Can you explain the forces in a turn?
From FlightSim
Q: I am having a little trouble understanding forces of an aircraft in a turn. I understand that lift is broken down into two components , horizontal and vertical component of lift. Giving a total lift. I also understand that weight and Centrifugal force combine to make a load factor. However I am unsure how all this comes together as it relates to an aircraft. Does total lift/weight=LF? I am really not even sure how to relate this question to all of you. But any web sites that you all may have that explain forces in a turn would be great!
A:
Sounds like you have the right idea coming along. Essentially, when an aircraft banks into a turn, the lift vector is divided (as you said) into vertical and horizontal components. As you decrease the vertical component of lift by increasing the bank angle (assuming you're holding altitude constant), you are increasing the Load Factor because you're increasing the lift generated by the wings, which, as you stated, is the lift generated by the wings divided by the weight of the aircraft.
Remember that because you are needing to generate more lift, you will need to pull back on the yoke to maintain altitude and this increases your angle of attack (AOA). Now you are flying closer to the critical AOA which means that your stalling speed in a turn goes up as the bank angle increases.
One more thing kind of off topic: for a given true airspeed and angle of bank, you will have a given radius of turn and rate of turn. In other words, if you are flying at 180 KTAS in a MD-11 banking at 25 degrees, you will have a given radius and rate of turn. If you also fly a 737 and fly it at 180 KTAS and 25 degrees of bank, it will have the same radius and rate of turn regardless of aircraft type, weight, CG, etc.
Hope this helps some..lemme know if I was babblin' too much. Safe flying!
- Colin
Colin has it right, but it might help a tad to add a comment or two. The "lift" force generated by the wings has to do double duty in a turn, providing both the lift for the aircraft to maintain altitude and the turning force pulling the aircraft around the turn. Of course the G-force you feel in your seat (2 Gs at 60º bank in level flight) is the result of your inertia fighting the pull of the wing, in addition to the force of gravity itself. The steeper the angle of bank, the more G-force you have to pull to maintain altitude, and the slower the aircraft will go (more drag from more lift, among other things).
The above is true so long as you are maintaining a constant altitude. Relaxing the back pressure, reduces the angle of attack, decreasing the lifting force, thus the nose will drop, generally allowing the airspeed to increase and the aircraft to descend, but the g-force on your seat will also be reduced, since you are no longer fighting ALL the gravitational force, but allowing it to cause you to descend. In addition, your turn won't be as tight.
Conversely, adding back pressure will increase the g-load and start you climbing -- up to a point. In steep banks (beyond 45º), most aircraft won't do much climbing, though you'll get a tighter turn and quickly get closer to the stall, because it takes a lot of power to climb from that configuration and most aircraft don't have enough at that point.
The tail surfaces of the aircraft can be thought of much like the feathers on an arrow, helping to stabilize the aircraft. The elevator is your angle of attack control, with a higher angle of attack increasing lift, up to the point of stall, which is airflow separation from the wing, causing a (usually) abrupt reduction in lifting force.
I expect it would be a bit easier to understand if you had experienced this for yourself. Try an introductory flight, if you get a chance.
Larry N.
See also the FAA's Airplane Flying Handbook Chapter 3.
