What Is the Maximum Propeller Diameter for a 1800 Shp Engine at 2000 RPM?

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SUMMARY

The maximum propeller diameter for an 1800 shp engine operating at 2000 RPM, aiming for a maximum speed of 350 mph, is calculated to be approximately 78.5 inches, adhering to the recommended propeller speed range of 0.7 to 0.8 Mach. However, comparisons with historical aircraft like the Spitfire, which utilized a 10-foot propeller at 3500 RPM with a reduction gearbox ratio of about 2.5:1, indicate potential discrepancies in this calculation. The discussion highlights that while exceeding the Mach threshold can lead to increased noise, it does not significantly impact efficiency.

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  • Understanding of propeller dynamics and performance metrics
  • Knowledge of engine horsepower and RPM relationships
  • Familiarity with Mach number and its implications for propeller design
  • Experience with reduction gearboxes and their impact on propeller speed
NEXT STEPS
  • Research "Propeller Efficiency and Mach Number" to understand performance limits
  • Study "Reduction Gearbox Design in Aviation" for insights on gear ratios
  • Examine "Historical Aircraft Propeller Specifications" for comparative analysis
  • Learn about "Noise Characteristics of Propellers at High RPM" for operational considerations
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Aerospace engineers, aircraft designers, and aviation enthusiasts interested in propeller performance and design optimization for high-speed aircraft.

chinook177
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Ok I'm trying to work out a few things with propellers but I am struggling to work out if I have got this right.

If I have an 1800 shp engine running at about 2000 rpm and I want my aircraft to have a maximum speed of approximately 350 mph what is the maximum diameter I can have the propeller. I have read in a few books that it is best to keep propeller speed between 0.7 and 0.8 Mach.

Working back from this I have calculated the diameter to be 78.5 inches however I know the spitfire used to run at 3500 rpm with at prop diameter of 10ft so I am assuming that I have done something wrong in my calculations.

Any help would be appreciated.
 
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The Merlins or Allisons used in Spitfire or Mustangs had a reduction gearbox that I think was about 2.5-1 So while the engine might have seen say 3500 rpm the prop was only turning at 1400 or so.

The rpm/mach number on your smaller prop actually sounds correct Might even be a bit on the high side. While you loose efficiency about all that happens is the prop "snarls". It gets loud as it breaks the mach. A Cessna 185 has a 310hp engine. When taking off it makes the usual noises until you have it full throttle and the prop tips bust the mach and then it gets a bit loud.
 

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