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All
Aircraft, large or small, necessarily have maximum
airspeed limits for operating flaps and landing
gear. Above these designated speeds, structural
failure will occur due to excessive aerodynamic
loads. In the case of our radio controlled jets,
knowing and adhering to these limits is especially
important because of the potential for high speed.
One would think that a turbine qualified pilot would
know about these restrictions, but, we have seen
evidence that prompted this notice.
Experienced R/C pilots can estimate flight speeds
close enough that they will not overstress airframe
components. Staying within 20mph of a published
limit is close enough for most model airplanes. If
one’s experience is insufficient, we are fortunate
to now have a wide selection of Telemetry equipment
to assist the R/C pilot. Choose one that
compliments your radio control system.
See:
http://www.bvmjets.com/Pages/Speed_Control.htm
Some
examples of structural failures that can result from
excessive speed are:
·
Flaps –
hinges broken loose from their mounting, servo gears
stripped, servo arm splines stripped, linkages
broken, and flap skin delamination. This kind of
damage to the flap system could cause a loss of
control at approach speeds.
·
Extending the landing gear at excessive speed can
damage gear doors that may interfere with the gear
reaching its fully down and locked position. Of
course, excessive speed can prevent proper landing
gear operation during both the “up” or “down”
selection process.
BVM
publishes Vne (Velocity to never exceed) for each of
our jet airframes. These speeds are posted on the
cover of each BVM instruction manual and are the
result of Flight Test Evaluation by the BVM
engineering and jet pilot staff. In all cases, the
200 mph limit imposed by the A.M.A. “Turbine Waiver”
rules is the controlling number.
Since all BVM jets and most others of good design
have stall speeds (Vs) in the 30-35 mph range, it is
reasonable to say that safe flap and landing gear
operating speeds will be very similar for most R/C
Jets.
Wing flaps serve to both increase lift and drag,
but this paper is not intended to be a tutorial on
the aerodynamics involved. Rather, it is intended
to caution inexperienced pilots about inflicting
unnecessary stress on model jet airframes.
Suggested Flap and Gear
Operating Speeds
Following take-off: Retract the landing gear as soon
as comfortably airborne but below 100 mph. The
take-off Flap position is usually 15°-20°
deflection, raise the flaps after reaching at least
70 mph but prior to 100 mph or after the first 180°
turn. Use throttle management or angle of climb to
control the speed until the flaps are up.
Prior to Landing: Slow the model to about 90 mph,
then select the flaps to the 1st
increment which will be the same 15°-20° used for
take-off. Extend the landing gear at 70-80 mph, and
then select “Landing” flaps which will be 35°-45° of
deflection.
Note:
For high winds, use 30°-35° for landing. Make this
adjustment in your transmitter before flight.
These
suggested speeds will provide a safe stall margin
and protect the airframe from excessive aerodynamic
loads. Certainly, we should all know that putting
the gear and flaps out at 150+ mph will likely cause
structural damage. |
