By Steve Krog, EAA 173799
This piece originally ran in Steve’s Classic Instructor column in the June 2023 issue of EAA Sport Aviation magazine.
How many times, hopefully in jest, have you heard this phrase? It’s frequently joked about among pilots, but it can be deadly serious. Aircraft weight and balance is critical to safe flight operations and to the life of your airplane.
Aircraft manufacturers calculate the maximum gross weight for each model produced to get the airplane FAA certified (previously CAA). They do this to ensure the airplane will be able to fly safely and to prevent excessive wear and tear on the airframe.
Sadly, once primary flight training is complete and you have a pilot certificate in your pocket, much of your weight and balance training is forgotten. For those of you who have acquired a general aviation single-engine pleasure aircraft, when was the last time you looked at the supposedly current weight and balance data? Was it even in the aircraft as required? When was it last updated? This document is the most often overlooked piece of paper when purchasing an airplane.
For example, let’s say you just acquired a 1966 Cessna 172. It was refurbished several years ago by the then owner. New exterior paint, new leather interior, and the instrument panel was updated with a transponder, radio, and ADS-B. The engine is low time, so it is a perfect airplane for you and your significant other to do some weekend trips and local pleasure flying.
After getting your new purchase home, the review of the aircraft’s paperwork history begins. It seems everything is in order, but the weight and balance document doesn’t indicate anything done to reflect the refurbishment of the airplane. The equipment list still shows the aircraft to have the old ARC radio and VOR receiver and an ADF radio. For you younger owners, you probably have never heard of either of these radios.
Further logbook investigation shows that different radio installations have come and gone, but the equipment list and weight and balance document were never updated to reflect all these changes.
As the current owner of this aircraft, it is now your responsibility to keep the weight and balance data current. If you are working with a good A&P/IA mechanic, they will check and confirm the weight and balance to be current and correct.
Faced with a situation such as this, your first move should be to make an appointment with your mechanic and reweigh your aircraft. You will probably find it to be 35-50 pounds heavier than when it came from the factory. Urethane exterior paint and plush interiors add pounds to the empty weight. Then do a full recalculation of the empty weight reflecting the changes made in the panel installations. This will be helpful for calculating balance when making future flights. Having taken these steps, your new purchase is current and legal regarding the weight and balance. However, that does not supersede the 337s and STCs required to support the other equipment installations.
Why is having the proper weight and balance so important to an airplane? What happens when an aircraft is consistently overloaded? What happens when the weight is not properly distributed?
Based on the aircraft design and the materials used to manufacture the airplane, the gross weight and balance are determined to provide for a long, safe life of the airplane. Exceeding these limitations creates an unsafe flight situation, or worse!
After many hours or years of flying an aircraft beyond the gross weight limitations, hardware like the landing gear bolts, strut, and spar fittings will show wear, sometimes severely. The engine will likely not make it to the recommended TBO (time between overhauls) due to the excessive load and strain. If you fly a tailwheel aircraft, the tailwheel leaf spring takes a tremendous beating when overloaded. The leaf springs will stretch, or worse, break, causing damage to the rudder, tail post, and bulkheads just forward of the leaf spring attachment point.
Most of the flights you make in your aircraft are either solo flights or with one passenger. You know how the airplane flies. But have you ever made weight and balance variations to explore the different flight characteristics? For example, staying within gross weight, have you ever loaded a case or two of oil in the luggage area? You’re still within the CG envelope, but the CG is as far aft as possible without exceeding limitations. Now go fly your airplane, preferably in smooth air. What is the trim setting now? Did you see an increase of 10 mph at cruise? How did it handle in a power-off stall? When landing, what did the control pressures feel like? This is all part of knowing your aircraft.
Several years ago, a friend of mine bought a plansbuilt experimental airplane. Although the build had been complete for more than a decade, the airplane had been flown only a handful of hours. The price was right, and my friend was now the proud owner of a great-looking two-place airplane.
After cleaning, lubricating, and inspecting the aircraft, it was time for the first flight. Normal climbs, descents, turns, and slow flight were performed. Soon after, my friend returned to land. After shutting down, he commented that the airplane didn’t seem right in flight. It had a “quirky” feel to it.
The paperwork, including the weight and balance, was reviewed and all seemed to be in order, so a second flight was made. Within minutes my friend returned claiming the aircraft definitely had something wrong. It didn’t want to recover from a simple power-off stall.
At this point, arrangements were made to reweigh the aircraft, and the empty weight was confirmed. Again, the prepared weight and balance was reviewed, and all seemed correct. A third flight was made, and several simple stalls were attempted but with the same results.
The aircraft was difficult to control and recover — the nose would pitch down and the aircraft would begin to roll, and there was initially not enough elevator authority to bring the nose back up without excessive back-pressure and multiple bursts of power. It was a squirrely situation and probably would have killed a novice. By this time the owner was obviously more than frustrated and wondered if he had purchased a dangerous airplane.
The airplane was weighed once again. Then exact measurements were taken from the recommended datum line, and new calculations were made. Once this information was tabulated, it was quite apparent what the problem was. The original weight and balance calculations were all wrong. The airplane was flying well outside the weight and balance envelope. Using the new data, some weight was added to the tail. This time the airplane performed as expected and, in fact, was quite docile. My friend has since enjoyed many hours of pleasure flight in it without fearing the airplane.
Another good friend and previous student bought an airplane that from all outward appearances was a nice machine. After all, it was owned by an A&P/IA mechanic. The radios and transponder all worked, so it seemed to be a good purchase. The aircraft was flown locally for about 30 hours after the sale.
A long cross-country was planned with the return flight being at night. About an hour from home the pilot smelled electrical smoke and shut everything down just as she had been taught and completed the flight. The next day, the aircraft was taken to a radio repair station to have the electrical system, including the radios, examined. A day later, a technician from the repair station suggested we come down and take a look at what he had found.
To our surprise, he showed us a number of wires he had removed from under the instrument panel. No length of wire was more than 10 inches long. It appeared the previous owner had saved every bit of scrap wire and soldered the pieces together to achieve the needed length for whatever was being connected. The bad wire causing the smoke was found as well. When the previous owner installed the radios, all of the old wiring had been disconnected and left in the panel. The weight and balance document stated, “Negligible weight change.”
At this point the young owner began questioning everything under the panel and decided to install a Garmin 430 to accompany one radio and the transponder. When the job was complete, we weighed the removed materials. Nearly 20 pounds of radio, soldered, and disconnected wires were removed from the aircraft.
Weight and balance can be your friend, but it can also be your enemy. Overloading the airplane or flying it outside of the weight and balance envelope can cause an incident or even a catastrophe. At the very least, it will cause excess wear leading to expensive annual inspections. However, it can also be your friend by placing weight in the proper location within the cabin. Adding a case of oil to the luggage compartment can move the center of gravity slightly aft but well within limits. Sure, weight is added, but the benefit is the airplane now flies in a more level attitude. A level attitude versus a slight nose-high attitude leads to better speed and fuel consumption.
Take some time and look at your weight and balance document. Has it been updated to reflect any changes you’ve made? Are you familiar enough with it to explore varying the center of gravity? Or do you just get in and fly? Knowing your airplane is just as important as knowing your own skill set.
Keep flying safely and enjoy the season.
Steve Krog, EAA 173799, has been flying for more than four decades and giving tailwheel instruction for nearly as long. In 2006, he launched Cub Air Flight, a flight training school using tailwheel aircraft for all primary training.