A question, for a change

[RonMiller]

Ok, you guys were talking about starting engines with wind, towing into the wind, jet engine blast starting another engine, etc.

I dont know how they are started as I only see them like 5 miles up in the sky. There have been references to a battery cart. Do the engines have an electric motor that spools them up and the battery carts provide that energy for the engine? I seem to remember something somwhere about using chevy engines hooked up to a blower of some kind to provide air for spooling up? Just wondered, as Galvin said something about having to be at 18% throttle or rpm or whatever that n number meant.

[Britbrat]

I'm kind of out of date with this (first generation jets), but the stuff I flew had 3 kinds of start-up systems.

One system had electric on-board starter motors, but used external electrical power to energize the starters.

Another was similar, but actually had on-board electrical power.

The third system used cartridge starters to provide a gas stream to spin up the engines.

The cartridge starters were the most fun -- it looked like the engines were on fire at start-up -- big clouds of black smoke.

There was a fourth method that was really exciting, but you didn't use it often (thankfully) -- you converted altitude to airspeed & spun the engines up that way --- after a non-destructive flame-out.

I haven't a clue what modern jets use.

[jetmex]

Most modern airliners use compressed air to start the engines (except for some of the Russian ones, which use a pull starter ;D), supplied by an APU, or auxiliary power unit. The APU is a small turbine engine used to provide electrical power and bleed air (for starting and air conditioning) to the airplane, to make it independent of ground equipment. Most APU's are installed in the extreme tail, but the 727's was installed in the main wheel well, as that airplane was originally designed without one.

I think the cartridge type starter is mainly military--I've never seen one. Many older jet engines used an electric starter that also doubled as a generator once the engine was running. Called a starter-generator, of course.

And, air and electrical power are available from various ground carts and from the jetway as well, in case the APU happens to be inoperative.

The N numbers that Galvin referred to are the RPM values recorded on the aircraft tachometers. N1 is usually assigned to the fan section, N2 to the turbine section. On the Rolls RB-211, there is also an N3 for the second turbine spool on that engine. The readings are given in percentage, because it's difficult to get a tach marked up to the RPM's the rotating parts of a jet engine will attain when running (10,000+ RPM)! There are separate tachs for each N....

[50PlusAirYears]

I used to work on several different start carts in the AF. There were several turbine air compressors that bled excess plenum pressure through about a 6 or 8 inch hose into a receptacle on the underside of a plane. Different ones for different planes. The AM32A-60 started replacing most of them sometime in the mid 60s. I was too close to separation to get sent to the -60 school. Last I heard, the cartridge start was still used as a back-up. B-52 used them for the alert planes, to avoid the need to start and spool up the ground cart. Most of the turboprops, and apparently most of our modern jets, at least the larger cargo and bombers carry their own turbine driven APU, just like the Herc did (and still does).
I think I got someone from a tdy squadron in a heap of brown stuff, once. Went to pick up an MA-2 , which is a 6000 pound support vehicle with a turbine compressor, conventional piston compressor, and a couple high power generators on a very short coupled medium truck chassis, and get it back to the ground power shop. Seems the last person to use it, and had in fact called in the service problem, had left a loaded start cartridge on the drivers seat. Backed out of the vehicle cab and called into the shop. Took 3 minutes for the SPs to arrive, and 4 for a tech from the proper shop to arrive on scene. Nobody appreciates leaving something that looks like a large oil filter and filled with several pounds of slow burning black powder lying around in a closed vehicle on a concrete pad less than a 100 feet from armed and ready F100s, especially when the outside temperature is getting close to 122 F. Base Maint officer bought me a coke, told me that I did the right thing, and if I had tried to handle it myself, I'd probably be sharing a cell. If I didn't set it off from static electricity. They apparently are quite sensitive, and the Sahara dessert is VERY conducive to generating static that time of year.

[RonMiller]

Speaking of cartridges, wasnt a cartridge start system used on that prop plane on the original flight of the phoenix? Didn't they mention somethning about using a cartridge that looked suspiciously like a 12 guage shell of some kind, or show one or mention it? I just sort of remember an argument on the movie where one guy wanted to clear the engine and another guy thought it would be a waste of time and cartridge to do that.

Also on the cartridge start system, I wondered how that worked, as a normal shotgun shell burns very very fast. I am beginning to see that the cartridge powder is slow burn and may provide several seconds burn time, depending on application?

[jetmex]

Cartridge starters were developed mainly for the military to start aircraft at forward bases that had no ground support equipment. It's basically a large "shotgun shell" filled with slow burning black powder. When fired, the gases produced by the burning powder force a piston down a cyclinder, actuating a screw mechanism that is geared into the engine's accessory drive. On a piston engine, you have to be quick on the controls, as the charge doesn't last very long. If you have a finicky engine, you might be in for a long day.....

