History


 

The idea started in January 1999 while flying from the Gariep Dam situated on the Orange River in South Africa at 30° 37' 22.55" S - 25° 30' 22.86" E.
Soaring conditions here are mostly excellent, but the out-landing possibilities because of the rugged terrain, are extremely hazardous if not at times non-existent.

Under these conditions a self-launcher would seem to be highly desirable, however, the prohibitive cost of a self-launcher led me to consider building one of my own.

The pop-up concept, because of the adverse effect it has on the glide angle at engine start-up, and various other uncomfortable factors, encouraged me to reject this principle.

My thoughts were to build a pusher-type craft with folding propeller at the rear, joined to the engine situated behind the wing by means of a drive shaft similar to that employed by a BD5, Mini-Moke or Graal.

My decision to go ahead with the project was taken some time in mid 2000.
I decided to name the project “Selene” after the Polynesian goddess of the moon, having been influenced by the fact that the general consensus of opinion at the time was that my idea was Utter Lunacy.

The wings would be from ASW 20.
The power plant would be a single cylinder, two-stroke, water-cooled engine of 30 kW.
A space-frame would extend from just behind the ASW 20 cockpit to the leading edge of the fin, and would mount wings under-cart and house the drive train.
The space-frame would have composite removable covers.
To give the propeller ground clearance, the fin would need to be both dorsal and ventral.
Investigation as to whether this system could be adapted to an existing 15m flapped glider appeared to be positive.

First steps:

Order the engine.
Build a hanger to house the project.
Design and build a prototype drive-train test rig.
Acquire an ASW 20.


These steps took place over the following few years, but not necessarily in the order stated above.
By the beginning of 2003 the hanger was ready and the design was on its way.
An ASW 20 had not yet been found but the design and building of the propulsion system had begun.

The drive-train test-rig was built using rectangular tubing and fitted to a small trailer for ease of maneuverability, which also made it possible to perform dynamic tests on the system.

The first drive-train assembly produced excessive vibrations, which were severe enough to adversely affect the carburetor function.
The reason for the poor performance of the original engine mounting system was simple but not easily identified, and turned out to be that the propeller was not directly connected to the engine as it would be on most other applications.
This meant that the flywheel effect of the propeller no longer stabilized the engine.
Various mounting systems were tried and eventually a 3 mount system and suitable flywheel made the engine run satisfactorily.
The drive-train at this stage consisted of a 3 piece shaft with a maximum propeller speed of 2350 rpm. And no torsional vibration issues were evident throughout the operating rev range.
At this point it seemed that the development would be less difficult than expected.

2004:

The engine was temporally covered as it would be in the aircraft and the cooling system evaluated.
This led to the fitment of a lighter aluminum heat exchanger having greater cooling capacity and a more powerful fan.
Some dynamic testing was performed by towing the rig up and down the runway at varying power outputs and simulating air starts.
These tests revealed nothing undesirable. However, the theory that forward motion would soften the violent propeller deployment when the engine is started with the propeller folded was disproved.

Difficulties.

Starting the engine when hot caused the propeller to deploy with more violence than would be acceptable.
This was because the engine would fire on the first compression stroke and the propeller would still be partially folded at this time.
Keeping the magneto’s switched off until the starter motor had fully deployed the propeller usually resulted in a flooded engine.
Similarly, keeping the throttle open until the starter motor had deployed the propeller did not work consistently.
A fully closed throttle was needed to start hot or cold and the engine would not idle smoothly at this throttle setting.
Propeller speed was too slow and needed to be increased.

During mid 2004 an ASW 20,  ZS-GMU  had a bad out-landing which resulted in some damage to the fuselage and I subsequently had the opportunity of purchasing the aircraft.


Now having an ASW 20 to work with, allowed the mass and balance considerations to be further investigated as the drive-train masses were beginning to be known.
By the end of 2004 the mass and balance issues were fully understood and the entire design was well on its way.

The cockpit section which will attach to the space-frame was repaired and the attachment ring temporally fitted to it.
The minor damage to the wings were repaired, wing-tip wheels fitted and provision was made for fitting the fuel tanks into the wings.

At this time it was decided to buy the machinery needed to perform all the machining as the cost and time consumption of outsourcing the work was prohibitive.
It should have been understood from the outset that a project of this nature would be protracted and would be best accomplished in-house.


2005:

In 2005 the material for the space-frame was imported and the building of it began.

The wings and mixing box were fitted and control rods made.
Header fuel tank and prototype wiring were installed.
The engine with new reduction ratio and revised drive shafts, bearings and folding propeller hub were fitted.

