HELIPORTS TECHNICA The H V Diagram Clarifying Some Misconceptions

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HELIPORTS TECHNICA The H V Diagram Clarifying Some Misconceptions Powered By Docstoc
					                                                                                                                  (I) For single-engine helicopters, full
                  HELIPORTS                     &       TECHNICA                                                  autorotation;     (2) For multiengine
                                                                                                                  helicopters, one engine inoperative
                                                                                                                  (where engine isolation        features
                                     The H-V Diagram:                                                             insure continued      operation of the
                                                                                                                  remaining engines), and the remain-
                              Clarifying Some Misconceptions                                                      ing engines at the greatest power for
                                                                                                                  which certification is requested.
       The helicopter height-velocity dia-                             terminologies     used by manufactur-           In order to develop the H-V dia-
       gram-or     simply, the I-I-V diagram                           ers, inconsistent use of terms used in     gram, the aircraft is loaded to maxi-
       or H-V curve-has     seemingly always                           the regulations,      and by the very      mum gross weight and worst center
       been an easy tool with which a pilot                            nature of the regulatory       process     of gravity. At this point, the test
       can check his/her aircraft perform-                             itself, whereby changes are made           pilots auto rotate from the different
       ance capabilities.  Published by the                            piecemeal and as a result, in an           combinations      of altitude and air-
       manufacturer of each aircraft model,                            inconsistent fashion, the interpreta-      speed. The curve is developed with
       it plots height above surface versus                            tion of the meaning of the I-I-V dia-      two main sections, the left side rep-
       indicated airspeed with several dubi-                           gram has changed to a point where it       resenting low speed performance of
       ous "cross-hatched" or "shaded" areas                           is not consistent with its original        the aircraft in autorotation and the
       where "AVOID" is usually clearly                                intent. Recently, after some initial       right side representing     the high-
       written.   Operating      within   the                          requests     by     HAl,   the   FAA's     speed portion of the I-I-V curve. The
       "AVOID" area of the H-V diagram,                                Rotorcraft     Directorate  and Flight     left side is further broken down into
       according to the FAA's Rotorcraft                               Standards     Service volunteered     to   an upper and lower section. Each are
       Flying Handbook,      may not allow                             develop a letter that clarifies much of    developed a little differently. The
       enough time for the critical transi-                            the H-V inconsistencies. After over a      lower section assumes the pilot is
       tion from powered flight to autorota-                           year of work, an outstanding product       performing a takeoff, and the pilot
       tion, hence the I-I-V diagram's other,                          was completed.    Prior to reviewing       enters an autorotation   one second
       more colorful     name, the "Dead                               the results of the FAA's work, an          after disengaging     the engine. The
       Man's Curve."                                                   examination of H-V and some of its         upper section assumes the helicopter
           Unfortunately,     this simple tool                         associated issues are in order.            is in cruise flight and a two second
       for pilots has turned into a continu-                               Figure J illustrates a typical H-V     delay between      engine cutoff and
       ing source of confusion for many oth-                           diagram. The curve, each developed         entering the autorotation      is intro-
       ers, including regulators and devel-                            as a result of manufacturer's      test    duced. These delays are to roughly
       opers     of guidance        material.                          flights, is in accordance with either      replicate typical pilot's reactions in
       Predominantly      because of differing                         Federal Aviation Regulation (FAR)          the two flight regimes. The right,
                  500      Shaded Areas. )               II -
                                                                       27 (normal category helicopters) or        high-speed side typically deals solely

./   I'S
           \\ \                Smoolh
                     Avoid Operation in Hard Surface.
                                                                       FAR 29 (transport category helicop-
                                                                       ters). FAR Part 27.79 states that if
                                                                       there is any combination     of height
                                                                                                                  with pilot reaction time, because fly-
                                                                                                                  ing fast and low greatly limits reac-
                                                                                                                  tion time in case of an engine failure.
                                                                       and forward speed (including hover)             The FAA, in its February 2002
           u. 350                                                      under which a safe landing cannot be       letter, speaks to four certification
           o                                                           made after an engine failure, a limit-     standards, and how the H-V diagram
           ~ 300
                                                                       ing height-speed    envelope must be       should apply. These certification lev-
           w 250
                                                                       established     for   that  condition,     els are FAR 27 (single engine), FAR
           0:1                                                         throughout the ranges of the follow-       29 (single engine), FAR 27 (twin
                  200                                                  ing: I. Altitude, from standard sea        engine), and FAR 29 (multi-engine).
                                                                       level conditions to the maximum alti-      As far as FAR 27 singles are con-
           ~ 150
                                                                       tude capability of the rotorcraft, or      cerned, the FAA states: "The H-V
                  100                                                  7,000 feet, whichever        is less. 2.   diagram is performance     information
                                                                       Weight, from the maximum weight            and resides in the performance sec-
                                                                       (at sea level) to the lesser weight        tion of the flight manual. It is adviso-
                    o                                                  selected by the applicant for each         ry in nature and is provided for pilot
                         o 10 20 30 40 5060       70 80 90 100110120
                                 INDICATED AIRSPEED KNOTS              altitude covered in J. For helicop-        planning    purposes."    As planning
                            (CORRECTED FOR INSTRUMENT ERROR)
                                                                       ters, the weight at altitudes above sea    material, the pilot can now make
                                                                       level may not be less than the maxi-       intelligent choices about which com-
                                    Figure 1                           mum weight or the highest weight           binations of altitude and airspeed to
                                                                       allowing hovering out of ground            use for a particular mission. Many
                                                                       effect, whichever is lower. The appli-     FAR 27 missions require flying in the
                                                                       cable power failure conditions are         shaded area of the H-V, but an aware

