust could not be right so I eliminated it. Could not fly straight up any more.
With any apply of power it strongly pulled to the belly. So back to what the designer has intended it to be. And he was right (offcourse) So yes it needs the upthrust.
Has to be something with the thrustline be way above wing and stab.
In general I think that the thrust down is wrong in F3A models.
Thrust down compensated by to much angle between wing and stab, compensated by a downline mixer to avoid veer to canopy in downlines is a wrong solution.
The Gaudius needs this upthrust. For the Contradrive exactly the same amount. No sidethrust however.
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Old 04-01-2012, 10:13 AM
  #704
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Hey Brenner, Hans,

I probably had the same problem with my 13 XL. Rotor was cracked and I thought that some dust had gone inside the motor and damaged it.
After sending 13 XL to Hacker they told me that the motor had overheated.
They suggested to take a 14 XL with electric part only(without gearcase).
I opened the belly a bit more and did 2 openings on the top of the fuselage.
After about 65 flights, ( setup : 2X22X20 9,89 ratio) with outside temperature 22 °C, Max motor temperature was 53 °C (127 F) and very often about 40 °C . Now flights are awesome.
I hope it will be cool enough. Before, the 13 XL motor was way hotter and was very long to cool.


Good flights
Vincent ...

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Old 04-01-2012, 10:47 AM
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Hey Vincent,

Wow, with that setup you must be getting huge power. I'm running a 13XL with the 10.33:1 gearset, and it's been on the edge as far heat rise is concerned. I'm definitely going to cut more cooling holes.

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Old 04-01-2012, 04:46 PM
  #706
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes


Quote:
ORIGINAL: Hans Meij

Hi Vince,
Have flown the Gaudius now for two years. This first thing two years agoI thought that this uphrust could not be right so I eliminated it. Could not fly straight up any more.
With any apply of power it strongly pulled to the belly. So back to what the designer has intended it to be. And he was right (offcourse) So yes it needs the upthrust.
Has to be something with the thrustline be way above wing and stab.
In general I think that the thrust down is wrong in F3A models.
Thrust down compensated by to much angle between wing and stab, compensated by a downline mixer to avoid veer to canopy in downlines is a wrong solution.
The Gaudius needs this upthrust. For the Contradrive exactly the same amount. No sidethrust however.
Good news. I've been measuring and measuring and wondering if I screwed up when I took the right thrust out of my Gaudius and accidentally created upthrust because it is definitely there. Glad to hear that it is supposed to be that way and more importantly flies right that way.

Thanks for making me feel better, Jim O
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Old 04-01-2012, 04:50 PM
  #707
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Just curiosity. Where you got the CG? That will help me a lot.

Thanks,

Vicente "Vince" Bortone
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Old 04-01-2012, 09:05 PM
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Just before the wingtube. Here the Gaudius thread with lots of info:
http://www.rcuniverse.com/forum/m_92..._5/key_/tm.htm
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Old 04-04-2012, 10:22 AM
  #709
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

I received a shipment of Contra front and rear props from APC yesterday, and the first thing I did was go out and fly them.

They seem to fly well. I flew them back to back with a mixed set of 22x22 rear and 22x20 front props, and the performance seemed very similar. The noise profile was also very similar. Both sets were pretty quiet in the air. Currently I'm flying with a set of tired 25C packs from last year, a 13XL motor, (with new bearings and rotor..) and a 10.33:1 gearset, and with this setup the performance we more than acceptable.

I have fresh packs on order, so I won't try different gearsets until I get them, but based on what I see now, I think there's quite a bit of headroom in the system. I didn't measure motor current, but I only took 3400 mah out of my packs for an AMA Masters flight with negligible throttle management.

I'm expecting to see a significant performance boost with new packs, another boost with a 10.15:1 gearset, and even more performance with a 9.89:1 gearset, so my final setup will reflect an appropriate tradeoff between performance, throttle management, and mah draw from my packs.

Brenner ...
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Old 04-04-2012, 10:48 AM
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Hi Brenner, very nice. Looking foreward to give them a try.
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Old 04-04-2012, 09:45 PM
  #711
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Great day flying today in Arvin. The day started overcast, windy, and cold but ended up warm and sunny with light winds. The highlight was the sound of the new APC props on Leon's Contra with the Neu motor. It is the best sounding pattern plane I have ever heard. It has been awhile since I heard the stock props and it will be interesting to hear the difference side by side but this sounded like a real airplane. There must be something in the lower rpm but I also thought I could hear a sound like a twin. I suspect the props were not turning at exactly the same rpm but man it sounded good. I would hope that someone can measure the rpm with a strobe and we can find out what they are turning but it will be hard to improve on what I heard today.

We ended the day sitting in the sun, telling war stories from the old days and were amazed at how Chip could remember all the dates and places. Then again he is so young he doesn't have near as much to remember as the rest of us.

