Twin Blade

Celebrating twin blade propeller airplanes

Great Aircraft from Yesteryear

Navion Microlight
Copyright © 2006 Kogo Under the Creative Commons GNU Free Documentation License

Bristol F2B Fighter of the Shuttlewoth Collection on a slow fly-by.

The Early Days

From the dawn of fight aircraft used fixed pitch propellers carved from laminated wood. The most common type had two blades. When metal bladed props came into use these too were usually two-blade, fixed pitch, propellers. These worked well since the difference between the take off/landing and maximum speeds was not that great, probably a ratio of less that 1:3. For example, the Bristol F2B had an approach speed of around 55 MPH and a maximum level speed of just 140 MPH.

Gloster Gladiator

With the development of more powerful aircraft engines things started to change. The last British biplane fighter was the Gloster Gladiator, which first flew in 1934. With a 530 HP Bristol Mercury engine the MK1 Gladiator had an approach speed just a little higher than the Bristol F2B and a top speed of just over 240 MPH, a ratio of 1:4.2 still using a two-blade, fixed pitch, wooden propeller. The MK2 version introduced a few years later with a later version of the Bristol Mercury engine delivering 850 HP had a top speed of 257 MPH. This was fitted with a Fairey three bladed, fixed pitch, metal prop as a Watts propeller of sufficient diameter to handle the higher power would give insufficient ground clearance.

The fixed pitch only offered a poor compromise between the fine pitch needed for rapid acceleration at low air speeds for take off, and the much coarser pitch required to provide sufficient forward thrust at higher airspeeds. Even so the mighty Spitfire and Hurricane fighters of World War Two originally used wooden two-blade Watts Propellers. These props were not able make full use of the powerful engines performance.