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  • Member since
    November 2005
Dumb question category
Posted by Anonymous on Tuesday, June 10, 2003 8:01 AM
I woke up in the middle of the night thinking about this...no, i dont have a wife to bug at that time of the night. Do the propellers on a twin engine plane both rotate the same direction? I got to thinking, wouldnt that create a terrible torque if they did. Sorry for being so stupid
  • Member since
    November 2005
Posted by Anonymous on Tuesday, June 10, 2003 8:30 AM
I think that most do, although some do have counter rotating props. The P-38 was one that had counter rotating props which is why pilots didn't have to worry about the torque. Don't worry though; in my opinion the only "dumb" questions are the ones that are never asked.
  • Member since
    December 2002
  • From: Canada / Czech Republic
Posted by upnorth on Tuesday, June 10, 2003 8:50 AM
I've seen a few pictures of S-2 Trackers with props that rotated in the same direction, I've also heard that the Tracker had some sort of powered rudder assist system to help keep the plane flying in a straight line against the torque.
  • Member since
    November 2005
Posted by Anonymous on Tuesday, June 10, 2003 8:52 AM
That's not a stupid question at all. Having flown aircraft with both types of engines, the only time the torque is a problem is when the left engine fails. Then, because of something called P-factor, the right engine creates alot of torque and the airplane wants to turn left.

Good question!
  • Member since
    December 2002
  • From: Lyons Colorado, USA
Posted by Ray Marotta on Tuesday, June 10, 2003 9:08 AM
Virtually all multi-engined aircraft's propellors rotate in the same direction.
The P-38 is an exception. upnorth---you're right about the STOOF. Both engines
rotate in the same direction. The aircraft has a system called "stab-aug"
it is a two part rudder which gives additional rudder control should an engine fail.
Ray

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  • Member since
    November 2005
Posted by Anonymous on Tuesday, June 10, 2003 10:02 AM
thanks for the info guys...at least i was a little knowledgeable about the torque. I am thinking about putting the photo etch "spinning props" on a PBY, and wondered about the spin direction;
  • Member since
    February 2003
  • From: Saratoga Springs, NY
Posted by Jeeves on Tuesday, June 10, 2003 11:53 AM
Just asked in a PBY forum I know of about your question....I'll let you know when I do ;)
Mike
  • Member since
    December 2002
  • From: Lyons Colorado, USA
Posted by Ray Marotta on Tuesday, June 10, 2003 11:54 AM
Counter-clockwise when viewed from the front.
Ray

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  • Member since
    November 2005
Posted by Anonymous on Tuesday, June 10, 2003 4:04 PM
Not a dumb question since i was thing that about 2 day ago !!!! when i decided to walk next door to a hobby store where the guy flys B-17's and he told me the same as thies fellows.
  • Member since
    November 2005
Posted by Anonymous on Tuesday, June 10, 2003 4:51 PM
heck, keep the questions coming! I think we should have more discussions like this.
  • Member since
    November 2005
Posted by Anonymous on Tuesday, June 10, 2003 6:09 PM
Heres a few more thoughts. P factor occurs on any rotating propeller no matter if its a single, twin, normal or counter rotating prop. The downward moving blade will always produce more thrust than the upward moving blade. This is due to the relationship between the angle of the blade and the angle of attack of the aircraft.

Torque is the twisting motion that is created by a spinning object. The effects of torque are always in the opposite direction of the spinning object. That is why any american single engine prop fighter always rolls to the left faster than to the right. Normal direction of rotation for american aircraft is clockwise as viewed from the pilots seat. Most other countries use counter clockwise rotation so everything is opposite.

Torque and P factor are counteracted partly by the design of the aircraft. Here are some of the ways. Counter rotating props, engine thrust line offset a few degrees off center, vertical fin offset a few degrees off center. Even with these, you still need a boot full of right rudder during takeoff in most aircraft.

One last thing...P factor also takes place on the advancing blade of a helicopter main rotor, But its not called P factor. I think they call it blade flap? or something...don't work on those so I have forgotten. They also have to deal with lead and lag but thats another forum.

HTH
Darren
  • Member since
    December 2012
Posted by FreedomEagle1953 on Tuesday, June 10, 2003 7:28 PM
... my 2 cents

First of all ... this was not a dumb question ... but a very interesting question. The responses by all were very informative and interesting. This is what makes this such a great site. My thanks to all ... and second ... I agree with timodeller we should have more discussions like this ... Approve [^].

