Counter-Rotation

[MuddyFox]

Hello,

Are there such a thing as gas powered engines that rotate in the opposite direction of traditional engines? I'm looking to build a craft that utilizes counter-rotating props. Any information you could give me on this subject would be appreciated.

Thank you.

[Dave Robelen]

Hi Muddyfox,
The counter rotating prop setup is driven by a pair of co-axial gearboxes on the front of a single engine. A few scale modelers have built this type of drive with success, but I have never seen a commercial offering.
Regards, Dave

[Bill TEller]

Dave is talking about 2 props on one shaft turning opposit
you sound to me like you want counter clockwise rotation
.... all reed valve & all piston port intake glow model engines will run either way ...you must always check witch side the propwash is coming from before you turn them loose . Cox engines with
the air intake in the rear thru the fuel tanks have reeds ,piston
ports have gone the way of the dodo ithink the old Ohlsson &
Rice 23 &29s are the last I can Remember They changed to
front rotors about 1952 or so. a lot of the string trimmer derived gas engines also have reeds & will run backward
if you can get the ignition to fire at the right side of tdc & work rotating backward.

Good Luck
Bill Teller

[MuddyFox]

Does anyone know of a decent online store where I can buy these types of engines (reed) at good prices?

Are there engines of this type that are strong enough to do aerial acrobatics?

Thanks.

[Dave Robelen]

Hi Muddyfox,
Several of the major engine manufacturers will sell a special crankshaft for the larger engines (.40-60) that reverse the timing for opposite rotation. I would check with Tower Hobbies ( OS, Super Tigre) and Horizon hobbies. The reed type engines that are available today are too small for aerobatics.
Rgards, Dave

[MuddyFox]

Thank you much!

[MuddyFox]

Ok it's me with more questions.... :p

How do engines react to being in the verticle position for extended periods of time? Do they flood, fail, etc?

I checked out tower hobbies, and noticed three engine types for sale. Glow fuel, gas, and electric.

What is the difference between glow fuel and gas? I live out in the middle of the Pacific, and will not have access to exotic fuels, but do have access to gas.


I'm also looking for an engine powerful enough to not only hang a craft on its prop but also climb out of the hang. I saw this done once.

Maybe I should describe what my goal is so I can get more specific advise. I'm aiming to create a four engine rotor-craft that will serve as a test bed for a flight control/navigation suite. The props will be oriented so that their rotation plane is horizontal. They will provide vertical lift. Thus the need for counter-rotation and verticle mounting. A helicopter is not suitable for my needs.

Thanks!

[Dave Robelen]

Hello MuddyFox,
Basically the difference between glow fuel and gas is that glow fuel is a premixed fuel consisting of alchohol, a lubricant, and nitromethane. It is generall known and sold as "model airplane fuel". There are a variety of specific blends, and a number of sippliers. There may well be one that would ship to you. Gas engines for our purposed relatives of either weedeater or chaisaw engines. They all run on a mixture of gaoline and 2 cycle motor oil.
There are large displacement versions of both types of these engines. The gas engines have more selections in terms of size and power, and, while you probably could not find one that runs in the opposite direction, many have the shaft sticking out both ends so that you could mount the engine opposite from normal to get reverse rotation. The only downside to the gas engines is that they are relatively heavy for their thrust in the more economical versions. There are some really powerful custom built gas engines that sell for well over $1000 ea. and up that are quite a bit lighter for their power. A good starting source would be Desert Aircraft. They manufacture a line of these engines. A search with www.google.com should turn up some options.
Regards, Dave

[Bearcat_Pilot]

Hi MuddyFox,
Just how big is this rotor-craft you are aiming to build? If it is small enough you might want to consider electric motors. These will spin in either direction depending on the battery circuit and are supposed to put out the same rpm. I don't know enough more about them to say anything more but not having to buy special engines could save you some money.
Whichever way you go, keep us posted.

[Dave Robelen]

Hi Muddy Fox,
Bearcat-pilot has a very good point. With the modern brushless electric motors, you can get some very powerful motors at a reasonable weight. If you have plans for varying the rpm's of the motors as a control function, I would strongly lean toward the electric option. It would be really difficult to match the throttle response of four seperate fuel type engines with any degree of precision.
Regards, dave

[MuddyFox]

I've considered electric, which would be quite favorable to my needs. My primary concern is thrust vs engine/fuel weight and fuel concerns.

I'm not sure about how long I could fly four engines off a fuel source vs flying four electrics off of one power source. Pound for pound vs flight time, which is the better choice? Electric is certainly the more economical.

Thanks

[Dave Robelen]

There is more to consider with a powered lift vehicle that has miltiple props than the thrust/weight issue. If this is any sort of a research effort, you may find the fuel engine option to be too fussy keeping multiple engines tuned over a range of rpm's. Each engine will have a slightly different response to the position of the carburetor arm. A lot of time can go into the tuning process.
Electric offers pretty much assured steady running over long periods with very predictable thrust characteristics. While I was working at NASA we did quite a bit of powered lift work, much of it multi engine. I don't know how far your machine needs to roam to do it's thing, but we made good use of an umbilical cord for most of the flights. This cord brought in electricity, and was also the connection for a data system that measured a number of parameters on the vehicle and transmitted the data to a ground computer. This can be accomplished with telemetry, and the machine flown on battery, but you may have other options.
Regards, Dave

[MuddyFox]

The umbilical cord is out. The vehicle will have a telemetry stream linked to various sensors and the flight control system. The electronics suite alone will be power instensive, which is why I was considering fuel engines. Perhaps I should consider a helicopter for this project. The rotorcraft would be more stable however.

I'll research the electric option. Unfortunately some manufacturers don't provide enough information on their products... at least from what I saw on Tower Hobbies.

[Dave Robelen]

Hi,
Quite a few of the major players in the engine field have their own websites with more engineering data. A quick search with www.google.com will turn up a few sources. You might also take a look at info on the small UAV's where you might find more meaningful powerplant data. The hype in Tower Hobbies is just a teaser for the seriously interested.
Regards, Dave