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The W&B thing: A friendly challenge to all RVators-

Hartstoc

Well Known Member
In my quest to find a good, flying RV-7A to buy(still looking!), I've encountered a disturbing trend among the aircraft that I have looked at or researched as potential candidates, one that I think it is worthy of general discussion here. I'm looking forward to hearing all of your comments and opinions.

I'm talking about Builder's frequent failure to amend the required W&B documentation for their RV's after making major alterations. All are pretty much forced to create an initial document in order to receive a sign-off in the process of obtaining an airworthiness certificate, but no one is there prodding you to make the required logbook entries and amend or replace the W&B after that. RV's are often flown extensively before paint, upholstery, or even wheel fairings are completed, and an amended W&B is in order after such things are done. In my humble opinion, failure to do so is not only a violation of the FAR's fraught with liability for the builder, it is downright unsafe. It may also give the insurance company means to deny a claim relating to an incident that is deemed to be loading-related.

This might be a good place to cite my own qualification to "hold forth" on this topic like Mr. Goodie Twoshoes. I'm a newbie here at VAF, but not to the world of homebuilts. I served on the CAFE Foundation B.o.D. from 1981 to 1999, and as test pilot/author for several of the CAFE Aircraft Performance Reports sponsored by EAA and published in Sport Aviation, including that for the RV-8A.

At CAFE, I served as payload management facilitator during all but one of the ten CAFE 250 and CAFE 400 efficiency races conducted during the 1980's. Fuel burn was the single most important factor in the score for most efficient entry, and we determined THAT by meticulously weighing each aircraft before and after the race on precision scales. In the course of all those events we weighed hundreds of aircraft, and we got used to sometimes needing to give their owners a moment to recover from the shock of learning exactly how much their aircraft actually weighed.

I'll save all the detailed reasons why this whole topic REALLY MATTERS for later in what I hope becomes a fruitful discussion here but, for now, here is my friendly challenge to all: Take a good look at that crumpled, oil-stained piece of paper tucked away somewhere in your airplane and ask yourself if it is really accurate, or if it was even done with appropriate care and accuracy in the first place, and if it might be a good idea to get together with your buddies and obtain access to some really good scale-decks and generate new, dated, signed and accurate Weight and Balance docs for your aircraft. While you are at it, go back and insure that any significant changes you have made to the aircraft were documented by appropriate logbook entries, including these new W&B docs. Once you have done these things, give yourselves a hearty pat on the back.-

Link to good W&B practices:

http://www.lightsportaircraftpilot.com/aircraft_weight_and_balance/FAA-H-8083-1A.pdf

Link to the CAFE APR's:

https://cafe.foundation/v2/research_aprs.php
 
Interesting topic, how many aircraft did you see that were like this? I'll start with one that did have the original W&B with paint interior and all pants and fairings installed. Maybe a Poll?
 
Practical

I tried to approach the W&B from a practical point of view.

1. Accurately weigh the unpainted plane in preparation for the Airworthy Certificate.

2. 40+ hours of phase I testing that included what the OP would probably call significant changes that were documented in a test diary and the excel spreadsheet.

3. Accurate W&B after paint and testing.

4. The only subsequent entry in my aircraft log and excel spreadsheet is for the EarthX battery -10 lbs on the firewall.
 
Good on you, Bret! It was not the large number(about 6) that led to my post, but the consistent similarity among them in this regard that led me to start this thread. I hope that my small sampling represents a statistical anomaly, but I wonder. A poll is a great idea, and I'd also love to hear from anyone who might be moved to act on my challenge. -OH
 
I have bought 3 Experimental Amateur Built aircraft built by other people. None of them had any W&B paperwork done sine the original airworthiness paperwork. Two of them were bought essentially for the airframes and were going to get new engines and lots of modifications, so new W&B before starting to fly again was a given.

The third was an RV-4 that I bought flying and had been flying for over 15 years. Because I could find NO W&B paperwork (though there was a mention of the original empty weight) with the aircraft anywhere, the first thing I did before flying it was to do a new W&B. Surprise, surprise, the airplane had gained over 20 pounds in those years.

In my book I don't worry too much about W&B when looking for an airplane to buy since I am going to redo it before I fly it anyway.
 
Surprise, surprise, the airplane had gained over 20 pounds in those years.

Or the difference in scales = 20lb. 20lb/~1000lb is 2%. How good to we think W&B is? It probably gained some weight, but just as much could be the precision of the measurement. The CG has even more uncertainty than the total weight.

