AK1-3 Helicopter

Silver AK1-3 helicopter flying against blue sky with white clouds.

Burgandy AK1-3 helicopter with cover mounted on small trailer with roters removed.

Helicopter flying over a field with yellow flowers.

AK1-3 helicopter spraying field.

The Amazing AK1-3 Helicopter

is a lightweight helicopter that has been designed and built for a wide range of practical purposes including:

· Surveillance, monitoring of borders, facilities and territories;
· search missions;
· geological exploration, aerial photography;
· pilot training;
· aerial spraying (crops);
· business and pleasure flights;
· aerial sports competitions.

The AK1-3 helicopter conforms to International Airworthiness Regulations (FAR, Part 27) for normal category rotorcraft and international noise abatement regulations. The AK1-3 is certified under The State Administration of Ukraine for Aviation Safety Oversight and bears a Type Certificate Number ТП 0008.

When empty, the helicopter weighs 390 kg. This allows it to be transportable by a small trailer attached to a car. The trailer serves as a mobile landing strip for the helicopter.

The AK1-3 Helicopter is designed according to the one-airscrew scheme with the rudder airscrew consisting of skid-equipped landing gear, a tubular chassis, power-plant, main reducer, main rotor and braced tail beam with a rudder reducer and plumage and a power floor on which the cabin is installed. The cabin is made of composite materials.

The cabin of the helicopter provides free accommodation for two members of the crew. The width of the cabin at shoulder level is 1200 mm (at helicopter R.22 - 1055 mm).

The large windows provide good visibility in all directions. The pilot seats are adjustable on the ground and are equipped with waistband and humeral seat belts.

The pilotage-navigating equipment of the helicopter allows for daytime flights in simple meteorological conditions according to the rules of visual flights. At the request of the customer, the system of onboard navigation GPS can be installed. The system of onboard registration of parameters of flight is in a stage of development.

The airscrew consists of three blades with elastic fastening blades. The blades are made of composite materials with a nonlinear construction.

The rudder airscrew consists of two blades with one general horizontal hinge. Blades of the rudder airscrew are made from composite materials.

In the helicopter, the power-plant on the basis of the piston internal-combustion engine with liquid cooling ЕJ-25 "Subaru" is installed. The engine uses automobile gasoline with fuel performance number 95.

Power from the engine is transmitted through a belt drive with overrunning clutch to a power shaft of the main reducer.

Cabin

The cabin is very spacious and comfortable for two large persons and at 1,353 mm wide you don't rub elbows, even when wearing bulky clothing. By comparison, the Robinson and Rotorway cabins are only 1,100 mm wide.

The composite cabin floor together with its lower triangulated aluminum sub-frame are the main structural elements. The floor is made of a 16mm plywood with machined out pockets so as to leave a light wooden grid. This wooden grid matches all the required attachment points for the sub-frame and other control attachment points. All the machined out pockets are filled with foam inserts. then a skin of composite material is applied to both sides resulting in a very light and rigged floor structure. The lower Duralumin frame is constructed of riveted together CNC machined elements which are attached to the rest of the airframe.

The seat frames are made from Titanium tubing, have a riveted aluminum sheet base to which the cushion material is fastened, then covered in leather. Each seat is equipped with a 4-point safety harness, the shoulder harness being anchored to the floor/sub-frame at the rear of each seat. There is a leather bag with approximately 10 L of volume located under the passenger seat for small items. A small fire extinguisher is located under the pilot seat.

The upper body of the rounded shaped cabin is made from composite material with four separate tinted polycarbonate windscreens bonded into place, thus forming one single light ridged structure.

The lower belly-panel, also made from composite material, is held in place with screws, thus allowing access to control linkages, the lightweight "Red-Top" racing battery and electrical wiring loom.

The composite door frames are bonded to the tinted polycarbonate windows and a rubber extrusion fitted around its inner edge. Each door is fixed with two hinges up front and closed with a simple latch at the rear. The doors can be easily removed if required. The VNE is limited to 150 kmh (80 knots) with doors off at sea level.

