vc10 engine start question

[yidal8]

Hi,
How were these engines started? also what kind of electric power generation systems are on the aircraft.
On the 1-11 , I understand that a very unusual system was employed. The generator CSD was used in reverse, applying pneumatic air to roots type motor/pump design, for engine start. This was called CSDS

[Tonkenna]

Each engine has a starter motor that is powered by air... the air can be delivered from an APU (on the RAF versions, the civil ones did not have an APU), from an external air starter (Paloustte) or, if you have one engine started you can do a cross-bleed start using air from the running engine.

Tonks

[Jelle Hieminga]

To add to Tonks' reply, the civil versions only ever had the option of either a low pressure external air source or on some versions one engine could be started from an external high pressure air source. The low pressure system is as described above, air is taken from a jet start cart (Palouste in RAF-speak) and fed into the pneumatic system and to the starter. From there you can cross bleed from one engine to the other to get the other three started.
Some civil aircraft had a combustion starter mounted on engine 3, this was a small combustion chamber which was fed high pressure air (usually from an external bottle) which was then added to fuel and a spark. The resulting energetic gas was I think fed through a small turbine to get the engine going but I'm not completely sure of that part. The advantage of having this system installed was that air bottles were more often available than a start cart and also you could easily carry a few air bottles in one of the cargo holds making the aircraft self supporting on remote airfields. Handy for some VIP aircraft for example.

Electric power is generated by four 40 KVA AC generators (one on each engine) connected through a Sundstrand CSD which keeps the generators running at 6000 rpm irrespective of the input rpm. These deliver 115/200V 400 Hz AC power for the main buses. There are also two 28V AC buses fed through transformers and two 28V DC buses fed through TRUs.

[1103]

The 1103's had the combustor start system installed.

In the tail cone, immediately below the rudder there were 3 3000psi air cylinders fitted so the a/c was self sufficient for one start attempt. If I remember correctly, the combustor gasses were fed directly to #3 Eng starter motor.


Update:- I took a look at my course notes today, and can confirm the combustor gasses were fed directly to the starter motor turbine

[Tom Weller]

I was reading a thread of misinformation about the starting system so I thought it was time to tell this tale.

First of all, no BOAC VC10 a/c Standard or Super carried 3000psi air bottles; the ARB would never sanction such dangerous items for certification. In common with the Conway powered 707 fleet, the VC10’s were never self sufficient for starting, always needing an outside air supply.

Up until September 5 1965 both fleets required a low pressure external air supply for normal starting or an external 1800 psi bottled supply for the, alarming, combustor device; a hot gas generator usually fitted to the number 3 engine, which supplied hot, low pressure air directly to the starter. The starter required air at 25 to 40 psi.

On that date in 1965, G-ARVI operated by Capt JB Brolly, SFO R H Lonsdale, SEO L. Chaves and myself brought that situation to an end. At around 10 that morning we set out on what should have been a pleasant day’s work, flying Nairobi, Lusaka, Salisbury and back to Nairobi. Things went rapidly down hill on arrival at Lusaka. The Ground engineer greeted us with the news that we would need to use our combustor to start on departure; their aging start truck had been sent to Salisbury for maintenance. The combustor was hardly ever used in anger; not to anyone’s surprise it failed to work. It was looking likely that we would have to wait for equipment to be driven down from Salisbury. However, the ingenuity of our flight engineer Larry Chaves was about to swing into action. Whilst we were twiddling our thumbs Larry had befriended the firemen who took him into their station. During his visit he noticed they had hoses of all sizes and he hit upon an idea; if he could make a piece of hose with which to connect the large diameter low pressure connection on the a/c direct to the small diameter high pressure bottled air coupling, it might just be possible to get an engine started. A message was sent to our people in Salisbury to send the LP coupling from our start truck via the Air Rhodesia flight. Larry then set to work with fire hoses and jubilee clips to fashion something that was christened the Elephants trunk, this had the HP. connection one end and the large LP. union the other. This was a pretty radical idea not to mention a highly risky prospect for the a/c pneumatic ducting. The ducting is normally controlled at 40 psi, with a duct relief valve set at 50psi, engine shut off valves operate at just under 70psi and a last ditch defence of a rupture disk which fails at 120psi. Clearly someone had had a healthy respect for the fragility of the ducting.

We were proposing to pipe air at 1800 psi directly into this system. Larry’s reasoning was that Boyle’s law would give him time to operate the start system, which is that the large volume of the a/c system would mitigate the rapidity of the pressure rise. A technique was worked out whereby the ground engineer would open the valve when asked by Roy in the co-pilot seat as Larry operated the starter, the starter consumes a lot of air which controlled the pressure rise, this rise was watched like a hawk by Larry ready to tell the ground engineer to shut down. The engine spun up in amazing fashion, Roy’s job then was to watch the N2 rpm and tell the ground man to shut down at 25% N2 before the starter cut out could operate. Apart from the tension, the start-up was copybook. Departure was made some seven hours after our arrival, instead of a transit of 45 minutes.

The Elephants Trunk was kept with the a/c, the Tech log written up. On arrival home the fleet management were less than impressed and Larry was threatened with the sack. That was until Vickers and, dare I say, Boeing got to hear of it, when Larry was invited to explain exactly how he had achieved his astounding feat.

BOAC set about modifying both the 707 and VC10 fleets with a properly engineered system, which I believe they patented, all combustors were removed and scrapped, saving thousands in maintenance not to mention the weight saving.

Larry was originally awarded £700 for his ‘suggestion’ but this was increased at the insistence of the company’s Chief Engineer

Tom Weller BOAC Capt. Retired

[1103]

First of all, no BOAC VC10 a/c Standard or Super carried 3000psi air bottles; the ARB would never sanction such dangerous items for certification. In common with the Conway powered 707 fleet, the VC10’s were never self sufficient for starting, always needing an outside air supply.

Tom,

I accept BOAC never had them but, the ARB appeared to have approved HP air bottles on the BUA VC10's and also approved the carraige of 5 (6 on the Super) Oxygen bottles pressurised to 1850 psi.

As an apprentice with BCAL in 1975 I spent some time removing the 3 bottles from the tail cone of the Air Malawi a/c for routine replacement. The time was taken while the 3000 psi was vented before removal.

On another occasion, during my apprenticeship, whilst under supervision, I was told to 'waggle' the rudders around while the decay rate of the rudder PCU's were checked. Very shortly afterwards a rather irate German came up to the flight deck as he wasn't impressed with working on the bottles with the lower rudder flapping about above his head.

Finally, I refer you to the second sentence & the final paragraph of these training notes dated Oct '63