by Jonathan Spencer
Do you know where the hazards are in your aircraft weight and balance? How often do you avoid checking CG because its a pain?
Dan Scharf of American Aeronautics thinks he has an answer to these problems. Hes created a weight-and-balance plotter (and a Web-based analog) that he says takes so much of the work out of doing weight and balance that it can become routine rather than a chore you avoid while blindly hoping for the best.
With Scharfs products in mind, we set out to answer two questions: Is he right? Does his plotter make it that much easier? And using his plotter, could we quickly define the hazardous places in the weight and balance of a variety of airplanes?
The plotter idea is not new, of course. Scharf has been making some variation of a weight-and-balance plotter since 1979. But Scharfs company now makes them for all airplanes, from Cubs to Boeings and everything in between. The plotters have obviously benefited from years of refinement. Each plotter is a different shape and size and all are made of metal. Price is $41 for light singles, plus the necessary paper graphs. Heavy singles cost $46, plus the graphs.
The pictures show a plotter and plotting sheet for a Cessna 172. You use them by first plotting your aircrafts empty weight and CG on the paper. You then place the zero-point for the front passengers next to that point and position the plotter so its top or bottom edge aligns with the horizontal rulings. Find the combined weight of pilot and front-seat passenger and draw a line from zero to that point.
Next, place the zero-point for the rear passengers on the plotter at the end of the line you just drew, align the plotter again and draw a line to the combined weight of your passengers. Repeat that for the two baggage areas.
Finally, place the zero-point for fuel on the plotter at the end of the line, align the plotter and see where (and if) the fuel scale goes outside the CG limits. Thats the maximum amount of fuel you can have at the start of the flight.
You have one more point to plot-your landing weight. Figure out how much fuel youll use, re-align the fuel scale of the plotter with the fuel line on the paper, mark the amount of fuel you plan to land with and you have your landing weight.
To stay within CG limits throughout the flight, the fuel line between the takeoff weight and the landing weight must stay within the CG limits.
One of the nice features of the plotter is that its easy to experiment. We see this as a real value for would-be buyers exploring the loading capabilities of an airplane they have in mind.
Some bigger single-engine aircraft-the Piper PA32 line comes to mind-have both forward and aft baggage compartments. Its not unusual to find that putting the bags in one compartment will put you outside of CG limits, while putting them in the other does not. This is easy to see with the AA plotters.
Of course, plotters arent for everyone. Our reference non-technical user (the authors wife) took one look at the plotter and announced that she would never be able to make it work-much too confusing. The Web version was designed for these folks.
One hazard of a plotter is that its only as accurate as the user. Alignment is critical. But AA says that if you keep it aligned within 2 degrees, the errors will be negligible. A 2-degree misalignment is actually quite noticeable, so reasonable care should ensure good results. The Web version-see sidebar-dispenses with the alignment problem.
The Good, The Bad…
With such easy weight-and-balance calculation at our fingertips, we wondered how various airplanes would stack up with regard to load-carrying ability and, more important, sensitive CG considerations. We ran 23 airplanes through several weight-and-balance tests. After a little experimentation, we settled on a set of standard profiles:
The heavy-lesson profile: Two 200-pound people in the front seats-a reasonably heavy pilot and his reasonably heavy instructor-nobody in the other seats and nothing in the baggage area. This is a heavy version of a typical loading situation for that BFR or IFR currency check and a good test of an aircrafts sensitivity to forward CG problems.
The guys-weekend-out profile: Two 200-pound people in the front seats, nobody in the other seats and 50, 100 or more pounds (if permissible) in the baggage area. For six-seat aircraft, we modified this to add two more 200-pounders in the middle seats. A more balanced load but still a lot of weight up front, which gives some aircraft trouble.
The family profile: A 180-pound/140-pound pair in the front seats, a typical husband/wife combination. (We will diplomatically refrain from specifying which one is the pilot.) We put 120 pounds of children in the next row and 100 pounds in the baggage area. For six-seat aircraft, we modified this to add another couple in the middle seats, with the children in the far back.
