Blackbird From , joined Dec 1969, posts, RR: Posted (5 years 11 months 2 days 7 hours ago) and read 4157 times:
What kind of means did the Boeing 707, Douglas DC-8's, the Boeing 720, and other such aircraft of those era use to start their own engines while on the ground? How did they work?
Charlienorth From United States of America, joined Jun 2006, 1077 posts, RR: 5 Reply 1, posted (5 years 11 months 2 days 7 hours ago) and read 4158 times:
All airstarts,the 707/720 normally started 3,4,2,1 if I remember correctly,the DC8 generally was the same but often times we would just start #3 and disconnect air and electric and perform cross bleed starts on the remaining engines,they did not like to do this on the 707's,the 70 series 8's did have an APU but it had problems and many times couldn't supply both air and electric during a start..on a side the Caravelle had an electric starter.
Lowrider From United States of America, joined Jun 2004, 3220 posts, RR: 11 Reply 3, posted (5 years 11 months 2 days 5 hours ago) and read 4114 times:
Typically air is supplied from a high pressure source, either a compressor or a pressurized bottle, through a fitting on the outside of the aircraft to a common manifold. The air is then routed to the desired starter. Once running, bleed air from the engines can pressurize the duct and be used for a "crossbleed" start.
The idea is not new, however. Radial engined aircraft have used air start systems for decades. They were commonly found in colder climates. Air is used to start the engine rotating, then fuel and spark are introduced. Air was supplied from a small bottle mounted on the aircraft that could be recharged with a hand pump, if needed. Some radials used blank shotgun shells to generate a pulse of compressed air.
Jetlagged From United Kingdom, joined Jan 2005, 2452 posts, RR: 17 Reply 5, posted (5 years 11 months 2 days 3 hours ago) and read 4089 times:
The starter motor, starter valve and ducting is part of the plane. Without an APU an external air source must be provided to start the first engine. Crossbleed can then be used to start the rest.
The glass isn't half empty, or half full, it's twice as big as it needs to be.
Charlienorth From United States of America, joined Jun 2006, 1077 posts, RR: 5 Reply 6, posted (5 years 11 months 2 days 3 hours ago) and read 4088 times:
No the airstart unit as a large piece of ground equipment that as Lowrider posted supplies high pressure air to the starter on the engine,resulting with rotation of the engine,with fuel and spark gives us our start,there is receptacle on the aircraft to hook it up to,you than select the air to the aircraft..normal procedure would be to address the captain through the headset..."Ready for start'...."Ready to start #3"..."you are clear start #3".....after 3 is started.."ready on #4"...'you are clear four" this is using a 707,we would go through 2&1 with the same discussion after the final engine was started the captain would say"we've had four good starts..you are clear to remove air and electric" after this was accomplished and all was disconnected and panels closed we would do the pushback procedure,This is also what we still do when the a.p.u is inoperative..the a.p.u is great..the amount of ground service equipment needed for an aircraft without an a.p.u. is a pain in the neck...besides the air start unit and groung power you also need an air conditioning or heat unit.
Lowrider From United States of America, joined Jun 2004, 3220 posts, RR: 11 Reply 7, posted (5 years 11 months 2 days 3 hours ago) and read 4088 times:
Quoting Blackbird (Reply 4): The airstart systems were external? I thought they were part of the plane
The aircraft you refered to used external air starting. You can have an internal system, but it requires an on-board source of compressed air, typically an APU.
In the broader sense, airstart simply refers to using compressed air to start the engine moving before introducing fuel and ignition. On a jet engine, compressed air is usually released or "bled" into either the engine itself, or across a starter turbine connected to the compressor. Once a minimum RPM is reached, the airflow through the engine is sufficient to sustain combustion and fuel and ignition are introduced.
Blackbird From , joined Dec 1969, posts, RR: Reply 8, posted (5 years 11 months 2 days 2 hours ago) and read 4072 times:
I remember the 707-138B had an interesting start system. You pressed a button, then started moving the fuel-levers forward to the idle position... the engine noise got louder and such, and eventually lit-off and idled out...
Fr8mech From United States of America, joined Sep 2005, 4246 posts, RR: 12 Reply 9, posted (5 years 11 months 2 days 2 hours ago) and read 4068 times:
Quoting Charlienorth (Reply 6): supplies high pressure air to the starter on the engine
An airstart actually supplies low pressure air (in the 35 - 40 pound range) at high volume.
