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COMPETITION REGULATIONS


 

 

RACING HOVERCRAFT

CONSTRUCTION   REQUIREMENTS
(up to 500 Kg unladen weight)

July 2006

Whilst every effort is made to ensure the accuracy of the information contained in these requirements, the World Hovercraft Federation cannot accept responsibility for any injury or damage sustained resulting from this information

First issued – 1996

Second issue – November 1999

Third issue – May 2000

Fourth issue – September 2002

Fifth issue – May 2004

Sixth issue – December 2005

This issue – July 2006

 

Publication Reference - WHF 002

 

  ã  World Hovercraft Federation

 

 

For further information regarding this publication please contact the Secretary

 

Christel Martens

World Hovercraft Federation

Franciscusstraat 41
6681 VP Bemmell
The Netherlands
Tel: +31-481-450471
E-Mail: worldhovercraftfederation@planet.nl


1.0  INTRODUCTION... 1

1.1  General 1

1.2  Purpose of these Requirements. 1

1.3  Application. 1

1.4  Interpretation. 1

1.5  Operation of the Requirements. 2

1.6  Appeals. 2

1.7  Method of Compliance. 2

1.8  Craft Design General Requirements. 3

2.0  STRUCTURE AND MAIN MACHINERY... 4

2.1  General 4

2.2  Strength and Stiffness of Structures. 4

2.3  Crashworthyness. 4

2.4  Buoyancy and Stability. 5

2.5  Main Machinery, Mounting and Transmissions. 6

3.0  ROTATING ASSEMBLIES.. 7

3.1  Design and Operation. 7

3.2  Fans. 7

3.3  Propellers. 7

3.4  Overspeed Conditions. 7

3.5  Positive Locking of Fastenings. 7

3.6  Guarding of Rotating Assemblies. 8

3.7  Transmissions. 9

4.0  SYSTEMS AND CONTROLS.. 11

4.1  General 11

4.2  Aerodynamic Control Surface Systems. 11

4.3  Engine, Transmission and Associated Controls. 11

4.4  Fuel Systems. 12

4.5  Electrical Systems. 12

5.0  FIRE SAFETY... 13

5.1  General 13

5.2  Fuel Tanks. 13

5.3  Hot Parts. 13

5.4  Fire Extinguishing Systems. 13

6.1  Stability. 14

6.2  Hard Structure Clearance. 14

6.3  Design Cushion or Bag Pressure. 14

6.4  Construction and Materials. 14

6.5  Damage. 15

7.0  HANDLING, PERFORMANCE AND OPERATIONAL SAFETY... 16

7.1  General 16

7.2  Demonstration of Characteristics. 16

7.3  Arrangements for Operational Safety. 16

7.4  External and Internal Noise Levels. 16

8.0  CRAFT CERTIFICATION... 17

8.1  General 17

8.2  Certificates and Log Books. 17

8.3  Registration. 17

APPENDIX A - TYPICAL DESIGN LIMITS AND MARGINS.. 18

1.0  General 18

2.0  Material Stresses. 18

APPENDIX B – Thrust Systems. 19

APPENDIX B – Thrust Systems. 19

1.0  General 19

2.0  Homologated Plastic Fans. 19

3.0  Fan Speeds for given Diameters. 19

APPENDIX C - Formula 25 Construction Regulations. 21

1.0  Engine. 21

2.0  Environmental 21

3.0 Safety. 21

4.0 Tow Points. 21


1.0  INTRODUCTION

1.1  General

         

1.1.1       These requirements have been prepared by the Scrutineering Committee and ratified by the Annual Delegate Committee of the World Hovercraft Federation. (WHF)  They are to be followed for the design, construction and safety of the Hovercraft running at all designated World Championship Meetings.

 

1.1.2.      The WHF takes no responsibility for the compliance of the racing Hovercraft to these regulations. NOTE THAT it is up to the craft user to give proof of compliance of his craft with the requirements. The craft user takes the complete responsibility for any hazard generated by his Hovercraft.

 

1.1.3.      This publication overall reflects the views of a substantial and well informed body of professional and amateur experience with which all constructors and operators of Light Hovercraft will consider it wise to comply.

 

1.1.4.      These requirements are the Copyright of the WHF but permission is given to National Governing Bodies to reproduce these requirements in their own language.

 

1.1.5.      It is the responsibility of all National Governing Bodies to ensure that copies of these requirements are available to competitors.

1.2  Purpose of these Requirements

 

1.2.1.      The purpose of these requirements is to ensure that Racing Hovercraft are designed, constructed, operated, and maintained in such a way as to prevent, so far as can be foreseen, the occurrence of accidents. Should an accident occur, the purpose of these requirements is to ensure its effects are minimised as far as possible both to persons and property.

1.3  Application

 

1.3.1.      These requirements apply to Racing Hovercraft having a dry weight of less than 500kg dry weight, for sporting use. Craft over 500 kg will need special consideration by Chief Scrutineer of the meeting.

 

1.3.2.      Craft built to these requirements are not necessarily suitable for use in open environments. Certification for use in open environments is provided for under the National Country Design, Construction and Safety Requirements for Cruising Craft.

1.4  Interpretation

 

1.4.1.      These requirements are not intended as a manual of Hovercraft Design but wherever practical examples of methods that meet these requirements are included. Alternative practices which provide an equivalent level of safety may be accepted at the discretion of the Scrutineers.

 

1.4.2.      Mandatory Clauses are denoted by "shall" or "must", whereas recommended but not mandatory practise is denoted by "should" or "may".

