The Turbine of the Turbo

This post looks at the PT-6 series of engines. A power plant of this family was used on CNR's Turbo train. As you already know, there was a fair amount of public/private partnership in this story.

I found an unexpected link between the Turbo train references and other books I have about technology. The person named below is key in interpreting the engine at the heart of the Turbo.

from: Flight International; Oct 9, 1969.

Howard Fowler wrote two books for what was then known as the National Aviation Museum - one on aircraft piston engines and one on jets. They were written 30 years after the events reported above.

The text below is from: The Evolution of the Jet Engine; Howard S Fowler; 1999; National Aviation Museum, Ottawa. 

'It is interesting to compare the two versions of a seven-passenger light aircraft, the de Havilland Beaver, which was powered by a Pratt & Whitney R 985 Wasp Junior air-cooled radial engine, and the Turbo-Beaver which was essentially the same aircraft but powered by the PT6-A6.

'The Wasp engine, of 450 hp, weighed 309 kg, while the PT6-A6 developed 578 hp, for a weight of only 131 kg. It is stated that the 'length of the cabin is increased by 2 1/2 feet, giving space for two more passenger seats. This, and the 12% increase in cruising speed, results in an improvement of 35% in operating economy'. The take-off distance is decreased from 381 to 274 metres, giving a considerable advantage in short-field ability. 

'The PT-6 had a most interesting history of development. The first engine was run on the testbed in November 1959, flew in May of 1961, and was certified in 1963. It began by producing 475 shaft horse power, and the series was ultimately developed up to 1350 shp. A most ingenious layout resulted in an overall diameter of only 48 cm, a total length of 152 cm, and a frontal area of 0.18 square metres. [The figure farther below] shows how this was achieved, albeit at the expense of a somewhat contorted airflow path through the engine. 

' ... There was a long series of PT-6 engines, in which continual development of compressor stages, of the turbine, and of fuel and control systems, raised the power output [as noted above].

' ... Ultimately it was decided to redesign the engine, as the PT-7, embodying all the lessons learned in the PT-6 series.

' ... The flow path was straightened out, and a nose intake capable of rejecting ice particles and other foreign matter was developed during the extensive testing in the National Research Council (NRC) icing tunnel.

' ... In the 1960s, the writer [Howard S Fowler] was asked by Dr MacPhail, his Director in the Mechanical Engineering Division of NRC, to look into the real flow in the channels of the impeller. Using data supplied by Pratt & Whitney, a ten-times full size model of the PT6 impeller was built and spun at 70 rpm, with the writer firmly fixed into its centre, and the actual flow was mapped using smoke streamers and a hot-wire anemometer. Some 200 hours of running and many more of analysis, revealed the true picture of the flow in the impeller ...

' ... This information was passed to Pratt & Whitney, whose aerodynamacists were then able to develop a greatly advanced mathematical treatment of the true flow, which enabled them to design a compressor with a predictable performance far in advance of previous machines.' 

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Jet versus Prop-jet

In these two schematic diagrams, the white arrows represents the relative energy flows. The black arrows represent the torsional force imparted to the central shaft. The general air flow through both engines is from left to right. 

First, looking at the pure jet engine: The top big white arrow represents the energy input of fuel. The fuel is aerosolized and ignited and the expanding gases (arrow pointing right) turn a turbine (vertical hatching). The torsional force is transferred 'upwind' by the shaft (notice the white curved energy arrow underneath). Near the inlet, this torsion drives the compressing turbine (vertical hatching). Compressing air causes it to heat up, and it also increases the amount of oxygen available (in a given volume of air) to support fuel combustion.

When the jet is ready for work: hot, oxygen-rich intake air is mixing efficiently with the fuel aerosol in the fuel burners. The tailend turbine is designed to steal just enough energy from the expanding gases to spin the compressor. The propulsion for the aircraft comes from the thrust out the tailend - the big white arrow at the right.

from: The Evolution of the Jet Engine; Howard S Fowler; 1999; National Aviation Museum, Ottawa

Now looking at the prop-jet engine schematic (above), the fuel/energy input is again represented at the top. There are two separate turbines at the tailend with concentric shafts: one shaft operates the compressor at the upwind end, the other turbine spins the propeller. The hot combustion gases exit the rear of the engine and provide some thrust.

The critical difference from the jet, is that energy is focused on turning that central shaft to turn the propeller.

Like the Turbo train application, the compressor turbine operates continuously during idling, BUT the power turbine (here for the propeller) is only engaged when needed for vehicle propulsion.

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from: The Evolution of the Jet Engine; Howard S Fowler; 1999; National Aviation Museum, Ottawa.

With the Turbo train's PT6 in an aircraft application (e.g. a Turbo-Beaver), there is no thrust out the tailend. As Howard Fowler noted, the air flow is relatively circuitous; the tailend of the engine is located at the cockpit firewall.

Similar to the prop-jet diagram, you can see that the compressor turbine is separate from the power turbine. The compressor turbine turns during idling with the power turbine engaged only when vehicle movement is desired.

