SPECIFICATIONS

scale model hovercraft Scale	¼ or 1/5.
Construction :	Wood-Epoxy
Overall dimensions with inflated skirt :	La 500 x lg 920 x ht 460 mm
Hull dimensions :	La 400 x lg 820 x ht 110 mm
Total weight with one battery :	2.5 kg
Skirt type :	'bag type', assembled by gluing
Lifting area :	?
Lifting compartments :	3 (2 at front, 1 at back)
Lifting motor :	type 500 with reducer 2.8 to 1
Pushing motor :	type 500 with reducer 4.5 to 1 *
Direction :	3 rudders chord 75 x height 175 mm
Pushing propeller diameter :	12 '' (305 mm)
Lifting fan diameter :	120 mm (4.7 '')
3 servos :	1 for direction and two for fore compartment opening
battery :	1 of 7 or 8 elements, 2400 to 3000 mAh
Empty hull weight : Servo box weight (no battery) : Stand weight :	590 g 320 g ? (Ouuuppps, I forget to weight it)
Radio :	programmable (for motor mixing, and mixing rudder/fore compartment opening)
	* This is not what exist on the prototype, but an untested suggestion, so take your risks

Tuning

Recommended centering

Recommended centering : 7-8 cm before aft couple. Former position at 6cm proofed to be too aft

For adjustment, prepare everything, hovercraft ready to flight. Install approximately your servo box with battery. Install windshield.

The model is now proposed with a servo box accepting two batteries. To adjust centering, you will have to choose for one or two batteries usage, there is no possible compromise. If you wish to be able to work either with one or two batteries, you will have to study a system to move servo box..

Set hovercraft on a tube (diameter around 1 cm), tube itself being installed on two returned glasses or two bricks (to have skirt far from ground). Roll hovercraft to front or back, till it will be in equilibrium on tube. Gravity centre go through tube axis.

To adjust centre of gravity, move the servo box. Once adjusted, you can glue the servo box clips to the servo box.

If you try the hovercraft with given centre of gravity, without propeller running, you will find the centering a bit aft, say, when opening the front compartment the hovercraft don't go down that easily.

Practically, with the propeller running and with skirt rubbing, it create a forward momentum which helps the front going down.

Note : With batteries in, the weight of the hovercraft is situated on the right. This will, at full power, counterbalance the couple of the propulsion propeller. This is for a right-turning propeller (the usual model)

Skirt adjustment

It is critical for good run of this hovercraft to trim front and partitions skirt.

Important notice : Distance between ground and parts of the skirt have neen increased on herebelow drawings, for ease of understanding. In reality, they are fairly lower.

Pressure P1 in front chamber is lower than pressure P2 in aft chamber. If the front of the hovercraft goes down, that close gap between ground and front skirt, and so the pressure in front chamber increase, which stabilise longitudinally the hovercraft.

Instructions for this adjustment are sent with the skirt drawings.

Servos adjustment
Compartment command :

Servos being only used (with the given radio programming) on half travel, you must position command lever in forward position (angle 30-40°) when servos are in neutral position.

>When servos are on neutral position, wire amplification levers must be positioned forward (angle around 35 °), in order to avoid contact with servo box, when they will be completely in aft position. When in aft position (command down and on the given side), the wire must be well tensioned and must firmly pull the command. It is requested to install a small spring to limit the effort on servo.

Rudder command :

The lever command must be installed perpendicularly to the command, when servo on neutral position, whatever type it is (rigid or with push/pull sheath).

Lubricate sliding points of a rigid command

Batteries coupling

Batteries will be parallel coupled and will supply commonly the two variators, because the two motors consumption may be fairly different.
Two identical batteries pack, with same wear must be used.
Current being lower for each battery than with only one battery, standard batteries plugs (Tamiya type) can be used. Though, you will choose high quality gold plated models.
A small fan similar to those which cool computers processors will be used to cool batteries during the run.

