Air-Minded: Get Your Motor Runnin’ (Updated 11/6/19)

I’ve been thinking about the different methods of starting aircraft engines.

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:

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:

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:

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):

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:

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 a German F-4F performing a cart start. The obvious advantages of jet engine cart starts: they’re fast and require no ground support.

Here’s an earlier 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:

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):

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 JFS (jet fuel starter): you pulled a T-handle in the cockpit to discharge a hydraulic accumulator, which started the JFS (itself a small jet engine). Once the JFS was running, it powered a drive shaft to a central gearbox, which in turn transferred power by shafts to start each main engine, one at a time. When both engines reached idle RPM the JFS shut itself down. It wasn’t as fast as a cart start, but no external power was necessary. In this video you can hear the JFS running, each main engine starting in turn, followed by the sound of the JFS spinning down:

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; additionally, when each main engine reaches idle and its inlet ramp slams 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:

Update (11/6/19): here’s one I hadn’t seen before! Hey, where there’s a will, there’s a way!

© 2019 – 2020, Paul Woodford. All rights reserved.


One thought on “Air-Minded: Get Your Motor Runnin’ (Updated 11/6/19)

  • Great article, Paul! Way back in the day, J57 powered KC-135A’s on alert had a cartridge in the #4 engine. The drill was to start #4 with the cart, run it up to pressurize the manifold running behind the wing & start the remaining engines. Worked well.
    In the early 70’s there was a mod to equip all 4 engines with their own cartridge to enable quicker alert response. The first time it was used at my base, it was a completely calm day (rare for Ellsworth). With alll the base brass present in their white-topped cars to watch the show, the crew pushed all buttons at once, all 4 carts fired and the spectacle began. While spinning up the engines, the black powder carts also generated a large cloud of dense, acrid black smoke that enveloped the aircraft. The crewchief backed up to get out of the smoke to the full extension of his intercom cable. He couldn’t escape the black cloud to see what was going on and was having a coughing fit. The assembled brass rolled the Fire Dept & it was a pretty wild scene for a short while. After things calmed down, it was decided to go back to the old method of single cartridge starts for the time being.

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