The instrument pedestal is constructed of riveted aluminum sheeting and the three separate front panels cascade down at varying angles to better match the pilots view. The pedestal also houses the cabin heating system with its plumbed hot water from the engine, small radiator and electric fan and its temperature controls.

The smaller factory-standard top panel is replaced with a wider panel for South African models.

The top panel houses a 9 warning light cluster, an LED rotor and engine RPM gauge, a 120 knot Airspeed indicator, a 2000 ft/min vertical speed indicator, a 20,000 ft sensitive altimeter with milbar subscale, an LED main rotor blade pitch gauge, the Enigma Stratomaster glass display and the Garmin GTX327 mode C transponder.

The Enigma Stratomaster is a truly amazing instrument and was developed and manufactured in Cape Town by MGL Avionics. The Enigma is fed information from an attitude sensor, Magnetometer, pitto tube, GPS antennae and the Remote Data Acquisition Computer or RDAC. The RDAC in turn is connected to engine sensors independent from those signaling the 9 warning light cluster. These sensors include oil pressure, oil and water temperature, manifold pressure, four Exhaust Gas Temperature probes (EGT's), fuel flow, rotor and engine rpm. There are many additional ports where if one wishes, you can add additional sensors. The Enigma also has an altitude encoder and provides information to the Garmin transponder.

The Enigma provides the following instruments and information type: Full VFR flight instruments as back up, an artificial horizon, full GPS moving map functions, highway in the sky (HITS) navigation, forward looking 3D terrain and airport views, horizontal situation indicator (HSI), terrain awareness and warning system, wind speed and direction components plus a complete engine monitoring system with a user choice of alarms including voice warnings to prompt the pilot if a parameter reaches a user programmable limit. This in brief is a summary of its main functions, but to learn more and try out the Enigma simulator visit www.mglavionics.co.za

The center panel houses a fuel gauge, water temperature gauge, MRG temperature gauge, the Micro air radio/com, the master, ignition and clutch switches and the cabin heat controls.

The bottom panel houses the electrical fuses and switches for MGL system Landing light, Navigation and instrument lights, Radiator fans, Rotor speed warning and governor system.

The Hobbs meter is fitted on the left side of the pedestal.

Engine

The AK1-3 is powered by the proven and extremely reliable Subaru EJ 25 motorcar engine.

The Subaru engines (all brand new units) use the mechanical / cable throttle control system, instead of the "electronic fly- by-wire" throttle control. The engine is a water cooled flat four cylinder, (Boxer) with fuel injection, single overhead camshaft, four valves per cylinder and solid state electronic ignition and duel fuel pumps. The engine's bore to stroke dimensions are over-square at 99.5 mm by 81 mm. This over-square characteristic typically allows engines to operate at higher rpm more easily without overstressing, and also enables the use of larger inlet and exhaust valves, thus allowing easier engine breathing at higher rpm. The engine is very smooth indeed at all engine speeds. The engine automatically adjusts the fuel mixture for varying altitudes, so there is no mixture adjustment required by the pilot. The Yanvar Engine Control Unit is a programmable ECU and is programmed to match helicopter requirements.

Helicopter Engine

The large and heavy "Varta" battery in the first machines has been replaced by an English made "Red Top" racing battery. This new battery is half the size, lighter and has been repositioned from the right hand side of the airframe, to under the cabin floor, just below the instrument console.

In the AK1-3 with the rotors turning at 565 rpm (105.5% - top of green band), the engine turns at 5,600 rpm so as to have full power available when lifting off or landing. Bottom of green band equals 5,000 rpm and level flight cruise with governor set to middle of green (100%) equates to 5,300 rpm. The Engine redline is 6,200 rpm.

