##E6B1v2.0

##Den?
##01
// Calculate  density altitude
disp("Compute Density Altitude")
P_Alt=in("Pressure Altitude?")
T=in("Air temp in C?")
// Correct for std temp at pressure altitude
T_s= 15-.0019812*P_Alt
// We use the simplified density altitude calc
D_alt=P_Alt+118.6*(T-T_s)
// Now round off
D_alt=round(D_alt)
out("Density Altitude:",D_alt)

##TAS?
##02
// Compute true airspeed
disp("Compute True Airspeed ")
Ias=in("Indicated Airspeed?")
P_Alt=in("Pressure Altitude?")
T=in("Air temp in C?")
// Correct for std temp at pressure altitude
T_s= 15-.0019812*P_Alt
// We use the simplified D_Alt calculation
D_Alt=P_Alt+118.6*(T-T_s)
Tas=Ias/(1-6.8755856e-6 * D_Alt)^2.127940
Tas=round(Tas)
out("True Airspeed:",Tas)
end(1)

##Wnd?
##03
// Unknown wind
clv(1)
tm(0)
disp("Find Unknown Wind")
Tas=in("True airspeed?")
Hdg=in("Heading?")
Gs=in("Ground speed?")
Trk=in("Track/Course?")
Ws=4*Tas*Gs*(sin((Hdg-Trk)/2))^2
Ws=sqrt((Tas-Gs)^2+ Ws)
round(Ws)
wait("Wind speed; R/S to continue")
y=Tas*sin(Hdg-Trk)
x=Tas*cos(Hdg-Trk)-Gs
Wd=Trk+atan2(y,x)
Wd=Wd+360
Wd=fmod(Wd,360)
Wd=round(Wd)
out("Wind direction",Wd)
end(1)

##Xwd?
##04
:start
disp("Compute Cross Wind/Drift")
WS=in("Windspeed in kts?")
WD=in("Wind dir in Degrees?")
menu=ask("Runway","Drift")
jmpif(menu,"Runway","Drift")
:Runway
RH=in("Runway Heading?")
hw=WS*fabs(cos(WD-RH))
xw=WS*sin(WD-RH)
round(xw)
wait("XWind, R/S to continue")
hw=round(hw)
wait("Headwind")
jmp("start")
:Drift
TAS=in("True airspeed?") 
CRS=in("Course?")
WC=(WS/TAS)*sin(WD-CRS)
HD=CRS+asin(SWC)
GS=sqrt(WS^2 + TAS^2 - 2*WS*TAS*cos(HD-WD))
HD=HD+iff(HD<0,360,0)
round(HD)
wait("Heading, R/S to continue")
round(GS)
wait("Ground Speed:")
end(1)

##Tmp?
##05
disp("Convert Temps ")
menu=ask("F to C","C to F")
jmpif(menu,"FC","CF")
:FC
F=in("Temp in F?")
C=round((F-32)/.18)/10
disp("Converted temp in C is")
end(1)
:CF
C=in("Temp in C?")
F=round((C*1.8+32)*10)/10
disp("Converted temp in F is")
end(1)

: General Comments
: One of 2 aviation program goups (E6B1 and E6B2) based on E6B by John Bell who
: based much of his work on the work ...
: "Aviation Formulary V1.43" by Ed Williams.
: Please refer to http://williams.best.vwh.net/avform.htm
: Some  of John's work is retained here, but I just made it more
: applicable to folks like me who do not fly heavy iron,
: as in single engine Cessna drivers.
: E6B mimics the basic E6B functions whereas NAV contains some
: basic navigation functions.
: I am Bruce Stafford, DO, find me at docstafford@cox.net,
: especially with suggestions or bug fixes. If you hack this further
: do it without cost to the benefit of all pilots.
:
: There are some basic simplifications in this group of calculations -
: 1. compressibility is ignored - my cessna 172 just won't go that fast!
: 2. we don't use mach numbers here (see 1. above)
: 3. altitudes are assumed to be less than about 36,000 ft
: 4. CAS is assumed to be IAS
: 5. miles are in knots
: 6. Temp calculations do nut use the K recovery factor