Ask Pete!

by Pete Schoeninger
Published in Midwest Flyer – February/March 2018 issue

Q. Have you ever done something really dumb in an airplane?

A. While I was fixed base operator and airport manager at Waukesha, Wisconsin, I had to fly to Iowa one early summer morning. The night before departure I refueled the airplane (Piper Archer), did a run-up to check mags and carb heat, laid out maps in the cabin, etc., so it would be ready to go the next morning. As dawn broke the next morning, I got into that Archer and taxied to Runway 28 and down the runway I went. Just as I was lifting off, the engine quit. I coasted some distance, then turned off on a taxiway. I looked at the fuel gauges, and was astonished to see they read empty. I got out of the airplane and looked inside each tank. Bone dry. Some crook had swiped all my gas overnight, and I was in such a rush to leave that morning that I never checked anything. I refueled the airplane, and flew uneventfully to Iowa. Had the thief left me 1-2 gallons of gas, I would have ended up in a subdivision and for sure on the front page of our local newspaper. How lucky I was that no one saw me. It was a really dumb move on my part. So, lesson learned… ALWAYS do a thorough preflight inspection immediately before each flight.

Q. There is one aluminum skin on my 1968 Cessna 172 that is sort of a dirty yellow color on the interior side. (The rest of the fuselage is still fairly clean aluminum.) The skin has been coated with zinc chromate according to my mechanic. He said that fuselages coated with zinc chromate are usually found on airplanes with a float kit, which I understand is needed to install floats. But he says that my airplane does not have a float kit. How can I tell if a Cessna has a factory float kit installed?

A. I have seen this (one zinc chromate skin in a fuselage) a few times and my best answer came from a guy at Cessna many years ago. He said on rare occasions Cessna production line workers would run out of a standard skin, and to keep the assembly line going, they would grab and install a skin that was destined to go on a float plane, as the skins are identical, except for the zinc chromate. Clues to tell if your C172 has a float kit are inside the fuselage. Also, look at the original equipment list. If all the skins have been treated with zinc chromate, the equipment list will also note that and you’ll know that you have a float kit installed. Note that a float kit adds a few pounds to the weight of the aircraft. There are other things to look for, but these are the easiest two.

Q. The weight and balance information (equipment list) on my Beech F33A seems pretty screwed up from numerous additions and subtractions of radio equipment, propeller changes, a larger engine installed, new paint, etc. My mechanic suggested the airplane be weighed to determine an accurate empty weight and center of gravity and wants $400 to do it. Isn’t that outrageous? I have some big scales. Can I do it myself? I am not a licensed airplane mechanic, but I can read a scale and do simple math!

A. No one can prevent you from weighing your own airplane, but it will NOT count as a legal weight and balance computation unless signed off by an Airframe and Powerplant mechanic.  Your mechanic will fill or empty fuel tanks, then place your airplane on three (3) certified scales inside a hangar, level the airplane per manufacturer maintenance instructions, then read scales and do calculations. $400 seems reasonable to me. For fun, I will bet you a lunch that your new actual weight is at least 15 pounds more than your current questionable computed weight.

Q. The recording tachometer on my 1979 Piper Warrior reads 3106 hours. There is an electric Hobbs meter, which indicates 3760 hours. I am the third owner of the airplane; the first two owners were flight schools. According to the airplane’s paperwork, it was delivered new with both instruments installed, and I could not find anything indicating that either instrument has been replaced. Why do they indicate substantially different hours?

A. Your recording tachometer is really a revolution counter set to indicate correct time at a specific (usually cruising) RPM. So, if you fly the airplane exactly one hour at 2400 RPM, the recording tachometer will indicate one hour. If you run the engine faster, or slower, the recording tachometer will not record correct time. During taxi you may only be running the engine at 900 RPMs or so, thus the recording tachometer indicates much less than actual time when taxiing. The Hobbs meter only detects electrical current flow, so it is either on or off. For a typical flight, the Hobbs meter will show a little more time than the recording tachometer because during taxi and descent, and other times you are using low power, the Hobbs meter is running at normal speed, but the tachometer is not. The typical difference is about 20%, and your numbers are close to that.

Q. What production airplane do you think holds up better than most?

A. In my experience, the winner is the humble Cessna 152. There are many 152s flying daily with over 15,000 hours of flight time – usually flown by students – and still going strong!

Q. I’ve seen some late 1940 classics like Piper J-3 Cubs and Taylorcrafts on straight floats, but I have never seen one on amphibious floats. Why not?

A. There are a few (very few) J-3s on amphibious floats, but the weight penalty of amphibs pretty much means there is no way you can legally carry a passenger. Small floats add about a couple hundred pounds to a Cub’s empty weight, and amphibs add maybe 80 pounds more. In some makes and models, a small gross weight increase is allowed for floats, but in spite of that, two people of average or less weight and half fuel and you are nudging gross weight limit. Add in 80 pounds more for amphibs and you are almost always going to be at gross weight with only one person in the plane. And watch for amphib floats on most four-seat airplanes, and you don’t see four people on board for the same reason.

Q. The Piper Aztec, and the Piper Super Cub, are significantly slower than the Cessna 310 and the Cessna 170 with similar power. Why?

A. All four are good airplanes! The Pipers use the USA 35B airfoil, and the Cessnas use the NACA 2412 airfoil. The Piper airfoil is a pretty much flat bottom, fat on top, high lift airfoil. It creates lots of lift (and drag.) The NACA 2412 Cessna airfoil is more streamlined. So, the Piper models you mentioned can fly slower, thus operate out of shorter fields. The Cessna 310 and 170 fly faster than Aztecs and Super Cubs, but land a little faster and need a longer runway. I’ve been in all four aircraft and they are all good airplanes, but remember, they are all great at some – but different – missions.

EDITOR’S NOTE: Contact Pete Schoeninger at with your questions for this column or for consultation on aviation business and airport matters. Pete has four decades of experience as a line technician, airplane salesman (300 aircraft sold thus far), appraiser, snow removal supervisor, airport manager, and as the manager/co-owner of a fixed base operation.

DISCLAIMER: The information contained in this column is the expressed opinion of the author only, and readers are advised to seek the advice of others, and refer to the Federal Aviation Regulations, Aeronautical Information Manual, Pilot’s Operating Handbook for the airplane(s) they fly, and other instructional materials before attempting any procedures discussed herein.

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