In the early years of flight, big bore slower turning motors were developed for propeller aircraft to avoid having a reduction gearbox between it and the propeller, to prevent the tips of the propellers exceeding the speed of sound. Also, electronics were not too reliable then either and it was prudent to have a back up (ie with twin magnetos). This in essence is the crop of traditional certified aircraft engines still manufactured and available today and they still all run on leaded Avgas fuel developed during the Second World War. These engines tend to be costly due to low volume production and with frequent technological advancements of the type-certified design impeded due to the crippling costs of re-certification each time major changes are done.

But we have moved on somewhat since the war, with motorcar and motorcycle engine technology surpassing the traditional aircraft engine by leaps and bounds in terms of performance per displacement and excellent high production volume cost efficiencies, reducing purchase and operating costs, whilst continually improving reliability.

For helicopters the operating speed of the motor is irrelevant, as it must be geared down to turn the relatively slow turning main rotors. Therefore higher spinning motors are no problem. Some helicopter turbine engines spin at 60,000 rpm. High speed petrol engines are slow by comparison.

Some folks will baulk at the idea of a single ignition system on an aircraft engine as magnetos do sometimes fail. However cars moved away from magneto ignition (50 to 60 years ago?) in favor of points and distributor, then finally to present day electronic ignition systems with no moving parts to wear out thus improving reliability and reducing costs.

Each set of spark plugs on the Subaru has its own ignition coil and the entire electronic ignition system is totally waterproof. I flew twice in rain (With HT ignition coils totally exposed to water, before they later installed the engine shroud) and their test pilots had flown several hundred hours, including in rain and snow without missing a beat. I did a little research myself by speaking to the two senior Subaru mechanics and asked them how often they had encountered an ignition failure or a catastrophic mechanical failure on any model Subaru car in the six years that the Bellville/Cape Town workshop has been opened. Their response? Not even once.

When last did you experience ignition failure in a car made in 1995 or later, or know of someone else who has experienced this problem? Don't confuse car alarm systems shutting the car off, as the AK1-3 does not have a burglar alarm!

I am no agent for Subaru, although I did discover it and purchased a 2.5 Subaru Forrester 18 months before I knew that the AK1-3 even existed, but to those who have never driven in a Subaru, be brave, forget status and test drive one to experience the motor! (The car by the way is also very nice to drive!)

All modern car engine designs undergo a 500 hour test at full throttle (100% power) after which the engine is dismantled and inspected. After such a test there should be minimal wear to any of the engine components.

Besides being an excellent engine (Subaru is the most popular motorcar engine used in experimental / amateur built / kit aircraft world wide) it is inexpensive to service or overhaul, as one is charged "car" instead of "aircraft" prices.

Another advantage is the substantially lower cost of petrol compared to Avgas (Approx. 30% cheaper) plus the big convenience of having it available almost every where. And being unleaded, it is also kinder to the environment.

Through experience I have found that operating on Avgas somewhat diminishes the flexibility and go anywhere advantage of a helicopter, as Avgas is usually only available from larger airfields or airports. Of course one can organize a ground crew to road-haul drums of fuel to where you want to fly, but what a schlep!

On the AK1-3 engine, the standard inlet manifold is rotated 180° so that the air filter faces rearwards. A new lightweight alternator is repositioned off center and fits in a specially made adjustable bracket. The exhaust system and silencer is manufactured by Aerokopter. The positioning of the engine on the AK1-3 makes it the easiest engine to service of any helicopter.

Power transmission system

Engine power transmission uses the traditional and proven design, consisting of primary engine speed reduction via pulleys and V-belts, driving a secondary reduction Main Rotor Gearbox (MRG) on one side and shaft drive to Tail Rotor Gearbox (TRG) on the other.

