CHAPTER 2 TECHNICAL AND TECHNICAL ASPECTS OF OPERATIONS

Contents

          Para      Subject

          2.1       Daily Inspections
          2.2       Recording of Defects
          2.3       Fuel
          2.4       Oil
          2.5       Tug Hangar and Fuel Pump Keys
          2.6       Moving aircraft by hand & Putting aircraft away
          2.7       Ropes
          2.8       Moving the Prop by Hand
          2.9       Washing aircraft - windscreens & airframes
          2.10      Counters for engine running time
          2.11      Flight Manual Limitations
          2.12      Engine Costs

          TECHNICAL ASPECTS OF TUG OPERATIONS

          2.13      Cold Starts
          2.14      Radio in Tugs - Useful Frequencies (Table)
          2.15      Warming Up
          2.16      Run Ups - Live Mags, etc
          2.17      Takeoff
          2.18      Climb
          2.19      Red  Operating rpm Band on Lycoming 180 hp Engines
          2.20      Action if an Engine Overheats
          2.21      Release - Critical Engine Handling
          2.22      What to do if you have an accident

This chapter contains material which concerns technical aspects, including maintenance, replenishment, turnround, and some aspects of flying operations which have a substantial technical or engineering bearing, such as engine handling after release, and overheating during the climb.

2.1 DAILY INSPECTION / CHECK A. Amendments to the Air Navigation Order (ANO) have made the DI a mandatory part of the maintenance schedules that exist for all aircraft. It is called the CHECK A. These Checks, which tug pilots are entitled and expected to do, also have to be recorded and signed for in a DI Book kept in the aeroplane. Treat each DI as though you know there is a fault in the aircraft and your life depends on finding it. Over the years people have found fuel leaks, live magnetos, excess play in tailplanes, loose flap guides, undercarriage problems, structural cracks etc that could well have lead to an accident had they not been detected. The Annexes include a guide for the DI of each type.

2.2 RECORDING OF DEFECTS. If an aircraft develops a defect, first write details of the defect on the aircraft's tug log sheet and put a more detailed account in the DI Book. Use words that will be easily understood by other pilots and hangar staff, words are cheap, misunderstandings are not. `Flaps U/S' is not an adequate description, it could mean one of many defects; describe the symptoms in detail. During midweek working hours take the aircraft to the tug hangar, unless the defect is minor, tows are needed, and there is no replacement tug. The hangar staff may be able to fix the defect quickly. Outside hangar working hours, if the defect is such that the aircraft is safe to fly, brief the next pilot on handover. If the defect makes the tug unsafe to fly, ensure an additional obvious notice is put in the cockpit (the log sheet will eventually be taken back to the office so you can't depend on that), inform a senior staff member (Manager, CFI, DCFI, Tugmaster) and finally put the tug into or outside the tug hangar ready for repair. Do not leave this for someone else to do, safety depends on you acting responsibly. The essence is that there should be no possibility of another pilot climbing in and flying the tug in ignorance of the defect that you have found. After weekend operations, the Staff tug pilot or the Manager will check all DI books on a Monday morning, and action any snags.

2.3 REFUELLING. When taxying up to the pump, ensure you do not blow stones into the tug hangar and pull the tug towards the peritrack before restarting it if the hangar doors are open. The hangar staff get very narked if you blow stones and dust at them, in addition they may have covers and cowlings off and the debris could do real damage to another aircraft. At another site an accident occurred when a car passing behind a tug being refuelled caught the rope and pulled the aircraft into the fuel pump. To avoid a similar incident at Lasham pilots must pull the rope clear of the peritrack as soon as they are out of the aircraft. Also, with tailwheel aircraft such as the Super Cub, the rope can get caught in the tailwheel assembly when you are turning the aircraft by hand before taxying away; if this happens and you don't notice it, the first evidence may be a loss of directional control when taxying; if you've put a lot of power on you could taxy into something before you can stop.

2.3.1 Use of Fuel. Fuel drawn must be correctly logged on the fuel sheet kept in the Oil Store alongside the fuel pump, and it is vital the correct aircraft is put down and the whole entry is legible, including your name. Once a fuel log sheet is full, please return it to the Lasham office. At Lasham we use 100 Octane Low Lead Aviation Gasoline (AVGAS 100LL). This is slightly more costly than approved Mogas and ensures safe and legal operation of our aircraft. We have tried approved Mogas and it although it works satisfactorily most of the time, we had problems at high summer temperatures with aircraft that use an engine driven fuel pump so the decision was taken to only use Avgas in our tugs.

