# aircraft banked turn

Discussion in 'General Science' started by Ajibade Tobi, May 11, 2015.

Apr 19, 2015
5
0
please friends,in other to maintain a constant radius(steady turn),which force balances the centripetal force.........I am getting confused,I said it's 'weight' but my classmate said it is 'lift'

2. ### joeyd999 AAC Fanatic!

Jun 6, 2011
2,674
2,724
There are four forces affecting an aircraft: thrust, lift, drag, and weight.

One of these provides the centripetal (center-seeking) force to accelerate the plane perpendicular to the direction of the velocity vector, and parallel to the ground. Which one could it be?

3. ### MikeML AAC Fanatic!

Oct 2, 2009
5,450
1,066
Here is a discussion. First couple of flight lessons I took 40 years ago, the instructor showed me the difference between a "coordinated" and an "uncoordinated" turn. You can tell if you are doing it right just by the forces on the cheeks of your butt. 4200 flight hours later, I do it by feel with out looking at flight instruments. Actually, it is a basic skill learned in the first few flight hours. Besides, uncoordinated turns make your passengers feel sick and vomit...

4. ### BR-549 Well-Known Member

Sep 22, 2013
1,981
388
I am not a pilot, but using joe's four forces, I would say thrust.

I disagree with a lot of Mike's discussion link. A plane banking vs ball on string is apples and oranges.

And would a good turn mean equal pressure on the cheeks?

5. ### MikeML AAC Fanatic!

Oct 2, 2009
5,450
1,066
Yes. You fly the airplane so that no sideways force is felt in the turn. A blindfolded passenger wouldn't know that the airplane is in turning flight, except that they might notice a slight increase in gravity pushing downward in their seat.

Here is the ultimate demonstration of that (by Bob Hoover, one of my favorite airshow pilots)

BR-549 likes this.
6. ### BR-549 Well-Known Member

Sep 22, 2013
1,981
388
That is a great video.

I am going to assume that to start this maneuver, you guide the plane up, to set the cup, until the turn(inertia) can hold it?

And do you try to hold the center line of the roll......just a ways above the cockpit?

If I get this.......the cup, coffee stream and pitcher formed a straight line of the radius.

It looked to me that the origin of that radius was maintained somewhere above the cockpit.

Is that right? Sorry, I don't know all the pilot terms.

7. ### studiot AAC Fanatic!

Nov 9, 2007
5,005
513
Thank you mike for both those links.

The point was very clearly made.

and goodness gracious great balls of fire, I agreed with joey

8. ### WBahn Moderator

Mar 31, 2012
17,720
4,788
I went out flying one day and when I started to preflight the aircraft I set a full (hadn't taken even a sip out of it), but opened, can of Diet Pepsi on the floor in front of the fuel-selector knob. Then I proceeded to forget about it. On that flight I did a lot of stalls, including accelerated maneuver stalls in which you establish a 45° banked turn and then pitch up until the plane stalls. I also did a lot of 60° banked turned about a point, S turns across a road, and figure 8s. When I got back down and was getting all my stuff out of the plane I noticed the can of pop still sitting there looking fat, dumb, and happy that hadn't spilled a drop. That was when I knew that I had truly done a good job staying coordinated throughout the entire flight.

9. ### WBahn Moderator

Mar 31, 2012
17,720
4,788

I don't know if they have ever corrected it, but the official FAA diagram of the forces acting on an aircraft in a turn was (is?) wrong for decades as it showed, properly, the horizontal and vertical components of lift and then the weight (thrust and drag were into/out-of the page and so weren't depicted). But then they just HAD to show the "centrifugal" force acting outward with the next result being that their diagram showed zero net force acting on the aircraft.

10. ### joeyd999 AAC Fanatic!

Jun 6, 2011
2,674
2,724
I just read an explanation somewhere (don't remember) that the centrifugal force exists as a 'real' force from the point of view of an accelerating reference frame (i.e. the frame rotates with the aircraft, so the forces are "balanced" with no net force on the craft). In an inertial reference frame (of which we are more accustomed to in real life), the presence of a centrifugal force that counters the centripetal force would quite obviously prevent the plane from changing direction, i.e. the forces must be unbalanced in order to effect a change in the velocity vector.

Another way to look at this: an object who's thrust exceeds its weight accelerates uniformly along it's direction vector. The imbalance causes the acceleration. If viewed from within an accelerating reference frame (coinciding with the instant velocity of the object), the thrust is balanced by the inertial mass of the object, thus the net forces become equal.

But I think we had this conversation already, a few weeks ago.

Edit: BTW, I wonder if the OP ever formulated the correct answer...

Edit 2: So not everyone is now thoroughly confused, in the second paragraph I referred to thrust and weight: I was thinking of, say, a rocket where 'lift' is provided by the thrust. In the context of an aircraft, please replace the concept of thrust with lift. It's all relative...

Last edited: May 13, 2015
11. ### WBahn Moderator

Mar 31, 2012
17,720
4,788
But if the view is from the accelerating reference frame of the airplane, then the plane ISN'T turning and the whole question is nonsensical. You can't ask about the forces that are causing a plane to turn unless you are talking about forces within a reference frame in which the plane is, in fact, turning.

As far as thrust exceeding the weight -- I'm not sure what you are talking about -- nor what direction vector you are talking about. The thrust of the vast majority of airplanes do NOT exceed their weight, yet they accelerate just fine as long as the thrust exceeds the drag.

12. ### joeyd999 AAC Fanatic!

Jun 6, 2011
2,674
2,724

Apr 19, 2015
5
0
i still haven't got an answer.....which among these forces:thrust,weight,lift and thrust?....

14. ### studiot AAC Fanatic!

Nov 9, 2007
5,005
513
Nothing 'balances' the centripetal force.

The centripetal force is a real force that is provided by the horizontal component of the lift, which itself is not vertical in a banking aircraft.

15. ### WBahn Moderator

Mar 31, 2012
17,720
4,788
It is the centripetal force that is keeping the plane in the turn. If you balance it, then the plane will no longer be in a turn.

The horizontal component of the lift IS the centripetal force.

16. ### DerStrom8 Well-Known Member

Feb 20, 2011
2,428
1,328
What other options were you given? I don't think either of those is correct.

17. ### WBahn Moderator

Mar 31, 2012
17,720
4,788
And it sounds more like guessing than thinking.

18. ### BR-549 Well-Known Member

Sep 22, 2013
1,981
388
I would guess that lift is the expression of centripetal force and mass(inertia of craft) is the counter force.

Is that close?

Mar 31, 2012
17,720
4,788
No.

Nov 9, 2007
5,005
513