Construction details for the Huntwing Experience JH2611910001.
What will be needed.
1) guide to materials.
b) Bolts and nuts.
d) Fuel tanks and connections.
e) Power plant.
f) Reduction systems.
g) Other parts ie Wheels, Nacelle etc.
3) Drilling holes.
4) Where to start.
5) Crosstube construction.
6) Putting it all together.
7) When to get it inspected.
8) Dealing with the paperwork.
9) First flights.
Guide to materials.
The Experience has been designed to be built with commonly available materials and in most cases the sources are quoted in the parts list complete with expected prices. Remember when purchasing materials that all receipts should be kept and where applicable any release notes kept. These should state the actual specifications of the materials used ie HT30TF etc and will be required at inspection time for scrutiny.
All round tubing used is HT30 TF and all square tubing used in the trike is HE30 TF. It is important that the aluminium components are adequately protected from oxidation and should therefore be either anodised or etch primed and painted. Plain anodising is more than adequate for the hidden tubing within the fabric of the wing, but for improved appearance of the aircraft it may be better to anodise the visible tubing(A frames sides and bottom, Kingpost and Trike structure) with a bright dipped or colour. Only a light etch should be specified at the time that anodising is performed.
All sizes and gauges are specified in the plans and it is essential that only these are used.
Nuts and bolts.
The majority of bolts and holes are specified as 6.3mm. This is a reference to 1/4" bolts and the majority of builders will wish to use 1/4" Aircraft quality bolts (AN). These are obtainable from many sources with grip lengths increasing in 1/16" increments. They are therefore ideal for the purpose. They are however expensive from British sources and it is often better to source them from America. Most of the major Aircraft suppliers in the US will happily take a faxed order with credit card and often are faster to supply than British companies. A list of suppliers is given at the back of the constructors manual. Care must be taken, when bolting aluminium components together, that there is no thread actually inside the tubes or fittings, because any vibration in the airframe will cause the thread to file the aluminium and enlarge the hole.
Other sizes used in the plans are 8 and 10mm. The 8 mm is directly replaceable with 5/16" and these are again available as aircraft quality bolts. The 10mm hangbolt specified is a commercial bolt(specification 8.8) and is easily available from any good fasteners supplier.
Commercial HT bolts with rolled threads can be used and those specified as 6.3mm can be replaced with 6.0mm bolts. However the holes will need to be drilled to 6.0mm not 6.3 if they are to be used.
The required quality for commercial bolts is 8.8 for the metric bolts and S for any Imperial bolts.
If metric bolts are used these will normally be coarse threads and if Imperial are used these will normally have UNF threads although BSF should be satisfactory.
All bolts should be plated, either cadmium or Zinc and will require passification to avoid embrittlement. Again AN bolts are preferable as they will be supplied ready plated. When having bolts plated it is essential to ensure that the they are passified after plating.(This will be performed by the platers.)
Various forms of nuts are acceptable. In all cases some form of locking is specified and this will normally be self locking nuts, although some pin locked castle nuts are called for at joints subject to rotation.
Any of the common self locking nuts should be acceptable but the most commonly available is the Nylok nut. These are available commercially and are usually plated for protection. Other acceptable nuts are Simmonds, K-lock etc.
All washers should be either plated or stainless and a washer should always be placed under a nut. As there is always a small radius between the head and shank of a bolt it is important to slightly countersink every bolt hole slightly to accept the radius, failing this place a washer under the bolt head.
The fabric used for the mainsail of the wing is 5.5oz Terylene(Dacron) and all high stress areas are 10oz. The Undersurface and leading edge pockets are 4.5oz and the sail is locally reinforced with webbing. The sail is a ready made component for the Wing and as such the materials used are specified on Mylar templates held and updated by Hiway Hang Gliders.
The main seat harness and seat belt webbing is either 2" Polypropelene or Terylene.
The fabric of the seat should be 7 to 10oz PU proofed nylon although other man made fabrics of a similar strength and weight could be used.
If a Nacelle is fitted the side skirts should be constructed of similar material to the seat.
Construction of the seat.
The seat consists of a tubular frame with a webbing and material support attached to it. A removable material and foam seat is velcroed to this and this can be removed and kept dry. The Webbing frame also contains 4 pieces of plywood which support the foam seat, allow a comfortable back rest to be formed for single seat operation and prevent the pylon from coming down to far during dismantling.