Components list

List by Pierre ROUZEAU 08 April 2002

Hovercraft model	Details	Dimensions
Prices in Euros, VAT included (19.6 % in France)			Nb	Unit price	Total price
Hull and propulsion stand materials
Plywood 8/10 mm	Plywood	600 x 200 mm	9	5.8	52.2
Plywood 10/10 mm	Plywood	600 x 200 mm	2	5.8	11.6
Plywood 15/10 mm	Plywood	600 x 200 mm	1	5.8	5.8
Rudders	Balsa	5 x 100 x 1000	1	4.5	4.5
Stick for front bottom hull skirt attach (internal) Link between rudders	Hardwood	6 x 2 x 1000	1	1.5	1.5
Reinforcement servo box cover, bottom of stand support	Hardwood	5 x 2 x 1000	1	1.5	1.5
Reinforcement aspiration fan protection panel	Hardwood	3 x 3 x 1000	1	1.5	1.5
Stick for servo support	Hardwood	8 x 8 x 1000	1	1.5	1.5
Stick for top main beams	Hardwood	12 x 6 x 1000	2	1.5	3
Back couple reinforcement + Motor stand	Hardwood	12 x 6 x 1000	1	1.5	1.5
Sticks for skis	Hardwood	6 x 6 x 1000	1	1.5	1.5
Stick for rudder attaches + fan skirt fan attach	Hardwood	10 x 5 x 1000	1	1.5	1.5
Sticks for sides	Hardwood	5 x 5 x 1000	2	1.5	3
Fan guard form reinforcement	Hardwood	10 x 2 x 1000	2	1.5	3
Round stick for servo box	Hardwood	Diam 5 x 1000	1	1.5	1.5
Round stick for propeller protection	Hardwood	Diam 6 x 1000	1	1.5	1.5
Guide tube for lines for forward skirt opening	Aluminium tube	diam 3 x 0.5 x 1000	1	1.5	1.5
Tube for motor stand reinforcment	Aluminium tube	diam 6 x 0.5 x 1000	1	2	2
Spi sail fabric (at kite supplier)	Colored	1580 x 600	1	6	6
Epoxy resin	Medium speed	200 g	1	32	32
Colloidal silica	Thixotropic agent	80 g	1
Epoxy glue in dual syringes	Fast	24 ml	2	4.5	9
Cyanoacrylate glue		5 g	1	2	2
Paint	Epoxy compatible		1	7	7
White glue for wood (rudder covering)
Plastic ball head pins	by 100	15 mm	2	1.5	3
Glass ribbon	200 g/m2	15 x 2000	1	8	8
Vynil gloves	20 pairs	set of 10 pairs	2	3	6
Throwable brushes	20	set of 4	5	2	10
Total hull and propulsion stand price					183
Miscellaneous equipment’s
Cables 2.5 mm2			1	5.8	5.8
Cables 1.5 mm2	May be replaced by above		1	5.8	5.8
Thermoretractable sheath			1	3.5	3.5
pair of golden PK plugs 4 mm2		set of 2 pairs	4	4.5	18
pair of golden PK plugs 2 mm2		set of 2 pairs	1	3.8	3.8
Weld for electric cables			1	4	4
Aluminium kwik-links rods		4 Minimum	1	3	3
Kwik-links		4 Minimum	1	4	4
Bolts + nuts, cylindrical head	minimum 6	diam 3 mm x 15	1	2	2
Bolts + nuts, conical head	minimum 12	diam 3 mm x 15	1	2	2
Screw 2mm (Variator switch fixation)			1	2	2
Fan 120 mm diameter			1	18	18
Propeller 12" x ??			1	6	6
Motor size 500 with reducer 5/1			1	50	50
Motor size 480 with reducer 4.5/1			1	43	43
Ordinary paper for rudder covering			/
Rubbers			/
Window insulation foam	self-gluing	25 mm width	/
Ordinary plywood for hull tool, 5 mm Thk	Reusable tool	500 x 1000 mm	1	9	9
Stick for hull tool	Reusable tool	10 x 15 mm x 2m	2	1.8	3.6
Miscellaneous total					184
Radio equipment of the model
Variator 25 A			1	47	47
Variator 50 A			1	55	55
Servos mini	24 g, 3 kg		3	23	69
Total radio on model					171
Useful tools
Small claws (Triplex brand or #)	by 4		1	3.5	3.5
Kwik-links removal tool			1	6	6
hot air blower			/
Clothes-peg	100		/
Radio and battery equipment
Graupner MC 12 radio TX + Receiver			1	177	177
Charger Robbe Infinity II	Luxuous		1	183	183
Battery pack 7 elements (8.4V)	Only one can be used if 3300 mAh capacity		2	53	106
					466
Big total (Euros)					1004