Locations

Globo-Daq

 
Context Description | Hot Air Balloons and Data Acquisition Systems
Update #10118  |  16 Oct 2014
 

Before we continue with the project development is necessary to introduce everyone to the basic aspects related with a hot air balloons and data acquisition systems (DAQ). There is plenty information on the Web and books related with these topics, here we present a short summary, information collected from different sources.

 

 

Hot Air Balloons

 

What is a hot air balloon?

There are several definitions to describe a hot air balloon, here we present two of them:

  • “A hot air balloon is a unique flying craft which works because hot air rises.” By Virgin Balloon [1]
  • “The hot air balloon is the oldest successful human-carrying flight technology. It is part of a class of aircraft known as balloon aircraft.” By Wikipedia. [2]

Concluding that a hot air balloon as a human carrying aircraft, operate by humans and rising by hot air.

 

How the hot air balloon works?

Hot air balloons are based on a very basic scientific principle: warmer air rises in cooler air. Essentially, hot air is lighter than cool air, because it has less mass per unit of volume. A cubic foot of air weights roughly 28 grams (about an ounce). To create a lift, air inside the balloon must be at least 100 degrees hotter that the outside air. [3] [4]

An example:  If you heat that air by 100 degrees F, it weighs about 7 grams less. Therefore, each cubic foot of air contained in a hot air balloon can lift about 7 grams. That's not much, and this is why hot air balloons are so huge -- to lift 1,000 pounds, you need about 65,000 cubic feet of hot air. [3]

To help the balloon rise, pockets of lifting air known as "thermals" must be present. These thermals are most prominent in the early morning, just after sunrise, and early in the evening (the reason why launches are scheduled at 6:30 AM & between 6:30 & 8 PM for the event). [7]

 

Hot Air Balloon Components

 

Balloon components

 

 

burner3burner1burner2

Burners: Control the altitude of with heat. When the pilot presses the blast valve switch, liquid propane is fed to the burners through gas lines. Once the propane reaches the pilot light, it is vaporize and the burner produces a flame. The heat is fed into the balloon. [4]
in_balloon

Skirt: is the nylon at the base of the envelope, is coated with special fire-resistant material, to keep the flame from igniting the balloon. [4]

basket

Basket: Where the pilot and passengers stand. It is made of wicker, a lightweight material that is durable yet flexible for landings. With capacity up to 20 passengers. [4]

tank1

t2tank3

Propane Tanks: are strapped to the insides of the basket and have protective coverings. Some tanks hold up to 20 gallons of liquid propane, which is enough for about 30 minutes of flight. Normally, three to four tanks are used. Flames may shoot up to 15 to 20 feet and make a loud, characteristic sound when the burner ignites. [4] [5]
envelope1 Envelope: Is usually made of coated ripstop nylon, a fabric that does not tear easily. The envelope is built by long nylon gores. The gores, which extend from the base of the envelope to the crown, are made up of a number of smaller panels.  Envelopes come in different shapes and sizes. The larger ones can hold up to 225,000 cubic feet of hot air and can carry 2 tons of mass. Envelops can cost as much as $100.000. [4]

parac1

parachute2parachute3

Parachute Valve: is a large flap at the top of the balloon. To lower the balloon the pilot can open the parachute with a cord (Parachute valve cord), allowing hot air to escape. [4]

 

How high a hot air balloon can fly?

To answer this question, is necessary mention some facts: [4]

  • 70,000 ft. In a pressurized cabin, Vijaypat Singhania of india set the world record in 2005 for the highest balloon flight, reaching an altitude of 69,986 feet. Temperatures at that height dipped to minus 135 degress Fahrenheir
  • 42,000 ft. The highest recorded balloon flight, at the time, set by Hawthorne C. Gray in 1927.
  • 12,500 ft is the maximum altitude allowed by the FAA for safety reason. After this height pilots must have oxygen onboard.
  • 500 ft - 3,000 ft is the highest that usually hot air balloons fly.

