Bell 429 Tail Rotor

[Agog]

I was wondering why the Bell 429 tail rotor is the way it is. I understand the x-shape is to reduce the noise signature, however...

It is a departure from the typical bell 2-blade tail rotor, so I assume that the 4-blade configuration permits a smaller diameter than an equivalent 2-bladed design.

My main curiosity is why they chose to go with two 2-bladed teetering tail rotors vs one articulated 4 bladed tail rotor. Is it because of the simplicity of a 2-bladed delta hinge tail rotor design, that two of them is an easier manufacturing/operating deal than one 4-bladed articulated tail rotor.

Thanks for any information you are able to share.

[Disguise Delimit]

The asymmetry reduces the noise from the T/R, or at least changes the way it sounds, away from the annoying aeroplane propellor sound. You may have seen how the original Dauphin has symmetrical fenestron blades, and emitted an awful screeching sound. Then they went asymmetric and it is almost quiet. Same on EC120.

Teetering Delta-3 is cheap to make, but it can thrash out its bearings.

 

[iChris]

On 2/13/2021 at 7:48 PM, Agog said:

I was wondering why the Bell 429 tail rotor is the way it is. I understand the x-shape is to reduce the noise signature, however...

It is a departure from the typical bell 2-blade tail rotor, so I assume that the 4-blade configuration permits a smaller diameter than an equivalent 2-bladed design.

My main curiosity is why they chose to go with two 2-bladed teetering tail rotors vs one articulated 4 bladed tail rotor. 

 

Bell’s technical description of their 429’s tail rotor follows: “Four blades stacked system, 65” diameter, with low tip speed, scissor arrangement, composite T/R blades with swept blade tips.”

 High blade tip speeds account for significant noise. Noise control can be accomplished by reducing rotor blade tip speed and increasing the number of rotor blades—studies done by members of Airbus, Sikorsky, and US Army referenced below.

The simplest way to permit flapping is to use a teetering hinge on two-bladed tail rotors. There are simply two teetering rotors spaced a short distance apart on those four-blade tail rotors. Bell stayed with what works. Their time-tested teetering two-blade tail rotor with delta-three.

 Two teetering rotors making up the Hughes/MD 500 four-blade quiet rotor and the AH-64 Apache tail rotor are not at right angles primarily because the scissors configuration simplifies the control linkage arrangement, and there is also some evidence the design is quieter. Note the similarities of three manufactures Hughes/McDonald Douglas,  Bell, and Sikorsky.

 Similarities between the old and the new tail rotor hubs, H269A/AH-64,  Bell206/Bell429, and S58/UH60 below:

 

https://apps.dtic.mil/dtic/tr/fulltext/u2/775391.pdf  pg. 115

 https://www.icao.int/environmental-protection/Documents/EnvironmentalReports/2016/ENVReport2016_pg42-45.pdf

Edited February 18, 2021 by iChris

[Agog]

Outstanding response, iChris.

Thank you.