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what drives the compressor in a jet engine? Answered

does a motor or something drive the compressor in a jet engine.


The exhaust gases drive the compressor, via the turbine, as you can see in the picture you have just posted !

but when the jet engine starts, what starts spinning the compressor blades. the compression leads to the exaust gases and not the opposite.

They are usually blown by big compressors forced through the engine until there's a bit of a wind blowing This video is very instructive. You can see how its done, from a test stand in someone's garden....

Engines like the J58 in the SR71 were started by compressors run by dual V12 engines.

Thank you very much for your answer. i have been wondering about it for some time.

i have another question: do get prizes if you are selected for best answer?

And compressed gas from one running engine is used to start the next
and so one ?

That's a lot different from how Bill Lear's crew started the famous bus
Steam Turbine in a pinch.
They would start by throwing a burning oily rag into the air inlet !


Some used cartridges. Basically big blank shotgun shells to get the turbine going. This had the benefit of not needing a start up truck or the extra weight of an APU.
"Some military aircraft need to be started quicker than the electric method permits and hence they use other methods such as a cartridge turbine starter or "cart starter". This is an impulse turbine impacted by burning gases from a cartridge, usually created by igniting a solid propellant similar to gunpowder. It is geared to rotate the engine and also connected to an automatic disconnect system, or overrunning clutch. The cartridge is set alight electrically and used to turn the starter's turbine." http://en.wikipedia.org/wiki/Components_of_jet_engines

Cartridge starters were for IC engine ( propeller ) aircraft.


The citation I found was for jet engines.(its only wikipedia but still) One of the guys on the airliners.net forum talked about using the system to start up F4 fighters. Some others talked about using them on B57's (canabarras). The system was common on piston engines as well. There was even a tractor that used 12ga blanks to start it.

Your, airliners.net. showed a single jet with external wires for start,
the rest were props.

I contend that Cartridge starters are not for jets.
Unless they were for APU  IC engines that were secondary starters.

This account on the cannabera sounds almost like a direct impingement system. There are other acounts of using them to start an apu as well.
yes, the starter cartridge in the older marks of Canberra was just a huge shotgun shell, albeit without the shot. There was an explosive release of gases which was channeled to the turbine to wind the thing up. The earliest marks B2, T4, TT18 had only 1 fitted per engine, so, after a failed start, it would take several minutes for the area to cool enough for the cartridge to be replaced, often resulting in a delay of 20 minutes or more.

The latter (early) marks, PR7, E15, T17, T22 had 3 per engine, 2 as spares. The last mark, PR9, used a really nasty explosive fuel called AVPIN, which was volatile in the extreme. One of our jeeps carrying the stuff through a small town, fortunately in an unpopulated area, caught fire spontaneously, the driver bailed, and the resultant conflagration melted the concrete of the sidewalk. You can imagine the effect this had on the local populous - we were thereafter banned from transporting it through residential areas.

The explosion from the starter cartridge was impressive: 4-foot flames would leap from 3 vents in the engine casing, the whole area would be wreathed in pungent cordite smoke, and pilot and supervising technician would watch the engine and each other nervously in case of engine fire. In 3 years, I only had to evacuate once because of a suspected fire, which turned out to be a false alarm. However, you can imagine that when the plane was fully fueled, we were out of there in a flash and up and running!

The gas release should take the engine up to about 2000 RPM, which was enough to energize the igniters and allow the engine to work with the start inertia to get it up to normal idling RPM (I forget the figure). The main thing you were watching at this stage was either for an internal fire, in which case the EGT gages would leap off the scale, or compressor surge, usually accompanied by a lot of popping and banging. In both cases, the actions would be the same: throttle closed, HP cock closed, LP pump off; for a fire of course, additional actions would be fire extinguisher shot through the engine (only 1 available) and evacuate (run for the hills!).

This is the account for their use on the F4 it sounds like the exhaust gasses from the cartridge were used in place of compressed air to spin up the turbine.
Flight152: I was an Air Force F-4 crew chief for three years; I can tell you a bit about cartridge starts on those aircraft. Under the belly is an access panel just below the starter, which you open to access the breech. The pneumatic starter on each engine has a "breech," a cylinder about 6" in diameter and about 9" long attached by a quick release coupling. You would slide the handle back and turn the breech about 90 degrees to remove it. The cartridges were sized to fit the breech, and made of something like solid rocket propellant. They would produce high-pressure, high-volume, hot gas for about 25 seconds. They had an electrical connection that fit into the top of the breech. The exhaust end of the cartridge was open, exposing the propellant. Drop the cartridge in, install the breech by placing it on the coupling and turning 90 degrees, and slide the handle up to lock it. The electrical connection was made through the handle. To start the engine, the crew had only to turn the battery on, the ignition on, and hit the start switch, electrically firing the cartridge. The gas produced by the cartridge exited through the starter, turning it the same way the ground pneumatic connection from the -60 did. In the photo, the F-4 appears to be using the newer "smokeless" cartridge, which still produced much smoke, but far less the the older "smoke-type" cartridges, that produced enormous amounts of solid black smoke. Occasionally a cartridge failed to ignite, so the crew chief would have to go under the belly, remove the breech and cartridge, and install another one. Always risky. Sometimes they would fire off then go out, causing an even more dangerous removal. They would sometimes "torch," meaning instead of producing hot gas, they would produce raw flame instead, which upon exiting the starter outlet would set anything under the plane on fire. Always exciting. And every once in a while they would just explode, blowing the breech off the starter and damaging the plane. Always ugly. Our F-4s could carry a spare set of cartridges in cavities under the inboard bottom of the wing root, accessible by removing a small panel. This cavity carries the casting for attaching the catapult bridle on Navy models. Air Force models, not having the casting, had instead a bracket to mount the cartridge in. We would sometimes carry spares if we were deploying to a base that didn't have sufficient ground equipment. We also installed cartridges on all the alert aircraft, as it was faster to start engines with the cartridges than firing up the -60 and dragging the hose around. Hope you find this informative. Regards,

Steveastro has it:


This guy explains it very thoroughly.

Right down at the bottom is quite a small conventional compressor, run off a starter motor, that spins up the turbine on an APU, these days, the APU powers the start-up of the engine, I don't think modern planes need the start cart.

What fun thing to have in the garden....

Not very efficient at ground level gardens :)

I've been on a transatlantic flight that was so tight on fuel, we were taxied to the runway by the ground tractor, and didn't start our engines until in line for takeoff. The APU at the back of the plane can easily power the engine starter turbine - you're right its more efficient to have a ground plugin or starter box.