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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?

• 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.

• 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 ???

• 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

What can you take from this?

Eq. Temp with Altitude

Net Forces, 86°C, 86.5°C

• Equilibrium Temperature

• neutral buoyancy

• Half a degree increase

• small net force upwards

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

• Rule of Thumb

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

• 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.

• 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)

• 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

• Temperature control !!

• Short burns

• Fast ascents – overheat.

• Fast ascents if very high – more overheat.

• Now we’ll look at what happens during a descent.

Resistance is proportional to the velocity squared.

Descent

Up

• What Av. Envelope Temp?

• How to maintain ?

85.5 °C

3 Kg

• 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

• Foot off the accelerator v. foot on break

• 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?

• 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.

• 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

• 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?

• 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.

• 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.