Phoenix
Page 2
About Phoenix
Integrated Rocket Motor
P
HOENIX has a carefully integrated rocket
motor for both good performance and good
behavior on boost. For example, the placement
of the rocket thrust line is critical for a stable
boost. With Phoenix’s high thrust to weight
ratio (5:1 for Phoenix versus 1.5 to 1 for a hot
power plane), Phoenix’s motor thrust line had
to pass through the CG or the model would try
to loop violently on launch. Phoenix’s motor is
located as close as possible to the model’s CG
to reduce the amount
of CG movement as
fuel is burned. Finally,
the motor mount
angle on Phoenix was
carefully tested with
over 100 flights to
minimize drag while
providing easy access
to the motor for
reloading.
Computer Designed
Airfoil
P
HOENIX uses a custom computer designed
airfoil, the BP4d™, for maximum boost and
glide performance. To achieve the best overall
results, the main design goal for the airfoil was
a significant reduction in drag. The BP4d
design did this, and is a significant improve-
ment over sections such as the S3021, a com-
mon RC sailplane airfoil. When compared with
the S3021, the BP4d has 33% lower drag at
launch speeds and 5 to 15% lower drag during
typical gliding flight, with only a slight
decrease in maximum lift. As a result , Phoenix
has a very wide speed range in glide, and
retains a good glide ratio at high cruising
speeds. Also, the Phoenix airfoil is slightly
thicker, for better strength and for adequate
room for aileron servos. With its substantially
thicker aft section, the ailerons are thicker,
reducing the possibility of flutter at high flight
speeds.
Two Aileron Servos
P
HOENIX has an aileron servo installed in
each wing panel for several important rea-
sons. First, by locating the servos away from
the center section of the wing, where the flight
loads are the greatest, less structural reinforce-
ment is required to maintain the designed
strength of the overall wing. The wing is
stronger and actually lighter by having two ser-
vos outboard in the wing instead of one in the
center surrounded by extensive reinforce-
ments! Second, by moving the servos into the
wings, closer to the ailerons, the result is stiffer
linkages which are much less prone to flutter at
high speeds, such as during launch. Finally, a
dedicated servo for each aileron gives more
accurate control for
precise roll authority,
as expected by expe-
rienced pattern fly-
ers. While this is not
essential for a sport
plane such as
Phoenix, once we
started using the two
ailerons and enjoyed
the roll response, we
couldn’t give it up.
Offset Vertical Tail
O
NE unique feature of Phoenix is its offset
vertical tail. If you haven't already noticed,
the tail is not on the centerline of the fuselage,
it is offset to one side! This is intentional
because it provides several distinct advantages
for Phoenix. First, it allows for the pushrods to
the elevator and rudder to be perfectly
straight, for better stiffness and minimum
weight. Second, the linkages and horns are
shielded from the hot rocket exhaust, so they
won't be damaged. Third, the larger fuselage
cross section gives a stiffer tailboom for con-
sistent and precise rudder and elevator
response. Even though the back of the fuselage
is larger than normal, the linkages are hidden,
so the drag is less than or equal to the total
drag of a conventional design. Finally, this
design is stronger because the tail is glued
directly to the side of the boom.
Although the plans show the vertical tail
mounted on the left side of the boom, you can
put it on the right side if you wish. You might
avoid having to reverse a servo, if you have a
radio without servo reversing switches.