2.3.2 Octane Ratings. 180 HP Lycoming Engines are considered to be high compression motors at 8.5:1 and must only be run on 100LL, not 80 or 80/87. At high power, lower octane fuel will cause detonation (knocking or dieseling) in the cylinders instead of controlled burning, and will severely damage an engine. If you are refuelling away from Lasham, remember that AVGAS is available in 4 colour coded grades, 100LL BLUE, 100 GREEN, 80 and 80/87 RED, 115 PURPLE.

2.3.3 Fuel Drain Checks. Therefore, when checking the fuel for water, get used to looking for the blue colour of 100LL, any other colour could mean problems or danger.

2.4.1 Use of Straight Oil. When engines are being run in they are run on STRAIGHT OIL, that is, oil without detergent. When we need it this will also be found in the oil store but will be clearly marked as Straight Oil, it will almost certainly be in a smaller container, probably 5 litre cans, than the usual 50 gallon drum and hopefully should be marked as to which tug it is intended for. Tugs on Straight Oil will be marked as such inside the cockpit or the cowling, and in the DI book. Never mix straight and normal oils, the engine will then take longer to run in since detergent which is designed to prevent wear will have been introduced.

2.6 MOVING AIRCRAFT BY HAND. Care must be taken in moving aircraft by hand, not only so that they are not pushed into things or damaged by people pushing on the wrong places, but also the PROPS MUST ALWAYS BE TREATED AS LIVE EVEN THOUGH THE SWITCHES ARE OFF. It is better to push on the wing tips or fuselage than pull on the prop, only do the latter as a last resort and make sure that it does not turn. See also para 2.8 on live mags. In the case of Regents, the nosewheel handle is not held in by a pin as it is with Rallyes; be careful if you are pulling hard on a Regent handle, if it comes out of the nosewheel fitting you may fall heavily on your back. Aircraft must be pulled clear of the stony ground before starting, since stones damage props and repairs are expensive.

2.6.1 Putting Aircraft Away. Aircraft must be refuelled and reoiled before they are put away at night, they should also be washed down to remove the corrosive effects of the exhaust fumes and the effects of any mud on the airframe and undercarriage. During the summer, Rallyes are put away with tanks 5/8 full (ie just over half), in the winter when the risks of condensation are higher, always completely fill the tanks. The last person to fly a tug in normal day operations is responsible for putting it away unless it is certain the aircraft is needed for the evening such as for a course or air experience trials flights. With the completion of the new Vehicle Building, tugs will be kept in the West end of the hangar. Ultimately we will have a purpose built hangar for the Tugs, which will make life even easier!

2.7.1 Rope Length. The longer the rope, the less chance of a `tug-upset', the uncontrollable nose down pitch due to tailplane stall induced by the glider being too high. An ideal length is 170 ft, in use this can be safely reduced to 150 ft through re-splicing. Currently, rope comes in Metric reels and new ropes are made using 50 metre lengths, (165 ft). 5 Metres can be cut off before an extra length needs splicing on. A quick length check can be made when refuelling, a full length rope will reach from the tug hangar to about half way across the peritrack, and 170 ft is also marked on the peritrack alongside the eastern caravans.
2.7.1.1 Long Tows & Retrieves. This is covered more fully in Chapter 6 (see para 6.3.2), which recommends tying or shackling two normal ropes together for all cross country retrieves (total 300 - 340 ft).

2.7.2 Rope Checks. Tug pilots are responsible for an initial check on the rope they are using. The first rope in use should be checked by whoever does the aircraft DI, and he or she should also check the second rope is on board and has no obvious defects such as missing or cracked rings. The following checks should be made:
2.7.2.1 Tug End - Rings & Weak Link. At the tug end there should be only a Large Ottfur Ring connected directly to the weak link. Check that both are free of cracks. The Weak Link needs 2 RED staples in place, try turning the ends of the staples to check them. RED staples break at 900 lbs. Replace bent or damaged staples from the box in the office.

2.7.2.2 Main Rope - Knots and Fraying. Check the Rope is free of knots and has no frayed areas or obvious wear near the Tost rings, re-splice if necessary.

