Botmite

Construction
Details &
Photos

details

Hooks to hang fuselage

   To suspend the airplane from above a couple hard points were added to the top of  the fuselage. Commercial steel closed loop threaded hooks are epoxied to two quarter round flat thin (3/16 inch thick) plywood and epoxied to both inside plywood plates.
     Locating the hard points to carry the aircraft were largely a matter of convenience. The first hook is  located adjacent to the nose in the LiPo battery section.  Second hook placement is just aft of the electronics (Section 4) but before the air  intake containing the servo Electronic Speed Controller (ESC).

Airspeed Pitot tubes to upper Nose

   A pitot  tube is a outside air pressure intake tube to direct air to a sensor which is used to compare static pressure to moving air pressure. This measurement instrument used to measure fluid flow velocity.  Here a dual quartz sensor is used to compare the two air flows.
     Note: one should examine the temperature range or limitations of the IC or chip  which provides this sensor data. Temperature falls with higher altitude. The “standard” or typical rate temperature lowers is called the adiabatic lapse rate. Many pilots use 3 degrees F lowering per 1,000 foot of altitude gain.
     On Earth, the dry adiabatic lapse rate is higher than the saturated (moist) temperature lapse rate. Typically, The dry adiabatic lapse rate is one degree Celsius of cooling for  every  100 meters (1C/100m, 10C/ kilometer or 5.5F/1000 feet).  The (wet) or saturated parcel of air has a saturated adiabatic lapse rate  (also known as wet adiabatic lapse rate) of 0.5C/100 m (5C/ kilometer or 3.3F/1000 feet). Both lapse rates are approximations and vary from this ideal. Calibrate measurement with local temperature and  pressure.
       Given temperature will typically lower with altitude gain, a 10,000 foot elevation climb above ground means ambient temperature at that altitude may be 30 degrees lower than ground temperature.  So a 50 degree F operating temperature limit for a sensor will not result in accurate airspeed sensor output at altitude.
       Heating the pitot tube pressure sensor is an option that requires available power and the sensor should be insulated to minimize waste.  Test important sensor use and accuracy before depending on its output  information. Remember, altitude is used to separate aircraft by 1,000 feet using 180 degree heading vectors and sensors provide that information via the IMU.

 Metal tubes protruding: 1. (red tip) static air pressure input, and 2. (open tip) airspeed pressure input. Both are connected to a sensor, the difference provides airspeed in electronic format for the IMU - onboard flight computer.

Wings

  The wings page details size, airfoil, weight, moment factors.

     The wings present a number of interrelated problems. First, the problem of  interchangeable wings Second, the problem of support of the aircraft through a turn in a 60 degree bank ( 2 gs ) followed by a turn of  smaller diameter - a stress of shear at the base of the wing to a design limit of 6 gs and the inclusion of a margin of error or safety  factor. Also, wing warping in turbulent air needs to be considered and addressed.
     Positive and negative g forces need to be considered  with regard to the aircrafts operating and maximum weight and wind conditions.
       External solutions trade additional drag, such as:  an additional support from the wing to the aluminum wheel struts for takeoff and landing.

Gyroscopic effect turns when the propeller is about 27% of the prop diameter or  larger. Prop: 14 in. / 98 in. wingspan = 0.14 or 14%.

Botmite Thrust to Weight Ratio: 1.2 to 1
141 ounces or 8.821 pounds thrust
Rate of Climb: (determined by availability of excess power)

Wing Loading: 6 lbs. per square foot for glider
Botmite (7.5 lbs.): 2.11 lbs. per square foot

Airfoil: cited Eppler 374 mod - as it is not produced to metal machining  standards, this is an approximation. This is a low Reynolds Number Airfoil.
http://www.ae.illinois.edu/m-selig/uiuc_lsat.html
It is defined as a sloped racer airfoil.
Wortmann FX 63-137 - another excellent choice airfoil
Typical Reynolds Number for model aircraft: 250,000 and
300,000 Re

Wing Strut view (above photo) with clips for attaching to CF rod inside wings.

         Version Four - an 8 channel in/out IMU

   Left side: power and signal input from rc receiver.
   Top across: various analog and digital bi-directional sensor communication.
   Right side: I/O PPM to Servos. Lower right: programming interface. Lower center: UART, interface to  magnetometer, airspeed, barometric pressure, various sensors.
   Bottom Left: Button battery: backup power. To its right: Two vertical sockets for GPS input. Center double row white: rc input. Top center: various sensors.  3 axis accelerometer and 3 axis MEMS  gyro on board.

[Photos] [Aircraft] [Electronics] [Sensors]

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