HELP - WEIGHT & BALANCE

I have a 2008 RV-7 that I bought in January. The weight and balance papers with the plane list the gross weight at 1900, with a usable baggage at 100. Everything I'm seeing online says 1800 for gross. I can't get an answer from anyone about it, so I thought I'd come here.

Can't get a hold of the shop. Can't get a hold of the builder. Not sure if this would affect my CG limits if the gross was really 1800 instead of 1900. I don't think I'll every be out above 1800, but again, not sure if my measurements for my aft and forward limit are affected.

Any thoughts? Thanks so much.

CG limits are based upon where the weight is in the airplane more so than how much total weight is in the airplane. You will need to use a Datum point and measure from that point and calculate the weight with the distance from the Datum. The kit documents should have info on calculating this. Hopefully you received the build documents that would include the plans and instructions for construction when you purchased the plane. There is a great deal of data in those documents that will help you. As for calculating CG, that is something you will have to perform if the builder did not do so.

Do the papers that have the 1900 lb info have CG data also? If you have the gross weight information you should also have the CG info.

Weight and Balance Briefing

Jesse,

Welcome to the RV community and congrats on acquiring your -7!

The W/B limits (inches aft of datum) are determined by the DESIGNER, with aft limits being critical from an aircraft handling/control perspective. The maximum allowable gross weight is determined by the BUILDER, validated by flight test, and should be annotated in the airframe log. Weight and balance information must be maintained in the cockpit (as with any aircraft certified or experimental). Van's website has a link to weight and balance quick reference for each type (under the support downloads tab): http://www.vansaircraft.com/public/downloads.htm. There is much history and discussion regarding operating at weights above designer recommended limits, as that reduces the structural margin of the airplane. The bottom line is that you won't ever be wrong if you operate within designer recommended limits. And if you haven't done so, you might consider re-weighing your "new to you" airplane to have accurate, reliable data. There is also a good discussion regarding weight and balance in the builder's manual for your airplane--if you don't have one, you can purchase a set of preview plans (which includes the manual) from Van's for minimal cost, you can even get an electronic version on a thumb drive if you prefer.

On the safety page, there is a sticky that contains links to transition training information including a link to a briefing explaining RV weight and balance: https://drive.google.com/file/d/0B8EIT6g2n8o_NzhVN1BGVk1JV3c/view?usp=sharing

Enjoy your new airplane (and associated grin); and fly safe,

Vac

I have to disagree just a little with Vac on this - both CG envelope and Max Gross Weight are determined by the designer of an aircraft. Yes, the builder can designate them anyway he or she wants from a legal perspective, but that doesn't change the engineering that went in to the design. Upping the gross weight arbitrarily, without documenting why the new weight is allowable when the structure and performance were designed for the original gross weight is just guessing - and the same would be true for determine the Cg envelope.

Now both of those can be re-determined by engineering analysis and flight test - but its not something that you do quickly, or with the stroke of a pen. CG envelope is a matter of stability (at the aft limit) and ability to flare/rotate (at the forward limit). There are aircraft where these numbers are not fixed, but vary with weight - so if you up the weight, you REALLY need to re-evaluate the CG limits as well. Testing aft CG limits can be scary if you aren't familiar with a wide variety of handling qualities, and ready for some aerobatics.

Upping gross weight is not just about eating into structural margins - it is also determined by performance. In RV's, unless you put a really tiny engine on the front, you probably won't have to worry about meeting minimum climb rate standards. But that is just one consideration.

Full disclosure - I have increased the gross weight of an RV above the factory value, but ONLY after consulting with the designer, and getting his concurrence. Don't be arbitrary, don't guess - do the work, and do it right.

Paul

Paul,

Actually, no disagreement at all--poor wording on my part, and you are correct. The engineer does, in fact determine limits, EAB rules mearly allow the builder to designate limits during the certification process for an individual aircraft, and that's an important distinction. As you state, with proper engineering and test, it's possible to deviate, but not advisable unless done properly.

I'm a firm believer in sound engineering and proper flight test, and I also understand that structural margin belongs to the engineer since most of us pilots occasionally need some of that margin...

I hope I made that quite clear in the briefing!

Cheers,

Vac

When I bought my 6, the paper work that came with it showed the builder also upped the GW to 1800lbs and 100lbs for baggage. ( VANS Specs= 965lb empty/1600lbs GW Baggage = 60lbs). My RV-6 is 1050lbs Empty.

Reading further it was easy to see how he balanced everything. He used a minimum 10-gal of fuel instead of 5 gal to keep it inside the AFT limits.

This can lead to some issues because his computations put the CG only .1 from the aft limit.

10-gal of fuel is an issue flying here in Alaska if you don't want to spend up wards of $7-10 per gallon.

That extra fuel needed to balance a 100lbs of bags, means short trips only.

With the required survival gear for Alaska, that 100lbs is easy to hit!

For my return to Alaska flight, was almost at full nose down trim for landing at Petersburg, with only 9.2 gals. I did locate my heaviest bag on the co-pilot seat to help.

Best regards,
Mike Bauer

I'd go to the logbooks - there should be an entry all the way back to when it came out of Phase I. The wording in the entry should include

I certify that the prescribed flight test hours have been completed and the aircraft is controllable throughout its normal range of speeds and throughout all maneuvers to be executed, has no hazardous operating characteristics or design features, and is safe for operation. The following aircraft operating data has been demonstrated during the flight testing: speeds Vso _____, Vx _____, and Vy _____, and the weight and CG location at which they were obtained.​

Although I can't put my hands on it right now, I seem to recall that the weight listed in that entry would be the limit you're looking for (specific to your airplane - as tested in Phase I). With that said, I used 2000 pounds for my flying whereas Van's has 1800. With the stroke of a pen, I did not improve on the engineering that led to 1800 - but it seemed like a good idea at the time.

Dan