 

1.4.3.      It is implicit in the requirements expressed qualitatively (e.g. "readily visible", "adequately tested" etc.) that the Chief Scrutineer of the meeting will adjudicate in cases where doubt of compliance exists.


1.5  Operation of the Requirements

 

1.5.1.      These requirements are brought into operation by the body of National Hovercraft Clubs affiliated to the WHF.  They are responsible for inspection of craft in order to issue a log book or certificate, and for subsequent inspection at National Hoverclub organised events, or at the request of an owner.

 

1.5.2.      Where a craft owner operates his craft alone (outside organised events) it is his own responsibility to inspect his craft for compliance with these requirements. Failure to maintain compliance invalidates the Log Book or Certificate for the period of non-compliance.

 

1.5.3.      The WHF reserves the right to amend any regulation herein in the light of practical application. Amendments to these requirements will come in to force immediately following sanction by the WHF council, and the new issue of these official WHF set of requirements.

 

1.5.4.      The WHF may grant special exemption from these requirements to "Historic Craft", for purposes to be defined, and in conditions to be defined by the Scrutineering Committee for each case.

1.6  Appeals

 

1.6.1.      In the case of an operator disagreeing with the ruling of a Scrutineer or the Chief Scrutineer of the meeting as adjudicator, he or she may appeal as follows:

 

              a)       Submit a complaint in writing to the Chief Scrutineer of the meeting and the WHF Secretary within one week of the incident.

 

              b)       Lodge a deposit defined in fees list with the WHF (no action will be taken unless this deposit is lodged, and cleared through a bank if paid by cheque).

 

1.6.2.      The appeal will be considered by a Scrutineering Committee of the WHF at its next scheduled meeting, or one specially convened.  Both complainant and Scrutineer will be expected to attend this meeting. The Committee will judge the case, taking whatever additional technical or legal advice is considered necessary.

 

1.6.3.      A final appeal can be made to the Governing Board of the WHF who’s decision will be final.

 

1.6.4.      In the case that legal or other professional advice need be taken, the cost of such constancy will be required to be paid by the complainant, whatever the outcome of the dispute.

1.7  Method of Compliance

 

1.7.1.      Compliance with these requirements shall be established by calculation, testing, or other evidence to the satisfaction of the Scrutineer. An example of "other evidence" may be a certificate of compliance from a WHF approved component manufacturer.

 

1.7.2.      Where an applicant proposes to use a proprietary component in a manner other than that provided for in its manufacturers certificate, then compliance shall be demonstrated to the WHF or its agents.

 

1.7.3.      Where a requirement is not susceptible to quantitative proof of testing, compliance must be established to the satisfaction of the Scrutineer, by inspection at part built stage of the craft, by reference to the precedent, or by reference to good engineering practise.

 

1.7.4.      Since it is not possible to prescribe requirements to cover every detail that designers may introduce, the Scrutineer may reserve the right to with-hold approval of a craft or part thereof, if in his opinion such a craft or part thereof is unsafe, even though it complies with the letter of these requirements. Any disagreement with this decision is to be resolved by the majority vote of all official Scrutineers for that meeting.  

1.8  Craft Design General Requirements

 

              The following general requirements apply to the more detailed specifications given in sections 2.0 to 6.0 below.

 

1.8.1.      All connecting elements essential to safe operation of the vehicle shall be provided with adequate means of locking against loosening from vibration, rotation and torque, or flexing of the craft structure.

 

1.8.2.      All personnel should be protected from contact with rotating components, surfaces with temperatures exceeding 70C, live electrical circuits, and sharp edges or corners.

 

1.8.3.      Services essential for personnel safety shall be operational at all times during operation, independent of the functioning of the main power unit(s).

 

1.8.4.      Adequate access shall be provided to all parts of the craft requiring periodic inspection.


2.0  STRUCTURE AND MAIN MACHINERY

2.1  General

 

2.1.1.      The structure of the craft shall have adequate strength to withstand all load cases as defined in 2.2 below, in either cushion borne or floating/static mode as appropriate, in such a manner that structural deformations occurring will not interfere with the safe operation of the craft.

 

2.1.2.      The stiffness of the craft structure shall be such that any vibrations due to engines or rotating equipment, or flexing of the structure due to dynamic loads, will not affect the safe functioning of the craft or machinery.

 

2.1.3.      The craft shall have buoyancy at least equal to the craft dry weight. The buoyancy shall be distributed in such a manner that when floating either intact or when damaged, the craft will not sink. In this context, to "sink" shall be interpreted as when the craft becomes completely immersed.

 

2.1.4.      The craft should float in a stable manner when intact such that flooding of open areas (e.g. the cockpit) will not immediately occur when floating, and personnel move around in the craft. Freeboard of 75 to 150 mm at the stern, when the driver is positioned to restart a rear mounted engine is advised. Less than this will mean the cockpit is likely to flood, so disabling the craft.

 

2.1.5.      Engines should be able to be restarted from cold with the craft floating in the maximum design environment without external assistance.

2.2  Strength and Stiffness of Structures

 

2.2.1.      The structure of the craft shall have adequate strength to withstand loads encountered under all conditions of operation. Load cases which should be considered by the designer are:

 

              a)       Manoeuvring:     forces applied to controls and machinery frame.

              b)       Floating:           forces applied to the hull.

              c)       Water impact:  forces applied to the front or side planing surfaces of the hull.

              d)       Transition:         forces due to craft dropping over a step.

              e)       Wind loads:       forces applied to the structure.

              f)        Impact:             forces due to skid stop over land.

              g)       Parking:            forces due to three point random support on the craft bottom.

              h)       Towing:             forces due to towing equal to twice craft weight.

              i)        Machinery:        forces on machinery mounts due to mass, torque and dynamic loads.

              j)        Collision:           forces due to collision with an immovable object.

