Buying, Flying and Maintaining a Motor glider
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Pete, photographed in his DG-800B by his wife Charmagne, founded the USA Self-Launching Sailplane Pilot's Association in 1988 (now known as The Auxiliary-powered Sailplane Association) and is a recognized authority on the subject. He has also recently written "Self-Launch! Retractable Engine Sailplanes" - a compendium of historical data and information covering 25 models. He flies from the Minden-Tahoe Airport, Minden, NV, USA and has logged over 1000 hours in self launching sailplanes.The ability to self-launch is part of the continuing evolution of sailplane design. Launch methods have progressed from foot propulsion by jumping off a cliff, followed by bungee cord launch off a hill, a tow rope tied to a team of horses, followed by aero tow and winch launches and finally to self launch using a propulsion system contained with the sailplane. Recent alternative propulsion systems under development are electric and solar power but the object is always the same:
Attain enough altitude to search for a thermal, secure the propulsion system and soar. This is the logical evolution path that has optimized and improved the launch method and thereby promoted and enhanced the sport of soaring. The powered sailplane will not replace those without power but simply provides an alternative launch method which today is attracting many new pilots into the sport of soaring.
This is an article describing what is involved in
1. Buying a Motor glider;
2. Motor glider Flight Disciplines and
3. Servicing and Maintaining a Motor glider.
A "hands on" approach is used to provide usable information to the prospective motor glider pilot. Flying a modern motor glider, self-launcher or sustainer engine sailplane is a rewarding experience. While enjoying the freedom this type of soaring provides, the pilot will discover the engine and its systems require careful pre and post flight inspection as well as periodic servicing and maintenance. He will also discover a new realm of soaring freedom far removed from tow lines, wing runners and out landing retrieves. The theme running through all of these articles is FLIGHT SAFETY.
Terms
In this and future articles, I have used the terms listed on this and the opposite page when referring to powered sailplanes that have the aerodynamic capability to climb in a thermal or rising air currents with the engine off. The word "sailplane" is often used interchangeably with the word "glider". By dictionary definition, this is a misnomer as a glider is not aerodynamically capable of climbing in ascending air. Sailplanes with engines are also sometimes referred to as auxiliary-powered sailplanes. The definitions used are as follows:
Motor glider: A sailplane with a fixed engine (tractor or pusher) that has the ability to self-launch and soar with the engine off. The motor glider is normally equipped with a propeller that can be feathered during soaring flight.
Self-Launching Sailplane: A sailplane that can self-launch using a retractable engine.
Sustainer Engine Sailplane: A sailplane with a low horsepower retractable engine. The Sustainer Engine Sailplane requires a tow to get airborne.
Who and why pilots fly powered sailplanes
Over the past ten years many pilots have contacted me regarding buying a powered sailplane. The first question I ask is "Why do you want to fly a powered sailplane"? Permit me to list some typical answers:
Pilot A: Loss of medical permit which in the US is required to fly a powered airplane. However, a US pilot does not have to have a current medical to fly a glider in the states because powered sailplanes, motor gliders and self-launching sailplanes are classified as gliders by the Federal Aviation Administration.
To pilot a powered sailplane requires a Private Pilot Glider rating and a checkout by a certified flight instructor in a powered sailplane. Pilot A is a power rated pilot who wants to continue flying and many of them are not yet sailplane rated.
Pilot B: This can be a power and/or a sailplane rated pilot, some with limited soaring hours, who wants to self-launch at will or does not desire to travel some distance to a sail port to get a tow. This pilot may desire to operate out of a non-towered airport alongside powered ships. Some have operated out of towered airports and returned to land with the engine secured by previous arrangement with the airport authorities.
Pilot C: This is a pilot with a good measure of non-powered soaring flight time who wants the convenience of self-launching
without waiting for a tow and/or the ability to save a flight using the self-launching or sustainer type engine. Most of these pilots are pure sailplane pilots who have switched to a motorized sailplane.
There are other reasons that can apply to all three pilot types such as no crew available or loved one unable to or not desirous of performing crewing duties for various reasons. Many pilots flying motorized sailplanes operate without a crew and use self rigging systems to assemble and disassemble their ships. Or they may own a motor glider that is hangared, some of which have foldable wings.
