bandicootf16

I have just finished reading all 59 pages of this thread. It contains a wealth of information from many very knowledgeable contributors and has really inspired me to consider a contra set up for my next aircraft.

Brenner how is the testing of the V4 drive going. Do you have an idea when it will be available. I am about to start setting up an Oxai Galatik and I'm considering using a contra setup. I would like to do it without any add on's if possible. Does anyone have any thoughts on the suitability of the Galatik for a contra setup. The Axiome seems to work well so there is a good chance it mIght work well with the Galatik too.

David...

Brenner

Hey David,

We are testing the V4 Drive over this summer flying season. This is an important phase of the development that can't really be cut short because we need to have a good understanding of the durability and reliability of the design before we start selling Drives to customers. Current expectations are that we will be able to offer Drives to customers sometime in the fall of this year.

The Axiome has proved to be an excellent platform for the Contra Drive, and so I think that the Galactik will also be a great platform as well.

We have have done quite a bit of testing with various types of planes, and generally, if you have a plane that has a proper amount of rudder fin area, it will have enough yaw stability to work well with a Contra Drive.

What has happened over the last decade or so, is that fuselages have become much deeper to improve knife edge performance, but in some cases the rudder fin area hasn't increased proportionately to match, which reduces the yaw stability of the plane. This reduction in yaw stability is also somewhat masked in a single prop setup because single prop setups use right thrust, which increases yaw stability enough so the overall reduction in stability isn't noticed.

However, when you switch to a Contra Drive setup, the need for right thrust is eliminated, so any plane that is marginally stable with a single prop setup will have yaw stability issues.

We are currently flying a design that has a very deep fuselage, but also a very large rudder fin area, and there is no issue at all with yaw stability. The rudder is powerful, due to the deep fuselage, but very linear in its effect.

I am currently using a VTR type of curve on my rudder where I have one rate for flying, and a higher rate that kicks in at about 75% of the stick position. I set the lower rate based on what I need for rolls, and the higher rate for what I need for stall turns. Neither rate has any expo in it. They are both straight linear curves, and the rudder feel is fantastic.

Another feature of this design is that it has a flying stab, which also seems to work well with a Contra Drive. What I have noticed is that elevator feel is also very linear. I have a single rate for general flying that currently only has 10% expo in it, and I'm not so sure that I need even that.

Another element that seems to be important in a Contra setup is the motor downthrust relative to the wing. I initially set my planes up for about 1 degree between the motor and the wing, and then I adjust the wing incidence until the plane flies perfectly flat without dropping the nose when I go from full throttle to zero throttle.

If the wing incidence is too high, the plane will zoom up, and if the incidence is too low, the plane will drop its nose, but when I get it properly balanced, I can throttle back and hold a perfectly straight and level line, regardless of throttle setting. In this condition the plane also locks on really well in windy conditions.

When set up this way, my plane usually needs a percent or two of downline elevator mix. I can eliminate this mix with less wing incidence, but I much prefer to have pitch stability than not need any downline mix.

Brenner ...

Jeff Worsham

My Feedback: (28)

Brenner,
Congratulations on your achievement with the V4! What size spinner dia will it have?

Brenner

Hey Jeff,

We are using the same spinner sections as the V3 Drive, so the spinner diameter will be 82mm.

Brenner ...

bandicootf16

Hi Brenner

Thanks for all the great information. A fall release would be perfect for me so hopefully the testing continues to go well. Are you still using the Kontronic Pyro 650. In a heli set up these motors run at a constant rpm which is quite different to what is required in an F3A aircraft. However I think you said you were impressed at the throttle response of this motor. I guess this is a function of the torque from the out runner.

Thanks for the info on setting up the wing incidence. How are you setting the down thrust in the first instance. I guess starting with the design down thrust would be a good starting point. Setting up the rudder using a VTR type curve is a cleaver idea. I'll have to give that a try.

How is the collet clamped to the motor shaft. Do you use the pinion bolt. If so will you be recommending a torque setting to avoid slippage and potential loss of the drive from the front of the aircraft.

David...

Brenner

Hey David,

I'm still using the Kontronik Pyro 650, but we are also testing other motors as well. We also have Kontronik Pyro 600 motors that have been rewound for 10s that we are going to try as well.

I typically set the motor up with 0.5 degrees of downthrust, and the wing with 0.5 degrees of positive incidence, and then adjust the wing from there. Usually I end up with something like 0.7 degrees of positive in the wing.

