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Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Old 09-03-2014, 02:45 AM
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Hey Guys,

Just in case you didn't know, the Contra Drive Allure has been flown. A link to Bryan's first impression video is over on the Allure thread here http://www.rcuniverse.com/forum/elec...-hebert-6.html

Cheers,
Jason.
Old 09-07-2014, 07:30 PM
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Over the past year, I have had the opportunity to fly a couple of Contra powered airplanes, and now I have the privilege of flying one in a BJ Craft Nuance. In my 40 + years of R/C flying, I would rate the modern computer radio and the Contra drive as the two largest leaps forward in model technology. The advantages of a symmetrical thrust line in a pattern airplane are a dream come true. No more fighting the offset thrust line. I have heard some of the supposed disadvantages of the Contra, most specifically the increase in battery draw. However, after learning the correct throttle management of the Contra system, my battery draw is matching what I expect to see from my Vanquish with the standard drive. The Contra drive coupled with the Nuance airframe is an awesome combination. I am looking forward to many, many more hours flying this remarkable system. Thank you Brenner, you are a real genius.

Robert
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Old 09-08-2014, 03:55 AM
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Are the prop pitches the same or different for the forward and aft prop. I would think that the aft prop would require more pitch to move the larger volume of air that the forward prop delivers???
Old 09-08-2014, 07:51 PM
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Originally Posted by N1EDM
Are the prop pitches the same or different for the forward and aft prop. I would think that the aft prop would require more pitch to move the larger volume of air that the forward prop delivers???
Front prop= 22 x 20
Rear prop= 22 x 22

You may be right.

Robert
Old 09-10-2014, 02:08 AM
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Hi,
Jason Arnold asked about contra prop tips recently someplace (on another thread maybe).
On the tips below I removed 3.5mm (rear) and 4mm (front) of chord at the tip TE tapering to 0 over 100mm and 120mm respectively.
This produces a TE that is getting thicker over the said span (100 or 120).
I then thinned this back down which effectively increases the washout. Removing the 100mm etc to 0 triangle also increases the washout.
I also re profiled the back side again increasing the washout.
All of this was done progressively over the 100mm etc span used.
Then I polished out the sanding marks.

I need to fly side by side with another contra with the same props in the original condition to hear the actual difference but it certainly seems a lot quieter. Hopefully this weekend.

Brian
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Old 10-07-2014, 02:32 PM
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Have a quick question regarding SFG's. Would it be more effective if they were placed towards the end of the stabilizer instead of being placed mid-span as most examples shown?
Old 10-07-2014, 09:35 PM
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Originally Posted by PeterP
Have a quick question regarding SFG's. Would it be more effective if they were placed towards the end of the stabilizer instead of being placed mid-span as most examples shown?
It would seem like the area is more important than the position.

Jim O
Old 10-20-2014, 06:47 AM
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Hi,

After a long break from pattern I have finally completed my model and currently have 18 flights on my Contra DeJaVu. I am impressed with the overall flight performance of the model and especially with the power train. The Hyde mount keeps the whole setup whisper quiet.

Thanks Malcolm for the ESC setup information. Thanks Tony F for your Contra setup details with 20x22 front 22x22 rear and 10.33 gear ratio - standard prop tips. I have flown pattern for a long time and I cant ever recall any new developments impressing me more than the Contra-drive. Well done Brenner and team.
Old 10-26-2014, 11:35 AM
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Congrats to Brenner and team for what is obviously a great contra drive. I'm looking at getting a Brenner contra with the Neu motor. I fly medium/fast speed (and fairly fast in windy conditions), and want a combination that has sufficent speed and power for windy conditions, but still has the ability to flying reasonably slowely in calm conditions. Which gear set and prop combo is recommended? I'd appreciate advice given the considerable development in the drive, props, and flying testing.

PS I hope to see several of you in Switzerland next year.

regards
Clint
Old 10-26-2014, 02:48 PM
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Hey Clint,

The 9.89:1 gearset seems to be a pretty good match for the Neu f3a motor. I think the most effective way to manage speed is with prop selection. However, one thing to consider is that the same props will behave differently with different airframes, so getting a setup really dialed in usually requires a little experimentation.

That said, the 20" front and rear props have the best speed range, and are generally recommended when the wind picks up. These props are also the quietest, and they are my personal choice for all wind conditions, but I fly in North America where the prevailing style is to fly a faster pattern than in Europe.

A good choice for calm conditions is a 22x20 rear prop matched with a 22x18 front prop. This combination will give you a good compromise between speed and stump pulling vertical performance.

A setup that will be something of a compromise between these two extremes is a 22x22 rear prop with a 22x20 front prop, and if you're looking for the slowest, most constant speed setup, you can run a 22x28 rear prop with a 22x18 front prop. Most people find this setup to be too slow.

One thing that you will notice is that the ESC braking changes noticeably between these setup. It is possible to use ESC braking on all of these setups, but you will need a lot less with the slower setups.

Also, you generally want to mismatch the pitches between the front prop and the rear prop, because this causes the rpm of each prop to also be slightly mismatched, which avoids the syncopating rhythm sound that you get when the props are rotating at the same rpm.

Brenner ...
Old 10-26-2014, 05:21 PM
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Hi Brenner,

I assume when you refer to the 20" props you are actually referring the the APC style of propellers.

Old 10-26-2014, 05:45 PM
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Hey Peter,

Yes, the carbon fiber 20x22.5 rear, with the carbon fiber 20.5x20.5 front.

Brenner ...
Old 10-26-2014, 10:22 PM
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Thanks Brenner,

it it then seems that a good compromise with the Nue motor is the 9.89:1 gear ratio with 22*22 front and 22*20 rear propos? If that is a bit fast would a slightly higher gear ratio also then be something to consider?