Many of these pilots are business professionals with busy schedules and time constraints. They desire to fly as soon as possible after arriving at the site. In some cases they fly out of their own private landing strip. Pilots who fly sustainer engine sailplanes are essentially pure sailplane pilots and use the engine as a safety net to sustain flight only if absolutely necessary to save an out landing and the inevitable retrieve.
Selection of powered sailplane type
After ascertaining what type of pilot I am talking with, I ask another question. "Do you want to motor a little and soar a lot or motor a lot and soar a little?" For those who desire to motor a little and soar a lot, the retractable engine self-launching or sustainer engine sailplane is the choice.
For those who want to motor a lot and soar a little, the motor glider becomes the choice. The last question is "Do you want to fly with a passenger?" If the answer is yes then normally a motor glider is the choice as most are two-seater ships. So there are basically two kinds of pilots that fly motorized ships, namely the pilot who desires to soar most of the time and the pilot who wants to soar now and then if conditions warrant.
Another key factor the prospective powered sailplane pilot must come to grips with is the responsibility of learning about the five basic systems found in all powered sailplanes. These are the airframe, engine, fuel, electric and the retraction-extraction System (propeller feathering system for the motor glider). A working knowledge of the servicing and upkeep of these systems is part and parcel of owning and flying a powered Sailplane.
The fact that the engine is not in a fixed position in the retractable engine versions requires specific inspection disciplines that are added to the normal inspections of the airframe. When the engine moves, so does its cooling, carburetor linkage, mounting and ignition systems.
Areas of mechanical and electrical scrutiny includes security of all nuts, bolts, torque values, safety fuel lines, spark plugs, ignition boxes and propeller, including the prop braking system. The list goes on and will be addressed in future articles.
Performance Comparisons
Consideration of performance is of prime importance due to the locale from which the aircraft will fly. Factors to consider are runway surface and length, temperature and density altitude.
As all example, only 80%, of the engine's rated power is available on a summer clay at a 5000 ft msl airfield. The density altitude will even be higher.
Making the decision
The next logical question is cost. This usually leads to a discussion of used versus new aircraft, specifications and performance, instrumentation, locations of used aircraft, currency of maintenance and service records, training required and compliance with air worthiness directives.
Buying a powered sailplane is a major financial decision. Add to this the engine systems learning curve and it becomes evident that the prospective owner has a lot of homework to do.
Counting the cost
Most used models are anywhere from five to 15 years old. They are usually well maintained and sell quickly. Delivery of new ships varies from six months to over two years. Prices for both new and used aircraft will fluctuate according to the current exchange rate.
Information regarding used and new ships is available from the factories, dealers and from The US Auxiliary-powered Sailplane Association.
The ASA was founded in 1988 to band together pilots who fly powered sailplanes and to disserninate helpful information and safety tips to its members.
For more information about ASA, contact Brian G. Utley, ASA Membership Chairman, 1930 SW 8th St, Boca Raton, FL 33486-5205, USA. or tel ++561 750 6876.
Most retractable engine sailplanes flying today were designed as sailplanes. In the case of a self-launcher or sustainer engine sailplane, the power plant was added to an existing sailplane airframe. This requires fuselage modifications including installation of engine mounting hard points, a fuel tank, a retraction system, a more robust electrical system and an engine/pylon control system.
DG-800B instrument panel: The DEI is the horizontal unit
with the LCD display, switches, LEDs and throttle lever.
The nose mounted fixed engine motor glider was designed with an airfoil that has the aerodynamic capability to climb in ascending air (wing spans of 53-57 ft) but has a lesser glide ratio (24-31) compared to the retractable engine sailplane (42-60). It also has the capability for continuous four stroke engine operation, whereas the two-stroke power plant used in the retractable engine sailplane was not designed for continuous operation but to provide power for self launch and climb to the nearest thermal or in the case of the sustainer engine sailplane to prevent an out landing.
An exception is the Stemme S10 which was designed from the ground up with a fixed four-stroke engine that has the capability for continuous operation or flight as a sailplane with engine off and propeller folded and stowed in the nose cone.