Details here:

www.enginehistory.org/accessories.htm

[ctdahle]

So I suppose a chicken stick wouldn't work so well...

[JimCasey]

>>Speaking of cartridges, wasnt a cartridge start system used on that prop plane on the original flight of the phoenix?<<

Yep, and on the recent film, too.

What's impressive is to see a B-57 Cranberry started with a cartridge! You's think all that powder would leave performance-robbing deposits on the turbine blades.

[Galvin]

The Kaufmann type cartridge starter has been used on both recip and turbine engines for starting since WWII. Aircraft using this type of starter have included the Hawker Tempest/Typhoon series, the Martin B-57/English Electric Canberra mentioned previously, the Hawker Sea Hawk, and many others. And yes, powder residue eventually does become a problem in the operation of the starter. As far as how big the cartridges are, I seem to recall that they are closer to 8 gauge in size than 12 gauge.

There are pictures on the web of mass starts of Kaufmann starter equipped aircraft in which there is a large black vertical plume of smoke over each aircraft being started and a resultant temporary blotting out of the sun.

The original German jets using the BMW 003 and Jumo 004 had a small Reidel two-stroke gasoline engine in the nose bullet. There was a little ring pull-starter at the very front of the bullet to get the starter motor going and, once running, the motor's clutch would be engaged to spin up an start the turbine engine. Jaime's pull-start joke was actually very close to the truth in this case.

The starter/generator system Jaime mentioned is the one generally used on smaller turbine and turboprop aircraft like the Lear Jet and King Air. A DC starter motor is used to get the engine up to start speed. Once the engine is lit and self-sustaining, a reverse current relay kicks in and the engine goes from being driven by the starter to the engine driving the starter as a DC generator.

Larger jet and turboprop aircraft these days are almost exclusively started by air pressure run through a turbine starter geared to the high pressure spool of the engine through the accessory gearbox. That air pressure can be generated by a turbine start cart, an onboard APU, an external set of high pressure air bottles (or, alternatively, one very large low pressure bottle), and cross-bleeding from a running engine on the same aircraft or through a large air hose from another with a running engine.

The pointing or towing of the aircraft into the wind or the blow-through of another aircraft running in front of the airplane having an engine needing to be started are in the category of circus tricks. These methods represent the last ditch solutions found to be successful by some to get an engine started that absolutely had no other method available at the time and are notable for their rarity rather than being everyday methods. They also run the risk of damaging or destroying the engine being started or the airplane it is attached to.

In a related subject, it was common back in the fiscal down cycles for some airlines to use the airplane's own reverse thrust to push the airplane back at the gate. The idea was to eliminate the need for a tug and driver and, in some cases, the need for more than one person on the outside watching airframe clearances.

It was found that the incidence of hitting something, putting the airplane on its butt by hitting the brakes too hard when moving rearward, sucking various items of ground equipment through an engine running at relatively high power levels, and the crew basically being unable to see behind them as they reversed out of the gate largely negated any savings that might have resulted from the non-use of more ground crew and a tug. That being said, there are airlines that still do it sometimes.

I'm sure Jaime can tell you many horror stories related to this once very common practice.

[jetmex]

Ah, the world famous powerbacks!! We only did those on the rear engined airplanes--DC-9, MD-80 and very occasionally on the 727. Doing something like that on a 737 was just asking for an FOD engine change.

Not only was that procedure hard on the airplanes, it scared the crap out of more than one ramper marshalling the planes out. Either something picked up by the engine (usually a piece of paper, but you could never know) would go whizzing by his head, or the airplane would do a tailstand when the drivers got on the brakes too hard. We could not do this unless we had four guys to see the airplane off--one on each wing and one at each end. We eventually gave it up.

I seem to recall a procedure for starting a DC-3 that called for wrapping a rope around the prop dome and attaching the other end to any convenient vehicle. You then drove off -- another variation on the pull starter. I never tried it, but it sure looked interesting.....

[Galvin]

The rope around the prop trick has been used on many aircraft. I saw a guy and his girlfriend start a P-51 over at Chino airport that way years ago. The airplane supposedly had a bad starter. It must have been bad for some time because the owner had made up a nifty little rope for starting the airplane that had four little canvas boots that fit over the prop tips sewn at intervals on the rope. He put one boot over each blade on the prop and his girlfriend, who was driving his Mustang (Ford) with the free end of the rope attached to the bumper, would peel out on his signal and the engine would turn over once.

Needless to say, the engine didn't just start right up. In fact, they had to make quite a few tries at it, the girlfriend yanking the prop around with the car and driving quickly around the airplane to re-attach the rope with its little booties to the prop. They made so many tries that she got rather efficient at getting the car back around the airplane and into position for the next try in minimum time. This proved to have its own set of risks because when that Packard Merlin finally did start, she didn't even see it because she was so occupied zooming around the airplane to get into position for the next try that she damn near drove into the spinning propeller in the process.

