Counter vs Co-Rotating Props

[Rash]

On a boat with twins, if the props spin inward you get more stern lift and speed.  Would this same rotation in a plane cause more lift?  Boat props spinning outward give you more stability, but you loose a little performance.

[bozon]

On planes that have the propellers close to the tip of the wings, outward turning props will reduce wingtip turbulence and increase the effective lift. I don't know what is the case in the V22. For the boat, this is a little different because you have an air-water boundary that significantly changes the flow, especially from above.

edit:
I just checked and V22 does indeed have outward props. Probably needs it because the wings are so short that it would otherwise loose a lot of lift to turbulence.
http://www.youtube.com/watch?v=4RkA47WPeX0&feature=related

[Rash]

True in a boat, the more you get it out of the water, the faster it will go.  But it looses stability.

[Anodizer]

Contra-rotating (single engine, 2 props) turned out not to be so useful. The weight was significant (and on the front of the plane, throwing CoG and balance off) and the added gain wasn't not very large. Later model spitfires tested contra-props but found little performance gain over the single-prop versions. Definitely not enough to be worth the headaches of maint/upkeep on them!  

But, that's all a side-point. Back to the regularly scheduled program!

Tu-95 Bear.....
One of the fastest prop planes(turbo-prop) ever made has contra-rotating props..


There are several Unlimited class racers that have single-shaft contra-rotating props..  
Here are just a few...




Everything I've read says contrary to what you're saying..   The only reason they really didn't take off was because jet-technology was becoming the mainstream..

I'd be more than obliged to read anything you can provide that says the contrary..
  

[RTHolmes]

great pic of the bear

actually looks quite elegant from that angle, apart from the chin. reminds me of

[Greebo]

Contra rotating props were a pain to develop in WW2. They often had big vibration issues due to the rear prop blades hitting the turbulence from the front set.

The racing planes get a bigger advantage from the prop than their WW2 forbears would have as they are developing a lot more power from the engine, albeit not for very long. The advantages in terms of drag, handling and the ability to transmit all that power into the air would more than offset the reliablity and weight issues.

The Bear is so fast the prop tips go supersonic and this is what limits the maximum diamater the props can be. Contra props were the only practical way the designers could transmit enough power.

[RipChord929]

The camshaft is what has to be ground in the reverse sequence, to make an engine run in reverse.  Crank throws will be in the same positions. All that is neccesary is to reverse the intake and exhaust valve sequence, and spin the engine the other way, Vroom!

Didn't the US and Russia, experiment with crescent shaped prop blades, in an effort to stop the supersonic tip problems?
Like applying the swept wing principal to propellers..  It didn't work.. Not well enough to use anyway..

RC 

[Old Sport]

An article I once read about the development of the F8B - Boeing's Navy attack a/c that was too late for WWII and beat out by the AD1 - it was fitted with a contra-rotating setup. One of the down-side issues was that the continual strobo-scopic effect of the blades crossing in the line of sight out front was nauseating to the pilots after an hour or so in flight.

[Anodizer]

great pic of the bear

actually looks quite elegant from that angle, apart from the chin. reminds me of
(Image removed from quote.)

   
Niice...

[thorsim]

those crafty germans had all that stuff solved long before that



yea i know not exactly but hey who can resist an opportunity to post a pick of a cool plane like the 335

a variant would probably made a very nifty executive prop job after the war

[smoe]

those crafty germans had all that stuff solved long before that

Everyone talks about how good the Germans are at creating things and how superior blah blah blah they are. However they never really fully understand that in the end, Germany was at the tail end of two world wars in a row, now that will be a record to beat for a very long time.

[2ADoc]

The camshaft is what has to be ground in the reverse sequence, to make an engine run in reverse.  Crank throws will be in the same positions. All that is neccesary is to reverse the intake and exhaust valve sequence, and spin the engine the other way, Vroom!

Didn't the US and Russia, experiment with crescent shaped prop blades, in an effort to stop the supersonic tip problems?
Like applying the swept wing principal to propellers..  It didn't work.. Not well enough to use anyway..

RC 

The schimtar style blades are in use now, the new C-130 has them.  So do many of the new civilian airplanes.