Educate me on countra rotating props.

GregP said:

If you can feather a coaxial prop, it is independent from the other one with no mechanical interconnection. Hence, it is NOT a cotra-prop, just a co-axial prop.

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Contra-rotating propellers


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For contra-rotating marine propellors, helicopter rotors and turbine fan blades, see Contra-rotating.

Not to be confused with counter-rotating propellers.





Contra-rotating propellers on a Rolls-Royce–Griffon–powered P-51 unlimited racer
Aircraft equipped with contra-rotating propellers, also referred to as coaxial contra-rotating propellers or high-speed propellers, apply the maximum power of usually a single piston or turboprop engine to drive two propellers in contra-rotation (rotation about the same axis in opposite directions). Two propellers are arranged one behind the other, and power is transferred from the engine via a planetary gear or spur gear transmission. Contra-rotating propellers should not be confused with counter-rotating propellers—airscrews on different engines turning opposite directions.

According to several former F-15 drivers, the Bear can out accelerate an F-15 for several miles.

A contra-prop is different from a coaxial propeller. Both spin in opposite directions, but a contra-prop has mechanical gearing between the props to cancel torque exactly. A coaxial propeller spins the propellers in opposite directions, but there is no mechanical interconnection and you can spin them at different speeds if you want, or even stop one of them.

GregP said:

According to several former F-15 drivers, the Bear can out accelerate an F-15 for several miles.

A contra-prop is different from a coaxial propeller. Both spin in opposite directions, but a contra-prop has mechanical gearing between the props to cancel torque exactly. A coaxial propeller spins the propellers in opposite directions, but there is no mechanical interconnection and you can spin them at different speeds if youw ant, or even stop one of them.

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Contra-rotating propellers; From Wikipedia, the free encyclopedia;Not to be confused with counter-rotating propellers.
Contra-rotating propellers on a Rolls-Royce–Griffon–powered P-51 unlimited racer
Aircraft equipped with contra-rotating propellers, also referred to as coaxial contra-rotating propellers or high-speed propellers, apply the maximum power of usually a single piston or turboprop engine to drive two propellers in contra-rotation (rotation about the same axis in opposite directions). Two propellers are arranged one behind the other, and power is transferred from the engine via a planetary gear or spur gear transmission. Contra-rotating propellers should not be confused with counter-rotating propellers—airscrews on different engines turning opposite directions.

Contra-rotating; From Wikipedia, the free encyclopedia;
A Soviet Ka-32 helicopter with coaxial contra-rotating rotors, in 1989
Contra-rotating, also referred to as coaxial contra-rotating, is a technique whereby parts of a mechanism rotate in opposite directions about a common axis, usually to minimize the effect of torque. Examples include some aircraft propellers, resulting in the maximum power of a single piston or turboprop engine to drive two propellers in opposite rotation. Contra-rotating propellers are also common in some marine transmission systems, in particular for large speed boats with planing hulls. Two propellers are arranged one behind the other, and power is transferred from the engine via planetary gear transmission. The configuration can also be used in helicopter designs termed coaxial rotors, where similar issues and principles of torque apply.

Contra-rotating propellers should not be confused with counter-rotating propellers, a term which describes non-coaxial propellers on separate shafts; one turning clockwise and the other counter-clockwise. Like the P-38 and tandem-rotor helicopters such as the CH-47 Chinook also use a counter-rotating arrangement.

The efficiency of a contra-rotating prop is somewhat offset by its mechanical complexity. Nonetheless, coaxial contra-rotating propellers and rotors are moderately common in military aircraft and naval applications, such as torpedoes, where the added maintenance cost is not a primary concern.

The point of these two, nearly identical articles is that all installations with two props on one axis are both Contra-Rotating and Co-axial Contra Rotating. Only when the two props are on different axii are they "Counter Rotating" Props.

You believe Wiki if you want. We are in the business and have built a Spitfire with a Contra-prop setup from a Shakleton. It was at the direction of the owner. Thankfully it has been converted back to a 5-Bladed Rotol at this time, so is representative of a real Spitfire mark now. There WERE real Spitfires with contra-props, but the one we converted wasn't one of them.

Contra-props are mechancially geared so if one moves, the other moves. An example would be the Avro Shakleton or the Soviet Bear bomber.
Coaxial counter-rotating props are NOT geared to one another. An example would be the Bugatti Model 100 racer in the EAA Museum in Oshkosh.

Simple counter-rotating props are, indeed, like the P-38 or other twins with props turning in opposite directions.

GregP said:

According to several former F-15 drivers, the Bear can out accelerate an F-15 for several miles.

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I spent three years in the "Peace Sun" Program in Saudi Arabia and knew and conversed planes with dozens of them on a weekly, or by weekly basis. I have had several check rides in the back seat. We also played cards and BBQ'd with the Brits who were there for Their Military Support Mission. None of them thought the Bear was anything but a slug. I think they were pulling your chain.
At that time, early to mid-'80s, the F-15 was the fastest accelerating aircraft in the world! With M0.8-1.2 in roughly half the time of the EE-Lightning and 3/4ths the time of the F-104. Unlike all other AC, it could take off in less than 400M pull up to the vertical before the gear was all the way up and then accelerate beyond the Mach in under 55 seconds while in the vertical climb, with the full CL Tank! While in formation shooting Pictures from the T-38, the F-15 would go from 300 knots to 500 in under 10 seconds, WO using the burner! There was simply no quicker plane on the planet.

