Download 01 - Basic Helicopters PDF

Title01 - Basic Helicopters
TagsHelicopter Rotor Helicopter Aerodynamics Lift (Force) Rotorcraft
File Size2.1 MB
Total Pages36
Document Text Contents
Page 1

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B3810 He//capters

He Wharekura-tini
Kaihautu 0 Aotearoa

THE OPE N
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OF NEW ZEALAND

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CONTENTS

Basic Operating Principles

Controls

Structures

The Powertrain

Safety In and Around Helicopters

Appendix: Table of Definitions

Copyright

{his material is for the sole use of enrolled students and may not be
reproduced without the written authority of the Principal, TOPNZ.

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FIG. 10 Fuselage structure assembly

A third form of construction now coming into use is the
composite structure, which uses carbon fibre reinforced stiffeners,
frames, and bulkheads, plus impact»resistant fibre reinforced
skinning (Kevlar) in the primary structure and high—quality glass
fibre in the secondary structure. The use of these materials gives
a great saving of weight.

THE POWERTRAIN

The components that transmit the engine power to the main
and tail rotors are collectively called the powertrain or the
transmission.

The essential components of a powertrain are

1. An engine-driven clutch (on piston-engined
helicopters);

2. A freewheel unit, which may be called a
sprag clutch OP a one—way clutch;

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_ 17 _

3. A main—rotor gearbox; M

H. A tail-rotor gearbox; and

5. Driveshafts from the engine to the main-
rotor gearbox and from the main—rotor
gearbox to the tail—rotor gearbox.

The functions of these components are as follows.

The engine~driven clutch is fitted to allow the engine to be

started without turning the rest of the powertrain.

Ehewfreewheel unit permits the two rotors to turn faster than
the engine. This could occur when the engine is throttled back
to idle rev/min.

The mainmrotorggearbgi changes the direction of the engine
drive and reduces the engine rev/min to the much lower rev/min
needed by the main rotor. It also provides drive pads for
ancillary equipment.

rhe tail~rotq;mgea;box changes the direction of the drive to
suit the need of the tail rotor. Depending on the helicopter type,
this gearbox may increase, decrease, or make no change in the
rev/min of the output shaft relative to the input shaft. This
gearbox may house the blade pitch—changing mechanism of the tail
rotor.

The driveshafts transmit the power from the engine to the
gearboxes. These shafts may also drive ancillary components, such
as cooler fan units.

In all powertrains, the main rotor is always mechanically
connected to the tail rotor so that at no time can one rotor turn
without the other. This fact, coupled with the function of the
freewheel unit means that, should the engine fail, both rotors will
keep turning and the pilot can make a safe and controlled landing.
This flying condition, known as autorotation, is the equivalent
of a fixed-wing aircraft gliding. Figure 11 shows three different
powertrains in schematic form.

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_33._.

Explain, with the aid'of a sketch, how a movement of the
cyclic control to the left will produce a small couple
to tilt the fuselage to the left.

Draw a helicopter powertrain and identify the components
shown.

In tabulated form, give a reason for each of the
instructions in Para 5.5 (1) to (8) of AC 93-82A
(page 2% of the assignment). would these rules be good
for people leaving as well as boarding the helicopter?

[email protected]?-ea

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