2006:

Early in the year the revised drive-train was run in the space-frame for the first time with some surprising and frustrating results.
There where torsional vibration problems which had come about due to the ratio change and space-frame mounting. This took many months to resolve.
Torsional vibration dampers were experimented with, flywheels altered and coupling types changed.
By mid 2006 the drive-train had 4 shafts and was performing well again with a minor transient vibration at 3500 – 3600 engine rpm.

The remaining problems were still:

Engine start-up reliability.
Inability to idle at start throttle position.
The violent propeller fling-out when the engine is started hot and with the propeller folded as will be the case when the glider is flying.

All these problems were eventually solved by replacing the carburetor with fuel injection.
A locally developed engine management system and a throttle body from a motorcycle were used to confirm that the fuel injection system would solve all the remaining problems, but the motorcycle throttle body would not fit into the final aircraft constraints.
Three throttle bodies were fabricated before optimization of the system was achieved.

At the end of 2006 cooling trials were again successfully conducted.

The space-frame and drive-train combination had been successfully run in constraint conditions, which closely approximate flying, taxiing and take-off.

The system had accumulated a total of 36 hours of test running, 11 in the original test rig and the balance in the space-frame.

Some test results as at December 2006:

Static thrust at 5900 engine rpm is 78kg and it is reasonable to expect 6100 rpm and 80kg+ at take-off speed.

An estimated 7 minute launch simulation:
30 second warm-up.
1 min 30 sec full power.
4 min climb power.
1 min idle.
This used 0,75 litre of fuel.

Possible cruise power settings, 3200 engine rpm at 3 litre per hour and 3800 rpm at 5 litre per hour.

2007:

In January work on the composite tail section started.

Michael Charl, an aircraft constructor who had learned his trade working for Shremp Hirth in Germany, ably consulted on the design aspects and performed all the many tasks required to produce aircraft quality components.


It was decided to build a new horizontal stabilizer and elevator.
As the ASW 20 unit weighed 9,2kg and a saving of 3kg could be realistically expected.
Reduced weight at the rear of the aircraft is a good thing in this design.
The elevator will remain in the same geometric position as it is an ASW 20 and will retain the same profile, but will be extended in span by 200mm.
The original unit was used in the construction of the mould.

Fin-Rudder and Rear Fuselage Cone:

The fin-rudder area and profile was used and the aspect ratio increased.
Polystyrene foam was hot-wire cut utilizing CNC cutting technology.
The plugs were made from these and subsequently the moulds from the plugs.
Calculations for the composite lay-up strength were performed.

The “mapping”, programming of the engine control unit was finalized in the winter of 2007, as cold weather was needed for this exercise.
The new under-cart which had been designed in 2004 was fabricated and fitted to the space-frame.

The cockpit was connected to the space-frame at the estimated position and the control system fitted.

A dummy fin and rear fuselage cone was made using the mould for the first time, which was then fitted to the space-frame.

The elevator control system was fitted.

The engine cowl system was designed and a prototype made and fitted complete with its actuator system

The need for engine instruments and the lack of space to fit them led to the application of a glass cockpit instrument system.

The original fuel supply system which consisted of two wing mounted aluminum tanks of 10 liter each, feeding a newly constructed fuselage mounted header tank of 1 litre was pressure tested and fitted.
However, there were just too many pipes which necessitated the design, manufacture and fitment of a new fuselage mounted fuel tank.
At this stage all components were evaluated for potential mass reduction and where feasible lightening was implemented.

 2008:

The next goal was to perform ground run tests with all the systems assembled as an aircraft, using the dummy fin and elevator, all controls, ancillaries, fuel lines and wiring installed as when the aircraft is ready to fly.

The drive-train ran well and there were no damaging vibrations in any of the components.
The 3500 – 3600 rpm range still had a vibration which made this rev range unsuitable for continuous operation.

It was decided to have the cooling fan on when the engine was running to avoid the complexity of a thermostatic switch or the unreliability of a manual one.
This resulted in a net battery discharge whenever the engine was running.
The fuel pump originally selected was of a higher flow rating than required and a more suitable one was acquired which gave the battery a small positive charge when engine revs were above 4500 rpm.

The aircraft was weighed with estimated masses added where components yet to be made would be situated.
The results indicated that the mass and balance were within the parameters envisaged and would not pose any problems.

The engine intake noise was significantly reduced by utilizing long, large diameter ducting joined to a Donaldson air filter

At this stage it was decided to change the method of connecting the space-frame to the cockpit.
Originally a 4130 steel tube was to be glassed to the cockpit structure.
This method was discarded in favor of making a composite flange to bolt the two assemblies together.
The cockpit was disconnected and the composite flange made after which the front section of the space-frame was revised to suit the new connecting method.

Next a flying tail-cone, fin and rudder were manufactured using aircraft quality material
The rear fuselage cone, fin and rudder assembly complete with tail wheel, control actuators and rudder mass balancing was fitted to the space-frame.

