Depending on the model and size of the helicopter, a helicopter’s blades, which are between 40-60ft long, spin from about 225 RPM to 500 RPM.
Speed is determined by the power of the rotor and the length of the blade.
The huge American twin-engined, tandem-rotor, heavy-lift Boeing CH-47 Chinook helicopter blades spin at approximately 225 RPM. A smaller helicopter might have blades that rotate at around 400 RPM.
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Helicopter Blades Can’t Reach Supersonic Speed
If you’ve ever been near a helicopter as it takes off, or even when it is flying overhead, you know that the noise its blades make as they spin can be immense, very much uncomfortably so.
It’s therefore only natural to wonder if the blades are spinning so fast that they go supersonic.
The answer is no.
This is due to the very nature of how a helicopter works.
If the blades rotate so fast that the tips go supersonic, it would result in the helicopter becoming uncontrollable.
This is thanks to what is known as “Dissymmetry Of Lift” (also known as “retreating blade stall”), which is when there is an uneven amount of lift on opposite sides of the rotor disc.
The blades are designed to rotate within 90-110% of a helicopter’s normal speed.
During climbing, descending, or cruising, the blades spin at within +/- 2-3% of normal speed.
During aggressive maneuvering and auto-rotation, the blades spin within a greater margin, though still within 10-15% of normal speeds.
Helicopter Blades Can Easily Kill You
Helicopter blades certainly have the potential to kill you if you get in their way when they are spinning.
There have been numerous deaths over the years due to a person or persons coming in contact with the blades.
Helicopter blades won’t decapitate and cut you in half as a guillotine would and what you might see in the movies.
As the blades are actually quite blunt, it would be like getting hit with a blunt object like a baseball bat at immense force – i.e. certainly enough to kill you and “displace” things but not enough to cut you in half.
If you’re planning on being near a helicopter anytime soon, we recommend following a few general rules.
- Never approach a helicopter from the front
- Never go near tail rotors
- Never approach or leave without first getting the go-ahead from the pilot or crew
- Enter and exit directly from the side doors
- Only exit on the downslope side if you are on a slope
Helen Krasner holds a PPL(A), with 15 years experience flying fixed-wing aircraft; a PPL(H), with 13 years experience flying helicopters; and a CPL(H), Helicopter Instructor Rating, with 12 years working as a helicopter instructor.
Helen is an accomplished aviation writer with 12 years of experience, having authored several books and published numerous articles while also serving as the Editor of the BWPA (British Women Pilots Association) newsletter, with her excellent work having been recognized with her nomination of the “Aviation Journalist of the Year” award.
Helen has won the “Dawn to Dusk” International Flying Competition, along with the best all-female competitors, three times with her copilot.