2.7.2.3 Glider End - TOST Rings. For the glider end only TOST LN65091 Rings sets are allowed. Tost rings have an oval large ring, check this and the small ring for cracks.

2.8.1 Turning over by Hand. Every tug pilot must know how to turn an engine over safely, it is part of the DI and cold start procedures. It is needed to circulate the oil and to avoid any possibility of cylinder damage due to a `hydraulic lock' or `hydraulic-ing', which is firing with sufficient oil accumulated in a cylinder for the volume of oil to impact with the piston and, in extreme cases, blow the valves or even the cylinder head off. It is also used to check the compressions; if one or more are weak, mention this in the DI book and monitor the rate of climb on your first tows to see that the engine is giving adequate power.
2.8.1.1 BEFORE TURNING A PROP DURING THE DI, CHECK:

               BRAKES -       ON
               MIXTURE -      CUT OFF
               MAGS -         OFF
               THROTTLE -     CLOSED

2.8.1.2 GENERAL TECHNIQUE FOR PROP-SWINGING. Remove any loose clothing, particularly scarves which might be sucked into a rotating prop, and your cap if you think that if it fell off you might be tempted to grab it if it was sucked towards the prop disc. Stand well in front of the prop with your weight balanced away from it, so that if it fires you will move away from the prop disc and not towards it. Grasp the prop by the trailing edge and pull it deliberately and firmly down. As you turn it, keep pressure on your hand away from the prop towards you, again so that if it fires or slips out of your grasp, your hand automatically moves out of the prop disc.

2.8.1.3 BEFORE STARTING BY HAND-SWINGING, ENSURE:

1. There is a Competent person in the cockpit, briefed to cut the switches if anything goes wrong.
2. The aircraft is on flat, non slippery ground.
3. Push the aircraft to try the brakes, if in doubt, use chocks.
Before trying to start an engine, always get the feel of it by turning it over a few times with the mags off, use gloves if possible. This will be needed to `suck in'. Then confirm `CONTACT' with the person in the cockpit, and swing with the ignition live. Until you gain experience, step back after each swing and pause before reaching for the prop again. However it is quite acceptable that those who feel nervous about trying to hand-start an engine should not attempt to do so. The four-bladed props are more difficult than two bladers because the impulse that you generate with a hand swing is less, and the next blade is close behind. If in doubt, find a staff member or a more experienced prop-swinger.

2.10 COUNTERS FOR ENGINE RUNNING TIME. Record the engine counter reading shown in the middle of the rpm gauge at the start and end of each day's flying on the aircraft's log sheet. If any cross country flying is done, note the start and finish counter readings. The counter readings are a great help sorting missing or other problem log sheets. They are important, please fill them in.

2.11 FLIGHT MANUAL LIMITATIONS. Advice, recommended practices, and legal requirements are to be found mixed together in the various publications relevant to towing. Documents such as the Air Navigation Order (Sect 37), Civil Aviation Publication 393 (CAP 393), CAA and BGA Information Circulars, BGA Laws and Rules and the Aircraft Flight Manual all contain valuable information some of which is mandatory either to the conduct of the flight or the maintenance of the aircraft and its equipment. Unfortunately, some of the information does not agree with others. As an example, Rallyes have a different placarded maximum towing weight to the one given in the Flight Manual. Whenever possible, stick to the Flight Manual as the manual is part of the Certificate of Airworthiness and is approved by the CAA. The aircraft must be operated within the limitations given in the Flight Manual (ie airframe & engine limitations such as Vne, Vra, Vm, Vflap, Vmin tow, rpm, oil temp/pressure, CHT etc) for the C of A and therefore the Insurance to be valid (unless the exceedance of a given limit was caused by a plausible course of action following a malfunction or emergency).

2.12 ENGINE COSTS. At the time of printing, a Lycoming 180 hp engine cost £12,000 to buy new or £9,500 to overhaul an existing engine. At Lasham we have only ever had two engines go past 2000 hours without needing cylinder repairs, in 2144 hours in G-BLGS from 78 to 83, and 2800 hours in G-BJUD up to the time of printing. Often the cost of the repairs reaches £2000 as a cylinder costs £1000 and a piston without rings £450. With sums as large as these involved it is obviously vital pilots take the utmost care of their engines from start up to shutdown.

