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PowerPlant
Recip Engines (Additional Q's by Jcarrig73)
| Question | Answer |
|---|---|
| What is the most common connecting rod arrangement on Radial Engines? | Master Rod on a single throw, with all other pistons connected to the master rod with link rods |
| What speed does the Camshaft rotate at, relative to the Crankshaft? | 1/2 the speed of the crankshaft |
| What is the purpose of valve overlap? | Helps scavenge pressure from the exhaust leaving the cylinder, helping to draw in the intake mixture |
| What are the types of piston rings in a recip engine? (3 Types) | Compression, Oil-Control, Scraper (Wiper) rings |
| If the valve clearance is too much, what impact will it have on the valve? | It will open late, and close early |
| If the valve clearance is too little, what impact will it have on the valve? | It will open early, and close late |
| What are Main Bearings usually made of for Radial Engines? | Steel-Backed, Lead-Alloy bearing inserts |
| What are Cam-ground pistons? Why are they used? | Pistons that are slightly oval-shaped (longer parallel to wrist pin) When they expand with heat, they become perfectly round |
| Why are two valve springs used on each recip-engine valve? | The different pitch and diameter of the springs causes them to vibrate at separate frequencies, which reduces valve float by making sure at least 1 spring is always exerting force on the valve |
| What do hydraulic valve lifters do for recip engines? | They reduce wear on valve-train parts by eliminating the clearance from the valve-operating mechanism (no gap/impacting parts) |
| What material makes up most piston rings? | Gray Cast-Iron |
| What is a Full-Floating Wrist Pin? | The pin is not clamped to either the piston, or the rod. |
| What keeps Full-Floating Wrist Pins from scoring the cylinder? | Soft Metal plugs |
| On what stroke does the exhaust valve open? | Power Stroke |
| What is the definition of Compression Ratio for Recip Engines? | Ratio: Volume of Cylinder with Piston @ BDC to Volume @ TDC |
| What is Detonation? What causes it? | Uncontrolled, explosive combustion. It occurs under excessive heat and pressure (mixture reaches critical pressure/temp). |
| Why are compression checks done? | Assess the seals between rings/cylinder walls, and the valves/valve seats |
| How can you tell how many throws a crankshaft has? (Horiz.-Opposed recips) | The # of cylinders |
| Why are some exhaust valves filled with Metallic Sodium? | Reduced valve temps. Sodium sloshes, transfers heat from valve head into valve stem, through the valve guide into the cylinder head |
| What is Hot Clearance used for? (Radial Engines) How does it differ from Cold Clearance? | Hot clearance used for Valve Timing. Timing set for valves in Cylinder #1, then all valves adjusted to cold clearance. |
| How far (from TDC is the piston head when ignition occurs? | ~30 degrees before TDC, on compression stroke |
| When does the intake valve begin to open? | During the exhaust stroke |
| When reducing engine power with a constant speed prop, which is adjusted first? Throttle (Manifold Pressure), or Prop RPM? | Throttle - When operating near BMEP, the throttle is reduced first, otherwise, high manifold pressures and low rpm cause damaging-high cylinder pressures |
| Radial engine master rod bearings are _ type bearings? | Plain-Type bearings |
| Operating at high power settings before proper warm-up can cause what? | Oil starvation of bearings, etc. |
| Why can aircraft cylinders NOT be oversized as much as automobile cylinders? | The walls are relatively thin, and may be treated (nitrided, etc). |
| How is crankshaft run-out measured? | Using a dial caliper, rotate for 1 complete revolution. Total Runout = Difference between Max and Min readings. |
| Why should Aluminum/Magnesium NOT be cleaned with Soap solutions? | The soap will be impregnated in the surface, causes engine oil foaming and contamination |
| In a cold engine, will oil pressure be higher, or lower than normal? | Higher |
| At what degree of crankshaft travel will piston-speed be the fastest? | 90 degrees after TDC (Accelerates, then decelerates before it reaches the end of the stroke) |
| If engine misses in both L and R mag positions, most likely problem is: | 1 or more Cold cylinders |
| After servicing, spark plugs should be reinstalled in what order? | Next in firing order, and swapped Bottom to top (from where they were removed) |
