The central idea behind Robinson helicopters is to provide an affordable and practical aircraft that’s a more accessible option for aviators from all walks of life. However, as you might have guessed, helicopters are expensive, with some models selling in the millions. Even the cheapest helicopters you can buy (and Robinson is on the list) start well into six figures, unless you’re willing to assemble kit models. Why so much money? Because these machines are complex, challenging to design, and subject to strict standards with regard to safety.
Robinson helicopters are less expensive because they’re smaller and strip away some of the complexity. The rotor system on Robinson’s models like the R22 and R44 employs a semi-rigid configuration that uses two blades on a teetering system. Think of the blades as the sides of a teeter-totter you remember from the playground. If one side is up, the other must be down and vice versa. Between the teetering rotor and the normal flapping articulation of the blades, the mast must be taller to prevent the blades from contacting the tail section (boom).
In addition, engine placement also plays a role, as Robinson helicopters have the powerplant placed low and to the rear of the cockpit. This design further exaggerates the appearance of the mast, as other helicopters, like the Bell 206, put the engine on top of the cockpit, which gives the mast a shorter appearance.
Robinson helicopters have received some negative attention surrounding safety
Despite their popularity, Robinson helicopters have raised concerns surrounding a phenomenon called mast bumping. To control the direction a helicopter flies, the pilot must move the cyclic control stick (a T-bar in Robinson models) to change the pitch of the rotor, altering the angle of the spinning blades. However, a quick and forceful input on the cyclic controls during flight can cause the rotor to angle beyond a safe point. This can cause the rotor head to make violent physical contact with the mast.
Mast bumping can occur in cases of low G, where the load is taken off the rotor momentarily, thereby failing to counteract the force of the tail rotor, causing the aircraft to roll dramatically. In an attempt to right the helicopter in an emergency situation, heavy-handing the cyclic controls is a natural reaction, but a potentially deadly one.
Mast bumping doesn’t describe a single contact between the rotor head and mast, but several. Given the blade’s rotational speed, a mast-bumping scenario could involve several hard impacts between components each second. This can potentially lead to catastrophic damage. One incident that took place in a Robinson R22 back in 1992 transformed a routine flight lesson into a disaster. After making a shallow turn at a height of over 2,000 feet, the tail boom was struck by the rotor blades, separating the aircraft into pieces mid-air and claiming the lives of both occupants. Authorities determined it was a case of mast bumping.
Improvements to help prevent mast bumping
The Robinson R22 is one of the hardest helicopters to fly for a variety of reasons, so improvements that provide additional stability and enhanced safety measures are welcome. One of the most significant upgrades to the Robinson helicopter series (initially the R66 but can be retrofitted to earlier models) was a redesigned tail stabilizer. Originally, the stabilizer, which is the horizontal piece of the tail, was only present on the right side, adjacent to the tail rotor. The newer iteration moves the stabilizer further up on the tail boom to allow a symmetrical stabilizer jutting out of both sides. The idea is that this will add stability, potentially reducing the chances of mast bumping.
Aviation technology companies have also been working to reduce dangerous situations like low G, which can lead to mast bumping. For example, Skyryse has developed a flight automation operating system called SkyOS, which won’t accept inputs that would place the aircraft in a low G scenario. Instead, the system works automatically to add load to the rotor, correcting issues before they escalate. While there are techniques pilots can use to manually recover from low G, it’s the split-second corrections required that make them difficult to execute.