Dear Rod,
I'm a little worried about the fuel gauges in both of our flying club's aircraft. These are two Piper Warriors, and the fuel gauges in each wiggle and wobble during flight. I've mentioned this to the president of the flying club but he doesn't want to spend the money to replace the gauges. I think this is a very unsafe situation and I am considering leaving the club. Am I being overly concerned?
Sincerely,
Amy
Greetings Amy:
My guess is that you may be overreacting here. I sure do admire your concern about knowing the precise amount of fuel in your tanks, but if you think that's what most airplane fuel gauges tell you, then you're in for a shock. Your fuel gauges actually only serve only one practical purpose--they tell you when you have a fuel leak. That's right. You can't count on the typical rheostat fuel measuring system found in most general aviation airplanes to offer any consistently reliable assessment of the fuel in your tanks (or at least you shouldn't).
Legally speaking, these gauges are only required to be accurate when the tank is empty (no useable fuel on board). Using a fuel gauge to tell you when your only remaining tank of fuel is nearly gone, however, has no practical in-flight value (mainly because you shouldn't be in flight in this situation). The fuel gauges shouldn't wobble and wiggle, but the fact is many do. As long as those gauges are accurate enough to show you when fuel is leaking out of your tank (that is, they are accurate and reliable enough to show a decreasing volume of fuel), they are serving their ultimate purpose.
Most pilots don't count on their fuel gauges to tell them how much fuel is in their tanks. Once you know the airplane and its fuel consumption rate for variable conditions of flight, you should be able to predict--within plus or minus two gallons--the amount of fuel used from any tank at the end of a reasonably long flight. So even if those gauges continue to wobble and wiggle, I wouldn't worry about them. Instead, I'd worry about becoming good at estimating your in-flight fuel use. Know how to predict this value and you'll never worry about fuel gauges again.
What altitude to lean?
Dear Rod:
I'm a flight instructor and I'm a bit confused about the altitude at which we should lean the mixture on a nonturbocharged airplane during a climb. Most of the time I hear that leaning should take place only above 5,000 feet. A few instructors at our flight school say it's 3,000 feet. But when I ask if this figure is mean sea level or density altitude, they don't seem to know. Is it msl or density altitude that I should be using?
D.K.
Greetings D.K.:
The reason we avoid leaning during climbs when more than 75-percent engine power is being generated is that this condition produces a great deal of engine heat. Fuel, among others things, helps keep the cylinders and their attachments cool. Let the engine heat increase beyond normal limits and valve warping, detonation, and other bad things might occur. This is why on nearly all modern airplane engines, when you move the throttle lever through its last inch of travel to the max-power, full-throttle position, an enrichment valve opens that increases the fuel flow by approximately 15 percent above normal. What does this extra fuel flow provide? It provides extra engine cooling during the climb, since the engine manufacturer assumes you're climbing, given the full throttle position. If you lean the mixture during the climb with full throttle, you deprive the engine of this extra fuel, and may generate engine-damaging heat.
Of course, there are times where you can climb at full throttle and not develop serious engine heat--when the air is thinner or the atmospheric pressure is reduced (or both) come to mind. For example, you might be at an elevation of 2,000 feet msl on a hot day where the density altitude is 5,000 feet. Because of the higher-than-normal temperature, the air at this airport is as dense at it would be at a 5,000-foot msl airport on a standard day. That means your engine is not likely to produce more than 75 percent of its maximum rated power during a climb, so engine heat isn't necessarily an issue here. Leaning is required in order to optimize the fuel/air ratio and thus obtain maximum climb performance.
On the other hand, you might depart an airport at 5,000 feet above sea level on a standard day. The air is neither too cold nor too warm at this airport; it's simply at a standard temperature for that altitude. But the air is still less dense since there's less atmosphere above you compressing the air (remember, you're at 5,000 feet msl). Said another way, the density altitude at this airport is 5,000 feet. During climbout, your engine is not likely to produce more than 75 percent of its maximum rated power. Therefore, engine heat isn't likely to be an issue here and you should lean the mixture to obtain maximum climb performance.
Lean the mixture during a climb at the altitude your POH recommends. If no altitude recommendation is offered, then 5,000 feet is a reasonable altitude to use. Unless marked otherwise, the altitudes referred to in your POH are density altitudes, not msl altitudes, even though the two are actually the same on a standard day. Now you have another reason to always ensure that you know the density altitude before takeoff.
Go for a spin
Dear Rod:
I know it may be hard to believe, but this South Dakota-born and -bred private pilot has never had to demonstrate (to any instructor, DPE, or FAA examiner) spinning an airplane or recovering from a spin. Most of my instructors refuse to demonstrate or share the spin experience or have had little experience in that art form. Have I been deprived of the education that I need to be a safe pilot? Your thoughts, please.
Neil
Greetings Neil:
First, the regulations only require that flight instructor applicants be taught spin entry, spins, and spin recovery procedures. Since I'm assuming that you're not a flight instructor applicant, then you are not technically being deprived of an appropriate flying education. On the other hand, and regardless of what the regulations say, it's a terrible shame that you haven't at least been introduced to spins, especially since you've asked your instructors to teach you about them.
The sad fact is that more and more instructors are becoming less and less familiar with spins (despite the federal aviation regulations requiring proficiency in them). Furthermore, many of the newer airplanes on the market are not spinnable (and in one model, if you spin it you're supposed to activate its parachute).
Personally, I don't recall having a private pilot student to whom I didn't provide spin training. It made them much more confident in the cockpit. The fact is that if an instructor communicates well, there's no reason why he or she can't teach students basic spin techniques without scaring them. Ultimately, this is why your local aerobatic instructor should become your newest BFF (best friend forever). I recommend you search for a good aerobatic instructor and take spin training. It's well worth the investment.
Rod Machado is a flight instructor, author, educator, and speaker. A pilot since 1970 and a CFI since 1973, he has flown more than 8,000 hours and is part owner of a Cessna P210. Visit his Web site.
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