Britannia 300 series engine ant-icing system

[brakedwell]

I'm writing an account of an engine icing incident we had on a 312, but my ancient memory has failed me. If anyone is still in possession of a Britannia Operations Manual could they give me the temperature range for switching on the engine ant-ice? I seem to remember the figures 0C to +6C, but I could be wrong.

[goudie]

Brakedwell Haven't read the whole article but this might give you a clue

jowett cars | entry guide | guide vanes | 1955 | 1318 | Flight Archive (http://www.flightglobal.com/pdfarchive/view/1955/1955%20-%201318.html)

[Warmtoast]

Brakedwell

The quote below refers to RAF Brits 252 and 253 Series and may be relevant. I have further info somewhere, but not immediately traceable!

Anyway passed on FWIW.



EGVs On
The first line of defence was heating of the engine entry guide vanes (EGVs). Air entering the nacelle met these vanes whose purpose was to suitably adjust the flow to meet the next engine component. The heating of these vanes had to be switched on if the aircraft entered cloud at any temperature. Two questions might cross the mind. One: why not have them on all the time? Answer: there was a fuel penalty; consumption was increased by 5%, which could be critical. Two: what’s the problem? You can see cloud. At night? That is why visitors to the flight deck in the dark might have found one or both of the pilots, sitting on the edge of their seats peering through the windscreen, possibly with a torch.

Cowl Heat on
The EGVs went on, no matter what the temperature. The next protection device was very temperature, and speed, sensitive. This was known as the Cowl Heat and was designed to combat the problem caused by the reversing of flow in the engine of air with a high water content at particular temperatures, such as are met in the tropics. It has been mentioned how the Britannia development met bad luck here in that it was not previously realised that such sensitive conditions existed.

Lumps of ice
Cowl Heat did just what its name implies. The outer surface of the engine air intake was heated as well as the rear walls and corners of the individual ducts by hot air bled from the engine. All this to stop the wet cold air depositing ice on the bend where the flow reversed. If ice was allowed to accumulate there, then when it reached a certain volume, it would detach itself and pass down the engine. The finely engineered components there were intended for the flow of gases, not lumps of ice, so damage could occur, the engine be temporarily stalled and, in the extreme, the flame of combustion extinguished.

Critical temperatures
One can imagine crews under training, learning of this deficiency, being somewhat relieved to hear that this icing phenomena was only critical at certain temperatures. Such relief would be dashed when it was discovered that those temperatures were just the ones met at the aircraft’s normal cruising altitudes in the tropics. It was a real problem.

The Cowl Heat HAD to be switched on, in cloud, between indications on the outside air temperature gauge of +2°C and +12°C. However, if the temperature was between +2°C and +6°C, then the speed had to be reduced to 200 knots first and the temperature rechecked to see if it was still in the ‘Cowl Heat On’ range of +2° to +12°. Just its use carried a large fuel penalty and if slowing down was also required, the result could be critical.

All this concentrated the minds of crews at the Meteorological Briefing and the subsequent pre-flight planning. Choosing the height at which to fly was like some aeronautical brain teaser; flying at the optimum height for fuel flow, airspeed and range could have the temperature right in the critical range. Lower height and the temperature would be alright but the fuel flow too high; as high as possible might bring the temperature below +2°C but the airspeed might be unacceptably low to cover the distance with the fuel available. It was certainly a nightmare situation for crews.

[brakedwell]

Thanks for jogging memories of the RAF system, Warmtoast. I will continue my search for the Civil B skin jets speeds.

[ONE GREEN AND HOPING]

........Herewith some bits to add to the above:


.....Below is a quote from the UK Flight Manual Doc.No.BL 3.5 for Britannia serial No.13431, a series 313. This aircraft was built at Filton for EL Al in 1959 already...

"If the IOAT is within the range of +12 to 0 degrees C, the B Skin Jets must be on (open) before entering cloud or precipitation, except when using Max Take-Off power.
Should these conditions be encountered and the B Skin Jets are not switched on in time, switch those on for the inner engines only, and wait for at least two minutes. When these engines have stabilised, switch on the B Skins for the outboard engines.
When the IOAT is outside the range +12 to 0 degrees C, the B Skins should not be on even in icing conditions except when, with the B skins already in operation, cloud or precipitation conditions persist and the IOAT falls below 0 degrees C. In this case, the B Skins should be left on until the IOAT falls below -2 degrees C.
Continuous operation in cloud or precipitation with the IOAT within the band +2 to -2 degrees C should be avoided"

Also there is a note which states, because of the resultant performance loss, B Skin Jets should not be used unneccessarily.



