Quick Question About Single Engine Planes

[Brett327]

I wasn't worried about the nerdy part - I just didn't think about the high probablity of someone jerkoff nickel and diming my answer to death because I left an i undotted or did not show the proper equations....

Oh, it is no doubt imminent - engineering tomes are being referenced and Poindexters are withdrawing slide-rules from their Naugahyde carrying cases.

Brett

 

[HeyJoe]

Aero for the rest of us

Oh, it is no doubt imminent - engineering tomes are being referenced and Poindexters are withdrawing slide-rules from their Naugahyde carrying cases.

Brett

No better way to understand than via hands on approach IMO

No joke...you're not going to have a lot time to run equations in the air so figuring out how things work from practical observation might help and they are called "Learning Models"

 

[insanebikerboy]

For some reason, this image comes to mind when thinking of people arguing about aero-crap.....

 

[Random8145]

Okay, so simple answer is the airplane engine is just too small to generate enough force to turn the plane, it does create a small effect though, the effect increases or decreases depending upon engine power and the angle the aircraft is flying at, the plane is engineered to counter this as best as possible, and the pilot has stuff they do to counter it as well.

Thanks!

 

[HAL Pilot]

Okay, so simple answer is the airplane engine is just too small to generate enough force to turn the plane, it does create a small effect though,

This part is wrong.

the effect increases or decreases depending upon engine power and the angle the aircraft is flying at, the plane is engineered to counter this as best as possible, and the pilot has stuff they do to counter it as well.

This part is right.

The effect can be quite significant or quite small, depending on the plane and engine.

Take the P-51 for example. If you did not give it a lot of right rudder on takeoff, it would flip over to the left and kill you. If you lost the engine as you were leaving the ground and did not immediately remove all that right rudder, it would flip over to the right and kill you.

Modern planes are better but some need significant rudder and can get a novice pilot in trouble quickly. This is more true with many of the twin engine planes and is especially a factor if they lose an engine.

My advise - fly jets. Then you don't have to worry about it....

 

[Steve Wilkins]

They do turn opposite or "spin" to some degree.

For the most part, U.S. aircraft are built with propellers that turn clockwise (right) when viewed from the cockpit. Because of this, they have left turning tendencies. The left turn tendency is caused by three things:

• P Factor: the downward blade (on the right side) has a higher angle of attack so it gets a "bigger bite" of the air. This causes a left yaw.
• Slip Stream: The the air from the prop goes in a spiral around the aircraft and ends up hitting the left side of the vertical stabilizer, again causing a left yaw.
• Torque: The prop turns to the right so the engine tries to go opposite (to the left). Since the engine is attached to the aircraft, the aircraft tries to roll left.

There is a fourth turning tendency, but it can be in any direction. During a climb it is a right turn tendency. It is called gyroscopic precession. A spinning prop has some of the properties of a gyroscope. If you apply a force to a gyroscope, you will get a resultant force (precession) occurring at a point that is 90 degrees in the direction of the spin. When you climb, you apply a force to the top of the propeller (i.e. push it back so it angles upward). The resultant force is felt 90 degrees to the right where the prop will also be pushed back, causing a right yaw. It is just opposite in a descent (left yaw). Similarly a left turn or yaw will cause a upward precession and a right turn or yaw a downward precession.

The aircraft are engineered so that in level flight at cruise speed, these forces are "trimmed" out. This is usually done with trim tabs, either fixed or movable. The size of the vertical stabilizer and rudder have a lot to do with this too. During descents, when there is less power on the engine, these factors are less noticeable. During takeoff and climb, when there is more power producing more of these forces, the pilot uses right rudder to counteract them.

I hope this helps but I'm not an aero guy and this is just my layman's explanation. Anything more just gives me headaches.

Thank you HAL. Probably better that you answered before I did. It wouldn't look too pretty for a SWO to have to explain these kind of things to a room full of NA's.

 

[HH-60H]

Having never flown a prop plane... Can someone explain how the descending blade has a higher angle of attack than the ascending?

If the air flow is perpendicular to the plane (no pun intended) of the prop, I don't get how that works.

We have a similar sounding phenomena with retreating blade stall in helos, but in that case the motion of the aircraft and the blades are in the same plane, so it's a "simple" vector thing. (as if anything in helo aerodynamics is simple)

 

[BACONATOR]

Having never flown a prop plane... Can someone explain how the descending blade has a higher angle of attack than the ascending?

If the air flow is perpendicular to the plane (no pun intended) of the prop, I don't get how that works.

We have a similar sounding phenomena with retreating blade stall in helos, but in that case the motion of the aircraft and the blades are in the same plane, so it's a "simple" vector thing. (as if anything in helo aerodynamics is simple)

I'm answering this STRICTLY as a private pilot.

Bottom line: the airflow isn't always perpendicular to the plane of the prop. For example, when you are climbing, the prop forms an angle with the relative wind (relative meaning you're moving forward a lot more than you're moving upward so the wind that the airplane feels is almost parallel to the ground). With this angle, the camber of the prop blade forms a larger angle of attack (for thrust) on the right hand side (descending side) than the left side. This causes the p-factor associated with positive angles of attack necessitating increased right rudder pressure. In level flight, the angle of attack on either side of the prop is equal, so p-factor is a non-issue.

 

[HAL Pilot]

Having never flown a prop plane... Can someone explain how the descending blade has a higher angle of attack than the ascending?...

http://www.faa.gov/library/manuals/aviation/pilot_handbook/media/faa-h-8083-25-1of4.pdf

Look in chapter 3, starting around page 3-21.

 

[Brett327]

Having never flown a prop plane...

Don't you helo guys start out in T-34s before the HTs?

Brett

 

[HH-60H]

Don't you helo guys start out in T-34s before the HTs?

Brett

Most do, but I was a Vance guy in the T-37.

 

[HH-60H]

http://www.faa.gov/library/manuals/aviation/pilot_handbook/media/faa-h-8083-25-1of4.pdf

Look in chapter 3, starting around page 3-21.

Thanks. Learn something new everyday. I was just envisioning the airflow being parallel with the shaft of the propeller. After hearing about p factor from all my T-34 buds, I always thought that was just a torque thing, but I now see what it really is.

 

[Steve Wilkins]

http://www.faa.gov/library/manuals/aviation/pilot_handbook/media/faa-h-8083-25-1of4.pdf

First aviation book I ever read. Definitely worth the read if you're brand new aviation. That and Stick and Rudder.

 

[Steve Wilkins]

I always thought that was just a torque thing, but I now see what it really is.

Then our job is complete here. Oh, and two gold stars for you too.