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Copyright 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013, 2014 by Paul Woodford. All rights reserved.

Air-Minded: Get Your Motor Runnin’

I’ve been thinking about the different methods of starting aircraft engines ever since I saw a video of an early jet performing a cart start. But I’ll get back to that.

Today you start almost all aircraft piston engines the same way you start your car: by turning on the ignition and engaging an electric starter motor. Of course this wasn’t always the way. In the beginning you had to hand-prop them. If you own a J3 Cub like the one in this video, you still do:

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Obviously hand-propping is sporty, and larger engines with higher compression demanded different (and safer) starting methods. One early solution was the inertial starter, a hand-cranked device that, although you really had to put your back into it, at least had the advantage of not putting you directly in the plane of the spinning propeller. In this video you can see a ground crewman’s head bobbing up and down as he cranks the inertial starter of a Boeing P-26 Peashooter:

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Another solution was a Rube Goldberg contraption called the Hucks starter, a gear- or chain-driven shaft powered by an automobile engine that engaged a boss mounted on the center of the propeller spinner. The Japanese used this starting method on many of their WWII-era aircraft, eliminating the complexity and weight of internal starters and batteries. Here’s a Hucks starter being used to crank up a Hawker Hind:

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Few people born into the jet age have witnessed large radial engines starting up. Believe me, even back in the day it was a sight to see. When radials aren’t running oil seeps past the piston rings into the compression chambers of the lower cylinders, creating smoke and fire on startup. Here’s a Lockheed Constellation using a conventional electric starter to crank up number one after an engine change (you’ll see the smoke gradually fade as the oil burns off):

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Many aircraft during the piston engine era had a backup starting system: the Coffman starter, aka the “shotgun starter.” The act of using the Coffman starter was called a “cart start” for the large shotgun-like cordite cartridges used to turn the engine. If you think you’ve never seen a cart start, think again … it featured in one of the most suspenseful moments of the original Flight of the Phoenix movie:

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I’d heard of B-52 bombers using cart starts during alert scrambles, but it never really registered with me that this was essentially the same thing as a piston engine cart start. When you cart start a piston engine, expanding gas from the cartridge detonation pushes a separate piston which drives a screw thread to turn the engine over. When you cart start a jet, the expanding gas is used to spin the engine’s compressor blades.

Here’s a video of two late-1940s deHavilland Venoms performing cart starts. The first start occurs 55 seconds in and is very dramatic. The second one happens at 4:56 and is even more dramatic. I think you’ll be able to spot the obvious advantages of jet engine cart starts: they’re fast and require no ground support. This is the video I mentioned at the top of this entry, the one that got me interested in the various methods of starting aircraft engines:

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By contrast, here’s another late-1940s jet, a two-seat deHavilland Vampire trainer like the one I photoblogged in a previous entry, using its internal starter motor to spin the engine up. Notice the electrical cable hooked to the right side of the fuselage: pilots typically use external electrical power when it’s available in order to spare their batteries. The ticking noise you hear is the spark igniter: once the engine’s spinning and air is flowing through it, fuel is introduced and the spark igniter lights it off:

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It’s probably a good thing modern airliner jet engines don’t light off with visible flames like those early engines did … you’d have passengers scrambling for the emergency exits every time you started up.

Like the Vampire in the above video, the T-37 I flew in the USAF used built-in electric starters to get its jet engines spinning. Later, when I flew T-38s, we hooked up to an external power unit called a Palouste (indeed, you couldn’t start without one). A Palouste uses a piston engine or small gas turbine to force a large volume of fast-moving air through a hose and into an aircraft’s engine. As with expanding gas from a cart start, air from the Palouste is ported into the engine’s compressor section to get it spinning. This video shows a Palouste being used to start the engines on an F-4 (you can see the ground crew disconnect the air hose after both engines are running):

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The F-15 Eagle I flew for most of my USAF career incorporated a self-contained starter system consisting of a small auxiliary power unit called the jet fuel starter: you’d pull a T-handle in the cockpit to discharge a hydraulic accumulator which would start the JFS (itself a small jet engine). Once the JFS was running, it would port bleed air to each main engine in turn to start them. When both engines were running the JFS would shut itself down and utility hydraulic pressure would recharge the accumulator. It wasn’t as fast as a cart start, but no external power was necessary. In this video you can hear the JFS running and each main engine starting in turn, followed by the sound of the JFS spinning down:

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You might not think so, but starting the F-15′s engines is just as noisy to the pilot as it is to the ground crew outside, maybe even more so. The JFS is tremendously loud and when the main engines reach idle and the inlet ramps slam down it’s a hell of a thump. Whenever I took non-pilot passengers up in the back of one of our two-seaters, I’d tell them there’d be a lot of strange and violent noises during engine start, plus plenty of shaking and alarming bumps, and not to get overly concerned unless they saw me jump out and run away.

Today almost all jet fighters, like the airliners we fly in, use self-contained APU starting systems similar to that of the F-15. Unlike military aircraft, civilian airliners are far more posh, isolating passengers from most of the noises and vibrations associated with startup (not to mention the flames and smoke of yore).

Naturally I haven’t hit on all the ways there are to get your motor runnin’, but fortunately for the curious someone has written a concise Wikipedia entry on the subject.

You didn’t think I was going to leave you hanging, did you? Never fear, here’s Steppenwolf:

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© 2012, Paul Woodford. All rights reserved.

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