Horizontal Lift

[groundpointsix]

In a steep turn, we know the vertical component of lift will equal the weight of the aircraft assuming level flight. Since the aircraft is banked, there must also be a horizontal component of lift. My question is, does the horizontal component of lift equal the centifugal force acting on the airplane? Does this change depending on whether the airplane is coordinated or not? Thanks.

 

[Guillotine007]

who do you have for the CFI training?

Klein

and did you take your multi ride yet, i have to keep a record of your passing (you better pass)

 

[Mmmmmm Burritos]

There is no centrifugal "force" in a coordinated turn. IF there was a force opposing horizontal lift, then how would you turn? Weight opposes vertical lift, and load factor opposes total lift. Now in an uncoordinated turn, the rudder can create a yawing moment which will oppose the horizontal lift. A slip is an example of this. The FAA made a mistake with this centrifugal force concept and it has since been corrected in the 1997 Pilot's Handbook of Aeronautical Knowledge. However, if you look at the turn diagram, you will see they forgot the load factor vector also! Oops!

(edit: but now the NEW handbook brings it back and opens up the can of worms again, saying it is equal and opposite "reaction". It really isnt a reaction, the airplane was going straight until you turned it. )

 

[dmspilot00]

There is no centrifugal force in a coordinated turn. IF there was a force opposing horizontal lift, then how would you turn? Weight opposes vertical lift, and load factor opposes total lift. Now in an uncoordinated turn, the rudder can create a yawing moment which will oppose the horizontal lift. A slip is an example of this. The FAA made a mistake with this centrifugal force concept and it has since been corrected in the new Pilot's Handbook of Aeronautical Knowledge. However, if you look at the turn diagram, you will see they forgot the load factor vector also! Oops!

This isn't correct.

First, a centripetal force is necessary in order for a body to rotate. The centripetal force describes the force that causes the rotation. Centrifugal force is an apparent force. It is equal and opposite to the centripetal force, and attempts to draw a body away from its center of rotation. It is caused by inertia.

In a coordinated turn, the horizontal component of lift would be the centripetal force. Having a centripetal force always produces an apparent centrifugal force. So to say there "is no centrifugal force" in a coordinated turn is completely incorrect.

To say that "if centrifugal force existed in a coordinated turn, it would oppose the turn, and the aircraft would not be able to turn," is a contradiction, because centrifugal force exists if a body is rotating, and it opposes the rotation.

To answer the original question, the horizontal component of lift does equal the centrifugal force, but only in coordinated level flight. The horizontal and vertical lift vectors result in the total lift vector, which would be diagonal in a turn. The centrifugal force vector (horizontal) and weight vector (vertical) would result in the load factor vector, which also would be diagonal in a turn. The total lift vector and total load factor vector would be equal and opposite to each other.

 

[Mmmmmm Burritos]

So if this centrifugal force is equal and opposite to the centripetal force (horz. lift) and is an apparent (observable) force, then how does the aircraft change heading??! You are talking about examples like a motorcycle driving on a banked oval track or twirling a rock on a string where there is an actual physical connection between the body in motion and the substance on which the force is applied to.

A motorcycle will bank like an airplane to derive more centripetal force. The driver feels a side load pulling away from the turn. So does the rock on a string. So does the water in the bucket. Yes, I know there is no physical connection between water in a bucket, but the bucket provides a barrier so the water cannot escape. The air provides no such barrier to an airplane.

In an aircraft you will feel this apparent force through the load factor. That is the force caused by inertia and changing motion. The quicker the turn, the more load factor you will ultimately feel.

There is no notable centrifugal force on a banked airplane in coordinated flight. Maybe on the ground when taxiing and turning... but not in coordinated turning flight. And how can you have centripetal force (horizontal lift) in coordinated level flight like you stated?

Anyway, NASA agrees with me.
Click me and read the second paragraph

 

[Ralgha]

So if this centrifugal force is equal and opposite to the centripetal force (horz. lift) and is an apparent (observable) force, then how does the aircraft change heading??!

