In-flight movment of CG
- Thread starter FOD
- Start date
mtsu_av8er
Well-Known Member
Well, the CG may shift, depending on the aircraft. The CG may shift do to fuel burn, gear movement...really, depends. Remember, if you burn fuel when you fly, that's a lower moment at that location (as well as a lower total moment). That can shift things around....
Did you have a certain aircraft in mind?
Did you have a certain aircraft in mind?
MidlifeFlyer
Well-Known Member
The best description might be three questions:
Take a simple CE-172 as an example.
1. When you do your initial weight and balance, what items to you calculate the weights and moments for?
2. Which of these change during flight?
3. How does that change affect the aircraft's CG?
Take a simple CE-172 as an example.
1. When you do your initial weight and balance, what items to you calculate the weights and moments for?
2. Which of these change during flight?
3. How does that change affect the aircraft's CG?
172 is a good example
1. Empty weight, pilot and front passenger, second row passenger, baggage, fuel
2. Obviously fuel changes in flight
3. This question is just another way of stating my original question.
I am just trying to figure out which way it shifts, why, and is there an easy way to prove this?
1. Empty weight, pilot and front passenger, second row passenger, baggage, fuel
2. Obviously fuel changes in flight
3. This question is just another way of stating my original question.
I am just trying to figure out which way it shifts, why, and is there an easy way to prove this?
stuckingfk
Well-Known Member
[ QUOTE ]
172 is a good example
1. Empty weight, pilot and front passenger, second row passenger, baggage, fuel
2. Obviously fuel changes in flight
3. This question is just another way of stating my original question.
I am just trying to figure out which way it shifts, why, and is there an easy way to prove this?
[/ QUOTE ]
In every plane I have flown, the station where the fuel is at has always been aft of the C.G. range (Warrior is 95 inches, normal C.G range is usually 85-90 based on how we fly it).
If weight is burned off due to fuel burn, which is aft of where your C.G. is, the only place for the C.G. to move is foward.
172 is a good example
1. Empty weight, pilot and front passenger, second row passenger, baggage, fuel
2. Obviously fuel changes in flight
3. This question is just another way of stating my original question.
I am just trying to figure out which way it shifts, why, and is there an easy way to prove this?
[/ QUOTE ]
In every plane I have flown, the station where the fuel is at has always been aft of the C.G. range (Warrior is 95 inches, normal C.G range is usually 85-90 based on how we fly it).
If weight is burned off due to fuel burn, which is aft of where your C.G. is, the only place for the C.G. to move is foward.
ananoman
New Member
In some older aircraft like the early Bonanza it is possible for the CG to shift aft as fuel is burned. On these aircraft you have to be careful when doing W&B, because some fuel may be unavailable for use. It is possible to burn yourself out of CG and cause an unsafe condition. It is very important in these aircraft that your CG be calculated for arrival at your destination and any required alternates.
Most modern aircraft this has been solved, but the answer to your question is that the CG can move either foreward or aft, depending on the location of the fuel tanks in the aircraft and their relationship to the 'normal' CG of the aircraft.
Most modern aircraft this has been solved, but the answer to your question is that the CG can move either foreward or aft, depending on the location of the fuel tanks in the aircraft and their relationship to the 'normal' CG of the aircraft.
You'll learn that this is especially true in larger aircraft. Especially in jets when you start putting fuel all over the airframe - wing tanks, center tanks, tail tanks, etc... In my current jet - assuming a full fuel situation - the CG actually moves aft, then forward, then starts moving aft again!!!
An easy way to show this in a GA aircraft?? Simply do a weight and balance at full fuel, 3/4 fuel, half fuel, and 1/4 fuel, and even zero fuel - in a Warrior or a 172 you probably won't see much of a shift since the weights and moment arms are relatively small but you should be able to see it.
Jason
An easy way to show this in a GA aircraft?? Simply do a weight and balance at full fuel, 3/4 fuel, half fuel, and 1/4 fuel, and even zero fuel - in a Warrior or a 172 you probably won't see much of a shift since the weights and moment arms are relatively small but you should be able to see it.
Jason
stuckingfk
Well-Known Member
[ QUOTE ]
An easy way to show this in a GA aircraft?? Simply do a weight and balance at full fuel, 3/4 fuel, half fuel, and 1/4 fuel, and even zero fuel - in a Warrior or a 172 you probably won't see much of a shift since the weights and moment arms are relatively small but you should be able to see it.
[/ QUOTE ]
Here are the different C.G.'s of one of our P28-161's with two 175 lb persons up front
86.43 @ 48 gallons
86.14 @ 36 gallons
85.82 @ 24 gallons
85.48 @ 12 gallons
The C.G. moved close to an inch foward due to fuel burn from full tanks to 1/4 tanks.
An easy way to show this in a GA aircraft?? Simply do a weight and balance at full fuel, 3/4 fuel, half fuel, and 1/4 fuel, and even zero fuel - in a Warrior or a 172 you probably won't see much of a shift since the weights and moment arms are relatively small but you should be able to see it.
[/ QUOTE ]
Here are the different C.G.'s of one of our P28-161's with two 175 lb persons up front
86.43 @ 48 gallons
86.14 @ 36 gallons
85.82 @ 24 gallons
85.48 @ 12 gallons
The C.G. moved close to an inch foward due to fuel burn from full tanks to 1/4 tanks.
MidlifeFlyer
Well-Known Member
[ QUOTE ]
172 is a good example
I am just trying to figure out which way it shifts, why, and is there an easy way to prove this?
[/ QUOTE ]Sure. Take my questions one step forward. Run a weight and balance with full fuel and another with empty tanks. You'll see that the CG has moves forward. lruppert is correct about the position of the tanks.
There are weight and balance programs and spreadsheets that will do this - show start of flight and end of flight numbers or zero fuel numbers. Not usually a big deal in a 172, but it can be in some other aircraft
172 is a good example
I am just trying to figure out which way it shifts, why, and is there an easy way to prove this?
[/ QUOTE ]Sure. Take my questions one step forward. Run a weight and balance with full fuel and another with empty tanks. You'll see that the CG has moves forward. lruppert is correct about the position of the tanks.
There are weight and balance programs and spreadsheets that will do this - show start of flight and end of flight numbers or zero fuel numbers. Not usually a big deal in a 172, but it can be in some other aircraft
GregCollins2
Well-Known Member
In my Champ the datum is located at the leading edge of the wing, and the fuel tank is located behind the engine compartment with a -15 arm. The CG moves back as fuel is burned and can even move out of the manufacturer's type certificated range with a back seat passenger. I always run the numbers for both full and empty fuel when I'm taking students up.
MidlifeFlyer
Well-Known Member
Just as an illustration, here's a weight and balance graph for a fully-loaded 172P starting with full fuel and 4 170 lb souls on board
