Simulation of hydrogen balloon, User´s Guide

NOTE: This is a separate window. In case the main screen "disappeared" when you opened this window - reduce the size of it and you will see the main window again!

Let's start at the bottom left of the page. There you can see this beutiful picture of a balloon with sail and drag ropes (cut in the picture, for practical reasons), arranged just as it was on the "Eagle". The picture is stolen from the home page of the Andrée museum - sorry, I could not resist the temptation!


A bit further down to the left on the page - below the balloon picture - there are two buttons:
   This will produce a "printer friendly" (or rather "user friendly") output, that you can save or print as you like.
   This shows the change list for this simulation program and the home page.


On top of the page is a header frame with logo and a header. Below that you find a frame "Simulation", a frame "Background", three diagrams and a table.

   Copy right for this logotype is owned by Erik Kullberg, who is also the designer and owner of this program.
A click on the logo in the header frame will start your email program with address to the program designer filled in. Your comments and suggestions are welcome!

The frame "Background" contains background and reference material.
The frame "Simulation", the diagrams and the table will be gone through in detail below.



Simulation

This is a so called "off line" simulation, which means that all influence from the user is made before start of the simulation. The time it takes to run such a simulation is much shorter than the simulated time - in our case it takes maybe 5 [s] to simulate 2000 [s] (about 33 minutes) of flying.

The "Simulation" frame - shown to the right - contains all maneuver devices for the simulation. Two groups - one for simulation type and one for atmosphere - are framed to mark the kinship within respective group. The upper one changes its content depending on choice of start case, see "START" below.
Time length [s] for the interval to be simulated. The value is chosen from a drop down list.
Max simulation time (per interval and total) is 2000 [s]. The simulation stops when max simulation time is reached, no matter how it is reached.
Start Start case is chosen from a drop down list.
The choice must be confirmed by use of the button "Confirm". If the wanted start case is the same as last run, it is not necessary to confirm again.
"Start from ground"
Lrout is needed - it determines the altitude.
"Start on altitude"
The wanted trim altitude must be specified.
The ballast drop - if allowed and needed - is performed directly in the beginning of the new time interval. Note that if ballast drop is needed for trim but not permitted, the wanted altitude cannot be maintained.
"Continue ..."
Lrout must be given.
By dmdrop you can specify an amount of ballast to be dropped. The dmdrop input value returns to zero after simulation, to avoid mistakes.
Note: Do not run Continue directly after using any of the links - like "Users Guide"! That will cause the program to derail and you will have to close the program and start from the beginning. This is due to a program error that will be fixed asap.
  Length of drag rope "out", meaning length of drag rope outside the relling.
The drag rope has two functions, partly to vary the load and thereby give altitude control, partly to generate a breaking force and thereby a wind speed relative to the balloon.
In all start cases, the specified/calculated length Lrout is out when simulation starts.
Max available rope length is 333 [m], so at H > 333[m] the ropes do not reach the ground. The standard value is Lrout = 260[m], which gives H = 150[m] in zero wind.
Note: The ropes are assumed to hang vertically down between basket and ground - the function for stretching out the ropes is not yet in use.
  Required altitude for trim [m]. The wanted value is chosen from a drop down list.
You can trim at wanted altitude without using ballast as long as it can be done with ropes only. If ballast reduction is needed but not allowed, it shows as inability to maintain the required altitude - the balloon sinks to the highest altitude at wich it can be balanced (trimmed) with ropes only.
Note: In case "Start on altitude", the simulation starts at trim altitude and with the balloon at rest relative to Earth. If wind speed is > 0, there will be an acceleration phase.
  Regulation level for the pressure regulation valve [Pa], the maximum value for the overpressure in the balloon. The value used in the "Örnen" was (PG - PA) = 100. Here it can be changed to facilitate experiment.
If the value "Shell" is chosen, the balloon cover becomes rigid and the pressure valve is closed. Then mass and volume of the contained gas are held constant, regardless of surrounding pressure. Thereby the balloon is converted to a "flying submarine" - a zeppeliner. This has nothing at all to do with Andrées balloon - it is a pure experiment facility.
Note: "Shell" is not available in the start case "Start from ground"!
Sail  Choose one of four sail configurations, namely
"Down" - sail is down and without effect. The balloon is drifting in the wind direction.
"Left" - the sail is up on the left side and produces a force to the left. The balloon drifts to the left of the wind direction.
"Forward" - the sail us up straight forward. It produces some extra thrust in the wind direction. The balloon drifts in the wind direction, but with a little higher speed than in case "Down".
"Right" - the sail is up on the right side and produces a force to the right. The balloon drifts to the right of the wind direction. 
  Air temperature on the ground (sea level), °C.
Air temperature TA, pressure PA etc at a certain altitude, vary with altitude in accordance with standard atmosphere.
Note:   The temperature TG of the gas inside the balloon, is approximated as TG = TA at all times. In reality there is a considerable delay between TG and TA. This delay was not modelled,since it has little or no influence on the characteristics that are of interest here.  
  Wind speed [m/s]. 
Upwind  A mark in the square will give a vertical wind gust - an upwind (positive for direction upwards) at time = tsim/4. The duration and the amplitude are chosen from drop down lists "Durat." [s] and "Ampl" [m/s]. The mark is non resistent, but "Durat." and "Ampl" will keep their values until they are changed manually.
The simulated gust is a square pulse. It is independent of altitude (perforated ground plan - the "Marilyn Monroe effect").

