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Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Old 04-26-2011, 04:48 PM
  #251  
mithrandir
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

well... I ain't never gonna be a contender right?.... and if my plane weighs 11 pounds, or 11.5 pounds.. prolly I couldn't really appreciate the difference...
so... wouldn't it be pretty easy to make a Counter-rotater from two Co-Axial Outrunners turning opposite directions? Seems to me I saw someone do this a while back.... Outrunners are getting more efficient right???

Seems a lot easier then a Gear box... at least from a cost standpoint....


hmmmm???
Old 05-04-2011, 06:21 PM
  #252  
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

I've finally been able to start flying. It's still bitterly cold here in Southwest Michigan, (45 deg F / 7 deg C) but it's stopped raining and snowing, and the wind is starting to settle down as well. I'm running Tony Frackowiack's setup except that I'm running with a Hacker C50-14XL, and Thunder Power G6 65C 5000 mah packs. I'm pulling about 85 amps static, which is 15 amps above predicted. These packs are very nice. The cell resistances are from 1.1 mohms, to 1.4 mohms, and I'm charging at 25 amps. I get a full charge in about twelve minutes.

It's still very early yet, but right now things are going great. I'm running 22x20 props front and rear with a 9.89:1 gearset, and the plane is much faster than last year. It handles the wind much better. The plane is also noticeably quieter than last year as well. I know this because Mike is running the same Drive that I ran with all last year, and it has a noticeable bark that my Drive doesn't have. My plane still makes noise, but the frequency of the sound seems lower, so the "sound quality" is much improved. Right now I can't imagine anyone having even the slightest complaint about the noise. In fact, I think the single prop Neu setups are louder because of the Neu gearbox.

I'm pulling about 4000 mah out of my packs for the 2011 AMA Masters pattern, which is perfect. I wouldn't want to pull any more because of concerns about the life of the batteries, and I wouldn't want to pull any less, because I don't want to leave any performance on the table.

The next thing for me to try is running with the 22x18 on the front, and the 22x20 on the rear.

Brenner ...
Old 05-05-2011, 05:21 AM
  #253  
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Brenner in my opinion you'd be better to get the consumtion down to about 3600 for the Masters pattern. It's shorter this year.
This time of the year in our conditions I'd expect a tad less than what you'll need come warm weather and competition time. I know I don't have the Contra but my Axi F3A with a boatload of power is pulling about 3400 mils on a wide open fast flight at about 80 amps. Power in equals power out according to the great Jim Oddino. I thinkhe's right.
So what I'm asking is, do you need to be on the hairy edge of performance? I've found that strict adherence to the rule that uses less than 75% of the packs capacity makes for a happier and longer life on the lipos.
I've just started getting out myself. Dave has a head start on us and while I've yet to see him fly all reports are glowing. This season is going to be a blast and I look forward to watching your developement. Mike
Old 05-05-2011, 06:45 AM
  #254  
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Hey Mike,

One of the benefits of the Contra Drive is that is has replaceable gearsets, so it's very easy for me to swap the 9.89:1 gearset for a 10.15:1 gearset and bring the mah down to about 3600 mah. I'm going to watch the power consumption as the weather warms up, and swap the gearsets if it becomes needed. Also I haven't tried mixing a 22x18 front and a 22x20 rear prop combination yet. Dave says that this combination is saving him 300 mah or so, with no loss of performance.

Brenner ...
Old 05-08-2011, 05:32 PM
  #255  
Jeff-RCU
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

We were at our place up north this weekend and I stopped by the Watervliet International Airport and met Brenner and got to watch his plane fly and another fellow who's name I didn't catch fly. The planes make an interesting noise, not like a twin, but it was not objectionable either. You certainly knew that it was different. The thing you really notice is the constant speed, especially in the verticals. Power was beyond adequate (at least from a bystanders viewpoint).
Old 05-12-2011, 09:37 PM
  #256  
TonyF
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Here are the latest additions I made to the Onas with the Contra Drive installed. They are an added dorsal and some triangular pieces on the TE of the rudder. The net affect is increased yaw stability that the pair of props up front reduce. And a much softer rudder response. The Contra Drive removes the spiral slipstream affect and greatly increases the fuselage lift. Probably somewhat similar to the canalizer. I had reduced my normal mode rudder throw and increased the expo, but I was getting into expo values of 85 to 90% and I just didn't like that feel. The triangles allowed me to increase the throw and reduce the expo. They did change how the model stall turns and it took some changes in settings to get happy with them again. The positive affect was that it just about eliminated any yaw wobble after the stall turn.