Engine power is transmitted inline with the crankshaft via a rubber flex-coupling to the primary reduction drive unit's bottom six V-belt pulley. The V-belt pulley reduction drive unit is made up of two machined Duralumin side frames held apart by a central box rib spacer. Between these side frames are the small bottom and larger top aluminum drive pulleys. Each pulley is bolted to a steel shaft and is supported by large sealed bearings on each side. Each reduction drive bearing sits in a steel bearing holder which is bolted to each side frame. The upper pulley has the Sprague clutch (free-wheeling unit) incorporated into it. The steel Sprague clutch is connected to the splined MRG pinion shaft and supported by a large sealed bearing in its steel sleeve at the rear. The 40 mm diameter steel pinion gear shaft is supported by two large tapered roller bearings, lubricated with MRG oil. These two tapered roller bearings fit into steel housing, and this housing is in turn bolted to the CNC machined MRG housing. The sealed bearings in the reduction drive unit have a tela-temp to check bearing conditions in pre-flight. The poly-V-pulleys drive six Kevlar reinforced V-belts and the top end of the reduction drive unit is covered with a composite shroud on each side to keep the rain water off and fingers out.

Power transmission system.

When starting the helicopter engine, the rotors have to be disengaged, so the six un-tensioned V-belts are used as a clutch on start up. After the engine has started, the clutch switch mounted on the instrument panel is switched to "engage", The amber clutch light will indicate that the clutch is engaging, slowly tensing the six V-belts using an electric actuator. The V-belt tensioning is via a rocker arm and idler pulley assembly pushing the v-belts towards the center. Tensioning the V-belts in this manner increases the "wrap angle" around the drive pulleys thus ensuring no slippage with less belt tension. The belt tensioning is pre set using a built-in compression spring and takes less than one minute for the clutch light to extinguish indicating the clutch is fully engaged.

At the rear end of the MRG pinion gear shaft is a flex-plate coupling that connects to the front of the tail rotor drive shaft, with another flex-plate coupling connecting to the tail rotor gearbox at the rear. The tail rotor gearbox is constructed from a machined Duralumin casing and two steel housings attached at 90° housing the bearings. There is a hardened spiral- bevel gear set with a large oil sight-glass at rear. There is no chip detector, but a tela-temp is fitted.

The AK1-3 is designed for use in two configurations, namely as a two person craft, where the maximum gross weight is 650 kg due to center-of-gravity limitations, and also as a future crop-spraying craft. The MRG is designed to operate continuously at the engine's maximum output of 156 hp and at an all up weight of 740kg for the crop-spraying configuration. (The crop-spraying system will only be available later.) The large MRG casing is machined from solid billet and has a protrusion machined on the rear to house the pinion gear assembly within its steel housing. The CNC machined and internally ribbed top casing houses the larger taper-roller thrust bearing, whilst the bottom externally ribbed casing supports the smaller taper-roller bearing that holds the main rotor shaft. The large 280 mm diameter spiral-beveled ring-gear and matching pinion-gear are both hardened.

A steel gear journal bolts to the inside of the ring-gear and is fastened to the main rotor shaft on a 64 mm diameter splined section to transfer the torque. A 10mm section of the main rotor mast above where the ring gear is attached protrudes 78 mm in diameter and this protrusion is what carries the helicopter weight via the large thrust bearing. All the parts I examined looked more than capable of handling several times greater than the mere 740 kg gross weight of the aircraft. The MRG has no chip detector, but has a magnetic plug, a large oil sight-glass and a temperature sensor. I can say that the gearboxs both run cool, as after a 30 minute hovering session in the factory yard with two on board, the operating temperature was approximately 60 to 70°C and the TRG was only luke-warm. It was however a cold day with the outside air temperature at 14°C.

Rotor system

The rotor head design used on the AK1-3 is unusual and unique for such a light helicopter. The technical name is a "Laminated Blade Retention System" also sometimes called a laminated torsion bar system. This system is currently used on both the American Apache-Longbow and the Russian Black-Shark attack helicopters. It is also used on some Hughes helicopter models. The main rotor has three composite blades rotating clockwise, whilst the tail rotor has two composite blades. The main rotor blades operating speed range markings are 460 rpm = red range low rpm limit, 465 to 505 = lower cautionary range, 505 and 565 rpm = green band, 570 to 595 rpm = upper caution band and 600 rpm = red range high rpm limit.

helicopter rotors

The Laminated torsion bars (Lam-TB's) are each made from a stack of sixteen Y-shaped steel plates. These lam-TB's are very flexible up and down, twist easily and replace the more conventional, but bulky and heavy lead-lag, flapping and feathering hinges commonly used. The best comparison I can think of is a stack of engine feeler gauges that also bend and twist easily.

