OhD

Thanks Dave, exactly what I wanted to hear. I was planning on the same configuration and it is good to know it has worked for you. I don't have the motor yet, but it looks like the manifold is slightly different now but the dimensions from the mounting plate to the back of the spinner shouldn't be affected by the motor configuration if I am seeing it right. Is that correct Brenner?

Chris, I am aware that Jerry has different isolators and I'll check with him to see if I have the right ones. Thanks for the help guys.

Jim O

Brenner

Hey Jim,

I believe that since Dave put his Spark together, that we modified the Adapter Manifold so that it would work with the New Neu Motor as well as the Old Neu Motor. You should be good.

Brenner ...

Hans Meij

The CD fits nice into the Gaudius too.

wagen017

now why does that not come as a surprise to me!! Looking great Hans!!

Volkert

PILOTAGNIK

Hello,Brenner,by (DmitryZagitov,Russia) putthe installation ontheir aircraft.
EUROPA,EUROPApro

Thank you, very happy!

Brenner

Howdy,

Both planes look fantastic. How do they fly with the Contra? Also, it looks like the top Europa has a modification on the trailing edge of the rudder. Can you tell me how it works?

Brenner ...

PS-> The Gaudius looks great too! Very clean installation...

PILOTAGNIK

smcharg

My Feedback: (1)

Vyacheslav,
   I, for one, am very impressed with your creativity.  It amazes me how you all come up with ideas on how to accomplish things.  You have my total respect and regards.

Scott

Cross_link

Brian,

I also made my maiden with the midrex yesterday. In the knife edge I need some mix rudder to aileron (2,5-3%). CG about 110mm. I also had to set the angle of incidence. My first immpression was positive but not exiting.
The snaps are not as precise as they are with my own construction (with is based on theAdventure from Naruke, total wood construction 4750g incl. battery and Contra). The air resistance seems to be lower which means the setting of the brake is different.
We will see if the performance at the end is as good after all adjustments (due to the price it should be better).

Christian

PILOTAGNIK

Thank you Scott McHarg. Now I have to fly, prepare for the season 2012.

Brenner

The grey triangle strip on the trailing edge of the rudder is similar to what I've been using on my Integral, and it makes a big difference.

The bubbles on the trailing edge of the rudder look very smart. They are more elegant that what I have on my Integral for sure.

Brenner ...

OhD

This might not be the best place to ask, but what is the best torque wrench to buy for our use? Do most work in both directions? Any recommendations?

Jim O

shannah

My Feedback: (5)

Good question Jim. I bought a couple cheapo's at Harbor Freight, but I have no good way to check and see if they are even close to being accurate for lower torque settings. I don't know about the reverse direction. I'll check mine.

Regarding the rudders: What negative effects are the rudder trailing edge designs compensating for? What does the plane do without the rear TE modifications?

Dsnow

Hi Steve, last year we noticed some yaw instability, mostly in the exits of maneuvers, in the three planes that Brenner / Mike Gaishin and I were flying and after some experiments it seemed like if the trailing edge of the rudder was thickened the instability was eliminated or at least greatly reduced. This year with more planes using the contra and being on a variety of models it looks like the yaw instability that we were seeing is plane specific. Several planes that we have seen that do not require any modifications is the Valiant and the Visa, planes that appear to need a modification are the Integral and Spark. Why do some planes need a modification and others do not, I'm not sure but I bet we will get some input from others. Luckily the modifications are easy to make and things that have been tried and work are the thickened rudder trailing edge, fences on the stab and a dorsal fin. Are there other modifications that would work, I'm sure there are but after Brenner/Mike and I used the thickened trailing edge and I added some fences to the Spark to get a good locked on feeling we stopped looking. I hope this helps some.

Dave Snow

shannah

My Feedback: (5)

Thanks Dave.
That helps me out. I will be flying a Visa so it sounds like the rudder will be fine.

I should have mine ready this week, but with a house full of visitors arriving next weekend I may have to wait until after thanksgiving (unless I get a chance to sneak out).

Hans Meij

Maidened the CD today. Now I know what many of you have encountered and are trying to eliminate.
Obviously the Gaudius is susceptible to this phenomena too.

My other Gaudius I fly with the Rasa folding prop. When I flew it with a fixed prop it had that behaviour in a lesser extend too.
When I switched to a folding prop especially the ones where the blade area near the center is strongly reduced,
(Like this one: http://www.f3aunlimited.com/webstore...products_id=90)
the phenomena that when gravity is driving the plane it looses ability to track disappeared.