Just for the record, in UK speak,the 'Flight Manual' is assumed as the term used for the legal Government doc issued for each individual aircraft. (On my previous longhaul type, the only company Ops manual was kept in the office)

I've also had a peak at my Transglobe manuals covering the 302; Mexican Hot'n High 100/300 hybrid, plus the 309 and 314. ( I may have my Caledonian manuals somewhere in the far reaches of the loft, and which covered several customer numbers up to 324.) I think it's safe to say that the Engine ant-ice drill is going to be the same for all the 300 series. I'm guessing that the last Britannia built, which seems to have been a 253 for the Royal Airforce will have stuck with the Cowl Heat system.
(In transglobe, a significant number of our Brit crews were pinched from the RAF via an advert placed in the back of the Lynham Globe.....only once though)

Quoting also from the Bristol Siddeley Proteus 765 Aircrew engine manual we were issued with at the factory:
"When the temperatures are known to be +4 degrees or higher, the B Skin Jets may be left off at the pilot's discretion, thus avoiding unnecessary loss of performance. (2.5% to 3%........my note)

Also, now I've got the book open.........

With Auto selected and below 5 degrees C ( Ice Warning Light on) the EGVs were activated, along with the Elevator Horn Balance, Props on short cycle, and Tail unit cyclic on low voltage.
IOAT below 12 degrees C, you had to keep the EGVs on 15 mins after leaving cloud.

Our basic ground school (mixed RAF/Civilian for most lectures) was at Filton in 1965, and I've kept the Bristol airframe manual for the exceptional quality of the dozens of full page technical drawings. I think that by the time we had also been through Smiths at Cheltenham for the Flight System, ground school must have been around six weeks. (Flight Engineers longer) The draw-back was that whilst at the main Filton facility, (over the road from the engine place), Canteen lunchtime rations for customers included two free pints of beer. Afternoon lectures even after one could be a bit of a struggle. Fortunately I think Electrics must have been in the mornings.

Ice could be a nuisance on the Brit.......not just scrabbling around at night trying to shine a torch on those sloping forward screens, but also the way it could pick up fuselage ice on slow Winter climb-outs. However on the North Atlantic in Winter, it was bliss compared with our company DC7Cs who could be squirting precious neat fuel at the carb flaps of four spluttering Turbo Compounds for hours. When it came to props, I seem to remember the Brit had around 17KW for each one? As a schoolboy, I remember the commentator at the Farnborough Air Show calling it "The Whispering Giant". It didn't seem like it on the inside.....

[brakedwell]

Thanks for your informative description of what was a complicated system to prevent ice building up in the swan neck intakes. I flew 252/3's for 8 years and thought the cowl heat system worked quite well, apart from the inconvenience of having to use low/high cruise profiles in the tropics to avoid reducing speed to 200 kts when the IOAT was between +2C and +6C. I then flew 312's for two years and on my last rostered line flight before starting a DC8 course lost power on all four engines (30,30,40,30 torque) on a dark winter night over Zagreb in 1976. With the speed decaying and the IOAT hovering between -6C and -8C, way outside the range for switching on the B skin jets, the engines started flaming out. We spent ten minutes acting like one armed paper hangers, relighting multiple flame outs while descending to MSA with the stick shakers rattling away. When the engines did recover we pressed on to Baghdad with both ASI's stuck on 80 kts and only one (F/O's) altimeter working.

BTW I endured the long Filton course in 1976, followed by yet more weeks of ground school at Lyneham. We certainly envied the Laker crews who spent three weeks at Filton, took the ARB exam and scarpered.

[pjac]

To put my twopence worth in, in Eagle-we used the +12 to 0 for B Skin jets before entering precipitation areas. The thinking was that in turning the corner (in the intake), the air temp would drop to the +5 to -5 range. You may recall with the adverse weather systems, we used the letters, HELP being Horn Balance, Electric windshield heat (incresing), Leading edge and Propellor deicing. These were turned on automatically with by the ice sensor.