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Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Old 11-30-2014, 03:13 PM
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[QUOTE=cartercg;
The Peridot has never really liked to fly slow, but it's speed envelope with the contra is significantly wider. It is now able to fly slower while retaining control. Downwind rolls can be done with lower airspeed. Even at fairly low throttle settings there is sufficent flow over the tail to keep rolls axial and give good control.


Regards
Clint[/QUOTE]

Thanks for sharing this detailed report. I have often wondered how a plane can still fly smoothly at a slower speed? The wing loading hasn't changed. Does the cleaner airflow make the aircraft more efficient?
Old 11-30-2014, 10:24 PM
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I think that what happens is that the aerodynamic effects from single prop setups become more and more noticeable as the air speed of the plane is reduced.

This is due to several causes. Firstly, the spiral airflow from a single prop is much stronger at low airspeeds with high power loading, because the air passing through the prop disk is accelerating much more than it is when the plane is flying fast, and the motor is also supplying maximum torque into the prop, which then has to react out against the fuselage, and both of these things are changing as the speed of the plane changes, resulting in more workload for the pilot to keep the plane flying straight.

What a Contra Drive does is straighten out the spiral airflow and cancel out about 90% of the reaction torque that has to go into making the props turn, which makes the plane appear to be flying in a much more predictable way at slow speeds.

Brenner ...
Old 12-01-2014, 02:48 AM
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The rudder and elevator are both more sensitive with the contra drive. I guess that the straighter airflow over the tail improves the efficiency of the fuze and the stab, which means that even at low throttle settings these surfaces are very efficient, and that translates into more control at lower throttle settings. There is perhaps also less speed dependency with right thrust (no longer required), so the plane holds heading better when rolling at lower airspeed. That said, the Peridot still flies better at higher speed so I will still fly it relatively fast. The advantage is when having to do downwind rolls (like the four roll combo in the F15, or the two rolls on 45 in the P15), as ground speed is high but airpseed is low, and the contra makes it easier to do axial rolls with the lower airspeed.

I agree with the feedback from Brenner....the airframe has a natural speed range within which it which it flies best. The contra can just broaden the speed envelope. A plane that likes to fly fast should still be flown fast with a contra. But I've only got a couple flights with the contra, and these are my first impressions.

Cons of the contra is having to find 160g saving to cater for the additional weight (as compared to my Pletti with extra light carbon spinner and prop). Having to move the battery tray back 5cm to retain the same CG. Having to grind the front of my OXAI plane off :-(

I find my present setup does not have the speed/acceleration I want, but I expect that will be addressed via props with more pitch.

Efficiency is very similar to a single prop setup flown at the same speed and distance. I probably used around 3200mAh for a P15 flown at a moderate pace in calm conditions. If guys with contras are using lots of mAh it has more to do with their flying style and not the drive itself. I'm using Hyperion 4600mAh packs, and don't expect a problem with capacity.

Regards
Clint

Last edited by cartercg; 12-01-2014 at 03:06 AM.
Old 12-01-2014, 03:00 AM
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Some pics


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Old 12-13-2014, 09:42 AM
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For those interested we just started listing the Mejzlik Contra Props on our site:
http://www.f3aunlimited.com/contra/contra-propellers
We have 2 of the popular front 22x18 and 22x20 and 2 rears available 22x22 and 22x20.
Mejzlik does not produce the APC clones yet. The props are of the high quality you've come to expect from Mejzlik.
These props are in stock at F3AUnlimited's facility and ship right away. Very stiff and light.
Thanks, Mike Mueller

Last edited by mups53; 12-13-2014 at 09:44 AM.
Old 01-08-2015, 09:37 AM
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Cancelled wrong link attached

Last edited by mups53; 01-08-2015 at 09:40 AM.
Old 01-08-2015, 09:43 AM
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Default Neu New Contra motor 1512/2Y

We now have a second Neu motor option available. It's lighter and shorter.
It has been tested and is prefered by Dave Lockhart. Dave claims it can be a superior setup but requires a sophisticated setup using the tech-Aero throttle tech's.
Maybe he can chime is as he has extensive data that proves it's worth. I watched Dave flying with this setup and it's amazed me. He has extraordinary throttle control.
Here is the 2Y motor in stock:
http://www.f3aunlimited.com/neu-cont...he-contra-unit
Mike
Old 01-20-2015, 03:47 AM
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Hi Brenner,
Some new competition in the contra market - not exactly a surprise !!
http://www.ralphschweizer.com/startseite.htm
More a copy of/upgrade to the Seba approach, it would seem.
At 1290.00 ($1500.00), not including props, it is a little more expensive and without gearing or motor options.
I've posted here as it is now in the public domain anyway.