BTW, the dorsal is 3/32" balsa cobered in Carbon Ultracote and the triangles are 1/2" x 1/8" balsa covered with the same Ultracote. They are then both taped on.

It sure would be fun to design a new model from the ground up for the Contra Drive!

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Old 05-13-2011, 06:07 AM
  #257  
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Tony, I'm having some difficulty trying to understand the need for additional modifications to your Onas as a result of your change to the Contra Drive unit. I was led to believe the Contra Drive would all but eliminate the inherent problems associated with spiral slip stream we all have to contend with on all standard inrunner and outrunner motor installations. Is part of the problem based on the current design (built-in right hand thrust) of most, if not all, 2m pattern planes that are available today? If this is the case than I have second thoughts about making the change. I hesitate because it seems somewhat counter productive if many more changes to my planes are needed as a result of changing out the gearbox on my Neu F3A motors. Perhaps it would be best to have a 2m plane designed to accomodate the Contra Drive unit. I would appreciate your response and encourage Brenner to give his thoughts as it relates to my concerns. Thanks in advance and wish you continued success this year__Everette
Old 05-13-2011, 09:09 AM
  #258  
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Tony,

I would be curious if you added a horizontal fin to the rudder similiar to Heberts Valiant design how it would affect your rudder authorty and change rudder authority.

Chuck
Old 05-13-2011, 09:33 AM
  #259  
Doug Cronkhite
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

When I talked to Tony a couple months ago he mentioned he felt the Onas needed a bit more vertical fin area, so I'm guessing this might be more of a 'while I'm making changes' sort of thing rather than purely as a result of the contra-drive. By increasing the vertical fin area, he's increased the static yaw stability, requiring more rudder surface deflection for a given response.

Removing spiral slipstream and the resulting required right thrust could theoretically also 'unload' the fuselage making it feel a bit more 'loose' in yaw around neutral. I'm probably not explaining very well what I'm trying to say. The spiral slipstream applies a force moving the tail right. The right thrust counters this force, and the two forces working against each other creates almost an aerodynamic inertial effect making the airplane more resistant to yaw changes around neutral.

Sorry if I'm rambling...
Old 05-13-2011, 11:56 AM
  #260  
Brenner
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

What Doug is saying definitely rings true. A consistent effect of using a Contra drive is increased rudder sensitivity. This is something that I believe I mentioned way back at the start of this thread. What I found was that I was increasing my rudder exponential up to 85% plus in order to soften the rudder around neutral. Also, when I released the rudder, I had to release it slowly or the tail of the plane would swing past center before settling back in line.

What we have found is that increasing the width of the rudder trailing edge dampens these effects, and pulls the tail of the plane back into line. It's kinda like putting a tail on a kite. What I did with my Integral is put two 1/2" triangular strips on the trailing edge of the rudder. This resulted in a softening of rudder sensitivity, and a "dampening" of any yaw oscillation when I released the rudder. This made the rudder much more precise around neutral. Now I can input very subtle rudder inputs, which are very difficult to see from the ground because there's no oscillation. When I fly I'm constantly working the rudder, but the plane still looks like it's tracking straight as an arrow.

The end result is a plane that is an absolute dream to fly because its trim doesn't change with airspeed. It carves like a knife, and tracks like an arrow across the top of Humpty Bumps, and at the end of long verticals. One very beneficial effect is the way it tracks on a vertical line. It can put vertical point rolls on a string, and then continue on a perfectly straight track after the rolls. Also, these same effects make it much easier to do perfect stall turns, because the wings don't twist out of plane as the plane pivots.
Old 05-13-2011, 12:34 PM
  #261  
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Brenner, I appreciate both you and Doug's explanation and have a better understanding of the changes Tony F had made to his Onas. So, you both can appreciate my concerns as it relates to
the right thrust built into most of the current 2m designs. I can see the benefits of the Contra Drive once I understood how it effects the flight characteristics of a given pattern plane and the additional changes one might have to make to the current designs ie, grinding/modifying the nose to remove the built-in right thrust, replacing the firewall, increasing the vertical fin area and increasing the width of trailing edge of the rudder, etc. All of which I feel I am capable of doing now that I understand. Again, I thank you both and look forward to flying with you later this year. Everette
Old 05-13-2011, 02:17 PM
  #262  
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Keep in mind... Tony had told me he felt the Onas could use a bit more vertical fin area BEFORE he went to the contra-drive setup. It's likely the contra-drive only made the issue big enough that Tony decided he needed to fix it.
Old 05-14-2011, 01:22 PM
  #263  
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes


ORIGINAL: TonyF

.....The Contra Drive removes the spiral slipstream affect and greatly increases the fuselage lift.

