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Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Old 05-06-2013, 11:28 PM
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Hey claude,

About 470 gr with the servo. It's possible to make much lighter with monokote or with another painting than CARF painting (brillant direct for the mold).
Here is the weight during the build.


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Old 05-07-2013, 03:08 AM
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Hello Vincent

Thank you. Wing is very light.
You use Japanese method powder + varnish (V33) ?
Résult is awesome
Claude
Old 05-07-2013, 03:21 AM
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

I have the same wings on my Wind S Pro, and they are 355g per panel, ready to fly with servos and linkages installed.

Brenner ...
Old 05-07-2013, 06:16 AM
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Hi Brenner,

What is the construction method of your wings. Clearly composite painted wings are usually heavier. The Gaudious wings are 419 grams for Gadious 2 and 452 grams for Gadious 1 ready to fly. These are composite painted in the mold. I think is important to report wing area when discussing wing weight. These are about 986 sq.in. or 0.6361 meter square. I think the Gaudious wings are above average wing area but not 100% sure now.
Old 05-07-2013, 06:27 AM
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Hey Brenner,

<span lang="en" id="result_box"><span class="hps"><span lang="en" id="result_box"><span class="hps">This</span> <span class="hps">is the weight</span> <span class="hps">that the</span> <span class="hps">wings</span> <span class="hps">should have been</span> <span class="hps">if all</span> <span class="hps">the steps</span> <span class="hps">were followed.</span></span></span></span><span lang="en" id="result_box">
<span class="hps">Anyway I'm happy</span><span class="hps"> because</span> <span class="hps">these wings</span> <span class="hps">are more efficient</span><span>.</span> <span class="hps">Sure</span> <span class="hps">200g</span> <span class="hps">less is</span> <span class="hps">definitely</span> <span class="hps">something else </span></span><span lang="en" id="result_box"><span class="hps">and </span><span class="hps">it's a shame</span> <span class="hps">because</span> <span class="hps">this kit is</span> <span class="hps">exceptional.

Vincent
</span></span>
Old 05-07-2013, 11:28 AM
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Hey Vince,

My wings are monokoted, not painted. That's why they are so light.

I am very happy with them. In my mind they are a perfect match for the Contra Drive, because they open up the speed range of the plane, while reducing draw from the battery packs.

Mike Gaishin also has a set on his Integer, and they work great there as well.

One interesting thing about Mike's Integer is that he specifically built it with about 20% extra side area on the rudder fin, and moved the center side area for the rest of the fuselage back, and now the plane is rock solid in the air.

Mike doesn't use rudder strips, or stab fences, but there is absolutely no hint of yaw instability,, and the plane flies like it's on rails. It also handles the wind extremely well. The wings never seem to move, regardless of how strong the wind is blowing.

Based on this, we are speculating that over the last decade or so, pattern plane side area has slowly increased in order to improve knife edge performance, but rudder side area hasn't been correspondingly increased, which has resulted in a lack of yaw stability for some plane designs.

As far as the Contra is concerned, this suggests that careful management of rudder fin side area versus fuselage side area is maybe the key to designing the next generation of planes that work well with the Contra Drive.
Old 05-07-2013, 01:22 PM
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Old 05-07-2013, 01:49 PM
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes


ORIGINAL: flyncajun

Care to elaborate Bryan?

Cheers,
Jason.
Old 05-08-2013, 02:47 AM
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Hey Brenner,

Regarding the increase of the slide area at the back of the fuselage for the plane not to slip, there is something I can't clarify.
If we take the case of a glider (I compare with a glider because with the Contra Drive the 2 props cancel the slip stream), there is almost no side area at the back of the fuselage and the gliders flies like arrows and don't slip at all.
Is it thanks to higher rudder or is it something else ??

Vincent ...

Old 05-08-2013, 06:20 AM
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Hey Jason
The smile was like ringing the bell for the correct answer

Brenner was right on the money with his statement about fin rudder area verses fuse area.
This is where throttle to rudder mix started to come in , it`s a design problem nothing more." Problem" not being a bad word.
Over reaching for one improvement lead to the loss of effeciency elsewhere.
Strakes, Fences, and dorsals , are required on planes due to our modern changes, thinking they were improvments (this only covers one of them)
The Contra unit shined a brighter light of truth on these issues it could not correct them it magnified them.

I hinted at this some time ago in another Thread, I was tempted to spill the beans However,
some are figuring it out now. Seba`s new bipe, Naruki ,Accuracy, Assular bipe,and a few other no one has seen yet
to run the cg at 35-40% you have to have good yaw stability in the rear and one other criteria ,, (I`l save that one for now
Here my Quote from the Chip Hyde CG thread.

"SO forgive me if I can demonstrate there is no design criteria for eleminating the SSS or that it even effects what we do.
Most of what it is blamed on it is due to Poor design or poor trimming.
Our fuses have become the size of garbage cans and our props have doubled in size. Yet ,Our understanding of these two dynamics are stuck in the 70`s design formulas, from our teen age Hero`s. "

Now,I can`t give away the farm BUt I do like to drop crums from time to time
Common sense rules again,

Bryan
Old 05-08-2013, 08:52 AM
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Hi Bryan,

How is your contra design coming along?