The rotor blades are mounted with a slight rearward lag angle relative to the rotor mast center. The precise angle has been calculated to try to neutralise the effects of drag and centrifugal force, so that both arms of the "Y" remain under similar tension. For rotor blade pitch control, a composite torque-tube is placed over the Lam-TB's, fixed to the steel blade grip on the blade side and has a central pivoting bearing on the rotor hub side to allow for blade feathering and flapping. On the outside section of the torque tube nearest the hub is a machined Duralumin "ear" that the pitch-links connect to. There are four large inspection holes at the front and back of each torque tube to allow easy inspection of the LamTB's during pre-flights. The LamTB' are non-serviceable items and replaced "on-condition". The replacement of these torsion bars does not appear to be very difficult to perform. The major advantages are mechanical simplicity, massive weight savings, ease of inspection and no service maintenance. The tail rotor torsion bar is replaced at the helicopter's design service life of 2000 hours.

The tail rotor hub

1) Body 2) Socket 3) Fork 4) Hub 5) Fork Nut 6) Damper 7) Laminated Tension Rod 8) Torsion Bar Bushes 9) Fork Washer 10) Fork bearings 11) Bushes 12) Nut & Washer

Rotor blades

The composite main rotor blades have a non-linear -9.5° twist and a variable profile NACA 63012 / 63015. They are constructed by first creating a high tensile rectangular box shaped spar from composite material which is cured in its electrically heated mould. This spar is then placed into the blade mould where profiled lead weight is added to the outboard 2 meters of the front leading edge and Rohacell foam added as trailing edge inserts. This whole assembly is then skinned in composite material and cured. Stainless steel bushes are placed at attachment points and the leading edge wear strip is applied once the blades have been cleaned and painted. Each finished blade weighs approx 7.5 kg.

The tail rotor blades are also made of composite material and Rohacell foam with a leading edge wear strip. Both the main and tail rotor blades have no time life and are only replaced "on-condition". The outside appearance and quality of the rotor blades was excellent. None of the AK1-3 helicopters I have flown in had trim-tab blade adjustments, yet were all smooth in flight, even during steep turns and at VNe.

The tail rotor hub:

helicopter rotors

1) Body
2) Socket
3) Fork
4) Hub
5) Fork Nut
6) Damper
7) Laminated Tension Rod
8) Torsion Bar Bushes
9) Fork Washer
10) Fork bearings
11) Bushes
12) Nut & Washer

Photo of the helicopter tail roter hub

Flight controls

The AK1-3 has standard helicopter dual controls with both cyclic and collective sticks having adjustable frictions. The cyclic friction is on the left stick (Pilot in command seat) and uses a floor mounted dome friction system with a rotating collar around the base of the stick for adjustment. The collective friction is at the base of the central collective stick and is adjusted by means of a horizontal wheel. I did not notice a throttle friction, but in flight the throttle stayed pretty much where you left it, so there did not appear to be a need for one.

helicopter flight controls

The collective stick movement is well correlated with the throttle and does a good job of keeping engine and rotor rpm in the "wide green band" with only small pilot input required during transitions and aggressive maneuvers. A throttle governor system is offered as a factory fitted option to make pilot control even easier. This governor system consists of a Subaru "cruise-control" unit adapted for helicopter use. It is switched on and off with a push-button on the cyclic grip. This governor system is fine for sedate type flying and cruising and is not as responsive as the governor on the CH-7 Kompress or the R 22. On the cyclic grip, there are three other push buttons, one for the radio, and one spare which I now use to change radio frequencies. There is also a "Coolie hat" 4-way toggle switch on top of the cyclic stick which is not used at present.