The collet is split into three sections, which collapse onto the motor shaft when the pinion gear bolt is tightened. We will be recommending a proper torque for the pinion gear bolt, but typically what we do is tighten it as much as we can using a 100mm hex key.

The connection is designed to to be very stiff, so it can take a very high tightening torque. This is contrary to the collapsible collets that are used in outrunners, which have a compliant prop hub in the stack that limits the maximum tightening torque that can be used.

Brenner ...

bandicootf16

Hi Brenner

Sounds like the drive connection will be bullet proof.

The modifications to the Pyro - the extended shaft an extra front bearing, we're these parts available from Kontronic and were they easily done.

Can you add me to the list for a V4.

David ...

Brenner

Hey David,

The extra front bearing is just a drop-in change, but we also put a brass spacer tube between the front bearing and the rear bearing as well, which required us to remove the rotor and the rear bearing.

We made the extended shaft ourselves. We pressed out the existing shaft, and pressed in a longer one. We also eliminated the flat on the stock shaft as well.

You're on the list!

Brenner ...

bandicootf16

Hi Brenner

That's great.

So I guess there is space in the 650 case to place the additional bearing. What was the reason for putting the brass spacer between the front and rear bearing. If you go with this motor for the V4 drive will you be making these parts - longer shaft etc available.

David ...

blake26m

Some greasing and maintenance tonight on the Contra. 240 flights on the drive so far and preforming very well. Replaced two 0 ring seals also. Really loving the drive.Thanks Brenner.

Dean Pappas

Hi All,
I had a chance to take part in a pre-NATs tuneup with Ron and Dave Lockhart last Saturday and I can happily report that the Allure has the proper yaw stability with a Contra.
Regards,
Dean Pappas

sober.chain.smoker

Smart idea to be working on Contra current version and beyond to take advantage of RC Heli motors.
RC Helicopters are experiencing some terrific grow in popularity I think.
Around 1000 (plus or minus) heli pilots show up at IRCHA each year.
Currently a new area inside of the RC Heli camp that is drawing some increased interest is speed RC helicopters with new 700 and 500 sized speed heli being introduced just recently.
Hopefully RC helicopters will continue to drive motor advancements.

bandicootf16

Hi Brenner

Congratulations on your third place in Masters. I guess you were flying the V4 contra. Any chance on getting some info on your setup.

Thanks
David

Mavpro

Thanks for a very interesting thread. I've just purchased a second hand Integral in very good condition, and I'm looking into Contra drive for it. I'm gathering as much info about this propulsion as I can get. It's been years since I sold my Dr Jekyll II, YS91AC powered, but now, time is back to start training again

Brenner

Hey David,

The brass tube is needed to transfer the thrust loads from the rotor housing to the front bearings.

Yes, if we go with the Kontronik motor we will have to supply an extended shaft, a brass tube, and an additional front bearing. We'd like to be able to convince a motor manufacturer to make these changes for us. We're still working on this.

Brenner ...

Brenner

Hey David,

I was flying a plane that was scratch built by Mike Gaishin. Mike calls it the "Integer". It's a plane that has been designed specifically for the Contra Drive.

I used a prototype V4 setup with a 22x22 rear prop and a 22x20 front prop. I was also using a Kontronik Pyro 650-83 motor that was ATV'd back to 94%

I was using an Emcotec SPS Safety Power Switch, with an Emcotec DualBat RX switch.

I also used a Mezon 130 Lite ESC, and I used the BEC on the ESC in combination with a 450 mah Lipo for backup.

The plane with this setup weighed 4730g with 5100 mah Power Unlimited packs.

Brenner ...

pippy

Hi Brenner, congrats on 3rd place. Any pictures of your plane?

bandicootf16

Hi Brenner

Thanks for all the details of your set up, 4730g is certainly a great weight. How many amps are you pulling with the Pyro 650-83 . I guess you are using the 6.75 gear ratio.

David

bandicootf16

Hi Pippy

There is a photo of Brenners Integer back on page 58

David

pippy

Oops you are right David. Old age is terrible. I see it has an all flying tail. I do like that on my inspire.

Brenner

Hey David,

My setup is pulling about 90A with this setup, and yes, I am using the 6.75:1 gear ratio.

Our season is about half over now, and the V4 testing is going well. Here are a few of our learnings so far:

1/.. Our grease reservoir system seems to be working very well. The centrifugal force inside the gearbox keeps just the right amount of grease in the gear mesh, and not more, and the increased quantity of grease in the reservoir has pretty much eliminated the need for regreasing. (at least so far...) My next objective is to try and get through a complete season without having to regrease the Drive.