As I recall, some B707 type aircraft did have a single shot start system installed. It was comprised of a set of nitrogen bottles and the associated controls, tubes and valves. As implied by the name, you had one opportunity to start an engine, after which you used cross-bleed air to start the other engines. The bottles were charged on the ground from a high pressure source.
I do know that some DC8's had an APU installed in the #2 pit area.
I believe some military aircraft use a cartridge start system. I don't know much about it, but I suspect it uses an explosive charge to generate the necessary pressure and volume.
Charlienorth From United States of America, joined Jun 2006, 1077 posts, RR: 5 Reply 10, posted (5 years 11 months 2 days 2 hours ago) and read 4062 times:
Quoting Fr8mech (Reply 9): An airstart actually supplies low pressure air (in the 35 - 40 pound range) at high volume
my bad, I meant hi volume,some aircraft need two start units,the Y-adapter can be a mother to handle after a start.
Quoting Fr8mech (Reply 9): I do know that some DC8's had an APU installed in the #2 pit area.
Mostly on the 70 series,I understand thay had a tendency to overheat..TransAmerica had that set-up...I don't know if UPS improved it when they got those AC
the ex military pilots at UAL always ask about a "bottle start"
Fr8Mech From United States of America, joined Sep 2005, 4246 posts, RR: 12 Reply 11, posted (5 years 11 months 2 days 2 hours ago) and read 4054 times:
Quoting Charlienorth (Reply 10): I don't know if UPS improved it when they got those AC
I believe they were removed before entering service with UPS. I want to say it was 2 aircraft. 819 and 812, maybe? I'd have to look at the aircraft.
VC-10 From United Kingdom, joined Oct 1999, 3677 posts, RR: 37 Reply 12, posted (5 years 11 months 2 days 1 hour ago) and read 4048 times:
The 707's I worked on had large HP air bottles located in the wing to body fairings aff of the wing for engine starts where there were no air start trucks on station.
The VC10 had a combutor start system where air supplied from 3 air bottles located in the tailcone below the rudder was ducted to a small combustor attached to the #3/4 eng firewall. In the conbustor kerosene was mixed with the air and ignited. The exaust gasses were then supplied to the #3 Eng starter to turn it & fire up #3 engine. Once again this was a last ditch arrangement for when there wasn't an air start truck was available
Ah yes, the use of the start cart! Many times we have had to use a diesel driven start cart to start the engines of 747's or A330's. The massive cloud of thick black smoke that comes out of the roof mounted exhausts of the diesel as it starts to spool up the engine is amazing ! With respect to the 707, I believe that the ones I worked on a while back had an APU fitted as a modification. Nonetheless, to spin the engines in the hangar, we used to use a start cart that was basically a 737 APU on wheels. The sound of this thing spooling up was frightening!
I seem to remember from a book I flicked through that the SR-71 uses a piston engine for starting as well. In this case, I think that the start cart is a supercharged V-8 engine. This engine is connected to what I assume would be the external gearbox on the J-58 by a vertically orientated shaft. This shaft then mechanically turns the engine over for starting.
The air-conditioning and start cart trucks are usually very large rigid chassis vehicles. This is in contrast to the APU which is about the size of a large refrigerator. It has always fascinated me how you need several large diesel engine powered devices (air-con, electrical) to replace one broken down APU.
Regards, JetMech
JetMech split the back of his pants. He can feel the wind in his hair.
411A From United States of America, joined Nov 2001, 1826 posts, RR: 9 Reply 14, posted (5 years 11 months 2 days ago) and read 4024 times:
Some ( but certainly not all) B707 aircraft had a high pressure start system, which consisted on one (PanAmerican had two, however) high pressure air bottle installed in the left wheel well (PanAmerican, L&R side) which provided high pressure air to the stater, to provide engine rotation.
In cases where external electric power was not available, a BATTERY start was completed.
The start SWITCH (either rotary or toggle, depending on the mod status...and NOT a 'button') was moved to the 'high pressure start' position for these HP starts and, the fuel lever was moved to the 'start' position at the first sign of N2 rotation.
When the engine was running in a stabilized condition, the start lever was moved to 'run', the GFR, GB, and BTB were closed on this engine, and full electrical power was then available.
The ONLY engines that could be started with the HP system were engines 2 & 3.
Each of these engines had turbocompressors installed, and the TC was started at this time, the power advanced on the operating engine, and a cross-bleed start procedure was then used to start the remaining engines.
Usually, number one engine was equipped with a TC, but the HP (bottle) air could not be routed to this engine, for starting, so it was 2 or 3 only.
