Ultralights: What are they REALLY?

Ultralight Vehicles and Light Sport Aircraft are those flying machines that exist at the bottom of the powered-airplane pecking order. In fact, the FAA doesn't recognize ultralights as "airplanes" Even though the FAA refers to them as "vehicles" (FAR 103), we aviators still regard them as "airplanes" at heart since we're pilots! They have been designed and built as "minimalist" flying machines, and are an excellent means for pilots to learn and master basic aeronautics. They come in different levels of specification:

FAA (USA): Part 103 Ultralight Vehicle
FAA (USA): Light Sport Aircraft category
Canada: Basic Ultralight Aeroplane (BULA)
Canada: Advanced Ultralight Aeroplane (AULA)
Europe/Australia/New Zealand: Similar to Canada

USA (FAR 103 Ultralight Vehicle):

In the USA, a powered Ultralight Vehicle is,amongst other types, a very small (and unofficial) "airplane" that is used for manned flight by a single occupant; it's used for recreation or sport purposes only. It is usually a powered hang-glider or paraglider. The Rans S-17 is a fairly typical example. Since it's intended to be the very minimum, it's limited, amongst other things, to the following:

It must weigh less than 254 pounds empty;
a fuel capacity not exceeding 5 U.S. gallons;
a maximum speed of not more than 55 knots at full power in level flight;
a power-off stall speed not more than 24 knots

An exemption to FAR 103 is provided for two-seat trainers which must be used ONLY for instruction purposes. The FAA is very nervous about small unregulated "airplanes" that can be used for anything other than sport flying. That said, the FAA offers an alternate category of ultralight similar to the Canadian specification, called the "Sport Plane" type, which is similar to the Canadian (and European) types. Common to all regions is the notion that unregulated aircraft are OK for solo flight and instruction. Carrying of uninformed (non-pilot) passengers is nearly always limited to airplanes that conform to some sort of engineering standard.

The Light Sport Aircraft (LSA) category is outlined (approximately) by the FAA as follows:

"Light-sport aircraft are simple, low-performance aircraft that are limited to 1,320 lbs. (600 kg) maximum weight, two occupants, a single non-turbine powered engine, maximum stall speed of 45 knots, maximum airspeed of 120 knots, and fixed landing gear. Aircraft categories include airplanes, weight-shift-control vehicles, powered parachutes, gyroplanes, gliders, balloons and airships. Due to their complexity, helicopters and powered-lifts are not permitted under this rule."

Canada:

The Basic Ultralight Aeroplane (BULA) version is the present-day incarnation of the older unregulated single-seat ultralight. It's uncertified, a crash helmet is required, and passengers are prohibited. Again, the Rans S-17 is a typical example. Two-seaters exist for the sole purpose of flight instruction, although two pilots are permitted to fly together (each presumably to check on the other!). The owner is permitted to modify a BULA as much as desired. Floats, cameras, doors, windows, can me made of any material and screwed onto a BULA without any restrictions (except for the weight limit). Some were completed under an older 496lb empty-weight limitation, but newer types are restricted to 1200lbs (545kg) MTOW.

The AULA is usually a factory production, as either a kit or complete 1232lb (560kg) flying machine. It can arrive from the factory with a "Statement of Conformity" which verifies that the aircraft has been designed and built to a DOT approved standard. The Murphy Rebel and the Tecnam are examples.If it's kit-built, the SofC must be secured after construction. With the DoT, if a standard exists, it'll be on the Internet; go to Transport Canada's Ultralight Info site.

With a factory SofC, an AULA can be used for carrying a non-pilot passenger. An AULA cannot be modified without invalidating the SofC. The AULA must be inspected periodically to ensure that it still conforms to the original design (just like a regular aircraft).

If you want to carry passengers AND modify your aircraft (by putting floats or skis on, for example), you will need to look at building your plane as an "amateur-built". This is a completely different category, requiring over 50% owner-built content, and is a favorite category for technical geeks who have all the fancy shop tools (and a 500 sqft shop!) required to build an aircraft. An AULA can be built as an "amateur-built" aircraft, but then it won't be an AULA, if that makes any sense.