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Thursday, March 1, 2012

Feedback March 2012

Aerodynamic Braking

After reading Ernie Stephens’ Sikorsky S-92 Pilot Report (February 2012, page 32), I thought I would take a couple of moments to identify some clarifications regarding the article.

FlightSafety does not train nor does Sikorsky recommend “aerodynamic braking.” While that specific reference is not used in the Rotorcraft Flight Manual, the guidance in the RFM does include the following phrases: “Use collective to cushion landing” and “After touchdown, neutralize cyclic and simultaneously reduce collective to minimum.” The danger is a potential for the main rotor system to come into contact with the tailboom. That situation is always a bad thing. In fact, braking capability in a rolling landing event is improved once all gear are on the ground once the collective is lowered and the cyclic is neutralized. This is due to the negative lift (not very much) and increased friction that is available in that situation.

In the paragraph that starts, ”Of special interest…” Mr. Stephens mentions the “in-flight diagnostic system.” I have to assume that he is referring to the health and usage monitoring system (HUMS) identified one paragraph earlier. While he correctly indicates that the aircraft can perform a track and balance examination, it’s misleading to claim that the system makes the appropriate adjustments to permanently correct the problem while cruising at altitude. The track and balance sub-routine Mr. Stephens references is actually only collecting vibration data, analyzing and generating a recommended adjustment schedule to be accomplished by a technician once the aircraft returns to the ground. It remains very much a hands-on technique of correcting track and/or balance issues with weights, turns of flats, bending trim tabs, etc. Additionally, that very HUMS function is actually making and storing those calculations any time the aircraft is operated in any of the predetermined regimes for specified period of time. Those are then downloaded with the rest of that flight’s data collected for review by maintenance technicians. The system recognizes when those regimes are flown and the data is captured without prompting by the pilot. However, the pilots can command track and balance data collection when such a need exists.

R&W’s Question of the Month
What do you think of Bell Helicopter’s decision to name its 525 super medium transport ‘Relentless’? Let us know, and look for your and others’ responses in a future issue. You’ll find contact information below.

In the next paragraph, the sentence that includes “that same set of force generators” appears to be a continuation of the previous thought but is actually unrelated. The force generators are associated with the built-in vibration control system (labeled AVC on the left overhead panel in the cockpit). Those force generators (either three or six pairs) do isolate rotor vibrations and produce a counter vibration of up to 500 lbs per pair that effectively tunes out the undesirable vibratory loads. However, with the exception of the preproduction flight test prototypes, the system cannot isolate, or tune out the vibrations in or to a particular area of the aircraft.

Lastly, only a small percentage of the main rotor blades are titanium. That material is limited to the erosion strip along a portion of the leading edge. The blades themselves are fiberglass skin, a graphite and nomex spar, and a nomex honeycomb core. The article suggests the entire blade is titanium, which would be somewhat prohibitive. Despite some of the desirable attributes of titanium, it would not be a suitable primary ingredient in the manufacture of any M/R blades.

Casey Duke
Director of Pilot Training
FlightSafety International

 

From Facebook

The following comments appeared on Rotor & Wing’s Facebook page: www.facebook.com/rotorandwing

(Responding to a photo of the new Bell Helicopter 525 Relentless):

Wow, there is a cool ride! Can’t wait to see the numbers!!

Jeff Labbe

[It] looks like a Bell 214ST and an AgustaWestland AW139 had a baby.

William Riddell

Can I get that to go with missiles, rockets and guns, please?

David Shahal

Wow, nice!!! I see the Sikorsky S-76 and AgustaWestland AW139 in this design.

Emile Sheriff


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