The seat is extremely comfortable in both one and two seat operation.
Drawings of the webbing support are supplied on 26-10.
First cut out enough nylon material to form a long bag 220mm wide and 1125mm long. Allow plenty of material for turning over and on one long edge enough material to fold over and form a velcroed seam.
The webbing is only attached to the rear of the material and so this must be sewn on before closing the bag.The Velcro used to attach the seat must also be applied before closing the bag. The cross webbing should be cut and sewn as a tight fit on the frame. The buckles at the top allow the seat to be altered and tightened for single or two seat operation.
1/4" plywood supports should be cut to a tight fit in each of the 4 compartments. For single seat the upper seat should be turned inside out and the top of the nylon and plywood support placed under the seat frame tube upper. The buckles can then be tightened to prevent the seat back collapsing backwards.
The bottom of the cross webbings should be pulled up the frame to a distance of 180mm from the centre of the hinge joint. This position can be maintained, if required, by a 180mm length of 1.25" oversleeve on the seat frame upper replacing the washers under the hinge attachment.
The detachable foam filled part of the seat is left to the individual, but a suitable, and comfortable, component is available from Hiway and will give a very good finished appearance to the aircraft.
Fuel tank and connections.
Deciding on the type of fuel tank or tanks and their positioning has been one of the harder parts of the design of this aircraft. Many options are available to the builder varying from the total fabrication of a tank from Aluminium or Steel sheet to the purchase of ready made tanks supplied for the purpose.
When choosing the type of tanks to be used consideration should be given to the type of flying that is anticipated and the availability of fuel at the sites that the aircraft will be flown from and to.
If all flying will be performed from an airfield and it is unlikely that out landings at unknown fields will occur, then a fixed single tank can be used, but if there is a possibility that out landings will occur then consideration should be given to portable removable tanks. In particular if you anticipate competition in any of the long rallies removable tanks are a must.
On the prototype I have compromised by using two tanks, one removable and transportable and one fixed. As the engine is inverted I have used an over engine commercially produced 25L Raven tank, streamlined shape, complete with drip tray. These types of tank can either be purchased new from the manufacturers or occasionally can be found secondhand.
The removable tank is a commercially available outboard engine tank constructed of thick polypropelene and easily available from any outboard engine stores. This tank contains 22L, has a built in fuel gauge in the filler cap and is manufactured by CAN. It has a concave ridge, which helps locate the tank, on the underside and by mounting the tank well forward on the trike keel tube, facing crossways and directly behind the front seat back, it is possible to fold the trike down to a point where the wing can be removed without removing the tank. The wooden seat supports within the seat support material acts as a stop and prevents the trike from crushing the tank. An alternative to this tank would be a commercially produced underseat tank such as the Raven long distance tank but the cost of purchasing these would be extremely high as a percentage of the total cost of the aircraft.
To a great extent I have left the fine details of the fuel system to the individual builder but it must be remembered that there are a considerable number of specific requirements in Section S regarding the fuel tank and connections and the Senior inspector will need to be quite certain that all of these are fulfilled.
Summary of fuel tank requirements.
1) Max capacity of tanks 50L.
2) Tank must be capable of withstanding a minimum pressure of 1.5PSI and 9g forward.
3) No more than one tank to be drained by one pump at the same time.
4) There must be a drip tray under any tank fitted over the engine and engine fires should be unable to impinge on the tank.
5) A fuel tap with positive detents and an off position must be fitted.
6) Fire resistant fuel hose must be used at least within 18" of the engine.
7) The tank should be capable of being drained down to less than 5% of the stated volume and still run at all possible flight and take off angles of attack.
8) The tank must be mounted to withstand 9g forward, 3g sideways, 4.5g downwards and 4.5 g upwards.(Full weights)
9) The fuel system must be able to supply 150% of the take off fuel consumption for any gravity fed systems and 125% for the pumped systems.
The constructor will almost certainly need to consult BCAR section S if any derivation from the prototype is used and the relevant sections are S951 to S995.
The requirements of S561 also apply.
The fittings for the underseat tank consist of a Glass reinforced tray that was moulded using the bottom of the tank. PTFE mould release liquid was applied to the tanks base before the resin and 3 layers of 2 oz glass were used. A webbing strap with attachment buckle is used to hold the tank to the moulding and the moulding is attached to the trike keel by a 5mm bolt at the front and rear. The tray also has a 1.5" moulded wedge incorporated into it which hold the tank high at the front and allows the maximum amount of fuel to be drained from the tank. The tank is further restrained from forward movement by a second webbing strap which is bolted to the trike keel. This tank is easily removed by dropping one side of the sideskirt, releasing the sideways webbing strap and pulling out sideways. The fuel pipe is attached by a quick release bayonet fitting (Outboard style).
