HiFlyer TRAINING MANUAL VOLUME 2 TETHERED GAS … · hiflyer training manual volume 2 tethered gas...

TATM Volume 2 Issue 1.1 1

HiFlyer TRAINING MANUAL VOLUME 2

TETHERED GAS BALLOON PRINCIPLES

Lindstrand Technologies Ltd Maesbury Road

Oswestry Shropshire SY10 8HA

TEL: 01691 671 888 FAX: 01691 679 991

All rights reserved. No part of this manual may be reproduced or transmitted in any form or by any means, electronic, or mechanical, including photocopy, recording, or any information storage and retrieval system, without permission in writing

from Lindstrand Technologies Ltd, Maesbury Road, Oswestry, Shropshire, SY10 8HA, England


CONTENTS PAGE 1. Buoyancy 4 2. Gas Cell Volume 4 3. Air Density 4 4. Superheat 5 5. Helium Pressure 5 6. Super Pressure 5/6 7. Helium Inflation 6 8. Freelift 6 9. Aerodynamic (wind) drag 7 10. Dynamic (wind) pressure 7 11. Unladen Free Lift 8 12. Helium Fill Level 8 13. Operational Free Lift 9 Figures Figure 1 HiFlyer Layout 10 Figure 2 Gondola Layout 11 Figure 3 Loadcell Assembly 13 Figure 4 Winch Cable 14 Figure 5 Superheat from Radiation 15 Figure 6 Helium Pressure Head 16 Figure 7 Superpressure 17 Figure 8 Balloon Control Pressure Control 18


Figure 9 Envelope Pressure Diagram 19 Figure 10 Control Panel 20 Figure 11 Freelift Principle 21 Figure 12 Freelift / Wind Relationship 22 Figure 13 Typical Freelift Example 23 Figure 14 Windspeed and Drag 24 Figure 15 Wind Drag / Balloon Pressure 25 Figure 16 Unladen Freelift Configuration 26 Appendix 2 Typical Freelift Calculation 12 Appendix 3 Passenger Load Chart 27/28


LINDSTRAND TECHNOLOGIES LIMITED

HIFLYER TRAINING PROGRAMME

1. BUOYANCY The lift of a balloon is proportional to the volume and density of the air it displaces. The lift is generated by the difference in density between the lifting gas and the displaced air. For 100% pure Helium, the lift is 1.045kg per cubic meter. Lift is directly proportional to purity, therefore, for 99.5% pure helium the lift is 1.040 kg/ m3 2. GAS CELL VOLUME The larger the volume of the gas the more air it displaces and the more lift it generates. The volume and lift will increase as temperature rises and decrease as it falls. The ballonet volume will adjust to compensate for the change in gas cell volume. 3. AIR DENSITY The lift will change with the density of the air being displaced. The greater the air density the greater the lift. Air density changes with atmospheric pressure, and elevation of the balloon. The higher the elevation the less the air density and lift.


4. SUPERHEAT Superheat is the temperature increase above ambient temperature inside the helium cell. The increase is generated by solar radiation penetrating the envelope. See figure 5. The effect of the temperature rise is to expand the Helium volume. This in turn increases the volume of displaced air and hence lift. The pressure is not increased as the ballonet volume will decrease to compensate. The ballonet pressure will not be affected as it is controlled by the fan and P.R.V. On sunny days the superheat will always generate additional lift. In extreme conditions the Helium pressure should be carefully monitored incase the ballonet ‘bottoms’ out and the pressure rises. (See figure 8) 5. HELIUM PRESSURE Unlike water which increases in pressure with depth, Helium pressure increases with height. See figure 6 The pressure gradient is approximately 1mm WG (1kg/ m2 or 10 Pa) per metre of height. Therefore the pressure at the top of a 20m high gas cell is 20mm WG (200Pa). The lift is generated by the pressure acting on the upper surface of the balloon 6. SUPER PRESSURE The ballonet performs two functions: A) It compensates for change in helium cell volume. B) It applies superpressure to the envelope. Superpressure is pressure above atmospheric pressure.