Recently I was breaking in a new set of batteries by running 5 minute, less than half throttle runs in the Integral on my side patio. I tied my fuse to the gas pipe with a rope over the fuse just forward of the vertical stab and under the horizontal stab back to the pipe. I did not have the wings attached and I left the canopy off to read the ammeter.

I was surprised at the back and forth movement of the fuse in yaw at about a half Hertz rate even at this low throttle setting. I assume this was due to the spiral slip stream but I'm sure the surrounding objects contributed. It sure would be impressive to see if this would be eliminated with the contra drive. Maybe I could push and pull some decent corners if it would.

Jim O
Old 05-15-2011, 09:27 AM
  #264  
Brenner
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Hey Jim,

Pulling tight corners is something that is a lot easier with a Contra Drive. In fact, there are two tight corners in the current masters pattern where I am finding the Contra to be very helpful. There is the half triangle with four point roll, and the 45 degree upline with 2 of 4 followed by a 180 degree loop and a 45 degree downline with a half roll. In both maneuvers the Contra tracks through the corners like it's on rails, and it doesn't matter if you push or pull with the last maneuver. It tracks exactly trhe same.

In my view, one of the things that happens with single prop setups is that the trim becomes "speed sensitive", which makes sense if you think about what's happening. This is because when the plane is flying fast, air is accelerated less at it goes through the prop disk than when the plane is travelling slowly. The biggest effects are when you accelerate during takeoff and climb out because you are flying with maximum power and slow speed. These effects are also very noticeable at the end of long vertical climbs because you are also flying slowly, and with maximum power.

The smallest effects are when you are flying without throttle, like on a downline, because you are flying with zero power, or even negative power if you are using ESC braking. In between these two extremes you get a whole range of effects that change as the airspeed and power of the plane change. What the Contra does is make the trim of the plane the same under all these different conditions, even braking.

Obviously, this makes it a lot easier to dial the trim of a plane in, and it also eliminates all the tradeoffs associated with using large diameter props. This means that with a Contra we can successfully run a pair of 22 inch diameter props, and take advantage of the tractor like vertical thrust and huge braking power that you get with large props. I did some calculations, and I figure that a pair of 22 inch props is about equivalent to a 30 in diameter single prop setup, but no one in their right mind would consider using a 30 inch diameter prop because all of the torque and slipstream effects would probably make the plane unflyable.

An additional benefit of running with a pair of 22 inch diameter props is that larger diameter props are inherently more efficient due to the reduced power loading per square inch of prop disk area. I am calculating that a pair of 22 inch props are from 15% to 20% more efficient than a 21 inch single prop setup.

However, none of this means that you still don't have to "fly the plane". You still have to put the plane where it needs to be, and you still need to correct for wind, so none of the aforementioned is a substitute for pilot skill. What the Contra Drive does do however, is make pattern much more enjoyable to fly. I liken it to racing with Toyota Prius, and then switching to a Ferrari. The Ferrari is much more pleasurable because it is better suited to the task.

I know that in my case I would find it very difficult to switch back to a single prop setup. First off, the change itself would be a shock because now I am aclimated to flying with a Contra. Then I would notice that my vertical performance sucks because the plane keeps slowing down on vertical climbs, and then zooming on vertical downlines. It would also seem to squirt all over the sky at the top of humpty bumps, or any large maneuver where the plane slows down a lot. It would also be very frustrating when I tried to do stall turns, because the wings would keep twisting out of the plane of rotation. Also, snaps would be an endless source of frustration because the plane would never snap the same when snapping in opposite directions.
Old 05-15-2011, 09:44 AM
  #265  
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Brenner, I have designed a General Dynamics XFY-1 Pogo, she is scaled to 1:4, as it was that smallest size that seemed to want to fly using MotoCalc8.0 and the HiMaxx CR6320-240 setup, seemed to need the larger size to get enough wing area. I am very interested in you gear box.
Old 05-15-2011, 05:31 PM
  #266  
Brenner
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