Because it's not a force. It's inertia, nothing more.

 

[dmspilot00]

I don't see how the NASA link you gave me agrees or disagrees with anything that has been said so far. It doesn't even bring up the topic, so it is irrelevent.

For a body to rotate you need a centripetal force. Whenever centripetal force is present, there is an apparent equal and opposite centrifugal force due to inertia. If a body is rotating, it has centrifugal force. Also, it makes absolutely no difference if the rotating body is "attached" to a "string."

If there was no apparent centrifugal force present, then that must mean that there is no centripetal force, which must mean the body must not be turning. Any body that turns will experience both forces. If a body only experiences one of them, then that would be breaking the laws of physics!

If you were to fly with the wings banked in a condition in which there was no centrifugal force, that would be a slip, for example, and the aircraft wouldn't change heading.

Since you brought up load factor, and I already said this, I will say it again: the load factor is the combination of centrifugal force and weight. So with your reasoning, "if there is load factor in a turn, then how is it possible the aircraft will change heading?"

You are a CFII/MEI?

Anyway, I just checked and the new FAA Handbook of Aeronautical Knowledge agrees with me. See pages 3-17 through 3-18, specifically Figures 3-20 and 3-21: http://av-info.faa.gov/data/traininghandbook/faa-h-8083-25-1of4.pdf. This answers grountpointsix's original question (yes).

Ralgha is right in that centrifugal force is essentially inertia, but I can't help how it was named.

 

[crowbar]

Don't worry about any of that trash, just go fast and pull up.

 

[Mmmmmm Burritos]

You don't see how? Read: "As long as the aircraft is banked, the side force is a constant, unopposed force on the aircraft."

The 1997 Pilot's Handbook of Aeronautical Knowledge does not have centrifugal force in there. The old Flight Training Handbook DID have centrifugal force. So it looks like we're not the only ones having this argument.

Anyway Ralgha says it's not a force, it's inertia. You agreed with him with your last statement. If it's not a true force, then how can it actually act against the airplane?????

Yes I am a CFII/MEI. I teach aerodynamics almost every day. I teach for two FAA examiners who share the same viewpoint. I have sent maybe 30 private, commercial or multiengine checkrides (which actually need to know about aerodynamics, instrument rating doesnt count.). I've never had the subject raised on a checkride.

Gotta go, I'll be back later

 

[dmspilot00]

The new Handbook of Aeronautical Knowledge came out last year.

"As long as the aircraft is banked, the side force is a constant, unopposed force on the aircraft." And where does it say there is no centrifugal force? It doesn't even bring it up. NASA does not "agree with you," but it merely agrees with the definition that centrifugal force is only an apparent force, which I have been saying from the beginning.

You are acting as if I have attempted to redefine centrifugal force to be a "real force" that "cancels out" centripetal force, but I have never given any other definition than the official, correct one. Go way back to my original post and you can see that I did, in fact, say it was an apparent force due to inertia. This does not mean that there is no centrifugal force. How can you have centrifugal force on the ground while turning, as you said, but not in the air while turning? You are contradicting yourself.

The bottom line is groundpointsix is correct in that the horizontal component of lift in a coordinated turn is equal to, by definition, centrifugal force. The combined centrifugal force and weight make up load factor.

 

[Ralgha]

I think the problem arising from your definintion, while correct, is that you are still referring to it as a "force". Yes it appears as a force, but it is not a force. It is inertia and only inertia.

There is no centrifugal force. The horizontal component of lift is not defined by the imaginary centrifugal force, it is defined by the angle between the lift vector and vertical, and the magnitude of the lift vector. Inertia (the imaginary centrifugal force) has nothing to do with the strength of the horizontal component of the lift force.

 

[AxisVDP]

The side force IS the centripetal force. Think about swinging a rock on the end of a string above your head. You keep the rock spinning by providing a force towards you (In the direction of the rock's turn). The force you place on the rock is pretty much the same force that pulls the aircraft around a turn.

