Plans are offered - for free - for the MacDonald S-21 and S-22 amateur-built airplanes.

The light-weight S-21 has an open cockpit, an uncowled engine, and a battery-powered radio. It is constructed entirely of aluminum except for the fuselage structure from the firewall to one bay aft of the seatback where chrome-moly tubing is used. First flight was in 1972.

The S-22 is the result of a major rebuild in 2009-10 that incorporated many new features. A sliding canopy that can be opened in flight was installed, as was an electrical system and starter, a cowled engine, and an avionics package. Because of the many changes, the model designation was rolled from S-21 to S-22.

The two aircraft are compared:

Aircraft Comparison
Length18' 6"18' 6"
Displacement, Power1500cc, 53 hp1915cc 65 hp
Vstall38 mph45 mph
Vcruise90 mph at 3300 rpm100 mph at 3000 rpm
Vmax115 mph125 mph
Vne (never exceed speed)162 mph162 mph
Rate of climb850 ft/min850 ft/min
Fuel Usage3.5gal/hr3/0 gal/hr
Empty Weight462 lbs573 lbs
Fuel,10 gal @ 6 lbs/gl60 lbs6o lbs
Pilot180 lbs180 lbs
Baggage18 lbs21 lbs
Gross Weight720 lbs834 lbs
Limit Load Factor @ Gross Weight4.4 gs3.8 gs
Ultimate Load Factor @ Gross Weight6.6 gs5.7 gs

MacDonald S-21. Photo courtesy of Downey and Associates.

MacDonald S-22. Photo courtesy Steve Berg.

S-21 plans consist of 29 24" by 36" sheets organized as follows:

S-21 Plan organization
Drawing Group Component
00 General Arrangement and Specifications
10 Forward Fuselage
20 Wing Center Section
30 Aft Fuselage
40 Tail
50 Wing Panels
60 Landing Gear

S-22 plans incorporate the S-21 plans and add 8 new sheets:

S-22 Plan organization
Drawing Group Component
80 General Arrangement and Specifications
81 Canopy
83 Engine Installation and Cowling
83 Lifting Surface Tips, Wheel/Strut Fairings

The S-21 appears in an article in the February 1973 issue of EAA's Sport Aviation magazine.

The S-22 is described in an article in the August 2015 issue of Sport Aviation.

The S-22 is currently owned by the Port Townsend Aero Museum, 105 Airport Road, Port Townsend WA 98368. The phone number is 360-379-5244 and the web address is

The aircraft is maintained in airworthy condition by the Museum staff and is on display there.

- Robert A. MacDonald, designer and builder, September 16, 2021