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RV-12 forward CG limits?

tgoke

I'm New Here
I'm trying to setup weight and balance in FOREFLIGHT for the RV-12, but it needs the FORWARD CG LIMITS and REAR CG LIMITS in inches and also a unique weight. Can't find this in the POH, any suggestions??
 
Welcome to VAF!

Tim, welcome aboard the good ship VAF:D

If all else fails, call the factory??
 
Nevermind, I found it. For future reference, you have to get the numbers off the actual FLIGHT ENVELOPE, not W&B chart. This is found in section 6-8 (page 67).
 
Just a reminder, there are different kinds of RV-12's.
Some have been certified as Experimental Amateur Built, not LSA, in which case the builder is free to ignore Vans and set his own W&B limits.
 
Tim

That graph is pretty much bounded by straight lines in the weights we are interested in which means the limits hold through the usually experienced loads.

Rich
 
I'm trying to figure this out also for Foreflight.

I cannot seem to get it.

80.49-85.39 at 1320 lbs seems to be the answer for one of the catagories but what is the light weight forward and rearward CG?

I cannot get it right as it says the plane has a to forward CG when I use those #'s in both the forward as well as the rearward CG/Weights.

Any help?

I have:

Forward CG Limit: 68 @ 840 lbs
Forward CG Limit: 80.49 @ 1320 lbs

Aft CG Limits: 68@840 lbs
Aft CG limits: 85.39@1320 lbs
 
I agree with Rich Schaller. The CG limits do NOT change with aircraft loaded weight. The CG limits are 80.49 - 85.39 regardless of how the RV-12 is loaded. Someone please correct me if wrong. The subject of weight and balance can be confusing. I can see where that number 68 came from on the flight envelope chart. But that number is not a CG.
I use an Excel spreadsheet for weight and balance. You can download a copy HERE. Hover your mouse pointer in the black area near the top of the page and click the down arrow to download the spreadsheet to your computer. Only change yellow-highlighted numbers.
 
Plugging hypothetical numbers into the spreadsheet mentioned in my previous post, the aft CG will be exceeded if a solo pilot weighing 150 lbs or less loads the RV-12 with full fuel and 50 pounds of baggage.
 
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.
 
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.

WBPHBZT.jpg
 
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.
 
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.. ??
 
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.
 
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.
 
This forum got me interested in the ForeFlight Weight & Balance.

Here is the first picture of my Setup:

29yob38.png


Here is the second picture of my Setup:

16kbz7k.png


Here is the first picture of a sample Load:

9h7383.png


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

727ipv.png


Curious if others are similar in Setup and Load examples.
 
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.

 
I too was puzzled by the unusual envelope shape.

I interpolated the POH Flight Envelope - shown here:

2corh2e.png


With these calculations:

2z70lrs.png


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, ?????
 
Must have something to do with how it gets entered into FF. My interpolations were not exactly what yours are but only very slightly different - not enough to make a difference. You did two more points than I did - I only had one point each at 1260 and 975 but I don't see that making a difference since the additional two points are just at some midpoint of a straight line.

Beats me ...
 
Small changes in the interpolation of the Flight Envelope do make a difference. Here are changes - shown in parenthesis - I made to the Flight Envelope interpolation:

1zwgd4n.png


And, after entering the revised data in ForeFlight Weight & Balance Setup, here is the new envelope:

2n05umx.png


Now, the ForeFlight Flight Envelope looks like a fat POH Flight Envelope.

It would be nice if we had some Flight Envelope data points from Van's; yet, I think, this is pretty close.
 
With help from Joe I got closer...

I just added the following data:

Forward:
67" - 840 lbs
100.5" - 1260 lbs
108" - 1320 lbs

Aft:
67.5" - 840 lbs
83" - 974 lbs
107.5" - 1275 lbs
111" - 1320 lbs

The graph looks about 98% the same... The CG of course will not work as I get "Caution: If you burn more fuel than planned, your CG may become to far aft"

Load is set with single person (180 lbs) and 15 gal of gas...
 
No, it does not matter what order you list the forward or aft CG limits/weights in ForeFlight. When you are in Setup, press Edit. Three grey bars will appear to the right of each CG Limit - you can press on the three bars and move the line to any position you want. I mixed up all the different limits, and, it did not have an affect on the Flight Envelope (Graph).

Interpolating the POH Figure 6-2 Flight Envelope may give us each slightly different numbers; but, they should be fairly close. I agree with others that the CGs should be somewhere between 79 and 86 inches.
 
Did anyone every figure out how to get this to work properly?

If so can you share all the info you put into Foreflight. New RV12 owner would like to just plug it in if you guys got it to work.

Thanks!
 
If so can you share all the info you put into Foreflight. New RV12 owner would like to just plug it in if you guys got it to work.
Thanks!

From one new RV12 owner to another:

I'm not able to post attachments, but if you'll send me an email, I'll return screen shots of my Foreflight Weight & Balance pages so you'll be able to see what worked for me.

Lon
[email protected]
 
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