The anti-torque foot pedals are not adjustable, but the seats can be adjusted forward or backward slightly by releasing the four bolts mounting it to the cabin floor and rebolting. (Not something you would do quickly or often.) I did find all the controls comfortable, easy to reach and operate, and for my height of 1.81 meters, all were well placed.

The collective and cyclic control inputs are transmitted to the rotor system via Duralumin tube control rods and levers. The anti-torque control inputs are transmitted via a combination of levers, cables and pushrods. All moving parts of the control system rotate in sealed bearings and all fasteners are either safety-wired or use castle-nuts with split-pins for security.

The collective lever has an unusual "neutral-stick" feature fitted just below the cabin floor. The purpose of this feature is to hold the collective down when not in use and once lifted up, as in flying, it becomes neutral in weight and stays pretty much in place with minimal collective friction applied. This prevents pilot left arm fatigue on longer flights, but still allows one to lower the collective in an emergency. It achieves this mechanically via a spring loaded override mechanism. The detail mechanical workings of the control system below the cabin floor can be studied from attached photos of an unpainted factory mock-up.

Three long control-rods, for cyclic and collective control, route vertically aft of the cabin and connect to three small walking-beams attached to the front of the MRG. From the opposite side of each walking-beam is a short control rod that links to the static lower swash plate spider. Then from the top rotating swash plate spider are connected the three blade pitch control rods.

helicopter flight controls

The swash plate has rubber bellow covers top and bottom protecting the fiber ball and rotor mast from dust and water where they slide against each other.

Anti-torque control inputs are transmitted from the foot pedals via rods to a quadrant cable pulley below the cabin floor. Attached to this quadrant pulley are two 3mm stainless steel control cables going aft and guided by numerous grooved rollers to another identical quadrant cable pulley at the rear of the tail boom. From this rear quadrant pulley is a short control rod connected to the tail rotor pitch control lever. The tail rotor pitch slider also has two rubber bellow dust covers to keep water and grime out. All the grooved cable guide rollers have ball bearings and a safety bar above the control cables, thus preventing the possibility of a slack cable jumping out from the guide rollers.

My general impression of all the control components are that they are well machined, robust and should comfortably last the 2000 hour life of the helicopter before overhaul.

A little background

The Ukraine State Border Committee recently sought a light helicopter for border patrol from a Ukranian-based company within the aviation industry, as imported helicopters had proved too costly. Aerokopter was selected to fulfill their request.

Founded on 14th December 1999 by I.V. Polituchy, A.N.Zapishny and A.I. Polituchy, the Poltava-based Aerokopter design team was chosen as winners of a competition initiated by another existing company called Aviaimpex of Kiev to co-develop and later manufacture a light helicopter. Unfortunately the two design teams split up within months, with Aviaimpex forming its own design team in Kiev. So from 3rd May 2000, Aerokopter worked independently. Just one month after, their chief designer, Zapishniy Alexander Nikolayevich, was killed in a motor hang glider accident. The group found the strength to carry on under the leadership of Slava Sherbak, a talented and skillful designer. To honour Alexander, the new helicopter would bear his nickname, "AK1-3".

Helicopter designer stnading outside with open door in the rain.

Zapishniy's idea of a two seat helicopter of truss structure proved popular and the design team has not looked back since. The core design team consisted of passionate individuals of different technical disciplines, including former military test pilots. Much of the experimental research was done in close co-operation with post graduates and professors of the Kharkov National Aeronautic University. Additionally, a specialist aeronautical company was engaged to design the power transmission and gearboxes.