Jim O
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Old 04-05-2012, 12:02 AM
  #712
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

But Brenner,

The APCs don't look nearly as sexy as your carbon props!

Malcolm
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Old 04-05-2012, 02:57 AM
  #713
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

What he said
Cheers
Greg
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Old 04-05-2012, 05:37 AM
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Brenner what's the weight difference between the APC's and Mike's CF props? Isn't weight in the nose with the Contra an issue for balancing? Thanks, Mike
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Old 04-05-2012, 07:13 AM
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Hey Mike,

Mikes Props are 50g +/- 5g. The APC props are 90g, so you have about an 80g difference considering both props.

This does shift the CG, so anyone wanting to use APC props will have to be able to shift their packs around to compensate. In my own case, I just wanted to get a quick impression, so I didn't worry about changes in the CG, and in my experience, Contra powered planes seem to be quite tolerant to a foward biased CG. Anyway, the plane still few great.

What I'll probably be doing is moving my battery tray rearward so that I can play around with CG, because now I have new Dave Snow Spark wings as well, so the proper CG needs to be re-determined.

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Old 04-05-2012, 09:28 AM
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Hey Brenner,

You didn't say what sizes you got from APC. Where do we go for more info?

Jim O
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Old 04-05-2012, 10:44 AM
  #717
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Brenner,

The APC site lists a 20.5x 20.5 @ 4.34 oz and a 20x22.5 counter rotating @ 4.09 oz. If these are the props you are referring to, the weights do not agree. Gary
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Old 04-05-2012, 04:37 PM
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Hey Gary,

The actual weights, as measured on my scale, are:

Front Prop: 89g
Rear Prop: 97g

I'm only guessing here, but maybe someone at APC weighed them while still in the packaging. I weighed my props in the packaging, and the numbers are close to what you are reporting.

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Old 04-06-2012, 05:40 AM
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Brenner,

I spoke with APC this morning and they re-weighed the props. The website numbers currently displayed are incorrect. Should be 3.1 oz and 3.35 oz.

Gary
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Old 04-06-2012, 08:54 PM
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Here is a brief explanation as to why we might be hearing a sound difference.


The primary source of propeller noise comes from supersonic tip speeds. Swept or elliptical tips help reduce prop noise. Keeping the prop tips subsonic is highly recommended both for efficiency and noise.
A secondary source of propeller noise is propeller blade resonance. The natural frequency of the blade (or resonant rpm) depends on the density, stiffness and damping of the propeller material. Hand made carbon blades are typically lighter, stiffer and have less damping than glass/nylon props. These factors contribute to a higher resonant frequency in carbon props that is very lightly damped. As a result, carbon props tend to be louder than glass/nylon props. Much like a ceramic tuning fork vs. one made from lead.

Hope this better explains it.

Chip

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Old 04-07-2012, 01:30 AM
  #721
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Hey Brenner, Dave,

New wings and anhedral stab on the Integral ?
Is anhedral stab to make knife flight easier ?
Could you please tell me why this new aerodynamic setup.

Vincent ....




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Old 04-07-2012, 06:11 AM
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Hey Vincent,

The primary reason for new wings and stab is to reduce weight. Both the wings and the stab are built up, so there is about a 150g savings in weight.

As far as performance goes, the thinking behind the anhedral stab is that it will marginally increase the effective rudder side area when the plan yaws, hopefully acting as a sort of yaw damper. I'm still evaluating this, so I'm not making any claims yet.

The wings are Spark wings. The intention here is keep the airflow attached out the near the wing tips at high angles of attack, making snap rolls easier, and making spin entries much more controllable. The wing does both of these things, so I can definitely make claims in this regard.

Also, the wing chord thickness tapers out towards the wing tips more aggressively than the stock Integral wings, which reduces drag and increases the speed range.

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Old 04-07-2012, 12:29 PM
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Hey Brenner,

Thank you very much for your explanations. It's really interesting. Do you think it is possible to do a spark wing and a stab for my Integral ?

Vincent ...

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Old 04-07-2012, 01:33 PM
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Hi Vincent, fitting the parts to the Integral is no problem, shipping is. I built the wing and stab panels Brenner is flying and basically hand delivered the parts to him so no shipping was involved, but to France built components would be very costly. I do have kits for the wings and stabs that I’ve sent internationally without too many problems. Here is a build thread showing how they go together, http://www.rcuniverse.com/forum/m_10841584/tm.htm . The wing you will save the most weight, typical weight ready to fly 14 oz but with very good wood – 3/32” wing sheeting 14 to 15 grams each – we have built several Spark Evo wings at 12 oz.

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Old 04-09-2012, 09:58 AM
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Hi Dave,

I saw your built thread. It's really awesome!
I think it will be too difficult for me to build it though, because it looks like it takes some skills and tricks to build the elliptic wing and stab from scratch.
Do you have any idea of what it would cost to ship the whole set to France ?
Thanks a lot

Vincent ...
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