2/.. The idea to have the grease re-circulate through the main bearings is probably not going to pan out because it's too challenging to keep the grease from leaking out of the rear of the drive when it exits the rear bearing. Instead I think what we'll do is use seals on the rear bearing to stop grease recirculation, and keep grease inside the drive. So far this approach is working well.

3/.. One consequence of reducing the weight of the Drive by 160g, is that the resonant frequency of the mounting system has increased. In hindsight I suppose I should have predicted this, but what it means is that we will probably be switching to two mounts on the front motor plate instead of three, which will have the added benefit of more reduced weight. This will reduce the stiffness of the mounting system by 33% to match the 20% reduction in system mass.

4/.. We have seen a certain amount of fretting on the motor shaft where the rear support bearing is attached. This is easily stopped by using a drop or two of Loctite on the bearing inner race, but this isn't a good permanent fix. What we'll probably do long term is use a shaft that is surface hardened to RC60, and then run a needle bearing directly on it instead of using a roller bearing. This approach actually ends being lighter, so we also save a few additional grams as well.


Brenner ...

bandicootf16

Hi Brenner

Good to hear that the grease reservoir system is working well. How many flights do you do in a season? It would be great to only have to re grease every 200 flights.

What effect do you see from the higher resonant frequency of the drive. It would seem that a two point soft front mount would make mounting in a tight space a little more difficult especially if using Budd mounts.

I guess using a roller bearing for the rear shaft will require a special bearing housing. Will this require regular lubrication.

Is 90 amps a peak figure. Would a Jeti spin 99 do the job or would you recommend the Mezon 130. I suppose an advantage of the Mezon is that it has a bec so you can get by with just a single rx lipo if redunancy is required which is a nice thing with any model.

David

Brenner

Hey David,

I typically get about 500 flights in a season.

Right now I don't think 200 flights without regreasing is going to be too much of a problem. The real issue is finding a way to properly validate whatever service interval we come up with. We need to try and think of all the ways that the system can get screwed up, and find ways to mitigate these failure modes and effects.

The higher resonant frequency means that that the critical natural frequency that the Drive has to accelerate through when the throttle is accelerated will be at a higher rpm, and the rotational kinetic energy involved will be higher. This energy is actually proportional the square of the prop rpm, and if there is too much energy involved, the system can become unstable.

This effect can be seen if you try to run a Contra Drive without the props and the spinners. In this condition it will be difficult to accelerate the Drive as you advance the throttle, and under some conditions the system can become unstable. This is because the props and spinners have a weight in excess of 130g. Also, this is weight is up front in the Drive, which makes things even worse.

In any rotordynamic system the displacements in the system are in-phase with the forces in the system when the rpm is below the first critical natural frequency, and 180 degrees out of phase when the rpm is above the first critical natural frequency. This means that rotordynamic systems are unstable as they approach, and pass through the first critical natural frequency of the system, and stable after they have passed through the first natural frequency of the system.

One workaround is to make sure that the system is perfectly balanced, but this is a bandaid, because any inherent system instability still exists, regardless. The best design approach is to make sure that the first critical natural frequency in the system is low enough so that the system is robust to uny unbalances.

This is done by tuning the mass in the system, the location of the mass in the system, and stiffness of the mounting arrangement.

As far as space concerns with a two point mounting system. The V4 has a lot more radial space available for rubber mounts, so this shouldn't be an issue.

A needle bearing for the rear support shouldn't be much different from a roller bearing. In fact, there are needle bearings that you can get that have rubber seals. We will probably try and get one of these.

90A is a peak figure, and the Jeti 99 should work fine. I am using a Mezon 130 because I am testing a lot of different motors, and some of these motors draw more than 120A.

Also, you are right about the BEC. it makes things a lot more convenient.

Brenner ...

OhD

I tried a 5 point curve to duplicate your VTR curve today and it looks very promising. At first I banged the stick over and it looked like hell, but I found if I flew the plane through the stall turn with rudder and throttle I had complete control. I probably need to fine tune it but I am very confident I will be doing better stall turns.

Jim O

Brenner

Hey Jim,

Coordination between rudder and throttle is definitely the key.

With the Contra it should be possible to control the rate of yaw all through the stall so that the yaw rate is mostly constant, and because there's no motor torque, you don't have to fiddle ailerons and elevator to keep the wings in plane.

Brenner ...