The upper tank is mounted in the same manner as on the Raven.
Which power plant.
The original Huntwing built before 1984 was powered by a Robin 440. This was highly reliable, obtained a noise certificate and flew a considerable distance, including one return trip to France. This engine is now on the first Section S machine having been replaced by a Rotax 462 on the original.
Basically the power plant needs to be capable of producing between 45 and 60HP at a weight not exceeding 50Kgs.
The Rotax 462 LC is a really good engine for the purpose and certainly allow a faster, quieter and more fuel efficient aircraft. It is also a more available engine than the Robin and spares are considerably cheaper. The Rotax 447 and 503 are also suitable, but the extra power of the 503 is preferable. The Rotax 582 should also be a good power plant although it may be a little heavy.
Whilst the engine mounts, shown in the plans, are for the Robin 440, they can be used to mount the other engines by slight alteration of the mounting plate. Of course the engine is shown mounted inverted and the manufacturers instructions must be followed when inverting the water cooled engine to ensure that the cooling systems get no air locks. It is also advisable to fit a water temperature gauge to the cylinder head.
The Rotax 532 could be used but has rather a checkered history and is likely to be phased out shortly.
It should be remembered that the Robin 440PM is the only variant with a Noise certificate that is current legal. The 462 whilst legal for a pre 86 machine was 0.2dB over the current 2 seat requirement and would therefore require re noise testing.
The addition of a intake silencer has almost certainly removed that 0.2dB and achieving the required 80dB should be easy.
The other engines will also require noise testing and some thought would need to be given to this when choosing an engine.
The fact that a noise test is required for these however should not preclude their use and I would be more than happy to help sort this out.
Other engines worthy of consideration would be the Hirst range, the Arrow range, the Hewland, Norton Wankel, and possibly the twin carb Rotax 512 four stroke.
For the really adventurous there could be some mileage in looking at both the BMW and Motoguzzi 4 stroke bike engines which can be picked up at a reasonable cost from Bike breakers.
This would require a lot of careful forethought however and is probably better left as a secondary project.
A Sharp reduction unit has been used on the Robin engine and these are often available with secondhand engines, as are the Nicklow units. Both of these are toothbelt reduction systems that were in common use.
Both of these reduction units suffered from the use of low quality shafts and before use it is essential that these are replaced with EN 24 material. In the case of the Sharp reduction I would recommend that the dimension of the shaft are increased so that the shaft diameter at the propeller end plummer block is 1 1/4" and the seal area of the shaft is 1 3/8". I would also suggest that the shaft is made straight, not eccentric, and that the belt is tensioned with shims under the plummer blocks.
In order to comply with the noise certificate as used on the original aircraft a reduction of 2.78 and a Nicklow type 60 x 36 prop is used. It is however likely that builders will use other reductions and propellers and will therefore require a further noise test. Before deviating from the standard a call to Tech office or myself would be appropriate as noise testing can be an expensive and time consuming exercise if the wrong combination is used. Other makes of seconhand reduction such as the Mainair system and Ultrasports should be quite suitable but again a phone call would be prudent.
On the Rotax engines the easiest option is either of the available gearboxes. For the 462LC the B type box is compatible with the 62 x 44 Newton prop and gives a very good performance.
All other parts are specified in the plans but in many cases may be exchanged for similar of adequate strength.
For example the wheels used and recommended are readily available but in some cases builders may have a preference to use Nylite wheels or their Aluminium equivalent. Before embarking on the use of an alternative it would be prudent to discuss their use with the designer or BMMA technical office and in many cases this will be deemed acceptable.
Whilst the design does not call for a Nacelle (Pod) to be fitted, the final aircraft will be much more pleasant, both visually and in terms of comfort, if one is fitted.
No particular pod is recommended but the basic Minimum and Maximum sizes and weights recommended are as follows.
Maximum Width 26" Maximum weight 14 lbs
Minimum width 23"(must be able to accept folded seat width. Minimum weight not relevant.
This will allow a variety of sources to be utilised and covers the spacious Mainair Alpha type down to the Pegasus Xl type.
