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finParameters.m
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%Inputs: provide 4 points which dictate fin geometry. Assuming Trapezoidal
%Geoemtry
%terminology note: root implies base of the fin, or along the rocket body,
%while tail is the opposite end. Front implies closer to nosecone, while
%back implies closer to base
%Inputs
% P_frontRoot = [0;208/1000];
% P_backRoot = [0;0/1000];
% P_frontTrail = [140/1000;68/1000];
% P_backTrail =[140/1000;0/1000];
%
%default open rocket fin setup
% P_frontRoot = [0;10/100];
% P_backRoot = [0;5/100];
% P_frontTrail = [3/100;7.5/100];
% P_backTrail =[3/100;2.5/100];
%
% P_frontRoot = [0;15/100];
% P_backRoot = [0;5/100];
% P_frontTrail = [10/100;8/100];
% P_backTrail =[10/100;3/100];
%x axis is span, y axis is height
P_frontRoot = [0;4.9/100];
P_backRoot = [0;.4/100];
P_frontTrail = [2/100;2.4/100];
P_backTrail =[2/100;.4/100];
backOffset = -0.4/100; % difference between rocket base and back root. (if back root further back than base, positive)
%General setup values
% bodyLength = 0.4;
% noseConeHeight = .15;
% bodyDiameter = 5/100;
% finLeadingEdgeCGxlength = (45-42/5)/100;
finLeadingEdgeCGxlength = (45-42/5)/100; %idt this matters
%General calculations
finRootChord = abs(P_frontRoot(2)-P_backRoot(2));
finTailChord = abs(P_frontTrail(2)-P_backTrail(2));
finX_t = P_frontRoot(2) - P_frontTrail(2);
finSpan = abs(P_frontTrail(1)- P_frontRoot(1));
finArea = (finRootChord+finTailChord)*finSpan/2; %pretty sure this is also planform area
% finAerodynamicLength = P_frontRoot(2) - P_backTrail(2); %used in fin friction drag calc, i believe should be full fin length
finCentroidAxial = finSpan/3 * ( (finRootChord + 2*finTailChord)/(finRootChord + finTailChord) ) - backOffset;
frontSweepAngleRefVector1 = [1;0];
frontSweepAngleRefVector2 = P_frontTrail-P_frontRoot;
finFrontSweepAngle = acos(dot(frontSweepAngleRefVector1, frontSweepAngleRefVector2) / (norm(frontSweepAngleRefVector1) * norm(frontSweepAngleRefVector2)));
%Chord related calculations
P_halfChordRoot = (P_frontRoot+P_backRoot)/2;
P_halfChordTrail = (P_frontTrail+P_backTrail)/2;
midChordAngleRefVector1 = [1;0];
midChordAngleRefVector2 = P_halfChordTrail-P_halfChordRoot;
finMidChordSweepAngle = acos(dot(midChordAngleRefVector1, midChordAngleRefVector2) / (norm(midChordAngleRefVector1) * norm(midChordAngleRefVector2)));
%Mean Aerodynamic Chord (MAC) Calculations. Based on Open Rocket equations
%3.30-3.32. Simplifications of these expressions for trapezoids can be found
%here: https://www.pmac-rc.org/Files/MAC.pdf
%define chord length as function of span (or x position)
leadingEdgeCoefficients = polyfit( [P_frontRoot(1), P_frontTrail(1)],[P_frontRoot(2), P_frontTrail(2)], 1);
trailingEdgeCoefficients = polyfit( [P_backRoot(1), P_backTrail(1)],[P_backRoot(2), P_backTrail(2)], 1);
chordLength = @(x) ( leadingEdgeCoefficients(1)-trailingEdgeCoefficients(1) )*x + (leadingEdgeCoefficients(2)-trailingEdgeCoefficients(2) );
%calculate MAClength f(x)= c^2(x)
chordLengthFunction = @(x) (chordLength(x)).^2;
finMACLength = integral(chordLengthFunction, 0, finSpan)/finArea;
%calculate MacSpanwise position f(x) = x*c(x)
chordLengthFunction = @(x) (chordLength(x)).*x;
finMACSpanwisePosition = integral(chordLengthFunction, 0, finSpan)/finArea;
radialMACPosition = finMACSpanwisePosition + bodyDiameter/2;
%calculate MAC effective Leading Edge location f(x) = X_le(x)*c(x)
leadingEdgePosition = @(x) leadingEdgeCoefficients(1)*x; %relative to top if leading edge (the P_frontRoot point)
finMACLeadingEdgeLocationFunction = @(x) leadingEdgePosition(x).*chordLength(x);
%IMPORTANT note, this value is negative, but should be positive realtive to
%nosecone (since further from nosecone), hence the abs() function
%iirc, distance from top root point of fin to intersection of MAC and
%leading edge
finMACLeadingEdgeLocation = abs( integral(finMACLeadingEdgeLocationFunction, 0, finSpan)/finArea ) ;
axialDistanceMACCGx = abs(finMACLeadingEdgeLocation) + finLeadingEdgeCGxlength;
%Distance from MAC middle to nosecone
finLeadingEdgeNoseConeDistance = bodyLength + noseConeHeight - finRootChord + backOffset; %distance from leading edge to noseCone, used for fin CP, (same thing as finMACNoseconeAxialDistance)
finMACNoseconeAxialDistance = finLeadingEdgeNoseConeDistance + finMACLeadingEdgeLocation+ 1/2*finMACLength ; %line 225 FinSetCalc.java Openrocket, detemrines fin pitch damping
% plotFin (P_frontRoot, P_backRoot, P_frontTrail, P_backTrail, P_halfChordRoot, P_halfChordTrail,finMACLength, finMACSpanwisePosition, finMACLeadingEdgeLocation);
function [] = plotFin (P_frontRoot, P_backRoot, P_frontTrail, P_backTrail, P_halfChordRoot, P_halfChordTrail, finMACLength, finMACSpanwisePosition, finMACLeadingEdgeLocation)
hold on
plot([P_frontRoot(1),P_backRoot(1), P_backTrail(1), P_frontTrail(1),P_frontRoot(1)] , [P_frontRoot(2), P_backRoot(2),P_backTrail(2), P_frontTrail(2),P_frontRoot(2)] );
%mid Chord Plotting
plot( [P_halfChordRoot(1),P_halfChordTrail(1)], [P_halfChordRoot(2),P_halfChordTrail(2)])
%quarter Chord Plotting
plot( [P_frontRoot(1), P_frontTrail(1)], [P_frontRoot(2)- (P_frontRoot(2)-P_backRoot(2))/4, P_frontTrail(2)-(P_frontTrail(2)-P_backTrail(2))/4])
%plots cross sections for MAC Span purposes
% plot( [P_frontRoot(1),P_backTrail(1)], [P_frontRoot(2) + (P_frontTrail(2)-P_backTrail(2)),P_backTrail(2)- (P_frontRoot(2)-P_backRoot(2))])
% plot( [P_backRoot(1),P_frontTrail(1)], [P_backRoot(2) - (P_frontTrail(2)-P_backTrail(2)),P_frontTrail(2)+ (P_frontRoot(2)-P_backRoot(2))])
%MAC plotting
plot([finMACSpanwisePosition,finMACSpanwisePosition], [-finMACLeadingEdgeLocation+P_frontRoot(2),-finMACLeadingEdgeLocation+P_frontRoot(2)-finMACLength])
grid on
axis equal
end