Lift and stuff.

[old man emu]

Before going on, view this video, there's a question to be answered

 

 

An 8-point roll involves rolling the aircraft around its longitudinal axis in a series of 45 degree stages with a pause between stages, and all the time maintaining the same altitude.

 

QUESTION: If the aircraft's wing produces sufficient Lift in level flight equal to the kilogram-weight of the aircraft, how much Lift does the wing produce when the aircraft is paused at the 45 degree stage of the roll? 

 

Give your answer with one word.

[facthunter]

Sufficient. Nev

[facthunter]

When it isn't you haven't maintained the altitude which was specified as a condition. In this manoeuver as distinct from a balanced turn the Keel surfaces play a part in providing lift. At the 90 degree points the wing's cannot provide lift.  Inverted it will have a negative value as distinct from a barrell roll where you won't spill a cup of coffee, IF it's done well,  but you don't maintain a fixed altitude during the process. . More than one word there.   Nev

[old man emu]

4 hours ago, facthunter said:

More than one word there. 

Nothing wrong with what you said, but you've crossed a bridge too far.

 

Here's the question again: 

5 hours ago, old man emu said:

If the aircraft's wing produces sufficient Lift in level flight equal to the kilogram-weight of the aircraft, how much Lift does the wing produce when the aircraft is paused at the 45 degree stage of the roll? 

 

I'll make it multiple guess:

A. More

B. Less

C. Same

D. I don't know.

[facthunter]

Less. Nev

[Thruster88]

Can't wait for your correct answer. In the real world the lift produced will depend on the angle of attack and airspeed,  both pilot controlled. Angle of bank is irrelevant.  

[facthunter]

I doubt I will agree with it but we'll keep that between us for the moment. Nev

[old man emu]

Damn and blast! Whenever I try to frame a question simply, five minutes after I've posted it, I see a complication that I should have ruled out. I should have further restricted the parameters by saying

 

, how much Lift does the wing produce the instant that the aircraft is first paused at the 45 degree stage of the roll? 

 

I hope that those additions will really fine tune the question. 

8 hours ago, facthunter said:

At the 90 degree points the wing's cannot provide lift. 

 

3 hours ago, Thruster88 said:

In the real world the lift produced will depend on the angle of attack and airspeed

 

Think about those statements in terms of the restated question. Just consider the very instant in time, the nanosecond,  when the aircraft reaches 45 degrees. Forget about what the pilot does next. 

 

[nomadpete]

Obviously, as Nev said,

'sufficient'.

[Jase T]

one word??? Irrelevant.... At the instant its stopped at 45 degrees of roll there are a lot of other forces acting not he aircraft including the aerofoil. Not the least of these are  Mister newtons first and third laws.. so in an instant the lift is probably irrelevant.... 

 

[old man emu]

2 minutes ago, Jase T said:

At the instant its stopped at 45 degrees of roll there are a lot of other forces acting not he aircraft including the aerofoil

When will people read what is written?

 

25 minutes ago, old man emu said:

how much Lift does the wing produce

I have already agreed that other factors will come into play, but they all tend to relate to keeping the plane flying.

 

How about we add a further factor to the question? Consider this question in terms of a wing in a wind tunnel. 

 

Does that eliminate all the extraneous factors so you can concentrate on the guts of the question?

[Jase T]

OK I need to clarify here. Is your intent to pose questions to spark discussion? Or is it just to prove you know more than everyone else and will word questions in 3 different ways to confuse and when people try to answer you will be condensing and arrogant? Just so i know whether its is even worth trying to answer because you keep moving the goal posts. You want a specific answer yet your questions are so open you can get any number of different ones. Then you post comments like "When will people read what is written"... Well I did, then you wrote something else... So when will you pose a question and accept someones answer that is different to what you wanted?

 

Edited March 28, 2021 by Jase T

[Thruster88]

Are we just looking for the trigonometry answer of 0.7071067812 times straight and level?

[Blueadventures]

C

[Roundsounds]

No

[old man emu]

10 hours ago, Jase T said:

Is your intent to pose questions to spark discussion?

Yes. But first I want to get people to really think, and to question what they believe. I'm sorry that I had to keep modifying the question by adding refinements. I did that to stop people wandering away. All I wanted people to do was to answer the question with one of the four choices. You know - the same way BAK exams are set. I even have given a clue that this is a "trick question", so beware. I wanted people to give their answer, and then I was going to get to the point. 

 

It will please some that I don't need to get into algebra or quantum physics to explain my point, which is about the psychology of learning. Here's another clue. Think about how you learned about Lift.

 

I've got to go out today, but I promise that I will give the answer and explanation of why I posed it tonight.

10 hours ago, Jase T said:

Or is it just to prove you know more than everyone else and will word questions in 3 different ways to confuse and when people try to answer you will be condensing and arrogant?

Jase T, that smarts. I don't set out to show anyone up. I just try to expose general misunderstandings. Sometimes it's like trying to convert a rabbi to Islam.

 

10 hours ago, Jase T said:

So when will you pose a question and accept someone's answer that is different to what you wanted?