Pilot-static and total energy probe was fitted to the nose of the aircraft.
The horizontal stabilizer and elevator were made, and when fitted enabled the aircraft to undergo taxi testing.

Taxi Testing:

Initial taxi testing indicated the main wheel not being far enough forward of the center of gravity, causing the aircraft to pitch nose down too easily.
As a result the main wheel was moved 160mm forward which optimized ground handling.

2009:

Ground vibration tests were performed on the aircraft in January 2009, at the CSIR (Council for Scientific and Industrial Research) in Pretoria.

Next, the covers were made and fitted.
Originally there would have been blisters in the covers to accommodate the carburetor on the right side and the exhaust outlet on the left.
As it subsequently turned out, the injector throttle body was small enough to enable the engine to be moved over by 50mm eliminating the need for blisters.
 This repositioning of the engine and realignment of the drive-shaft had a very positive overall effect, inasmuch as the entire rev range became continuously usable with no perceivable torsional vibrations.
This would be due to the added damping effect caused by the drive-train realignment.

Final Inspection:

The aircraft was disassembled, components inspected and reassembled using new fasteners with a view to airworthiness.
The wiring harness was remade, reconnected and tested.
The aircraft was weighed and removable ballast fitted to bring the flying center of gravity to the forward third of its allowable limits for the pilot concerned.
Control surface deflections were measured and adjusted.
Stabilizer to wing incidence was measured and adjusted.
Taxiing tests were performed with all covers fitted. During these tests the propeller leading edges were eroded by runway debris, which had not occurred during the previous taxiing tests which had been done without covers fitted.
The debris had most likely lodged in the fan and radiator during the previous tests.
A wheel guard  was developed and fitted to prevent this and propeller leading edge protection was applied.

Finally, an annual inspection procedure was performed by two competent persons and the appropriate forms completed.
 
First Test Flight:

The first test flight took place on 23rd December 2009 at 6am

Date:    23-12-2009
Take-off mass:  420kg
CofG:    30% behind forward limit
Ambient Temp.:  20° C
Airfield elevation:  5100ft
Maximum height:  6500ft
Air speed:   ASI malfunction due to poor static port selection
Ground roll to lift-off:  ±500m
Maximum climb rate:  400ft/min
Maximum decent rate: 600ft/min
Flight duration:  26 min

Take-off was achieved when the flap lever was moved to the second positive notch.
No elevator input needed.
Climb-out was kept quite flat because of the lack of airspeed indication, but felt stable and safe.
At 6500ft the roll, pitch and yaw were gently checked and found to be good.
Landing flap settings with decent power (engine idle) and air-brakes were checked and the landing configuration decided on.

An approach to stall in the landing configuration was tried, to get a feel of the aircraft on final approach.

Next, a low power level flight in neutral flap was tried and felt stable and safe, but the engine lost power at this low throttle setting and only resumed when the throttle was advanced.
The landing happened with the tail wheel touching down slightly before the main.
There was no bounce and the roll-to-stop was ±300m.
In general the handling of the aircraft was very pleasing.
Unfortunately the flight data recording facility of the Enigma instrument was not correctly set up resulting in the flight data not being recorded.


Second Test Flight:

The second flight took place on the 31st December 2009 also at 6am.

For this flight the static port was disconnected and cockpit static was used.
The propeller pitch was increased by half a degree which brought static rpm down from 5900rpm to 5600rpm.
Take-off was good and climb-out was done at 100kph indicated.
At 6500ft the engine was shut down, cowl closed and under-cart retracted.
This process was reversed without any problems.
Again at a low power setting the engine lost power and recovered on application of power.
This seemed to be more pronounced than on the first flight.
Landing was made as before with indicated airspeed of 90kph over the fence.
On this flight, again the flight data recorder did not work due to inadequate set-up.

The aircraft was then de-rigged and the covers removed.
On inspection all was ok except that the fuel line to the injector appeared to be pressing against the cover.
Redesign and remake of the injector fitting solved this problem.

A prolonged ground run with covers fitted, which required special cooling of the cover in the exhaust outlet area, indicated that the fuel in the feed pipe to the injector was becoming overheated.
This was suspected as the cause of the engine misbehavior.
Changing the fuel-line plumbing so that fuel is returned from the injector back to the tank, instead of being dead-ended at the injector, stopped the fuel heating. However, it did not solve the erratic engine behavior.
This was eventually traced to one of the wire terminals connecting the pick-up to the engine control unit.
The terminal connection became intermittent due to engine vibrations and the method of connection.
This method of connecting wiring to the engine was revised at all terminals to prevent a reoccurrence of this problem.