Anyone who has flown a helicopter with a two-bladed, semi-rigid rotor system, has been trained on the dangers and causes of mast bumping. This phenomenon can be so perilous that some pilots won’t step foot in a helicopter prone to this issue. For those unfamiliar, mast bumping is a condition that occurs when a helicopter's rotor hub strikes the main rotor mast, which can lead to severe damage or even rotor separation from the mast. It is the result of improper recovery from entering low G conditions and, unfortunately, the vast majority of mast bumping incidents are catastrophic.  

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Pilots can avoid mast bumping by understanding the limitations of the aircraft, staying away from certain maneuvers, and properly evaluating weather conditions. However, environmental conditions and pilot error, even from the most experienced pilots, can still lead to mast bumping events.  Consequently, this remains a looming concern and ongoing cause of helicopter accidents.

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When a rotor system is “unloaded” from a cyclic pushover into low G flight or from turbulence, a rolling motion to the right can occur as the tail rotor is still producing horizontal thrust with an ineffective main rotor. With an unloaded rotor system and right roll, an abrupt input to level the aircraft would be devastating and can cause the rotor blades to strike and separate from the rotor mast (mast bump). The correct action would be to apply aft cyclic or nose up to “reload” the rotor system and then level the aircraft. 

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Here are a few situations that can lead to mast bumping in helicopters with a two-bladed, semi-rigid rotor system
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• Low G pushovers - pushing the cyclic forward rapidly 
• High speed in turbulence
• Leveling off rapidly with the cyclic after a climb
• Descent using the cyclic only
• Abrupt entry to autorotation
• Up/down drafts in mountainous terrain with abrupt control inputs

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Robinson Helicopter Co. has provided guidance in the Pilot Operating Handbook (R22, R44, R66) as well as required training through SFAR 73 on low G avoidance, and proper recovery from low G flight conditions. Their recent addition of a new symmetrical horizontal stabilizer also provides improved roll stability during high-speed flight, where the aircraft is at an increased risk of mast bumping.

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I trained in a Robinson R44, and have 20+ years of experience flying Robinson Helicopters. It’s ingrained in my mind to avoid low G pushovers, and to slow down in turbulence. However, when under pressure and in a nose down right roll, or inadvertent low G... am I 100% confident that I’ll make the correct split-second control inputs? What if, instead of relying on me to do the right thing, the aircraft could do this for me nearly instantaneously, or better yet, not allow me to enter these conditions in the first place?

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SkyOS is the answer to these questions. This operating system dramatically reduces the potential for mast bumping by actively avoiding control inputs that can cause low G and detecting inadvertent low G caused by turbulence. In these situations, SkyOS automatically inputs the correct recovery to load the rotor system. It is another reason why the Skyryse One™ is the safest, simplest, and smartest single-engine helicopter in general aviation. Based on the Robinson R66 platform, the Skyryse One takes an already proven and reliable helicopter to a whole new level of safety and simplicity with the addition of our advanced fly-by-wire architecture.

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SkyOS prevents pilot entry into low G flight, and automates recovery from inadvertent low G

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Fly-by-wire (“FBW”) technology has been proven to increase stability, safety, and efficiency in a range of commercial airliners, business jets, and military aircraft. Skyryse incorporates FBW within our operating system, SkyOS, which enables inherent hands-free stability, flight envelope protection, and automation to keep the aircraft in a safe operating envelope during all phases of flight.

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Here is how SkyOS prevents low G mast bumping in the Skyryse One aircraft: 
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• Three triply-redundant Inertial Measurement Units (IMUs) or “sensors” constantly measure the G load of the aircraft.
• If IMUs detect low G, the rotor is reloaded automatically by pitching the nose up.
• SkyOS doesn’t permit low G pushovers - it’s not an allowable input using the single control stick or touchscreens.
• Inherent stability, where the aircraft is always trimmed for one G flight, prevents the pilot from over-controlling the aircraft in turbulence.
• SkyOS software manages rotor disc load in descent and during level-off from a climb.
• Entry to autorotation is automatic, preventing abrupt low G in an entry to an autorotation
• If SkyOS detects turbulence severe enough to cause low G, it will automatically slow the aircraft down to a safe speed.
• Envelope protection prevents excessive speed and retreating blade stall.
• Skyryse One includes Robinson’s new symmetrical horizontal stabilizer as a standard feature.

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When it comes to mast bumping, and other leading causes of aviation accidents, don’t think of SkyOS as just a safety pilot or CFI who doesn’t take up a seat. It’s much, much more than that - it's an operating system that prevents you and the aircraft from ever getting into a situation where these types of accidents can happen. It doesn’t just help you recover from these situations, it makes them almost impossible to occur to begin with. 

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For more information about Skyryse One, or Skyryse, contact us at +1 (213) 816-6435, or sales@skyryse.com.

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