This 1/4 scale model Bentley BR2 rotary engine was built by Paul Knapp, of Arizona, in 1993. The model weighs almost 12.5 pounds without stand. L=14″, W=12.5″, H=14″. 

Paul Knapp constructed this model with the help of Lew Blackmore’s book, Bentley BR2 and computer aided design drawings by Bill Mazak, of Arizona. The engine is machined from stainless steel with aluminum cylinders and heads. The engine burns regular gasoline on spark ignition, has a pressurized lubrication system, and a carburetor like its full-size counterpart.

The rotary engines of World War I rotated with the propeller. The hollow crankshaft that extended from the back of the engine was fixed to the airframe and the crankcase was attached to the propeller. Thus, the crankcase and cylinders rotate with the propeller about the stationary crankshaft. The Bentley BR2 was produced in England and was the largest and most powerful rotary engine used in WWI. It powered many airplanes, most of them biplanes.

Paul built four of these engines—two in stainless steel like this one and two of aluminum. Watch a video of one of the aluminum versions powering a model airplane called the Gigantic, made by Robert Cooper. Mr. Knapp’s engine powered the  12-foot wingspan airplane on its maiden flight. 


This flight purportedly broke two world records on December 4, 2009—the first flight by a 1/4 scale rotary engine and the first flight by a model of a Bentley BR2. All of the people involved: Mac Hodges (pilot), Ray Williams, Dale Cavin, Robert Cooper and Paul Knapp.

Exhibit added: May 1, 2008 - Last modified: June 28, 2023

Presented by The Joe Martin Foundation for Exceptional Craftsmanship