Still flying the Valiant now and again. Great plane, which really benefited from the fuz strake. Just wondering why you didn't just design it with a larger fin instead of having an add on? I'm looking into increasing the fin area. Personally I'm not that fond of rudder flares (increases drag) or fins on the tailplane. Might as well just add it to the fin itself IMO. Where it is supposed to be.

Just one last nugget of info. During the war (say it in an Albert Trotter voice please), they found the Spitfire more and more sensitive in yaw/sensitive to power changes. Basically the rudder and to a lesser extend the tailplane which were adequate for 1000hp were found to be too small for the 1500hp and above engines they later fitted (with the corresponding bigger propellers). The designers didn't add tail fins or fancy rudder trailing edge flares, they just increased the fin area...and it worked. Compare the MkI up to the early MkIX's with a Mk 22 and you will see how much they eventually increased the area.
Old 05-08-2013, 09:16 AM
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Hi Angus,
Are we to understand that you have worked out how to increase the fin/rudder area without 'adding' drag .

Brian
Old 05-08-2013, 09:30 AM
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

I've been talking about the need for increased fin area with the Contra for a while. I never did like using drag devices to add stability and from the testing I've done they do not work as well as area. You of course can't add area without adding some drag but it is very minor compared to the flares and other devices I have seen.

Just making the fin bigger and proportioned properly is one way of doing it. That is fine if you're designing a new model and have a blank sheet of paper. But if you're working with an existing model, and so far there are no available kits designed just for the Contra, then the stab fences seem to do a very good job with minimal weight. They may even be better then an enlarged fin since they are flat plates which may make them more sensitive to small changes in AoA then an airfoiled surface.

Back at the 2010 or 2011 Nats I asked Bryan why he added the strakes to the Valiant since previously he had been so adamantly against "band-aids". He said they worked better then just making the fin bigger. If that is correct then my guess is that along with the added area his strakes provided they also made the leading edge of the fin airfoil sharper, making it more sensitive to slight beta changes, improving the yaw stability.

As to mods to WWII fighters, it's very interesting to look at the development of the Martin-Baker MB-5. It was never produced as it came out at the very end of the war. It looked a lot like a Mustang but it had Contra props. They initially had yaw stability issues with it until greatly enlarging the fin. Along with the Spit, a lot of WWII fighters got bigger fins or ventrals as the power/prop size increased.
Old 05-08-2013, 10:21 AM
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Hi B,

Are we to understand that you have worked out how to increase the fin/rudder area without 'adding' drag
Yes

Like Tony says, the drag increase with area increase will be minimal. Watch this space old bean

Yes stab fences do seem effective Tony, just the idea of increasing the fin size is more appealing to me than adding area on the tail plane. Whilst no planes have been built specifically for the contra yet (as far as I know), the Valiant is very good straight out of the box. However, I think the Oxai Raybird would be just the ticket. Slim nose and massive vertical fin

Interesting plane the MB-5 Tony, will need to look into that further. On a separate issue, do you know much about the Republic F-84H Thunderscreech? Been trying to find a video of it flying including the noise of the props but I can't find any.
Old 05-08-2013, 11:10 AM
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Angus,
Yep a fine pair of fins alright ;
+ another one (edit);

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Old 05-08-2013, 11:45 AM
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

In actuality, I think the stab fences may be even better then just adding fin area. It depends on where you put the area. What I have been seeing with the Contra is that most models are not bad when doing a negative corner. With the fin running in the clean air in an inverted corner they are stable. But when I would do a positive corner they would wander a bit. That is because there isn't as much fin area on the bottom as on the top. Now the stab fences are always running in "clean" air, so maybe they are more effective then just adding the same amount of area to the fin.

I've read about the F-84H. I guess it was incredibly loud, to the point that pilots and ground crew were getting bad headaches from it. A big reason why it was dropped, along with the advent of jets.
Old 05-08-2013, 12:34 PM
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Hi Angus

My Contra design is moving , Fuse is 90% bult wings are ready to sheet stabs are done ,although slow, I`m trying to get a bipe ready for SA Brett wont fly the Contra on a Mono ,,LOL

I figured out this enhancement by accident playing around with every body elses gadgets at the request of Jason Shulman. I just threw my own one in as a joke to the club members whatching me test that day, Boy was I surprised!
There are other peices to the puzzle , I won`t go into them here , or some one will miss quote me again and or take credit for the info later.If you look up the old Valiant Thread I go into detail about what it does and WHy I used it.

No adjustment will fix a bad design not even to the wings, stab, Thrust, no matter what system you are running. Either the design is good and can be trimmed or you chase it for ever throwing things on and screwing wing adjusters.