Sometimes I ask rhetorical questions. Sometimes I ask questions to test people's beliefs and understanding. If I post in Student Learning, I'm obviously testing the latter. Would you accept an answer of "13" for the sum of 9 + 5?

 

See you all tonight!

[facthunter]

The wind tunnel is not helpful unless you include all the factors involved and I think it's therefore of very limited value. because there's more to this than just presenting a tilted wing to an airflow. So far the question as posed cannot be positively answered. What may seem to be able to be simply analysed isn't.  Hesitation rolls  can be done best in fast(er) aeroplanes and in some would be pretty horrendous to even attempt. Nev

[Roundsounds]

Facthunter, what are your thoughts on this process?

[facthunter]

You may notice I usually don't get involved in these  as it's not producing productive outcomes.. In this one, something behaving (partly) ballistically is beyond assessment on a forum. Be OK in a room with the right presentation and an informed and interested audience. Maybe?  Nev

[old man emu]

Back now to give the answer to the question I posed:   how much Lift does the wing produce the instant that the aircraft is first paused at the 45 degree stage of the roll? 

 

Before I go further let me say that my answer refers only to the very instant that the wing reaches 45 degrees from the horizontal. Call that instant "T0".  Things happen at time (T0 + 1 unit of time) that are not relevant to the question as asked. I acknowledge that and as Jase T correctly said, 

21 hours ago, Jase T said:

At the instant its stopped at 45 degrees of roll there are a lot of other forces acting on the aircraft

but that is at (t1 + 1 unit of time), and that 1 unit of time can be a small as you like. I agree with Jase T,  so it should be unbelievably small.

 

The cigar goes to 

10 hours ago, Blueadventures said:

C

C. Same

 

Here is why I come to that answer. 

 

As I said, 

9 hours ago, old man emu said:

my point, which is about the psychology of learning. Here's another clue. Think about how you learned about Lift.

Which of you has not seen diagrams or photographs like this:

or this one:  

 

 

In both, we are presented with a view of the side elevation of a wing. These images are implanted in our minds, and affect the way we think about situations. Now, if you are using a mouse, pick it up. If not use a pen or ruler to represent a wing. Put the thing down on the desk and look at the top side. Imagine that is a plan view of a wing. As it sits on the desk it represents a wing that is moving through the air, parallel to the Earth's surface.

 

We know that before the aircraft moves, it is being acted upon by a vertically downwards force caused by the acceleration due to gravity. Call it the "weight force" To get the aircraft into the air, we have to cause the wing to generate a vertically upwards force that, for level flight, has to equal the vertically downwards weight force. For the wing to generate Lift, air has to pass over and under the wing. For best Lift, that flow has to be from leading edge to trailing edge. A flat plate will generate Lift, but we have learned to get more Lift by better design.

 

So, let's go back to the 8-Point Hesitation Roll. Prior to beginning the roll, the aircraft is flying with its wings parallel to the Earth's surface. The direction of the air (which we call the relative airflow if our frame of reference is the leading edge of the wing from tip to tip), is from directly in front. As a result of all the aerodynamic mumbo-jumbo, the amount of Lift produced by the wing is equal to the weight force acting on it. The forces are balanced, so the wing and attached aircraft neither rises nor falls.

 

Pick up you mouse, ruler, pen and hold it horizontally in front of you to represent the plan view of a wing. Now, lower one end of the "wing"  45 degrees. The relative airflow is still coming from the front. Therefore, at that instant, the Lift generated by the wing in relation to the relative airflow is exactly the same as when the wing was horizontal to the Earth's surface. 

 

That is at T0 . At T0 + 1 things go to pieces. We know that because the Lift Force is a vector that is the result of adding (in a two-dimensional representation) the vertical component and the horizontal component. If the Lift vector is offset from the weight vector by 45 degrees, then the vertical component will be less than the weight force, and things have to be done if the pilot wants to keep the aircraft on the same heading and the same altitude. That's where this comes in.

14 hours ago, Thruster88 said:

Are we just looking for the trigonometry answer of 0.7071067812 times straight and level

The vertical component of Lift is ~ 70% of the straight and level component of lift. Therefore, as everyone knows, the amount of lift required to maintain a 45 degree bank is

(1/0.7) x weight

= 1.42 x weight.

There is a number of actions a pilot can take to increase the Lift force, but that are things most of us know and mentioning here does not add to this particular discussion.

 

To get to the psychology of learning, we are so used to thinking of the generation of Lift, and things like Angle of Attack based on these side elevation images that have been planted in our minds from textbooks and whatever. We fail to have in our minds that the air is all around our wings, but our wings don't know up from down. All a wing wants is for the relative movement of air to be from leading edge to trailing edge. We have to be careful about what images we put into our minds as illustrations of concepts. 

[Bruce Tuncks]

At 90 degrees, the fuselage provides the lift. At 45 degrees, the wings would provide most of the lift but the fuse would be providing some.

When you see a model flying in this mode, you sure see a high angle of attack for the  fuse/wing.

I am talking about a hesitation roll.