           26                         Spring 2002
pilot with the proper information                   With respect to the first grouping,     does not actually exist when operat-
about H-V will know how to react if              the present standard allows for the        ing under Category "A" performance
something goes wrong with the air-               removal of the I-I-V limitation for air-   requirements,     as long as the pilot
craft. If the I-I-V curve information            craft weighing      less than 20,000       flies the published procedures.
were intended as limitations, they               pounds if passenger seating is nine or          In its summary, the FAA states
would be placed in the limitations               less. For older aircraft, where the I-I-   "aircraft certification   requirements
section of the flight manuals. The               V is a limitation in the original flight   have purposely       been modified       in
FAA continues:          "The preamble            manual,      a Supplemental       Type     recent years to change the I-I-V from
material     associated    with virtually        Certificate (STC) or kit supplement        a limitation to performance informa-
every iteration of the H-V regula-               typically defines a nine (or less) pas-    tion for most aircraft. The regulatory
tions make it very clear that the                senger-seating     configuration    that   stance is that this information is advi-
intention has always been to permit              also moves the H-V to performance.         sory in nature unless it is a limitation.
operation inside the H-V for smaller,            For the. second grouping, operating        There are no operating regulations
utility-type helicopters."                       rules would likely require Category        that specifically restrict flight within
     For single engine helicopters cer-          "A" performance if an aircraft config-     the H-V unless it is in the limitation
tificated under Part 29, these aircraft          ured for ten or more passengers were       section of the Rotorcraft       Flight
(usually older, mid-weight            class)                                                Manual. Category "A" would likely
have      been     grandfathered         into                                               be mandated under such a scenario,
Category       B performance           rules.        "Operating within the                  which would therefore negate con-
According to the FAA, the !-I-V dia-                                                        cerns associated  with operations
                                                     "AVOID"area of the                     within the H-V The aircraft certifica-
gram for this small group of aircraft
 is a limitation only when configured                H-V diagram, accord-                   tion and operating      regulations    are
 to carry more than nine passengers.                                                        consistent."
 For all other cases, the I-I-V is intend-
                                                     ing to the FAA's
                                                                                                These clarifications to many long
 ed for performance           information            Rotorcraft      Flying                 held misunderstandings      by regula-
 only.                                               Handbook, may not                      tors can be very critical in the future
     The third certification       category                                                 development of vertical flight infra-
 addressed by the FAA deals with twin                allow enough time for                  structure.  Heliport development,      in
 engine FAR Part 27 aircraft. These                  the critical transition                many cases, has been held hostage to
 helicopters     are limited      to 7000                                                   the whims of advisory          material
                                                     from powered flight to
 pounds maximum gross weight and                                                            drafters and those who approve heli-
 seven passengers. "The gross weight                 autorotation,    hence                 port sites, because of the insistence
 and passenger limits ... are purpose-               the H-V diagram's                      on I-I-V being a limitation.      As a
 ly limited commensurate          with the                                                  result, potential heliport sites were
 philosophy that this certification cat-
                                                     other, more colorful                   limited due to misunderstood         air-
 egory provides a lower level of safety              name,     the    "Dead                 space constraints.     Additionally,    as
 than transport        category     aircraft         Man's Curve."                          instrument     approach       procedure
which      are also certificated            to                                              development    is becoming more and
Category    "A" performance      stan-                                                      more common,        I-I-V has had the
dards." Since all models in this cate-                                                      potential to limit this growth, again
gory have      been   designed     and                                                      due solely to the misunderstanding
approved to Category "A", these air-             to be used for scheduled     air carrier   of I-I-V as a performance       indicator
craft have a "single engine I-I-V"               operations.   It is important to note      'md not as a limitation. The recent
which is performance      information            however, that there is ample evi-          efforts    of the FAA Rotorcraft
and not a limitation.                            dence that this grouping of aircraft       Directorate      and Flight Standards
    Multi-engine   FAR Part 29 air-              can be operated to avoid the I-I-V,        Service in analyzing and creating a
craft, the fourth category addressed             while still achieving an 8:1 clearance     "for-the-record"     clarification will go
by the FAA in its I-I-V letter, have             plane criteria that is recommended         far in ensuring that vertical flight
had the I-I-V standards softened over            for heliport design. Recent testing by     infrastructure    development      will not
time through relieving amendments.               several manufacturers       show that      be impeded         to the extent       that
There are three groupings of these               pilot technique can be varied to safe-     seemed likely only several months
aircraft: I) those weighing less than            ly and consistently      achieve   the     ago. R
20,000 pounds with passenger seating             required    climb gradient.   For the
for nine or less; 2) those weighing              third grouping, the aircraft must be       William C. Sanderson is director of
less than 20,000 pounds with more                operated    under Category "A" per-        heliports and technical programs for
than nine passenger seats; and 3)                formance requirements regardless of        HAl.
those weighing more than 20,000                  passenger configuration. It should be
pounds.                                          emphasized     that an I-I-V diagram

                                                                                                      Spring 2002                  27

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