Z-20 and now Z-20F
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Z-20 and now Z-20F
Remember9 back in the late 80s... Sikorsky sold several S-70C Blackhawks to PRC.....and in lieu of T Square, suffice to say all support dried up. Anyhow the fleet still airworthy and now Z-20 Red Hawk, which is new battlefield helicopter, which resembles a five bladed version of the S-70/UH-60 family.
And now it’s also emerged that there is a naval variant, similar to the S-70B/MH-60R SeaHaawk called the Z-20F
https://www.thedrive.com/the-war-zon...licopter-clone
And now it’s also emerged that there is a naval variant, similar to the S-70B/MH-60R SeaHaawk called the Z-20F
https://www.thedrive.com/the-war-zon...licopter-clone
Sikorsky was one of the first to cant the tail rotor. At the time Sikorsky believed correctly that the Canted Tail Rotor provided additional vertical lift at a very small total increase in tail rotor power required. If one looks at the law of cosines. Canting the tail 20 degrees reduces the anti-torque thrust by 34% (sine of 20 degrees) thus requiring addition scale up of the tail rotor for anti-torque. At the same time the cosine of 20 degrees provides for 94 % of the thrust going to lift. In essence the tail rotor is carrying its own weight. Other manufacturers are following Sikorsky’s lead on this.
Sikorsky was one of the first to cant the tail rotor. At the time Sikorsky believed correctly that the Canted Tail Rotor provided additional vertical lift at a very small total increase in tail rotor power required. If one looks at the law of cosines. Canting the tail 20 degrees reduces the anti-torque thrust by 34% (sine of 20 degrees) thus requiring addition scale up of the tail rotor for anti-torque. At the same time the cosine of 20 degrees provides for 94 % of the thrust going to lift. In essence the tail rotor is carrying its own weight. Other manufacturers are following Sikorsky’s lead on this.
Right. The cosine term goes to anti-torque and the sine term to aircraft lift, which isn’t quite how your text read. For a very small increase in power required for anti-torque, a significant amount of lift is produced and at a location that helps the unfortunate tendency for tail heavy helicopter designs.
The Sikorsky flexbeam tail rotor and the tail rotor cant are two of the more elegant pieces of engineering to happen on the rear of a VTOL machine in generations.
The Sikorsky flexbeam tail rotor and the tail rotor cant are two of the more elegant pieces of engineering to happen on the rear of a VTOL machine in generations.
AFAIK, the canted tail rotor on the UH-60 was largely driven by the UTTAS requirement to transport two airframes by a USAF C-141. At the time, this was thought to be the primary means of deployment to Europe and Asia. The Boeing YUH-61 competitor met the requirement by folding the tailboom at approximately the 2/3 point, allowing two helicopters to fit (length and height). Sikorsky choose an angled fold at the aft end of the tailboom, and shortened the length of the nose in order to fit. The shortened nose of the UH-60 created an aircraft with a predominant aft cg and reduced cg range. The canted tail rotor was incorporated to overcome these shortcomings. Fly by wire at the time was discounted because of its considerable technical risk (on the stabilator it posed problems for years), so a mechanical mixing unit helped deal with the cross-coupling created by the canted tail rotor. Both aircraft incorporated stabilators to further improve handling qualities, with the UH-60’s also assisting with the aft cg issues of extreme nose high attitudes during hover and low-speed. During early testing, lost tail rotor thrust also necessitated removal of a large chunk of the UH-60's cambered vertical fin.
Last edited by JimEli; 16th Oct 2019 at 14:50. Reason: added: cambered vertical fin
