I've been told that the best kinds of planes to train in are very small ones, like Cessna 150s and 152s. But I've never been clear as to why. I know they are cheaper to operate, so is operation cost the only thing? Or are there aerodynamic properties that 152s have that make them "easier"? What makes for a good training aircraft?
Cost is certainly a primary factor in choosing smaller planes. It makes training much more accessible to people with less money to spend.
Small planes are also easier to fly for various reasons. They fly slower and respond more quickly than large aircraft, which gives the pilot much more margin for learning. Being more maneuverable can help them escape tricky situations.
These planes are also generally designed to be resistant to and recoverable from common aerodynamic disasters like stalls and spins. See this related question for more information. There are FAA requirements for single-engine planes in FAR 23.221.
Smaller planes generally also have fewer and less complex systems, which makes the necessary training easier to complete.
They can also operate from smaller airports, which gives a student more choices of where to do their training.
Of course, there are always exceptions to these qualities, and large planes can have similar ones, but they hold true in general.
The Cessna 150/152 is considered a good trainer aircraft for a combination of desirable qualities:
- Low cost - An older 150 airframe is comparable in price to a car (between \$25k and \$50k usually depending on internal instrumentation), making the loan payments a little easier than that Gulfstream.
- Mechanical simplicity - One engine with fixed-pitch prop, fixed landing gear, cable control linkages, manual everything. This gives three main advantages:
- Less to break. When things break on an airplane, you can't just pull off to the side of the road and call a tow truck. So, the simpler the system, the less that can go wrong.
- Less to have to learn. More complex aircraft increase the pilot's workload for standard procedures such as approach and landing (and variations like the missed approach/go-around). Retractable gear and variable prop pitch, plus flaps, define a "complex" aircraft in FAA regs requiring a special endorsement.
- Less to inspect and maintain. Preparing to fly an aircraft always incorporates a preflight "360" walk around the aircraft checking control surfaces, intakes and engine compartments, lights, external components of instruments like the pitot tube and stall horn, etc, followed by an internal check of systems like the radios, control linkages, flight instrument displays etc. This takes more time the more systems you have on board to check. Those same systems also have to be inspected more thoroughly for the annual mechanical certification (a more in-depth counterpart to a car's safety inspection) which will increase the "total ownership cost" of a more complex airframe.
- Docile handling - The 150 is nicknamed the "Land-o-matic" for its reputation for being an extremely forgiving, easy-to-fly aircraft. Cessnas in general tend to handle very well for "everyday" flying because of their high-wing design; this generally makes them less susceptible to entering fatal upsets like the spiral dive (they can still spin-stall on you).
- Full instrumentation available - If you want your instrument rating, you need access to a plane that will allow you to practice IFR, and that includes the full set of IFR navigation instruments. The 150/152's instrument panel, while small and simple (like the rest of the aircraft), is fully decked out for radionavigation, and a GPS unit is typically pretty simple to add.