On my first visit in June 2005, the Aerokopter design office was equipped with modern computing hardware and software including Auto CAD, NASTRAN, Mechanical Desktop, Fluent, X-foil and other integrated packages. While touring the factory I witnessed some of this integration software at work. With the whole helicopter having been designed using Computer Aided Design (CAD), one operator demonstrated on his PC the ability to disassemble the helicopter part for part, zooming in on individual components showing every detail. Further software integration involved the calculating of the machine-tool paths which was then passed down to some Computer Numerically Controlled (CNC) machines in the machine shop, where many components are manufactured. These CNC machines comprised mostly older generation, but solid, Lathes and Milling machines that cut out the component from a solid piece of raw material. There were still several skilled artisans working traditional (Non CNC) machines turning out components as well. Although costly to initially set up, this CAD and Computer Aided Machining (CAM) manufacturing strategy would pay dividends down the line by shortening the design-to-production time considerably, whilst able to maintain very small tolerances and yield a high quality of finish during production runs. The machining of components from solid metal billet is more expensive than casting, but the due to better raw-material grain-structure control, is generally stronger than castings for a given size. Aerokopter use in house manufactured Titanium bolts instead of the more familiar "AN" bolts in most applications, for its strength, light weight and anti-corrosion properties.

Ukraine arial view of beautiful town.

On 12th October 2001 the first experimental prototype helicopter, the AK 1-5, flew. This was used for proof of design concept, assessing flight dynamics and ground and factory tests so that constructional elements could be improved and manufacturing processes and tooling could be established for production. This experimental helicopter had a five blade rotor head and tested with different Subaru engines including the 3.0 L flat six, the 2.0 L turbo and 2.5 L normally aspirated power plants.

The second helicopter built, the pre-production prototype AKAK1-3, flew in July 2003. This was the helicopter I test flew during my visit.

The factory currently covers an area of over 1200 mІ with additional existing old hangars still being renovated which will then become the main assembly area. 65% of the components were manufactured in house in 2005 and this percentage is increasing to improve quality and shorten lead-time by eliminating some unreliable subcontractors. One has to slow down and be very patient in the Ukraine, as time is not yet seen as a limited resource and deadlines are usually not adhered to. Pilot production started in June 2005 with five helicopters being built. Production capacity is slowly increasing and at last count was at twelve machines a year. This will be increased over time as demand dictates. The factory quote production lead time, specifically time to manufacture the components and assemble, varies from approximately 12 to 14 months depending on their work load.

There are relatively few mechanical design changes to the production-series helicopters, testament to a good initial design and the design teams expertise in getting a complex machine right first time. Aesthetically the interior of the cabin has also been made much smarter than the utilitarian layout used in the SN 0001 prototype model. All these changes have necessitated an upward revision of the factory selling price of the basic helicopter, but compared to what is available in the market currently, I believe that the AK1-3 still represents good value for the quality and performance offered and without a calendar time limitation before overhaul.

The AK1-3 received its APU - 27 (FAR - 27) Ukrainian Type-Certificate on 30th June 2006. In Ukraine, type certification can be obtained for an aircraft including its installed engine, unlike in most western countries where the engine has to be independently certified. The AKAK1-3 is powered by a non-certified, normally aspirated Japanese manufactured Subaru EJ-2.5 L motor car engine, therefore the factory built and assembled AK1-3 helicopter will be imported into South Africa as Non Type Certified Aircraft (NTCA) the same as kit-built or ex-military aircraft. These will be registered with the South African Civil Aviation Authority (SA CAA) in the NTCA category with the prefix ZU in the aircraft registration.

The advantage of non-type certified or ZU registered aircraft is that you are allowed to maintain and service the aircraft yourself if you so wish, and provided that you are technically minded and competent, thereby substantially reducing your operating costs. In addition engine service parts and engine overhaul costs are lower than for traditional aircraft engines, as parts can be obtained direct from the nearest Subaru dealer who can also perform or arrange for engine overhauls.

The down side is that you may only use it commercially under the more restricted operation as defined in part 96 of the CAA regulations, which are currently under review. For example, you can use it for "flipping" provided that you have been issued with a class II – type N1 domestic air service license, which restricts you to take off and land from the same spot. You are also compelled to disclose to fare paying passengers that the aircraft is non-type certified and that they fly at their own risk. The helicopter may also be used for training purposes, provided the operator is the holder of the appropriate aviation training organization approval, issued in terms of part 141 of CAA regulations.

The AK1-3 has been designed to be easily transported by road trailer if required, even with a small car. The three main rotor blades can be removed or installed in 10 minutes with two persons.