Flying a Motor glider
To the pure sail plane pilot, flying a motor glider adds new responsibilities and procedures above and beyond "normal" soaring flight. Events such as arranging and waiting for tow or winch launch are replaced with more lengthy check lists, power plant inspections, an engine start and run up, a powered take-off, engine securing and retraction (propeller feathering in a fixed engine motor glider), air starts, the possibility of landing with the engine running, the retraction system and engine emergencies. To a pilot with experience in powered aircraft, new disciplines are also to be learned, especially the power plant extraction and retraction sequences.
Check Lists
A review of the pilot's flight manual of a retractable engine sailplane will reveal several check lists including cautions and emergency procedures covering all aspects of the engine and retraction system. One of two engine control instruments are used - the ILEC or the DEI (Digital Engine Indicator).
These instruments permit the pilot to control the throttle, engine position, starting and stopping, ignition tests and propeller blade position and braking. Liquid Crystal Displays (LCD's) and Light Emitting Diodes (LED's) allow the pilot to monitor fuel quantity, battery voltage, generator output, engine rpm and temperature, propeller and engine pylon position.
There are safety interlocks built into the system to immobilize the starter until the engine is fully extended and prevent pylon retraction until propeller blades are positioned properly.
Prior to the first flight, the pilot should conduct a very thorough study of the Flight Manual and create a complete set of cockpit check lists covering all ground, flight and emergency procedures. Nothing should be left to chance.
If the pilot is not totally familiar with the functions of every engine control instrument switch and visual indicator, he or she is not totally prepared to fly the aircraft. In the motor glider, the power plant controls and indicators are much like a power aircraft with the addition of a propeller feathering system. Learn the limits of all indicators and the time it takes to extend the engine or unfeather the propeller.
Pre-Flight Inspections
This inspection requires more time and attention to detail than a pre-flight of a pure sailplane. Systems to be inspected include fuel hoses and carburetors, extraction and retraction, cooling, engine pylon and mounting integrity, engine bay and doors, exhaust and muffler, drive belt, propeller, starter and starter ring gears, throttle cable, spark plug connections, engine flywheel and propeller braking, wiring bundles and ignition boxes, battery condition and engine control instrument operation. The items to be inspected are found in the flight manual. They should be itemized on a hard card list and checked off during the walk around ground inspection.
Starting And Warm Up
For the motor glider, starting is similar to a powered aircraft:
check battery voltage, fuel on, propeller unfeathered, throttle set at idle, ignition on, choke if required and engage starter. In the retractable engine sailplane the basic sequence is similar, except the engine must be first fully extended to the start position. When the ignition is turned on, the fuel pumps and coolant pumps (as applicable) come on line and the starter circuit is blocked until the engine is fully extended.
This sequence is automatic on many ships. When the ignition is turned on, the engine raises to the start position (engine position travel lights illuminate), all pumps come on and a pylon position light indicates when the starter button can be pushed.
The pilot is able to monitor these events on the ILEC or DEI engine control instrument. After warm up and a test of the dual ignition system, a full power run up is made to check for proper rpm output and generator on line indications.
If any part of the engine run up, such as an excessive rpm on one magneto or the engine fails to attain rated rpm, the flight should not be attempted until the discrepancy is corrected.
Taxi
Some self-launchers have a steer able tail wheel and wingtip wheels that permit taxi operations. Others do not and require ground handling to reach the runway. If able to taxi, always test the tail wheel (or nose- wheel in some aircraft) steering system and conduct a main wheels /brake test. Extended taxiing may cause spark plug fouling requiring a high rpm run up prior to take-off.
Avoid high speed taxi operations and sharp turns. Know where the wing tip wheels are and keep the low wing tip wheel clear of obstacles. Be particularly watchful of runway/taxiway lights and markers. Visibility of other aircraft on the ground is not as good as it could be due to the low seating position. Take time to make sure all is clear before moving into the runway for take-off.
Take-off
This is the most critical phase of a flight. Reduced engine performance, including total engine failure especially after lift off, is an emergency that requires immediate action. Some ships are airborne quickly and climb steeply. Others require a long take-off run followed by a shallow climb.