... and last ... I am glad that I am not the only one who wakes up in the middle of the night wondering about things like this very subject. I do have a wife ... and let me tell you ... she wouldn't enjoy being awakened in the wee hours of the morning to be asked ... "honey, which way do the props on a P-38 Lightning rotate" ... Smile [:)]

FreedomEagle1953

Chicago, IL area

"keep on building 'em ... but don't glue your fingers together"

  • Member since
    February 2003
  • From: Panama City, Florida, Hurricane Alley
Posted by berny13 on Tuesday, June 10, 2003 7:41 PM
FreedomEagle1953.

When your wife pops you on your head after awakaned up from her sleep, which way does your head rotate? Big Smile [:D] Big Smile [:D] Big Smile [:D]

Berny

 Phormer Phantom Phixer

On the bench

TF-102A Delta Dagger, 32nd FIS, 54-1370, 1/48 scale. Monogram Pro Modeler with C&H conversion.  

Revell F-4E Phantom II 33rd TFW, 58th TFS, 69-260, 1/32 scale. 

Tamiya F-4D Phantom II, 13th TFS, 66-8711, 1/32 scale.  F-4 Phantom Group Build. 

 

  • Member since
    November 2005
Posted by Anonymous on Tuesday, June 10, 2003 7:47 PM
now thats funny!!!
  • Member since
    November 2005
Posted by Anonymous on Tuesday, June 10, 2003 7:50 PM
Most planes that have counter-rotating props will have the right engine counter-clockwise and the left engine moving clockwise when viewed from the back. The P-38, however, was opposite. The reason for counter-rotating props is to remove the "critical" engine, which is the engine which would cause the most adverse aircraft handling if failed. With counter-rotating props essentially both engines become "critical", but less so, because the center of thrust of each engine is closer to the aircraft centerline.

It's been a LONG time since I have had to give a Vmc brief...:)

flyguycaa
  • Member since
    February 2003
  • From: Saratoga Springs, NY
Posted by Jeeves on Tuesday, June 10, 2003 9:50 PM
Hmmm...a little discrepancy here...my source says same direction. I wonder if different variants didn't have different prop types?? I didn't specify which variant when I asked...
Mike
  • Member since
    February 2003
  • From: United Kingdom
Of course, some go both ways at the same time!
Posted by U-96 on Wednesday, June 11, 2003 3:29 AM


Big Smile [:D]
On the bench: 1/35 Dragon Sturmpanzer Late Recent: Academy 1/48 Bf-109D (Nov 06) Academy 1/72 A-37 (Oct 06) Revell 1/72 Merkava III (Aug 06) Italeri 1/35 T-26 (Aug 06)
  • Member since
    November 2005
Posted by Anonymous on Wednesday, June 11, 2003 6:00 AM
During ww1 German pilots noticed that rotary engined allied aircraft turned quicker one way than the other and could predict which way the other guy would turn. Sopwith camels were produced with clockwise and anti-clockwise engines to give them a shock. Merlin engined Spitfires had clockwise rotation and Griffons anti-clock whilst an anti-clockwise Merlin was produced for Hornet and Sea Hornet aircraft.
This leads me to another question on propellor design. As 2000hp+ engines came on the scene, many British designs used 5 blade airscrews, but US machines stuck to 4. Look at the 5 blader on a Sea Fury, a pitch so coarse its nearly feathered and a blade chord like light aircraft wings. Now look at an unlimited racer with twice the power and the prop wouldn't look out of place on the front of a Liberty engine!
  • Member since
    November 2005
Posted by Anonymous on Wednesday, June 11, 2003 3:35 PM
I recall reading a long time ago that the props on the P-38 rotated in the same direction on some variants and contra-rotated on others. There was a reason given for this, but like so many other things, I forget what it was. Any P-38 nuts out there who know?
Great question! It's one of those items that is right in front of us that we hardly ever give any thought to.
Tony Ryan
  • Member since
    November 2005
Posted by Anonymous on Thursday, June 19, 2003 7:43 PM
The direction in which an airscrew rotates on multi engined aircraft in dependent on the make and mark of the aircraft. some Piper Twins had counter rotating props others didnt. The reason the Sea Fury had a five blade airscrew is to keep the tip speed below the seed of sound at which point it looses efiency. At one stage in my Naval career I worked with these beautiful aeroplanes. Unfortunately it was helping to cut up 12 withan axe. One of my worst days.

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