Kasserine06

This is more to the original poster and an alternative to the walking analogy. Next time you are driving in an empty parking lot, turn the wheel a ¼ turn and drive at 5 mph. You will be driving a tight circle and you will complete that circle quickly. Then step on the gas but keep the wheel where it is. As you pick up speed, your forward velocity (speed) will increase while your horizontal (wheel angle) remains constant. This causes your car to drive in larger circles than when you were only moving at 5 mph. That explains the radius/speed relationship.

The rate/speed relationship occurs because you have to travel a longer distance to travel at a higher speed because your radius is large. Think about a race on an oval track. Those race cars can take up to 15 seconds to turn 180*, but I can easily turn 180* in less than 5 seconds in my 10 year old civic in a parking lot. That is all because I am traveling slower which generates a smaller radius which creates a shorter circumference that I must travel. That is not a perfect analogy because steering angles (bank) are not the same in those too cases, but when you do it in a parking lot, you will notice that it takes longer to do a circle fast than slow with the same steering angle.

Once you get that in your head, then you can have some fun trying to figure out if it is better to get out of a box canyon by turning at Va pulling maximum Gs, or pulling flaps and turning with the stall horn going off. Of course, if you want to think outside the box to get out of the box, do a half spin and recover .

shdw

What?! To my knowledge a 60 degree bank = 2g at 100 knots or 10 million knots. Am I misreading this?


OP: Uhg all this math. While the math makes it logical, that won't help some students and might have you lost in the numbers. I would ask you to try a practical experiment:

Take a car to a parking lot that has as few light polls as possible.

The steering wheel = bank angle and gas pedal = throttle.

Turn the steering wheel to a point and hold it, making a slow constant radius circle. Now increase the speed with the gas and watch the result.

That should give you a clear visual of what happens to radius with speed. The why is mathematical, and unnecessary for certain people. For some, just seeing that it works in a familiar environment such as the ground in a car will suffice.

To understand rate you need to understand the definition. The number of degrees turned over a period of time. Increase the radius makes a larger total circumference or distance to travel. Larger distance to travel means more time and more time means a decreased rate.


Edit: PS I avoided giving the math or even bothering to check it for accuracy in this post. It looks like it has been beaten to death in the previous 2 pages and I am sure between ryan and cub there is an accurate conclusion that I need not repeat.

ryan1234

Sounds like you should be teaching this stuff somewhere

gestrich19

Thanks for the answers everyone. After thinking through several of the examples, I think I have it now. Please let me know what you think. I'll start with the basics of turning just to make sure I am not making the wrong assumptions. Let's at least assume a constantly-banked level turn:

The aircraft turns due to the horizontal or sideways force induced from banking the aircraft.

The horizontal component of lift changes the direction of the relative wind which is now to the left or right of the nose of the aircraft. It could be said that the direction of the relative wind is directly opposite the flight path.

The longitudinal axis of the aircraft will align with the relative wind which results in a change in the heading of the aircraft.

If you INCREASE the speed of the aircraft in a level, constant banked turn, you will increase the forward force while keeping the horizontal force relatively the same. This will cause the flightpath to be more straight off the nose. In other words, moving faster will re-vector the relative wind closer to the longitudinal axis of the aircraft. This will slow the rate of turn and increase the turn radius.

Am I on the right track here?

shdw

This is right. The rest, go back to the drawing board IMO. I would avoid discussing forces to explain rate and radius. First, you clearly don't understand what you are talking about. Apologies if that sounds harsh, I am only trying to be straight with you. Second, most students, even when explained forces by a teacher that has a thorough understanding of them, will still be lost.


Also: Not it could be said, it is. Relative wind is parallel to, and directly opposite, the direction of flight.

UAL T38 Phlyer

Gestrich:

When you say the turn causes the relative-wind to come from the left or the right....not quite.

If the relative wind is coming from a direction other than straight-ahead, that is YAW.

And in a coordinated turn, there should be no yaw.

The horizontal force from the horizontal component moves the airplane at the same rate as the change in direction of flight (and therefore, relative wind), such that there is never any yaw.

Ryan:

I am (but you knew that).

gestrich19

Ouch - Anyone else want to help?

gestrich19

If the relative wind and heading change simultaneously (one does not cause the other), then why does the aircraft change course? What is the cause directly preceding the change in direction of flight? I thought it was the slight change in relative wind which caused the aircraft to align with it due to the force of air on the vertical stabilizer and fuselage. Although it may happen in an instant, the relative wind changes first and the longitudinal axis then aligns with the new relative wind. Do I misunderstand?

ryan1234

I'm not sure I understand what it is you're asking, but I'll try to start from scratch and explain as best as I can...

We know that... during a steady, coordinated turn that lift is inclined to produce a horizontal component of lift equal to the centrifugal force in the turn. ... a steady turn is achieved by producing a vertical component of lift equal to the weight of the airplane. If either one of these values do not equal the respective value (i.e. horizontal lift does not equal centifugal force, etc) the airplane will be out of symmetry and some type of acceleration (either positive or negative) will occur (i.e. uncoordination, etc).

I think what you're trying to get at is static stability and dynamic stability. If it is please let us know... that's a whole 'nother topic...but I'll try to give a brief intro:

There is equilibrium... when the sum of all forces and moments equal zero. In this condition there is no acceleration (i.e coordinated flight). If you put a control deflection in, you'll unbalance the moment of force and some type of acceleration will result (i.e. positive or negative).

Static stability: The tendency of an aircraft to return to equilibrium. Postive static stability is the tendency is return to equilibrium if disturbed. Negative static stability is the tendency to continue in the direction of the disturbance. Neutral static stability is somewhere in the middle (remain in a displaced condition). When dealing with static stability, the resulting motion is not a factor.

Dynamic stability: same as above, but deals with motion in time.

The Rudder helps to overcome adverse forces which try to bring the aircraft out of equilibrium during a turn. A yaw string attached to the nose shows the relative wind... in a coordinated turn the relative wind comes from straight ahead.

shdw

Yes, UAL nailed it.

Edit: <Section removed> Check your private messages.