Contra Prop from WC

[frank williams]

Any comments available from WC travelers about the performance of the GB with the contra-prop.  Was it an active or passive system?  Did it seem to work well?  Was the pilot happy with the performance?  I know the pattern guys use them, and I've looks at various applications for stunt.   Curious minds want to know.

[pmackenzie]

"Active" system, in that both props are driven.
In-runner motor and from what I could gather (language was a bit of an issue ) it was  geared down 2:1.
Gear box is sealed and oil filled. From the looks of the gear box shape it uses simple spur gears, nothing planetary.
Price was I think $1200. Or perhaps $1200 Euros? Either way not cheap!

Pretty sure the pilot of the plane shown (Krystian Borzecki) was happy with it, he did make the finals after all:)
Main advantage was supposed to be very constant speed, particularly on "down lines" (F3A/P terminology)

Very unique sound of course.

I will try to confirm the price, a local guy was in Poland earlier this year and knows more about it.

Pat MacKenzie

[frank williams]

Thanks Pat, for the info

Pattern usually leads the way for power technology.  They are after the same things that we are .... and have more $ behind them.

To me, the gear box is more attractive for "contra" rather than two motors.

I think we'll get there before its all said and done.

Frank

[jose modesto]

We were offers one for 250€ we passed. Should of taken one. The designer and builder of the sister was there. It sounded like a sewing machine during flight. The system performed every flight. Including practice flying
Jose modesto

[Igor Burger]

It comes from Pawel Dziuba, I posted picture several times here. Still the same :- )))

Yes, my active timer & spin ESC

[pmackenzie]

I think the newest ones look a bit different, the gear case is milled (i.e. not round) instead of turned to make it a bit more compact.
Also anodized black.

[RandySmith]

Any comments available from WC travelers about the performance of the GB with the contra-prop.  Was it an active or passive system?  Did it seem to work well?  Was the pilot happy with the performance?  I know the pattern guys use them, and I've looks at various applications for stunt.   Curious minds want to know.

I have seen it before, my comment is  I love it, but think it would be better done with a planetary system , I would really like to see the system fly in a stunt ship and would enjoy flying it.  I would  also like  to know specs and  longevity of the  gear box, how much power it uses, max RPMs  it will  effectively turn the props.  NICE system

Regards
Randy

[Igor Burger]

but think it would be better done with a planetary system

tried, did not :- )))

[RandySmith]

tried, did not :- )))

hmm  That is interesting  you think it cannot be done in a efficient planetary setup,  Igor  do you know of anyone who has tried 2 engines together with 1 double shaft ? I know the  weight be be somewhat more, but no gear box  and maybe smaller motors
Also   do you have any information on how the  gears hold up ?

Regards
Randy

[Igor Burger]

I know 2 attempts (3 if I count my small motor for indoors) of planetary gear box. It has problem with our high rpm and turning in corners. They have usually short shaft and with combination to 2 blade props it is killing game for them. So simple solution for Pawel was that system. It is realtively new, so I see often some kind of repairing on contests, but I think sooner or later it will come to usefull stage.

I am not sure what you exactly mean - one shaft and 2 motors, if you mean contraprop with 2 motors and shaft inside other hollow shaft, then yes, I have one here close to me in box for "open projects". Axi makes them also for F3A, also another czech company PJS and I saw some on hobbyking. May be once ... but I want it less and less. Disadvantage is 2 ESCs necessary, small bearings (you know what bearings you have in ICs now imagine it must fit to SHAFT ... and what is size of one ball, what RPM it must have at 10 000 prop RPM). But they have much better sound.

Advantage of both solution is clear, lower precession and little improved efficiency, but since we can easily deal with precession with light props and Rabe rudder, I do not see good reason to use it, at least until they solve life time, and that terrible sound. However someone must push development, so I keep them fingers :- )))) They will certainly not stop, it is Pawels child and Pawel supports Krystian, so I think they both will continue, espcially when Kristian goes up every year.

[Igor Burger]

https://www.modelmotors.cz/product/double-axi-5330/

[RandySmith]

https://www.modelmotors.cz/product/double-axi-5330/

Hi Igor 
 Thank you   and  yes  I was asking about  double shaft, one inside of the  other
and  yes   I understand bearing problem, I have a small one on the  shaft of  IC engine, it is tiny so it needs  to be  replaced about every 6 to 8 hours  of  run time
Regards
Randy

[pmackenzie]

Matt P got back to me on the price. He was told 1000 Zloty for the motor, and 4000 Zloty for the gear box.
That works out to just about 1200 Euros. Not sure if that includes the props and the spinner.

To put that in perspective an F3P contra setup is about US$450

http://www.pauzuolis-rc.com/rc-shop/equipment/coaxial-thrust-systems/alexey-lantsov-coaxial-thrust-system-al-12-110-1s-16-inch-props-f3p

F3A contra $1700

https://www.precisionaeroproducts.com.au/shop/category/60-crs

Good thing that for now at least ( and unlike in F3P) the contra is not "de rigueur"

[Howard Rush]

If you use two motors, wouldn't it be less bother to separate them horizontally by at least a propeller width? 

[Crist Rigotti]

If you use two motors, wouldn't it be less bother to separate them horizontally by at least a propeller width?

Nice one Howard.