The Valiant was designed to be Agile, snappy and easy on batteries for the electric guys , I wanted to give them flexibilty on power systems and be able to run glow or electric , It`s a tough chore.

When you design a FAI Model you shoot for that market as best you can ,However the guys flying AMA class want to be able to enjoy a new model as well so, it`s one of the reasons I had the Strake added to the Kit. It does make the airplane a little more solid, and the snap exits are cleaner as well as giving a expo effect around Neutral.

There are many Guys out there flying the Valiant who are quite happy without the strake I call it a enhancement , it was not added to solve a problem or fix a mix or yaw instability, or to counter the Spiral Slip Stream!
And what do you know, My Fuse is not Narrow in the front ( Myth and speculation ) But the Contra worked for you right out of the box

The problem is there are probably guys whittling away at a plug for the contra right now with a Pencile nose because of what they read in this thread! Sorry

Model setup (wing Inc and CG placement is king) until thats right, no add on, will give you the entire package.
I`m not against add on`s I`m againt thinking they can fix a design flaw or poor trimming.
and when the add on`s start causing problems with trimming what have you gained?

Bryan
Old 05-08-2013, 02:11 PM
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

So it seems that consensus is that increased vertical fin area will achieve the stability needed for a contra drive.

Has anyone tried adding a dorsal type fin to the vertical fin instead of stab fences?

Cheers,
Jason.
Old 05-08-2013, 03:54 PM
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Yes, I added a dorsal to the Onas. It did very little compared to the stab fences. Oh wait, maybe I should have kept that secret? I can't start letting everyone know what I do! Yea I can, it won't take long.

I have seen no negative to increasing the yaw stability, just positives. I know years ago some thought that a model entered a snap better with less fin area. That might be true but they sure don't exit one as well. And I've seen no issue in spins either. The only thing you might have to do is move the rudder more to do some maneuvers.
Old 05-08-2013, 04:18 PM
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Hi Tony,

How big was your dorsal fin (height) and how long was it i.e. the whole fin length or just on the top section?

Cheers,
Jason.
Old 05-08-2013, 06:09 PM
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Hi Jason, I think this thread shows a picture Tony's Onas that he flew a few years ago: http://www.rcuniverse.com/forum/m_11487238/tm.htm

Dave Snow
Old 05-08-2013, 06:11 PM
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Thanks Dave,

I was thinking more of continuing the dorsal right up to the top edge of the rudder. Would be an interesting trial...

Cheers,
Jason.
Old 05-08-2013, 06:40 PM
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

I had a chance to take a closer look at Mike's Plane, and this is what he told that he did:

1/.. He added an extra inch (25mm) to the front leading edge of the rudder fin, and to the top of the rudder fin, so the rudder now has more area and is taller.
2/.. He experimented with canopies that had different heights, from tall to very low like in the attached picture. The low canopy is the one that performed the best. Taller canopies started to create yaw instability.

One interesting thing is that this plane in it original form was the worst plane that Mike or I ever flew as far as yaw instability, but now it's one of the best.

Another interesting thing to note is that in its original configuration the top of the rudder was actually about an inch (25mm) below the top of the canopy, whereas now it's at least an inch (25mm) above the top of the canopy, which lends credence to Tony's point about the rudder flying in clean air.

Brenner ...
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Old 05-08-2013, 07:19 PM
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

Brenner, so far I have about 20 flights on my new plane and I have not seen any of the yaw instability we were originally seeing a few years ago. I'm going to try and post a side view here but the fin/rudder is large compared to most planes and the rudder does not extend to the top of the fin, I saw no reason to have too large of a rudder. The highest point of the fuse is 14.5" and the fin is 17" tall, the fin extends 4" above the canopy, this might be overkill. I'm not sure any of that really means anything on it's own but so far it's been a really good plane to fly.

Dave Snow
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Old 05-09-2013, 12:13 AM
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Default RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

ORIGINAL: Brenner

I had a chance to take a closer look at Mike's Plane, and this is what he told that he did:

1/.. He added an extra inch (25mm) to the front leading edge of the rudder fin, and to the top of the rudder fin, so the rudder now has more area and is taller.
2/.. He experimented with canopies that had different heights, from tall to very low like in the attached picture. The low canopy is the one that performed the best. Taller canopies started to create yaw instability.

One interesting thing is that this plane in it original form was the worst plane that Mike or I ever flew as far as yaw instability, but now it's one of the best.

Another interesting thing to note is that in its original configuration the top of the rudder was actually about an inch (25mm) below the top of the canopy, whereas now it's at least an inch (25mm) above the top of the canopy, which lends credence to Tony's point about the rudder flying in clean air.

Brenner ...
Hi Brenner,
That's an interesting change in performance ; 1- It's dramatic and ; 2 - It's to a pre existing model ( One which ,to your credit, you openly described as being very poor in yaw with the Contra).

Is this the model that had the really blunt fin (edit) leading edge.

Also did Mike experiment with canopy shape before and/or after the fin changes.

Brian

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