aerodynamics=student pilot style

[Cessnapilot29]

Hello fellow pilots and students... I need help I have spent money on the Sporty's private pilot dvd set. I bought 2 books, asking my instructors the exact question.... I need a book that goes more into detail and is more friendly about explaining certain things that does not expect me to already know it. I am getting close to starting my cross country and this is putting me on hold because I can't seem to understand it....

1.Gyroscopic precession- The cessna 172 sky hawk does not have a adjustment for the blades on the propeller? Please correct me if I am wrong... The assending blade has a higher angle of attack then the desending blade correct? I understand that the wings and the cord has a angle of attack. My instructor said there is also a angle of attack with the propeller which makes me confused thinking of a mental picture of this. I understand the blades have an angle to them... This is my biggest challenge trying to understand this...


Spiraling slipstream- The blades move the air which causes it to travel to the tail section and push the aircraft to cause it to yaw to the left with high power and low airspeed?

Torque- Without torque there is no p-factor right?

Last question I promise- I have typed this into Google what is the difference between the slipstream and p-factor is this not the same?

Thank you all for reading this and your efforts.... Happy landings....

[Maurus]

I think you have some of these confused.

P- factor: This is caused by the descending side of the prop taking a larger bite out of the air. You will not see this in level flight. Think of the prop as a wing. When in level flight the angle of attack remains constant all around the prop. Once you pitch the aircraft up, the prop will have a new angle of attack. The descending prop will have a greater angle of attack increasing its lift and causing it to push the nose of the aircraft to the left.

Gyroscopic Precession: In this case the prop acts like a gyroscope. When a force is applied to a gyroscope it is transfered 90 degrees in the rotation of the gyroscope. With the aircraft if you were to lift the tail (or descend) this would cause a force at the top of the prop thus causing the the force to shift 90 degrees to the right side of the prop (sitting from the cockpit, 3 o'clock position). The force will push that part of the prop forward which will cause the aircraft to yaw left.

Torque: Torque is only a left turning tendency on the ground. Once in the air it is turned into a left rolling tendency. You can experiment with torque by taking a rubber band airplane and hold the prop letting the aircraft spin. When the aircraft is on the ground the torque can't roll the aircraft, so it just turns left.

Spiraling Slipstream: This is caused by the propeller of the aircraft. The prop causes the air to spiral to the back of the aircraft where it "hits" the vertical stabilizer thus causing it to yaw to the left.

[troopernflight]

Originally Posted by Cessnapilot29

Hello fellow pilots and students... I need help I have spent money on the Sporty's private pilot dvd set. I bought 2 books, asking my instructors the exact question.... I need a book that goes more into detail and is more friendly about explaining certain things that does not expect me to already know it. I am getting close to starting my cross country and this is putting me on hold because I can't seem to understand it....

1.Gyroscopic precession- The cessna 172 sky hawk does not have a adjustment for the blades on the propeller? Please correct me if I am wrong... The assending blade has a higher angle of attack then the desending blade correct? I understand that the wings and the cord has a angle of attack. My instructor said there is also a angle of attack with the propeller which makes me confused thinking of a mental picture of this. I understand the blades have an angle to them... This is my biggest challenge trying to understand this...


Spiraling slipstream- The blades move the air which causes it to travel to the tail section and push the aircraft to cause it to yaw to the left with high power and low airspeed?

Torque- Without torque there is no p-factor right?

Last question I promise- I have typed this into Google what is the difference between the slipstream and p-factor is this not the same?

Thank you all for reading this and your efforts.... Happy landings....

#1, Gyroscopic procession: Is a tough one to understand. If you have a gyro spinning in open space, and you apply a rotating force on that gyro it will react in the direction of the rotation of that force. How do I put this in understandable terms???.....In other words the propeller is rotating clockwise in front of a gyro, and the reaction on the gyro causes a reaction to the gyro approximately 90 degrees ahead of the point where the rotation is applied. What will happen if you point a fan at a piece of paper held level to the ground? If the fan is rotating to the right as opposed to the piece of paper, the paper will rotate to the left. What you are referring to sounds like P-factor, with the ascending and descending propeller blades. When you are at a high angle of attack the ascending blade has a smaller angle of attack, as opposed to the descending blade which has a larger angle of attack. This causes more thrust on the descending side and hence the asymmentrical thrust.
#2, Spiral slipestream is exactly as you described it. The air flow from the propeller rotates around the aircraft in the direction of the propeller rotation and strikes the vertical stabilizer and causes the resulting yaw. At high power and low airspeed the vertical stabalizer has less stablizing effect (slower airflow) and allows the spiral slipstream to have more effect on the yaw of the aircraft, not to mention the stronger slipstream as a result of the higher propeller speed.
#3, Torque and P-factor are separate things. When dealing with Torque, just remember "for every action, there is an equal and opposite reation". When the propeller rotates in one direction, the opposite reaction would be the aircraft rotating in the other direction. There you go, you now have torque effect.
Don't confuse torque effect with P-factor. Torque effect has to do with the equal and opposite reaction, and P-factor deals with the angle of attack of the propeller blades and asymmentrical thrust.

[Kevin.Held]

Maurus beat me to it, but I can elaborate a little more on P-Factor which is also referred to as asymmetric thrust.

Since the propeller is an airfoil with its own cord line, each prop forms an angle of attack between its cord and its relative wind (the air that it "cuts" into, not the airplane's relative wind). A higher angle of attack results in a bigger "bite" of air, thus more thrust.

