My Aviation programs for 35s Message #1 Posted by Vincze on 17 Aug 2007, 11:15 a.m.
Okay, here is my listing of Aviation programs for the 35s. It is only for two two calculations right now, but I plan on extending it for others. It take me a while to write as I had a lot to learn about calculator, and also it takes me longer to write so it does not sound like a fool who does not speak english well wrote it. Here you go. Please let me know if there are any ways to optimize the programs.
Aeronautical Functions on the 35s
Víncze
Aeronautics has many calculations that the pilot uses when flying. For many decades, many pilots have relied upon the tried and true E6B flight computer to do these calculations. The E6B is nothing more than a fancy slide rule device that can compute such as time, speed and distance problems, fuel consumption, conversions, altitude and speed corrections, wind and heading issues and a few more calculations.
A disadvantage of the E6B is that it is a manual process, and takes a bit of concentration while in flight. In recent years, computerized E6B’s have come out that can perform some of these tricky manual calculations very precisely, and quickly. In fact, the HP41C series calculators had an expansion pack that could do these very nicely.
My thought is why not use our trusty and inexpensive 35s to do these. I will present here, two of the programs that I have programmed on my unit.
True Heading and Ground speed conversion
When flying, just because you choose a certain course, it does not mean that is the true course that you must fly to reach your destination. Many factors affect the true heading that you must steer, and the true ground speed. One of the major factors is the wind direction and velocity. In this program, there will be four variables that you must know to determine the true heading and the ground speed. They are true wind direction, wind velocity, true course and true airspeed (TAS). I will indicate these as variables D, V, C, and T respectively.
Program Listing
H001 LBL H
H002 CLVARS
H003 SF 10
H004 WIND VEL
H005 PSE
H006 INPUT V
H007 TAS
H008 PSE
H009 INPUT T
H010 WIND DIR
H011 PSE
H012 INPUT D
H013 COURSE
H014 PSE
H015 CF 10
H016 INPUT C
H017 
H018 STO A
H019 SIN
H020 RCL V
H021 *
H022 RCL T
H023 /
H024 ASIN
H025 STO+ C
H026 RCL A
H027 X<>Y
H028 
H029 SIN
H030 RCL A
H031 SIN
H032 /
H033 RCL T
H034 *
H035 RCL C
H036 X<>Y
H037 RTN
Notes
On lines H004, H007, H010, and H013 you will notice text. This is entered by pressing the EQN key, then RCL and the alpha key until the text is entered. After the text entry, press ENTER to exit EQN mode. More information may be found on pages 1316 – 1318 of the manual.
SF 10 is set with left shift, 2.0. The . will input a 1. CF 10 is set with left shift, 3.0. If you need more explanation, see page1317 or 1411 in the manual.
Example
Let us assume that the Wind direction is 240°, the wind velocity is 38 knots, the true course is 300°, and the TAS is 165 knots. [One note, it does not matter if your wind speed or air speed are in knots, MPH, KMH, all that matters is that you are consistent between the two.] So, V= 38, T= 165, D = 240, and C = 300. When we run the program, we will notice that in the Y register, we have 288.49, this represents the True Heading in degrees, or what we must adjust to in order to compensate for the wind if we wish to have a true course of 300°. In the X register, we see 142.68, which is our true ground speed, with the effects of the wind.
Distance Between Two Latitude/Longitude Points
When planning a flight between two points, one must know the actual distance, in nautical miles, that you must fly. This is essential for fuel planning, time in flight and filing you flight plan. There are a number of ways that you can do this, but one thing that we must do is use great circles since the earth is round. Two formulas are generally relied upon. The first being the Haversine formula which tells us greatcircle distances between two points. It is a bit more complicated, and we will not use it here. The second formula is the spherical law of cosines, which gives well conditioned results down to distance as small as 1 meter. The exact formula is:
Spherical Law of Cosines
Where d is the distance, and R is the earth’s radius, (we will use nautical miles). Lat and Lon will be in the format of ddd.mmmsss (or degrees.minutes seconds), so if out Latitude is 33° 57’ 00”, we would enter 33.5700. This should all be entered in the degree mode, as the program will convert everything to HMS and radians.
Program Listing
D001 LBL D
D002 CLVARS
D003 RAD
D004 SF 10
D005 LAT1
D006 PSE
D007 INPUT A
D008 HMS >
D009 >RAD
D010 STO A
D011 LON1
D012 PSE
D013 INPUT B
D014 HMS >
D015 > RAD
D016 STO B
D017 LAT2
D018 PSE
D019 INPUT C
D020 HMS >
D021 > RAD
D022 STO C
D023 LON2
D024 PSE
D025 CF 10
D026 INPUT D
D027 HMS >
D028 > RAD
D029 STO D
D030 RCL A
D031 SIN
D032 RCL C
D033 SIN
D034 *
D035 RCL A
D036 COS
D037 RCL C
D038 COS
D039 *
D040 RCL D
D041 RCL B
D042 
D043 COS
D044 *
D045 +
D046 ACOS
D047 3440.065
D048 *
D049 DEG
D050 RTN
You will notice in line D047 that there is a constant there. This will apply the answer towards the mean radius of the earth in nautical miles. If you wish to use kilometers, then the constant would be 6371.
You will notice that there are four variables. They are defined as follows:
A = Lat1, B = Lon1, C = Lat2, D = Lon2.
Example
Let us assume we are flying from LAX to JFK. LAX is located at 33° 57’ 00” N, 118° 24’ 00” W. JFX is located at 40° 38’ 00” N and 73° 47’ 00” W. Our variables would therefore be:
A = 33.5700 B = 118.2400 C = 40.3800 D = 73.4700
When entered into the program, it will return an answer of 2,145.17 nm. If you wish to convert that to km, then you would multiply that by 1.852 to get the kilometers.
Special Thanks
I would like to thank a number of people who have helped this Hungarian better understand how the unit works. Because I am fearful that I may forget someone, I will just say thank you to the folks over at moHP who have helped. They know who they are, and I thank you sincerely.
