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Units
The metric system is taken as fundamental, this being the educational basis in the UK. Imperial units are still used extensively, however, particularly in the USA but also by industry and other organizations in the UK. For dimensional examples in the text and diagrams, therefore, those units are used which it is felt have stood the test of time and may well continue to do so. Often units in both systems are quoted; in other cases reference may need to be made to the conversion tables set out below. In either system, units other than the basic one are sometimes used, depending on the context; this is particularly so for velocity, where for example aircraft flight speed is more conveniently expressed in kilometres/hour or in knots than in metres/second or in feet/second. The varieties used in the book are included in the table.
|
Quantity |
Metric unit and symbol |
Imperial equivalent |
|
Primary quantities: Mass |
kilogram (kg) |
0.0685 slug |
|
Weight |
newton (N) |
0.2248 pound (lb) |
|
Length |
metre (m) |
3.281 feet (ft) |
|
Time |
second (s) |
1.0 s (sec) |
|
Temperature |
kelvin (K) |
Celsius (°C) |
|
Temp(K) = temp (°C) + 273.15 Derived quantities: Weight (force) |
kilogram force |
|
|
9.807N (kg) |
2.2046 lb |
|
|
Density |
kg/m3 |
0.00194 slug/ft3 |
|
Pressure |
N/m2 |
0.0209 lb/ft2 |
|
Velocity |
0.1020 kg/m2 m/s |
3.281 ft/sec |
|
3.600 km/h |
196.86 ft/min |
|
|
Acceleration |
m/s2 |
1.941 knots 3.281 ft/sec2 |
|
Accel. of gravity |
9.807 m/s2 (g) |
32.2ft/sec2 |
|
Power |
watt, N m/s (W) |
0.7376 ft lb/sec |
|
Metric horsepower |
75 kg m/s (mhp) |
0.9863 HP |
|
English horsepower |
76.04 kg m/s |
550 ft lb/sec |
Abbreviations
|
ABC |
Advancing Blade Concept |
|
ADT |
Actuator disc theory |
|
Aero. J. |
Journal of the Royal Aeronautical Society |
|
AFCS |
Automatic flight control system |
|
AGARD |
Advisory Group for Aerospace Research and Development |
|
AIAA |
American Institute of Aeronautics and Astronautics |
|
ARC |
Aeronautical Research Council |
|
ASE |
Automatic stabilization equipment |
|
AUW |
All-up weight |
|
BERP |
British Experimental Rotor Programme[1] |
|
BET |
Blade element theory |
|
CFD |
Computational fluid dynamics |
|
CG |
Centre of gravity |
|
DOF |
Degree of freedom |
|
FAI |
Federation Aeronautique Internationale |
|
FOM |
Figure of merit |
|
FUMS |
Fatigue and Usage Monitoring System |
|
HUMS |
Health and Usage Monitoring System |
|
IFR |
Instrument Flight Rules |
|
IGE |
In ground effect |
|
ISA |
International standard atmosphere |
|
JAHS |
Journal of the American Helicopter Society |
|
NACA |
National Advisory Committee for Aeronautics (now NASA) |
|
NFA |
No-feathering axis |
|
NFP |
No-feathering plane |
|
NPL |
National Physical Laboratory |
|
OGE |
Out of ground effect |
|
PIV |
particle image velocimetry |
|
RAE |
Royal Aircraft Establishment |
|
RAF |
Royal Air Force |
|
RLD |
Really low drag |
|
R&M |
Reports and Memoranda of the ARC |
|
SAE |
Society of Automotive Engineers |
|
SA |
Shaft axis |
|
sfc |
Specific fuel consumption |
|
SHM |
Simple harmonic motion |
|
SL |
Sea level |
|
SNP |
Shaft normal plane |
|
TPA |
Tip-path axis |
|
TPP |
Tip-path plane |
|
TRLF |
Transmission loss factor |
|
UAV |
Unmanned aerial vehicle |
|
UK |
United Kingdom |
|
USA |
United States of America |
|
VRS |
Vortex ring state |
|
VTOL |
Vertical take-off and landing |
|
WHL |
Westland Helicopters Ltd |
