Aircraft inputs and operating conditions

Parameter	Description	Unit
M	Aircraft mass	kg
N	Number of rotors: 4 or 6	—
B	Blades per rotor: fixed at 2	—
R	Rotor radius	m
R_a	Cylindrical arm radius	m
L_a	Arm length	m
d_ap	Clearance from the rotor disk to the arm surface	m
d_wb	Wheelbase	m
d	Distance from the aircraft to the observer directly below	m

1. Select an aircraft to load its parameters, or select “Custom aircraft” and enter the values. Editing a preset switches the selection to Custom aircraft.
2. Use kg for mass and m for lengths. Enter the rotor radius for R; divide diameter measurements by 2 before entering them.
3. Enter nadir distance d and observer ear height h in metres. The horizontal receiver plane follows h; source height above ground is d + h. Body dimensions L, W and H affect only the 3D view.

• C_T is the rotor thrust coefficient and σ is rotor solidity. Both are dimensionless.
• Select “Known value” and enter a positive value when available. Otherwise select “Unknown · range” and enter the lower and upper limits.
• The default ranges are 0.008–0.020 for C_T and 0.07–0.15 for σ. Each parameter can independently use a known value or a range. Range results open on the upper envelope.
• Both limits must be positive, with the lower limit no greater than the upper limit. Equal limits treat the parameter as a fixed value.

1. Select “Calculate levels”. The results panel shows total, tonal and broadband sound pressure levels in dB.
2. When a parameter range is used, results show the lower and upper sound levels within that range.
3. Expand “Total OASPL directivity” to view levels by direction. θ = 0° is directly below the aircraft, θ = 90° is to the side, and φ is the azimuth angle. Range results provide lower and upper views and a complete numerical table.
4. Calculate again after changing inputs. A red ring means the current inputs do not yet have a valid calculation result; a blue ring means the current inputs have been calculated successfully.
5. Correct invalid inputs using the messages beside each field; the error summary links to the affected fields. If a request fails, retry it. Entered values and the last successful result are retained.
6. The directivity plot and its downloads use their own level range. The sphere and receiver plane share a scene range. All views follow the selected palette and continuous or banded display.
7. Directivity downloads use input distance d; sphere downloads use the displayed actual radius. The horizontal receiver plane at the selected observer ear height is a free-field direction-and-distance extension, not a prediction of ground reflection.

The sphere uses the scene's distance scale, and sound levels are calculated at its actual radius. This radius does not establish far-field validity.

The spherical cap covers θ = 0–120° from the downward vertical under the model’s uniform-azimuth assumption. The horizontal receiver plane recalculates the nadir model at each slant distance and applies the same directional correction. It is a free-field receiver plane at the selected observer height, not a prediction of ground reflection; atmospheric absorption and obstacles are also excluded.