Our colleague had his P-51 replica in his office for around 20 years and mentioned that it was never flying before. It is a completely custom built plane, mainly from plywood and balsa wood. A very impressive work with a precise construction and a great surface finish. He equipped it originally with a OS 45 motor with 8ccm as electrical motors were not that powerful and light in the mid 90s. As he does not follow RC models anymore, we are proud to take over this project and drive "Lutzie" (as we named the plane to appreciate the builder) to its maiden flight.

 

Dimensions of the plane:

Span

Length

Wing Surface (incl ailerons)

Horizontal Stab Surface (incl elevator)

Vertical Stab Surface (incl rudder)

Weight:

Measured without Motor, Servos, Receiver

1.3kg

With installed components, approx:

1.8 kg

 

Motor Dimensioning:

Estimated target weight: 1.8kg

Motor Options - Turnigy D3548/6 790KV  || Dymond GTX 3546 910kV / 650kV

Propeller - 14 x 6

Controller (ESC) - 60A

With this configuration we reach a static thrust of approx 1.8 kg.

The thrust to weight ratio is at approx 1:1.

This is calculated with E Calc. http://www.ecalc.ch/

Battery Pack:

3S 3000mAh

With the motor setting this will lead to approx 10 mins flight time.

Motor Tests

For testing the motor configuration, we build a static thrust testing platform. A luggage scale is used to measure the force. The following schematic shows the setup for testing motors.

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Servo Dimensioning:

Estimated Airspeed with the motor setup: 72 km/h = 20 m/s

Drag coefficient of a rectangular (estimated, see literature)

Control surface dimensions:

Aileron Surface (each): 0.35 m x 0.045 m = 0.016 m² | width/height = 7.8

Elevator Surface: 0.48m x 0.045m = 0.022m² | width/height = 10.7

Rudder Surface: 0.21m x 0.055m = 0.012 m² | width/height = 3.8

 

c_w Aileron: 0.86

c_w Elevator: 0.87

c_w Rudder: 0.85

 

Assuming the control surface would stand upright, the force calculates to:

Lets assume air density rho with: 1.293 kg/m3

F_ail = 3.5 N

F_ele = 4.86 N

F_rud = 2.54

Torque required for the servos.

On a parallel air flow to the surface (standing upright, 90° deflection), we can assume that the resulting force attaches half of the surface height. This results in the torques

T_ail = 3.5 [N] x 0.045/2 [m] = 0.079 [Nm] = 7.9 [Ncm] - 0.79 kg/cm

T_ele = 4.86 [N] x 0.045/2 [m] = 0.109 [Nm] = 10.9 [Ncm] - 1.09 kg/cm

T_rud = 2.54 [N] x 0.055/2 [m] = 0.07 [Nm] = 7.0 [Ncm] - 0.7 kg/cm

These torques apply if the surfaces would be deflected to 90° upright position. As the control surfaces will only be deflected to max 45°, the existing torques will be even less.

Wing Profile:

The wing profile is a NACA2412 (tip) / 2415 (root) semi symmetric profile. It usually is a robust profile with moderate flight characteristics.

Quelle: https://upload.wikimedia.org/wikipedia/commons/d/d3/NACA_2412.png

The wing is made of a Styro - Balsawood construction.

Moments of Inertia:

 

Building a canopy:

There is no canopy

Landing gear:

There is currently no landing gear installed. We are trying to find different options to create a light weight and high landing gear (as the prop is very long).