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From Theory?. A better understanding and the basis to learn more quickly. Concepts, Figures and Explanations. Primarily concerned with understanding the detail of how a balloon goes up and down. Some surprising facts and reasons why. Some practical stuff.

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from theory

From Theory?

A better understanding and the basis to learn more quickly.

concepts figures and explanations
Concepts, Figures and Explanations
  • Primarily concerned with understanding the detail of how a balloon goes up and down.
  • Some surprising facts and reasons why.
  • Some practical stuff.
  • Understanding the principles allows you to work it out for yourself.
equilibrium temp
Equilibrium Temp
  • What is ET at take-off for a 77,000 with an all up weight of about half a metric tonne and ambient temperature of 16 °C ?
  • Stand-up temperature approx. 40°C (200 Kg)
  • Maximum envelope temperature is ???
77 000 519 kg 86 c
77,000, 519 Kg: 86°C
  • Exact conditions
    • All up weight: 519 Kg
    • Temperature: 16 °C
    • Altitude: 120 ft (ground amsl)
    • Lift is 10 grammes (0.01 Kg)
    • From Liftcalc/MiniSim (website)
  • Warmer & Heavier
    • Temp 23 °C, AUW: 564, ET = 105 °C
net forces 86 c 86 5 c
Net Forces, 86°C, 86.5°C
  • Equilibrium Temperature
    • neutral buoyancy
  • Half a degree increase
    • small net force upwards
false lift
False Lift

Aerodyamic effect of a curved surface

net forces 86 c 86 5 c1
Net Forces, 86°C, 86.5°C
  • Equilibrium Temperature
    • neutral buoyancy
  • Half a degree increase
    • small net force upwards
  • Take care
    • need to overcome inertia
ascent rates
* Ascent rates which will be maintained.

What two points can take from this?

Ascent Rates
ascent rates1
* Ascent rates which will be maintained.

If you know the envelope temperature can you predict what the balloon will do?

Ascent Rates
heating 77 000 cu ft
Heating: 77,000 Cu ft
  • Rule of Thumb

1 second of burning increases average envelope temperature by 1 °C

cooling 77 000 cu ft
Cooling: 77,000 Cu ft
  • Rule of Thumb

10 seconds of not burning decreases average envelope temperature by 1 °C

staying at equilibrium flying straight and level
Staying at Equilibrium Flying straight and level
  • How often do you burn?
  • This is replacing heat due to cooling.
  • What affects this frequency?
    • Differentiate between those things that give you a higher equilibrium temp. at take- off
    • and those that affect heat input or loss.
normal response times
Normal Response Times
  • Attaining but without haste.
  • From neutral to 100 fpm up
    • 10 seconds (2 second burn)
  • From neutral to 100 fpm down
    • 30 seconds (cooling)
  • From 300 fpm down to zero
    • 40 seconds (6 seconds of burner)
  • From neutral to ascent of 500 fpm
    • 50 seconds (16 seconds of burner)
emergency response times
Emergency Response Times
  • Achieved by leaving burner full on, attaining and exceeding the target
  • From 100 fpm down to 100 fpm up
    • 10 seconds
  • From 200 fpm up to 200 fpm down
    • 20 second (two 5 second dumps)
  • From 300 fpm down to 300 fpm up
    • 25 seconds
  • From 500 fpm down to 500 fpm up
    • 32 seconds
what have you learnt
What have you learnt?
  • Temperature control !!
    • Short burns
  • Fast ascents – overheat.
  • Fast ascents if very high – more overheat.
  • Now we’ll look at what happens during a descent.
descent
Descent

Resistance is proportional to the velocity squared.

Descent

Up

descent of 100 ft min
Descent of 100 ft/min
  • What Av. Envelope Temp?
  • How to maintain ?

85.5 °C

3 Kg

descent of 500 ft min
Descent of 500 ft/min
  • What Av. Envelope Temp?

Temperature control not so critical

78 °C

50 Kg

slowing a descent by increasing envelope temperature
Slowing a Descentby increasing envelope temperature

Equilib T Reached

Exceeded

Temp Up

Downward force

Deceleration rate increases

Descent rate

above et slows more quickly
Above ET slows more quickly
  • Foot off the accelerator v. foot on break
question
Question
  • From 300 fpm down to 0 fpm from 150 ft agl
    • 40 seconds (about 4 seconds of burner)
  • Does it matter when you put the burn in?
  • How do you avoid over burning?
  • Is the ET Exceeded?
  • How would you stop the balloon more quickly?
what have you learnt1
What have you learnt?
  • You may be falling but accelerating upwards.
  • Once you reach the equilibrium temperature your rate of deceleration will increase.
  • If you continue putting in the same burns all the way down you will over-burn.
  • Half as much is a good rule.
  • Now look at landing.
landing
Landing
  • Tony Brown – Concorde
  • Always aim for the field before
  • Line to the ground
  • Adjust all the way down – under control
  • Stop descent slightly above ground
  • When ready, rip out in air and lock.
  • Get ready for landing.
which field slow
Which Field ? (slow)

600 ft

Steep descent (45°) possible

3 knots

which field fast
Which Field ? (fast)

1,000 ft

Steep descent not possible – why?

10 knots

adrenalin
Adrenalin
  • You are in a 1,000 ft / minute descent, there is only 400 ft before you hit the ground. If you put the burner on and leave it on will you avoid hitting the ground?
control
Control
  • Never do anything else (except fly the balloon) for more than 10 seconds.
  • If you are 500 ft above the ground a controlled descent rate is 500 ft/minute.
  • 400 ft: 400 fpm
  • 300 ft: 300 fpm
  • Etc.
to control a balloon safely
To Control a Balloon (Safely)
  • Need to know what is happening at any point in time and understand why.
  • Need to know what the balloon is capable of and its limitations.
  • Understand the basic concept of the equilibrium temperature and the wide range (60 – 120) and how these relate to what the balloon does.
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