 

[Mmmmmm Burritos]

ap·par·ent ( P )
adj.
1. Readily seen; visible.
2. Readily understood; clear or obvious.
3. Appearing as such but not necessarily so; seeming: an apparent advantage.


Stop being so condescending, then step back, take a deep breath and take a fresh look at this. I am saying there is no actual centrifugal force. You are saying by stating right out of some book that this force is definitely there, however it is not real, but apparent. Are not we saying basically the same thing?

I agree 100% that centrifugal force can be felt in a car rounding a corner. Go fast around a corner, and you will be pressed up against the side of the seat. If there was a glass of water on the dash, it would stay going stright, but to you it is flying to the side. It's like coriolis force. The wind blows, the earth spins, and it looks like the wind is curving when it's really not. The car will even lean away from the turn. The thing is here, the centripetal force is being applied to the tires' contact with the road, and all of the car's weight is above that. The tires are essentially pulling the car from the bottom toward the turn.

In an airplane in a coordinated turn you feel nothing but load factor pushing you into your seat. You are not pushed toward the side of the plane. Your chart in your lap doesnt go flying into the other seat. It does with turbulence of course, but that's different. So where is this centrifugal force?

Now in an uncoordinated turn, the rudder causes a total lift vector perpendicular to the vertical stabilizer and perpendicular to the total wing lift vector. The rudder's total lift causes both vertical and horizontal components of lift, just like the wing does. The rudder's horizontal component of lift is what will oppose the wing's horizontal component of lift. So now, we have TWO centrifugal forces? We definitely have two horizontal components of lift, or two centripetal forces. Where's the centrifugal forces if the airplane isnt even changing heading because of the slip? It has two centripetal forces acting on it and cancelling each other out. Draw it out on paper. Realize the truth. Watch the X-files, not everything you see on paper is true 100% of the time

That's great you can recite what you learned in physics class. I learned the same stuff. But to answer the original question again... you can draw out however many fake forces you want, but the only turning force that acts on the airplane in a coordinated turn is the horizontal component of lift. Tell me again that this fake centrifugal force is "equal and opposite" and I will e-slap you!

OK OK, in a 90 degree bank coordinated turn, the horizontal component of lift is equal to the centrifugal force. That is because the horizontal component of lift is the same as ALL lift and the centrifugal force is all load factor at that point.

Oh and thanks Ralgha for backing me up!

 

[Ralgha]

Centrifugal force exists equally in a banked coordinated turn as it would in a turn of the same radius and speed across the ground.

No! Centrifugal force does not exist, ever. It is inertia, not force. You feel the effects of inertia equally in both cases, just in different directions.

Get away from centrifugal force entirely in your arguments and they will start to make more sense.

 

[dmspilot00]

I am taking a fresh look at this...

Note: When I say "centrifugal force" I realize it is, in fact, inertia; but as I've said before, I cannot help how it was named. To say "centrifugal force does not exist" would be saying inertia does not exist. They are merely synonyms, but I agree the term should not be used and I will try avoid it in the future.

Oh and one more thing, more proof that you read and preach without thinking through... your new Handbook of Aeronautical Knowledge is NOT out yet even though you say it came out last year. Yes it does say 2003 on that link you gave us but that current FAA AC checklist (AC 00-2) still says AC 61-23C is the current book.

Excuse me, but you have the nerve to call me condescending, then you say something like this. That book which you say is not out yet is sitting on my desk. I will take a picture with a digital camera if you'd like!

You and Ralgha are not in the least bit saying the same thing, so don't go there.

I agree 100% that centrifugal force can be felt in a car rounding a corner...In an airplane in a coordinated turn you feel nothing but load factor pushing you into your seat. You are not pushed toward the side of the plane.

You keep contradicting yourself. Either centrifugal force exists or it doesn't. It can't just exist sometimes. You do not slide across into the next seat in an airplane because the airplane is banked, the same way you would not slide across the seat in a car if the road was banked. The load factor you feel is the combined inertia (aka centrifugal force) and weight.