The best policy is to start the take-off run using the complete runway length. This provides a measure of safety for an aborted take-off if problems occur. If the engine is not developing the required rpm at the beginning of the take-off roll, reduce throttle to idle and abort the take-off.
If engine problems occur after lift off, a decision (depending on the altitude) must be made to continue straight ahead or return for a downwind landing. After applying full throttle, scan the engine instruments for rpm and temperatures. At lift off, establish the climb airspeed and continue climbing to at least 1000 ft above ground before departing the circuit.
Be prepared for the rate of climb to decrease as you pass through sink areas. Note the nose attitude required to maintain the recommended climbing airspeed. Long straight out departures are acceptable if you know where the thermals are. Otherwise, it's smart to stay within gliding distance of the field as you search for the first thermal.
Engine Securing
The best way to describe flying a self launching retractable engine ship is when the engine is running you are flying a motorized sailplane with the capability to sustain flight or climb. Once the propeller stops and the pylon is not retracted, you are flying in a very high drag condition with a glide ratio as low as 10-12/1.
This is no time to be close to the ground and time is of the essence to either restart the engine if lift not located, or to stow the engine as soon as possible to restore an acceptable glide ratio.
In the motor glider, the drag is not as great and the altitude loss not as critical while unfeathering the propeller for an air start. For the retractable engine ship, the basic sequence of events in securing the engine is to locate lift and begin circling. Make sure you are at the recommended retract (propeller feathering) airspeed, then reduce power to idle and allow for a short cooling period. Maintain proper airspeed and shut off the ignition.
When the propeller stops (manual or automatic braking), align the propeller for retraction and retract. In many retractable engine ships this is fully automatic when the ignition switch is turned off. It can be accomplished manually and should be practiced as automatic systems are not totally foolproof. Once the engine is put away or the propeller is feathered, soaring flight continues in a normal fashion.
Air Starts
Know the loss of altitude you can expect during engine extraction or propeller unfeathering during an air start. Should the engine not start and an out landing becomes imminent, initiate an air start at an altitude that provides a reasonable altitude safety cushion (2000 ft above ground level is recommended) near a suitable landing field.
While the propeller is unfeathering (motor glider) or the prop pylon is extracting (retractable engine) sink will be increasing as the glide ratio deteriorates. The sequence of events is to slow down to engine extract (propeller unfeather) airspeed, set flaps as required, turn on the ignition, raise the power plant (unfeather the propeller) and press the starter button. Priming may be necessary for a cold soaked engine.
If the engine does not start, the propeller can be wind milled by increasing airspeed. Altitude above the ground is critical. If the engine does not start, abandon the windmill dive, retract the engine and be prepared to land. Do not continue to try to start as the aircraft is in a high drag condition. Retract the engine and fly it as a glider in preparation for an out landing.
If unable to start or retract the engine, it is possible to land with the engine extracted. The drag is equivalent to fully opened spoilers and care should be taken to keep flying speed all of the way to touch down. Use of spoilers can result in a hard landing. For the motor glider, a non powered landing becomes the choice if the engine will not start and the drag condition is not as high as the exposed pylon/engine on a self-launcher.
Landings
Most landings in a motor glider are with the engine running. In the retractable engine or sustainer engine sailplane, the majority of the landings are as a sailplane (engine retracted). Wing loading is higher in powered sailplanes due to the engine and its systems (100-130 lbs). Add fuel weight and the wing loading becomes comparable to a ballasted sailplane.
To the pilot this means a higher landing approach speed and touch down followed by a longer ground roll. Flying weights range from 1000-1800 lbs with an average wing loading of about 8.5 lb/sq/ft.
For this reason a non-powered landing requires more space and preferably a smooth hard surface. After landing, if you need the engine to taxi, use it but remember other aircraft may be landing behind you. It's best to clear the runway prior to starting the engine for taxi.
Emergencies
The emergency situations peculiar to the retractable engine sailplanes include engine failure on take-off and during flight, fires, electrical power failure, air windmill starts, landing with engine extended and stopped and emergency retraction or extension of the engine. Some aircraft have a fire warning light that illuminates if the engine bay temperature exceeds a certain limit.
