Counter Rotating Props
 

Hi,

Was wondering if anyone could point me in a direction of a website which has a diagram of the arrangement of a counter rotating prop assembly (as one unit rather than a single prop on each wing rotating in different directions :D)? Just curious about the gearing arrangements.

Thanks!

I was partly involved in some research on contra-rotating props in the 80s, mainly looking at the acoustics and aerodynamics.

The only examples we could get for flight testing were the Fairey Gannet and the Avro Shackleton.

The Gannet had twin Mamba engines driving into a co-axial hub arrangement, and the propellers could be varied in pitch and RPM independantly of each other. If one engine failed you simply stopped and feathered its propeller.

The Shackleton I believe uses a planetary gear arrangement between the Griffin engine and the propeller and the propellers are geared to rotate at the same speed in opposite directions.

Unfortunately I didn't take any interest at the time in the transmission arrangements, but I hope this is of some use.

You might do a search on Google for an Americn experimental military aircraft nicknamed Pogo (can't remember the official designation, TGIF). VTOL, mid-50s. If I remember correctly The project was shortlived, as were the aircraft.

Isn't there a Russian long-range bomber, swept wing ("Bear"?) with counter-rotating props?

Good luck. I'm not an aerodynamicist but it just doesn't seem logical to whack away at the air one way and then, 30cm back, whack away in the other direction. And the gearing must be diabolical.

Thanks guys, will do some surfing. :cool:

CCCP
 

Back in the days when there were design proposals for unshrouded turbofans, Flight International published a proposal for the Collaborative Carbonfibre Contra Propfan, perhaps the April 1 issue:D

(For the Cyrillic-challenged, CCCP is the Russian acronym for the once USSR)

props
 

V B
There have been several a/c mentioned which have contra-rotating props, Shackleton, Tu-95 Bear,being the most notable. A few later mark Spitfires /Seafires also had Griffon engines with contra-props, also the Martin-Baker MB-5.A replica is being built in the USA at present,and "Red Baron",the racing Mustang also had a Griffon fitted.I recall that there was also an Italian racer which had two engines in the fuselage,one in front of the cockpit and one behind driving two props through a common g/box.
Contra rotating props would technically be props driven by the engine through a common g/box to give the opposite rotation.
Counter rotating props can be either conventional twins (usually) with each prop turning in the opposite direction of rotation,and seen from the cockpit props rotate (top blade) inwards , or outwards from the fuselage. The former would be the DH Hornet(the fastest fighter twin-piston ever,and best looking; and the P-38 would be one of the latter. I think some Piper/Cessna/Beech twins also have counter -rotating props as well. There is also a thread on "Aviation Nostalgia"- "more than 4 engines" which has some pictures of other a/c with multiple engine/prop combinations...:p

just a little more on props, as most of you will probably already know....... but here goes.....the prop has to absorb the engine power, the bigger the engine the bigger the prop and or more blades, ok so far?... but..... the blades can only be of a certain length because of the tips speeds, ie if they approach the speed of sound you get all sorts of aerodynamic problems, so add another blade he says, then the problem is when the blades are too close together the air is too disturbed for the next blade to obtain any 'lift'. next answer was the counter rotating prop but by then the gas turbine eng was taking over........the rest is history.
cheers guys, us girls aint all dumb blondes;)

Contra-rotating props.
 

Slightly off the subject, but can anyone explain the term "critical engine" in the context of a twin turbo-prop. I believe that in the situation of an engine failure one of the engines can be more of a problem than the other.

critical engine
 

Flysundone

If you have only one engine---that`s the critical one!
If you have two c/l engines (Cessna337/o-2),then I think maybe the rear one is the critical one,as the performance on that engine alone is better than on the front one alone(less drag from prop -wash over fuselage( but I await correction as I`ve not flown that type).
If you are in a twin or multi-engined a/c (piston or turbo-prop) then the critical engine will be the one that has prop blades that( viewed from the rear) have their down-going blades on the side nearest the aircraft fuselage.
The reason it is "critical" is that in the event of failure,the engine(s) on the other wing have their thrust-lines to the right of the engine centre-lines ,and therefore apply a greater yawing moment "with" the dead engine,which can limit the a/c`s control ,both on the ground and in the air. The reason the thrust is greater is due to the relative airflow angle on the prop blade when inclined,produces greater thrust,and this will be also offset outboard,producing greater yawing moment,which must /will show as a greater rudder deflection,or foot-force to overcome. For certification purposes limit loads are between 150-180 lbs depending on the a/c`s Certification Authority/ age. On some a/c ,failure of a critical engine may require a reduction of power on the live engine to maintain control-Canberra PR-9?
Referring to my earlier post,the DH Hornet had handed engines,(both turning "inwards"), to prevent the critical problems of the Mosquito, as also a Naval a/c doesn`t want to be going sideways on a deck t/o; so, it didn`t have a "critical"-per se; the P-38 Lightning prototype also had a similar configuration,but during flight testing it was found that there was a lot of fuselage buffeting due to the direction of prop rotation,so the engines were swopped around,and it worked okay.So,one could say the a/c has two "critical" engines,but it does fly well on either one and does not have a significant handling problem...Must have another glass of "vino collapso " after all that!!;) ;)

Contra-rotating props
 

Sycamore,

thank you for a most eloquent reply.

A couple of things I picked up here and there:
- The Fairey Gannet had two engines with their own props, so all you needed was some sort of 'mixing unit' to get the power to the co-axial shafts. A similar system must have been used on the Macchi MC72 (the italian racer), this airplane had two V12s bolted end to end with seperate twin bladed props. I'm guessing they had seperate shafts as they probably weren't up to keeping a V24 engine running smoothly in those days.
- On an airplane like the Shack or a contra-prop Spitfire (one of which is flying again in the US!) you've got one engine, the output of which is split into two co-axial shafts in the gearbox, each with their own prop. You also need something called a 'translational bearing' (if my memory is correct) to transfer the prop pitch setting from one prop to the other. There have been instances of this piece of kit failing and the whole unit (all six blades) going to flat pitch. No matter what amount of power you can get from your engine in such a situation, you'll be going down fast! After 'Red Baron' another Mustang was fitted with a contra-prop Griffon: 'Precious Metal', this one was once belly-landed after such an incident. The aircraft was repaired though and is once again active at Reno.

Indeed the TU-95 'Bear' has contra-props too. Also the Bristol Brabazon, the Saunders-Roe Princess, MB-5 and Koolhoven FK56 (can someone find a photo on the net of that one, just to check if I got it right! :D )

Some info. and great pictures of "Precious Metal" in action sporting her fantastic, polished contra props at these websites.

What a noise!.



http://www.aafo.com/racing/2001/race38/

http://www.imagesoflightonline.com/airracers/r38pm/a2a/

Back in the early 80's, Boeing did some data gathering on contra-props with a Gannet (until they ran out of tyres) - they were doing the Unducted Fan (UDF) at the time. I was told by a denizen of their Advanced Project Office that the real advantage of the twin props was that it reduced losses due to swirl in the airflow - if memory serves saving up to 5%.

There's a Double Mamba with gearbox at the Fleet Air Arm Museum at Yeovilton - a check of their website might provide what you want. Otherwise try looking up TSAGI, the Russian agency that did the Bear prop developement.

Thanks guys and gals, great stuff! :)

Contra Props
 

Try the Shackleton Web Site for more information