Bubblehead
Well Known Member
I almost always fly alone so cg and gross weight is not an issue. When my wife flies with me I know where to put the baggage to keep in cg but I started running some weight and balance scenarios to see what the max passenger weight would be for different conditions of baggage and fuel.
The scenarios gave me data points but no wisdom, insight or understanding.
Over the weekend I started thinking about how to mathematically work it out and possibly chart the results in a way that with a glance I could know the max passenger weight. I started reading up on nomographs and learned a lot but generating them takes a lot of time. I finally decided that even if I developed one it would be difficult to use. I wanted something simple.
Here's the progression of charts based on a pilot weight of 225 lbs. (i.e. me). Each line is a different baggage condition and the horizontal axis is fuel on board in gallons. Pick the config and fuel and read the max passenger weight on the left.
Step 1 - Limiting rear seat passenger weight based on Standard Category 1800 lb max gross weight generated this graph. It is pretty straightforward. Don't worry about the curved portion at the bottom. That is just caused by the compression of the 42 gallon to 40 gallon portion of the graph. This relationship is linear. If you have full tanks your passenger cannot weigh as much as if you had only 1/2 fuel..
Step 2 - Limiting rear seat passenger weight based on the Standard Category most aft cg. This addresses the fact that less fuel means a more aft cg so the passenger weight gets more critical as fuel burns off. Note that the lines for different amounts of baggage slope down - the opposite way of the gross weight curves. Note that adding baggage to the front compartment helps with maintaining cg. Not a surprise but the effect was larger than I expected.
Step 3 - Limiting rear seat passenger weight based on either gross weight or cg, whichever is more limiting. Funny looking chart but very interesting if I have the math correct.
Conclusions:
1) with baggage in the rear and full fuel you can't have a very heavy passenger!
2) Baggage in front helps below 20 gallons of fuel but limits passenger weight with full fuel due to gross weight limits.
3) THE BIG ONE - if you look at the cg one only, you will see that cg moves aft with fuel burn, so you could be in cg early in a flight and out of cg aft late in the flight. If the flight is long enough and the passenger big enough you could get into trouble.
4) The other BIG ONE - when using the chart consider fuel state throughout the flight. For example, with full baggage (red line) and 25 gallons of fuel everything is cool with a 181 lb passenger, but as fuel burns off the passenger would have to loose weight to keep in cg limits! At 10 gallons the passenger would have to be 161 lbs to still be in limits!
This should be an interesting discussion!
The scenarios gave me data points but no wisdom, insight or understanding.
Over the weekend I started thinking about how to mathematically work it out and possibly chart the results in a way that with a glance I could know the max passenger weight. I started reading up on nomographs and learned a lot but generating them takes a lot of time. I finally decided that even if I developed one it would be difficult to use. I wanted something simple.
Here's the progression of charts based on a pilot weight of 225 lbs. (i.e. me). Each line is a different baggage condition and the horizontal axis is fuel on board in gallons. Pick the config and fuel and read the max passenger weight on the left.
Step 1 - Limiting rear seat passenger weight based on Standard Category 1800 lb max gross weight generated this graph. It is pretty straightforward. Don't worry about the curved portion at the bottom. That is just caused by the compression of the 42 gallon to 40 gallon portion of the graph. This relationship is linear. If you have full tanks your passenger cannot weigh as much as if you had only 1/2 fuel..
Step 2 - Limiting rear seat passenger weight based on the Standard Category most aft cg. This addresses the fact that less fuel means a more aft cg so the passenger weight gets more critical as fuel burns off. Note that the lines for different amounts of baggage slope down - the opposite way of the gross weight curves. Note that adding baggage to the front compartment helps with maintaining cg. Not a surprise but the effect was larger than I expected.
Step 3 - Limiting rear seat passenger weight based on either gross weight or cg, whichever is more limiting. Funny looking chart but very interesting if I have the math correct.
Conclusions:
1) with baggage in the rear and full fuel you can't have a very heavy passenger!
2) Baggage in front helps below 20 gallons of fuel but limits passenger weight with full fuel due to gross weight limits.
3) THE BIG ONE - if you look at the cg one only, you will see that cg moves aft with fuel burn, so you could be in cg early in a flight and out of cg aft late in the flight. If the flight is long enough and the passenger big enough you could get into trouble.
4) The other BIG ONE - when using the chart consider fuel state throughout the flight. For example, with full baggage (red line) and 25 gallons of fuel everything is cool with a 181 lb passenger, but as fuel burns off the passenger would have to loose weight to keep in cg limits! At 10 gallons the passenger would have to be 161 lbs to still be in limits!
This should be an interesting discussion!