Any comments from other pilots that have been running these props with the Nue motor?

regards
Clint
Old 10-26-2014, 10:38 PM
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Hey Clint,

Yes, you can mix and match props with different gearsets.

Brenner ...
Old 10-27-2014, 01:32 AM
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In Ireland we have 4 pilots using the Brenner contra and we all use the 10.15:1 gear ratio with the 22x20 rear and 22x18 front props. We do like the slower flying style in general and this set up seems to suit most weather conditions here. We seldom get extremes of heat during summer. Occasionally if it is very windy I would put on the 22x20 front for more pull.
I also like the APC style carbon props as a very good alternative. They suit my Episode quite well for any weather above a small breeze.
Old 10-27-2014, 11:28 AM
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Originally Posted by cartercg
Thanks Brenner,

it it then seems that a good compromise with the Nue motor is the 9.89:1 gear ratio with 22*22 front and 22*20 rear propos? If that is a bit fast would a slightly higher gear ratio also then be something to consider?

Any comments from other pilots that have been running these props with the Nue motor?

regards
Clint
I wouldn't call that a good compromise. It is really an extreme. You have the longer props with higher pitch (a large load) and a lower gear ratio which is what we'd call high gear in a car. No doubt they would work great on the right motor but it will take a lot of power to drive them, more than you want to pull from your batteries. And they would be harder to accelerate.

For slow flying with good acceleration you want longer props with lower pitch. For speed you want shorter props with more pitch. I fly the carbon fiber 20x22.5 rear, with the carbon fiber 20.5x20.5 front most of the time with the 9.89 gear ratio but that gear set will also work fine with the 22x20 rear and the 22x18 front. In another thread on this subject, I believe Tony F said the 22x22 and 22x20 on the 9.89 required a lot of throttle management to keep the power consumption down. Hope this helps.

Jim O
Old 10-27-2014, 12:34 PM
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Thanks Jim O. You feedback makes a lot of sense. It then seems that I need to decide on 22*22.5 rear with 20.5*20.5 front, or a 22*20 rear and 22*18 front, both with the 9.89 gear set. I'd appreciate further opinions from those that have flown both. Alternatively the 22*22 rear and 22*20 front with a higher gear ratio. I expect that the likes of Tony F have played a lot and can cut to the chase....seems that there are a number of good options that all work well :-)

regards
Clint
Old 10-27-2014, 05:25 PM
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One thing to remember is that the airframe has a big effect on the best setup.

I have had quite a few planes with Contra Drives, and some work best with some setups, and others work best with other setups.

My wind S Pro worked well with the 9.89 gearset, and the 20" props, but I had an Integral that was quite sluggish with this setup. The Wind S Pro had excellent speed range, and average draw from my packs, whereas the Integral was like driving a car in too high a gear, and the draw from my packs was about 300mah more than the wind S Pro.

I ended up running a 10.15 gear set and a 22x2 rear prop and a 22x20 front prop on my Integral. This made it feel more like the Wind S Pro, and it reduced the draw from my packs, but I still didn't have the excellent speed range that I had with the Wind S Pro.

Speed Range is good because it lets you fly slow when the wind is calm, and fast when the wind picks up. However, this does require more throttle control, so everything is a tradeoff.

Based on our experience with different airframes Mike Gaishin is building three planes this winter that have the following characteristics.

1/.. Skinny Proteus wings from Dave Snow
2/.. Fuselage width just wide enough to fit a V4 Contra in the nose. (coming soon...)
3/.. 25% more rudder fin area
4/.. Fuselage as deep as an Episode Fuse.
5/.. Canalizer

The extra rudder fin area will provide yaw stability with the deeper fuse, and the deeper fuse will improve rolling and knife edge performance.

The skinny wings and the narrow fuse will reduce drag for maximum speed range, which will let me push the plane out and fly fast when the cross wind picks up at Muncie.

Brenner ...
Old 10-27-2014, 05:31 PM
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Now we need the details on the V4 Brenner!
Old 10-27-2014, 05:54 PM
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Prototypes are being built right now. The plan is to fly the first one in a couple of weeks, and then test it properly over next summer.

It will be quite a bit more compact than the V3, and considerably lighter.

Brenner ...
Old 10-27-2014, 06:06 PM
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Originally Posted by Brenner
Prototypes are being built right now. The plan is to fly the first one in a couple of weeks, and then test it properly over next summer.

It will be quite a bit more compact than the V3, and considerably lighter.

Brenner ...
Hey Brenner,

Will the V4 be backward compatible with regards to mounting?

Cheers,
Jason.
Old 10-28-2014, 02:21 AM
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Hey Jason,

Not at this time. We may be able to get there, but I don't have time to look at it until after we fly the first one.

Brenner ...
Old 11-17-2014, 11:49 AM
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Hi Brenner,

I got my contra today, and it is a great piece of quality engineering. I am however a bit perplexed as to how the gear case attaches to the motor adaptor using the m2.5 screws. Included is a pic of my gearcase. I can only conclude that the four 2.5mm holes for the bolts were not drilled (I can see the small marks where I would expect them to have been drilled)...or am I missing something, in which case apologies for my ignorance.



Regards
Clint
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Old 11-17-2014, 11:54 AM
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Hi Clint,

looks like you you have four holes there for screwing to the motor. Did you take a look at the manual?

Cheers,
Jason.
Old 11-17-2014, 12:18 PM
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Hi Jason,

Yip did look at the manual. The four holes are each about 4mm and way too big for the m2.5 bolts. Looking at the manual it appears that there should also be four smaller holes.

Cheers
Clint

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