SHOOTER said:

I spent three years in the "Peace Sun" Program in Saudi Arabia and knew and conversed planes with dozens of them on a weekly, or by weekly basis. I have had several check rides in the back seat. We also played cards and BBQ'd with the Brits who were there for Their Military Support Mission. None of them thought the Bear was anything but a slug. I think they were pulling your chain.
At that time, early to mid-'80s, the F-15 was the fastest accelerating aircraft in the world! With M0.8-1.2 in roughly half the time of the EE-Lightning and 3/4ths the time of the F-104. Unlike all other AC, it could take off in less than 400M pull up to the vertical before the gear was all the way up and then accelerate beyond the Mach in under 55 seconds while in the vertical climb, with the full CL Tank! While in formation shooting Pictures from the T-38, the F-15 would go from 300 knots to 500 in under 10 seconds, WO using the burner! There was simply no quicker plane on the planet.

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PS. Just for your information from open source Wiki;
"Private ownership[edit]
According to the FAA there are 2 privately owned Su-27s in the U.S.[37]

Two Su-27s from the Ukrainian Air Force were demilitarised and sold to Pride Aircraft of Rockford, Illinois, USA. Pride Aircraft modified some of the aircraft to their own desires by remarking all cockpit controls in English and replacing much of the Russian avionics suite with Garmin, Bendix/King, and Collins avionics. The aircraft were both sold to private owners for approximately $5 million each.[38]" Neat, who knew you could by such a neat plane for only 5M$?

Yeah, I guess it IS you Neoconshooter. Hi Stuart.

The F-15 drivers I have met say the Bear is one fast accelerating animal from 200 to 400 mph or a bit faster.

What the Russian crews do is leave the props in coarse pitch, come up on the poiwer to full, and then snap the pitch to fine. They walk away from the F-15's because the F-15 drivers aren't expecting it and, by the time they respond, the Bear is already several hundred yards away and opening the distance rapidly. Now, if the F-15 guys KNEW the Bear was going to play with them, it might be a different story. But they don't and so get caught flat-footed. In such a manner, they regularly embarass the F-15's ... just a bit, because they KNOW when they take off that they are merely giving the F-15 a great shot at the Bear from behind ina wartime situation. It is only a peacetime game.

When the F-15 came out, it WAS the fastest-accelerating plane on the planet. When the Su-27 came out, that was no longer true. It wasn't far behind, but WAS behind and still is against an Su-27/33/35/37 and maybe even the Su-34. I can't say for sure, and nobody else can either except any pilots who tried a drag race side by side. Who knows, maybe somebody HAS.

Just to make the point, propeller aircraft in general accelerate faster than jets under almost all circumstances because the engines change RPM rapidly and the props also change pitch rapidly. Jets have "fixed-pitch props" (turbine blades) and don't change rpm rapidly. Yes, the jets can go faster, but no, they usually aren't really good at changing speeds rapidly unless the engines are already up to speed, as in a takeoff in full afterburner where the engine(s) is already at high power when the brakes are released.

GregP said:

Just to make the point, propeller aircraft in general accelerate faster than jets under almost all circumstances because the engines change RPM rapidly and the props also change pitch rapidly. Jets have "fixed-pitch props" (turbine blades) and don't change rpm rapidly. Yes, the jets can go faster, but no, they usually aren't really good at changing speeds rapidly unless the engines are already up to speed, as in a takeoff in full afterburner where the engine(s) is already at high power when the brakes are released.

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I think it is more to do with the fact that props work better at low speeds than jets. Jets are more efficient at higher speeds.

Contra-rotating propellers should not be confused with counter-rotating propellers

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"Contra" is Spanish/Latin for... wait for it... "counter", meaning opposite. The Contras in Nicaragua were not named as such because they supported the revolution.

Regarding the nomenclature for "dual-row" propellers, the most helpful thing I have read was in the "Duplex Aircrews" article in Flight magazine on 26 December 1946 (part 1) and 2 January 1947 (part 2).

Technically, words can have multiple meanings and different words can have the same meaning. Counter, contra, coaxial—it all begins to be similar and the root words mean basically the same thing. The Flight article states that coaxial props are two rows of independent blades, each being a separate unit. Contra-rotating props are two rows of blades that are dependent on each other and making one single unit. The latter could also be referred to as "coaxial contra-rotating propellers" if one likes to use extra words.

Note from Flight:


Coaxial:
MC.72
Bugatti 100P
Arsenal VB 10
XB-42
Fairey Gannet
Brabazon
P.24-powered Battle
Etc:


Contra-rotating:
Typically, a single engine CR application, like the Griffon


In addition, the Joint Fighter Conference at NAS Patuxent River, MD in October 1944 had a few interesting things to say about coaxial/contra-props. If I remember correctly, they stated a theoretical gain in efficiency of around 5% (keep in mind this is 1944 technology here). But in practice, they saw no discernible gain between aircraft that had CR props and those that did not. The big question was if the added weight and complexity of the CR units was worth eliminating the torque factor. It was felt that in carrier operations, the answer was most definitely yes, especially how piston engine power and prop size were continuing to increase.

It was felt that as engine output continued to rise, CR props would be needed to properly transfer that power into thrust. The prop tips need to be kept under the speed of sound (unless you are the Russians), so the prop could only be so big. With more power comes the need for more prop area. If you can't make the props longer, then maybe you can add another blade. But at some point, you can no longer fit another blade on the same hub, so you need another hub. And now you have a "Duplex Airscrew" (nod to the Flight article).

As an afterthought, I have uploaded the Duplex Airscrews article from Flight.
View attachment Flight 1946 Duplex Airscrews.pdf

There was a nice display of the Mamba at the Nowra FAA museum I visited recently. Pressing a display button, the port turbine "whirls" and drives the front prop. The starboard turbine drives the inner prop...