The single-pilot profile: A 180-pound pilot alone in the airplane; the business-pilots profile.
One of the first things we noticed was that the heavy lesson profile put many aircraft close to their forward CG limit and limited their fuel load.
Throwing some weight into the baggage area, however, brought most aircraft back into a more flexible region of the envelope. So in many cases, the heavy-lesson profile had to be converted to the guys-weekend-out profile to make the loading reasonable. Memo to heavy pilots: find a skinny instructor.
For many aircraft, the plotters specify forward and aft sections of the baggage area. Were not talking about nose baggage areas here, but stations within the rear area. In most cases, we found its advantageous to load the baggage areas from back to front, to take advantage of the longer CG arm of the rear area.
Pilots of those few aircraft with nose baggage areas have a particularly flexible situation, but also a potentially dangerous one. Choosing where to put the bags can have a significant effect on the CG when the choice is either all the way forward or all the way aft. The wrong choice can easily put the airplane out of CG limits.
Next, we noticed how many aircraft can carry more fuel than they can use with most of the profiles. This is nothing new, of course, but its worth reminding pilots of those airplanes that full fuel should not be the default.
And we noticed that an airplanes empty weight and CG can have a big effect on its load-carrying ability. In one case, we found that the difference between an average heavy airplane and an average light airplane increased our legal fuel load from 35 gallons to 75 gallons for the same payload.
We found that the empty weight and CG can vary significantly from airplane to airplane within the same model. Whether this is due to real differences between airplanes or an artifact of the weight and balance process is not clear. Some of the discrepancies may be the difference between calculated and actual weights. (Has any airplane ever weighed less than its calculated weight?)
We suspect that many of these weights and CGs are based on calculations rather than actual weighing, with the usual possibility of cumulative mathematical errors. Even some of the original weights may not be accurate. Dan Scharf pointed out that the early Piper PA28 series aircraft were never weighed but instead started out with a calculated weight and later weighings have proven many of those calculated weights to be wildly optimistic.
Finally, we found that the single-pilot profile was a non-issue. All aircraft handled that with ease, although in many cases we decided we would feel better with some weight in the baggage compartment to move the CG further aft of the forward limit.
Load With Abandon (Almost)
These airplanes can take most normal loadings without exceeding limits. In some cases, theres a caveat, such as adding some baggage to keep the CG out of the forward limit, or limiting fuel to something less than full. But after satisfying that caveat, the airplane is well-behaved. First the heavy haulers:
Cessna 210-Load it, fly it. One of the biggest load haulers.
Cessna 206-Load it. Place 100 pounds or so in the aft baggage area. Then go. Very big load hauler, but then thats what its designed for. The 206 has one of the most complex plotters of any of the light aircraft because of the many ways it can be loaded, but its still hard to load it out of CG.
PA32R-301 (Saratoga) – Limit the fuel to 60 to 70 gallons and you can load it freely. A big load hauler. But watch out for the nose baggage area.
Cessna 182-Newer ones: Just make sure theres some weight in the baggage area, preferably the rear area. Older ones with long-range tanks and lower gross weights: be careful about filling those tanks. If you limit fuel to 60 gallons, its easier to load.
Beech A36-Dont use full fuel unless youve checked W&B carefully. But with limited fuel, its a good hauler if not a good distance runner.
Next, airplanes that dont haul as much but are still easy to load:
Cessna 172-Not for heavy people but the family profile works.
Cessna 177RG Cardinal-With heavy weight up front, put 50 to 100 pounds in the baggage area. Otherwise, few restrictions.
Cessna 177B Cardinal (FG) – With heavy weight up front, put some weight in the baggage area. It fits the family profile well. The heavy-lesson profile can be a little dicey depending on the CG, which seems to vary quite a bit from airplane to airplane.
Cirrus SR22 -Watch the fuel quantity (or limit it to 60 to 70 gallons), load it and go. CG tends forward, which is noticeable on landing; elevator authority isnt generous.