Is it possible that the four blades of the contradrive wich are quite wide near the center are acting like a closed disk at the center when gravity is driving the plane.
And therefore flow over the tailsurfaces is to much disturbed?
Suggestion: make the prop more narrow near the hub...

shannah

My Feedback: (5)

I wonder if the canalizer contributes to this effect in any way.

Brenner

Hey Hans,

So far the problem has appeared to be airframe specific. Some planes have more of a problem, some planes have less of a problem, and some airplanes don't have the problem at all.

One thing we have speculated is that since the Contra straightens out the airflow over the fuselage, that the aerodynamics of the fuselage becomes more effective, and the distribution of area from front to back is either enhancing yaw stability, or negatively affecting yaw stability.

Mike Gaishin had a plane that he designed himself that was noticeably worse than my Integral, and what he did was make a new canopy for it that was much flatter and slimmer, which helped quite a bit. This is what led us to suspect the fuselage shape as a contributing cause. Then I think it was Brian Carolan who suggested that we try increasing the width of the rudder trailing edge, which I tried on my Integral, and this was like throwing a switch.

What was happening before was the plane would oscillate back and forth in the yaw axis when I applied and released rudder. I always had to be very careful to release the rudder to minimize this effect, but now I could apply rudder and just let go of the stick and the plane would just yaw back into line without any oscillation at all. The precision of the rudder around neutral also increased tremendously as well. Now it was very easy to constantly be applying small rudder corrections and never have them show up because the fuselage never over traveled in the yaw axis.

One other theory that we have had is that the lack of right thrust with a Contra Drive is eliminating a steady state balance of forces that locks the fuselage in the yaw access when you have right thrust, so when the plane is flying in any kind of straight line, all it takes is a tiny side force to start the fuselage moving in the yaw access. One analogy would be the preload in a spring. If a spring is preloaded by statically compressing it, then any force that compresses it further has to exceed the initial preload. However, if the spring isn't preloaded, then any non zero force will cause the spring to compress.

Regardless though, I recommend that you try attaching some 12mm triangular balsa strips to each side of your rudder trailing edge using double sided foam tape. If this works, then there are lots of ways to accomplish the same effect if you don't like the look of the triangular strips.

Brenner ...

Doug Cronkhite

My Feedback: (34)

I'm almost 100% certain the instability is caused by the CD removing the surface pre-load effect generated by spiral slipstream. The thickened trailing edge is reapplying that preload in a different way.

Hans Meij

Hi Brenner,
Thanks for all the input. I was triggered by the remark of Dave about exiting a maneuver where I exeprienced it the most too. That made me think of being power on-off related. Time to experiment that is for sure.

Some data:
Motor C50 13XL 10.15 gear 22*18 prop front and rear.
Motor is not overloaded consumption about the same as single prop setup.
A bit higher pitched prop will suit my flying style better.

Brenner

Hey Hans,

I think Dave was flying a Wind S Pro when he made the observation about exiting maneuvers. If memory serves, he said that the Wind S Pro was better than my Integral in this regard, and that he only saw yaw instability when he was exiting certain maneuvers. My Integral was quite a bit worse than Dave's Wind though, and I experienced yaw instability not just on exits. (I'm also wondering if the wing fences on Seba's Wind S Prop are intended to manage yaw instability ...)

By the way, props are in the mail. I think you'll like the 22x20 props quite a bit better, because there is a significant jump in speed.

On a side note, Mike Gaishin has done a little testing with mixed props, and he's telling me that it doesn't seem to matter if you have a higher pitch prop in the front or in the rear, the net effect is the same. I haven't tried a 22x18 in the rear with a 22x20 in the front yet myself, but if you look at the math, the drive should equalize the power absorbed by both props regardless.

Hey Doug,

I think you're exactly right. When a plane with a single prop setup flies there is always a complicated balance of forces due to right thrust, spiral slipstream, etc, all of which are speed dependent, and the Contra Drive eliminates all of this, which I think bodes well for the design of planes in the future that are specifically configured to take advantage of what the the Contra does.

Brenner ...

shannah

My Feedback: (5)

There may be some historical support for the stability issue. The Fairey Gannet (contra rotating props) had to add vertical fins on the horizontal stabs. They reported that after they added the AEW sensor to the belly then it was necessary to improve stability. All versions had the stabilizers.

The AEW version kind of looks like my Visa..... Any issues and I'll put the stabilizers on my horizontal stabs.

gdaddy

Jeskys Krill has a set of these on the stab. He said it took the wiggle out of pulling to level from a downline. Sure looked good from where I was sitting.

Brenner

I never noticed the SFGs on the Fairey Gannet before.

It all makes sense now.

Brenner ...

Alex Voicu

Westland Wyvern is another good example. Even with the huge fin area, still had some stability issues and small vertical fins were added to the stabs.