TECHNICAL ASPECTS OF OPERATIONS

2.13 COLD STARTS. The following applies to the first start of the day all year and to every start when the engine is cold during the winter months. Before turning the engine over with the starter, pilots should give 4 primes on the throttle and then, taking the precautions listed in para 2.8.1, turn the engine over at least 4 compressions by hand. Turning the engine over will check for hydraulic locks and good compressions, it will also circulate the oil and draw in some mixture to aid starting.

2.14 RADIOS IN TUGS. Radio switches and controls are deliberately small for low weight and minimal space requirements, so operate them gently - we have had some pulled off! Inevitably their small size makes these controls easily broken and vulnerable to mishandling. The radios are designed for aircraft use and so should be OK to be on during start up and shut down, after all, at some airfields you have to ask Air Traffic for start clearance and you can't do this without radio! However, some people say that radios last longer if you turn them off during engine start and stopping since the aircraft electrical system may produce an uneven voltage while the alternator runs up or down; at Lasham there is no evidence either way so it's your choice. Pilots without R/T Licences are reminded that they should be working for one, and no new tug pilots will be accepted unless they have an R/T Licence. The radios are a big help in retrieves, especially into airfields, and across zones. If you are restricted to the BGA frequencies, ie by not having an R/T licence, and are unable to talk to Air Traffic, you are likely to be increasingly restricted to flying at Lasham only.

USEFUL RADIO FREQUENCIES (MHz, listed in numerical order)

2.15 WARMING UP. As soon as an engine responds to the throttle and the oil pressure is satisfactory, ie not too high and not too low, the aircraft can be taxied onto the airfield ready to run up. It may seem surprising but it is actually bad practice to try too hard to `warm up' an aircooled engine (liquid cooled engines are different). In their engine manuals, Lycoming stress that adequate cooling and even cylinder temperatures are only provided by the forward speed of the aircraft and that ground running should be kept to a minimum using only a maximum of 1000 to 1200 RPM. Lycoming also suggest taking off as soon as the engine responds to the throttle without faltering, rather than waiting for a set oil temperature on the gauge. The reason for this advice is to avoid local hot spots developing in cylinder walls that can wear the cylinder and its piston. In practice this means that, at normal ambient temperatures, an aircraft that has been taxied out and run up is going to be warm enough for take off. It does not mean that in the dead of winter you can take off safely straight away, use common sense and when it's cold, warm the engine for longer. Where an aircraft has stood alongside the aerotow point, run it at 1000-1200 RPM until the oil temp is obviously rising and the CHT nearing 125°C before commencing a take off; idling rpm is too low as it can cause plug oiling. The higher rpm gets the fuel flowing through the carburettor and also avoids any tendency for a `rich cut' on takeoff due to overfuelling as you go to full power.

2.16 ENGINE RUN UPS. Position the aircraft on the airfield on short grass well away from any stones. Check the nose is into wind to aid cooling, make sure that the propwash will not affect anyone else, and check that the way ahead is clear just in case the brakes fail. Check the mags at 1800 RPM on 180HP engines. Ensure there is both a mag drop and a recovery to the original rpm.

2.16.1 Live mags. If, on switching off one mag during the mag check at 1800 rpm, a lack of any mag drop at all indicates not that the remaining mag circuit is in perfect health, but that the mag you just switched off is still live. Twin mag engines are designed to run better when both plugs are firing in each cylinder because the burning of the fuel/air mixture is more even. With only one mag firing per cylinder, the flame front will spread through the cylinder in a less symmetrical way, the engine will be less efficient, and the rpm will drop slightly from the normal two mag rpm. If you are in any doubt about a possible live mag, throttle fully back, allow the rpm to decay to a minimum, and shut down by turning off both mags rather than using the fuel cut. Never switch on again as the rpm is decaying since this causes shock loading of the crankshaft; always allow the engine to stop and then restart from scratch. This procedure will always show a live mag since the engine will continue to idle with both switches off. A live mag should ground an aircraft, since if you lost part of the prop or suffered severe engine damage (broken conrod, etc) in flight you have to be able to stop the engine very quickly before vibration causes more damage. Your survival may depend on how quickly you turn the mags off, since in extreme cases engines have vibrated clean out of their mountings, leaving the airframe with a rather aft C of G ! You can stop an engine by leaning the mixture fully, but this takes longer than switching off the mags.