| Increased water vapor (higher humidity) has what affect on a recip engine? | Decreased engine power @ constant RPM /Manifold Pressure (water vapor 5/8 weight of dry air, less power produced) |
| The amount of energy released by burning fuel-air mixture is determined by the _ of both the fuel and air | Weight (Water vapor is 5/8 the weight of dry air, so less power produced) |
| How is valve stretch measured? | Caliper to the stem diameter (thinner/smaller when stretched out), or radius gauge (between stem and the head) |
| What type of piston rings may be used in Nitrided, or Chrome-plated cylinders? | Cast iron rings |
| Can chrome-plated piston rings be used in chrome/nitrided cylinders? | No (they can be used in plain-steel cylinders |
| Increase in manifold pressure, with constant RPM causes the bearing load to _? | Increase |
| The floating control thermostat regulates oil temp how? | By controlling air flow through the oil cooler |
| If an overhead valve engine has too small valve clearances, what will most likely happen? | The valves will not fully seat during start/warmup, since the clearance opens up as the cylinder head expands. |
| Excessive valve clearance will reduce _ on recip engines? | Valve Overlap |
| What is the best indication of worn valve guides? | High oil consumption |
| Most likely cause of a Backfire at low rpm? | Lean mixture |
| Does a dead cylinder show up on a magneto check? Why/Why not? | No, because the cylinder is not firing on either magneto. |
| If an engine is running rough, manifold pressure is higher than normal at all rpms, and mag drop is normal, what is the likely cause? | Dead cylinder: throttle is higher to obtain the same rpm, leading to higher manifold pressures. Mag check won't show, since cylinder won't fire on either mag. |
| Why are mineral solvents used instead of water-mixed degreasers? | Soap based residues cause oil contamination and foaming, and may corrode aluminum/magnesium parts |
| At how many revolutions of the crankshaft does each cylinder fire? | Every other revolution of the crankshaft (Engine will have to turn 2x as fast to obtain a set # of firings per minute) |
| Most likely cause of detonation? | Using fuel with too LOW an octane rating (Octane rating is measure of detonation resistance) |
| What does the Octane Rating of a fuel describe? | The measure of detonation resistance |
| Engine Crankshaft runout is usually only performed when? | At Engine Overhaul, or after any "Sudden Stoppage" event. |
| An excessive valve clearance affects the valves how? | Decreases the amount of time the valves are open. |
| The main purpose in setting proper valve timing and overlap is? | To obtain the best volumetric efficiency, and lower ops temps. (If the mixture burns BEFORE the piston goes down, the walls won't overheat) |
| Hydraulic lifters, when the engine is NOT operating, should have a greater/lower clearance? | Greater: When the lifters are flat, the gap opens up. When they are full, the gap is closed (during operation) |
| What is the purpose of choked/tapered cylinders? | Provide a straight cylinder bore @ operating temps. |
| Master rod bearings (radial engines) are usually what kind of bearings? | Plain bearings |
| Compression Ratio is the measure between_? | Cylinder volume at BDC and TDC |
| What tool is used to measure crankshaft rotation in degrees? | Timing disk |
| When operating with a fixed pitch prop/test club, a "Weak Engine" is indicated by what? | Lower than normal static RPM @ full throttle operation |
| Reduced air density (on carbureted engines) reduces engine power by _ the mixture? | Excessively Enriching the fuel/air mixture. (The air is less dense than SL, The fuel metered for the same VOLUME of air will be too rich. |
| In a constant speed prop, Manifold pressure is controlled with what? | Throttle |
| 14 CFR 43 Appendix D requires what to be performed during a 100hr/Annual? | Compression check |
| Ideally, when should the combustion process be completed by? | Just after TDC |
| If the intake valve were to open too early in the cycle, it could cause what? | Backfire (burning exhaust gases enter the induction system and ignite the mixture. |
| The altitude at which a turbocharged engine can no longer maintain SL pressure is called what? | Critical Altitude |
| On a radial engine with a floating cam ring, what must be done while adjusting the valves? | You must depress the valves on the opposite side of the engine, which allows the cam ring to pull towards the bearing on the side being checked. |
| Engine with low oil pressure and high oil temp could indicate what? | Leaking oil dilution valve |
