User Guide

Flight Instruction
235
Flight Instruction
234
You don’t have to get very far below the surface, though, to
find the original de Havilland 125. The airplane retains its classic
layout, with moderately swept wings, a cruciform tail (the hori-
zontal is mounted about two thirds of the way up the vertical fin),
and the traditional de Havilland entry door, with its arched top.
Systems layout is classically European, and the cockpit retains a
“pukka British” look and feel, right down to the somewhat
strange-looking “handlebar” control columns (which it shares
with the Concorde!). The airplane may not be the fastest in its
class, but its cabin is among the roomiest and most luxurious, and
the Hawker is built not only with old-world craftsmanship (even
if it’s now, once again, put together in Wichita), but with staunch
British values: “Why use tiresome sheet metal when you can have
this lovely forging?”
JETS 101A:
Turbojets vs Turbofans
Why are turbofans more economical, so much so that virtually
all jets now use them? For that matter, what is a turbofan, anyway?
For the answer, let’s look back for a moment at what makes a
jet (or, for that matter, any airplane) fly. Right before he got really
famous for inventing that fig-filled cookie, Isaac Newton stated that
“for every action, there is an equal and opposite reaction.”
Airplanes stay up in the air by pushing down with a force equal to
their weight; and they go forward by pushing back with a force
equal to their drag. At slower speeds, they push back with a pro-
peller; at higher speeds, by shoving air out the back of a jet engine.
What makes a real difference is how much air gets shoved
aft: you can either shove a lot of air slowly (a propeller) or a little
air fast (a jet). The problem is that shoving air really fast is waste-
ful - there’s no point in putting it out the back all that much faster
than the airplane is moving forward. The bigger the speed differ-
ence, the less efficient the engine. Fast air is noisy, too - and ener-
gy wasted in making noise isn’t helping move your airplane.
“Pure” jets, then, work well in very fast airplanes - military
fighters, for instance. When business jets first appeared, there
were no turbofans (and jet fuel cost something like nine cents a
gallon), so efficiency wasn’t a prime concern. Neither was noise -
just listen to the nasty crackle of an old “straight pipe” 20-series
Learjet getting underway.
THE HAWKER JET:
A Piece of History
Just about everyone - even most pilots - thinks that the Learjet,
which first flew in 1963, was the first small corporate jet. By that
time, though, in England, the celebrated old firm of de Havilland
had already been flying their DH-125 for well over a year.
The airplane was originally conceived as a VIP liaison trans-
port for the RAF, and called the “Dominie.” The name means a
lower-ranking prelate of the Church of England...go figure. It
served very well in that role; in fact, for many years, one was
reserved for transporting the “V-est of IPs” in England: H.M.
Elizabeth II. At the same time, it gained immediate popularity as a
corporate transport. Over subsequent years, the basic design was
stretched through –400 and –600 airframe versions, while the
thrust of its Rolls Royce Viper turbojets was upped from 3360 to
3750 lbs each.
The biggest change came in 1977, when production, which
had briefly wandered as far afield as Beech Aircraft in Wichita,
returned to Hawker-Siddeley in the UK. One of the main com-
plaints about the 125 had been its relatively short range, and plans
were afoot to retrofit earlier versions with the much more fuel-effi-
cient Garrett TFE-731 turbofan engine, which produced almost
the same thrust (3700 lbs) while burning about 40% less fuel (see
below). With the –700, the fans went on right at the factory. The
–800 version appeared in 1984, with thrust upped to 4300 lbs a
side and a sleek curved windscreen replacing the angular flat-
paned “wheelhouse” of earlier versions. Most recently, the XP ver-
sion (for “extended performance”) appeared in 1995, with
improved avionics and engines uprated to 4660 lbs each for bet-
ter performance at higher temperatures and altitudes.