That's awesome Mike! I hear that it is a lot quieter. How does it handle in a left crosswind? I'm about 35 hours in to my commercial Heli add-on in the R44 and there is a lot of paranoia (on my part) about hitting something with that tail rotor way back there. Luckily the R44's tail rotor is pretty effective (from what I'm told, I have zero reference for comparison), went out practicing in 25 knot crosswinds yesterday. Is there much translating tendency in the MD NOTAR models?
That MD looks like a nice machine!
Did my CFI/I in the R44 when I added those to the airplane CFI, so got to experience the fun of that machine.
The NOTAR has always been an awesome machine. You can duck the tail into bushes and at worse, scratch the paint. It’s a heck of a lot quieter because the high noise from the fast moving tail rotor isn’t there.
The anti-torque with a NOTAR is actually pretty interesting. And how it works depends on what phase of flight you are in. If you look at the tailboom, where it attaches to the aft part of the body, there is a fan inside that. A duct forward of that fan leads to the mesh screen you see on top of the cowling aft of the mast. That mesh screen is an air intake for the fan. Aft of the fan is the tailboom ducting.
On the tailboom at the 3 o’clock and 5 o’clock, there are horizontal slits running there. This is where the first anti torque occurs. Blown air from the fan goes down that ducting and out the slits. At the same time, the main rotor downwash is going down around both sides of the tailboom. Because of the high velocity air running inside the tailboom, there’s low pressure air exiting the slits on the right side of the tailboom. The Coandă Effect causes the main rotor downwash to hug the tailboom surface as it blows down onto the tailboom. With low pressure air on the right side of the tailboom and high pressure air on the left side of the tailboom....just like any airfoil...... it gives the tailboom a right-direction (nose left) force as the high pressure seeks to move to low pressure, and that is the first part of the anti torque. Press the left (power, or antitorque) pedal, more air is pushed down the tailboom by the fan and thus anti torque is increased. Push the right pedal, less air is pushed and less antitorque results.
The second part of the anti torque is the remainder of the air blown down the inside of the tailboom to two vents that cover the bottom half of the tailboom back end and that are covered by a rotating cone that also moves with the pedal pushes and directs the remaining air out one side of the vent or the other, or even both sides with centered pedals.
The third antitorque is the two vertical fins. Each fin is independent. The left vertical fin is directly connected to the pedals and moves left pedal, and right with right pedal. The right vertical fin is connected to a yaw rate gyro that applies a requisite amount of fin deflection commensurate with the amount of turn rate the gyro senses is being demanded.
The three methods do not work at the same time. In hovering, about 70% of the antitorque is Coandă effect and 30% is the tailcone. The vertical fins are nearly useless at a hover due to no relative wind across them. You’ll see the left fin move with a hover pedal turn just because it’s connected to the pedals, but the right one moves very little. Accelerating through ETL, Coandă reduces as Transverse Flow effect is passed and rapidly becomes more and more ineffective as induced flow is severely lessened and rotational relative wind and resultant relative wind begin becoming much closer together. Through ETL, the vertical fins start becoming more and more effective with relative wind moving across them, and antitorque shifts from Coandă being very little, to the fins and the rotating cone as forward speed increases.
Because there is no tail rotor physically pushing air at the 3 or 9 o’clock (depending on main rotor rotation direction), there’s no translating tendency to have to overcome, and the helicopter hovers level rather than left skid low.
At the same time as it comes to the factors that affect ETL un a hover, there’s no tail vortex ring state from a left crosswind, as again, there’s no tailrotor generating tip vortices whose side wash can be negatively affected by high volume inflow resulting in VRS. Same thing with a Fenestron tail rotor...due to the structure around it, tip vortices cannot form, and the localized thrust through the fenestron system is such high volume, it would take an extreme amount of crosswind to affect that. Similarly, left quartering headwind as it relates to main rotor downwash over the tail rotor isn’t an issue. Only the left/right quartering tailwind, as it affects the vertical fins when it hits them from the tail on the left/right sides of the fins and makes a bit of a pedal dance, is the only effect that occurs.
That’s the only way those things fly. It’s not physics.