| Why does an engine with more cylinders operate more smoothly? | The power pulses are spaced more closely together |
| Fuel detonation characteristics, Design limitations, and the amount of Supercharging all effect the _ of the engine? | Maximum Compression Ratio |
| On opposed-engines with hydraulic lifters, how is valve clearance adjusted? | Replacing the Push-Rods |
| Which causes the least amount of rolling friction: Ball bearings, or Roller bearings? | Ball Bearings |
| For compression ratios, the number is expressed as the Volume at _ to the volume at _. | BDC to TDC. (Think the full amount of air, squeezed down to how little space) |
| Is the mixture for Best Power richer/leaner than Best Economy? | Richer |
| For Radial engines, is operating valve clearance greater/smaller than Cold Clearance? | Greater: the Cylinder head expands further than the rest of the cylinder, which opens up the gap. |
| Moveable counterweights on crankshafts help reduce what kind of vibrations? | Torsional Vibrations |
| The thrust bearings in most Radial engines are what kind of bearings? | Deep-Groove Ball Bearings (better for reducing friction, while carrying both thrust and radial loads). |
| Propeller reduction gears allow the engine rpm and power to increase, and have what effect on the prop? | Allow the prop to remain at a lower, more efficient RPM |
| Pre-oiling is usually required during what kind of maintenance? | Engine Overhaul/Installation |
| If the Hot clearance is used to set a cold engine, how will it affect the operation? | The valves will open late and close early (shortens the time the valves are open, since the gap is greater). |
| High manifold pressure, High intake-temperature, and an overheated engine can all contribute to what? | Increased tendency to detonate |
| A mixture leaner than the manual lean mixture of .060 can cause overheating where? | The exhaust valve, since the leaner mixture will continue burning into the exhaust system. |
| To check for hydraulic lock, the engine should be turned 3-4 rotations in what direction of rotation? | Normal direction of rotation |
| You should check for hydraulic lock if the engine has been shut down for more than _ minutes? | 30 Minutes |
| As you increase in altitude (without a supercharger), will the Volume, or Density of the air decrease? How will it affect engine operation? | The density of the air decreases, leading to a decrease in engine power. |
| In a dry-sump engine, how do you tell if the engine is pre-oiled sufficiently? | When oil flows from the return line, or indicator port. |
| On Dyna-Focal engine mounts, the shock mounts point towards what? | The Engines' Center of Gravity |
| How to you measure piston-ring end-gap clearance? | With the ring in the cylinder, and use a feeler gauge to measure the gap between the ends. |
| The actual horsepower delivered to the propeller is called what? | Brake Horsepower |
| What purpose does firing order serve in an opposed engine? | Balance, and eliminating vibration as much as possible |
| If non-magnetic (non-ferrous) particles are found in the oil sump and filter, where are they most likely from? | Could be from the plain-type bearings, or the pistons, since they are not magnetic. The cause should be investigated further. |
| Is a small induction air-leak more noticable at High or Low RPM? | Low RPMs, because the relatively small amount of air coming in the intake is affected more by the additional air, which has a greater affect on the mixture. |
| Multiple valve springs are used in order to eliminate what? Why? | Valve spring surge, or "Vibrations". The springs are different sizes to prevent both from vibrating at the same resonant frequencies. |
| When inspecting Engine Control Push/Pull rods, how do you check for proper thread engagement? | Using the inspection hole. If you can pass a piece of safety-wire into the hole, then it may not be engaged far enough. Check the amount required. |
| If the oil pressure gauge fluctuates between 0 and Normal, what is the likely cause? | Low oil supply. It drops to 0 when the pump draws air, and returns to normal when oil passes through. |
| When does valve overlap occur? | End of the exhaust stroke, beginning of the intake stroke. |
| The horsepower developed in the cylinders is called what? | Indicated Horsepower |
| When does Ignition normally occur in recip engines? | Just before TDC on the Compression stroke |
Created by:
avandermey
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