Upload
robbertmd
View
216
Download
0
Embed Size (px)
Citation preview
Notar makes
the grade
Tail rotors are a necessary evil on single-rotor helicopters.
Aerospatiale made them less dangerous with its fan-in-fin
fenestron
but now McDonnell Douglas plans to abolish the tail
rotor entirely. raham W arwick reports.
very act ion has an equal and
opposi te react ion. In s ingle-rotor
hel icopters this basic t ruth
makes the fuselage rotate in the opposi te
direct ion to the rotor unless prevented
from d oing so by the ant i- to rque tai l rotor .
A tai l rotor ma y be necessary, bu t i t is a
l iabi l i ty . Hovering in confined spaces
carr ies the r isk of the tai l rotor s tr iking
something, while i ts scything blades are a
menace to those on the ground and, in
combat , a target for smallarms f ire .
Now McDonnel l Douglas Hel icopte rs
has decided to seek commercial cer t i f ica
t ion for a no-tai l -rotor (Notar) MD500, to
pave the way for i ts tai l -rotorless MDX
light helicopter in the early 1990s.
Th e decision is based on successful
Notar f l ight tests on a modified OH-6,
whic h first flew in 1981. W hile th e test bed
tours the USA demons t ra t ing the benef i t s
of tai l -rotorless f l ight , MDH is working
towards commercial cer t i f icat ion of the
Notar concept by the end of 1989.
The cur ren t -produc t ion MD500E and
hot -and-h igh 530F were bo th in t ro
duced by Hughes in 1982, the 500E
powered by a 420 s .h.p. All ison 250-C20B
an d the 530F by the 650 s .h.p. C30 varia nt .
Two new higher-performance versions are
planned by MDH, a 520L to be cert i f i
cated in December this year , and a hot-
and-high 530K to be cert i f icated in June
1989.
Th e two varia nts wil l bot h feature
increased-diameter main and tai l rotors
which increase l i f t ing capabil i ty and oper
at ing al t i tude, and decrease noise. Based
on the 500E, the 520L is powered by the
new 450 s .h.p. All ison 250-C20R, while the
530K retains the C30 pow erplan t of th e
exist ing 530F.
The ta i l - ro tor less MD500, des igna ted
the 520N, wil l be based on the new 520L,
with i ts C20R engine and increased-
d iameter main ro tor . MDH plans to bu i ld
two Notar-equipped prototypes, the f i rs t
of which will fly in May 1989, wit h certifi
cation set for late 1989.
The tai l -rotorless hel icopters wil l be
pro to types because MDH is no t ye t
comm it ted to p roduc ing the 520N, bu t th e
differences between prototype and pro
duction aircraft will be small, it says.
Wh ether the comp any proceeds in to 520N
production wil l depend on market
response, however.
MDH delivered 69 MD500s in 1987,
down from 76 in 1986, bu t ended the year
with i ts largest order backlog—28
aircraf t—in recent years . This level of
sales would not be enough to launch the
520N, however. The company is looking
for a s l ight ly bet t er m arke t , and bel ieves i t
wil l material ise in the next 18 months.
Already there are s igns.
So MD H is be ing cau t ious about in t ro
ducing Notar , a l though i t bel ieves the
concept to be the most exci t ing tech
nology in recent years .
The Notar tai lboom is , in effect , a
circular-sect ion circulat ion-control aero
foi l . As main-rotor downwash f lows over
the boom i t meets higher-veloci ty air
exi t ing from slots running the length of
the pressurised boom's s tarboard s ide.
The mixing of these f lows causes the
downwash to adhere to the boom on that
side while i t separates on the other . This
has the same effect as camber on an aero
foil, generating a sideforce which opposes
main- ro tor to rque .
Th e Notar tai lboom is pressuris ed to
about 0-51b/in
2
by a fan driven from the
engine gearbox. Fan p i tch is varied to keep
boom pressure, and therefore s lot exi t
velocity, fairly constant at about four
t imes the downwash veloci ty.
Circulat ion control provides about
two- th i rds o f the an t i - to rque mom ent
26 FLIGHT INTERNATIO NAL 27 February 1988