VC10 From United Kingdom, joined Nov 2001, 1381 posts, RR: 17 Reply 16, posted (5 years 11 months 1 day 16 hours ago) and read 3974 times:
Quoting VC-10 (Reply 12):
The VC10 had a combutor start system where air supplied from 3 air bottles located in the tailcone below the rudder was ducted to a small combustor attached to the #3/4 eng firewall. In the conbustor kerosene was mixed with the air and ignited. The exaust gasses were then supplied to the #3 Eng starter to turn it & fire up #3 engine. Once again this was a last ditch arrangement for when there wasn't an air start truck was available
That might have been the case with military VC-10, but none of BOAC aircraft had this facility. I understand that the pre production aircraft had a HP bottle in the tail cone ,but I thought the only civilian operator to retain this was Ghana Airways , but I could be wrong
The emergency starting system for BOAC was to get a group of HP bottles [6 I think] connected in parallel and you used them to start one engine then cross bleed start start the others. There was a special procedure for this though and if it was not followed there was a chance you would blow some of the aircraft ducting with too high a pressure air.
The Concorde had no APU and no across the ship cross bleed either ,only x-feed between the adjacent engines on either side. It was normal therefore to have two Ground air start units one per side and start the 2 inboard engines and the x-bleed start the outers after push back from their adjacent engine.
411A From United States of America, joined Nov 2001, 1826 posts, RR: 9 Reply 17, posted (5 years 11 months 1 day 11 hours ago) and read 3919 times:
Yes, some operators eliminated the turbocompressor from the number one engine (altho the cowling stayed much the same)...American Airlines comes to mind, with some models of their B707's.
411A From United States of America, joined Nov 2001, 1826 posts, RR: 9 Reply 18, posted (5 years 11 months 1 day 10 hours ago) and read 3900 times:
Whooops, my mistake.
Scratch engine one, replace with engine FOUR.
So, HP start air available only to engines two and three. T/C's on those engines, and (usually) number 4.
American, on some models, eliminated the T/C from engine 4.
DeltaGuy From , joined Dec 1969, posts, RR: Reply 19, posted (5 years 11 months 1 day 10 hours ago) and read 3900 times:
Quoting Lowrider (Reply 3): Radial engined aircraft have used air start systems for decades. They were commonly found in colder climates
The Yak-52 and CJ-6 are two that come to mind...designed to be operated in Siberia-style conditions, cold and rigid engines. You only get a few shots at starting it before the air tank is gone, hence why alot of folks bring along a scuba tank for those missed starts.
Uscgc130 From , joined Dec 1969, posts, RR: Reply 20, posted (5 years 11 months 1 day 6 hours ago) and read 3855 times:
Quoting 411A (Reply 14): Each of these engines had turbocompressors installed, and the TC was started at this time, the power advanced on the operating engine, and a cross-bleed start procedure was then used to start the remaining engines.
Interesting. I knew that the TCs supplied air for cabin pressurization, but until now I thought that the air used for cross-bleed engine starts was tapped directly from the engine compressor, C-130 style.
I didn't realize that the turbocompressors needed to be manually started. It had always been my impression that they were connected directly to the engine via a radial shaft or an accessory drive, and spun up automatically when the engine did.
What is the engines' percent RPM at idle? The relevance is that reading about cross-bleed starts on the KC-135 and now the 707, I note that power needs to be advanced on the operating engine before the remaining engines are started. This struck me because no power advance is necessary on the C-130 -- but of course the T56 is a constant-speed engine and runs at 100% RPM at normal ground idle. I'm curious just how much the power needs to be advanced on a JT3/4 in order to generate sufficient manifold pressure.
Viscount724 From Switzerland, joined Oct 2006, 21465 posts, RR: 24 Reply 21, posted (5 years 11 months 1 day 6 hours ago) and read 3842 times:
Quoting 411A (Reply 17): Yes, some operators eliminated the turbocompressor from the number one engine (altho the cowling stayed much the same)...American Airlines comes to mind, with some models of their B707's.
Assume you're referring to the early non-turbofan 707s where the engine cowlings/pylons looked the same on all engines. But on JT3D turbofan-powered 707s it was easy to tell that the No. 1 engine lacked the turbocompressor as it had a much thinner pylon than the other 3 engines.
Almost all 720s only had 2 turbocompressors on #2 and #3 engines, again easy to spot by the thinner pylons on #1 and #4 engines on JT3D-powered 720Bs.