2.16.2 Mag Drop. Accept mag drops of up to 125 RPM, rough running is a worse symptom than the magnitude of the actual rpm drop itself. Plug oiling (due, for instance, to running at idle rpm) can cause both greater drops and rough running. To burn off any oil, increase to a max of 2200 (the maximum allowable on the ground) and then try the mags again at 1800. On older engines you may find one mag is giving a drop of around 250 RPM accompanied with rough running and in this case it is worth trying increasing the RPM to 2200, and leaning the mixture until the revs start to decrease; at this point pause, then go back to full rich, reduce to 1800 and try the mag again. At these higher rpms, make sure that the aircraft does not move forward against the brakes, or in the case of the Cub, does not tend to nose over. Also, check that the slipstream does not hazard anything or anyone behind you.

2.16.3 Carb Heat Check. Applying full Carb Heat at the mag check RPM should cause a drop of between a 100 and 200 RPM with a full recovery as you go back to cold air. No drop might mean that the Carb Heat is permanently ON, with consequent loss of power, particularly on takeoff.

2.16.4 Idling RPM. The last part of the run up is to check that the idling rpm is between 500 and 700 and that the engine does not tend to stop with the throttle closed. Because this check is usually done before the engine has reached its normal operating temp the tickover may well be slow, this is acceptable whereas over 800 RPM would need adjustment before flight as it would lead to prolonged landing runs and fast taxying.

2.18 CLIMB. Climbs while towing should normally be carried out at full throttle. The engine has a full power mixture enrichment jet that provides an over-rich mixture to help cool the exhaust valves, this is brought into use by the last 10% of the throttle movement and there is the danger that if you reduce power you may shut this jet off, making things worse for the engine. Lycoming say there is no advantage in climbing at reduced power. The enrichment jet also greatly reduces the possibility of carburettor icing while it is in operation; some say it eliminates it but in severe icing conditions there must be a possibility of it occurring, at least upstream of the point at which the enriched mixture is injected into the carb venturi. Monitor the CHT, which must not exceed 260°C (500°F). The oil temp must also be watched carefully, it must not exceed 118°C (245°F), see para 2.20. As oil is progressively overheated, it loses a lot of its lubricating qualities and engine bearings can be damaged. Use of the mixture control to lean the mixture is not normally recommended above 75% power. However when doing a high or long tow it is acceptable to lean an engine even at full throttle just sufficiently to restore smooth running, but this should not be necessary below 4000 ft. Do not attempt to lean an engine to gain extra RPM.

2.19 THE RED OPERATING BAND ON 180 HP ENGINES. The Lycoming 180HP Engine comes in many versions, each of which can be fitted with a variety of different propellers Unfortunately tests and bitter experience have shown that certain combinations of engines and propellers interact between 2150 and 2350 RPM. This interaction is caused by the engine being a high compression design with 4 big cylinders; each firing stroke transmits a healthy punch to the crankshaft which flexes in torsion and develops a significant torsional vibration in the speed range quoted. This vibration is picked up by the propeller which translates it into a point of maximum vibration about 10 inches in from the propeller tip, this has caused the fatigue failure and loss of individual blade tips in flight resulting in severe engine vibration, emergency engine shutdowns and forced landings into fields. The engine/propeller combination most at risk is the hollow crankshaft A2A and A3A series engines fitted with a fixed pitch metal propeller. Fortunately at Lasham we have pursued a policy of solid crank A3A and A4A engines, and wooden four-blade propellers. At the time of printing, there is no red band restriction on any of our tugs. However most other clubs still operate the hollow cranks, so be aware if we have a visiting tug on site.

2.20 ACTIONS IF AN ENGINE OVERHEATS. In hot weather, the tug pilot may notice either the cylinder head temperature or the oil temperature reaching the red line. If this happens, speed up the tow by 5 to 10 Knots. If this fails to halt the temperature rise try reducing rpm by 50-100 and if this fails, wave off the glider and land. After landing, check the following:

2.20.1 Oil. Allow about 5 mins for the oil to drain into the sump, then check the contents and top up if necessary. If anyone tries to tell you that engines run cooler with less oil than full because the oil will be going through the oil cooler more often ignore them, we have tried it and full engines run cooler. It is also bad airmanship to deliberately run with low oil, you are closer to losing oil pressure and/or damaging the engine in the event of high oil consumption or an oil leak developing.

