What Every Pilot Needs to Know
Whether or not you’re flying a lightweight two-bladed coach or a multi-blade heavy-lifter, your rotor system performs a key function in how nicely it handles, responsiveness, potential design dangers, and upkeep necessities 🔧
Typically it’s simple to take the fundamentals as a right, so at this time we go over:
🔸 How pilot inputs are transferred to every blade
🔸 The several types of rotor techniques
🔸 What the design variations are: the professionals and the cons
🔸 What mast bumping is, and why it may be a big risk
🔸 How all of this impacts you as a pilot
Every rotor system has benefits, drawbacks, and distinctive flight traits. However this isn’t just a few dry piece of concept.
These variations can have an effect on the best way you fly, the way you handle stress in your plane, and even the way you react in emergencies.
Let’s have a look 👀
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How Does a Helicopter Rotor System Work?
A helicopter rotor system has 5 essential capabilities:
1️⃣ Present safe blade attachment to the mast
2️⃣ Permit for pitch management from the pilot’s enter
3️⃣ Soak up aerodynamic forces performing on the blade
4️⃣ Dampen vibration and supply stability
5️⃣ Make upkeep as simple and environment friendly as attainable
So how does it do all this? There are three essential steps concerned:
We begin with the pilot controls, which offer enter in direction of the rotor hub. The problem right here is that we’re making an attempt to maneuver blades which are turning very quick.
A management enter rod isn’t rotating, however the blades are. So how can we clear up this?
How are Pilot Management Inputs Transferred to Every Blade?
There are three essential parts that enable us to vary a rotating blade’s place:
🔸 A stationary swashplate
🔸 A rotating swashplate
🔸 Pitch hyperlinks connecting every blade
These two swashplates mixed management the angle of the disc, and our total pitch angle on the blades.
So how does it do that?
The management inputs from the cyclic and collective go in direction of the stationary swashplate first. This one shouldn’t be “connected” to the rotating swash plate, it’s separated by a bearing.
When the stationary swashplate adjustments its angle, the rotating swash plate mimics it (whereas rotating with the mast).
A pitch hyperlink is connected to every particular person blade, which change the pitch of every blade and due to this fact the angle of the disc.
The Three Methods a Rotor Blade may Transfer
Because the blades flip round the principle hub, they ‘need’ to maneuver in three essential methods:
🔸 Feathering: the motion that will increase or reduces a blade’s pitch angle, brought on by the management inputs from the pilot. The blade feathers across the feathering axis, like this:
🔸 Main / Lagging: the dashing up or slowing down of the blade because it rotates. That is brought on by numerous aerodynamic results like flapping up and down, which we’ll go over in a future article.
🔸 Flapping: the motion that causes your complete blade to go up or down because it turns.
So, as a blade makes one full rotation, it’s not simply going across the rotor hub, it’s consistently coping with forces which are performing on it within the three essential methods we’ve simply talked about. We mentioned this here:
What units rotor techniques aside is how a lot freedom a blade will get to behave out these actions.
We’ll go from “most restrictive motion” to “most quantity of freedom” per blade ➡️
Inflexible Rotor System
A inflexible rotor solely permits a blade to feather: improve or cut back its pitch.
Just a few good examples of helicopters with a inflexible rotor are the H135, H145, and the MD902.
It appears to be like like this:
Discover the way it appears to be like pretty easy in comparison with the others we’ve proven under. Not numerous hinges, only some parts, and the blades are instantly linked to the mast itself.
This has fairly a couple of professionals and cons:
The professionals:
✅ Easy development with fewer factors of failure
✅ Decrease upkeep prices
✅ Elevated manoeuvrability
✅ Extra appropriate for top velocity flight, due to the elevated stability (much less motion in any course apart from the aircraft of rotation)
✅ Usually thought of to have the bottom vibrations (relying on the kind) we’ll dive into why in a future article
However….
🚨 Greater structural stress: flapping, main and lagging nonetheless WANT to happen, however these actions are absorbed by the construction now with out the hinges in place). They find yourself being absorbed by the blades and the mast, which can expertise fatigue over time
🚨 Greater manufacturing prices: the blades should endure extra forces, in order that they must be manufactured to a better normal with versatile composite supplies, which aren’t low cost!
🚨 An absence of freedom for flapping and main / lagging additionally makes the rotor much less adaptable to very dynamic and turbulent circumstances, however analysis on that is nonetheless progressing
Semi-Inflexible Rotor System
A semi-rigid rotor system permits blades to feather and flap, however not lead or lag. What does this seem like? Effectively, whereas there isn’t a ‘rule’ on what number of blades this rotor system can have, however the sensible implications slender it right down to 2 blades.
