As new pilots, most of us do one of two things almost immediately - both of which can lead to the same potential problem. If we learned in a four-seater aircraft like a Cessna 172 or Piper Archer, we immediately call all of our friends and family and ask them to go flying with us. Or, if we learned in a two-seater like a Cessna 152, we get checked out in a larger airplane (it usually takes two to three hours), then start looking for people to load into those empty seats. Soon after that, we start planning that trip to California/Nantucket/Miami or Peoria we've always wanted to take. In other words, one of our very first moves as a super-green pilot is to load an airplane to the gills and take it someplace far outside of our local area.
Instructors almost never get to expose their students to the way in which an airplane can change personalities, given different loads and operating conditions. Fortunately, most aircraft likely to be flown by a new pilot are forgiving and will let him safely fumble through those first encounters with high density altitudes, sloped runways, and assorted unpredictable factors. Too often, however, a new pilot gets himself into a situation where a number of factors stack up and the resulting personality change in the aircraft catches him un-aware. It's an accident in the making.
Often a pilot gets into this kind of trouble as part of that first ambitious cross-country - the one that takes him well outside the geography that he knows from his student days.
Student cross-countries don't necessarily prepare a student for the real world because they are invariably selected by the instructor to make it easy on both the student and the instructor. We don't send a flatland student out over the mountains, and we don't allow them to fly trips that are likely to give them navigational heartburn. We do this because the student needs a challenge that he can handle safely. Unfortunately, as a result, the majority of students get their certificates without ever having experienced situations that may cause their airplanes to change personality.
The major factors that cause aircraft personality changes fall into two categories. The first we'll call "environmental" because they involve factors outside the airplane itself, such as density altitude, runway characteristics, and so on. The second category includes those things within the aircraft itself that cause changes the student may not have experienced during training.
Flying at full gross weight for the first time is the number-one aircraft change that is likely to catch a student unaware. Seldom if ever does a student training in a C-172 or some other four-place aircraft experience the surprising decrease in performance that results from simply putting two bodies in the back seat. Also, in many western training environments, a trainer is seldom flown with fuel tanks more than three-quarters full to keep the weight down. So, the student gets his certificate having always seen the airplane in light-weight operating scenarios.
There is an interesting rule of thumb that came out of a Cessna POH (pilot's operating handbook), which says that increasing an airplane's weight by 10 percent in-creases its takeoff roll by 20 percent. All runway charts in POHs are predicated on full gross weight, so we're not talking about lengths beyond those in the POH. What we're talking about is an airplane that is suddenly going to take 40 percent more runway than the student is used to using. This type of change can be critical because all pilots, new ones or otherwise, are creatures of habit. Most of the takeoffs they've made in this particular airplane have taken about the same amount of runway and time. They've come to expect the airplane to fly after waiting a certain number of seconds. Anything that increases that period of time significantly puts them in new territory, and they are likely to react exactly the way they shouldn't. They'll be thinking, "Surely the airplane should be ready to fly by now," and they'll try to force it into the air. If there's plenty of runway, they'll eventually stagger into the air and make it. However, if other factors further aggravate the weight-induced change in personality, they may not.
Assuming that they get the airplane off the ground safely, the pilots will then be flying an airplane that really doesn't want to climb. At least not the way they are used to. They'll be tempted to ignore best-rate-of-climb speed and pull the nose up a little more, further degrading climb performance. In most aircraft, adding two people cuts the climb performance by 30 to 40 percent, sometimes more. The first time a new pilot sags into the air in this kind of situation, he or she will notice that the trees suddenly look a lot taller.
Adding weight to an airplane also changes the way an airplane "feels" because additional weight almost always drives the center of gravity back. As the CG approaches the rearward limits of the airplane's envelope, the airplane gets more sensitive in pitch, and the pilot may get a little spooked because the airplane doesn't feel the way it used to.
If you're that brand-new pilot, take heart. There's a simple way to handle these kinds of problems. Book some dual time and make some maximum-gross-weight flights with an instructor before attempting them solo. This need not be done before you get your certificate, but it certainly should be done before loading up the airplane and taking off for distant horizons.
