2009 05 weight wait dont tell me

Vintage Instructor THE

BY DOUG STEWART

Weight . . . wait, don’t tell me Not too long ago, a potential client called me seeking training for a tailwheel endorsement. He had heard that I conducted the training in my Piper PA-12 Super Cruiser and was hoping that he would fit inside. Needless to say, the bells and whistles went off inside my head. “Fit inside?” I asked. “Umm, yeah,” he replied, “you see, I’m a little on the heavy side.”

“Well, how much do you weigh?” I asked. “You are aware that there is a maximum certified weight limit for the airplane that we can’t exceed.”

“I weigh about 330 pounds,” he answered. Doing a quick calculation in my head I realized that between us, plus the empty weight of the airplane, we would be close to max gross weight, and that wasn’t even accounting for any fuel. “That will be pushing our weight limits,” I responded, “but if we start with only half fuel we should be okay.

You realize, though, that in order to remain within the center of gravity envelope you will have to sit in front, and it might be a bit tight for you up there.”

He replied that he understood what I was saying, but he had been searching for an airplane and an instructor for quite some time and I was the first one he had found who was willing to give it a try. He was willing to make the long drive to the airport where I’m based in order to see if he would fit.

I had my doubts, but as I almost always will go the extra mile to help someone who wants to fly get in the air, I wasn’t going to deter this gen-

32 MAY 2009

tleman. However, I must say that this was not the first time I had received this type of request, especially since the advent of the light-sport certificate. Many people have called me wanting to receive training who are just too heavy to fit in any of the airplanes that qualify for operation under light-sport rules, i.e. a maximum certified gross weight not to exceed 1,320 pounds.

…it is so easy to exceed the limits that many instructors take a very cavalier approach and tell their clients, “Just a few pounds overweight won’t matter.”

My guess is that most of these folks, whose avoirdupois is on the large side, typically also have some type of medical problem associated with their obesity that prevents them from obtaining a third-class medical certificate. What with the light-sport certificate requiring only a “driver’s license” medical, they see this as their avenue into the air.

They see a way around the rules, but if they weigh all the consequences,

they will realize there is one law for which there is no escape: the law of gravity. It’s as if they are saying: “Weight? Wait, don’t tell me.”

Seeing as how many of the legacy aircraft we fly easily fit into the light-sport aircraft (LSA) category, it seems like it might be worthwhile to review the many issues that need to be considered relative to weight and balance. Let’s look at maximum certified gross weight first, as that is the area that most often will be at or over the limits, particularly with airplanes like Cubs, Champs, Vagabonds, Taylorcraft, and even that venerable trainer for so many pilots, the Cessna 150/152 (which, by the way, does not meet LSA rules).

For many of these airplanes, with pilots of today’s typical weights, it is not very difficult to exceed the max gross weight limits. In fact it is so easy to exceed the limits that many instructors take a very cavalier approach and tell their clients, “Just a few pounds overweight won’t matter.” In doing so a horrible mentality is created, especially for neophyte pilots who are so susceptible to the “rule of primacy”: The things we learn first are the things that stick.

Thus they start off their flying careers thinking that it’s no big deal to exceed the weight limits of our airplanes.

As an examiner I often ask an applicant if an airplane will fly if it weighs more than max gross, provided the center of gravity (CG) limits are not exceeded. I usually get the true answer of “yes, it will.” But then I follow up with the question of what is

the greatest danger of flying in this condition. I’ll typically get theses answers: It will take more runway to take off and land, the stall speed will be higher, and it won’t climb as quickly.

All of these answers are correct, but it’s almost as if I have to go fishing to get to the greatest danger, and for that there is only one answer: the risk of structural damage. I am amazed at how many pilots don’t come up with that answer immediately.

I’ll then follow up with questions relative to the center of gravity. I ask, what are the dangers of exceeding the forward CG limits? Most pilots answer correctly that it will be difficult, if not impossible, to rotate on takeoff and that when landing it might be hard, or again impossible, to flare. Some appropriately mention that it will raise the stall speed.

I then move on to the dangers of having the CG aft of the limits. To this I will often get answers again related to the takeoff and landing phases of the flight. Some will discuss the fact that it will be less stable with the CG aft. But when I ask about the greatest danger of having the CG aft of the rearward limits, it concerns me that not every applicant comes up with the immediate answer that in that condition it might be impossible to recover from a stall.

I then move on to another weight-and-balance scenario. In this scenario, two pilots, Jack Sprat and his wife (you remember them, “Jack Sprat could eat no fat, his wife could eat no lean.”) are going for a flight in their Piper Cub. The winds aloft are blowing and there is an AIRMET for moderate turbulence along their route. I now ask, if you were them, how would you load the airplane? Who would get to sit in the front, Jack or his wife?

Unfortunately, not every pilot can answer this type of question. Most, if not all, pilots know how to calculate weight and balance. They know that weight times arm equals moment, and that if you total the moments and divide that number by the total weight, the number you will get is another arm. That arm is the center of

gravity of the airplane, as loaded.

Virtually all pilots know that when dealing with weight and balance, weight is equal to 16 ounces to the pound, the arm is not an appendage coming from their shoulder but a distance from a measuring point (the datum line), and that a moment is more than a short period of time while they think up the answer, but a number representing a force (when you calculate weight and balance may the force be with you). Most pilots are also keenly aware of the dangers of exceeding the limits of weight and balance, but not all pilots are truly aware of the ramifications of moving the weight around in the airplane while remaining within the limits.

In the course of a practical test, a flight review, or an FAA Wings program, I ask them about how they would load the airplane for a given condition. Do they consider the loading relative to possible turbulence or their desire to have the most stable aircraft they can have? If instead I present a scenario where the highest cruise airspeed or greatest endurance is sought, many of the pilots I interact with are unable to answer.

They are either unaware, have forgotten, or perhaps were never taught that the farther forward the CG is the more stable the aircraft will be, and also that it will have a higher stall speed. Conversely, the farther aft the CG is located, the airplane will be less stable and thus less down force will be required by the horizontal stabilizer, and since the horizontal stabilizer will be flying at

a lesser angle of attack, there will be less induced drag, yielding a higher cruise speed and thus greater range.

The reason for this lack of knowledge is most likely rooted in the fact that too many instructors are just teaching to the practical test standard rather than teaching the practical application of the knowledge of the consequences of weight and balance. I can understand if someone enamored of flight, who has been waiting most of his or her life to finally be able to begin flight training, might not yet be aware of the issues of weight and balance, but for those who are ready for a practical test, or worse yet are already certificated, there is no excuse.

Now, lest you say, “I waited, but you didn’t tell me,” unfortunately the gentleman referenced in the beginning of the article was unable to fit inside my PA-12. I couldn’t help but feel the man’s disappointment, but there really was nothing I could do to help him out, or in, for that matter.

Regardless of the size of the airplane you fly, please remember that it is susceptible to the effects of weight and balance. Ensure that it falls within all the limits relative to not only maximum certified gross weight, but also the fore and aft limits of the CG envelope. And hopefully you won’t have to wait . . . for blue skies and tail winds.

Doug Stewart is the 2004 National CFI of the Year, a NAFI Master Instructor, and a designated pilot examiner. He operates DSFI Inc. (www.

DSFlight.com) based at the Columbia County Airport (1B1).

VINTAGE AIRPLANE 33