dkroc67

I am very interested in putting contra-rotating propellers and was wondering if anybody out there is willing to share any info, pictures, words of wisdom etc... I have heard it has been done and I have seen some grainy photos out there. I have two articles on two systems one by George Miller and the other by Bill Young. Both of these articles are excellent I think George Miller's system looks a little more my style. Building contra rotating propellers has always been on my experimental/cool thing to do list. [/size] [/size]

twinman

My Feedback: (2)

This topic is often discussed in the twin engine forum..Somehow I think you maybe talking about something beyond two engines that rotate oppositely. Are we talking one engine with a gear drive system of what?
Are we talking about gas engines or glow?
Propellers are readily available from Zinger APC and Master.
Twinman

SCALECRAFT

My Feedback: (13)

Although I have never tried it, a respected scale modeler said that by chainging the position of the (by rotating) front case on a three piece 2 stroke engine, such as an old OS 40,45 FSR the rotation will reverse. When I build my HE 111 I will try this with my OS 46VF engines.

Steve

dkroc67

Sorry for the confusion it has seemed I did not make myself clear in my first post. I am looking to do contra-rotating propellers which are two propellers on the same engine going opposite directions. Such as a Convair Tradewind or TU-95 Bearcat. I am looking to have this on a glow fuel engine. I thought it would be a good topic for the scale forum since many real aircraft from the 50's and 60's had this system. I thought wouldn't it be cool to have an aircraft such as a TU-95 with real contra-rotating props? There is also something called counter rotating props, this is having two seperate engines each rotating in a different direction to eliminate torque or left turning tendencies. This is not what I am looking to do.

William Robison

My Feedback: (3)

Kroc:

Counter-rotating, or "Contra-props" by whatever name you call them, were always a lot of trouble. Not only mechanically, but aerodynamically as well. Just one small thing, the rear blades had higher pitch than the front ones as the air entering had already been accelerated by the front blades.

The reason they were used was to get more blade area without having the prop tips hit the ground. Of course the actual prop disc area was the same, the gains weren't all that great.

With a radial engine, a special version was usually built with the reversing gearbox built into the nose cover, with both shafts extending froward to mount the props.

You mentioned having a separate engine for each prop. The Bristol "Brabazon" was built that way, with eight engines driving four prop sets. The last of the large British flying boats was similar (don't remember the name, "Princess?) having ten engines, eight driving contra prop sets with the outboard engines having a single prop. Neither of these planes was a success.

So far as I know, the only successful plane with contra-props was the TU-4 Bear you mentioned, and its derivatives.

All that having been said, the gear boxes are on the market for rubber power and small electric motors. A money order for $26.00 payable to "John Regalbuto" and mailed to : Regal Solutions, 11 East Street, Georgetown, MA 01833 will get a unit shipped to you. It wont take the power of your glow engine, but you can get an idea from it, or maybe you can talk John into building a heavier one for you.

Hope this helps.

Bill.

abufletcher

I remember seeing a thread here on RCU somewhere about a guy prototyping a coaxial contra-rotating setup for a glow engine, but now I can't find it. There was even some video of it running. On the other hand, I did come across this description of a contra-rotating electric system. Scroll down a bit to find the description of Keith Shaw's 1/5 scale Bugatti racer.

http://members.aol.com/kmyersefo/amp...ec04.htm#KEITH

Chevelle

My Feedback: (2)

The idea is appealing but since the technical advantage of counter-rotating props isn't required for R/C, I think an easier solution would be to have the second propeller sit on a bearing on the shaft and just free spin in the opposite direction. A reversed pitch propeller would be required of course.

ampbomber

My Feedback: (7)

Hi,
I'm currently building a Tu-95MS, 1:18.5 scale, aprox. 107" span. I've been working on it for a year and a half. If you go to this site:
http://www.aviation.ru/contrib/dmaiorana/
you can access info on all of my projects for the last 10 years. At this site under item #41 (Tu-95MS) you will be able to see video and pictures of my prototype electric contra-rotating gear box and Tu-95 project. The gear box is running on a 5S Kokam 2100ma HC pack, drawing 35 A at 4800 RPM and having 70 oz of static thrust. I ran the initial tests with two bladed props to see if the box would survive. After the initial test sucess I made up a set of (tractor/pusher) variable pitch CF 4 blade props to the proper scale diameter for the Tu-95 model and installed the unit in my 80" H9 Cub. The Cub has 8 flights on it with the contra-rotating gear box (see video at above site). I hope to test fly late this year "in primer" and have it completed by next spring.