Another loss-of-performance learning experience may come the first time that a new pilot rents an airplane from an operator other than his flight school. This introduces the sometimes significant differences between seemingly identical airplanes that are part of different operations. For instance, although all C-172s may be created equal, they certainly don't stay that way. Age and maintenance levels vary from rental fleet to rental fleet, and these factors all take their toll on aircraft performance. As an airplane ages, it experiences wear and tear and loses performance. On top of that, the engine is aging, and what used to be a 160-horsepower engine may be only cranking out 145 hp or so.
And then there's the propeller. All props are not created equal because they weren't meant to be equal. Each airplane/ engine/prop combination is certified to permit a specific range of propeller pitches, and the performance difference from one end of the range to the other can be really eye-opening. If you've been flying a C-172 with a climb prop that would turn up 2,400 rpm static, and you find yourself in a rental with a cruise prop that only delivers 2,100 rpm static, you're going to think that the airplane will never get off the ground. If enough other environmental factors are working against you, you might be right.
"Environmental factors" that can change an airplane's personality for the worse include just about everything about a flight that's not hardware-oriented. Factors such as density altitude and runway length, slope, and surface are all lurking out there just waiting to surprise a new pilot.
The density altitude thing is the most misunderstood environmental factor. Something as seemingly benign as getting your certificate in December and taking your first maximum-gross-weight cross-country in July has its ramifications. In that situation, your runway that had a density altitude of around 300 feet in December is suddenly up around 4,000 feet in July. The difference in performance is shocking.
What will come as even more of a shock is your first en route takeoff from an airport at 3,500 feet msl or higher. The density altitude there may be around 6,000 feet, and your trusty Lycoming or Continental will be hard pressed to put out 70 to 75 percent power. Between the decreased power and the decreased efficiency of the wing, all runways begin to look ridiculously short.
POH rules of thumb say an increase in altitude of 10 percent means a 10 percent increase in takeoff roll. Raise the temperature 10 degrees Celsius (18 degrees Fahrenheit) and you can tack on another 10 percent. A slight slope of about 1.5 degrees, which is just enough that you can tell the airplane is working up hill, will add another 10 percent.
So, let's say that you're carrying two extra bodies whose weight adds 20 percent to the airplane weight. Between their weight and a higher altitude, you've added 30 percent to your takeoff roll. Then, assume it's late summer and 20 degrees F hotter than you're used to. There's another 10 percent increase in runway needed. Now you've increased the takeoff length by 40 percent over what you're used to. So far, this isn't even remotely dangerous as long as you don't try to rush it off the ground.
Now let's say there's a slight slope, about 1.5 degrees. Going up hill will cost you around 10 percent more runway. So you turn around and go down hill, but that puts a leisurely little 5-knot wind on your tail (10 percent of the takeoff speed). This will increase the ground roll 20 percent, but the downhill slope will help to shorten that. How much, we're not sure. OK, now we're all confused.
See what's happening here? There are about a dozen things working on the airplane that are going to change the amount of runway it needs to get off the ground. To let an airplane run until it's ready to fly in a high density altitude or weird runway situation without yielding to temptation and forcing it off the ground takes a lot of self-control. Unfortunately, self-control is based on experience - both of which may be in short supply in a newly certificated pilot. And then think about the compounding effect of a combination such as high density altitude and gross weight and a cruise prop. Here we have an airplane that doesn't remotely resemble the airplane the student trained in, even though it is the same make and model.
We haven't even mentioned changes in the way an airplane lands because of such factors. This is because most of the changes, while significant, are not likely to get a student into serious trouble. Yes, the airplane lands at a higher ground speed when the density altitude is up. Yes, a heavy airplane stalls at a higher speed than a light one, and it takes more runway to stop. These differences only become factors if the pilot is trying to put the airplane into a runway that would be considered short for the situation at hand. Hopefully, a new pilot won't be venturing out into the bush or challenging tiny runways until he or she has more experience.
So, what's the cure for lack of experience in these types of situations? Training! And it won't take much. The ingredients are simple. Start with a willing instructor and two fearless friends, top the tanks, and make sure you've loaded your trusty steed right up to gross. Then all you need is an hour of bashing around on every kind of runway you can find. The name of this particular game is staying ahead of an airplane's changing personality by learning its quirks. It'll be an hour well invested.
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