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  #11  
Old 05-13-2015, 10:50 AM
Rik Rik is offline
 
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I'm confused..

The POH gives the ranges but the graph gives different #'s than the 80.49-85.39.

Putting in the figures from the chart and I still get an error. ?

tgoke, you apparently have this figured out for foreflight?

Mitch, I appreciate what you are saying but FF requires (WHY???) a forward CG, twice, and an AFT CG, twice.

All I can figure is that the forward CG low weight, and Forward CG Heavy, and Aft CG light weight and Aft CG Heavy. If I do this I get a vertical envelope of CG and the POH has a different looking envelope for the CG so I'm doing something WRONG.
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  #12  
Old 05-13-2015, 11:52 AM
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Gagarin737 Gagarin737 is offline
 
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Quote:
Originally Posted by Rik View Post
I'm confused..
Mitch, I appreciate what you are saying but FF requires (WHY???) a forward CG, twice, and an AFT CG, twice.
Most probably you have to insert 4 or 5 points in ForeFlight to make a square (I work with SkyDemon and PocketFMS, I have not worked with ForeFlight)
Thats why you need two forward CG points and two aft.
1) 80.49 / empty weight or 0 lbs
2) 80.49 / 1320 lbs
3) 85.39 / 1320 lbs
4) 85.39 / empty weight or 0 lbs
5) 80.49 / empty weight or 0 lbs (depending on program to complete square)
(Foreflight W&B demo)

Thereafter insert the stations:
Plane_____________W&B
Pilot______________78.85
Passenger_________78.85
Fuel______________110.28
Baggage__________110.81

The POH graph works in a different manner. You will enter the graph at page 4.6POH with TOTAL moment and weight. For simplification the moment number is divided by 1000 (so moment 100 is originally 100000).
The graph used by the nav programs will go one step further; divide the total moment through the total weight. With that you get a number in inches which has to be between 80.49 and 85.39 which is easy to plot.
For example: In the picture below you can see the numbers with red boxes 1292.86lbs with a moment of 109794.93. At page 4.6 you can enter the graph with the number 1293 and 110 the Van's way. Forelight will present the graph as in my excel sheet.

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  #13  
Old 05-13-2015, 05:16 PM
Mich48041 Mich48041 is offline
 
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Quote:
The POH gives the ranges but the graph gives different #'s than the 80.49-85.39
Notice that the graph, FIGURE 6-2 FLGHT ENVELOPE, in the POH shows weight and moment, but NOT CG. The CG can be calculated from the graph. Notice the number 75 on the moment scale intercepts the weight scale at 925 pounds. 75 x 1000 / 925 = 81.1" Notice that 77.5 on the moment scale intercepts the weight scale at 925 pounds. 77.5 x 1000 / 925 = 83.4 At a weight of 925 pounds, the flight envelope CG range is 81.1" to 83.4".
Regardless of how the graph is interpreted, the CG range is 80.49" - 85.39". Do not enter CG numbers outside of that range into ForeFlight.
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  #14  
Old 05-13-2015, 05:31 PM
Rik Rik is offline
 
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Quote:
Originally Posted by Mich48041 View Post
Notice that the graph, FIGURE 6-2 FLGHT ENVELOPE, in the POH shows weight and moment, but NOT CG. The CG can be calculated from the graph. Notice the number 75 on the moment scale intercepts the weight scale at 925 pounds. 75 x 1000 / 925 = 81.1" Notice that 77.5 on the moment scale intercepts the weight scale at 925 pounds. 77.5 x 1000 / 925 = 83.4 At a weight of 925 pounds, the flight envelope CG range is 81.1" to 83.4".
Regardless of how the graph is interpreted, the CG range is 80.49" - 85.39". Do not enter CG numbers outside of that range into ForeFlight.
So then you have a 738 lbs with moment of 80.49 for the forward CG and a 738 lb 85.39 CG?

Cannot get forflight to look like the POH or to even say the plane will come into CG as with those #'s alone the plane has to far forward of a CG to fly.

Doing a CG though as per the POH example it comes out fine.. ??
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  #15  
Old 05-13-2015, 06:45 PM
Mich48041 Mich48041 is offline
 
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I was playing around with the Excel spreadsheet calculating weight and balance and came up with the following:
As long as the combined pilot and passenger weight is between 155 and 500 pounds and gross weight does not exceed 1320 pounds and baggage weight does not exceed 50 pounds and fuel level never goes below 3 gallons, then CG limits will NEVER be exceeded.
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  #16  
Old 05-13-2015, 07:23 PM
Rik Rik is offline
 
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Thanks. I think part if the confusion centers around the CG limits not the CG range.

I put in a lower weight and moment and the graph looks better but it still doesn't CG correctly. The numbers on the graph are both within and outside the CG limits and those are the number that need to be accurately entered apparently.

Example. At 738 lbs what's the moment as it's not on the graph hence part of the problem.
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  #17  
Old 05-13-2015, 08:17 PM
Mich48041 Mich48041 is offline
 
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Rik, I sent you a PM
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  #18  
Old 05-14-2015, 03:27 PM
ChuckC ChuckC is offline
 
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This forum got me interested in the ForeFlight Weight & Balance.

Here is the first picture of my Setup:



Here is the second picture of my Setup:



Here is the first picture of a sample Load:



And, here is a second picture of a sample Load:



Curious if others are similar in Setup and Load examples.
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  #19  
Old 05-14-2015, 04:20 PM
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tomkk tomkk is offline
 
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I don't know anything about ForeFlight. Maybe that's the problem but I guess I'm a bit confused by the odd shaped envelop. It seems that the envelop should look one of the following. The one on the left plots Moment vs Weight that's in the POH and the one on the right plots Arm vs Weight.

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  #20  
Old 05-14-2015, 08:04 PM
ChuckC ChuckC is offline
 
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I too was puzzled by the unusual envelope shape.

I interpolated the POH Flight Envelope - shown here:



With these calculations:



And, these calculations produced the unusual envelope.

I have run several load problems through the ForeFlight W&B, and, the results seem to make sense. Yet, the envelope shape puzzles me. Maybe I made a math error? Or, ?????
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