Re: Contra vs Counter Rotating Props

John Goddard Tue Apr 24, 2012 12:34 pm

Cz10 wrote:I just sent her an email for 2 - for the two Venom II I just received to go on my Sterling P-38 that will be in this paint

Guess I'll need a couple of red rubber spinners too.....

Wish I could source a pair of 3 bladed props that were the same shape in both rotations...

Surely you want contra rotating props on a twin?
Very Happy

nitroairplane Tue Apr 24, 2012 12:41 pm

John Goddard wrote:
Cz10 wrote:I just sent her an email for 2 - for the two Venom II I just received to go on my Sterling P-38 that will be in this paint

Guess I'll need a couple of red rubber spinners too.....

Wish I could source a pair of 3 bladed props that were the same shape in both rotations...

Surely you want contra rotating props on a twin?

"Wish I could source a pair of 3 bladed props that were the same shape in both rotations"
Yeah that's what he said lol.

fit90 Tue Apr 24, 2012 2:00 pm

I prefer counter rotating to contra rotating. Contra rotating is typically faster but counter rotating offers greater directional control if one engine tanks.

Cox International Tue Apr 24, 2012 2:04 pm

fit90 wrote:I prefer counter rotating to contra rotating. Contra rotating is typically faster but counter rotating offers greater directional control if one engine tanks.

???

Either a prop spins left or right.... or is there more to this?

nitroairplane Tue Apr 24, 2012 2:15 pm

Cox International wrote:
fit90 wrote:I prefer counter rotating to contra rotating. Contra rotating is typically faster but counter rotating offers greater directional control if one engine tanks.

???

Either a prop spins left or right.... or is there more to this?

No one you have the you swap the LH and RH engines around and its different.
So both props spinning inwards or both spinning outwards.

fit90 Tue Apr 24, 2012 2:20 pm

On counter rotating props the props spin inward. On contra rotating props they spin outward. When they spin inward then if one engene fails the effective thrust line of the operating engine is on the inside of the engine. On contra rotating the effective thrust line is on the outside of the engine.

fit90 Tue Apr 24, 2012 2:23 pm

Sorry for the confusion. The props are either left or right handed. The direction they spin relative to the aircraft center line makes them either contra or counter rotating.

Cox International Tue Apr 24, 2012 2:48 pm

... um yes.... I misunderstood that Smile

However, still one prop spinning left and the other right.

nitroairplane Tue Apr 24, 2012 2:49 pm

Cox International wrote:... um yes.... I misunderstood that

However, still one prop spinning left and the other right.

Yes

Ivanhoe Tue Apr 24, 2012 3:37 pm

I've never lost track of a thread so fast as this one! Surely "Contra" rotating and "Counter" rotating are simply two ways of saying the same thing?? i.e, the props rotate in opposite directions?
Or am I missing some deep technical point here??

Huh...

nitroairplane Tue Apr 24, 2012 3:40 pm

Ivanhoe wrote:I've never lost track of a thread so fast as this one! Surely "Contra" rotating and "Counter" rotating are simply two ways of saying the same thing?? i.e, the props rotate in opposite directions?
Or am I missing some deep technical point here??

Counter is inward contra is outward.

nitroairplane Tue Apr 24, 2012 3:45 pm

A sketch that may help
Contra vs Counter Rotating Props U2NbR

fit90 Tue Apr 24, 2012 9:40 pm

A picture is worth a thousand words.

Good job Indra,

Bob

fredvon4 Wed Apr 25, 2012 9:03 am

Does the red 8cc stunt tank provide some Coriolis effect to the propellers? confused

WingingIt74 Wed Apr 25, 2012 10:13 am

nitroairplane wrote:Counter is inward contra is outward.

I don't think that's right Indra...

Contra-Rotating Props
http://en.wikipedia.org/wiki/Contra-rotating_propellers

Counter Rotating Props
http://en.wikipedia.org/wiki/Counter-rotating_propellers
Contra vs Counter Rotating Props PiperPA-44-180SeminoleC-FLZJ02

Contra vs Counter Rotating Props PiperPA-44-180SeminoleC-FLZJ02

fit90 Wed Apr 25, 2012 10:27 am

For the Seminole in the second picture, and most conventional twin engine aircraft, counter rotating props spin inward and contr rotating props spin outward.

WingingIt74 Wed Apr 25, 2012 10:30 am

fit90 wrote:For the Seminole in the second picture, and most conventional twin engine aircraft, counter rotating props spin inward and contr rotating props spin outward.

That's not correct, contra is a counter rotating stacked props, as shown on the Spitfire.
Counter rotating, there are inward and outward couter rotating props. The Seminole has inward counter rotating props.

WingingIt74 Wed Apr 25, 2012 10:44 am

The P-38 is a good example of a Outward Counter Rotation.

WingingIt74 Wed Apr 25, 2012 10:57 am

fit90 wrote:I don't know anything about the stacked props like those pictured on the Spitfire. On general aviation multi engine planes with the engines oriented left to right (or right to left) planes such as the Seminole and later Senecas have counter rotating props (they spin inward) to aid in single engine directional control while planes such as early P-38's had contra rotating props (spinning outward) to give an increase in speed, but at the expense of single engine contrability. I am not sure if counter rotating and contra rotating are listed in CFR 14.1 but they are definitely used in light general aviaton aircraft certified flight manuals. However, words and terms that are only a small step above "aviation slang" have found their way into flight manuals so this might just be different usages of the same terms.

Bob

Yes, but in those manuals or whatever, it is used incorrectly. Contra is not Outward Counter Rotating Props.

fit90 Wed Apr 25, 2012 11:10 am

Help me out here...

By definition, counter rotating props are any pair (or more) of props that spin in different directions, either way, but spin on different shafts (points of rotation). Contra rotating propellers are two or more props that spin in different directions about the same point? Sounds simple enough once I unlearn decades of FAA lingo.

Kind of like the old FAA Advisory Circular AC 61 (I think) "The Flight Training Handbook" and its definition and description of lift and how it is created. That should be a whole new thread.

Thanks for the patience,

Bob

WingingIt74 Wed Apr 25, 2012 11:18 am

now you got it

fit90 Wed Apr 25, 2012 11:18 am

Cool!

Thank you

Ivanhoe Wed Apr 25, 2012 11:25 am

nitroairplane wrote:
Ivanhoe wrote:I've never lost track of a thread so fast as this one! Surely "Contra" rotating and "Counter" rotating are simply two ways of saying the same thing?? i.e, the props rotate in opposite directions?
Or am I missing some deep technical point here??

Counter is inward contra is outward.

Well, that's news to me!

WingingIt74 Wed Apr 25, 2012 11:28 am

Ivanhoe wrote:
nitroairplane wrote:
Ivanhoe wrote:I've never lost track of a thread so fast as this one! Surely "Contra" rotating and "Counter" rotating are simply two ways of saying the same thing?? i.e, the props rotate in opposite directions?
Or am I missing some deep technical point here??

Counter is inward contra is outward.

Well, that's news to me!

See my posts above...

WingingIt74 Wed Apr 25, 2012 11:39 am

Not all twins (or multi-engine aircraft) have counter rotating propellers.
Contra vs Counter Rotating Props Dehavilland-dh98-mosquito

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