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Hawker Siddeley Trident 3B and its fourth "booster" engine

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Hawker Siddeley Trident 3B and its fourth "booster" engine

Old 13th Apr 2023, 13:39
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Hawker Siddeley Trident 3B and its fourth "booster" engine

Hi all,

I recently read about the interesting powerplant configuration of the Hawker Siddeley Trident 3B.

For those who don't know, the Hawker-Siddeley Trident, HS-121, was a British trijet of the 1960s similar in overall configuration to the Boeing 727. The aircraft was equipped with three Rolls-Royce Spey RB163 turbofan engines, each of around 46 to 53 kN of rated thrust (depending on variant). Its last variant, the Trident 3B, featured a fourth RB162 booster engine of 23 kN of thrust which added 5% extra weight to the aircraft but provided an extra 15% thrust on take-off. It was used on demand when needed.

Since there's very little information available on this interesting and odd powerplant configuration, I'd love to hear from anyone who knows more of the Trident 3B. I'm particularly interested in the actual operation of the fourth engine. Was it used only for take-off and then shut down? If so, when exactly was it shut-down? Would it be left on for the whole flight? What about shutting it down during cruise but later relighting to comply with potential go-around climb gradient requirements? What were the normal procedures and limitations? How was the fourth engine controlled in the cockpit: did it have its own lever? was the lever the same as the other three? was it rather more like an "on/off" control? Did the pilots or the flight engineer control it? Was it operated in a similar way to those water injection systems on older turbofans like on the 707 and 747?

Any sort of insight into this feature of the Trident 3B beyond what's available on Wikipedia would be greatly appreciated.
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Old 13th Apr 2023, 13:51
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And, above all, where did they place the fourth extra engine in an airplane with that engine configuration???
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Old 13th Apr 2023, 14:01
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The fourth engine was positioned at the base of the fin above the #2 Spey. It was a mainly, plastic on/off turbojet with a total loss oil system. Needed topping up regularly.
A quick search on PPRUNE reveals multiple threads over the years, this is quite a good one.

Trident engine locations ?
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Old 13th Apr 2023, 17:32
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I think Blind Pew is probably your man...he lurks on various forums on here.
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Old 13th Apr 2023, 19:23
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Originally Posted by iggy
And, above all, where did they place the fourth extra engine in an airplane with that engine configuration???
See here:
The no.2 engine is in the fuselage with the 'booster' above it at the base of the fin.
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Old 13th Apr 2023, 20:25
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Not me..whilst I did have a couple of rides up front I avoided the big boys fleet and was long gone when they decided that it was within the abilities of lesser pilots to fly all 4 marks.
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Old 13th Apr 2023, 21:44
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So where is the inlet for the 'booster' engine - does it get the air from the conventional center engine inlet? Of is that an inlet just above the center engine inlet?

Boeing did something different for the 727 for Mexico City - they mounted some JATO bottles in the wheel wells - if they lost an engine during takeoff the JATO bottles would fire to give that extra thrust needed. Testing resulted in some pretty spectacular videos...
Eventually they were able to uprate the JT8D engines enough that they could get rid of the JATO assist.
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Old 13th Apr 2023, 22:07
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Originally Posted by tdracer
So where is the inlet for the 'booster' engine - does it get the air from the conventional center engine inlet? Of is that an inlet just above the center engine inlet?
Neither of the above (the inlet above the No 2 inlet duct is for the APU). The boost engine inlet doors only opened when the engine was operating.



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Old 14th Apr 2023, 04:25
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So this Trident has five engines
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Old 14th Apr 2023, 06:38
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Since no one has answered re operation iirc
it was started on taxi out and had to be warmed up for around a minute. Then a selection was made on a toggle switch into the take off mode. Once the throttles were opened up on take off then it too developed take off thrust. Think it generally ran for around a minute then cut out.
Might had shut down latest at noise cut back from throttle position.
‘Don’t know anything about cooling period.
Couldn’t be restarted as as mentioned lubricated by total oil loss system like speedway bikes.
Two notable incidents with lack of performance on the 3..one out of Malaga where they diverted into Madrid having lost an engine but didn’t check WAT limits (approach climb)..and were forced into a go around by ATC but continued flying downhill..skipper realised and besides flying down a valley accelerated and cleaned up to get onto the front side of the drag curve.
The second was a night take off out of Malta where they took some approach lights out then flew below 50ft radio altitude with the stick shake going until they were able to accelerate. Whoever put the books together added 1km to the available runway length. Got the jump seat from a skipper who had been a copilot on that flight and said what a fabulous bit of flying he had witnessed.
On the T2 we had water injection.
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Old 14th Apr 2023, 07:38
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Originally Posted by stilton
So this Trident has five engines
Hmmm. There's a reason they're called APUs and not AEs.

