B707 Enginer Pylons

[airsmiles]

Not sure this is the correct forum to ask this, but I thought you'd be the guys to know.

Why is that some JT3 engine pylons are curved on top and go all the way to the front of the engine intake, whereas others are straight but don't come as far forward as the engine intake?

Invariably you see a mix of straight and curved pylons on the same aircraft. On some photos on airliners.net you see one outer engine with a straight pylon but the other outer engine with a curved pylon.

Also, some engines seem to have a series of vents around the circumference of the engine intake, whereas others don't. (I've noticed that early B747 JT9's had these vents as well, but not later ones).

Can anyone explain these differences please.

airsmiles

[Tempsford]

Turbocompressors were mounted on top of some of the engines. On the B707-300, #2,3,4 has T/C. On the 707-100 and 720 T/C are on #2 and 3. There were other T/C permutations as I am
sure some folk will point out. The intake for the T/C was directly in front of the T/C hence the hole and the blunt fairing appearance. On non T/C fitted engines the fairing went down to just aft of the Nose Cowl.
The cowl for the T/C is called the 'Dog Kennel' and could be fiddly to fit (shoot bolt latches that required a boot to 'assist location' sometimes)
The vents are called Secondary Air Inlet Doors and are sprung loaded shut. They open at High Power seetings to allow additional air into the engines. Some JT3 had large inlet doors and some had narrower ones. The narrower doors were normally found on the 720 and 100 series 707.
I hope this info helps and I feel sure that others will provide a more detailed response. Anyone, please feel free to correct anything I have said as I have not worked on or been near a B707/720 for many years and the memory is now a little unclear.

Temps

[Perrin]

HA THE MUCH LOVED B707 YES YOU ARE CORRECT AS TO THE FAIRLINGS TEMPSFORD BUT I WOULD NOT CALL THEY FIDDLY TO FIT ON A COLD WINDY NITE AT PRESTWICK AFTER SITTING ON TOP WHILE RUNNING AN ENGINE BEATING OR SHOULD I SAY ADJUSTING WITH HAMMER TO THE SOV, MANY HAPPY DAYS.

[airsmiles]

Thanks tempsford, that make perfect sense. I presume the turbo compressors were used to run internal a/c systems like air-conditioning.

airsmiles

[Tempsford]

Airsmiles,
T/C were used for pressurisation. T/C was run off engine bleed and then air went to Air Conditioning Packs if I remember correctly. T/C was either on or off when selected.

Temps

[airsmiles]

Thanks. Think I got it now.

[Volume]

So T/C are similar to turbochargers ? Using hot compressed bleed air from the engine to compress fresh air for the cabin ?
What is the benefit from doing so, and not using the bleed air directly ? Cabin air contamination ? Why don´t we have T/C any more ?
What air do you use for deeicing on such airplanes ? Direct bleed air ? Precooled bleed air ? Exhaust bleed air comming from the turbine of the T/C ?

[nilnotedtks]

They were an FAA requirement in the early days of jet engines and pressurisation. It bypassed the need of the engine air being directly used for pressurisation and air conditioning, if you have any internal bearing chamber or compressor distress, it is possible to introduce smoke and/or fumes into the cabin, most undesirable. A T/C would, as correctly stated, draw ram air from the intake, compress it and sent it straight to the packs for A/C. If I too remember my 707 days at Gatwick, the covers were a sod to fit. Best method was to sit astride the monster and beat the latches liberally with the heels of a size 10 ! Oh, happy days . . . .

[morroccomole]

Tempsford: I do believe it's some years since you actually worked on any aircraft, let alone a 707 / 720B?

[Tempsford]

Morrocomole,
Cutting, but very true.
Temps