The Force That Makes a Vehicle Continue Straight Due to Speed on a Turn

07-09-2012,04:53 AM

A- The horizontal component of lift.
B- The vertical component of lift.
C- Centrifugal force.

Which is right？

07-09-2012,06:49 AM

the deflection of air? every action creates a equal and opposite reaction.

07-09-2012,07:34 AM

The correct answer is A. When you bank the airplane the horizontal component of lift causes the airplane to turn. At least that's what the "book" says!!

07-09-2012,08:30 AM

While Joe is correct that that is the answer the FAA is looking for, and it may very well be true, I always struggle getting my head around these kinds of questions.

sj

07-09-2012,08:35 AM

Think of it as a banked turn. Compare what you experience in a car to what you experience in a plane. A turn in a car, even on a slightly banked road, will push your weight to the outside of a turn. A properly executed aircraft turn will result in increased pressure under your butt.

http://en.wikipedia.org/wiki/Banked_turn

07-09-2012,08:45 AM

I thought they always turned towards your wallet!

07-09-2012,09:20 AM

Are you looking for the "test answer" or the real answer?

The horizontal component of lift that is often referred too in text books regarding the "theory" of lift usually forget to include the basic laws of physics and that the reason an airplane wing creates lift is due to the AOA. We all know a cub can fly at 45 miles an hr but to do so requires a high AOA. According to the theory of lift the flow of air across the top of the wing creates lift, the faster you move that air the lower the pressure. Well at 45 mph there is not much air going across the wing and you are relying mostly on AOA to keep the plane in the air not the vertical component of lift. Even at 100 mph a cub wing Average chord line still has some positive AOA to maintain level flight. If a fully symmetrical wing is placed in a 45% bank with out applying any increase to the AOA of that wing the aircraft will not turn. Fully Symmetrical wings rely mostly on AOA not the vertical or horizontal components of lift as defined by the "theory" of lift. Each airfoil/aircraft will turn different due to the forces based on wing loading, speed, L/D, AOA, CG, and bank angle. There is no one size fits all answer.

I HIGHLY recommend reading "stick and rudder" It should be a required text book for all pilots.

Jason

07-09-2012,11:07 AM

Quote Originally Posted by jgerard View Post

Are you looking for the "test answer" or the real answer?

The horizontal component of lift that is often referred too in text books regarding the "theory" of lift usually forget to include the basic laws of physics and that the reason an airplane wing creates lift is due to the AOA. We all know a cub can fly at 45 miles an hr but to do so requires a high AOA. According to the theory of lift the flow of air across the top of the wing creates lift, the faster you move that air the lower the pressure. Well at 45 mph there is not much air going across the wing and you are relying mostly on AOA to keep the plane in the air not the vertical component of lift. Even at 100 mph a cub wing Average chord line still has some positive AOA to maintain level flight. If a fully symmetrical wing is placed in a 45% bank with out applying any increase to the AOA of that wing the aircraft will not turn. Fully Symmetrical wings rely mostly on AOA not the vertical or horizontal components of lift as defined by the "theory" of lift. Each airfoil/aircraft will turn different due to the forces based on wing loading, speed, L/D, AOA, CG, and bank angle. There is no one size fits all answer.

I HIGHLY recommend reading "stick and rudder" It should be a required text book for all pilots.

Jason

Any symmetrical wing flying S/L needs an angle of attack to create a vertical component of lift.... that's how it maintains a constant altitude. If you roll into a 45* bank without increasing that AOA, the aircraft will turn, it just will not maintain the altitude as the "wing lift component" must increase to maintain the "vertical component" to maintain level flight.

The high/low airflow theory of lift is much less significant to the total lift of a Cub wing versus the deflected air when flying at a high drag AOA. There is also a more significant "lift" vector addition from the high AOA "thrust" vector...... In other words, the wing at a high AOA of an aircraft weighing 2000# will have a lift of less than #2000 as the thrust has a small "lift" component..... the total lift component will still equal 2000#.

As good a book as "Stick & Rudder" is.... it has several flaws. There's another book, "Fly the Wing" (don't recall author) that more accurately explains what happens dynamically in flight.

07-09-2012,11:21 AM

As for turning.... I've often flown a Cub in a 75* bank (or greater) at about 40 mph (or less)..... unstalled...... and YES, it was turning. In 90* knife edge, I imagine the elevator turns the aircraft.... but any less bank, I would put my bet on the horizontal component of lift.... Hmmmm, actually, in the 90* case, the elevator would be supplying the horizontal component of lift, right..??