This project will be focus on the commercial hot air balloons, which fly between 500 ft and 3000 ft.

 

How the hot air balloon moves?


Horizontal Movement h_move

Is controlled by wind currents, which change direction at various altitudes. The pilot use these current to steer the balloon. [4]

 

 



v_moveVertical movement

Vertical lift is caused by the expansion of the hot air in the balloon and the vertical drop is caused by releasing air from inside the balloon or allowing it cool. [4]

To move in a particular direction, a pilot ascends and descends to the appropriate level, and rides with the wind. [4]




How fast a hot air balloon can fly?

Balloons fly as fast or as slow as the wind that carries them. Since a hot air balloon has no propulsion system, speed is completely dependent on wind velocity. [7]

Almost all balloon flying is done in relatively benign weather conditions and mild winds. Most pilots prefer to launch and fly in winds less than 7 knots (8 mph | 12.87 km/h). While balloon flying is performed in higher winds, pilots accept that the faster the winds, the more they are exposed to risk and injury.[6] For this reason the desired wind speed to fly is between 4 to 6 mph (6.44 – 9.66 km/h), 12 mph max.

 

How big is a hot air balloon?

A typical hot air balloon is 63 feet in height (almost seven stories high) and 55 feet in diameter. The weight is 214 pounds for the envelope (the proper term for the colorful balloon part) and 450 pounds for the entire system including fuel and passengers. Most envelopes have a volume of 65,000 to 105,000 cubic feet. [14]

How long can hot air balloons stay up?

Commercial hot air balloons can fly between 1 -3 hours depending on the outside temperature, the wind, the weight carried and the fuel (propane) quantity. However, ideally speaking a hot air Balloon can fly all year round with calm winds. [5]

 

Chase crew

Generally, there are always a number of dedicated crew people, they have two different areas of responsibility: inflation/launch and chase/recovery. Both are usually referred to as ground crew. Passengers often serve as inflation crew, become passengers for the flight, and crew again after the balloon has landed. Before the noise and activity make discussion difficult, the pilot should give the crew briefing and discuss any requirements before inflation. [6]

The number of crewmembers is a matter of individual preference and depends upon the size of the balloon, purpose of the flight, terrain, and other factors. [6]

 

Where do balloons land?

Since a balloon travels with the wind, it is not possible to determine an exact landing site prior to launch. However, a pilot is able, through the study of wind currents, to determine the general direction of the flight.

 

Weather conditions

The information presented below is directly extracted the article post by Battle Creek Field of Flight Air Show and Balloon [8].  

Weather conditions must be almost ideal in order for a Hot-Air Balloon Launch to take place. If there is any sign of a potentially non-safe flight, then the launch must be CANCELED. Here is some weather information on ballooning flights. [8]

  • Winds: Winds are obviously the most critical weather phenomena that effects balloons. Winds are the #1 reason that Balloon Flights are canceled. Balloons fly best with wind speeds ranging from 4 to 6 miles per hour. Balloons will never fly in winds higher than 12 mph. Strong winds can not only damage the balloon, but it can make a pilot overshoot a target, cause a hard landing and require more space for landing.
  • Winds Aloft: Winds aloft (or winds at higher altitudes) can also cause a flight to be canceled. There may be almost no wind at the ground, but at altitude, the wind may be blowing at 20 miles per hour. Winds aloft must also be taken into consideration when deciding whether to fly or not.
  • Visibility: Balloon Pilots operate under FAA VFR conditions. This means they must have a certain amount of visibility in order to be able to fly (which means NO NIGHT FLYING). Depending on flight location, the visibility must be at least 1 to 3 miles. For the most part, there will be NO flying in fog.
  • Rain: Balloons do not launch in the rain. Rain can damage the balloon and decrease visibility. Besides, would you want to fly in a Hot-Air Balloon in rainy weather?
  • Fronts: There must be no fronts in the area for a balloon launch to occur. Fronts usually come with a change in wind direction or increased wind speeds. If pilots can plan ahead for this, then it may be possible for a launch. But if the front will move through during time of flight, the launch must be canceled.
  • Thunderstorms: There must be NO thunderstorms within 100 miles of the launch point for a balloon launch to take place. Thunderstorms present hazards to any type of aircraft, but a balloon is the one aircraft that would be affected most by any type of weather condition. A lightning strike to a balloon is an extremely dangerous hazard. In addition, gust fronts can occur up to 100 miles in advance of a storm or line of storms, which could heavily impact a balloon.