Suggested sources are.
a) The local flying field where it is common to find apparently badly damaged pods that have been replaced. These are easily repaired with Glass and styrene. However to ensure that cracks do not reappear it is important to grind out all cracks and sandwich them between at least 2 layers of Glass cloth.
Filled and carefully sanded the pod can be resprayed either commercially or at home and often look better than the original.
b) The back pages of Flightline or Popular flying. There are several manufacturers with Pod moulds advertising but often the price and finish need scrutiny. Some have a less than perfect finish and the price of having it sprayed may take the cost over that of a decent commercial pod.
c) It is possible to make a mould but the time and effort for a "one off" aircraft is unlikely to be worthwhile. However as a group it may be practical.
Rear wheel spats and possibly a front wheel spat are also recommended within the Max and specifications given and all of the previous suggestions apply.
Fuel filters come in a range of types but steer clear of the paper element type which have often caused problems with fuel flow and can tend to be unpredictable. The best appear to be the nylon filter type as supplied by Cyclone hovercraft and have the advantage that they can be backflushed and cleaned.
Engine ignition switches are also a source of problem and it is essential that at least 250V and fairly high amperage(ie 3 amps) is used.(12 volt car type are unsuitable). A metal lever is essential for the switch.
Steel work and Welding
Good commercial grade gas fusion welding or TIG is acceptable for all welded parts used in the construction.
All welded joints will require normalizing a Obviously the quality of the welding will be carefully inspected by the responsible inspector.
All steel work will require adequate protection and ideally this will be Zinc plated and passified. However a good quality primer and paint is acceptable.
Plastic coating(Powder coating) is unacceptable because it hides any cracks or defects from inspection and under no circumstances should it be used.
If a pillar drill is available this can be used to ensure that all holes drilled in tubing are square. If the pillar drill is to be used for drilling round tubing, a V block or equivalent will be required and it is essential that all holes are at the correct angle to one another. In many cases this will mean that the holes are either in line or at 90 degrees to each other. For this reason, on long tubes it is worth drawing a datum line using a length of appropriate channel and a fine felt tip pen(Do not use a scriber to mark components.). It is worth, therefore, investing in 4 or 5 metre length of 11/8" channel (Aluminium) for that purpose.
If only a normal pistol drill is used it is worthwhile producing a series of carefully cut and square drilled oversleeves for all the tube required and using these to mark both sides of the tube.
It should be possible to get any engineering firm to cut and drill a series of these tubes (again Aluminium) but these should only be used to mark the holes and not for use as a drilling guide.
Before drilling the tubes proper, spend some time practising on any short lengths of scrap and ensure that the guides are square and central by marking the tube using the oversleeves and then rotating the oversleeves and checking that the holes still line up.
When using this system always pilot the holes with 1/8" drill first, from both sides, and check the position and accuracy before enlarging the hole size.
The square tubing is extremely easy to drill accurately and squarely by careful measurement and the use of a set square the position of the require hole can be marked on both sides.Again when using a pistol drill the hole should be drilled from both sides.
Where to start.
The first task to be undertaken by the constructor is the sourcing of parts and materials for the machine. The majority of possible sources for each component is listed in the parts list but the constructor will need to decide from the start how much of the construction will be performed by him and what parts will be purchased complete.
Whilst many constructors will wish to make every last part(at a considerable cost saving) others will wish to have the steel parts and welding performed for them.
One part that will require purchase is the Sail. This is because the tolerances required necessitate the use of full size Mylar plans which cost several hundred pounds to produce. These plans are not easy to work from and the normal facilities available to the homebuilder are unlikely to include the use of a sail loft and industrial sewing machines. It is also suggested that the seat, seat belts and associated fabric is purchased ready made which allows a far better finish to be achieved and this will reflect in the value of the aircraft. Details are included of the basic seat and belts.
Whether the constructor starts with the Wing or the Trike is personal preference. It is a good idea to start with all the brackets, plates, and channels for both as these can be sent off for anodising and plating which can take several weeks. Normally the tubing will be anodised before work starts on the construction.
Construction is extremely simple and a basic scheme is
Leading edges, Cross tubes, Keel, A frame and Kingpost components.
To assemble wing.
Bolt all of main frame together minus sail. Leave the lower and upper side wires free of the cross tube ends. Do not attach lower fore and aft wires to the Keel only to the A frame bottom. Do not fit any upper wires. Do not attach A frame bottom and tie the A frame side to each other so that they are parallel and not opened out.