Also, go here:
http://www.djaerotech.com/dj_askjd/d...ntra-prop.html
to access more info on contra-rotating propellers. Search the site for more info.

Best Regards,

George

CoosBayLumber

My Feedback: (1)

One of our readers from Singapore had developed a planetary device for use in a Convair V.T.O.L. aircraft powered by a 20 or 25. He posted pictures of the item back in late 2002, and asked for if there was an interest into getting more made up. Sort of on a production run.

No responces.


Wm.

dkroc67

Thanks for all the great info so-far. I like the idea of buying the already made gear box that you mentioned Bill. Do you have anymore info on it? I have seen similar designs to the TU-95 gear box and I really like the design. Where did you get the parts from to build it? I have limited machining experience.

William Robison

My Feedback: (3)

Kroc:

All the information I have on Regal Solutions is from the March issue of Model Aviation, page 120.

Parts for your own? I can suggest Boston Gear Works, I've used them in the past. Almost any gear you might want off the shelf, and they also stock a lot of small sprockets for Gilmer (toothed) belts, and a good selection of small Gilmer belts.

If you want to play with electrics, there were some experiments in past years allowing the motor to rotate in its mounts with the rear prop screwed to the motor casing and the front prop mounted normally. One side of the motor power was carried through the frame and motor mounting, a separate brush and slip ring was used for the other side. These were conventional brushed motors, of course. Brushless could be set up this way also, but you'd need at least two brushes and slip rings. Worked by using the torque reaction of the front prop to spin the motor, and the rear prop. Advantages were having no gears at all, and the props were automatically dividing the power by the air flow controlling their rpm.

With a piston engine I suppose you could build a sort of combination radial and rotary engine to work the same way, but it would be a whale of a project, and probably not work too well. I think gears would be better.

Anyway, some things to think about.

Bill.

410524

Hi,

I built one from two Turnigy motors to fit my 7,5 scale model of the Bugatti 100.

Attached is a PDF showing how I did it.

Regards
Staffan Mansson [email protected]
Sweden

olenorski

Check this out on ebay:

FREEFLIGHT Lockheed XFV-1 VTO TAKEOFF NOTE & PLAN onCD # 290373691391

Boomerang1

Here's one available ready to go off the shelf from:

http://www.arm-rc.com/ARM/Default.aspx

I have seen video's of larger units from a big electric fly in in the US.
Electrics make everything simpler for scale models, including contra rotating props. - John.

ww2birds

My Feedback: (14)

One of the Top Gun competitors, Dave Wigley, has been flying a contra-rotating prop setup where the rear prop is driven conventionally and the front prop freewheels on bearings built into the spinner. The front prop has contra pitch, and of course rotates the other way.

It looks good, sounds good, and is really simple! The airplane, a Westland Wyvern, is absolutely beautiful. Dave is an excellent designer and craftsman, and seems like a really nice guy too. If you can track him down, I am sure he'd offer his comments on how he did it.

Dave McQueeney

ARUP

Hi- an airplane (Westland Wyvern?) was featured on the AMA magazine's cover and contact info contained therein a couple of months back. Seems the modeler had one prop 'windmilling' in front of the other. You might consider that. Good luck ARUP

EdoMcGowan

"Macchi M. C. 72, Italian aircraft designer, Mario Castoldi,reached the pinnacle of his career. Built for speed and competition in the Schneider Trophy races, this plane used one 2,850 hp Fiat A. S. 6 24-cylinder double V-12 piston engine (essentially two V-12 engines in tandem joined by a single crankshaft, each driving one of the two contra-rotating propellers via a co-axial shaft, counter rotating propeller"see:http://ehangar.com/printgallery/prin...l.php?o_id=464

David Bathe

This is how I did it 30 plus years ago using a webra speed .61.
Surprizingly home made... and trouble free.

Today, using bigger engines I'd machine a few more parts but the concept remains the same.

DenisCullinan

I've seen a bevel-gear box for contrarotating coaxial-shaft props. It looks simple enough to build yourself. (See first attached picture 1). I designed a super-simple gear train too, using only spur gears (picture 2)
Editing alert! The gear train on the right is bummed out. There's a hideous error in the rotation direction of the idler gear. Mea culpa. It win't happen again. I think.
I'm attaching a similar, but vorrect gear train by an unknown model person living somewhere in the Cloud.