Mooney M20F, J (201) – Not for heavy people, but handles the family profile easily. Just make sure you have 50 to 100 pounds in the baggage area. Full fuel wont be an option due to gross weight limitations, not CG.
Mooney M20K (252) -Close to forward limit with two people. But add 100 pounds of baggage and you can load fairly freely. Just watch the big tanks with heavy people and note that overall payload is low.
Mooney M20M,R,S (Bravo, Ovation, Eagle) – Observe the usual Mooney caveat about adding weight in baggage area to keep the load well within limits. Also note that large tanks usually cannot be filled. But limit fuel to about 65 gallons and you can load without much thought.
PA28-181 (Archer) – Watch the fuel at heavy weights. Actual empty weight/CG can have a big impact on loading difficulty.
PA28-RT201 (Arrow III) – The big tanks can be a problem. But limit the fuel, throw some weight in the baggage area and youre in good shape for most missions.
Pay Attention Here
These airplanes require some care when loading. Some can get out of limits easily, others simply reach the maximum weight easily. Most have caveats that can help.
Early Bonanzas-Once you get beyond a certain weight in front seats, almost any combination in the other seats and baggage area will be out of CG. For some configurations, low and high baggage weight puts you out of CG, but middle weights dont.
Beech V35 series -Handles heavy folks in front well, but watch out for rear CG limits as you add weight in rear seats and baggage area. Fuel limits can be a concern in earlier (lower MGW) models.
Beech Sierra-As a two-person airplane (or two-plus-two) it can be loaded with abandon. But be careful if you start loading the rear seats.
Grumman Tiger-Almost impossible to put two full-sized people in with full fuel.
Lancair Columbia 300-Be careful of the aft CG limit when loading good-sized people in the rear. The Columbia has a zero-fuel weight, although we found it takes some very heavy loading to reach it. Large fuel capacity is an issue also-limit to 60 to 70 gallons. And also note that this aircraft has a maximum landing weight.
PA28-180 series -Only the single-pilot profile lets you use full fuel. Watch the forward CG limit, especially at higher weights. Owners typically fly these forward of the limit.
PA28R-200 (conventional-tail Arrow)-Two relatively light people and 100 pounds of baggage allows full fuel. Any other loading should be done with careful attention to fuel load.
PA32-300 series (Cherokee Six, Lance)-Wide variation in empty weight. If you have a light one, its a relatively simple airplane to load, although it still helps to carry some weight in the aft baggage area. If you have a heavy one, watch the forward CG and the fuel quantity. And use the nose baggage area sparingly.
PA46 (Malibu)-If youre carrying a group, load the third row first and then load the second row carefully. Creative use of the nose baggage area can keep a heavy load from going beyond the aft CG limit. And watch fuel quantity when carrying a heavy load-the big tanks can easily take you over max gross weight.
We did this analysis using both the plotter-based and Web-based versions of the AA system. Our preference is for the Web-based version, especially for doing analyses like this, since you can make changes quickly and easily. For normal operations, its more a personal choice.
The manual plotter makes it easier to have a permanent record if required, especially if youre using the CD-based version and arent near a printer. But the online version comes closest to being fun to use.
The American Aeronautics Website also notes that their products are useful if youre looking for an airplane to fulfill a specific mission. This is particularly true for larger aircraft such as heavy turboprops or business jets, where the loading and range calculations can be complex. The cost of plotters for all the candidate aircraft would be a very small percentage of the total cost of the airplane.
But even for small aircraft, we think we could easily justify the cost of several plotters (at $51 to $56 each) if we were trying to choose between models, model years, or just specific aircraft.
The more we worked with these plotters, the more we feel that you shouldnt leave your hangar without one (or something equivalent). Even the aircraft that are easy to load have gotchas that could bite you when you least expect it. Anything that encourages pilots to do a W&B calculation for almost every flight is a good thing in our opinion and the best way to do it is to make it easy and maybe even fun.
-Jon Spencer is a Cardinal owner, freelance writer and Web developer. He lives in Newton, Massachusetts.