Garmin Pilot: how to add Envelope Points

[birdus]

I'm trying to set up my W&B info in Garmin Pilot for a Luscombe 8E. It's asking me to enter 3 envelope points. For each one, it wants Weight and Longitudinal CG.

I already entered the empty CG (13.04). I have forward and rearward CG limits (12.3 and 13.7) in my documentation.

So, what three pairs of values do I enter for Weight and Longitudinal CG?

 

[smv]

I used four.

Max Weight, Max Fwd CG
Max Weight, Max Aft CG
Min Weight, Max Fwd CG
Min Weight, Max Aft CG

 

[smv]

Actually I just took a second look at this...

The POH I am using has entire tables dedicated to Weight/Moment limits and very little info on Weight/CG limits (yah, I could do the math...) so I changed the option in "Aircraft Setup" in the W&B section from "Weight / Longitudinal CG" to "Weight / Longitudinal Moment". Doing that allowed me to emulate the W&B Gross Weight Moment Limits chart shown in the POH. There are hundreds of Weight/Moment values in the tables but you only really need four for each category (the extreme corners) to create the envelope.

I would include a screenshot but I did this on a borrowed iPad and I have not yet figured out how to send photos to other devices from the iPad using Bluetooth...

 

[flyingron]

While some aircraft have perfectly rectangular envelopes (needs four points to define), many have a forward limit that moves backward with the weight increase, so for most you need five (though you can probably intuit the last one assuming that the empty weight and the rear limit are constants).

 

[birdus]

After adding the 4 points, I'm getting results that don't make any sense. With just fuel and me, the CG is way out of bounds. Below, I've added screenshots of the airplane's empty CG, my envelope setup, and the W&B page with full fuel and me...no 2nd person or any baggage. Any idea what's going on?

 

[smv]

Do you have the CG stations for Fuel and Seats correctly entered?

 

[tsts4]

Where’s your datum? The cg numbers look odd to me, more like moments/1000.

 

[birdus]

 

[smv]

Something not right there. A CG spread of 1½" and passengers and fuel 6" behind the aft max? I would start by checking the max aft numbers.

 

[birdus]

QUESTION: The TCDS says that the EMPTY weight CG range is 12.3 to 13.7. Those are the numbers that I was using for my envelope setup in Garmin Pilot. However, I was also using those for two of the points with gross weight numbers. I also just read this in the TCDS:

When empty weight C.G. falls within the pertinent range, computation of critical fore and aft C.G. positions is unnecessary.

Does this mean, that I can load 2 people and bags in any combination up to my gross weight, and just not have to bother doing CG computations? Does this mean I shouldn't even be putting any of this into Garmin Pilot???

 

[Stewartb]

Start at the front lower and enter the points clockwise. Empty forward CG, gross forward CG, gross aft CG, and empty aft CG. Then fill in your station locations.

 

[birdus]

I figured out the problem. It's the same problem I run into a lot. I'm an idiot! I was using the empty weight C.G. range. The TCDS also has a C.G. range that you're supposed to use for loaded W&B. Not 12.3 - 13.7 but 13.6 - 16.8.

D'oh!!!

 

[SbestCFII]

I'm trying to set up my W&B info in Garmin Pilot for a Luscombe 8E. It's asking me to enter 3 envelope points. For each one, it wants Weight and Longitudinal CG.

I already entered the empty CG (13.04). I have forward and rearward CG limits (12.3 and 13.7) in my documentation.

So, what three pairs of values do I enter for Weight and Longitudinal CG?[/QUOTE
I'm a GP user since it came out, but use "Weight and Balance Pro" App. The sliders make it quick and easy.

 

[smv]

I figured out the problem. It's the same problem I run into a lot. I'm an idiot! I was using the empty weight C.G. range. The TCDS also has a C.G. range that you're supposed to use for loaded W&B. Not 12.3 - 13.7 but 13.6 - 16.8.

D'oh!!!

So it looks more like a parallelogram than a straight vertical block now?

 

[birdus]

So it looks more like a parallelogram than a straight vertical block now?

No. It's still a rectangle, just not quite so tall and skinny, because the C.G. range is 3.2 instead of 1.4.

 

[Stewartb]

I’ve never flown a plane that had a wider CG range at gross than when empty. How does that work?

 

[birdus]

I’ve never flown a plane that had a wider CG range at gross than when empty. How does that work?

I'm a student pilot. Don't ask me. The numbers are straight out of the TCDS. Maybe someone else can edumacate us.

 

[Lindberg]

QUESTION: The TCDS says that the EMPTY weight CG range is 12.3 to 13.7. Those are the numbers that I was using for my envelope setup in Garmin Pilot.

This range is a "limitation" for evaluating the CG of the empty airplane when it is weighed. For the purpose of computing weight and balance, you should be using the actual empty weight and CG of your particular airplane.

However, I was also using those for two of the points with gross weight numbers. I also just read this in the TCDS:

When empty weight C.G. falls within the pertinent range, computation of critical fore and aft C.G. positions is unnecessary.

Does this mean, that I can load 2 people and bags in any combination up to my gross weight, and just not have to bother doing CG computations? Does this mean I shouldn't even be putting any of this into Garmin Pilot???

It means that as long as your airplane's empty weight is within the stated range, and you don't load any station above the maximum weight for that station, and you comply with any other pertinent limitations, then you will be within the CG range.