I have done W&B on my airplane twice so far. Once initially, and once part way through Phase I.
 
Or the difference in scales = 20lb. 20lb/~1000lb is 2%. How good to we think W&B is? It probably gained some weight, but just as much could be the precision of the measurement. The CG has even more uncertainty than the total weight.

I have done W&B on my airplane twice so far. Once initially, and once part way through Phase I.

Observing other builders do a W&B I would also be concerned about levelling and measurement accuracy.

I've witnessed "it doesn't really have to be level" and "it's close enough" when looking at a plumb bob measuring an axle location that is clearly 1/4" off.

Vans defines the W&B for RVs to 1/10 inch, we should at least equal, and probably better this when we measure and weigh.

http://vansaircraft.com/public/downloads.htm
 
Good discussion. I bought my -4 from a fella that had recently painted my bird and the only W&B paperwork I could find was the original from the builder. With that in mind, I didn't waste any time doing a new W&B. My -4 did gain some weight, but still under 1000 lbs and the CG's are great.
 
I recently performed the initial W&B for our "project" aircraft. I had the level checked by an independent set of eyes, and I had that set of eyes also verify wheel stations, measured to 1/16". The wheel stations were a real surprise as they came in at quite different values from the company prototype upon which the W&B sample calculations were based. This caused a double- and triple-check of the wheel stations because it is so easy to make a small measurement error which, through the miracles of multiplication, become large errors in the completed W&B.

With respect to weigh scales, our "flying" aircraft was weighed using our EAA chapter's then-current bathroom scale setup. Then I went through several modifications, installing light-weight starter, alternator, battery and prop. My guess from weighing the original components was that I should see something on the order of a 25lb weight drop, but it was not to be so. The chapter purchased a new set of load cell scales, accurately calibrated and I was one of the first to use them. Imagine my surprise when the weight of the aircraft went UP by 18lbs instead of down by 25lbs! Oh well... Bathroom scales aren't always the best way to weigh an airplane, or so it seems!
 
I recently performed the initial W&B for our "project" aircraft. I had the level checked by an independent set of eyes, and I had that set of eyes also verify wheel stations, measured to 1/16". The wheel stations were a real surprise as they came in at quite different values from the company prototype upon which the W&B sample calculations were based. This caused a double- and triple-check of the wheel stations because it is so easy to make a small measurement error which, through the miracles of multiplication, become large errors in the completed W&B.

....

Yes, I forgot to mention that one. I heard from a few builders that they didn't actually measure the axle distances, they just used the numbers in Vans W&B instructions example.

In my case the nose gear was about 1.5 inches different and the mains 3/4 inch different.
 
scales

Great topic Otis. My guess is that there are two reasons why people don't do it - availability of scales and math.
 
Great topic Otis. My guess is that there are two reasons why people don't do it - availability of scales and math.

A lot of EAA chapters have scales they will loan to you. As to the math, almost everyone seems to have a computer these days. An Excel spreadsheet will do the math for you once it's set up, making changes easy. I have kept mine up to date, including adding wheel pants, weight of ADSB-in box, difference in weight and balance when I deleted my panel mount transponder and added a remote mounted one, etc.
But, thanks for the reminder. While I am confident my home computer W&B is up to date, I'm not sure I have the latest version in the airplane! I need to check.

And, one more time, I'll remind RV-10 owners to check the cg at zero fuel, as well as takeoff fuel. The cg can move toward (or past) the limits as you burn gas. A spreadsheet makes this easy (or can be programed to do it automatically).
 
Very good thread! I've done four W&B's over the 16 years mine has been flying. Original - all paint and fairings. 2nd was when I junked the 28lb battery in favor of a 13lb one. 3rd was when the mags and Lasar junk was removed and replaced with dual Lightspeeds. Finally, the last one was when I redid the electrical system and panel this past winter. I'm happy to report it got lighter each time!
 
An actual W&B every once in a while is not hard to do. Most of us have access to scales through our EAA Chapter.

While the W&B may have not been kept up to date a current one should be done during the prebuy inspection. They are not hard to do. Once the scales are procured the actual weighing only takes about 15 minutes.
 
Agreed that weight and balance is important, and when I bought my already flying RV-4, the weight and balance calculation was, shall we say, farcical.

