로블록스 항공 물리 아키텍처: 양력-항력 폴라 곡선, 받음각(AoA) 실속 및 조종면 토크

--!strict
local RunService = game:GetService("RunService")
local Workspace = game:GetService("Workspace")

local FlightEngine = {}
FlightEngine.__index = FlightEngine

export type AircraftConfig = {
    RootPart: BasePart,
    WingArea: number,
    AspectRatio: number,
    EmptyMass: number,
    MaxEngineThrust: number,
    StallAngleDeg: number,
    PitchAuthority: number,
    RollAuthority: number,
    YawAuthority: number,
}

export type FlightState = {
    Config: AircraftConfig,
    Throttle: number,
    IsStalled: boolean,
    CurrentAoA: number,
    AirDensity: number,
}

local GRAVITY = Vector3.new(0, -Workspace.Gravity, 0)

function FlightEngine.New(root: BasePart): FlightState
    local state: FlightState = {
        Config = {
            RootPart = root,
            WingArea = 28.0,
            AspectRatio = 7.2,
            EmptyMass = 1200.0,
            MaxEngineThrust = 16500.0,
            StallAngleDeg = 16.0,
            PitchAuthority = 8500.0,
            RollAuthority = 12000.0,
            YawAuthority = 4500.0,
        },
        Throttle = 0.8,
        IsStalled = false,
        CurrentAoA = 0,
        AirDensity = 1.225 * 0.0019,
    }
    return state
end

local function CalculateLiftCoefficient(aoaDeg: number, stallAngle: number): (number, boolean)
    local rad = math.rad(aoaDeg)
    if math.abs(aoaDeg) < stallAngle then
        -- 선형 얇은 익형 구간
        return 2 * math.pi * rad, false
    else
        -- 실속 기류 박리 구간
        local sign = math.sign(aoaDeg)
        local postStallCl = sign * (1.1 * math.sin(2 * rad))
        return postStallCl, true
    end
end

function FlightEngine.Step(state: FlightState, pitchInput: number, rollInput: number, yawInput: number, dt: number)
    local root = state.Config.RootPart
    local cfg = state.Config
    local cf = root.CFrame
    local vel = root.AssemblyLinearVelocity
    local speed = vel.Magnitude

    if speed < 1.0 then return end

    local forwardVec = cf.LookVector
    local upVec = cf.UpVector
    local rightVec = cf.RightVector

    -- 받음각(AoA) 계산
    local forwardSpeed = vel:Dot(forwardVec)
    local verticalSpeed = vel:Dot(upVec)
    local aoaRad = math.atan2(-verticalSpeed, math.max(forwardSpeed, 0.1))
    local aoaDeg = math.deg(aoaRad)
    state.CurrentAoA = aoaDeg

    local cl, isStalled = CalculateLiftCoefficient(aoaDeg, cfg.StallAngleDeg)
    state.IsStalled = isStalled

    -- 유도 항력 및 유해 항력 연산
    local cd0 = 0.025
    local inducedCd = (cl * cl) / (math.pi * cfg.AspectRatio * 0.85)
    local cd = cd0 + inducedCd

    local q = 0.5 * state.AirDensity * (speed * speed)
    local liftMagnitude = q * cfg.WingArea * cl
    local dragMagnitude = q * cfg.WingArea * cd

    -- 양력은 상대풍에 수직, 항력은 반대 방향
    local velUnit = vel.Unit
    local liftDir = rightVec:Cross(velUnit).Unit
    local dragDir = -velUnit

    local liftForce = liftDir * liftMagnitude
    local dragForce = dragDir * dragMagnitude
    local thrustForce = forwardVec * (cfg.MaxEngineThrust * state.Throttle)

    local totalForce = liftForce + dragForce + thrustForce + (GRAVITY * root.AssemblyMass)
    root:ApplyImpulse(totalForce * dt)

    -- 동압에 비례하는 조종면 토크 인가
    local dynamicRatio = math.clamp(speed / 80.0, 0, 1.5)
    local pitchTorque = rightVec * (pitchInput * cfg.PitchAuthority * dynamicRatio)
    local rollTorque = forwardVec * (-rollInput * cfg.RollAuthority * dynamicRatio)
    local yawTorque = upVec * (yawInput * cfg.YawAuthority * dynamicRatio)

    local totalTorque = pitchTorque + rollTorque + yawTorque
    root:ApplyAngularImpulse(totalTorque * dt)
end

return FlightEngine