Superpressure is necessary to maintain the spherical shape of the balloon, and keep it taut. This reduces the wind drag, and improves the appearance of the balloon. The ballonet is pressurised by a fan which cuts in at 6mm WG (60 Pa) and out at 8mm WG (80 Pa). A relief valve (P.R.V.) limits the ballonet pressure to 14mm WG (140 Pa). (See figure 8) The ballonet pressure is transferred to the Helium cell through the bladder. The pressure in the Helium cell adjacent to the ballonet will be the same as the ballonet, but will rise toward the top of the balloon at the rate of 1mm WG per metre height. Thus the pressure at the top of the balloon and the Helium valve will be ballonet superpressure plus Helium pressure rise. (See figure 9) Should the pressure at the top of the balloon exceed 40mm WG (400 Pa) the Helium valve will open as a last resort to reduce the pressure to a safe level. Ballonet and Helium pressure are displayed on the control panel. (See figure 10) In stormy weather when the balloon is low moored the superpressure can be boosted by connecting the ground fan to increase both pressure and recovery after gust impact – see Operations Manual Supplement 1. 7. HELIUM INFLATION When the balloon is filled or topped up, the mass of Helium transferred from a pressure cylinder to the balloon remains constant. The volume will expand by the ratio of the cylinder pressure to ambient, once the temperature has stabilised. 8. FREELIFT Freelift is the excess lift above the load the balloon is lifting. (See figure 11) This freelift is measured by a load cell as tension at the top of the winch cable. (See figure 3)


The greater the freelift, the more stable the balloon is in windy conditions. (See figure 12) The passenger load is therefore controlled by the allowable freelift. See Operations Manual Appendix 3. In calm conditions more passengers can be carried. In windy conditions less passengers can be carried. (See figure 13) The freelift is measured under different loading conditions to monitor various factors:

unladen freelift – to monitor helium fill

elevated freelift – to determine passenger payload

operating freelift – to ensure adequate lift for stability in windy conditions See Operations Manual – Section 2.18.1 Section 3.3.d Section 3.4.2.3.c Section 3.4.11 9. AERODYNAMIC (WIND) DRAG The drag on a balloon increases as the windspeed squared. (See figure 14) For example the drag at 2 m/s and 6 m/s increases by:

the ratio 22 to 62 = 4 to 36

The drag at 6 m/s is 9 times the drag at 2 m/s. To stop the balloon being blown sideways causing discomfort and possibly damage, the freelift must be increased by reducing the passenger payload. 10. DYNAMIC (WIND) PRESSURE The effect of the wind on the balloon creates a force on the envelope, indenting it out of shape, and increasing the drag force even more. (See figure 16) To resist the deformation it is necessary to maintain superpressure in the envelope.


This can be done by switching the ballonet fan on to manual thus raising the pressure from the nominal 8mm WG (80 Pa) fan cut out to 14mm WG (140 Pa), when the PRV opens. 11. UNLADEN FREE LIFT The Unladen Free Lift with the gondola grounded and the cables slack, must be recorded. This value gives a good indication of the Helium fill in the balloon and is used to track Helium loss rate and Helium top-up requirement. See 3.4.11 – Page 47 Operations and Maintenance Manual. The Elevated Free Lift must be recorded on the test ride with the balloon at maximum ride height, with only the operator on-board. This value is used in conjunction with wind speed and operating free lift to determine passenger capacity. See Appendix 3. The Operating Free Lift is the free lift indicated at maximum ride height with passengers aboard and must not fall below the minimum stipulated in limitation. The Operating Free Lift is not recorded in the Tech Log, but should be noted along with the number of passengers for each ride. See 3.4.2.3 Operations & Maintenance Manual (Page 38). 12. HELIUM FILL LEVEL The free lift used as a basis for the Helium fill level is the unladen free lift, that is the free lift with the balloon raised so that is restrained by the winch cable with the load cell under tension, but with the gondola on the deck with the cables slack. See 3.4.11.1 - Operations & Maintenance Manual (page 47). The unladen free lift will measure the lift of the Helium less the weight of the balloon assembly (envelope, net and load ring). As the weight of the HiFlyer balloon assembly may vary slightly according to the individual specification, the recommended unladen free lift range will be specific to each balloon. Recommended unladen free lift range: Maximum: 4.2 Tonnes Minimum: 3.9 Tonnes The balloon may be operated below the minimum recommended free lift level, but the passenger capacity will be reduced.


Unladen free lift will vary with temperature, atmospheric pressure and Helium purity. The unladen free lift must be recorded in the Tech Log before and after Helium top-up and on a daily basis in order to monitor the Helium level. 13. OPERATIONAL FREE LIFT The operational free lift is the lift that is indicated on the load cell readout when the balloon is being normally operated. The maximum number of passengers that may be embarked is firstly established at the completion of the test ride, at the beginning of the day. See Appendix 3. However, it is the responsibility of the operator to further modify the maximum number of passengers in response to changing conditions. If the wind speed increases or slackens then the maximum passenger load must be modified so that the minimum operational free lift requirements are met. It is recommended that the load cell indicator is reviewed just after each ascent phase has started to ensure that the free lift figure is not below the required levels plus 280 kg (616 lbs). For example, if the wind speed is 3 knots the minimum free lift is 900 kg. Therefore the load cell reading just after ascent has started will be 900 + 280 = 1180 kg (2596 lbs). The additional 280 kg (616 lbs) accounts for the extra weight of the cable which will be carried when the balloon is at its normal ride height of 120m (394 ft). The operator is also responsible for reviewing the embarking passengers. The maximum number of passengers is based upon an average passenger weight of 77 kg (169 lbs). If the embarking passengers are obviously heavier than this figure, the operator should reduce the maximum number embarked. See 3.4.2.3 (c) Operations & Maintenance Manual – Page 38.