Here's where our opinions might diverge a bit... it seems to me that in general aviation, historically, there has been a perceived need to calculate performance, weights, fuel burn, etc., to an overly precise degree, as if doing a maximum range flight in a four engine aircraft. For example, I don't really care what Vy is because I usually climb faster than Vy for a cruise climb, or for forward visibility, or for engine cooling. In mountain flying, I fly with fat margins so that Vy is never required. Plus, with GPS groundspeed, the assumptions of uniform air mass and wind components are easily seen to be flawed, although it is still not all that hard to hit waypoints within a minute if you're careful.

When I go cross country, I like to land with two hours of gas in the tanks so that in case there's no gas where I land (has happened), or I need to go somewhere else right away for any other reason, I can. And it's also the case that fuel tanks are seldom 100.0% completely filled, so a five gallon fuel reserve might actually turn out to be three. Plus, with two wing tanks and lousy fuel gauges, you might not really know how much of that three gallons is in each tank.

And similarly for weight and balance. The wings aren't going to fall off at five pounds over design gross weight, but I've flown RVs that required extra attention even before you got to full aft c.g.

My point is this: know your individual airplane and fly conservatively. If you do, you'll be well within the numerical limits, but don't count on flying at the edge of the kit designer's numerical limits to guarantee your safety.

Ed
 
"...Here's where our opinions might diverge a bit... it seems to me that in general aviation, historically, there has been a perceived need to calculate performance, weights, fuel burn, etc., to an overly precise degree, as if doing a maximum range flight in a four engine aircraft. "


Wow! It is encouraging to see all of the interest and shared experience this thread is generating. Those points about knowing actual wheel stations, the accuracy of the scales themselves, and proper leveling techniques(don't forget to close the canopy before weighing!!) must all be taken into account to achieve valid results. Thank you all for taking this topic seriously!

Ed(quote above)- We don't disagree. Knowing your airplane is more important than doing a lot of nit-picking calculations for every flight. My concern is that each owner have accurate underlying W&B stats for his or her aircraft, particularly if purchased used. These fancy paint jobs(and don't forget the lead needed to re-balance the control surfaces afterward) can add 50 pounds or more to an RV. If you buy a beautiful RV and rely upon a W&B that does not include the paint you may be courting disaster. One important point to keep in mind is that painted surface area is biased aft of the CG range. A lightweight FWF installation+heavy paint + full luggage+ big pax+ empty tanks scenario could mean stick force reversals and significant power required for sufficient control authority to recover from an unintentional stall near the ground.

Safe flying all- O.H.
 
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I've bought one amateur-built aircraft. It came with zero W&B data at all, except for the plans, which explained how to do it and what the CG limits were. I weighed it myself so that I had good data to begin with.

When I sold it, the new owner never asked and didn't seem to care. But I gave him the as-weighed data (which was still current) when he first inquired about the plane.

Dave
 
.....


And similarly for weight and balance. The wings aren't going to fall off at five pounds over design gross weight, but I've flown RVs that required extra attention even before you got to full aft c.g.

......
Ed

Correct, the wings may not fall off, but as mentioned earlier a low fuel landing can easily put you in a rear CG position - the couple of lbs over gross may be a fairly low risk, but I don't think you can say that for an unknown CG position aft of where Vans says it should be.

My flight instructor from a long way back crashed his RV-6A returning to his CA home field after a same day flight from Oshkosh - two full-size folks, low fuel and camping gear apparently caused a too high, non-controlled flare and a bent wing.
 
a low fuel landing can easily put you in a rear CG position

Yup. On my RV-4, I used a weight and balance cheat sheet, based on me in the front seat, with a grid using baggage weight on one axis and rear passenger weight on the other axis. The grid was filled with the number of gallons of fuel required to keep the c.g. forward of the 31% aft limit.

With an aft c.g., the same pull that gave a 2G turn solo would give 5 Gs.

It really made you feel good to do a wheel landing with an aft c.g. and not be able to feel the wheels touch. I also discovered that you could get a pitch oscillation on takeoff with an aft c.g. if you kept it on the ground too long.

I never really liked flying with the c.g. that far aft, but I knew my A game was working when I could fly it well.
 
An accurate W&B is important for sure. One aspect when weighing your airplane that may not have been mentioned here - I didn't read every post on this thread, so maybe it has - is to make sure wind isn't affecting your results. Best way is to close your hangar door and don't turn on ceiling fans. Even though these are pretty small airplanes, air currents/wind can have a noticeable effect on results, even if there's not mush of a breeze.
 
Many W&B are a farce. There was a builder on our field that wanted a copy of our POH so he could write his own. Needless to say his weighed exactly the same as mine. go figure.
 
