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Gross weight calculation

Getting ready for our airworthiness inspection, we weighed our RV-7A yesterday, and came up with a puzzle:

My understanding of a gross weight calculation is that you load your spreadsheet until you run into the Van's recommended GW limit (1800) or some other limit. Another parameter is the FAA's "standard" passenger weight of 170.

I tried three alternatives that put the CG at aft limit; none got to 1800 lb. When I plug in two people at 170 plus 100 lb. of baggage, total weight is 1725 and just within aft CG. Using pilot and passenger weights of 207 and 208 with 83 lb in baggage gives 1783 lb total at aft CG. Using full baggage weight of 100 and people at 175 and 170, weight is 1730 with CG at aft limit.

So the question is, which to use and what's my gross weight limit. 1783 lb seems to be the max possible, but that disregards the FAA's 170 lb standard. Also, these cases are takeoff W&B, and CG is out of limits as soon as fuel's burned. Should I use more conservative pax and baggage weights and GW to show, say, CG at aft limit with an hour fuel reserve?
 
If you use max baggage weight and fuel fuel, then make the pilot and co-pilot big enough to hit the 1800 pounds total, is your CG in spec? If so, this is your answer.

Carl
 
BUT, you must remain within CG for the entire flight!! Van’s design gross weight is 1800 lbs. If during a flight, your CG will be out of limits, you must adjust loading accordingly for each flight. The ultimate gross weight number is still 1800 lbs.
 
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Was it built to plans, with recommended engine and prop?

Is the battery and other heavy items in the factory recommended locations?

What is the empty C/G location?

What is the factory recommended/expected C/G?
 
I suspect you have a light weight composite prop up front. My -7A has a Saber 4" spacer and 20 lb crush plate to compensate for the 12 lb Catto 3 blad prop. With this setup, it is difficult to have CG too far aft. The 20 lb plate gives me enough leeway to replace my 15 lb PC680 with a 4 lb EarthX on the fwd firewall.

You can also add stations for multiple baggage locations where you put the heaviest stuff in front of the spar (secured), just behind the seats and the lighter objects against the bulkhead.

As others have suggested, you should load the plane without baggage and see what is available for luggage throughout the planned flight.
 
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You will notice that as you burn fuel the CG will move aft. Most likely you will only run into an aft CG issue with heavy pilots/min. fuel/heavy baggage.
 
The 170 lb passenger weight is an ancient FAA standard for certificated aircraft. They now have average weights for airline passengers, with seasonal adjustment for heavier winter clothing. The more recent ASTM standard for people is 190 pounds. Ignore all of them.

You're doing the right things by looking at various loading combinations. Try a most forward cg (probably full fuel, no baggage, and the rest of the payload being people), and do a bunch of variations starting from there. And don't forget that if you take off with full tanks, the cg will move aft as the fuel is burned off.

Don't know about the -7, but the -4 and -8 have smaller envelopes (both gross weight and aft limits) for aerobatics.

Ed
 
Do the math ahead of time for a passenger in the 200, 220, 250 pound range and know where the CG will fall with full tanks, 2/3 tanks, 1/3 tanks. One day you'll have a situation where someone wants a ride, or you offer a ride, and it's politically incorrect to ask their weight - you will have to guestimate and know if you are OK, close enough to OK that it doesn't matter, or close enough to the limit to throw political correctness out the window. This is not a situation you want to approach without having thought about it first.

The largest passenger I've taken in my 9A was 330 pounds - and it was a challenge to get the seat belt on, but she was happy and it all worked out.
 
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Although it is not a legal requirement, Vans has a load limit for the nose gear. Since you are doing the math anyway, why not add that calc to see if you are close and what the tendencies are.
 
Getting ready for our airworthiness inspection, we weighed our RV-7A yesterday, and came up with a puzzle:

My understanding of a gross weight calculation is that you load your spreadsheet until you run into the Van's recommended GW limit (1800) or some other limit. Another parameter is the FAA's "standard" passenger weight of 170.

I tried three alternatives that put the CG at aft limit; none got to 1800 lb. When I plug in two people at 170 plus 100 lb. of baggage, total weight is 1725 and just within aft CG. Using pilot and passenger weights of 207 and 208 with 83 lb in baggage gives 1783 lb total at aft CG. Using full baggage weight of 100 and people at 175 and 170, weight is 1730 with CG at aft limit.

So the question is, which to use and what's my gross weight limit. 1783 lb seems to be the max possible, but that disregards the FAA's 170 lb standard. Also, these cases are takeoff W&B, and CG is out of limits as soon as fuel's burned. Should I use more conservative pax and baggage weights and GW to show, say, CG at aft limit with an hour fuel reserve?

Sounds like you are getting your definitions confused:

Recommended Gross weight limit from Van's is 1800 lbs.
For the AW insp all you need to provide is empty weight and CG.

Loading calculations are done by the pilot to ensure the aircraft is withing the CG/gross weight limitations. If the AW inspector wants to see sample loading caluculations thats fine but it has nothing to do with Gross weight.
 
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