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:
|Length||18' 6"||18' 6"|
|Displacement, Power||1500cc, 53 hp||1915cc 65 hp|
|Vstall||38 mph||45 mph|
|Vcruise||90 mph at 3300 rpm||100 mph at 3000 rpm|
|Vmax||115 mph||125 mph|
|Vne (never exceed speed)||162 mph||162 mph|
|Rate of climb||850 ft/min||850 ft/min|
|Fuel Usage||3.5gal/hr||3/0 gal/hr|
|Empty Weight||462 lbs||573 lbs|
|Fuel,10 gal @ 6 lbs/gl||60 lbs||6o lbs|
|Pilot||180 lbs||180 lbs|
|Baggage||18 lbs||21 lbs|
|Gross Weight||720 lbs||834 lbs|
|Limit Load Factor @ Gross Weight||4.4 gs||3.8 gs|
|Ultimate Load Factor @ Gross Weight||6.6 gs||5.7 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:
|00||General Arrangement and Specifications|
|20||Wing Center Section|
S-22 plans incorporate the S-21 plans and add 8 new sheets:
|80||General Arrangement and Specifications|
|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 www.ptaeromuseum.com.
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