Helicopter Aerodynamics

[pkopic]

Question:

Why is the Horizontal Stabilizer Aerofoil, located on the tail section, on a Bell 407/412 (possibly others) oriented upside down (ie. produces lift downwards)?

Is this to balance the rotorcraft about the c.g. at higher airspeeds?


Cheers,

 

[gugu]

The negitive camber of the stablizer,is to pull the nose up to streamline the helicopter for less drag (Higher cruise)

 

[bwellman]

At high speed, the equilibrium attitude of the rotor is tipped into the wind by an uncomfortable number of degrees. Since the rotor shaft tends to orient normal to the tip path plane, this means that the pilot and pax wind up hanging from their straps. Also, as pointed out above, the fuselage is draggy in this attitude. So, designers added a horizontal "stabilizer" which pushes the tail down into a more comfortable position for the pax and a less draggy state for the fellow who has to pay the fuel bill.

Fixed stabilizers may be found on a wide variety of light helos, not just the Bell 407/412. More sophisticated flying stabilizers are used on a variety of [mostly] military helicopters. In cruise, their function is the same as their fixed counterparts.

 

[klyde]

I was led to believe that the horizontal stabilizer was to tip the nose down so that the tip path plane would be more perpindicular to the mast. All helos that I have set in vibrate more when the tip path plane departs very much from perpindicular to the mast. With the fuselage level in level flight, the tip path plane must be at an angle to the mast. The faster the more the angle. At least this was my understanding. I have my horizontal stab (symmetrical airfoil) set to push the nose down...Can't say that I've detected much affect up to 80mph.

Stu Fields Safari pilot

 

[Sparweb]

Bell's own manuals state that the horizontal stabilizers permit a broader range of CG's. Secondary implications are speed and vibration, which, as already explained, are related to eachother.


Steven Fahey, CET
"Simplicate, and add more lightness" - Bill Stout