*  *  *

from: Turbo-propulsion; W G Blevins; Canadian Rail Feb 1969; Canadian Railroad Historical Association. Collection of LC Gagnon.

In the Canadian Rail Turbo train illustration above, you can pick out the segments of the engine.
Below, in an aviation application, you can see the engine again.

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from: The de Havilland Canada Story; Fred W Hotson; 1983; Canav Books.

Above, is the PT6 turbine engine installed in a Series 300 Twin Otter aircraft. 

16 is a PT6A-27, free-turbine powerplant producing 620 shaft horsepower. 17 are two engine exhaust nozzles. 14 is the air intake deflector. 12 is the air flow duct. 18 is the engine air inlet.

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from: Overland Models advertisement; Locomotive & Railway Preservation; May-June 1991.

Rhetorical Corner:
Turbine engines in railway service are not used to lift the vehicle off the rails.
Is it therefore necessary for the turbine engine itself to be as light as possible?


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My father included this article in his Turbo train file.

On April 27, 1967, (this is based on an apocryphal story later published in the Montreal Gazette) Prime Minister Lester Pearson did not travel from Ottawa to Montreal aboard the CN's Turbo train to open Expo 67. This did not happen because the Turbo train was not ready by the date which had been advertised and promoted.

Over a year later - on September 14, 1968 - this cover story ran in the Weekend Magazine. This newsprint magazine and the comics section were included with the Saturday edition of many Canadian newspapers of that era. Near the end of the article is this passage:

" ST6 engines will whisk Canadian National's plane-type aluminum turbotrains ... "

... So, as this article was being printed, neither was Canada's current leader, Prime Minister Pierre Trudeau, going to be riding the Turbo.

The first image below is the initial two-page spread of the article - to show you the presentation. The text is removed and reproduced below in a more readable size.

Below, the Turbo train is (probably) seen approaching Kingston from the east at around mile 171. For a number of years, in regular service, its zone speed would be 95 mph, but it would have to slow to 40 mph to operate through the horseshoe curve at Kingston's 'outer' station - the curve being virtually unchanged since it was laid out by the Grand Trunk Railway in the 1850s.

In hindsight, the 'unspoiled' heritage roadbed and public crossing timing circuits would limit the Turbo's speed more than wind resistance or the absolute weight of the trainset and its power plant.

Perhaps this story idea was advanced by the Turbo partners at this point because of the delays in bringing the Turbo into revenue service  - a case of 'earned media' to help take a little pressure off the government-owned CNR as well as its private contractor, United Aircraft.

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In early 1966, a Canadian Rail article presented some early images of the arrangement of the turbines. This section will wrap up this post on the Turbo's power plant.

from: Turbine Motor Trains; Michael Leduc; Canadian Rail, April 1966; CRHA. Collection of LC Gagnon.

For motive power, I understand that two turbines were placed in each power car. Here, also, is the power transmission arrangement as it was foreseen in 1966. 

Only the American version of the Turbo, which would be under test primarily in the north-eastern US, needed the capacity to operate using a DC motor taking power from a third rail. As you know, particularly around New York City, the turbines could not have been operated in tunnels and other enclosed areas where a third rail power system had been established for safety reasons.

Jumping to a conclusion, the darkest of the THREE turbines on this unit is probably the trainset's fifth turbine - which would act just like an airliner's auxiliary power unit to provide 'hotel power'. The motive power turbine located closest to that APU is probably the one designated as its backup. If the APU turbine failed, it could be replaced in its function of powering climate control and lighting by switching over a designated turbine from propulsion to APU duties.

from: Turbine Motor Trains; Michael Leduc; Canadian Rail, April 1966; CRHA. Collection of LC Gagnon.

In this early image, you can see the general location of two turbines, without their exhaust stacks.
The latter ran up through the large partition between the passenger dome chairs.

You can see how blowing snow and road dirt could foul the turbines if intake air filtering wasn't highly efficient.

Central Station Turbo Maintenance Area, Turbo 1974-82

This post presents additional newspaper clippings my father filed about the Turbo train.
They span the period from 1974 to the Turbo's retirement in late 1982.

The captions aren't matched with the correct photos.

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This series on the Turbo train began because I wanted to get this artifact (below) on the internet so people who are interested in this subject, or those doing research in the future, could have access to it. The title of this post tags the document to make it easier to find.

This rough diagram of the lower level of tracks at Montreal's Central Station may originate from the Turbo's introduction to service, or it may have been produced later ... for example, in 1971, when the train length and configuration was being changed from its original. I have introduced it at this point because the article above mentions the United Aircraft of Canada employees working at this location.

I bought this diagram a number of years ago at the Kingston railway show. The vendor (I suspect, the original owner) had gone to the extent of producing an interpretive 'label' in the form of a sheet of paper with computer printer images of both Central Station and the Turbo on it. I assured him the diagram was going to a good home, and with this posting it is - yours.

The original is on heavy tracing paper which has become dark brown with age. The drawing and writing has been done with various sizes of black felt-tipped markers. The overall size is the equivalent of 4 sheets of 8x11 paper laid side-by-side.