 

2.2.2.      Compliance  with 2.2.1. may be proved by inspection and possibly trials carried out by an WHF Scrutineer.

 

2.2.3.      Inflatable structures forming a part or whole of the Hovercraft primary structure shall conform to Standard of the country where the craft is built.

2.3  Crashworthyness

 

2.3.1.      The craft shall be designed so as to minimise the risk of injury to the occupants in the event of a collision. This shall be achieved by craft construction conforming to 2.3.2. to 2.3.8. below.

 

2.3.2.      All major components and items of equipment shall be attached to the craft primary structure with arrangements sufficient to withstand inertia forces in any direction.         

2.3.3.      Machinery and frame mountings shall be fail safe by mounting design, or by secondary restraint.           

2.3.4.      A roll bar of adequate strength shall be built into all craft. This may take the form of structural members primarily designed for other purposes(engines mounts etc...) if they will maintain adequate clearance for the occupants when the craft is inverted.

 

2.3.5       Interior surfaces and edges of structural members within the cockpit and cabin areas shall be designed to minimise injury to occupants in the event of a collision, by protection with deformable or crushable padding.  Guarding shall be provided to prevent limbs being trapped in engine frames, structural members or exhaust systems.

 

2.3.6.      The exterior periphery of the craft shall be constructed so that any sharp edges or corners are protected by crushable material.

 

2.3.7.      No components such as handling points, towing eyes, exhaust pipes, etc..., shall overhang the hull structure, with the exception of aerodynamic control services.

 

2.3.8.      Removable items such as batteries, fuel tanks, fire extinguishers, etc., shall remain securely in position even if the craft is inverted.

2.4  Buoyancy and Stability

 

2.4.1.      Craft intended to be operated over water should be capable of floating in a reasonable attitude in the event of loss of cushion lift, with the crew aboard, either to allow the craft to be restarted, or until the crew can be rescued if the craft becomes flooded.

 

2.4.2.      Craft intended to be operated over water shall have minimum built-in buoyancy equal to the craft maximum gross weight.

 

2.4.3.      The units of buoyancy shall be so located in the craft as to provide adequate stability when the craft is water borne.

 

2.4.4.      Consideration shall be given to the provision of adequate buoyancy and stability of the craft when water borne when those units of buoyancy likely to be damaged have sustained such damage.

 

2.4.5.      Buoyancy sufficient to keep the craft afloat when swamped with water shall be provided by non absorbent foam, inspectable air bags, or multi cellular inspectable boxes.

 

2.4.6.      Temporary additional external buoyancy may have to be added onto the hull for meetings on rivers or at the coast.

 

2.4.7.      Designers are advised to add a design margin to the weight used to design the buoyancy, and to be careful to account for the fact that the effective buoyancy of foam filled compartments is reduced by the weight of the foam that is added to the craft. It is further advised that retrieval of a craft with a flooded cockpit using a tow rope is much easier and safer if it floats level.  Buoyancy should be placed in such a manner therefore, that the propulsion system, or any other major components above the line of the top of the craft hull are supported in air. This will generally require about 2/3 of the total craft buoyancy to be sited in the rear half of the craft length.

 

2.4.8.      Special note should be taken of designs having internal air ducting to segmented skirts. Any ducting areas extending below the waterline need to be designed to allow water to freely drain out when hovering up.

 

2.4.9.      Intact Stability:  The intact floating stability of the craft should be such that when floating in calm water, the crew are able to move about the craft within reasonable limits, and to restart the engine(s) without flooding the cockpit. The placing of buoyancy as in 2.4.7. above should therefore take account of the weight of the driver in the pull starting position.

 

2.4.10.    Damaged Stability: The craft shall not sink in the case of the cockpit being flooded due to an accident. The flooded craft shall retain sufficient residual buoyancy to allow the crew to hold onto it while floating in the water supported by their lifejackets.

 

2.4.11.    Hull Outer Surface Configuration: The outer surface of the hull shall be so configured as to provide a planing surface with a dihedral angle of 10o to 35o in the case that the skirt should totally collapse on one side, front, or rear of the craft, at maximum operating speed in still air over land or water. The planing surface(s) shall be present over a depth not less than that defined by the skirt outer and inner hull attachment points.

2.5  Main Machinery, Mounting and Transmissions

 

2.5.1.      All components of machinery and transmissions shall be constructed, arranged within the craft, and protected as necessary to ensure their safe functioning at all times.

 

2.5.2.      The possibility of failure of a given power unit, transmission or support system shall be considered. In any such case, the system shall fail safe, and not endanger the crew.

 

2.5.3.      Mountings and connections between main machinery and primary structure and between main machinery and rotating assemblies shall be positively locked. Such mountings and connections shall be designed in order that failure of 25 % of the mountings or connections will not lead to any subsequent failure, or endanger the safe operation of the craft.

 

2.5.4.      Pipe work and hoses on water cooled engines shall be designed and installed in such a way as to minimise the possibility of failure which may result in injury to the driver or bystander.


3.0  ROTATING ASSEMBLIES

3.1  Design and Operation

 

3.1.1.      All rotating assemblies shall be designed and operated such as to preclude as far as possible failure during normal operating life of the assembly.

3.2  Fans

 

3.2.1.      A number of proprietary fans are available and suitable for use on Light Hovercraft. The rotating speed of these fans is to be limited following the guide lines given in Appendix B.

 

3.2.2.      Propulsion systems designed for tip speeds in excess of 137m/s are likely to produce noise levels in excess of 78 BD at 15 m distance. A maximum design tip speed of 122m/s is recommended to be used for this reason where practical.