 

For more technical information, please refer to Balloon Flying Handbook by FAA (Federal Aviation Administration)

 

 

 

Data acquisition systems

 

Data acquisition systems (DAQ) measure, store, display, and analyze information collected from several of devices. Most measurements require a transducer or a sensor, a device that converts a measurable physical quantity into an electrical signal. Examples include temperature, strain, acceleration, pressure, vibration, sound, humidity, flow, level, velocity, charge, pH, and chemical composition [9] [12]. A simplified block diagram of a typical data acquisition system is shown below. [11]

daq_block

Transducer - Sensor

Definitions:

  • “A transducer is a device that converts a signal in one form of energy to another form of energy. Energy types include (but are not limited to) electrical, mechanical, electromagnetic (including light), chemical, acoustic and thermal energy. While the term transducer commonly implies the use of a sensor/detector, any device which converts energy can be considered a transducer.” [10] In DAQs, Transducers are devices that transform physical parameters (such as temperature, pressure, flow, and strain) into electrical parameters (such as voltage, current, and resistance). [11]
  • “A sensor is used to detect a parameter in one form and report it in another form of energy, often an electrical signal. For example, a pressure sensor might detect pressure (a mechanical form of energy) and convert it to electrical signal for display at a remote gauge.” [10]

We will continue speaking along the project about sensors, devices that detects events or changes in quantities and provides a corresponding output, in DAQs they are connected between the measured physical device and the signal conditioner’s input. [10]

Sensors come in numerous shapes, sizes, and specifications. Most sensors are purchased off the-shelf, but in some cases, they are custom made specifically for a particular measurement requirement. Regardless of input, however, the output signal is usually a voltage, current, charge, or resistance and all can be conditioned and handled equally well. Manufacturers frequently provide specifications, application notes, and principles of operation for their specific sensor to help users apply the device in the most efficient way [10].

 

Signal Conditioning

The sensor output signals must be optimized into a form that the data acquisition system can manipulate. There are several types of conditioning used [9] [12] [13]:

  • Amplification
  • Filtering.
  • Isolation.
  • Exitation.
  • Linearization
  • Signal.

Signal conditioners typically apply one or more conditioning methods to the signals. They also convert current to voltage and voltage to frequency, provide other functions such as simultaneous sample and hold (SS&H), and supply a bias voltage. [9]

In some data acquisition systems, the signal conditioning components are incorporated internally within the system. These systems can measure dc voltage, ac voltage, resistance, frequency, current, and temperature on any input channel without the need for external signal-conditioning components. [12]

It is important to understand the nature of the system signals, the configuration that is being used for the sensor to measure the signal and the effects of the surrounding environment. Based on this information is possible easily determine whether signal conditioning will be a necessary part of the DAQ system. [13]

 

Analog to digital converter (ADC)

Once the signal has passed through the conditioning process, continue to the input of an ADC. Which applies an analog to digital (A/D) conversion, changing analog voltage or current levels into digital information. The conversion is necessary to enable the computer to process or store the signals. There are several aspects to take into account with the ADC [11] [13]:

  • Input signal: if is continuous or not.
  • Number of channels: The number of analog channel inputs will be specified for both single-ended and differential inputs on boards that have both types of inputs. Single-ended inputs are all referenced to a common ground point. These inputs are typically used when the input signals are high level (greater than 1 V), the leads from the signal source to the analog input hardware are short (less than 15 ft.), and all input signals share a common ground reference.
  • Sampling rate: determines how often conversion take place. The higher the sampling rate, the better. It is possible that the aliasing effect is present, where the acquired signal gets distorted if sampling rate is too small.
  • Resolution: The number of bits that the ADC uses to represent the analog signal is the resolution.
  • Throughout: Effective rate of each individual channel is inversely proportional to the number of channels sampled.
  • Range: Minimum and maximum voltage levels that the ADC converter can quantize.