[M Spencer]

You get nice acoustics if the prop tips overlap . 

[Lauri Malila]

If you watch Alberto Soleras video of Krystians flight, his model starts and stops turning really nicely. Especially cloverleaf is quite impressive. Is that because of contraprop? Maybe.
But that noise makes me want to stuff some banana peels into his gearbox:)
Also Yuriy Yatsenko has been working some years with a contra rotating system. At the moment his way to go seems to be 2 motors. Looking forward for that. L

[proparc]

Knew this was coming.  Getting closer and closer to F3A. I think Randy Smith had this many years ago on a modified Sig Magnum.

[L0U CRANE]

Proparc,

I recall Randy mentioning his effort. AsIr, he ran the engine power to the front prop through a bearing for the aft prop, which was free turning in the prop blast. I think he said it did reduce gyro precession effects, but the doubled flywheel weight remained. ... that it did not corner easily or crisply, or words to that effect. He may have mentioned odd sound...

This is an entirely different matter.

Interesting! Contra-props were a good solution for high powered piston engine USNavy planes which needed to punch power very quickly for a go-around. In that situation, single rotation props dumped enormous torque into the airplane at the worst possible combination of low altitude, airspeed and control effectiveness.

Jet engines soon made that all moot, however. But because the early jet engines were very slow to spool up, considerable power was kept on until a sure trap was made.

[RandySmith]

Proparc,

I recall Randy mentioning his effort. AsIr, he ran the engine power to the front prop through a bearing for the aft prop, which was free turning in the prop blast. I think he said it did reduce gyro precession effects, but the doubled flywheel weight remained. ... that it did not corner easily or crisply, or words to that effect. He may have mentioned odd sound...

This is an entirely different matter.

Interesting! Contra-props were a good solution for high powered piston engine USNavy planes which needed to punch power very quickly for a go-around. In that situation, single rotation props dumped enormous torque into the airplane at the worst possible combination of low altitude, airspeed and control effectiveness.

Jet engines soon made that all moot, however. But because the early jet engines were very slow to spool up, considerable power was kept on until a sure trap was made.

NO  I really never said that,  the  rear  prop  was  driven the  exact same  way  your  automatic transmission  car is  driven, it is a  fluid drive, designed by  Scott Bair, and  made by Scott and myself. The  rear  prop went from  ZERO to near 10.00 RPM in about  1 second,  and  if you think its  not  driven, put your  finger in it while sitting on the  ground not moving, it will take it right off.
The Magnum turned  much harder than  it would before the C- props, and it was  much more of a  constant speed plane  up hill and  down hill.
There is  a video of it on YouTube ,  see  for  your self the  corner.
The  Gyroscopic Precession was  also  almost eliminated, and  it was  very bad before the  C- props.
In addition, the  maneuvers  and  turns  were  so much cleaner, it was like a totally different  airplane
It was  a  very positive  experience
The only negative was  the  rear prop bearing needed  changing every 6 hours of run time, The rear prop takes a beating from the crossing turbulences  of the  front blades  !

Randy

[Dan McEntee]

NO  I really never said that,  the  rear  prop  was  driven the  exact same  way  your  automatic transmission  car is  driven, it is a  fluid drive, designed by  Scott Bair, and  made by Scott and myself. The  rear  prop went from  ZERO to near 10.00 RPM in about  1 second,  and  if you think its  not  driven, put your  finger in it while sitting on the  ground not moving, it will take it right off.
The Magnum turned  much harder than  it would before the C- props, and it was  much more of a  constant speed plane  up hill and  down hill.
There is  a video of it on YouTube ,  see  for  your self the  corner.
The  Gyroscopic Precession was  also  almost eliminated, and  it was  very bad before the  C- props.
In addition, the  maneuvers  and  turns  were  so much cleaner, it was like a totally different  airplane
It was  a  very positive  experience
The only negative was  the  rear prop bearing needed  changing every 6 hours of run time, The rear prop takes a beating from the crossing turbulences  of the  front blades  !

Randy

     That video has been posted on the forum before, and I was there at Lawrencville when you flew it. You can see my back in the video somewhere. It made the MOST AWESOME sound spooling up and spooling down and I can vouch for the corner it had. You had to paint one side of the rear prop white so you could tach the engine or something like that, correct Randy? I would love to see and hear that in person again. Today's ceramic bearing technology might solve some of the bearing life issues, maybe??  I used to work in the torque converter rebuilding business and we built all sorts of higher stall speed torque converters for drag racers. I have often wondered how "tuneable" that fluid drive might be and what the affects would be, and how you would go about it
  Type at you later,
    Dan McEntee

[Bill Adair]

Lou,

I recall mention of that same free wheeling rear prop, but I don't recall the source of the article? Likely a magazine article.

Bill

[RandySmith]

Lou,

I recall mention of that same free wheeling rear prop, but I don't recall the source of the article? Likely a magazine article.

Bill

The  prop  did  not free wheel  until  after  the engine shut off, then it made a  unique  spinning down  sound, when the engine  was  running   the prop was  driven

Randy

[Dane Martin]

Knew this was coming.  Getting closer and closer to F3A. I think Randy Smith had this many years ago on a modified Sig Magnum.

I found a pic in the may 1991 FM mag I just ordered