watchyouralt

As you're rolling the aircraft and increasing the horizontal component of lift are you not in turn reducing the VCL and therefore requiring more back pressure to create more lift and maintain level? So as I roll the airplane into a steep turn I have to increase back pressure, accelerating the aircraft. Even if its only slight accelerations, until reaching the desired bank, you are accelerating. So at high enough speeds slight accelerations could impose a load. There really is no such thing as a perfectly level turn, and you cant initiate a roll without acclerating the aircraft to achieve a higher AOA and maintain level.
Just my opinion

I dont think youre wrong with what you're saying, it's just seemed to text book like.

Brian Z

I am missing your point on accelerating. How are you accelerating by increasing back pressure in a steep turn?

shdw

You are making an assumption that wasn't applied to the scenario. When rolling into knife edged flight, even if done slowly, the idea is not to turn. Instead, altitude is maintained by entering uncoordinated flight, a combination of rudder and elevator to maintain altitude, while at the same time, avoiding turn entry. When finally in a knife edge, the rudder acts as the elevator with regards to maintaining altitude.

The point is, Va is directly related to angular acceleration. You can bank the aircraft without having angular acceleration.


Brian: Angular acceleration is a biproduct of pressures on the elevator. For instance, a loop is nothing more than back pressure that causes and angular acceleration. To link it all together consider this: back pressure causes angular acceleration, angular acceleration results in g-forces.



Hope this helps you guys, I am a few drinks in tonight, so much for recovery Sundays! Cheers!

Foxy

(This was in response to a statement about knife-edge flight..)

Not necessarily. With the wings unloaded, bank angle is irrelevant. You can be at 90 degrees with no horizontal component of lift, with the vertical component of lift being produced entirely by the fuselage.

When referring to to maneuvering flight, "horizontal component of lift" and "vertical component of lift" are a bit simplistic.

Accelerating..? Accelerating the rate of turn slightly, yes. But that's secondary to the act of rolling the airplane.

I really do think it would behoove everyone to have a little bit of acro under their belt.. I'm often a bit confused by how people see the mechanics of maneuvering flight. I almost think we "simplify" things so much when teaching aerodynamics that we re-complicate them--but convey an essential misunderstanding of their nature.

~Fox

gestrich1311

I'll start with a definition then my .02

Per the PHAN "Any force applied to an aircraft to deflect its flight from a straight line produces a stress on its structure, and the amount of this force is the load factor."

Here are my personal thoughts on what's going on when the aircraft is descending in a turn:

An aircraft turning is not moving in a straight line therefore a positive load is placed on the wings. The "straight line" is constantly changing resulting in constant acceleration. But why does the load only seem to be experienced when altitude is maintained? Is it the altitude or bank that is producing the load? It is the bank - here is why-

When the aircraft's flight path is changed downward in a turn, a negative load is induced on the aircraft. Conveniently, the loss of vertical lift aids in decreasing the altitude so if the pilot decides not to adjust attitude at all in a turn, the aircraft will descend naturally. This will help to decrease the positive load factor from the wings.

The canceling effects of these two loads will only be experienced momentarily. Once the aircraft is stabilized in a downward flight path, the negative load factor will diminish however the positive load from the wings will not be cancelled out anymore.

In essence, maintaining altitude is not what produces the positive load, the turn causes the positive load... It just so happens that a downward pitch has the reverse effect on load factor which cancels out the effects of the load factor from the turn.

watchyouralt

Sorry I didnt even read the knife edge part, I tend to overlook things in parenthesis.
I was referring more to the original question bellow even though I quoted you on that one hahaha. Now I'm assuming the original poster wasn't planning on doing knife edge flight, but I could be wrong since he only said bank.

But in a scenario where a pilot enters into a steep level turn there would be that angular acceleration, correct?

So back to your original post:
How can a 60 degree bank level turn be initiated and maintained without there ever being any acceleration? If you do that at VNE the slightest accel. could over stress the plane.

plasticpi

Turbulence aside, you can do a 60, or even 70 degree banked level turn without exceeding normal category limits, whether you're at Vne or 1 knot. Load factor is a factor of bank angle in a level turn, and independent of airspeed in that case. A 60 degree level turn gets you a load factor of 2 Gs, at 1, 100, 1000 knots.