Prepare the frame on a clean surface, A frame up and with the leading edges pulled only slightly out from the folded position (ends about 9" apart.)
To prepare the sail the leading edge foam inserts must be pulled into the sail pockets provided. This is done by firstly pushing a length of batten tube into the upper surface pocket and then pulling a length of nylon cord through using the tube. This should be attached to the foam and then with one helper pulling at the back and the other feeding the foam from the front it is inserted into the sail one side at a time. The foam is inserted until the fronts are just touching.
Open the long zip on the undersurface of the sail and lie the sail on a clean surface with the ends of the leading edges about 1 ft apart and the undersurface uppermost.
Now push the frame through the zipped pocket making sure that the correct leading edge tube goes down the correct leading edge pocket.
NOTE the tubes do not go down the foam pocket but into the large pocket between upper and lower surface.
As the tubes are pushed into the sail the keel tube and fin tube must be fed out of the V slit at the back of the undersurface and into the Keel pocket. The Kingpost should be pushed through the appropriate hole.
The upper and lower side wires must now be fed through the eyelets and attached to the end of the crosstube as shown in the plans. The front and rear upper rigging can now be attached with the front rigging passing through the slit in the sail.
The lower rigging is now attached at the rear of the keel and the zip at the front can be done up and the velcro cover secured.
Roll the wing over and attach the fore and aft top rigging wires. The self tapping screws can now be inserted at the front of the leading edges to secure the sail forwards.. Erect the kingpost and push the front nose batten into place from the front of the wing.
Using a length of suitable cord (3 or 4mm nylon will suffice) tie a loop into the webbing at the end of the leading edge of the sail and pull it outwards so as to be able to insert the sail retaining bolt into the leading edge end. As this will be particularly tight with a new sail it may be necessary to use length of 1" tubing as a lever against the end of the leading edge. Repeat this operation on the opposite leading edge.
Now gently open the wing outwards with one person on the nose and one on either wing tip.
Once the wing is half open all the upper surface battens are inserted and the tip struts. Once the wing has been opened as far as possible, the pullback wires should be hauled rearward and the shaped tang placed over the retention bolt.
The end of the fin should be pulled out tight and the self tapper placed to secure it. It is highly recommended that 2 nylon and foam protective padding squares are sewn up and attached by velcro or bungee, so as to cover the crosstube to leading edge join. This will prevent chaffing of the sail during transport.
Details for crosstube inner alignment.
Two methods can be used to cut and drill the crosstube inner.
The first method makes use of a paper template and the second relies on the tube being cut carefully to 10 degrees.
1) Cut out the template (Page 15-07 spare supplied.) carefully and roll around one end of the crosstube. Mark both the 10 degree cut and the hole positions. Note that the crosstubes are "Handed" and that the holes on one side are 8mm below the lowest point of the cut and the opposite side is 8mm above the lowest point.
Carefully cut the end of the tube and drill, initially with a pilot hole.
2) The second method relies on carefully cutting the tube end to 10 degrees using a suitable mitre tool or cutoff saw. Mark the lowest point and measure 8mm above that for one side and 8mm below for the other. Drill the appropriate holes as shown
The fit of the crosstube inners should be carefully checked.
Assemble the airframe inverted (minus the upper rigging and kingpost) and prop up either end of the keel so that the crosstube can drop down at the centre to the full extent allowed by the retaining strap. Leave all the fastenings at the centre relatively slack so that some movement can be achieved. Load the structure lightly by attaching a suitable rope from one end of the leading edge to the other and tensioning sufficiently to bow the leading edges inward several inches. This will ensure that the crosstube centres and the pullback wire is loaded adequately.
It should be possible, by gentle twisting of the crosstube, to align the centre channels parallel to the keel whilst ensuring a good fit all around the centre join. Whilst it is important that the upper surfaces ( which will be underneath with the wing inverted) mate together it is permissible to allow a small gap on the underside of the join. This gap will enlarge slightly when the crosstube is allowed to sit on the keel. Small adjustments by filing may be required if the join is not good. Once a good fit has been achieved the Tube outer end spigot can be secured by drilling and pop riveting in place. This will normally require 2 pairs of hands , one to hold the tubing in situ and one to drill the holes. Finally tighten W0015008 and when the frame has been folded down the eyebolts W0015001 should be tightened.