2.20.2 OIL COOLER. Check it is not clogged with leaves or insects and the cowling around it is in good order.

2.20.3 ENGINE BAFFLES. Check for loose baffles and missing edging strips inside the engine bay. The baffles direct the cooling air inside the cowlings and if they don't work properly you get overheating. We had a problem in the past with a Cub that lost a large part of the engine baffles and this went unnoticed until a spell of hot weather caused the engine to overheat. Even then it needed comparison with our other Cub to understand what had happened.

2.20.4 SILENCERS. This has been a recurrent problem on the Cub. Loose baffles inside the silencer or distortion of the main tubing can increase the air resistance to exhaust gases. The back pressure on the exhaust manifold causes a loss of power and sometimes engine overheating, which in the worst case has prevented the aircraft sustaining level flight.

2.20.5 CARB AIR INTAKE. Check that the air filter is secure and not clogged, that the hot air ducting is in order, and that hot air is shutting off as it should.

2.20.6 OIL CONSUMPTION. Engines using more than a quart of oil for 20 tows probably have worn piston rings. During the power stroke, this allows some hot gases to blow into the crank case, thus heating the engine oil. Worn rings also let oil into the combustion chamber during the induction stroke, and this oil is then turned into carbon in the cylinder which in turn can cause pre-ignition, detonation (knocking or dieseling), and so further overheating and possibly damage to the cylinder and valves. There is also a power loss due to the lost gases, so monitor rate of climb to ensure that it is adequate, but throttle back if the engine shakes or knocks.

2.21.1 THIS IS WHAT ALWAYS HAPPENS. By the top of the climb the exhaust valve and its seat will be glowing red hot and the seat will have expanded as much as it can in the cylinder. Some of the stress of this expansion is relieved by the fact the cylinder will also have heated up and expanded. As the glider releases the pilot has two choices, either to handle the engine carefully or to demonstrate his poor airmanship to those watching and listening on the ground.

2.21.2 THIS IS WHAT HAPPENS WHEN THINGS ARE MISHANDLED. The glider pulls off, the tug pilot shuts the throttle and then dives quickly away. Inside the engine the valve seats are still red and expanded but the outside of each cylinder is now being rapidly cooled by the increasing airflow. This cooling is aided by the fact there is now no heat from combustion being fed to the cylinder walls. Cooling makes the cylinders try to contract but they cannot shrink around the exhaust valve seat which being of a dense steel takes longer to cool and contract. Within an inch of the exhaust valve seat is either of the spark plug holes and the stresses of having a hot expanded seat in a cool cylinder are sufficient to cause a crack to occur between the valve and a plug . It's a bit like banging a nail into a bit of wood (the cylinder), if the nail (the seat) is too big and too near the end (the plug hole) the wood splits.

2.21.3 THIS IS WHAT HAPPENS WHEN THINGS ARE HANDLED WELL. The glider releases, the tug pilot begins a turn, reducing power just enough to prevent overspeeding the engine. This is a throttle reduction of only about half an inch. Subsequently, he reduces power in several small stages in order to keep the rpm from increasing while he gradually increases speed, taking at least 10 seconds and preferably 15 before stabilising at 2000 rpm for the descent. If conditions make a turn inadvisable (such as proximity of gliders), adopt the same technique of a slow power reduction and a slow increase in speed, the tug may climb a little at first but this is acceptable and definitely preferable to cracked cylinders. Inside the engine, the valve seats are hot but now the pilot is also keeping as much power as he can in the engine, rather than just throttling back, the cylinders are cooling and contracting, but are not doing so too quickly. The heat from partial power is enough to keep the cylinders from cooling too rapidly while allowing the exhaust valve and its seat to cool. In addition, the airspeed is not being allowed to rise as fast as before and so the outside of the cylinder is not being subjected to such rapid cooling. It is generally accepted that this cooling from the peak temperatures actually occurs quite quickly, probably within the first 10 seconds of the descent. Therefore if you take 10 seconds to throttle back from full power to 2000 RPM and do not let the speed build up too fast, you are handling the engine correctly. Try counting 10 seconds in flight, it is longer than most people think! Using this technique also prevents the propeller driving the engine which is to be avoided as much as possible as it causes the rings to wear, the piston ring grooves, causing low compression and higher oil consumption.

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Last updated by John Leibacher on Sunday, November 5, 1995 at 17:47