Climb out airspeed is normally around 50 kts. Lift off and initial climb out is one of the most critical phases of the flight. If the engine fails after lift off, the airspeed will rapidly bleed off, requiring an immediate push on the stick to maintain flying speed.
Document all emergency procedures on check lists and review them often. Remember you are flying a powered sailplane until the propeller is feathered or the fuselage doors bang shut on the retractable engine ship. (The Stemme is the exception - the nose cone shuts.)
Post-Flight Inspections
This inspection is just as important as the Pre-Flight Inspection. If flying a retractable engine ship, extend the engine and inspect the engine bay, including all hoses, the propeller, the muffler and exhaust system. Look for coolant and/or fuel residue both in the engine bay, on the vertical fin and the underside of the fuselage. If loose hardware is found in the engine compartment after a flight, do not fly the aircraft again until the object and its source have been positively identified and a repair or replacement made if necessary.
Author's Notes: I am indebted to many motorized sailplane pilots from all over the world who have shared with me their operational and maintenance experience. This includes the airframe and engine factory personnel who have been most helpful in furnishing technical details.
I would also like to give due credit to my friend Karl Abhau who has been my mentor for the past ten years regarding powered sailplanes. Karl is recognized as one of Germany's most experienced powered sailplane pilots with over 2000 hours in various motor glider types and models.
Maintaining a Motor glider
A powered sailplane adds more pilot responsibility f or the proper servicing and care of the power plant, the extension/retraction system (propeller feathering system in a motor glider), periodic inspections, maintenance and troubleshooting.
Any pilot considering owning one is encouraged to find and establish a relationship with a qualified mechanic who has had experience in maintaining this type of sailplane. This includes obtaining a complete file of all technical notes and ADs, including the service and parts manuals and electrical wiring diagrams pertaining to the particular model flown.
Flying a motorized sailplane is indeed a most rewarding experience. However, when it comes to upkeep, this is where the rubber hits the road as most of the pilots who have experience flying this type of ship will agree.
Today's modern motorized ships are not mass produced using automated assembly line techniques. They are literally custom made and assembled by hand one at a time.
With the exception of the airfoil profiles and fuselage, improvements and slight modifications including additional parts are always in progress. For comparison, the modern motorized sailplane is not a Volkswagen or even a Mercedes. It is similar to a custom-made Formula 1 racing machine.
Keeping that in mind, the prospective owner should realize that it is, by nature, maintenance intensive and will require more man-hours of upkeep than a pure sailplane. Having said that, let us move on to what is required to keep the bird in the air and humming when a hum is necessary.
Engine Systems
Power Plants
The two-stroke engines installed in self-launchers were not designed for continuous engine on cruising. Overhaul times are in the vicinity of 3-400 hours. Makes include Rotax, Solo and Mid-West. Some are air cooled. Others are liquid cooled. Four-stroke engines used are Rotax 912 or 914, Limbach, Grob and Micron. These engines can be used continuously and have extended overhaul times compared to the two-strokes.
The two-stroke engine is basically designed to run at full power for five minutes after which it can be throttled back slightly. The objective with the two-stroke is to climb to altitude and search for a thermal.
Running time varies from 10-15 minutes per launch. By nature these engines run hot with a cylinder head temperature of 180-200 degrees C for the air cooled versions and 70-95 degrees C for the liquid cooled models.
Exhaust gas temperatures can be as high as 1000 degrees F. A proper mix of fuel/oil ratio is imperative for engine longevity. Follow the factory recommendations. To my knowledge there have been very few internal mechanical failures of two-strokes involving seized pistons, bearing failure and the like.
Most two-strokes that have been in service for ten years accumulate around 100-130 engine hours. Both Rotax and Solo have a long history of two-stroke engine production for many applications including water craft, snowmobiles, lawn mowers and various other non aviation uses.
The ASH-26E, ASH-25E and the ASW22BLE are equipped with a 50 hp AE5ORA rotary engine made by Mid-West in England. This is a relatively new engine used both in sailplanes and light aircraft. It runs very smoothly and has an elaborate cooling system using both forced air and liquid.