07-09-2012,01:28 PM

Jason is correct. It is the lift vector that turns the airplane. If you put a fighter (or any symmetrical) airfoil in a 60 degree bank and don't PULL to get some AOA the aircraft will not turn but the nose will slice down. Even a cub in a bank will not turn if you set the wing to zero AOA. No lift equals no turn. (or call it deflected air if you want). And that, folks is a key concept. If you are not demanding anything from the wing ie you are at low AOA the wing won't stall and the aircraft will not do anything weird (stall, spin, snap over the top, etc) but if you demand more than the wing can give - too much AOA - it will stall in any attitude and sometimes things get pretty exciting. Now, let me add, low airflow may cause the wing to develop insufficient lift to sustain level flight, but that does not mean the wing is stalled. When you are sitting #1 for take off is the wing stalled? No. There is no lift because there is no airflow but it is not stalled.

When students would come out of the T-37 with its big fat semi-symmetrical wing to the T-38 with a symmetrical airfoil we had to teach them to PULL around the final turn. It was a new concept and took a while before they got it, and in fact some figured out how to fly the final turn just fine but I don't think all of them truly understood what was happening under their butt. The final turn was a big learning hurdle for most students.

It is all about the lift vector and AOA.

Bill

07-09-2012,01:32 PM

To answer the poster's question, strictly speaking, I would say it is d) - none of the above. However, if this question was presented on an FAA test in which you are often expected to choose the least-wrong answer, they would probably expect a) - horizontal component of lift.

The most technically correct answer would be centripetal force. Admittedly, I looked up the answer after failing to remember the difference between centrifugal and centripetal force. Does it still count if I actually did know the answer in junior high?

This discussion of turns reminds me of a chapter in Rich Stowell's Emergency Maneuver Training book. Like Stick and Rudder as recommended by Jason, this is one of the books that gave me a few "aha!" moments.

Current flight training typically focuses on only two elements pertaining
to turns: First, the rudder doesn't turn the airplane. Second, the horizontal
component of Lift is the force that turns the airplane. Many training handbooks
and flight instructors, however, fail to continue beyond this to identify the true
turn control. Consequently, many pilots know which control surface doesn't
turn the airplane, but aren't sure which of the remaining two really does.

Anyone care to hazard a guess? Here's a link to an excerpt from chapter 5 - "curved flight" if you want to read the whole thing.

07-09-2012,02:00 PM

I just bank and yank.

Glenn

07-09-2012,02:42 PM

Quote Originally Posted by Bill Rusk View Post

Jason is correct. It is the lift vector that turns the airplane. If you put a fighter (or any symmetrical) airfoil in a 60 degree bank and don't PULL to get some AOA the aircraft will not turn but the nose will slice down. Even a cub in a bank will not turn if you set the wing to zero AOA. No lift equals no turn. (or call it deflected air if you want). And that, folks is a key concept. If you are not demanding anything from the wing ie you are at low AOA the wing won't stall and the aircraft will not do anything weird (stall, spin, snap over the top, etc) but if you demand more than the wing can give - too much AOA - it will stall in any attitude and sometimes things get pretty exciting. Now, let me add, low airflow may cause the wing to develop insufficient lift to sustain level flight, but that does not mean the wing is stalled. When you are sitting #1 for take off is the wing stalled? No. There is no lift because there is no airflow but it is not stalled.

When students would come out of the T-37 with its big fat semi-symmetrical wing to the T-38 with a symmetrical airfoil we had to teach them to PULL around the final turn. It was a new concept and took a while before they got it, and in fact some figured out how to fly the final turn just fine but I don't think all of them truly understood what was happening under their butt. The final turn was a big learning hurdle for most students.

It is all about the lift vector and AOA.

Bill

It is the tilting of the wing lift vector that creates the horizontal component of lift, which turns the aircraft.

And Jason is not correct. He stated that when entering a 45* bank without changing the angle of attack, the aircraft will not turn. It will, in fact, turn as the wing is producing lift and the wing lift vector is now tilted and creates a horizontal component of lift. When rolling into a bank, to NOT turn, the AOA must be reduced (to zero in the case of knife edge, non-turning flight for a symmetrical wing). Any time the wing is not horizontal (level), it will create a tilted lift vector relative to its design and the AOA that it has.... and be turning. When you roll a fighter wing from wings level flight descent (with an AOA relative to its stable airspeed) into a 60* banked turn, in order to NOT turn, the AOA (wing) must be unloaded. The pull required for a turn is to load the wing (and increase AOA) to maintain the vertical lift component...to do this requires the wing lift component to significantly increase to maintain the vertical lift component, which has not changed.