The ADC is the last in a series of stages between the analog domain and the digitized signal path. Some relevant aspects to mention are that data acquisition ADCs typically run from 20 kHz to 1 MHz with resolutions of 16 to 24 bits, and have one of two types of inputs, unipolar or bipolar. The unipolar-type typically ranges from 0 V to a positive or negative voltage such as 5 V. The bipolar-type typically ranges from a negative voltage to a positive voltage of the same magnitude. [9]

Summarizing, the ADC converts the conditioned analog signal to a digital signal that can be transferred out of the data acquisition system to a computer for processing, graphing, and storing. [9]

Digital to Analog converter (DAC)

Even though this modules will not be used in our project, is important to mention it.

The opposite of analog to digital conversion is digital to analog conversion. This operation converts digital information into analog voltage or current. DAC devices allow the computer to control real-world events. Several specification are taking into account on this conversion: settling time, slew rate, and resolution. Settling time and slew rate work together in determining how fast the DAC can change the level of the output signal. Settling time is the time required for the output to settle to the specified accuracy. The settling time is usually specified for a full-scale change in voltage. The slew rate is the maximum rate of change that the DAC can produce on the output signal. Therefore, a DAC with a small settling time and a high slew rate can generate high-frequency signals, because little time is needed to accurately change the output to a new voltage level. [9]

Computer – MCU

The computer, the last element of the DAQ, is in charge of processing, graphing, and storing. However the key factor is the software running on it, which transforms the computer and DAQ hardware into a complete DAQ, analysis, and display system. [13]

Software can be the most critical factor in obtaining reliable and high performance operation. There are different alternatives, programmable software and data acquisition software packages. [11]

For this project it will be develop a programmable software. Which involves the use of a programming language, offering flexibility as advantage but facing challenge like complexity and a steep learning curve. [11]

DAQ design – aspects to take into account

Reviewing the theory described before, can be concluded that there are some basic factor to consider when it comes to design a data acquisition system [11]:

  • Is it a fixed or a mobile application?
  • Type of input/output signal: digital or analog?
  • Frequency of input signal?
  • Resolution, range, and gain?
  • Continuous operation?
  • Compatibility between hardware and software. Are the drivers available?
  • Overall price.


References

[1] Virgin balloon flights, http://www.virginballoonflights.co.uk/ballooning-science.asp

[2] Hot air balloon, Wikipedia.

[3] http://www.howstuffworks.com/transport/flight/modern/hot-air-balloon.htm

[4] Megan Capinegro, Jeff Goertzen, High – flying festivals. The Denver post

[5] http://www.hotairballoon.org/vermont/faq.html

[6] Balloon Flying Handbook, FAA. 2008

[7] All about hot air ballooning https://www.udel.edu/PR/UpDate/98/4/all.html

[8] Battle Creek Field of Flight Air Show and Balloon Festival. http://www.bcballoons.com/balloons/balloon-launch-weather-criteria

[9] Data Acquisition Handbook. Measurement Computing. Third edition. 2012

[10] Transducer, Wikipedia. http://en.wikipedia.org/wiki/Transducer

[11] Risanuri Hidayat. Data Acquisition. Sonora University.

[12] Essential Components of Data Acquisition Systems. Agilent Technologies.

[13] Data Acquisition (DAQ) Fundamentals, National instruments

[14] All about hot air balloo, Dale Univeristy. https://www.udel.edu/PR/UpDate/98/4/all.html



More info www.globodaq.co

 

gmail       pinterest   twitter   wordpress     

 

Comments