THE HELICOPTER:

After some market research Aerokopter concluded that a need for a light two-seat helicopter in the 650 – 700 kg gross weight category existed. The end result of the design-team's creation is a helicopter capable of delivering a maximum vertical thrust of 800kg from its 115 kw (156 hp) motor. There are "flight performance graphs" from the Pilots Flight Manual available on the home page for those who wish to analyze the helicopters performance in more detail.

Airframe:

The small truss-type airframe is made of triangulated Chrome Alloy tubing with two separate upside-down "V" side frames used to attach the Main Rotor Gearbox (MRG) to the air frame. Also detachable are two engine mounting sub-frames that carry the engine weight via rubber insulated engine mounts below the engine. On each lower corner of the airframe is welded a large circular clamp through which the 51 mm diameter Titanium-tube skid legs pass through. At the front of the airframe are four attachment points that hold the cabin-structure in place. All structural bolts used throughout the Sanka are metric sizes and made from Titanium. The cabin floor is fastened on top of a triangulated Duralumin sub-frame and this sub-frame is attached to the Chrome Alloy airframe. Detachable side frames attach to main rotor gearbox.

These skid-legs are single-piece U-bent tubes and are secured via rubber bushes inside these circular clamps. The lower end of each Titanium skid tube has a steel foot attachment to which is fixed the Duralumin skids. This "under carriage" looks very robust yet is extremely light-weight. Each skid has a Duralumim Dolly-wheel attachment-point and on each side of the front legs are beautifully machined Duralumin foot pegs to assist entry into the cabin.

Helicopter Frame

The MRG and integral primary reduction drive unit together form an upside-down "L" with a cross brace linking the two ends to form a triangle. This triangle then forms part of the airframe structure and is the attachment point for the front of the tail boom and top engine mount. There are two Duralumin diagonal struts attached on each side, at the rear of the airframe and these attach to the underside of the tail boom to support it approx two thirds down its length.

The use of the MRG drive system as part of the airframe is unusual in a helicopter and is the same principal used in formulae-one cars and super-bikes where the engine-gearbox forms part of the chassis. By using this integrated truss-frame design has allowed the use minimal amount of Chrome-alloy steel tubing without sacrificing rigidity, but saving weight.

Helicopter skids diagram.

Note that the skid legs (2) are made of one single Titanium tube 51 mm diameter.

Tail boom:

The tail boom is made up of four rolled aluminum sheet sections, forming tubes and riveted together using solid rivets. At the three joins connecting these four tube sections, are large machined ribs that hold the three tail rotor drive shaft support bearings. There are four additional smaller machined ribs positioned midway the length of the four tube section for maximum rigidity. Each of the tail rotor drive shaft bearings is held in a rubber pad, which in turn rests inside an aluminum housing bolted to the large ribs, thus allowing some "float". The drive shaft is a single length 22 mm chrome alloy steel tube with collet bushings clamped onto the shaft in line with the support bearings. At each end of the drive shaft a electroplated steel coupler is fitted using two conical bushes and a Titanium bolt. Next to the front coupler is a light steel gear wheel with 24 flat teeth. This "gear wheel" is the rotor RPM magnetic sensor trigger, with each gear tooth passing over the magnetic sensor generating an electrical pulse to power the Rotor RPM instrument. In the event of complete electrical and power failure, the Rotor rpm instrument will still work during autorotation.

Helicopter tail boom

The tail boom has re-enforcing gusseting added at strategic locations, such as at the tail boom mounting points, at the vertical and horizontal stabilizer attachment points and where the anti-torque control cable guide pulleys and rear control quadrant are attached. The horizontal and vertical tail fins are fabricated from riveted aluminum sheet onto CNC machined ribs and end caps. All the tail boom bracketry is CNC machined and any material not adding strength, is machined away to save weight. Where ever a Titanium mounting bolt needs to pass through the Aluminum structure, a stainless steel or Titanium collar is first inserted

As shown in the photos, the attention to detail and workmanship is excellent.