Fuel and Carburetion
If a two-stroke engine is installed, the fuel/oil ratio should be carefully observed and the fuel filters changed once a season. When pumping fuel, always pump through at least one filter. Never use a fuel/oil mixture that is over two months old. Carburetors used in two-strokes include Tillotson, Mikuni and Bing.
These are basically diaphragm carburetors and are sensitive to contamination, if any minute particles of dirt enters the needle valve system. Clean fuel filters are a must as well as flushing the system once a season.
For the Tillotson, the correct main jet size should be used according to the field altitude you are operating from. The Mikuni's high and low speed jets are controlled with tommy-screw needles and great care should be taken to set these needles correctly to prevent an overly leaned mixture.
Ignition:
Most engines use a Contact less Dual Magneto Ignition system (CDI). The ignition boxes and coils producing the spark to the plugs have been known to fail, leaving only one plug firing in each cylinder head. Systems include Bosch and Ducati, with Ducati now used on all new aircraft. Vibration appears to be the cause of ignition box failure as the boxes are mounted on the engine.
Some of the new powered sailplane models now mount the ignition boxes remote from the engine. There is a trouble shooting procedure to isolate which box is defective. Vibration has also been known to rub the insulation off wiring bundles, exposing bare wire which shorts against other metal objects and mimics an ignition box failure.
Ignition wiring bundles are usually wrapped with electric tape and tie-wrapped to the engine or the pylon. If looking at a used powered ship, make sure all ignition circuits are tested during a power run-up.
Cooling:
If the power plant is air cooled make sure all spring attachments of the muffler are secure. The exhaust system must be able to move and vibrate so do not over tighten the spring suspension system. Just make sure all springs are secure and the bolts holding them in place are paint marked.
Clean dirt and grime from the cooling fins. If there is an air guide installed to direct cooling air over the engine, it should be secure and not cracked or broken. For liquid cooled engines, keep the radiator topped up with the proper mix of water and antifreeze. Check especially the radiator hose connections for leaks and be aware that old radiator hoses can partially collapse restricting coolant flow. If the radiator hoses become soft, change them.
Extension / Retraction And Propeller Feathering Systems
For the retractable engine ships there are two basic systems. This includes complete extraction of engine and propeller into the slipstream or extraction of a propeller pylon only. In some models such as the ASH-26E, the engine remains stationary in the fuselage.
On other models like the DG-800B, the engine is attached to the bottom of the propeller pylon and rotates 90 degrees upon retraction, disconnecting the exhaust manifold from the muffler.
In all cases the engine is mounted to a platform that is hinged to the fuselage. Power to extract and retract is supplied by a spindle drive powered by an electric motor. Various relays control the travel of extraction or retraction, the arming of the starter motor and the positioning and braking of the propeller. There are manual over-rides that bypass the automatic sequencing allowing the pilot to directly control engine position and propeller braking.
Some older self-launchers, like the PIK 20E/30, have a manual crank to raise and lower the power plant. Airspeed must be carefully controlled during engine raising or lowering. In essence, anytime the engine or propeller pylon is moved many parts must move, including the engine and propeller, the fuel lines to the carburetors, the wiring bundles to the ignition, the muffler and the liquid cooling system if installed.
This complexity is part and parcel of the retractable engine ship and is subject to vibration, slipstream forces and ground taxi shock forces. In comparison, the motor gliders fixed engine system is quite simple, since the engine and its systems do not move and vibrations are absorbed by the engine mounts. Therefore the retractable power plant system must be inspected carefully before and after each flight to ascertain its integrity.
Also the power plant is contained in a very limited space in the aft fuselage where it is possible for wires, bungees, cables and fuel hoses to become fouled unless they remain in their proper positions.
The propeller on extract or retract can strike the aft fuselage doors if the propeller brake malfunctions. The mating of the exhaust pipe with the muffler is another critical area. To monitor position and control the movement of the engine, the pilot uses buttons and switches and observes Light Emitting Diodes (LED's), a Liquid Crystal Display (LCD) and a rear view mirror.
