Chinook Question?
 

Hi All

I am currently reading Eye of the Storm by Peter Ratcliffe about his time in the SAS.
In this book he mentions getting onto a Chinook in Saudi Arabia during desert storm when " The aircraft began to shake preparatory to take-off, the pilot suddenly shuts down. The racket and vibration suddenly began to dininish and the rotors began to slow.The pilot announced we have a problem its either a fuel blockage or its the hydraulics. If it is fuel it will be 30 min if it is hydraulics we'll be at least 2 hours."
It ends up been hydraulics and the flight is delayed.

When I first read this I dismissed the facts initially as I could not think of any problem on the types I fly that would have me confused between those two systems. So my initial reaction was that the author probably has his facts mixed up. However in his book he appears to try to be factual so to any Chinook drivers out the is there any problems you can develop that would need checking both systems and what would cause them? or has the Author made a mistake?

Cheers

Is this your paraphrase, or a verbatim quote from the book?

Cheers

Whirls

It is a quote from the book although I did remove some non relevent sentences from the paragraph.

Either something stops suddenly or it gradually slows - it can't suddenly fade ....

If that's the standard of Peter Ratcliffe's English, then I would take the "facts" with a pinch of salt. :}If it's a paraphrase, then exact wording would be more helpful.

Cheers

Whirls

I can't think of anything which would create confusion between fuel and hydraulics; especially with excessive vibrations during run-up. I suppose "preparatory to take-off" could mean anything from initial start-up to before take-off checks. The AFCS hydraulics are an obvious culprit with vibes since there could be adverse feedback, air in the system, or any number of other problems. A fuel blockage though should really only starve an engine and cause it to run weak or shut down completely (assuming it is beyond the cross valve). :confused: I think I would be more worried about imbalances in the driveshafts or rotors.

I'm with Whirlygig, take this with a grain of salt!

A side note
 

Peter Ratcliffe served about twenty five years in the British SAS and was the RSM when he left. He states in his book that it was written to correct some of the nonsense that has been written about the SAS in recent years, especially after books like 'Bravo Two Zero" and "The One That Got Away" came out. I didn't think the book was that well written from the grammatical sense, (as if I would know!). I think he was concentrating on giving an accurate account from the Army point of view rather than an aviation one.

Ratcliff's book has been criticised quite strongly by some of those he accused of talking 'tosh' - we will never know!

It would have been a Mark 1 Chinook, though I can't think of why a fuel blockage would cause vibration, maybe someone else could shed light on it.

The vibration could stem from any number of problems with the hydraulics, in common with most helicopters.

I also thought the author was probably mistaken however I dont know anything about Chinooks so I have not presumed to be correct.
Without getting stuck on words there was a problem and the pilots shut down. The phrase "its either a fuel blockage or its the hydraulics." is the bit that had my focus.
I have had vapour in the fuel lines on start and that can be quite noisy and also have vibrations. It is not hard to diagnose though.
With the hydralics/AFCS I understand how vibrations could occur and need ground inspection to work out where the problem is coming from.
Personally though the issues I have had, it has been apparent which system is playing up.
My question for Chinook drivers is, can you have a problem where you would be unsure as to the origin,either from the fuel or the hydralics?

Cheers

AS an ex Chinook driver, the two systems are completely separate and there is 'artistic licence' applied here for effect. However, knowning the RAF maintainers the greatest artistic licence is in the phrase: "If it is fuel it will be 30 min if it is hydraulics we'll be at least 2 hours." The maintainers would never work that fast. No wonder the flight was delayed!

As I said yesterday, I can think of no instances where I would be confused between hydraulics and fuel. In addition, I can think of no reason why the fuel system would cause vibrations of any kind.

Fuel tank, cross feeds, engine. Done. If there was a block in the tank the other tanks would feed the blocked engine. If there was a block in the cross feed the tanks would feed the engine on their respective side. If there was a block at the engine, I would imagine it would simply stop running. None of these scenarios should be coupled with vibrations.

Generally, vibrations on takeoff are caused by blades, shafts, or hydraulics.

Ignoring vibrations completely and I still can think of nothing which would create confusion between the two. Fuel obviously is used only for the engines and the APU. The only time hydraulics even gets close to these parts is during initial start-up. Stored hydraulics pressure gets the APU spinning and then it creates pressure to start the main engines. It is very easy to differentiate between a hydraulics problem versus fuel problem on start-up: doesn't spin, it's hydraulics; doesn't fire, it's fuel.

Clear as mud?

Great thank you Hooker47 and Heliaviator and others for your replies that was what I was after.
Incidentaly Hooker47 I have had partial light offs in a engine (s76) which can be interpreted as vibrations however nothing like rotor/shaft unbalance. I guess it depends on how one defines vibrations. As you said though crossfeeding for the start and priming the engine solves the problem quickly if it does not just stop itself.
From the Authors perspective he may have heard the pilot wrong or just remembered it wrong. I just wanted to check.

Cheers

P.S
I really enjoyed the book. Although it was not writen that well. It was still a good informative read. If you like that type of book I would recommend it.

CH-47 Startup
 

I am a former CH-47D IP, and here is an answer.

The author probably did not intend to imply that the shaking or noises were caused by a fuel or hydraulic problem. I think you may be reading that into the story.

Unless the section of the book goes on to further connect the problem with the physical description of a normal aborted startup, he was just describing the events (although I see how you could think they were connected). He was overly descriptive of a normal startup and shutdown and, without stating it, went right into stating the cause of the entirely normal "sudden shutdown". Most likely, the shutdown was initiated because a crewmember spotted a leaking fluid that had yet to be identified. (Yeah, yeah, I know. If a hook doesn’t leak that means it's empty.)

If you want to know why the shaking made it in the book, if it was "normal", read on:

So why would a writer who has possibly ridden on plenty of helicopters, maybe even Chinooks, think that the shaking was notable? Short answer: Big tandem rotors shake the bird a lot during run-up.

Almost everyone who sits on a hook during startup, especially someone who has little experience sitting on tandem rotor helo's during run-up, will notice quite a lot of shaking and noise. Both are completely normal. They are caused by the imbalances that are experienced as the rotors transits through various rpm bands that are experienced only when the rotor is spinning below normal operating speeds.

All full size helicopters’ rotors are only balanced for specific operational ranges. The tandem design just makes startup particularly rough because they have two unbalanced rotors that are displaced in plane of rotation, waterline, blade pitch, and, most notably, arm. The offset main rotor systems create oscillations that interfere with each other.

The great thing about the Chinook is that you could have a full formal dinner actualy inside it with about 25 present. I only say this because despite having 800+ hours on the beast I've forgotten the tech.