These instructions replace all previous instructions on inner crosstube alignment.
Date 13 2 94.
Order power plant and propeller.
Pylon,keel, axles, front tubes, bracing tubes.
Seat frame. Cold formed using correct forming tools in "Hilmor type bender".
Put seat together.
Assemble the main frame minus engine and engine.
If a nacelle is being used fit at this point and side skirts.
Fit Seat belts.
Fit any underseat tank attachments.
Fit the engine frame to the trike.
Fit mounting plates to engine with "Lord Mounts".
Fit engine to trike.
Fit any upper tank and fittings.
Fit upper wire bracing.Fit exhaust and propeller .
Wire in all electrics and instrumentation.
Connect fuel tanks and fittings.
Getting the aircraft inspected.
The BMAA has established a number of Senior inspectors around the country who will be responsible for stage inspections on new homebuilt aircraft. The BMAA Chief inspector should be consulted for advise on who is the most appropriate Senior inspector.This should be established before starting the project because the Senior inspector will need to discuss the project before commencement
Whilst the actual number and time of inspections has not been finally decided with the BMAA, as ye. It is likely that only a couple of inspections will be required due to the ease with which a flexwing can be inspected. It is probable that an inspection of the proposed working area will be required initially
Stage 1:(Wing) Inspect all parts before fitting the sail. This will involve carefully checking that all the required sleeving has been carefully installed. That the general workmanship is good, that holes are drilled square, that adequate protection has been used to prevent damage to the materials(anodising etc). That the correct bolts have been used and that there is no squashing of the tubes due to the incorrect bolts being overtightened. Check wires have been correctly crimped. Check that centre of crosstubes is correctly butted together when lifted into flying position. Check frame for symmetry.
Stage 1:(Trike) Inspect all parts before the fitting of any Nacelle and side skirts. Check all receipts and details of materials that have been used in the construction. Check that the correct sleeving has been installed. Check bolts,welding and wires.
Stage 2:(Wing) Check that sail is fitted correctly. Check centre of crosstubes. Check all bolts are correctly tightened. Check battens against the batten template. Assemble wing and check that the sail fits correctly around the tips. The sail should show no signs of strain at any point and should have a smooth upper surface. Some small creases will be evident in the lower surface but these will smooth out when the sail is loaded in flight.
Stage 2:(Trike) Ensure that all bolts are correctly tightened. Check all aspects of the fuel system including that fuel flow is adequate. Check the throttle and choke cables. Check the ignition switch both for accessibility and function.
Dealing with the paperwork.
This can be divided into several headings.
a) Registration. This is the easiest piece of paperwork and involves phoning the CAA registration department on 071 379 7311 and requesting that an application form for registration is sent. Fill this in enclosing the fee requested and return. When completing the designation of the aircraft is Huntwing/Hunt Avon Trike.The serial no for the aircraft is written on the front of the individual plans and should only be quoted for one aircraft. If you want a specific, out of sequence registration number this can be arranged but will cost considerably more.
b) The BMAA will require that the project is registered with them and this will probably be subject to a registration fee of around £25. This will cover both the cost of paperwork associated with the project and some return on the initial work put in on the machine by Technical office. The project will be issued with a serial number and an inspection booklet will be issued for that project. This will be filled in and signed by the Senior inspector for the project at the appropriate stages.A copy of the MAAN current for the Huntwing will also be sent to the builder and this will be the final document that the Senior inspector will need to sign against for issue of the Flight test permit.
c) If the Aircraft is fitted with an engine and propeller which has already been Noise tested a certificate should be obtained from the Safety regulation group of the CAA at Aviation house, South area, airport, Gatwick.(Quote the certificate no 92M. If the Variant built does not have a Noise certificate then an application will need to be made for a temporary permit to be provided for test flying and noise test. Contact the technical office for details.
d) Once the aircraft is nearing completion paperwork signed off by the inspector(confirming that the aircraft conforms to the current Airworthiness notice(MAAN) for that aircraft) will be sent off to Technical office or CAA. Any changes from this will need to be documented and some contact with the Tech office will be necessary so as to ascertain the degree of extra paperwork required. Of course any extra work will almost certainly be subject to a fee from the technical office staff.
A permit to test should now be sent back from the CAA and it is likely that there will be a short period of test flying required (probably 6 hrs).A final request and the required fee is now sent to the CAA and the full permit should be returned.