 

3.2.3.      Fan Speeds for Given Diameters: The table in Appendix B indicates fan r.p.m. for the limiting tip speeds, based on the recommended limits of 122m/s for normal operation, 137m/s for design maximum, and 168m/s which is the absolute limit for Multiwing Z and Nylon blade fans and Breeza plus blades.

3.3  Propellers

 

3.3.1.      Wherever possible it is recommended that reliable commercial units (with a test certificate) are used. If it is essential to home produce a propeller or fan, the material should be very carefully selected, and if possible tested for tensile strength. Wooden blades shall be laminated. It is very important to provide adequate blade cross section in the region of the blade root. Glass Fibre is unreliable for propellers - even when laid up under carefully controlled conditions - and should be avoided. On no account shall cast materials (aluminium, resin, etc....) be used. If accurate materials and stressing data is not provided, then maximum permissible tip speed shall be 137 m/sec for normal operation.

 

3.3.2       Every prototype propeller should comply with the "prototype propulsions guide lines" given in Appendix B.

3.4  Overspeed Conditions

 

3.4.1.      The normal operating rotational speed for craft with more than one fan unit driven from a single engine must allow for the overspeed of the remaining unit(s) resulting from a single failure in the transmission system. The limiting stress in rotating assemblies shall not exceed 0.66 x the material design stress for the overspend conditions as follows:

 

Failure

Overspeed

1 from 2

30%

1 from 3

15%

2 from 3

50%

 

Overspeed Conditions

 

 

3.5  Positive Locking of Fastenings

 

3.5.1.      Inspectable positive locking devices (wire, split pins, nylon nuts) will be employed in the rotating assembly and its mounting structure, where loosening might cause a dangerous misalignment. Adhesive (Loctite or Casio ML or equivalent) will not normally be deemed adequate.

3.6  Guarding of Rotating Assemblies

 

3.6.1.      All rotating assemblies shall be guarded in such a way that under all operating conditions no part of a person or his clothing may enter the space swept by the rotating assembly, or force the guards or the duct structure into that space whether the person be:

              a)       in collision with...  or

              b)       manhandling....  or    
              c)       operating......the Hovercraft.

 

3.6.2.      A fail-safe device shall be fitted to all transmission shafts transmitting more than 15 kW per shaft, in order to prevent shaft "flailing" in consequence of bearing or bearing housing failure. Suitable flail guard devices include a suitably sized metal strap over pedestal bearing housings or suitably sized plates with a clearance hole around the shaft to act as temporary plain bearing, and limit shaft movement. Such flail guards should be securely attached to a substantial part of the transmission mounting frame in order that the shaft movement will not cause failure in the guard itself.

 

3.6.3.      Minimum Guarded Area:  Fans and propellers must have guards at the intake, around the periphery and at the discharge side of the unit, to the following standards:

 

              a)       The INLET SIDE of all fans or propellers must be guarded to the standard of 3.6.4. and 3.6.5. below.          

              b)       The PERIPHERY of the volume swept by the fan or propeller must be surrounded by a guard extending at least 125 mm (5 inches) forward and 250 mm (10 inches) aft of the swept volume, to avoid fingers gripping the edge of the guard from contacting the blades.

 

              c)       Special care shall be taken to provide adequate guarding at the exit area from a fan or propeller. There shall be no open areas greater than 300 mm diameter (12 inches) at a position 250mm aft of the fan or propeller swept volume. Guarding may be provided in the form of rudder(s), elevator(s), duct support framework, fan centre bodies or flow straightener vanes, or wire mesh conforming to the strength requirements of 3.6.5. below.           

 

              d)       All rotating shafts, transmission belts, chains or gears shall be guarded by containment inside a closed space (engine compartment, fan centre body, engine or component solid cover) or by wire mesh guarding to the requirements of 3.6.5. below.  

              e)       No guard shall extend beyond the edge of the main hull structure. Local extensions to the hull shall not be considered part of the craft main hull.

              f)        Quick release (Insuloid etc.) guard clips shall be mounted at intervals of no more than 300 mm around the periphery of each guard.

 

3.6.4.      Guard Material and Configuration:  Guarding may be provided in the form of wire mesh, wire rod, tubular metal framing, and solid wall ducting. Where wire mesh is used to make a guard, the following mess sizes shall be the maximum acceptable:


 

    

Distance from

Device Swept Volume

Maximum Mesh

Dimension

< 150 mm (6 in)

12 mm (0.5 in)

< 800 mm (32 in)

50 mm (2.0 in)

> 800 mm (32 in)

300 mm (12.0 in)

 

                                                                                                                         Minimum Mesh Sizes

 

3.6.5.      Guard Overall Strength and Rigidity:  No guard or structure shall deflect into the swept volume of the rotating device when a force of 50daN (50kg) is applied over an area of 1 cm at any point of the guard. This is to prevent failure of the rotor, or injury to a third party in the case of a man falling onto the guard and taking the impact on one hand.

 

3.6.6.      Containment of Failed Blades

 

              a)       All fan and propeller guarding shall be designed to contain so far as is possible, failed blades or blade pieces caused by collision or ingestion of foreign objects.

 

              b)       Fans:  Polypropylene blade materials tend to break into many pieces while Nylon or Delrin blades tend to fail at the blade root or into larger pieces. Minimum thickness of G.R.P. ducting over an area 100 mm forward and aft of the centreline of the rotor swept volume shall be 4 layers of 450 g/m2 chopped strand mat for maximum tip speed of 137m/s. Where tip speed is > 137m/s duct reinforcement shall be added to by 2 x 450 g/m2 layers chopped strand mat (CSM). The addition of stronger materials such as woven rovings, Kevlar or wire mesh within the laminate is highly recommended.     