HIFLYER LAYOUT FIGURE 1


GONDOLA LAYOUT FIGURE 2


HELIUM GAS LIFT AT 100% PURITY = 1.045 Kg/m³ AT STANDARD SEA-LEVEL ATMOSPHERE

TYPICAL FREELIFT CALCULATION

APPENDIX 2


LOADCELL ASSY FIGURE 3


WINCH CABLE FIGURE 4


SUPERHEAT FROM RADIATION FIGURE 5


HELIUM PRESSURE HEAD FIGURE 6


SUPERPRESSURE FIGURE 7


BALLOON PRESSURE CONTROL FIGURE 8


ENVELOPE PRESSURE DIAGRAM FIGURE 9


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Control Panel OPERATIONS MANUAL REFERENCE: SECTION 1.3.2. Control Panel

FIGURE 10


FREELIFT PRICIPLE FIGURE 11


FREELIFT / WIND RELATIONSHIP

FIGURE 12


TYPICAL FREELIFT EXAMPLE

FIGURE 13


WINDSPEED – 1 KNOT = 0.515 m/s = 1.15 miles per hour 1 m/s = 3.60 Km/h = 1.94 knots

WINDSPEED AND DRAG

FIGURE 14


WIND DRAG / BALLOON PRESSURE FIGURE 15


UNLADEN FREELIFT CONFIGURATION

FIGURE 16


AAPPPPEENNDDIIXX 33

HIFLYER PASSENGER LOAD CHART Elevated free lift – recorded on operator only test ride Operating free lift with passengers limited by wind speed as Table 1 Passenger payload is elevated free lift minus operating free lift Maximum passengers (at 77 kgs each) for payload as per Table 2

Table 1

Peak Wind Speed

((kknnoottss))

Minimum Operating Free Lift

((ttoonnnneess))

EElleevvaatteedd

FFrreeee LLiifftt

((OOppeerraattoorr oonnllyy))

((ttoonnnneess))

PPaasssseennggeerr

ppaayyllooaadd

((ttoonnnneess))

MMaaxxiimmuumm

ppaasssseennggeerrss

ffrroomm TTaabbllee 22

00--55 00..9900

66--1100 11..2200

1111--1155 11..6600

1166--2200 22..2200

2211--2244 22..8800

TTaabbllee 22

Passenger Payload (tonnes)

Number of passengers (at 77 kgs)





2.16 28 1.47 19 0.77 10

2.08 27 1.39 18 0.70 9

2.00 26 1.31 17 0.62 8

1.93 25 1.24 16 0.54 7

1.85 24 1.16 15 0.46 6

1.77 23 1.08 14 0.39 5

1.70 22 1.00 13 0.31 4

1.62 21 0.93 12 0.23 3

1.54 20 0.85 11 0.15 2

Check wind speed and operating free lift at the top of each ride and confirm operating free lift does not fall below minimum limit. Reduce passenger load on next ride if necessary.


Worked example of Passenger loading using hypothetical values Peak wind speed recorded on test ride – 12 knots Elevated free lift with operator only on test ride – 2.80 tonnes From Table 1 Minimum operating free lift at 12 knots = 1.60 tonnes

Passenger payload = elevated free lift minus operating free lift 2.80 – 1.60 = 1.20 tonnes From Table 2 1.20 tonnes payload is equivalent to 16 passengers

Peak Wind Speed (knots)

Minimum Operating Free Lift (tonnes)

Elevated Free Lift (Operator only) (tonnes)


Maximum Passengers from Table 2

0-5 0.90

6-10 1.20

11-15 1.60 2.80 1.20 16

16-20 2.20

21-24 2.80

Note: - standard passengers taken at 77 kgs each. Reduce numbers if the

passenger group is obviously overweight - numbers may be increased if passenger group is obviously underweight, for

example a group of children - Confirm minimum operating free lift does not fall below limit at the top of every

ride

HiFlyer TRAINING MANUAL VOLUME 2 TETHERED GAS … · hiflyer training manual volume 2 tethered gas...

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