I'd be very interested to find out how the Himax CR6320-240 works for you. I think it's going to rev up a little high than our Contra Drive, so it'll probably be more noisy. For a scale setup it should work well.
Old 05-16-2011, 03:21 PM
  #267  
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Hi Brenner,

What is the weight penalty using your contra drive unit and props Vs a typical electric setup say C50 with gearbox APC prop and spinner. I currently dont fly electric so I dont have anything to compare to but I am in the process of getting a model together and your product is being considered if I can get the model at the correct weight.
Old 05-16-2011, 07:11 PM
  #268  
Brenner
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

It's always difficult to make these types of comparisions because there are endless permutations and combinations of motors, props, spinners, motor mounts, etc, but if I am being asked to generalize, then I would say that the weight difference between a system consisting of a Contra Drive and a Neu Motor with Budd Mounts, and your Hacker C50 system with an APC 21x14 prop, a Tru-Turn Spinner, and also with Budd Mounts, is about 57 grams.

However, if you substitute the Neu motor with a Hacker C50 motor the difference will be more because the Neu without a gearbox is lighter than a Hacker without a gearbox. Also, if you don't use Budd Mounts for your single prop system the difference is more still, etc...

Ignoring comparisions, the all up weight of a Contra Drive system with a Neu f3a Motor, our latest 22x20 props, (at 65 grams each ..) and Budd Mounts, is about 810g +/- 5g. The tolerance is needed because there is variation from prop to prop.

Generally, if you have enough weight margin for an outrunner, then you have enough weight margin for a Contra Drive.

Brenner ...
Old 05-18-2011, 03:41 AM
  #269  
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Dave,
In an earlier post you were pictured with a Sebart Wind Pro. In relation to main wing, what incidence did you set stabilizer?

Thanks,
Gary
Old 05-18-2011, 06:47 AM
  #270  
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Hi Gary, I basically did what Arch did here in post #177: http://www.rcuniverse.com/forum/m_91..._8/key_/tm.htm
Except my stabs adjusters are at the limits.

Dave
Old 05-18-2011, 07:13 AM
  #271  
rcpattern
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Dave,

Mine are basically at the limits as well.

Arch
Old 05-21-2011, 02:34 PM
  #272  
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Hello,

Finally got the Contra fitted to new Amethyst for WC in Muncie.

I have attached some pics, showing the setup used ( Amethyst Mod-YGE 90-Neu f3a-Thunderpower 25C 5000s and 4400s- 22x20back 22x18front )

Had 6 trimming flights Friday. and the power is fantastic, much more vertical performance then similiar setup on Amethyst with Hacker 13xl last year.

I had 4 flights on this model last month with Hacker 13xl before I fitted contra, waste of effort! Completely needed to start from scratch with trimming, throws were dramatically reduced.

Far less rudder needed, less right aileron needed, NO mixes needed ( may need a touch in downline but wasnt calm enough to be sure )

As previous posts show it definetely makes surfaces more sensitive, nothing that cannot be tamed with expo and reduced rates, will just take some stick time to adapt.

Sounds fantastic in my oppinion,more pleasing to my ear then previous contras I have heard, well within sound check barrier.

Had 3 x p09 flights and uses similiar or less current draw then 13xl mono prop.

Weight penalty is negligible, I reckon about 85g net increase from my mono setup, easily absorbed in modern airframes.

Overall a fantastic combination and for sure is a step forward from anything I have previously flown.

Rgds

John Martin.

PS The first pics show the mounting system Brian Carolan has come up with , the 3 bolts on triangle mount can be openned and the complete unit ( inc. motor ) can come out through front, in about 30 seconds, very wel thought out.





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Old 05-21-2011, 03:37 PM
  #273  
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Very nice John. Look forward to seeing it fly
Old 05-22-2011, 06:12 PM
  #274  
Brenner
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Hey John,

That has to be one of the cleanest installations that I have ever seen. The finished plane with Contra installation is absolutely beautiful. I am really looking forward to seeing it fly at the Worlds in Muncie.

Brenner ...
Old 05-23-2011, 04:34 AM
  #275  
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Does anyone know of a good technique to locate exit holes for rudder cables? On these composite fuselages you really only get one chance to get right. Do most installations require crossing cables?

Thanks,
Gary

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