Many W&B are a farce. There was a builder on our field that wanted a copy of our POH so he could write his own. Needless to say his weighed exactly the same as mine. go figure.

It is troubling to hear of such things. Pilot/builders who disregard reality endanger themselves and others, and probably generate a goodly share of the high accident rates that plague our delicate corner of aviation.
 
editorial

You know, with all the money we're spending on building and flying an airplane, and the critical nature of your W&B, why not just buy your own scale? They're not that expensive these days. I paid $163 for an Adam CPWplus 200. The unit is very accurate and besides checking my W&B after modifications, it's also very handy for weighing other things. I use it for weighing items that I sometimes carry with me in my plane, like my tool bag, parts bag, O2 bottle, spare tire, canopy cover, and all that stuff. Those numbers and moment arms go in my Foreflight W&B screen where I can simply check whether they are onboard or not. I also use the scale for weighing gas that I drain out of my wings occasionally in order to fine-tune my fuel totalizer calibration. As an added bonus, you can use it for a bathroom scale when you're not weighing your airplane :)
 
W&B and safety

I have found several RVs that I have completed condition inspections on (not conditional inspections) had grossly incorrect W&B data sheets, if any. After weighing one RV-6, it was found that the actual empty weight was 1106s lbs, not the 1033 lb in the POH and it was pretty tail heavy. Another RV-6A was found weigh in at 1214 lbs empty and was very nose heavy. The nose wheel weight was 350 lbs. One of the complaints was that it was difficult to land smoothly....I flew it a few times and found that it was so nose heavy that it rotated at 65 mph, Vso was 67 mph. The previous owner carried 40 lbs of ballast in the baggage area, so the empty weight was more like 1264 lbs. The original POH stated the GW was 1650 lbs, so with full fuel act weighed 1492 lbs, which leaves 158 lbs for a pilot....but it was being flown with two 200 lb people.

How many of these overweight RVs are being flown for acro and ignoring the limits? RV-6s have a 1375 lbs limit, yet folks try to rationalize that its OK to do proportional weight vs G limits.

There was a great post a while back about turning stalls / spin entries. Not many folks realize that your stall speed (not AoA) goes up as CG moves forward. At a forward CG you may just get a sharp stall break instead of a buffet and mush at aft CGs. In tandem RVs, stall entry and spin recovery is significantly different at fwd and aft CGs. I cant speak for others, but my own RV-8 has about a 5 KIAS delta in stall speed between full fwd and aft CGs. I have not spin tested my RV-8 at full aft acro CG, but spin recovery at a fwd CG is crisp within a 1/4 turn, going aft it becomes sluggish at 1/2 to 3/4.

I see a trend in a many second hand RVs, folks buy them without knowing the W&B limitations or the actual W&B....which has an impact on safety.
 
I have found several RVs that I have completed condition inspections on (not conditional inspections) had grossly incorrect W&B data sheets, if any. After weighing one RV-6, it was found that the actual empty weight was 1106s lbs, not the 1033 lb in the POH and it was pretty tail heavy. Another RV-6A was found weigh in at 1214 lbs empty and was very nose heavy. The nose wheel weight was 350 lbs. One of the complaints was that it was difficult to land smoothly....I flew it a few times and found that it was so nose heavy that it rotated at 65 mph, Vso was 67 mph. The previous owner carried 40 lbs of ballast in the baggage area, so the empty weight was more like 1264 lbs. The original POH stated the GW was 1650 lbs, so with full fuel act weighed 1492 lbs, which leaves 158 lbs for a pilot....but it was being flown with two 200 lb people.

How many of these overweight RVs are being flown for acro and ignoring the limits? RV-6s have a 1375 lbs limit, yet folks try to rationalize that its OK to do proportional weight vs G limits.

There was a great post a while back about turning stalls / spin entries. Not many folks realize that your stall speed (not AoA) goes up as CG moves forward. At a forward CG you may just get a sharp stall break instead of a buffet and mush at aft CGs. In tandem RVs, stall entry and spin recovery is significantly different at fwd and aft CGs. I cant speak for others, but my own RV-8 has about a 5 KIAS delta in stall speed between full fwd and aft CGs. I have not spin tested my RV-8 at full aft acro CG, but spin recovery at a fwd CG is crisp within a 1/4 turn, going aft it becomes sluggish at 1/2 to 3/4.

I see a trend in a many second hand RVs, folks buy them without knowing the W&B limitations or the actual W&B....which has an impact on safety.

That's what I'm talk'n about- thanks for this!
 
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