Rolling into a 60 degree level turn will not itself overstress the aircraft, no matter the airspeed. Now, if you do it with full aileron deflection at Vne, we might have some problems, but we're not talking about that. At Vne, you could roll into a normal steep turn, and never exceed any limitation of the aircraft, not any more than you would at Va.

Think of sitting on an airliner going several hundreds of knots rolling into a 30 degree turn. You don't feel any more acceleration than you do in a 152 going 80 knots rolling into a 30 degree turn. The difference shows up in the turn rate. The airliner is going to turn at a degree or two per second (estimated), the 152 several degrees per second.

shdw

Fox (Is this actually your name or just a forum name? I don't typically see people sign their "forum" name.) Anyways, I agree completely, with this and the necessity for at least some aerobatics.



Gestrich: I am totally lost, why are we descending? What scenario are you trying to introduce? What is the goal of introducing this scenario?

It is neither the bank nor the altitude that induces load, in essence, they are irrelevant. Load is produced, as previously mentioned, by angular acceleration (not to be confused with a turn, bank, or altitude). Instead, it is the direct result of forward or aft pressure on the yoke.



Watchyouralt: I suggest you go back and reread then. As you asked, "without there ever being any acceleration," cleverly in bold I might add. That has been answered at least twice in previous posts, by me and another poster.

I would also ask, what acceleration are you referring to and how do you suspect it would happen? From your wording I am assuming you mean an increase in speed?

Fly Boy Knight

getrich: I have to say after 3 years as a CFI, I never did think of it like that but I do have to say, I think you are right however, I think we are loosing site of which load / Acceleration we are concerned with with regards to over-stressing/over "G-ing" an aircraft

getrich is correct in saying that when we bank (just bank, no mx altitude), an acceleration is taking place with regard to displacing the aircraft from a straight line thus some load is being imposed on the aircraft however, this acceleration /load is (more or less) a lateral (transverse) load, not a positive/negative wing load. If you are sitting in the airplane as it rolls, lift still goes straight up however, gravity still pulls toward Earth which is now to you left or right (which ever way you are banked). This means that gravity instead of simply pulling straight down, is now pulling the aircraft to the side which is loading the airplane in the lateral (transverse) direction (much like simply stepping on the rudder in level flight would do, just not so drastic). So, finally, getrich is right, the act of banking period does, itself, impose a load/acceleration on the airplane.

That said, When the FAA/PHAK talk about turns and load factor, they are referring to positive/negative wing loading. With respect to turns, the only loading that the FAA / PHAK / Va / over-stressing the wings are concerned with are positive/negative G loading and if the pilot rolls into a 60 degree bank without maintaining altitude, there is no additional lift being produced by the wings therefore, no additional load is being produced (REMEMBER Positive Wing loading ONLY is of interest here, not lateral load)

The lateral load caused by the bank itself is insignificant with respect to over stressing the aircraft. Think of lateral load like a slip. There is no limitation to my knowledge of a max speed where you can slip an airplane (using max rudder = max lateral force) therefore regardless of speed, there is no real chance of damaging the airplane via lateral acceleration short of knife edge flight into the ground

When we maintain altitude during a 60 degree bank turn, we increase the amount of lift produced by the wing therefore, we induce additional positive wing load. This is the load of interest when we are talking about the load factor experienced in a turn and this is the load where Va comes in.

More or less my $0.02. (more like $0.15)

Listening to myself type is fun

shdw

Consider this, with a model aircraft. Bank that aircraft, using normal pressures to keep 1G flight and sufficient rudder to remain coordinated. This action produces absolutely no lateral load. The only acceleration is a resulting forward acceleration from descending flight.

Without the application of rudder, making the flight uncoordinated, there is and never will be a lateral load. If this helps, consider that the inclinometer (ball) is designed to show the pilot when a lateral load is introduced.

A lateral load can only be introduced with application of the rudder or some outside force. An aircraft in knife edge, is therefore, experiencing a 1G lateral load, since weight is supported by this lateral lift.


All acceleration loads are, "regardless of speed." Load, from acceleration, are nothing more than degrees traveled over a given time. This is evident by the units used for angular acceleration, typically radians/sec^2. Speed is not part of it, never will be.

Let's take this slightly further, recall a knife edge is 1G lateral load. Assume an aircraft is capable of flying at Vne in knife edge, highly unlike, but let's assume. Even at Vne, in knife edge, they still only have 1G, just like level flight at Vne produces a 1G load on the wings.