JetMech From Australia, joined Mar 2006, 2587 posts, RR: 53 Reply 22, posted (5 years 11 months 1 day 3 hours ago) and read 3821 times:
Quoting Uscgc130 (Reply 20): It had always been my impression that they were connected directly to the engine via a radial shaft or an accessory drive, and spun up automatically when the engine did.
IIRC, the TC's on the 707 were driven by bleed air taken off the engine. I was sure that this bleed was taken off after the combustion chamber, but I recall someone stating in an earlier thread that is was in fact taken off before the combustion section.
Quoting Viscount724 (Reply 21): But on JT3D turbofan-powered 707s it was easy to tell that the No. 1 engine lacked the turbocompressor as it had a much thinner pylon than the other 3 engines.
Did Conway powered 707's have TC's on all four engines ?
411A From United States of America, joined Nov 2001, 1826 posts, RR: 9 Reply 23, posted (5 years 11 months 1 day 2 hours ago) and read 3800 times:
9th stage bleed air was the source of air to operate the turbo compressor.
T/C's needed to be started AFTER engine start, via an electrical toggle switch on the F/E's panel and were then operated to either supply pressurization and air conditioning, or for cross bleed starting of the remaining engines.
If, for example, the number three engine was started first, it's T/C was then started, the throttle was advanced to 70% N2, air conditioning packs selected OFF, and a second engine (usually number 4) was then started, it's T/C' started, and the number three engine was returned to idle thrust, as the output from two operating T/C's with corresponding engines at idle was sufficient to start the remaining two engines, normally number two first, then number one.
Regarding RR Conway powered airplanes, normally 4 T/C's were fitted, but some operators removed the T/C from the number one engine, but the cowling appearance remained the same.
Going further, could the cabin of the B707 be pressurized with straight bleed air, not T/C air?
The answer is yes, but only on certain B707's, and then only on the airplanes that were equipped with air cycle machine (ACM) air conditioning packs.
NOT possible with those airplanes that had vapor cycle air conditioning, either old or new style.
Many MANY different variations, according to original customer requirements.
PanAmerican, for example, had quite a mix...vapor cycle (new), vapor cycle (old), and ACM air conditioning were fitted to models in their quite large fleet.
Viscount724 From Switzerland, joined Oct 2006, 21465 posts, RR: 24 Reply 24, posted (5 years 11 months 1 day 1 hour ago) and read 3792 times:
Quoting Viscount724 (Reply 21): Assume you're referring to the early non-turbofan 707s where the engine cowlings/pylons looked the same on all engines. But on JT3D turbofan-powered 707s it was easy to tell that the No. 1 engine lacked the turbocompressor as it had a much thinner pylon than the other 3 engines.
Re my comment above, have discovered after some further research that AA was unusual in ordering 707-320B/Cs with only 2 turbocompressors. AA's -120Bs, both those converted from turbojet -120s, and those delivered new as -120Bs, also only have 2 turbocompressors. I believe those may be the only 707s built with only 2 turbocompressors. Photos below showing the narrow pylon on #4, same as #1, like the 720B.
Quoting 411A (Reply 23): PanAmerican, for example, had quite a mix...vapor cycle (new), vapor cycle (old), and ACM air conditioning were fitted to models in their quite large fleet.
I noted a comment in an earlier thread (there are quite a few on this subject) mentioning that PA also removed the turbocompressor from engine #4 on some 707-320B/Cs but didn't change the pylon so you can't tell whether there is one or not.
25 CaptOveur: Two buick racing V8s.. I think they were somewhere in the 400cu inch range.
26 Dougloid: A lot of our older Hobarts at Garrett had Chrysler Hemis. We had two air sources at Douglas for pressurizing MD11s on the ramp and the two together w
27 ClipperNo1: And what do you do when you land your DC8 at a place where all GPU's are inop? Yeah, to the joy of everybody at the airport and around, you leave one
28 Charlienorth: I remember the big deal in 1983 when Global International landed a 707 in LSE,no airstart available,they had to keep an engine running and Republic's
29 Broke: Douglas had an option on the DC-8 which included a compressed air reservoir mounted in the mid service center which was located between the forward lo
30 TristarSteve: Older engines with low bypass ratio did not produce enough air at idle for a x bleed start. The B737-200, which idled at 60pcN2 needed to be run up t
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! With respect to the 707, I believe that the ones I worked on a while back had an APU fitted as a modification. Nonetheless, to spin the engines in the hangar, we used to use a start cart that was basically a 737 APU on wheels. The sound of this thing spooling up was frightening!
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