[aro]

1 hour ago, old man emu said:

Pick up you mouse, ruler, pen and hold it horizontally in front of you to represent the plan view of a wing. Now, lower one end of the "wing"  45 degrees. The relative airflow is still coming from the front. Therefore, at that instant, the Lift generated by the wing in relation to the relative airflow is exactly the same as when the wing was horizontal to the Earth's surface.

That is true if the aircraft is instantaneously rotated around an axis perfectly aligned with the airflow.

 

But it's not real life. In real life, even at maximum roll rate it takes time to go from 0 to 45 degrees. It also depends on the skill of the pilot, but lets assume the pilot can fly the roll perfectly.

 

As the pilot begins the roll the lift vector is pointed to the side, which would begin to turn the aircraft. To prevent the turn, opposite rudder is required and the aircraft is in uncoordinated flight. At 45 degrees, the wing provides half the lift, and the side force on the fuselage due to uncoordinated flight provides the other half. The wing and fuselage produce equal and opposite sideways forces which means the aircraft does not turn.

 

The wing is providing half the vertical lift at a 45 degree angle. That requires less total lift than supporting the whole aircraft at zero degrees bank.

 

To fly it perfectly, the rudder needs to be increased and AOA of the wing decreased as the aircraft rolls from 0 to 45 degrees.

1 hour ago, old man emu said:

The vertical component of Lift is ~ 70% of the straight and level component of lift. Therefore, as everyone knows, the amount of lift required to maintain a 45 degree bank is

(1/0.7) x weight

= 1.42 x weight.

 

That is for a 45 degree coordinated turn, not a roll. A turn is totally different to a roll. In a turn, lift required increases as bank angle increases. In a roll, lift from the wing decreases as bank angle increases.

 

At 90 degrees angle of bank in a roll (knife edge flight) the lift required from the wing is zero. At 90 degrees angle of bank in a turn the lift required from the wing is infinite i.e. a coordinated 90 degree banked turn is impossible.

[APenNameAndThatA]

This is ludicrous. You are presenting yourself as a teacher on this forum when you believe a) That a spirit level can be used to measure angle of attack and b) something with a weight of 3 kg has a mass of 0.3 kg. It would be fine, except some people will believe what you write. The more well-respected posters to this forum should not stand for it. 

[old man emu]

1 hour ago, aro said:

That is true if the aircraft is instantaneously rotated around an axis perfectly aligned with the airflow.

I really do give up. No matter how much I try to clarify and have people's attention hone in on the point I'm making they have to go past the point I want to stop at.

 

What is so unclear about this? If the Lift vector is offset from the weight vector by 45 degrees, then the vertical component will be less than the weight force, and things have to be done if the pilot wants to keep the aircraft on the same heading and the same altitude.  Lower one end of the "wing"  45 degrees. The relative airflow is still coming from the front. Therefore, at that instant, the Lift generated by the wing in relation to the relative airflow is exactly the same as when the wing was horizontal to the Earth's surface. That is at T0 . At T0 + 1 things go to pieces.

 

And finally, There is a number of actions a pilot can take to increase the Lift force, but they are things most of us know and mentioning here does not add to this particular discussion.

 

Go back an look at the video. Can you accurately measure to time it takes for that plane to go from straight and level to the first 45 degree point? 

 

How about this. We take a scale model wing and put it in a wind tunnel and do what needs to be done to measure the Lift force with the wing horizontal. Then we arrange the measuring system to measure the Lift force when the wing is at a number of different angles from the horizontal. In the wind tunnel we have airflow relative to the wing. We have a way of holding it so that it does not turn. Then we can look at the data and see if there is variation in the Lift Force.

 

And just to smooth ruffled feathers. What aro said is completely true and I agree with him. However, he has taken the discussion into an area where the question wasn't dealing with. 

 

 

[old man emu]

7 minutes ago, APenNameAndThatA said:

This is ludicrous. You are presenting yourself as a teacher on this forum when you believe a) That a spirit level can be used to measure angle of attack and b) something with a weight of 3 kg has a mass of 0.3 kg. It would be fine, except some people will believe what you write. The more well-respected posters to this forum should not stand for it. 

The sharks think that there is blood in the water.

 

a) That a spirit level can be used to measure angle of attack

If you bothered to read   https://www.recreationalflying.com/topic/37354-will-someone-settle-up-on-a-bet/?tab=comments#comment-504372  I said, "I never said that a simple bubble spirit level would be the ultimate answer to the problem of indicating the proximity of the chord line to the stall angle. I said that it could be used to give an indication." I did a bit of work and asked someone from the Shuttleworth Collection for an opinion. 

 

I get the impression that you have never had the experience of designing, planning and making anything. If you did, you would know that some ideas start off simply, but during the making show that modifications need to be made. 

 

b) something with a weight of 3 kg has a mass of 0.3 kg.

Again, you didn't bother to look at this: https://www.topperlearning.com/answer/what-is-one-kg-wt-how-many-newtons-makes-1-kg-wt/ez2t3ii 

 

By the way, can you show me where and when I purported to be a teacher? As far as I believe, I pose some questions and do the research to support answers I give.

 

I wait with bated breath for you to post something that leads to an intelligent discussion.