You should have seen this rotor in small trainers just like the R22 and R44, in addition to the Bell 206 Jetranger and the well-known UH-1 Huey:
The blades on these helicopters are ‘coupled collectively’, primarily to attain flapping synchronisation (one blade going up, the opposite happening), in addition to mechanical simplicity. That is known as a ‘teetering hinge’.
So, the flapping is feasible however there isn’t a hinge put in to permit for main or lagging like with absolutely articulated techniques which we’ll focus on subsequent.
So, what are the professionals and cons of a semi inflexible rotor system?
✅ Simplest mechanical design
✅ Lightest design
✅ Upkeep pleasant
✅ Low cost to function
However:
🚨 Much less Manoeuvrability and danger of Mast Bumping (extra on this under)
🚨 Stronger vibrations, particularly underneath increased masses
🚨 The blades being coupled collectively may result in elevated put on, and if one blade experiences issues, the opposite one will as nicely
🚨 Diminished stability throughout excessive velocity flight
What’s Mast Bumping?
Mast bumping is a harmful situation that occurs to semi-rigid rotor techniques. It refers to a state of affairs the place the rotor hub makes contact with the mast as a consequence of extreme flapping (and due to this fact teetering), like this:
So why does this occur, and why is it a danger that comes with semi-rigid rotor techniques?
In regular flight, the teetering hinge permits the blades to flap up and down, and this isn’t a problem in any respect.
Nonetheless, in a low-G situation (while you push the cyclic ahead abruptly), the rotor hub can teeter excessively in comparison with the placement of the mast.
In low-G flight, the disc is not ‘loaded’. Loaded signifies that the thrust created by the disc is ‘carrying’ the fuselage.
Nonetheless, if the disc is not carrying the helicopter, any management enter that adjustments the disc angle doesn’t outcome within the fuselage ‘following’ that angle.
On this state of affairs, the tail rotor thrust will trigger the nostril to yaw left (for counter-clockwise rotor techniques), and can trigger a roll to the precise.
Instinctively, you’d put the cyclic in the wrong way (left), inflicting the separation between the mast and the hub to be even much less, probably leading to mast bumping (which by no means ends nicely…).
So to summarise, to keep away from and proper for mast bumping:
✅ Do apply light aft cyclic to load the disc once more
✅ Do use left cyclic afterwards to roll the plane degree
✅ Do maintain cyclic inputs easy and managed always
✅ Do cut back airspeed in turbulence, to keep away from sudden aerodynamic forces
🚨 Don’t push the nostril forwards, this may trigger low-G flight
🚨 Don’t apply left cyclic if the disc shouldn’t be loaded but
Absolutely Articulated Rotor System
A completely articulated rotor system permits the blades to flap, feather, and lead / lag. It has freedom to maneuver in each course that it needs to aerodynamically.
This implies we’d like:
🔸 Flapping hinges to permit the blades to maneuver up and down
🔸 Lead lag hinges to permit motion contained in the aircraft of rotation (dashing up and slowing down of the blade)
🔸 Lead / lag and flapping dampeners for stability
Most greater helicopters have absolutely articulated rotor techniques, take a look at this image of a totally articulated rotor system (discover the hinges in comparison with the earlier image):
So how does it stack as much as the opposite two?
✅ No danger of mast bumping
✅ Higher elevate effectivity, with much less wasted vitality going into the blades
✅ Bigger management authority as a result of freedom of motion
✅ A better VNe as a result of potential to compensate for dissymetry of elevate higher
✅ Longer blade lifespan
✅ Higher absorption of aerodynamic forces, leading to higher dealing with in turbulence
🚨 Most complicated design in comparison with the opposite two techniques
🚨 Greater upkeep necessities to maintain serviceable, as a result of totally different hinges and dampeners which may want changing recurrently
🚨 Heavier than different rotor techniques
🚨 Dearer to function
🚨 Better potential for failure of elements
🚨 Most vulnerable for corrosion and common put on as a result of linkages and hinges which are typically uncovered
Much more advantages, but additionally numerous downsides!
Conclusion
Understanding helicopter rotor techniques isn’t just a few theoretical novel – it instantly impacts the way you fly, the way you deal with emergencies, and the way a lot upkeep your plane wants.
Every rotor system has its strengths and weaknesses. Inflexible rotors supply extra exact dealing with and fewer complexity, however place extra stress on the airframe.
Semi-rigid techniques are easy and light-weight however include the danger of mast bumping. Absolutely articulated designs present the smoothest trip and greatest dealing with in turbulence however demand extra upkeep to maintain going.
Both manner, it’s vital to grasp your plane, anticipate its limitations, and work with the traits it provides! 🚁