 

              c)       Ducted Propellers:  Where propellers are guarded by a duct system with mesh guarding at the inlet, the duct shall have metal plate or heavy gauge wire mesh reinforcement over an area 100 mm both forward and aft of the propeller swept volume. The reinforced duct shall be of sufficient strength to contain a blade component in the manner and condition of isub-section (d) below. The duct outlet may require mesh guarding to contain a blade component as in sub-section (d) below.

 

              d)       Propellers with Mesh Guards:  Where guarded by wire and tube mesh cage(s), the propellers shall be guarded by mesh to the sizes as in 3.6.4. above.  The guard shall be of sufficient strength to contain a blade component comprising the outer two thirds of a single blade, ejected in any direction from directly ahead to 45o aft from the propeller swept disc at a rotational speed corresponding to the application of maximum engine power, plus a margin of 10 % of engine power.    

              e)       Failure Conditions:  It should be noted that the requirements in sub-sections (a to d) above DO NOT require that the guarding shall remain undamaged in failure conditions. The requirement is for containment of rotating components. Gross deformation of the guard structure is acceptable, though the designer should bear in mind that in such a case the craft is likely to be disabled.

3.7  Transmissions

 

3.7.1.      Machinery transmissions shall fulfil the requirements of section 2.0 above.

 

3.7.2.      Transmission shafts of capacity greater than 15 kW shall be protected by flail guards sufficient to contain a failed shaft rotating as specified in section 3.6.2. above, in addition to bearing failures.             

3.7.3.      Transmission shaft linkages and support bearing mountings shall be positively locked to the requirements of section 3.5. above.

             

3.7.4.      All transmission rotating components shall be guarded to the level of section 3.6. against contact with personnel.


4.0  SYSTEMS AND CONTROLS

4.1  General

 

4.1.1.      This chapter specifically covers the following:

 

              a)       Aerodynamic control surface systems                    
              b)       Engine, Transmission and associated controls        
              c)       Fuel systems            
              d)       Electrical systems.   

4.1.2.      All systems and controls shall be designed to be safe in operation and where possible fail-safe when released by the operator. Any systems and controls installed in a racing Hovercraft which are not specifically referred to here should be designed and constructed to this same principle. Acceptance of such systems will be at the discretion of the National Hovercraft Club Scrutineering Committee.   

4.1.3.      The designer should keep in mind the environment in which the controls and systems will operate. Where systems are likely to be sensitive to dampness, salt water, sand ingress, vibration, and relative movement of craft substructures, they should be rejected or designed for protection against such effects.

4.2  Aerodynamic Control Surface Systems

 

4.2.1.      Aerodynamic control surfaces may be of two types:

 

              a)       Fixed Surfaces providing aerodynamic stabilising forces while in operation, which are fixed or able to be moved (trimmed) when the craft is stopped such as fixed elevators, fins or fan straightener vanes.

 

              b)       Moving Surfaces providing aerodynamic control forces, such as rudders, controllable elevators, or elevons.                    

4.2.2.      Fixed surfaces shall be attached to the craft structure with arrangements sufficient to maintain them securely in position under the maximum design airspeed over the device, at the position of maximum control force generation.

 

4.2.3.      Moving surfaces shall be attached to the craft structure with hinging  arrangements sufficient to maintain them securely in position under the maximum design airspeed over the device, at the position of maximum control force generation.                 

4.3  Engine, Transmission and Associated Controls

 

4.3.1.      Craft with one main power plant shall have a throttle control which has a spring return to the engine idle position.    

4.3.2.      Craft with separate lift and propulsion power plant shall have spring return throttle(s) on propulsion engine(s) to engine idle position.

 

4.3.3.      Manually operated control systems should be designed with adequate safety margin against the following load applied with the maximum lever arm possible :

 

              a)       FOOT controls                 60kg

              b)       STICK LEVER controls     50kg fore and aft, and 30kg lateral

              c)       WHEEL controls              50kg fore and aft and 20 x D kg.m torque, where D = diameter

              d)       HANDLEBAR controls      50kg fore and aft, 25kg in rotation

 

4.3.4.      Control cables, chains, torque tubes and push rods should have an adequate safety margin against the loads applied in section 4.3.3. above.

 

4.3.5.      All primary controls shall be capable of operation by the driver when in the normal driving position, with sufficient ease, and smoothness of operation, to permit the proper performance of their function.

 

4.3.6.      Full movement of every control shall be possible when the driver is in place while wearing appropriate protective clothing and safety equipment.

4.4  Fuel Systems

 

4.4.1.      All tanks, containers, pipelines, structure and equipment shall be designed to comply with the strength requirements of the vehicle as described in section 2.0, and the Fire Safety Requirements of section 5.0.

 

4.4.2.      Fuel tanks shall be fuel tight against the operating conditions of the craft whilst providing for fuel expansion due to temperature changes, prevent siphoning of fuel through vents, and minimise entry of water through fillers. Fuel tanks shall be capable of drainage to completely empty condition.           

4.4.3.      Fuel tanks and supply lines shall be so located that, in the event of a leak occurring, the escaping fuel is prevented, so far as possible, from making contact with any of the hot parts (e.g. engine, exhaust pipe etc.), or electrical circuits of the craft.

4.5  Electrical Systems

 

4.5.1.      Electrical systems shall be so designed that their normal operation will not create a fire hazard, and also that additional hazards will not be created in the event of a fire in a designated fire zone.        

