G-force

[Panther91]

First of all, G-force and load factor is the same thing, right? If it is then I'll get to the point.

1. On wikipedia when I was reading what is load factor, I read that that's the ratio of the lift on an aircraft to the weight of the aircraft. So it means that an aircraft in straight and level flight has a load factor 1 which means that lift is equal to weight.

[michaelb15]

I dont really know, to the exact science, but I understand the concepts..

I think the one thing thats missing is angle of attack.

beecause say your plane's wings are stalling, but just sheer engine power is keeping it in that bank.

there are many variables as well.. Wing surface area.. Wing design.. speed of the aircraft.. altitude.. weather variables..

the only way to bring this to a science I think is test each individual aircraft.

2 g's is probably just an average number.

[Reno]

Firstly, NEVER try to find the realistic number in FS9, especially with the fighters. The IRIS F-15 for instance, it stalls at 10* AoA.

AoA is the big thing.

Load Factor is the EXACT same thing a G-Force.

60* bank, speed depending, will give you about 2G's. Tried and tested. Even fighters at cruise speed will give you 2G's in a 60* bank.

But most of the time it's pretty much within .2G's of 2.

Cheers
Reno:cheesy

[michaelb15]

hers a good wiki article

http://en.wikipedia.org/wiki/Banked_turn

[Panther91]

Firstly, NEVER try to find the realistic number in FS9, especially with the fighters.

Of course. It was the Falcon 4 Allied Force F-16.

[Reno]

Oh, well then, yes, trust that.

[DaveSims]

When it comes to the bank angles, 60 degrees will require 2g's to maintain altitude.  The reasoning is it takes 2g's of lift, or 2x the lift to maintain the same altitude that 1g will give you in level flight because some of the lift is now being directed horizontally and causing the aircraft to turn.  

Aircraft weight doesn't have an effect on G-Force.  G-force is like a multiplier for the weight.  At 2g's the aircraft now ways 2x as much, including the pilot.  Thats why high G turns affect pilots so much, at just 5gs a 200 lb pilot now weighs 1000 lbs.  

The difference in rate of turn is due to the speed difference.  The faster you go, the less you turn.  Imagine you are driving.  To experience a high force turn at slow speed you have to turn pretty sharp, but at high speed just a smaller turn will put you in the passenger seat.  

The Cessna is not designed for high G, 3 or 4 is all you'll get out of them just due to aerodynamics.  There is a lot more to it, manuevering speed etc.  If you have any specific questions I see if I can help out some.

[beaky]

First of all, G-force and load factor is the same thing, right? If it is then I'll get to the point.

1. On wikipedia when I was reading what is load factor, I read that that's the ratio of the lift on an aircraft to the weight of the aircraft. So it means that an aircraft in straight and level flight has a load factor 1 which means that lift is equal to weight.
   When I was reading on wikipedia about G-force it said that g-force quantifies the apparent gravity caused by acceleration expressed in units of standard gravitational acceleration, nominally 10m/sec2.
I don't see the connection between these two terms (load factor and g-force). On what acceleration are they reffering?

Gravity itself is not a force, but simply a tendency for stuff to accelerate towards the center of a mass. "G-force" feels the same as gravity because of acceleration not so much in terms of increasing airspeed, but in terms of speed along an arc-shaped path, whether one is rolling or looping, turning or pulling out/pushing over. Whenever a mass swings around a point, it experiences acceleration more or less at a right angle to its curved path. Tie a rock to a string and swing it in a circle, and it "gets heavier" and pulls on the string more than when it's just dangling. It's the "centrifuge effect".

 Any time you transition from straight and level flight to a maneuver that "increases G", you are accelerating whether your airspeed increases or not. Some maneuvers, like a perfectly-executed barrel roll, don't add any G, because the changes are very subtle, there's not much up or down elevator involved, and of course the loading counteracts the normal pull of gravity during the inverted portion.

