HEADQUARTERS OH-58A, Technical Manual, Page: 194 / 292

TM 55-1520-228-10
7-4
7-3. GENERAL.
The data presented covers the maximum range of con-
ditions and performance that can reasonably be ex-
pected. In each area of performance, the effects
altitude, temperature, gross weight, and other parame-
ters relating to that phase of flight are presented. In
addition to the presented data, your judgment and expe-
rience will be necessary to accurately obtain perfor-
mance under a given set of circumstances. The
conditions for the data are listed under the title of each
chart. The effects of different conditions are discussed
in the text accompanying each phase of performance.
Where practical, data are presented at conservative
conditions. However, NO GENERAL CONSERVATISM
HAS BEEN APPLIED. All performance data presented
are within the applicable limits of the aircraft.
7-4. LIMITS.
Applicable limits are shown on the charts as red lines.
Performance generally deteriorates rapidly beyond lim-
its. If limits are exceeded, minimize the amount and
time. Enter the maximum value and time above limits on
DA Form 2408-13 so proper maintenance action can be
taken.
7-5. USE OF CHARTS.
a. Chart Explanation. The first page of each sec-
tion describes the chart(s) and explains its uses.
b. Color Coding. Chart color codes are used as
follows:
(1) Green is used for example guidelines.
(2) Red is used for limit lines.
(3) Yellow is used for precautionary or time-lim-
ited operation.
c. Reading the Charts. The primary use of each
chart is given in an example and green guideline is pro-
vided to help you follow the route through the chart. The
use of a straight edge (ruler or page edge) and a hard
fine point pencil is recommended to avoid cumulative
errors. The majority of the charts provide a standard
pattern for use as follows: enter first variable on top left
scale, move right to the second variable, reflect down at
right angles to the third variable, reflect left at right
angles to the fourth variable, reflect down, etc. until the
final variable is read out at the final scale. In addition to
the primary use, other uses of each chart are explained
in the text accompanying each set of performance
charts. Colored registration blocks located at the bottom
and top of each chart are used to determine if slippage
has occurred during printing. If slippage has occurred,
refer to chapter 5 for correct operating limits.
NOTE
An example of an auxiliary use of the
charts referenced above is as follows:
Although the hover chart is primarily ar-
ranged to find torque required to hover,
by entering torque available as torque
required, maximum skid height for hover
can also be found. In general, any single
variable can be found if all others are
known. Also, the tradeoffs between two
variables can be found. For example, at
a given density altitude and pressure al-
titude, you can find the maximum gross
weight capability as free air temperature
changes.
The primary advantage of the helicopter over other air-
craft is the capability to hover and takeoff and land verti-
cally (zero air speed flight). To more rapidly calculate the
performance trade-offs in hover mode, a Hover Ceiling
Chart has been included.
7-6. DATA BASIS.
The type of data used is indicated at the bottom of each
performance chart under DATA BASIS. The applicable
report and date of the data are also given. The data
provided generally is based on one of four categories:
a. Flight Test Data. Data obtained by flight test of
the aircraft by experience flight test personnel at precise
conditions using sensitive calibrated instruments.
b. Derived From Flight Test. Flight test data ob-
tained on a similar rather than the same aircraft and
series. Generally small corrections will have been
made.
c. Calculated Data. Data based on tests, but not
on flight test of the complete aircraft.
d. Estimated Data. Data based on estimates using
aerodynamic theory or other means but not verified by
flight test.