In straight and level flight, each prop is taking an equal size bite. In a climb, because the nose is pitched upward, the descending prop (right side) takes a bigger bite than the ascending prop (left side). I'm gonna try my best for a visual: If the propeller aoa is 15degrees in straight and level flight, then in a 7degree climb, the descending prop takes a 22degree bite, while the ascending prop takes an 8 degree bite, producing more thrust on the right side, and thus a left turning tendency. The numbers may be off, but hopefully you get the idea.

[Cessnaflyer]

The best demo I had of gyroscopic precession was to have a bicycle tire on an axle that you can hold on one side like a propeller connected to the engine. Basically what you would do is then spin the tire very fast like a propeller and then move the axis like you would when you pitch the aircraft. This would then show the force 90 degrees to the rotation of the gyroscope or propeller.

[Cessnapilot29]

I think I am starting to understand this better now... Thank you all... My instructor always says to me. You over think things too much... I understand that the propeller goes clockwise... Its like a ceiling fan, you feel all the forces when your under it... In this case being behind a Cessna with the engine running. You feel all the power behind it not the front... Only thing I still don't understand is this 3 o'clock term... Correct me if I'm wrong the engine that forces the propeller to spin clockwise turns the propeller 90 degrees from 12 0 clock to 3 o clock this is what takes the biggest bite out of the wind in this case the high angle of attack? When I first read this I figured the 3 0 clock position of the propeller the forces leave the propeller at 3 0 clock. Then I questioned and said well what if the propeller is staying at the same constant speed... Before you guys think gee this dude needs some help and ask me to tell u when I'm gonna fly again and where? Hey I'm still a student pilot I still have that excuse... So yes I'm still confused on this gyroscopic precession... Thanks again...

[tpaRob]

Why is this keeping you from your XC?

[Cessnapilot29]

If your referring too cross country my instructor wants me to have a good understanding of everything. Plus I figure when I become an instructor someday... If a student ever asked me why this or why that... I would hate to say I don't know it just does...

[tpaRob]

Has your instructor let you solo? Have you taken your FAA written? Are you still spending money flying locally while you're trying to figure this out?

I think your instructor should be more concerned about teaching you about airspace and communicating with a tower. I think I would rather have my students (when I get my CFI) learn how to plan a flight from one airport to another than understand: Gyroscopic Precession

I'm sure you'll figure this stuff out. Don't let it stop you from moving forward with your XC (yes, XC=cross country).

Your going to have at least another 200 hours of flight before you become an instructor. You'll figure it out. Have some fun flying.

Trust me, I'm not trying to dog you for wanting to learn.

[JA Yawd Bwoy]

At 30 hours, if you don't know what a XC is, you have a GREAT CFI!

[tonyw]

Originally Posted by tpaRob

Don't let it stop you from moving forward with your XC (yes, XC=cross country).

Your going to have at least another 200 hours of flight before you become an instructor. You'll figure it out. Have some fun flying.

Trust me, I'm not trying to dog you for wanting to learn.

I've got my ticket and I couldn't explain the reasons why the airplane tends to turn to the left as well as Maurus did, but you know what?

I passed the checkride. The examiner didn't ask me anything about precession or p-factor, he just wanted to know that I understood that at relatively low speeds at a high angle of attack, the airplane was going to want to turn to the left.

[Cessnapilot29]

Yeah I went up with another instructor we did my 1st x/c flight from KORL To Tampa International, and he was shocked that when I said I don't know how to read charts and maps and navigate with 40 hrs total flight time... This is all spread out though. I've been keeping a constant 30 hrs or so, and I'm still doing basics... I have not done solo yet, I have practiced communication but my instructor said the normal flight time is around 50-75 hrs. flight time... Is this true? Some friends of mine are saying they are milking me for hrs... Or should I not be concerned? Thanks for your help guys...

[charlie1017]

Originally Posted by Cessnapilot29

but my instructor said the normal flight time is around 50-75 hrs. flight time... Is this true? Some friends of mine are saying they are milking me for hrs... Or should I not be concerned? Thanks for your help guys...

If he's talking about normal flight time to go for the PPL checkride then yeah I agree. If he's talking about time before the first solo, then it's time to ditch the CFI...

[tpaRob]

Have you been solo in the local area yet? Either way I think you are being milked. Are you ready to take your FAA written exam yet?

I am at 31 hours. I did my first solo at 13 hours. I just completed my first XC solo of 4.3 hours a few weeks ago. I have already taken my written (I am already studying for my intrument written). I need to do 3 more hours with an instructor, knocking out some instrument and night flying requirements. But, that's it. At the 40th hour I plan on doing a practice checkride with an instructor and scheduling the real thing shortly afterwards. I'm paying too much money to have my instructor up with me and not having a plan of action. Right now lack of money is keeping me on the ground for another week. (that solo XC cost me almost $500).

You will still have a minimum of 10 hours XC solo to do before your checkride. So, you can automatically tack that on to your already extended hours.

I think it's time for you to dump your instructor or have a meeting with him/her to talk about your progress. You need to have him/her lay out in front of you what needs to happen next and when. Make a checklist of things you have left to do. After each flight with my instructor we talk about what needs to happen next.

Take your written!!! If you keep putting it off, you're going to get rusty on your flight skills while you wait to take it and you're going to have to pay for more flight time to polish your skills for your checkride.

Good luck and keep up posted.
Feel free to email me... tamparob (at) gmail.com

Rob