Piper Twin Comanche PA 30 vs PA 39

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Piper Twin Comanche PA 30 vs PA 39

Postby bullet » Mon Dec 12, 2011 9:16 pm

How much of an advantage does the counter-rotating prop PA 39 have compared to the normally rotating PA 30 ?
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Re: Piper Twin Comanche PA 30 vs PA 39

Postby PRDT » Mon Dec 12, 2011 10:28 pm

Most say it doesn't really make a difference in performance if both engines are operational, but...
Obviously, the counter-rotating PA39 has both downgoing propeller blades (which produce the most thrust) closer to the fuselage and centre of gravity thus eliminating the problem of the critical engine which in the case of the PA30 is the left engine. I would presume the PA39's right donkey is easier to reign in when the left one is dead and may be safer/easier to maintain Vyse due to the fact that control surface deflection should be less (=relatively less drag) as thrust is closer to the centreline of the fuselage? Uncle Jim and co?

Just for interest sake, the one thing I've noticed on the PA30 is the the wing area left of the left engine and the right side of the fuselage and wing root area has more stone and sand damage (on the side of the upgoing blade). I would suspect the sandblasting when operating a PA39 off gravel would happen left of the left engine and right of the right engine saving the right side of the fuselage.

I have no idea how much more expensive that right engine and propeller will be though? Anyone?
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Re: Piper Twin Comanche PA 30 vs PA 39

Postby bullet » Tue Dec 13, 2011 6:53 am

My apologies, my initial question should have contained the following info:
The safety advantage when one engine quits is what I`m curious about between the two models and the difference in effect (if any) of whether the left or right hand engine quits.
Is the safety advantages of the PA 39 such that you would rather wait for a PA 39 to become available and ignore a PA 30 which is available or not ?
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Re: Piper Twin Comanche PA 30 vs PA 39

Postby jimdavis » Tue Dec 13, 2011 7:51 am

bullet wrote:My apologies, my initial question should have contained the following info:
The safety advantage when one engine quits is what I`m curious about between the two models and the difference in effect (if any) of whether the left or right hand engine quits.
Is the safety advantages of the PA 39 such that you would rather wait for a PA 39 to become available and ignore a PA 30 which is available or not ?


Hi Bullet. I believe that there is very little, single-engine, aerodynamic advantage in having the right engine turn the wrong way. It is meant to eliminate the "critical engine" problem but I think it was more of a marketing ploy because the Twinco got a bad rap initially for training accidents. The problem was that being the cheapest twin on the market it was the one everyone used for training, so it was bound to have more accidents. Also the FAA brought in ridiculous rule that said critical yaw had to be demonstrated at (I think) no higher than 1000' AMSL - in order to have the max possible power on the good engine. A very silly rule which killed a lot of folks. I understand they eventually did away with it.

I have tried to see the difference in the air and not had any joy. If there is a difference it is probably counteracted by banking an extra 1 or 2 degrees into the live engine.

Anyhow, I believe the short story is that contra-rotating props were more a marketing thing than an aerodynamic one.

Soes that answer your question?

Jim
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Re: Piper Twin Comanche PA 30 vs PA 39

Postby bullet » Tue Dec 13, 2011 12:54 pm

Yes, thanks Jim. I appreciate it.
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