4.5.2.      It shall be possible for the driver of the craft to switch off engines and power to all electrical systems while in the normal driving position. Switches must be of the positive-off type. The electrical cut off switch(es) shall be marked by an 80 mm red equilateral triangle, bounded by a white border 10 mm wide, within triangle dimensions.

 

4.5.3.      Battery power supplies should in addition have a separate circuit breaker in a clearly accessible position outside any fire zone, and marked by an 80 mm sided RED equilateral triangle bounded with a white border 10 mm wide, within the triangle dimensions.

 

4.5.4.      All engines shall have a pull-out type lanyard ignition kill switch, the lanyard of which shall be attached to the driver at all times during operation, so that in the case of an accident where the driver is thrown out, the craft will be stopped. The operation of this lanyard switch will be regularly checked by Scrutineers or Marshals as part of a pre-race checkout.              

4.5.5.      Engines shall have adequate Radio Frequency (RFC) suppression fitted, as required by common law in the country of operation. It should be noted that RFC suppression relates particularly to ignition systems, including spark plug leads and caps, and coils/condensers. Suppressed plug caps are available, as are low emission leads, or RFC chokes for leads, in most car parts stores.

              A simple check of the effectiveness of RF suppression is to turn on a transistor radio in proximity to the craft. If there is substantial interference, then the craft RF suppression is not adequate.

 


5.0  FIRE SAFETY

5.1  General

 

5.1.1.      The design of craft shall be such as to minimise the risk of fire occurring.

 

5.1.2.      Engine exhausts shall be designed so that no appreciable amount of gas can enter the air cushion system of a no-flow bag skirt. The exhaust outlet must be clear of the lift fan intake suction on a no-flow bag skirt.    

5.1.3.      Craft designed with a substantially or totally enclosed cockpit shall be separated from the engine or engines by flame resistant on non flammable bulkheads. Metal or metal clad bulkheads are recommended.            

5.2  Fuel Tanks

 

5.2.1.      Fuel Tanks and supply lines will be constructed and mounted so that any vibration or distortion of the craft structure during operation will not damage the tank, or cause leaks in the supply line(s). 

5.2.2.      Gravity feed fuel tanks shall be fitted with a cut-off tap which can be easily operated by the driver.          

5.2.3.      Fuel tanks with feed from the base of the tank shall be fitted with a cut-off tap, easily operable by the driver, so that if the fuel line fails, the tank can be stopped from draining out.           

 

5.2.4       Fuel containment systems shall be so designed that liquid fuel cannot leak and directly contact any hot parts, or electrical components when the craft is inverted, or in any attitude such that fuel may leak from the vent or breather systems.              

5.2.5.      Fuel lines of PVC or other plastics which degrade over time shall be replaced annually.

5.3  Hot Parts

 

5.3.1.      The parts of a craft within 50 mm from hot parts, for example engine exhaust pipes or silencers, shall be of non-flammable or fire inhibiting material.

             

5.3.2.      Hot parts shall have an adequate supply of cooling water or air to maintain a steady design temperature during all normal operations.

 

5.3.3.      Hot exhaust pipes or silencers should be protected by a stand-off wire mesh guard if mounted in locations close to normal craft manhandling points.

5.4  Fire Extinguishing Systems

 

5.4.1.      Structures surrounding all enclosed engines and petrol tanks shall be fitted with readily accessible aperture(s) for the purpose of efficiently extinguishing a fire.

         
6.0  SKIRT DESIGN AND ATTACHMENT

6.1  Stability

 

              The skirt system as fitted to the craft should be such as to ensure adequate stability when hovering under all possible operating conditions. Adequate stability is defined as follows:

 

6.1.1.      For the craft trimmed level in a static hovering condition, the skirt shall provide sufficient righting moments in the conditions of maximum design speed, and maximum design environment of wind and waves or hard surface, so as to prevent plough-in during application of a moment equal to transfer of 10 % payload fore and aft or cross the beam of the craft the maximum distance feasible for the craft design.       

6.1.2.      The righting moment generated by the skirt system in pitch and roll shall steadily increase at a linear or greater rate with rotation, to the point that the hull contacts ground or water.        

6.1.3.      The skirt system shall be intrinsically stable in heave (vertical motions) at any power setting.

6.2  Hard Structure Clearance

 

6.2.1.      Hard structure clearance shall not exceed 12.5% of hard structure width (Hard Structure Width / 8.0) unless it can be demonstrated that both dynamic and static stability characteristics are adequate, by calculation and/or trials, in accordance with section 6.1 above.

6.3  Design Cushion or Bag Pressure

 

6.3.1.      In order to avoid collapse of the skirt system at high speed, the pressure in the skirt bag, inflated segment area, or the cushion itself if there is no area inflated at a higher pressure around the periphery, shall not be less than the dynamic air pressure as in the table below:

 

Pressure

Maximum Design Speed

lb./sq.ft

kph

mph

3.1

48

30

7.0

72

45

12.3

96

60

   

              As an example, a craft with a cushion area of 50 sq.ft. or 4.64 sq.m. must weigh at least 350 lbs or 158kg if it is designed to operate at 45 mph or 72 kph.

6.4  Construction and Materials

 

6.4.1.      Skirt material should be coated, woven material with high resistance to ripping in any direction.             

6.4.2.      Attachments of the skirt to the hull shall be of sufficient strength that no damage is caused to the hull attachment if the skirt material is ripped or snagged with sufficient force to break the skirt connecting device.

 

6.4.3.      Attention should be paid to the configuration of seams on a bag or loop so that rips will be stopped by the seams, rather than guided by them.           


