From Theory?

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# From Theory? - PowerPoint PPT Presentation

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?

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
• 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
• 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
• Equilibrium Temperature
• neutral buoyancy
• Half a degree increase
• small net force upwards
False Lift

Aerodyamic effect of a curved surface

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 which will be maintained.

What two points can take from this?

Ascent Rates
* 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
• Rule of Thumb

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

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
• 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
• 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
• 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?
• 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

Resistance is proportional to the velocity squared.

Descent

Up

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

85.5 °C

3 Kg

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

Temperature control not so critical

78 °C

50 Kg

Slowing a Descentby increasing envelope temperature

Equilib T Reached

Exceeded

Temp Up

Downward force

Deceleration rate increases

Descent rate

Above ET slows more quickly
• Foot off the accelerator v. foot on break
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 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
• 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.
Which Field ? (slow)

600 ft

Steep descent (45°) possible

3 knots

Which Field ? (fast)

1,000 ft

Steep descent not possible – why?

10 knots