You are saying that just because in one instance you slide across your seat, and the other instance you are pushed into the seat, means centrifugal force exists in the first but not the second. Absurd. Either it exists in both, or it doesn't. Inertia exists equally in a banked coordinated turn as it would in a turn of the same radius and speed on the ground. It's just in different directions.

Consider this: you're in a car going 60mph, on a flat, circular track with a 100' radius. You're feeling a lot of "centrifugal force" (actually inertia) pulling you toward the outside of the turn. You feel your body sliding across the seat. By the way, you happen to be driving a car in which the seats are adjustable on all 3 axes. So, you decide to slowly tilt your seat sideways, toward the turn. Eventually you reach a point where you don't feel a sideways force, but a force into your seat. Does that mean inertia ("centrifugal force") has suddenly stopped, just because your chair is tilted?

(revised)

 

[Mmmmmm Burritos]

I found the new book online. $30 ouch, that's twice as much as the old one. $50 from the GPO. You'd think it'd be more prevalent out there having been published in Dec 2003. I bet they're just trying to sell off the old books before they sell the new.

Anyway we both have valid points and you present good arguments. I'm just trying to argue against a common misconception. I think we answered the original question.

The problem arises in that there's no way, in a coordinated banked turn, to have any significant "inertia" unless you are banking steeply. Then you feel it through the bottom of the seat as load factor. That force of course is very real. It can break wings off.

In a shallow or medium bank turn, the only way to feel the effects of a force acting out the side of the aircraft (away from the bank) are to yaw the aircraft with the rudder. But what that does is again to create two components of total lift, one from the wing and one perpendicular to that c oming from the rudder, which will result in a new total lift vector NOT perpendicular to the wing or the rudder. This new vector would be coming out of the plane diagonally. Then you definitely feel side force, which again is a result of the load factor being equal and opposite to the total lift.

And don't question my certification again. That was poor taste, especially since you only list four trainer aircraft and from my guess would be no higher than an instrument rating (unless you count 172RG/PA28R as 172/PA28)

Anyway, back to the airport...good day sir

 

[dmspilot00]

I'm just trying to argue against a common misconception.

Which one?

The problem arises in that there's no way, in a coordinated banked turn, to have any significant "inertia" unless you are banking steeply. Then you feel it through the bottom of the seat as load factor. That force of course is very real. It can break wings off.

The fact that you cannot feel it does not mean it does not exist. The inertia is equal to the horizontal component of lift in any coordinated turn. When the rate of turn is slow, you may not be able to feel it, but you've been saying all along it simply does not exist.

In a shallow or medium bank turn, the only way to feel the effects of a force acting out the side of the aircraft (away from the bank) are to yaw the aircraft with the rudder.

Not sure what the relevence of this is, as the whole point of this thread was to discuss coordinated turns. The reason you don't feel it in a shallow turn is because the horizontal component of lift is small in a shallow turn, but high in a steep turn.

 

[bigD]

As much as I cringe everytime I read yet another one of dmspilot's sardonic posts, he's right about the physics.

And Ralgha is just starting trouble for the hell of it, I guess.

 

[Ralgha]

Starting trouble? I'm just maintaining that it is not a force and shouldn't be referred to as such. So it was named wrong, doesn't mean you have to use that name.

Call it "centrifugal inertia" or something. Just don't call it a force. It makes things much more clear because it doesn't result in the whole "centrifugal force balances centripital" bit.

 

[Mmmmmm Burritos]

Anyone see Kill Bill vol. 1? I think they started a discussion about centrifugal force in that big fight scene in the Japanese club.

Can we all agree on this? Centrifugal force is not an observable force, but it magically causes a deflection in the force you actually feel (load factor).

