Counter vs Co-Rotating Props

[bozon]

For most planes counter rotating props gave no real advantage and just added mechanical complexity. Canceling torque is important almost only at low speeds and the planes were not supposed to fly slow, especially not in combat and even less in high alt combat that is more "energy" style - Do not take AH as an historical example. P-38 was somewhat "old" plane in its concept and design. The Germans for the 110 were more focused on energy fighters and wanted speed much more than slow turning ability, so did De-Havilland that built the Mosquito to fly as fast as possible as cheap as possible. It is not like P-38s did not enjoy the added stability, ease of landing/takeoffs and the rare occasions where this helped in combat - it did make it a "better" plane, but in the grand scheme of things, reliability, logistics and costs often make bigger difference than performance in a small part of the envelope the pilots were repeatedly told not to get into.

[Greebo]

The De Havilland Hornet twin engined fighter did have counter rotating props. IIRC Rolls Royce built a special low frontal area version of the Merlin with a removable reduction gearbox on the front. So the engine could be adapted from left to right rotation by just changing the gearbox and propellor.

Beautiful fighter, shame it was just too late for WW2.

[Citizen Iosef]

The P-38 design uses the relative ease of rotation direction change inherent in the V1710 Allison to good effect - the counter-rotating blades have often been stated as being a minor performance multiplier by some(probably the same that insist that the Merlin should have been shoehorned into the -38), but when the Brits bought the Lightning, they insisted upon same-directional allisons installed.  The performance was not exceptional, and Lockheed referred to these examples as "castrated" lightnings(if my memory serves).

This lends credence to the concept that counter rotational props, at least in the P-38 installation, had very real and substantial performance implications.

[morfiend]

The De Havilland Hornet twin engined fighter did have counter rotating props. IIRC Rolls Royce built a special low frontal area version of the Merlin with a removable reduction gearbox on the front. So the engine could be adapted from left to right rotation by just changing the gearbox and propellor.

Beautiful fighter, shame it was just too late for WW2.

 Yes indeed Greebo,it is a beautiful plane,IIRC DH built 1, count them,Mossie with counterrotating props.As has been mentioned,the preformance gains didnt outweigh the cost,logistics,etc.,same could be said about the dosal filet.If you look at the Hornet you'll see a dosal filet,DH knew the mossie could benefit from it's addition but the cost and disruption of assembly lines just weren't worth the trouble,instead Mossie pilots were told to be gentle on the rudder.

   

[SmokinLoon]

Its too bad the Mossi didnt get a fair shake w the counter rotating props.  Who knows how much better it would have been?   

[Ack-Ack]

The advantage of counter-rotating propellors is balancing out the effects of torque and p-factor and eliminating the problem of the critical engine.

The P-38 though was kind of special, in that it had 'reverse' counter-rotating propellors with the tops of the propellors rotating outwards.  This is what helped make the P-38 such a stable gun platform.


ack-ack

[WWhiskey]

the Allison is not that hard to "reverse" cam shaft,cam shaft drives, supercharger impellers  and starter motors, not crankshaft is the only major components that needs to be changed, if i remember right!
 i had one out of the left wing of a p-38 in an old pulling truck once.

[Karnak]

The specific reason the Mosquito did not have counter rotating propellers was because the RAF did not want to have the logistics complication of dealing with handed engines.

[SmokinLoon]

The specific reason the Mosquito did not have counter rotating propellers was because the RAF did not want to have the logistics complication of dealing with handed engines.

I had read that somewhere.  I was just stating the fact that it was a shame teh Mossi didnt get the chance to try out teh counter rotating props.  I wonder just how much faster it would have gone and just how much more capable it would have been.

[RedTeck]

and you could always get it completely wrong with counter rotating props. luckily they were able to just swap engine and carry on

"The XP-82 was to be powered by two Packard-built Rolls-Royce V-1650 Merlin engines. Initially, the left engine was a V-1650-23 with a gear reduction box to allow the left propeller to turn opposite to the right propeller, which was driven by the more conventional V-1650-25. In this arrangement both propellers would turn upward as they approached the center wing, which in theory would have allowed better single-engine control. This proved not to be the case when the aircraft refused to become airborne during its first flight attempt. After a month of work North American engineers finally discovered that rotating the propellers to meet in the center on their upward turn created sufficient drag to cancel out all lift from the center wing section, one quarter of the aircraft's total wing surface area."

[Karnak]

I had read that somewhere.  I was just stating the fact that it was a shame teh Mossi didnt get the chance to try out teh counter rotating props.  I wonder just how much faster it would have gone and just how much more capable it would have been.

It wouldn't have been any faster, just a bit easier on the pilots.

[thorsim]

i often wonder why they just didn't just flip the engines to counter rotate the props for the advantages they give an airframe.

col is the p-factor effect different when the torque is not on the center line of the airframe?

[Masherbrum]

i often wonder why they just didn't just flip the engines to counter rotate the props for the advantages they give an airframe.

col is the p-factor effect different when the torque is not on the center line of the airframe?

Flipping an engine, will change that particular engines Center of Gravity and would most likely have a negative effect on the craft.   

[W7LPNRICK]

But it does matter.  With both props turning the same direction (clockwise from cockpit) having only the right engine will cause more control problems than having only the left engine due to p-factor.  It's the down moving blade being farther from the center of the airplane that is the issue...or at least that's what they teach when you get the multi rating. <G>

I agree. I have seen this with B-26's with only Rt engine very difficult to stay airborn. 

[Krusty]

Flipping an engine, will change that particular engines Center of Gravity and would most likely have a negative effect on the craft.   

Flip the engine over and it still spins the same way. Roll a plane until it's inverted and that prop still turns the same direction!

 

To get it spinning the other way you've have to spin it around to a pusher. THAT's a setup (left push, right pull) I don't even wanna contemplate!