wonwinglo
SMF Supporter
- Joined
- Apr 18, 2004
- Messages
- 6,754
- Points
- 113
- First Name
- Barry
De Havilland's DH-88 Comet, the eternal beauty, was specially designed and optimized for the MacRobertson Race from England to Australia in 1934. With its two 230hp Gipsy Six engines, it had a cruising speed of 220 mhp. Three large fuel tanks gave it an ultimate range of nearly 3,000 miles.
As in all long-distance races, it was essential to be able to make take-offs in an overloaded condition, which made variable-pitch propellers highly desirable. The obvious choice was the American-made Hamiltons, but there were technical problems which could not be overcome in the short time available. Instead, they chose the French Ratier design, a two-position propeller of simple and rather clever design. Fine pitch was achieved on the ground with the help of compressed air.
When the aircraft was airborne and had reached 150 mph, a disc on the spinner was forced back to release the internal air pressure, and there was an automatic change into coarse pitch. This implied an obvious disadvantage. Once the coarse pitch had been selected, it was not possible to change this state of things without landing. Thus was it also practically impossible to make an overshoot. One definitive landing, that was all.
The device that delivered compressed air for the switchover to fine pitch was — guess what? A bicycle tire pump!
As in all long-distance races, it was essential to be able to make take-offs in an overloaded condition, which made variable-pitch propellers highly desirable. The obvious choice was the American-made Hamiltons, but there were technical problems which could not be overcome in the short time available. Instead, they chose the French Ratier design, a two-position propeller of simple and rather clever design. Fine pitch was achieved on the ground with the help of compressed air.
When the aircraft was airborne and had reached 150 mph, a disc on the spinner was forced back to release the internal air pressure, and there was an automatic change into coarse pitch. This implied an obvious disadvantage. Once the coarse pitch had been selected, it was not possible to change this state of things without landing. Thus was it also practically impossible to make an overshoot. One definitive landing, that was all.
The device that delivered compressed air for the switchover to fine pitch was — guess what? A bicycle tire pump!