I was never advocating that it does not ever exist, I was just saying that it doesnt exist as a force. That is probably why you feel I was contradicting myself. You just don't feel it the same in an airplane that you do in a car. This is the common misconception I speak of. Most books say centrifugal force is equal and opposite to centripetal force. But if it actaully was, then the aircraft wouldnt turn. Just like when lift and weight are equal in straight and level flight. The aircraft doesnt just climb, it maintains altitude.

You can draw a line that is "equal and opposite" to centripetal force, but it's just that, a line. It's easier to just say the load factor is equal and opposite to the total lift in a coordinated turn while maintaining altitude.

And yes it should be called something like "centrifugal confusing concept of misconception".

 

[bigD]

Ralgha - the problem is that the use of "centrifugal force" is so commonplace that when getting into any discussion related to this sort of thing, you're gonna have people that use the term. And most of the people that use it *know* it's not a force, but it's so ingrained in people's minds that it doesn't matter.

Does this justify using the term? Perhaps not, but calling people on it is kinda like correcting someone that says, "ATM Machine" or "go Xerox a copy for me", when the copy machine is not manufactured by Xerox. Technically you're right for correcting them, but it's pretty inane. At least to me. That's why I thought you were starting trouble.

 

[Mmmmmm Burritos]

Yeah. This is nothing more than an argument over semantics.

 

[bigD]

Heh! That tends to happen a lot on this board, doesn't it!?

 

[dmspilot00]

I agree with both BigD and Ralgha. It's hard not to use the term, but yet "centrifugal inertia" sounds like a better term to use.

That is probably why you feel I was contradicting myself. You just don't feel it the same in an airplane that you do in a car. This is the common misconception I speak of.

I agree centrifugal force is not a force, but the contradiction I speak of is in your comparison of a car and an airplane. From the start you have been saying that (to use a better term) centrifugal inertia in a car is completely different than centrifugal inertia in an airplane. They're not different. Case closed

 

[Mr. Cole]

Ok, glad we could all agree that centrifugal force is a ficticious force since a rotating frame is non-inertial and this "force" arises from our attempts to cast it in physics that only apply in an inertial frame. But the one issue that we shouldn't forget is that for circular motion the force must be central in that it points towards a center of motion. Horizontal lift alone doesn't cause a turn if it's not constrained to pass through the center of the circle. If we don't do this then the plane simply slips laterally to the side with no change in heading. Depending on the amount of bank, the rudder or elevator is what keeps the horizontal lift passing through the same point, allowing a coordinated turn.

Dave

 

[Ralgha]

And most of the people that use it *know* it's not a force, but it's so ingrained in people's minds that it doesn't matter.

Not intending to be argumentative or anything, but my experience has been exactly the opposite. Most people don't know it's not really a force.

 

[dmspilot00]

But the one issue that we shouldn't forget is that for circular motion the force must be central in that it points towards a center of motion. Horizontal lift alone doesn't cause a turn if it's not constrained to pass through the center of the circle. If we don't do this then the plane simply slips laterally to the side with no change in heading. Depending on the amount of bank, the rudder or elevator is what keeps the horizontal lift passing through the same point, allowing a coordinated turn.

My understanding and experience is almost the opposite: that you do not need rudder in an established coordinated turn. You do need rudder in order to cause an airplane to slip. However, I do recall that the book Aviators for Naval Aerodynamics or whatever , said that the elevator is what actually allows the airplane to turn, and I think the reasoning was that the elevator is what constrains the horizontal lift to pass through the same point, like you said. So, I'm not really sure I agree, but I don't disagree completely either. Maybe explaining more, or giving a reference would help.

 

[Mmmmmm Burritos]

Correct, the elevator/rudder is what actually makes the airplane start and continue in the circular path. You are using the elevator (and the rudder to an extent, especially at higher bank turns: think 70-80 degrees of bank) to maintain altitude. This causes rotation about the lateral axis which is pretty much aligned with the horizontal component of lift. The nose will lift into the turn. If you just bank the aircraft and let go of the controls, the airplane will slip down into the bank, and wont really turn.

I was trying to think how I can explain this one using eights on pylons but it's just too early in the morning to think clearly...