From Theory?
A better understanding and the
basis to learn more quickly.
1
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.
2
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 ???
3
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
4
Eq. Temp with Altitude
ALTITUDE
(FT)
EQUIL TEMP.
(DEGREES C)
DIFF. FROM GROUND °C
120
86
-
4,120
87
1
6,120
88
2
9,120
90
4
12,120
94
8
15,120
98 (*90)
12
*30 Kg fuel used, based on 500 ft/min.
What can you take from this?
5
Net Forces, 86°C, 86.5°C
• Equilibrium Temperature
– neutral buoyancy
• Half a degree increase
– small net force upwards
6
False Lift
Aerodyamic effect of a curved surface
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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
8
Ascent Rates
ASCENT RATE *
TEMP ° C
FORCE UP (KG)
0
100 fpm
86
86.5 (+0.5)
0
3
200
88 (+2)
10
300
500
91 (+5)
94 (+8)
25
50
600
720
99 (+13)
105 (+19)
75
100
950
120 (+34)
180
* Ascent rates which will be maintained.
• What two points can take from this?
9
Through an Inversion
H
T
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Ascent Rates
ASCENT RATE *
TEMP ° C
FORCE UP (KG)
0
100 fpm
86
86.5 (+0.5)
0
3
200
88 (+2)
10
300
500
91 (+5)
94 (+8)
25
50
600
720
99 (+13)
105 (+19)
75
100
950
120 (+34)
180
* Ascent
rates which will be maintained.
• If you know the envelope temperature can you
predict what the balloon will do?
11
Heating: 77,000 Cu ft
• Rule of Thumb
1 second of burning increases average
envelope temperature by 1 °C
12
Cooling: 77,000 Cu ft
• Rule of Thumb
10 seconds of not burning decreases
average envelope temperature by 1 °C
13
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.
14
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)
15
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
16
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.
17
Cooling? Descent!
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Descent
Resistance is proportional to the
velocity squared.
Descent
Up
19
Descent of 100 ft/min
• What Av. Envelope Temp?
85.5 °C
3 Kg
• How to maintain ?
20
Descent of 500 ft/min
• What Av. Envelope Temp?
78 °C
50 Kg
Temperature control not so critical
21
Slowing a Descent
by increasing envelope
temperature
Equilib T Reached
Exceeded
Temp Up
Downward force
Deceleration rate
increases
Descent rate
22
Above ET slows more quickly
• Foot off the accelerator v. foot on break
23
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?
24
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.
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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.
26
Which Field ? (slow)
600 ft
Steep descent (45°)
possible
3 knots
27
Which Field ? (fast)
1,000 ft
Steep descent not
possible – why?
10 knots
28
Final Slides
29
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?
30
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.
31
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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End
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