[jetmex]

And now, for some more really useless information----

There is a shutoff valve between the bleed air source and the starter. They occasionally fail closed, and can actually be manually operated. We call it "hand propping" a jet engine. Most start valves have a 3/8 square drive on the butterfly so they can be wrenched open. So you grab a breaker bar and a long extension, stick the extension into the valve through the access panel in the cowl and twist until you hear and feel air whooshing past you. Said air tends to be a little on the hot side, so gloves are usually a good idea. Since you have no idea how fast the engine is turning, or when you have to close the valve, you either have to be on the headset with the drivers, or be in view of someone who is.

Every now and again, the start valve fails open, and the starter "overboosts". The explosions that follow can be spectacular, to say the least!!

[RonMiller]

Ok, so, on a multi engine jet aircraft, evidently there is plumbing somewhere to route the said gasses or bleed air from one engine to another. So, take a 737 for instance, or others with engines in the wing for that matter. Are you guys saying that you can start one engine on one side of the aircraft, then start the other with the bleed air, with the air going through the plane so to speak?

I guess it is interesting to me to see how the various engines are started. I was at Goodland, Kansas on an electrical tour about 25 years ago, and it just so happened we were able to see how they started the huge diesel city generator engines. They used compressed air shot directly into each cylinder to attain the required rpm, and I was also fascinated that they contained no antifreeze, just water in the cooling system. They said that because they always ran, 24/7. If they ever had an extended off time they would just drain it of the water and then refill it.

Also, a couple years ago, we went on a cruise. What got me was in a placard on a wall on the ship said it put out x horsepower at 730 rpm, and also idled at 730 rpm. I guess it just depended on the pitch they put on the props and how much fuel they fed it to change speed. I have no idea how those engines are started, unless it is compressed air also.

[jetmex]

Ron, bleed air from a jet engine is used for three things on a modern airliner--engine starting, anti-icing, and pressurization/air conditioning. Using the 737 as an example; there are three bleed air sources on the airplane-the two engines and the APU. All are plumbed into a manifold that is distributed throughout the aircraft, and controlled by a series of valves that allow you to select what bleed source powers what system. Under normal conditions, the left engine bleed runs the systems on the left side of the airplane, same for the right. The APU bleed is not normally used in flight, but can be if needed. If you have a bleed failure, the other engine can be used to power the affected side. So, you can use air from one engine to start the other.

In addition, you can also use air supplied from a start cart (basically an APU mounted on a trailer) to power the pneumatics.

Anti icing is bacically raw bleed air piped into the leading edges of the wings and tail. It's temperature regulated and will shut the bleed/anti ice valves off if the ducting temps get too high.

Pressurization is provided by bleed air run through what is called an air conditioning pack, which is basically a compressor, heat exchanger and the ducting and valves to control it. The bleed air is compressed, cooled, heated back to a comforable temperature , then piped into the cabin. The 737 has two packs, each run from its respective engine--they can be powered from the opposite engine or APU if need be. The airplane should be able to maintain pressure on one pack, though sometimes this is a bit of a stretch if you have an old leaky airplane, or a system not quite up to snuff.

On Boeing airplanes, the packs are located in the lower fuselage, just forward of the wings. On Douglas airplanes (DC-9/MD-80), they are in the tail, which is why most people don't like sitting in one of these on a hot day. That cool air you like has to go a long way from the pack to first class and things can get a little toasty......

Jet engines have multi stage compressors, so bleed air is tapped from more than one location on the engine. On the JT- engine (727/early 737s) normal bleed air comes from the 8th stage compressor. When the demand increases, a regulator valve opens and allows air from the 13th stage (higher pressure) to augment what's already there. Where the bleed air is tapped will vary from engine to engine, but they all work pretty much the same.

Most APU's have electric starters, BTW.

Hope I didn't lose you through any of that.....

[RonMiller]

Thank you Jaime. Man, another session like this and "Frazzle Engine Manufacturing Co." will have a prototype out this winter, Oh yeah with lots of bleed air all over the place.

[coolie]

I was just enjoying the sights and thought I would share a relevant pic



Thats the Canberra that is resident at the Temora Aviation Museum in Australia.

[Galvin]

Here's a bit more on the Canberra/B57/Cranberry/ Whatever:

www.b-57canberra.org/b-57sounds.htm

[RonMiller]

wow I clear forgot about this thread.

[jetmex]

I was just enjoying the sights and thought I would share a relevant pic

Look at all the loverly smoke belching out....!!

That has to be a maintenance run. I don't know many pilots who would do a run up with FOD screens installed and maintenance stands that close to the airplane. Then again..... ;D

[RonMiller]

Ok, looking at the engine and wing of the Canberra, It looks to me like the engine is pretty much exactly in the middle of the wing. So how does the wing spar work on something like this setup? Some kind of bracing to go around the engine and thus make a "cage" of sorts?