6.5  Damage

 

6.5.1.      The craft should maintain stability sufficient to prevent capsize in the event that any part of the skirt should collapse and be dragged back by the water surface during operation at maximum operational speed in any direction.

 

6.5.2.      The skirt should be designed so that damage to any part or area of the skirt will not cause other parts or areas of the skirt to fall as a direct consequence.

 


7.0  HANDLING, PERFORMANCE AND OPERATIONAL SAFETY

7.1  General

 

7.1.1.      The general principles of operational safety for a racing light Hovercraft shall be that in the event of an accident, the driver shall be provided with reasonable means of escape and survival.

7.2  Demonstration of Characteristics

 

7.2.1.      The National Hoverclub shall reserve the right to call for a trial demonstration of craft characteristics of buoyancy, freeboard, stability, adequate control, emergency stopping, and safe performance.

7.3  Arrangements for Operational Safety

 

7.3.1.      Crash Helmets to the National Standard or better, MUST be worn by the driver whenever the craft is operated.

 

7.3.2.      A buoyancy aid to the National Standard or a life jacket (with at least inherent buoyancy to the National Standard specification) must be worn when a craft is operated over water.

 

7.3.3.      The driver must wear suitable protective clothing covering arms, legs and torso.

 

7.3.4.      The driver should have adequate all round vision directly, or by means of mirrors.

 

7.3.5.      All craft shall be fitted with handling points adequate for manhandling of the craft itself, and for grasping by personnel overboard. The handling points shall be handles designed for grasping, not cleats.

 

7.3.6.      Handles shall be a minimum of one on either side (2 per side for craft over 250kg dry weight), and one each at bow and stern.                   

7.3.7.      Craft should be fitted with a towing eye and permanently attached towing rope at the bow of sufficient strength to pull the waterlogged craft ashore. The fitted rope shall be at least 5 meters long (7 to 10 meters if possible), with a floating loop at the free end, the other end securely fixed to the craft. The rope breaking strength is not to be less than 200 kg.                

7.4  External and Internal Noise Levels

 

7.4.1              Static noise measurements shall be made at a distance from the craft of 25 metres with an instrument set 1.2 meters above the ground.  The craft will be positioned in a fixed position on flat open grassland with all engines on maximum power.  Measurements will be taken on all four corners of the craft. Craft exceeding 93dBA at any measurement point will be reported to the Race Director.

 

It should be noted that background noise in most outdoor environments generally only varies within 3 dBA, and noise meters are generally accurate to within 0.5 dBA.

 

 

7.4.2       The internal noise level at the driver's normal head position should not be greater than 105 dBA. Levels higher than this can cause permanent hearing loss. It is recommended that the noise level at driver's head be kept below 100 dBA if at all possible, for comfort reasons.


8.0  CRAFT CERTIFICATION

8.1  General

 

8.1.1.      A Light Hovercraft for racing use may be certified by the issue of a Log Book or Certificate of Compliance, following inspection by a National Hoverclub Scrutineer, the execution of such trials as are considered necessary, and provision of such appropriate design documentation as may be requested by the certification Scrutineer.

 

8.1.2.      Where special materials or methods are to be used in the craft design or construction, prior consultation with the Scrutineering committee, through the chairman, is strongly recommended, to ensure that such will be acceptable.

8.2  Certificates and Log Books

 

8.2.1.      Issue of a Log Book or Certificate of compliance constitutes a declaration by the National Hoverclub that it is satisfied that the design and construction of the craft concerned, at the time of inspection, gives rise to an acceptance level of safety for the purpose of issuing a Log Book or Certificate.

 

8.2.2.      The operator of a craft which has a Log Book or Certificate may be required to carry out the maintenance schedule approved for the craft by the National Hoverclub.

 

8.2.3.      Scrutineers are authorised to prevent further operation and withdraw the Log Book or Certificate if in their opinion the craft is no longer safe.   

8.3  Registration

 

8.3.1.      The craft registration number shall be clearly displayed on the craft hull using numerals not less than 50 mm in height.         

8.3.2.      The craft shall clearly display a Racing Number designated by the National Hoverclub and issued to the craft driver in letters not less than 250 mm high and 25 mm thick in positions such that the number is visible from either side. The recommended position is on the sides of the thrust duct or ducts.

 


APPENDIX A - TYPICAL DESIGN LIMITS AND MARGINS

1.0  General

 

1.1.         Design of a Hovercraft will involve estimating the weights of various components in order to determine the loads applied to the structure, and then estimating the local pressures at support points, or the buoyancy distribution of the floating craft.                 

1.2.         It is important to remember to apply a factor of 1:1 to all major masses during the design process. When estimating buoyancy it is advisable to use water density of 1.0 g/cc (fresh water), and to be careful not to overestimate the buoyancy volume of the craft, as freeboard is also defined by the buoyancy.                

1.3.         When considering the craft standing on three points, the local pressure applied by this case will probably determine the required floor thickness. A rule of thumb which may be applied for craft within these requirements, of typical hull geometry currently used would be minimum thickness 6 mm for plywood bottom, 3 mm for GRP and approximately 1.5 mm (16 SWG) for aluminium. Such thickness will avoid punching holes in the bottom. It should be noted that the use of dish type landing pads, landing strakes, or runners (stiffeners or GRP D rope) will both stiffen the floor panel and help further prevent punching damage.       

1.4.         If the craft floor is a sandwich construction with buoyancy foam between two panels then the lower panel should be as in the previous paragraph. The two panels should be connected with webs sufficient to transfer the load from the driver or passenger's feet, since otherwise the foam will crush, and the mechanical connection be lost.

2.0  Material Stresses

 

2.1.         Typical properties of materials which may be used for Hovercraft design values are shown in the table below.