2. Does g-force or load factor have anything to do with the weight of the aircraft? Does it have an influence on lift?

Load factor is usually mentioned in terms of changes, which occur regardless of weight, but sure, the more weight you put on a wing, the greater the load factor.
Changes in load factor influence lift indirectly, because the performance envelope decreases as load factor increases. In other words, if your straight and level stalling speed is, say, 70 knots, in a turn that number will be higher. It increases, in fact, relative to the square of the load factor, so your stall speed at 30 degrees of bank will be more than twice as much as the difference between zero and 15 degrees.  Shown as a graph, this stall speed increase has a very similar curve to the load factor increase.
So in other words, because the airplane is "heavier" in a turn or pullup from a dive, the wing becomes less efficient, as if there were more weight on it. Remember, the whole plane is set up so that in order to maintain level flight, the wing provides enough lift to counteract gravity... within a set weight limit.
High-G maneuvers simulate increased aircraft weight, so as you yank 'n' bank, the wing "thinks" the airplane is heavier.


[quote]3. On 60

[Panther91]

Sorry I didn't asked you this before but I didn't come up with any questions up until now.

1. If load factor is the ratio between lift and weight, then why is load factor=1 while the aircraft is staying still on the ground? There is no lift then so how come the ratio is 1?

2. G-force above 1 exists when the plane is accelerating, but why doesn't the g-meter never show it on neither aircraft? That is a "horizontal" g-force, right? The G-meter only shows g>1 when lift is increased due to turning or something else. So does it mean that the g-meter shows only the "vertical" g-force (ratio of lift and weight) and not g-force caused by acceleration?

3. How does a simple g-meter work? How does he know the ratio between lift and weight?

As far as I can understand the term load factor is only used in aviation when it comes to ratio between lift and weight, but the term g-force itself is used in many other things and does not mean only ratio but also acceleration, decceleration... Is this true?

[DaveSims]

1.  Not quite sure where you are getting a load factor of 1 on the ground.  G force on the ground is one, but the aircraft is not creating any lift.  

2. G-force in an aircraft is only measured in the vertical axis, a G-meter wouldn't read acceleration or deceleration forces in the horizontal.  

3.   In a nutshell, imagine a small weight on a spring attached to a dial.  The more G-s you pull, the heavier the weight gets, basically like a scale.  Electronic ones may have some type of contact type device.

[Panther91]

1.  Not quite sure where you are getting a load factor of 1 on the ground.  G force on the ground is one, but the aircraft is not creating any lift.

1. Does anybody know from where is the load factor of 1 on the ground coming from?

2. Under negative g-forces, would the pilot "fall" on his head upside down if his seat belts were not on and tight?

3. When talking about "horizontal" (from acceleration) g-forces, there aren't any positive or negative g-forces, right? We always say that's positive g-force, right?

[DaveSims]

2.  Yes he would, or if in an open cockpit plane, fall out.  

3.  I suppose you could apply positive and negative to the horizontal, but usually its just called g-force.

[Splinter562]

1.  Not quite sure where you are getting a load factor of 1 on the ground.  G force on the ground is one, but the aircraft is not creating any lift.

1. Does anybody know from where is the load factor of 1 on the ground coming from?

2. Under negative g-forces, would the pilot "fall" on his head upside down if his seat belts were not on and tight?

3. When talking about "horizontal" (from acceleration) g-forces, there aren't any positive or negative g-forces, right? We always say that's positive g-force, right?

1) That particular definition is only valid for an aircraft in flight. For an object to be in a steady state (not accelerating), the sum of the forces must be zero. In level flight, that means lift/weight, thrust/drag balance. On the ground, things get more complicated. When stopped (with no wind) the weight is balanced through the reaction forces between the landing gear and the ground. The thrust from the idling engine is balanced by the static friction between the tires and the ground. As you start a takeoff roll, the wings start supporting more of the weight and the gear less, until you become airborne and the wings are supporting all of the weight.

2) This is one of the many reasons most aerobatic aircraft have a 5 point harness. Needless to say, floating around the cabin would severely impede the pilots ability to fly the aircraft.

3) Airplanes are generally broken down into a 3 axis system. The Z axis points down through the floor of the aircraft. The X axis points foward through the nose of the aircraft. And the Y axis points out the right wing of the aircraft. These axes remain fixed to the airplane regardless of it's attitude. That is to say that if the aircraft were inverted the Z axis would point through the floor which would be up to an observer on the ground.

There can be positive or negative G-forces in any of the axes. The sign is positive if the force is acting in the same direction of the axis. So an aircraft doing a catapult shot from a carrier would have a positive G-force in the X axis and it would have a negative G-force in the X axis when trapping a wire on landing.