07-09-2012,03:17 PM

You are correct. If you keep the same AOA after banking the airplane will turn. ABOUT 1 DEGREE EVERY 5 SECONDS.
We are basically saying the same thing. It is the lift vector that causes an airplane to turn, but 1 g does not create much turn "rate". When we increase the AOA to maintain level flight that also increases the "tilted" (to use your term) vector which increases the turn RATE to something noticeable.

Bill

07-09-2012,06:23 PM

what I meant to say was a 45* bank with zero AOA.

the vertical component of lift in a 45* bank with a 0* AOA is not great enough in a cub or most light aircraft and the aircraft will loose altitude faster than it will change heading. Even worse in full symmetrical airfoil aircraft.

a cub in level cruise flight still has some positive AOA

the combination of the airfoil creating lift and the AOA of that airfoil is what creates the vertical component of lift.

Jason

07-09-2012,07:04 PM

What force make a helicopter turn?

07-09-2012,07:29 PM

Quote Originally Posted by sierra bravo View Post

What force make a helicopter turn?

Don't really think it does ...

The Earth just gets pizzed off and rotates around it.

07-09-2012,08:23 PM

Quote Originally Posted by sierra bravo View Post

What force make a helicopter turn?

$$$$$$$$$$$$$$$$$$$$$$$$$$

07-09-2012,09:37 PM

Quote Originally Posted by jgerard View Post

the combination of the airfoil creating lift and the AOA of that airfoil is what creates the vertical component of lift.

Jason

Any airfoil at various angles of attack (and airspeed) creates wing lift..... which may be equal to the vertical component of lift, but does not create it as such. In high powered aircraft flying at steep angles, the thrust vector is a major contributor to the vertical component of lift..... therefore, the wing creates only a portion of the vertical component of lift. It would be more accurate to say that as the wing changes airspeed, AOA and bank angle, the vertical component of lift will vary.

I'm not picking on you, Jason..... it's just a pet peeve of mine after hearing so many misconceptions of aerodynamics in the past 50 years.

07-10-2012,10:32 AM

I was doing some reading as a result of this discussion. I came upon an interesting comment about airplanes and how airplanes turn. A physics student, in response to a similar discussion with similar answers we've seen here, made a point that an airplane can "turn" without changing heading. Aileron rolls constitute a turn, right? No heading change. Toss that one into the physics of flight discussion.

07-10-2012,02:36 PM

I know you're not picking on anyone - LOL

I understand and agree on the thrust vector part of the equation.

Hmm, the aileron roll as a turn??? not sure but I bet that can be debated till the cows come home based on different definitions of what a turn is. Is it a turn or a rotation?

Jason

07-10-2012,03:00 PM

Quote Originally Posted by jgerard View Post

I know you're not picking on anyone - LOL

I understand and agree on the thrust vector part of the equation.

Hmm, the aileron roll as a turn??? not sure but I bet that can be debated till the cows come home based on different definitions of what a turn is. Is it a turn or a rotation?

Jason

Heck.... throw in a downwind flight condition and we really can have an argument... errr, I mean discussion..!!

07-10-2012,10:00 PM

If there is no altitude gain/loss as a coordinated turn should be then there is no vertical acceleration, therefore no vertical force, right?
The airplane is turning in a circle, some force is constantly changing the direction in the horizontal plane, the only force in the horizontal direction is the horizontal component of lift. A simple free body diagram explains the case, no aerodynamics needed.

Greetings

07-11-2012,10:55 AM

Ahh, the downwind thing again. I thought about it the other day while departing a very familiar strip with a familiar left crossing gusty wind and those pesky tall trees. In that tricky zone between the relative safety of ground effect and clear of obstacles I had the plane encounter a predictably unpredictable wind rotor and snap into a 30* right bank while still in the "slot" under the treetops. Hmm. Slow, in a defined space with little room to drift, little time to do anything about it, and with a gusty wind that wanted to push me right and initiated a right turn for me? And yet I elected to use full left aileron and patience to allow the plane to level out and reestablish a climb so I could turn the nose TO the wind to better avoid obstacles. All while staring tree foliage face-to-face, which tends to focus my attention. I guess I should have put stock in your advice and rode it out downwind? It would have been the path of least resistance, right? Until I impacted trees, anyway. I'll pass.

I know, I know, you theorists will say the issue wasn't one of aerodynamics but one of space. Turning a plane in a moving mass relative to a fixed spot on the ground. Funny thing, that's the world I live in. Y'all have a nice day.

The Force That Makes a Vehicle Continue Straight Due to Speed on a Turn

What force makes an airplane turn?

0 Response to "The Force That Makes a Vehicle Continue Straight Due to Speed on a Turn"

Post a Comment

Iklan Atas Artikel

Iklan Tengah Artikel 1

Iklan Tengah Artikel 2

Iklan Bawah Artikel