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Weight & Balance
Weight & Balance
Safety Wise

wpe5.jpg (5720 bytes)SAFETY WISE

November 1998

Which one of the following acronyms should be important to you as an acro pilot? - R&B, B&C, W&B, . Let’s see, R&B - nah, only if you like it, B&C - maybe because a certified one goes for around $500 plus, W&B - hot diggity dawg (flashing lights sound of angel music) ahhh, let’s delve into this murky subject. Of course I am referring to Weight and Balance. The last contest I was tech inspecting revealed to me some interesting view points on the subject. These view points ranged from blissfully ignorant, to intentionally ignorant, to just plain ignorant. I can count on one hand how many actually had a "clue" as to what they must have in order to comply with the tech inspector’s checklist item labeled Weight & Balance. Now, before you think I am preaching and chiding (actually I am), I would like to point out a sage old aviator saying "if you’re gonna bust a reg know what you’re bustin". Let’s get one thing straight, I AM NOT ADVOCATING BUSTING REGS! My purpose is to educate not pontificate. A quick refresher is in order.

An airplane is a balancing act. It must be within the balancing parameters (CG envelope) in order to remain within balance - think of a teeter totter, see-saw, whatever. The important thing is that if does not balance then the aircraft and you have entered into the test pilot regime. The actual point of balance is called the center of gravity (CG) it has an envelope which allows a small degree of travel fore and aft to accommodate shifts in loading preferences. The Feds come along and state that if it is to be a certified aircraft it must stall at 61 knots or less at max gross weight with the furthest aft CG. If it cannot, the W&B limits must be adjusted until it can do so. So what does this mean? Simply stated an aircraft can fly outside of its CG limit, however it will continue to become more and more unstable until it is uncontrollable as the CG gets farther and farther out of limits. The second factor has to do with the maximum weight the aircraft can accommodate and still perform to the requirements of Part 23. This part goes into millimetric detail as to gust loads, climb gradients, design fuel loads etc. Suffice to say after crunching numbers and looking at a bunch of performance graph curves, a maximum weight for a condition (normal and acro) is derived and then voila! you have a CG envelope and maximum weight for an aircraft. PE01812A.gif (808 bytes)As you "ze pilot extraordinaire" begin to cram your crap into the aircraft, fuel it up and squeeze yourself into the cockpit the laws of physics begin to apply themselves and those limits are starting to come into play. "What?!" you say, "but I have a single seat aircraft, surely (ok say it - ‘don’t call me Shirley’) if it has one seat I can fly it with out fear of exceeding those limits, after all what idiot would design a single seat aircraft that could have its limits exceeded when a solo pilot straps in to fly it". Well, let me burst your bubble,  any aircraft designed with one seat can have its CG and weight exceeded. Now to be fair, most of the time the weight part is not the problem, it is the CG location. Some of you may know that I have been looking for a new aircraft, as such I have flown a number of different aerobatic aircraft. As I started to play around with the W&B problems I was shocked to learn that many of our most famous and trusted aircraft can barely be flown legally according to their published W&B data. If you weigh over 190 lbs with a chute, or if you weigh less than 140lbs with a chute you will be amazed at how many aircraft will have their CG fore and aft limits exceeded. This does not mean to say that if you weigh less than 190 or more than 140 you are bulletproof, it only means to say that to assume anything when it comes to W&B is foolhardy.

So what is the tech inspector looking for? FAR’s state that you must have W&B figured out for every flight. This means that to be in one hundred percent compliance you must calculate a W&B each time you fly, unless of course you fly the aircraft loaded the same way every time. Then a pre-calculated W&B is acceptable. This W&B data must include the current data for you personally, not a theoretical. In other words let’s say you weigh about 170, the weight and balance data in your aircraft must show a situation with a pilot who weighs about 170, not a pilot who weighs 200.   If a Fed ramp checks your aircraft and you don’t have an applicable W&B problem worked out, you will be found in violation of Part 91.103 Pre-Flight Action (b)-2. The tech inspector should be verifying that you have a current (dated from your last aircraft empty weight log book entry determination) and accurate weight and balance problem for your particular conditions for that particular day. If you can establish that you are in compliance with a pre-computed W&B situation then that is just fine. Handing the tech inspector a copy of the "Sample Weight & Balance" from your aircraft manual does not comply either with the FAR or IAC contest intent and should be grounds for failing a tech inspection.

Don’t guess about your weight and balance, figure it out and know what you are dealing with.  Then you will be making an educated decision as to how to fly your aircraft as compared to having something bite your butt "out of the blue". W&B is very simple, but unless you are familiar with it can at first appear confusing, if you have any questions or if you would like me to help you get yours sorted out give me a call, I will be happy to help.

Capt. Ron Spencer can be contacted via email at - Ed.

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