That said, I recall that the TriStar's APU (Hamilton Standard ST6) was a thinly-disguised Pratt & Whitney PT6 - an engine I got to know much better in a later life, in its more conventional form.
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Old 14th Apr 2023, 10:42
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Living close to LHR and being an 'enthusiast' one soon got to know the distinctive noise of the Trident 3 , quite an achivements Tridents were pretty noisy anyway. Looking at the pics in the posts the engines look tiny compared to modern-day turbofans and I am not sure the Spey could really be called a turbofan as there is no separate exit for fan-generated thrust as was the case on the first fan jet 707s .

While on the subject I always wondered how a Caravelle would perform with only one engine since being an early generation jet it must have had a pretty heavy airframe and a hefty four wheel main gear

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Old 14th Apr 2023, 11:34
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Originally Posted by pax britanica
Living close to LHR and being an 'enthusiast' one soon got to know the distinctive noise of the Trident 3 , quite an achivements Tridents were pretty noisy anyway. Looking at the pics in the posts the engines look tiny compared to modern-day turbofans and I am not sure the Spey could really be called a turbofan as there is no separate exit for fan-generated thrust as was the case on the first fan jet 707s .

While on the subject I always wondered how a Caravelle would perform with only one engine since being an early generation jet it must have had a pretty heavy airframe and a hefty four wheel main gear
The Tridents made an absolute din coming over, only Concorde was louder
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Old 14th Apr 2023, 11:38
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Turbofan is a designation for any turbojet with a bypass. The Spey is a low bypass turbofan. The separate exits for cold stream air and core gases are only a design preference. The IAE V2500 and Trent 700? also have common nozzles for the bypass and core exhaust.
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Old 14th Apr 2023, 12:45
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I think the term Turbo Fan is not applicable to the RR Spey, it is a bypass engine. The front 4 or 5 compressor stages feed air into the core HP compressor or down a bypass duct.
A Turbo Fan engine has a single stage fan that feeds some air into the core compressors but most of the air goes down a fan air duct.
The RR Tay was a Fan development of the Spey.
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Old 14th Apr 2023, 13:17
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Dixi

Thnaks-bypass was the word I was looking for but could not remeber, the exhausts nozzles on the Speys look tiny in the pics on this thread. And I know things take time but as has often been pointed out the Spey didnt seem to have much development potential which would obviously limit the Tridents growth. Had it been able to push out another few thousands of pounds thrust then perhaps the T3 would not only have not needed a fourth engine but might have given the 727 more competition
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Old 14th Apr 2023, 15:54
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The Spey was developed into the Tay which was fitted to the B727s of UPS on the 1990s.
The Fanned Spey, as it was called in the early 1970s, was to be fitted to the BAC1-11-700 but never got off the drawing board.
I don't think a re-engine program for the Trident 3 would have got far as there were structural problems with the wing that limited their life.
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Old 14th Apr 2023, 15:55
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Originally Posted by dixi188
I think the term Turbo Fan is not applicable to the RR Spey, it is a bypass engine. The front 4 or 5 compressor stages feed air into the core HP compressor or down a bypass duct.
A Turbo Fan engine has a single stage fan that feeds some air into the core compressors but most of the air goes down a fan air duct.
The RR Tay was a Fan development of the Spey.
It's a low bypass ratio turbofan engine as opposed to a pure turbojet.

In any case, this is just semantics. Does it really matter what we call it as long as we know what it is? Not really...
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Old 14th Apr 2023, 15:57
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Originally Posted by blind pew
Since no one has answered re operation iirc
it was started on taxi out and had to be warmed up for around a minute. Then a selection was made on a toggle switch into the take off mode. Once the throttles were opened up on take off then it too developed take off thrust. Think it generally ran for around a minute then cut out.
Might had shut down latest at noise cut back from throttle position.
ĎDonít know anything about cooling period.
Couldnít be restarted as as mentioned lubricated by total oil loss system like speedway bikes.
Two notable incidents with lack of performance on the 3..one out of Malaga where they diverted into Madrid having lost an engine but didnít check WAT limits (approach climb)..and were forced into a go around by ATC but continued flying downhill..skipper realised and besides flying down a valley accelerated and cleaned up to get onto the front side of the drag curve.
The second was a night take off out of Malta where they took some approach lights out then flew below 50ft radio altitude with the stick shake going until they were able to accelerate. Whoever put the books together added 1km to the available runway length. Got the jump seat from a skipper who had been a copilot on that flight and said what a fabulous bit of flying he had witnessed.
On the T2 we had water injection.
Very interesting. Thanks a lot for these!
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Old 14th Apr 2023, 16:00
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Originally Posted by blind pew
Not me..whilst I did have a couple of rides up front I avoided the big boys fleet and was long gone when they decided that it was within the abilities of lesser pilots to fly all 4 marks.
Ah my apologies bp
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