The simulation starts when the button "Simulate" is pressed and released.


Result presentation

The result is presented in three diagrams and one table. Two of the diagrams are showing the time history for a number of variables and one shows the flight path seen from above. Symbols on the curves and a legend (up to the right) show what curve represent what variable and what curve to be read against which axis. The diagrams are described more in detail below.
In case the simulation is performed in one step (no continuation), a text line is shown above the x-axis. It gives the simulation command values - see "Table 1" below. It also gives a value "dpsi", which is (the last value of) the angle between wind direction and the flight path.
In the lower edge, to the right, date and time (down to seconds) is printed, which unambigously tells which (outprinted or stored) diagrams belong together ...

Diagram 1

H Altitude [m], see "About altitude" below. 
VG   Ground speed - the balloon´s speed relative to ground [m/s]. 
VT  True air speed - the balloon´s speed relative to the air [m/s]. 
DROG  Length of Drag Rope On Ground. This is the rope that is used to control the balloons altitude and to brake to generate airspeed. In reality it consisted of three parallel ropes - in this model they are regarded as one. 
BROG  Length of Ballast Rope On Ground. This was in reality eight separate ropes, meant to be used one by one as ballast. They were all 70 [m] long and hanging down from te basket. In this model they are regarded as one rope, 70 [m] long. 


Diagram 2

shows the simulated flight path, seen from above.
The first symbol on the curve marks the start point. The symbols have the same time space as the ticks on the time scales in the other diagrams (see third row of the diagram header).
The x-axis points along the wind direction, the y-axis is perpendicular to the wind direction.


Diagram 3

mGas  Mass of the contained hydrogen gas [kg]. 
VGas  Volume of the contained hydrogen gas [m3]. 
(PG-PA)  Pressure difference PG - PA, where PG is pressure in the balloon, PA is pressure of surrounding air. 


Table 1

Here the given simulation command values are presented, one row per simulated interval. The rightmost column gives the "dpsi"-value, which is (the last value of) the angle between wind direction and the flight path (in degrees).
The table can present a maximum of 13 rows - if there are more than 13 intervals, the rest fall outside the page and will not be presented.
The amount of remaining ballast is presented above the table. There is no stop to prevent this value to become negative.


About altitude

Altitude - on maneuver panel as well as diagrams and table - is defined as "pressure altitude". The generally used symbol is "H", but sometimes "Hp" is used, to underline the distinction between Hp and HG (geometrical altitude). Pressure altitude is used in aeronautics and air traffic, heavy as well as light, all over the world. Aboard the balloon "Örnen" they had a barograph (see "Balloon Training, Exercise 10"), calibrated in meters, so obviously it was used there too.
A pressure altimeter is simply a barometer that is calibrated in altitude units instead of pressure units. The calibration rests upon a certain relation betwen pressure, temperature and altitude - a "standard atmosphere". Pressure altitude Hp agrees with geometric altitude HG when air pressure and air temperature vary with altitude in accordance with the standard atmosphere. In this program Hp is automatically adjusted to zero at HG=0. The air temperature T0 at HG=0 can be chosen by the user. If T0 is set to T0=15, Hp will agree with HG at all altitudes.
When trimmed "on altitude" at H=300 or less, the drag ropes of the model are hanging down all the way till they just barely reach the ground. That means that Lrout in this case tells the value of HG. Run a simulation like that on say H=300 (trim with ballast) with T0=15 and one with say T0=-10 and compare the Lrout (=HG)-values with the Hp-values!