With use the complexity of a self launcher's cockpit wanes somewhat but still requires attention to details. This is one of the prices paid for not waiting for the tow plane. However, once the engine is stowed, the simplicity and the challenges of piloting a sailplane returns.
Feathering and unfeathering the propeller in a motor glider is a relatively simple chore but does require a time lapse to accomplish. The normal 13-15 seconds to erect the engine in a retractable engine self-launcher can seem like an eternity when close to the ground as the drag and sink increase. Properly done an extract and start should take no longer than 30 seconds with a minimum loss of about 2-300 ft. A windmill start takes longer and consumes precious altitude.
Servicing, Periodic Inspections And Troubleshooting
Power Plant:
For two-stroke engines, selection and continued use of a quality brand name two-stroke petrochemical based mixing oil is encouraged. Use of a 100% synthetic oil is not recommended.
The mixing ratio specified by the engine manufacturer should be carefully observed. For cross-country flights, some pilots carry a small container of two-stroke mixing oil. There is an engine inspection based on engine hours. Some pilots have this inspection completed once a year as engine time is accumulated slowly. The annual inspection does include some engine and propeller inspection items but is not as thorough as the specified engine inspection.
For safety's sake, the engine inspection specified by the maintenance manual should be performed at least every two years. This includes inspection of the carburetors, fuel, cooling, ignition and exhaust systems, including the removal of the exhaust manifold and a visual inspection of the piston walls and rings. It also includes confirming the torque value of the cylinder head bolts.
Pilots are encouraged to take the time to study the maintenance manual before problems occur. A copy of the engine parts and repair manuals should also be on hand to assist maintenance personnel servicing and repairing the engine.
Troubleshooting engine, ignition, carburetion and extraction problems can be time consuming. There are, however, some basic guidelines published in the maintenance manuals that should be reviewed. Symptoms vary but the two basic reasons an engine will not start or run after starting are fuel and ignition.
Here a few examples. The engine will not accept throttle or 'bogs down" when throttle is applied. Some suggested reasons are too rich idle mixture; air in the fuel lines; dirty carburetor needle valves or clogged fuel filters.
Rapid application of the throttle is not recommended as it changes the fuel/air mixture too rapidly. Pumping the throttle makes the problem worse. There is a cross-over from idle jet fuel flow to the main jets that occurs somewhere around 3000 RpM. Proceed slowly through this rpm area. If the main fuel valve is not on, the engine will consume what is remaining in the lines and quit.
To get a hot spark requires at least a 300 rpm crank which means the batteries must be fully charged. Once running, let the temperatures come up and stabilize.
Adding full power soon after starting shortens an engine's life. Always pull the prop through at least twice prior to starting. This assists in lubing and preparing the moving parts for the start.
Airframe:
During the normal pre and post-flight airframe inspections, pay particular attention to all bolt and nut connections, including control hook-ups and control rods. Unlike a non-powered glider, the fuselage, wings and tail and all of their components and parts are subjected to vibrations caused by the engine and propeller. It is vital to carefully inspect all nuts and bolt heads including nylon nut connections. Paint marking of critical nuts and bolts is recommended.
For retractable engine ships, if possible refrain from extended taxi operations and landing with the engine out and running as it can result in undue loads on the engine pylon hinge points. Always conduct a positive control check of all movable control surfaces during the pre-flight inspection. Also ensure the main wheel's braking system is operating correctly and all tires are inflated to the factory recommended pressure. If tail or nose wheel steering is installed, ensure the system moves freely to its limits.
Epilogue
lt has been a pleasure to put together an overview of flying and maintaining a powered sailplane. I realize that in some areas I have not covered all that needs to be known. Frankly, I am still learning.
Perhaps some pilots may be discouraged from entering this type of flying as it entails more than meets the eye compared to the normal joys of soaring. I hope not because powered sailplanes will continue to open up fresh new soaring horizons.
I would like to thank "Motor Gliding International" for permitting me to share some of the things I have learned about flying powered sailplanes. So the next time you see a motor glider leaving the ground or observe a pilot peering into an engine bay, hopefully you will have a better idea of what's going on.
It is Motor Gliding International who should be thanking Pete for starting us off with such an authoritative and interesting article which will undoubtedly be useful as a work of reference.