X250tm Assembly Instructions, Page 2
Technical Specifications...
In spite of the X250’s small size, it’s probably one of the
most carefully designed model aircraft ever kitted. Literally
hundreds of hours of computer time were spent optimizing the
design. Rather than just designing an aircraft, we designed an
entire system. There’s no point in designing an aircraft that
requires a motor, gear ratio, battery, or prop that doesn’t exist.
Instead we evaluated dozens of combinations of components
to come up with the optimum, complete system.
We know that some of you will be tempted to change
some of the components in the power system. We suggest that
you don’t. Our target was an aerobatic aircraft that would
easily do consecutive loops yet still give you 7 to 9 minutes of
aerobatic flight and 12 to 15 minutes of sport flying. The
X250 fulfills this goal. If you change any of the components,
you may gain a small advantage in one area of performance,
but you’ll definitely be losing performance in another area.
Here is our definition of Optimum Performance:
The following table lists the specific equipment we’ve
evaluated and tested to yield the above performance data. You
Aircraft SR X250 (aileron version)
Wing area 266 square inches
WingSpan 36”
Aspect Ratio 4.3:1
CG Limits 2” to 2.75”
Airfoil Computer Optimized by SR
Typical Wt. w/ 10 cell pack 24 oz.
Typical Wing Loading 13 oz. / sq. ft.
StallSpeed 13 MPH
Max. Speed 40 MPH
10 Cell Current Draw 10 Amps
Thrust 18 oz.
Climb Rate 900’/min. @ 23 MPH
Flight Time, Aerobatic 7 to 9 min.
Flight Time, Sport 12 to 15 min.
Minimum Sink Rate 2.761 ft./sec.
Maximum Glide Ratio (L/D) 11.595
Best L/D Speed 25.157 MPH
Optimized Performance
can purchase these items locally, or SR has several packages
available which will save you time and money.
Why the Jeti 350 Speed Control?
The Jeti 350 is overkill as far as current draw goes.
However, it has one feature we really like. Its BEC circuit is
designed to handle up to 4 servos rather than the usual 3. As
we’re using 3 servos, we liked the extra safety margin. In
addition, it’s one of the few speed controls that will allow you
to turn off the Brake function.
Why the SR 500 Max Series cell?
With a capacity of almost 600 mah, yet still having a very
low internal impedance, this cell is optimum for Speed 400
applications. At only .7 oz per cell it’s hard to beat.
Which prop, folding or fixed?
Originally, we recommended the CAM 9x5 folding prop.
The advantage of the folding prop was that it would fold back
rather than break if it hit the ground. However, after over
1,000 flights on our various test aircraft, we’ve come to the
conclusion that the fixed Slim prop gives a slight performance
edge for aerobatic flight. You wouldn’t be wrong if you
decided to use the CAM folding prop, but our first choice
would be the Graupner 9x5 Slim prop. If you do decide to use
a folding prop, be sure you turn off your speed control’s brake
so that the prop blades won’t fold back when you shut down
the motor in a stall turn.
Aircraft SR X250 (aileron version)
Prop Graupner 9x5 Slim, Fixed
Motor Graupner Speed 400, 7.2V
Gear Ratio 2.33:1
Speed Control Jeti 350
Cell SR 500 Max Series
Cell Count 10
Pack Shape Rectangular, 5x2
Connector Sermos
Alternative Prop Graupner CAM 9x5, Folding
Receiver Hitec, 555
Servo Hitec, HS-60
Covering Material Goldberg, UltraCote Lite
Optimized Components
