62 votes
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What instructions should I give to an untrained passenger for Hand propping Cessna 172N as a pilot?

That is crazy. DON'T just rely on an person who's new to airplanes and only training is 5 minutes of showing them what to do, who may or may not react correctly when it springs to life, as the only ...
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  • 105k
43 votes
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What is the loud noise of a helicopter when the rotors are not yet moving?

The sound you're hearing is the APU (Auxiliary Power Unit) running. Turbine (jet) engines turn at a much higher RPM than reciprocating engines. This means that an electric starter motor would have to ...
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42 votes
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Starting on the left magneto only - why?

The reasons seems to be that only the left magneto is equipped with an impulse coupling which delays and intensifies the spark during engine starting: Many opposed reciprocating engines are equipped ...
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  • 45k
35 votes
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Why do I hear the "real" engine noise only when the plane is on the runway?

When you have the thrust levers of, say, a 747 all the way back to idle, the airplane still has enough power to move. In fact, you will have to use the brakes to keep it from taxiing too fast. If you ...
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33 votes
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Why do ground crews rotate a radial engine's propeller before a motor/cartridge start?

Radial engines - especially older large-bore designs like you find in WWII era warbirds - can suffer from a phenomenon known as hydraulic lock. Basically while the engine is off and cooling some ...
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  • 67.2k
28 votes

Is center tank fuel required to start the 737-800 engines?

No, it is perfectly normal to operate without any fuel in the center tank. Until your fuel load is over about 17,000 lbs, the center tank should be empty. That’s enough for about 2 hours of flying, ...
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27 votes

Did people really hand-start big bombers in WWII?

When you shut down a radial the unscavenged oil in the case (oil coating the surfaces that didn't get pumped back to the reservoir tank) runs down and seeps past the rings of the cylinders directly ...
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23 votes
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Is starting a jet engine without ground support possible?

Modern jet transport category aircraft have APUs and they will be running if no engines are. Batteries on jets do not work very long with all electrical buses energized and the first thing you do ...
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22 votes

What instructions should I give to an untrained passenger for Hand propping Cessna 172N as a pilot?

I’ll second John K’s answer. Do not attempt to hand prop an airplane without receiving professional instruction on how to do it safely. It is a real easy way to get seriously injured or killed, as ...
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21 votes

What is the loud noise of a helicopter when the rotors are not yet moving?

You may be expecting the rotor to spin up in lock-sync with the engine. That's not quite what happens on a turbine helicopter. Turbine helicopter engines (turboshaft engines) have a turbojet ...
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20 votes
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How do you start a jet engine if the start valve is stuck closed?

Perusing the A380 Training Guide, Edition 01, 01 Sep 2008, Section 5 - Engine Starts, Subsections 5.8.6 (Engine Start Valve Stuck Closed), 5.8.6 Engine Start Valve Stuck Closed ECAM actions ...
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20 votes
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Why do aircraft piston engines require priming?

Modern car engines are really very sophisticated compared to most airplane piston engines, which are 70 year old technology. Modern cars typically have an electric fuel pump in the tank which is ...
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  • 49.6k
19 votes

Starting on the left magneto only - why?

Magnetos perform badly at low speed, and their timing will be too advanced during start, making the spark too early. Usually the left magneto has an impulse coupler, which is a coil spring driven cam, ...
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  • 49.6k
18 votes

Why do we monitor N2 speed rather than N1, when starting jet engine?

If it's a turbofan, N2 represents the core engine compressor/turbine spool that is creating the compress/burn/expand energy that drives the fan, and is exposed to the most energy, that is, velocity ...
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  • 105k
16 votes

Why are engines with carburetors hard to start in cold weather?

They are all harder to start in the cold, fuel injected engines included, and need an over-rich mixture for starting. The rich mixture is required because a lean one is harder for a spark to light ...
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  • 105k
15 votes
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Is it possible to hand start modern planes?

You sure can! In reality the engines in modern prop planes are not all that different (in some cases even identical) to the engines of the hand crank days. The reason many older planes were hand ...
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  • 96k
15 votes
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Why are the engines on the MAX and neo prone to bowing?

Rotor bowing is not unique to this generation of engines. It was an issue with the early IAE V2500. I remember initially they would have somebody manually rotate the fan some time after shutdown. This ...
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  • 5,692
14 votes

Why do ground crews rotate a radial engine's propeller before a motor/cartridge start?

It is oil. When the engine is cold, the piston rings don't quite seal the cylinder and oil leaks past and pools in the bottom cylinders. If the engine is started with oil above the pistons (looking ...
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  • 30.8k
14 votes

Can a jet engine be restarted after a catastrophic failure?

I have no desire to dispute what a fellow retired 747 captain said, so I'm wondering if there was some miscommunication between you and the captain. Or perhaps his definition of catastrophic is ...
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  • 38.7k
14 votes
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What are the consequences of pumping the throttle in an carburetor piston engine airplane during start?

Pumping the carb during a cold start, in an updraft engine such as the 152 has, is the #1 cause of engine fires, and can be eliminated by the proper and factory recommended starting procedure. The ...
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  • 17.4k
13 votes
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Why is engine No.2 started first, instead of No.1?

The isolation valve in Open or Auto ensures that the Auxiliary Power Unit (APU) bleed air reaches the engine number 2 starter. ...
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  • 3,530
12 votes

Is it possible to hand start modern planes?

If so, how do you do it safely without cutting your hands off or being pulled in by the propeller? The short answer is "very carefully." A longer answer, and the way my father taught me to do it (...
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  • 38.7k
11 votes

How are turbine engines started?

I guess now it is my turn to add exotic ways to start a jet engine. The Jumo 004 of the Me-262 and Ar-234 had a small piston engine in the central spike which was electrically started, but also could ...
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11 votes

How are turbine engines started?

Excellent answers so far. There are a couple other ways in which a jet engine can be started. The F-16 has the engine connected to a gearbox with a special, high-speed-balanced shaft. There is a ...
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  • 1,257
11 votes

Why must some aircraft get permission to start their engines?

Airliners usually push back from the gate and then start their engines when well clear. If the aircraft has an unserviceable APU, a ground based power supply must be used at the gate for the start. ...
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  • 32.2k
11 votes

Which commercial aircraft can perform a parallel engine start?

The main reason behind this capability is that the Boeing 787 starts its engines entirely on electrical power generated by the APU's VFSG (Variable Frequency Starter Generators) vs relying on APU ...
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11 votes
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Why don't all cylinders have priming lines?

The airplane maker will not normally install any more primer lines than necessary. In warm environments it's not usually necessary to prime more than one cylinder, so you will see airplanes operated ...
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