Material

Tensile Stress

(daN/mm)

Shear Stress

(daN/mm)

Aluminium GP30

11.0

17.5

GRP (csm)

3.5

17.0

Plywood

1.4

11.7

 

 

2.2.         These values are for guidance only. They are appropriate design values for non fatigue type stresses. Where there is vibration and so fatigue, then the material strength above should be divided by 2.2 to give a design value for steel and aluminium, and divided by 4.0 for GRP or plywood. National Standards Office give detailed specifications for all these materials, and designers will find comprehensive data in National Standards Office documents. Further advice on application to specific designs may be given by National Country Scrutineers on  request.       



APPENDIX B – Thrust Systems

1.0  General

 

1.1.         For the purposes of Scrutineering it is irrelevant what the propulsion system is called as long as it is safely constructed. So in conjunction with existing guide lines on plastic fans, it is agreed to collate the required information to homologate laminated wooden propulsions.

2.0  Homologated Plastic Fans

 

2.1.         A number of proprietary fans are available and suitable for use on Light Hovercraft. The use of these fans is to be limited to a combination of rotational speed and diameter giving blade tip speed less than the following:

 

Type of Fan Blade

Maximum

Tip Speed

Multiwing Type 2 - Polypropylene Blades

137 m/sec

Multiwing Type 3 - Polypropylene Blades

137 m/sec

Multiwing Type 6 - Polypropylene Blades

137 m/sec

Multiwing Type 2 - Glass Filled Nylon

168 m/sec

Multiwing Type 3 - Glass Filled Nylon

168 m/sec

Multiwing Type 4Z - Glass Filled Nylon

168 m/sec

Multiwing Type 5Z - Glass Filled Nylon

168 m/sec

London Fan Co. ‘Breeza’ Small Hub

137 m/sec

HasconWing HV PAG (White Blades)

168 m/sec

HasconWing HF PAG (White Blades) see note 3

168 m/sec

Centrifugal Fans see note 1

85 m/sec

 

Typical Fan Speeds

 

Note 1 Centrifugal fans should not be run at speeds exceeding manufacturers recommended design value, but in any case should not exceed the values above.

 

Note 2  The use of "Truflo" axial fans with pressed steel hubs and nylon blades is expressly forbidden upon Racing Craft, as from 01.03.87.  The use of Truflo fan blades with other than pressed steel hubs may be considered by the Scrutineering Committee by application through the Chairman.

 

Note 3 The use of Hasconwing HF PAG white blades is allowed only if retained by the addition of an M6 bolt through the root of the blade attaching it to the hub.

 

 

2.2.         The duct shall comply to rotating assemblies protection requirements.

 

2.3.         The guard shall comply to rotating assemblies protection requirements.

3.0  Fan Speeds for given Diameters

 

3.1.         The table below indicates the fan speed in RPM for the limiting tip speeds, based on the recommended limits of 122 m/s for normal operation, 137 m/s for design maximum, and 168 m/s which is the absolute limit for Multiwing Z and Nylon blade fans and Breeza plus blades.


 

Tip Speed

Diameter (m)

122 m/sec

RPM

137 m/sec

RPM

168 m/sec

RPM

0.50

4660

5233

6417

0.60

3833

4360

5348

0.65

3585

4025

4936

0.70

3329

3738

4584

0.75

3107

3489

4278

0.80

2913

3271

4011

0.85

2741

3078

3775

0.90

2589

2907

3565

0.95

2453

2754

3377

1.00

2330

2616

3208

1.10

2118

2379

2917

1.20

1942

2180

2674

1.30

1792

2013

2468

1.40

1664

1869

2292

1.50

1553

1744

2139

       

Typical Fan Limiting Tip Speeds

 

              Wooden or fabricated propellers are also subject to close manufacturing limits, but for small Hovercraft applications tip speed should not in any case exceed 200m/s where blades have been stressed for 300m/s.

 

3.2.         Propulsion systems designed for tip speeds in excess of 137 m/sec. are likely to produce noise levels in excess of 78 dBA at 15 m distance. A maximum design tip speed of 122 m/sec is recommended to be used for this reason where practical.

 

 

 


 

APPENDIX C - Formula 25 Construction Regulations

 

The following Formula 25 Regulations are in addition to those in the main section of the WHF Racing Hovercraft Construction Requirements.

 

Preamble

 

A racing class to address environmental efficiency achieved by the choice of a 4-stroke, low-reving engine, the reduced maximum limit on developed noise and the inherent fuel efficiency that flows from these constraints. Restrictions on internal engine modifications are designed to keep operating costs low (constrained).

1.0  Engine

 

1.1                     The engine or engines shall be four cycle internal combustion based upon a generic commercial/industrial engine designed to run at 3600 rpm. Operational rpm to be no higher than 3600 rpm when craft is static. The total installed power shall not exceed 25 shaft horsepower measured at the output shaft of the engine(s). The competitor may be required to provide proof of this power output.

1.2                     No internal performance enhancing modifications are permitted

2.0  Environmental

 

2.1                     Noise – The maximum noise limit for a Formula 25 craft at full power is 80 dBA measured at the standard noise measurement position for a particular race circuit. This is perceived as a noise level three times quieter than a standard racing hovercraft (10 dBA less than the racing standard).

 

2.2          Measurements to be taken at various points around the craft.

3.0 Safety

 

3.1          The hull design should make the craft intrinsically stable whilst floating with power off. The natural buoyancy of the craft should be sufficient to support the un-powered craft and pilot.

4.0 Tow Points

 

4.1          The craft must be fitted with a substantial tow point. This is defined by the ability to drag the empty craft with power off on land.