Brian
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Old 01-20-2015, 07:54 PM
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Mike,

Thanks for the kind words. My prior post (1343) has most of the details of my setup, but if anyone has any questions, I'll do my best to answer. ~ 2 more months of winter, and then I can switch from my Glavak Contra (70 gram indoor plane for F3P) back to the Brenner Contra
Old 01-20-2015, 08:45 PM
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Originally Posted by DaveL322
Mike,

Thanks for the kind words. My prior post (1343) has most of the details of my setup, but if anyone has any questions, I'll do my best to answer. ~ 2 more months of winter, and then I can switch from my Glavak Contra (70 gram indoor plane for F3P) back to the Brenner Contra
And an Allure?
Old 01-20-2015, 08:49 PM
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Originally Posted by Jason Arnold
And an Allure?
It is a plan!!!!
Old 01-21-2015, 08:37 AM
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Originally Posted by DaveL322
Mike,

Thanks for the kind words. My prior post (1343) has most of the details of my setup, but if anyone has any questions, I'll do my best to answer. ~ 2 more months of winter, and then I can switch from my Glavak Contra (70 gram indoor plane for F3P) back to the Brenner Contra
Hi Dave,

I am planning to use a Contra Drive on my next plane and I have a basic questions:

Is the side trust should always be zero with a Contra Drive?

If a plane has a certain amount of down trust with a single prop and fly perfectly, does with a Contra Drive it should has a different down trust or it can stay with the same down trust?

Best regards,
Isaac Najary
Old 01-21-2015, 10:33 AM
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Isaac,

From my experience with the Contra, I would not change downthrust.

Side thrust should be zero. ....or very close to it. While the torque is balanced, that does not necessarily mean the airflow off the props will be perfectly straight. On the Contrast, the spiral flow is actually hitting the right side of the fin / rudder, but it is so minimal that the tiniest amount of left thrust in the plane is not visible.
Old 01-29-2015, 02:15 PM
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Anyone using a Hacker C-50 14XL with OS ESC on their contra? I'm having an issue with it dropping about 20A at full throttle at the start of the flight. Just wondering what I screwed up.
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Old 01-29-2015, 02:35 PM
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Originally Posted by JAS
Anyone using a Hacker C-50 14XL with OS ESC on their contra? I'm having an issue with it dropping about 20A at full throttle at the start of the flight. Just wondering what I screwed up.
JAS....whaaaat is that?!
Old 01-29-2015, 02:46 PM
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Originally Posted by can773
JAS....whaaaat is that?!
It's a Mystery

Last edited by JAS; 02-12-2015 at 01:49 PM.
Old 01-29-2015, 02:54 PM
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Oh, for a second there I thought you had 4 prop blades!
Old 02-04-2015, 08:43 AM
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Hi Jason,

Not sure why that is happening. Is it a new motor? I was running the OS ESC on a standard Hacker C-50 14lx drive with no issues. I have since gone Contra with the Neu motor and OS ESC with no issues so far. What is your timing and khz set to? How do you find the contra so far?
Old 02-12-2015, 01:27 PM
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Hi Brenner,
My new model,designed for contra rotating drive.Today make first test fly,model under construction.


















https://www.youtube.com/watch?v=L3T3ZXYERC8

Last edited by andreyengin; 02-12-2015 at 01:29 PM.
Old 02-12-2015, 01:59 PM
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Originally Posted by blake26m
Hi Jason,

Not sure why that is happening. Is it a new motor? I was running the OS ESC on a standard Hacker C-50 14lx drive with no issues. I have since gone Contra with the Neu motor and OS ESC with no issues so far. What is your timing and khz set to? How do you find the contra so far?
The motor is from the 2006/7 season. It was in one of my '07 Worlds planes for sure though. I've got it set per how I set it normally with the 6.7 gearbox on. And after trying my old Comp-99 (same year as Comp Hacker) and talking with Brenner and a few others, we believe that my contra has an older style clutch. I just received my updated clutch and will install it in a few more flights (almost have 50 flights on it). I've read where re-greasing after 50 flights has gone up to more, but for the first 50, it's a good excuse to clean it, install the new clutch and just make sure all is going well with it.
So far I like it. I still have to fly more unknowns to make sure I can hammer it if need be and not run out of battery.
Old 02-13-2015, 05:02 AM
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Hey Andrey,

Your plane looks very nice. There are lots of bipes that use Contra Drives, and they all fly well.

I think it's because the canopy on a bipe is usually placed behind the wing, which has the effect of increasing the effective rudder fin area.

Brenner ...
Old 02-14-2015, 06:07 AM
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Hi Brenner,thanks,
Yesterday i made 5 test flight, weight of model with battery (4500ma -1060gr) 4610gr. I am installed gear ratio 10,33 and props 22x18 front,22x20 rear with NEU F3A motor.The rudder deviation with contra really small,.Plane flight very straight without any mixer, can fly very slow.The next steps adjustment rudder shape and flight condition.A few photos and video( quality video is poor)












https://www.youtube.com/watch?v=jKfywdpD4Vk


https://www.youtube.com/watch?v=HQkq9WW7dtA


https://www.youtube.com/watch?v=Fl4b3JmU1ns

Last edited by andreyengin; 02-14-2015 at 06:45 AM.
Old 02-14-2015, 03:45 PM
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Hey Andrey,

Congratulations! It looks like a very successful project.

Brenner ...
Old 02-15-2015, 10:09 AM
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We are starting to get our V4 prototypes ready for flight tests.

This is a picture of one of the first prototypes on our scale. This weight is without carbon fiber plates, or rubber mounts, so the final all-up weight will probably be something close to 700 grams.

Brenner ...

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Old 02-15-2015, 10:19 AM
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Will that unit fit in place of the V3 ?

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