This software platform often frustrates my attempts to post larger items in sufficient detail that readers can read or download them. In all cases below, you will need to scroll to the right to see the entire document. It took a number of tries to find a size and format which made the document useful to readers.

The first image shows the entire document as an overview.

Then, the following two images show two halves of it in sufficient detail so you can read all the written characters. The word 'SOUTH' is duplicated on both halves to serve as an anchor - if you want to stitch them back together. 

The two halves (below) ...

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There is a significant gap of a few years in my father's clipping file on the Turbo - maybe everyone got tired of reading about it. The last article (March 1972) in a previous post foretold of a Turbo return in early 1973.

I have left out a Toronto Star clipping from June 23, 1973. This pits the speed of a Turbo trip against an Air Canada flight - using downtown Toronto and downtown Montreal as the travel points. The reporter took the Turbo east and Air Canada west, back to Toronto. Other key points: His flight left Montreal 80 minutes late and he checked his bag on the plane, requiring a delay at the carousel.

Excerpts ...

"A ride on the super-train ... Turbo Beats Jet by 35 Minutes" 

' The Terrible Turbo - Canadian National Railways' super-train with a remarkable propensity for breaking down - has made a comeback. ' 

' Now, almost a year and a half and some 100 modifications later, the Turbo is back ' 

' However, the [other] Turbo from Montreal to Toronto arrived at Union Station last night 56 minutes late. The lights went off and the air-conditioning failed, giving passengers an unscheduled 35 minute stop at Cornwall. This train made the 337 mile run in 5 hours and 6 minutes with one engine shut down after the Cornwall stop. ' 

There is a lengthy comparison of leg room, etc, and the food and drink offered.

' [On the reporter's train]: Most complaints centred on the fact that CN has dropped the traditional dining car. [passenger quote]: "It seems to me that this eating at your seat might be efficient but I hate to see the passing of the train dining car. There is something quite elegant about dinner aboard a train. It was the worst thing they could have picked up from the airlines." ' [end of article]

*  *  *

April 26, 1976

... That's quite a model of the Turbo you have there!
The jumble of text includes non-Turbo trains.

My first ride on the Turbo was in April or May 1976 - returning from a job interview.
I remembered it as being low to the ground, fast and hard-riding.
And now I wonder if I could have had a train with a dining car.

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June 12, 1976

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July 23, 1976

That's quite a drawing of the Turbo you have there!


In case you are not a Turbo fan, here is a brief digression.
It's another distance expression for the public which invokes the moon
from a 1950 Trains magazine.
It seems that almost every aspect of the Turbo had already been 'done' somewhere else before.

*  *  *

December 20, 1976

They are like heavily-laden prospectors of the late 1800s, at a northern Ontario flag stop, clambering aboard from the level of the ballast. They are herded in through one door into one car, so they can be supervised. Shack is the conductor today, and no one is going to ride for free!
(cf. Emperor of the North)

You take this exquisitely engineered greyhound of the rails, bank it at high speed through the curves ... but you don't do anything to ameliorate dwell time or 'customer experience'.

*  *  *

March 11 1977

Don't be confused by spin: The 'next generation' is very different from a 'new generation'.



May 31, 1979

In a later article in another paper, a fuel line leak was speculated to be a possible cause.

This article was preserved as a photocopy.

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The images below come from the dinnertime arrivals of the Turbos to Kingston. I probably took them in 1982. In the first you can see the tower of Collins Bay Penitentiary in the distance. It was also during this time in VIA history that the Canadian travelled between Montreal and Toronto through Kingston.

The westbound gets a pull-by inspection by some passengers as it stops at the station.

At least one more post will follow with the enthusiastic and optimistic
 late-1960s descriptions of the Turbo technology and what it was expected to achieve.

What's really the trouble with the Turbo train?

by: Timothy Hackworth

Timothy Hackworth is the pseudonym of a Montreal authority on rail transport.

from: The Montreal Star, 

January 7, 1969

Collection of LC Gagnon.

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End of the January 1969 article.
To illustrate some of the author's points, a few images appear below.

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Locomotive Prototypes

Further postings will look at the Turbo's own equipment in more detail.

 Unlike the locomotives below,
the Turbo's turbine engines were geared directly to the driving wheels.

Trains; July 1949; Kalmbach

GE 101 (above) was a gas turbine-electric.
A diagram of its power plant is shown below.

Trains; July 1949; Kalmbach

Trains; October 1949; Kalmbach

The UP 50 is the experimental GE 101
after it was renumbered and repainted for Union Pacific.

UP ordered larger turbine locomotives for freight service
to take advantage of cheap bunker fuel.

Trains; May 1949; Kalmbach.

Chesapeake and Ohio coal-fired steam turbine-electric - built by Baldwin.
In service 1947 to 1950 (scrapped)

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Passenger Trainset Prototypes

Modern Railways; Cecil J Allen; 1959; Faber and Faber.

The GM EMD Aerotrain and the rubber bellows (right) employed as part of its suspension system.

Trains; June 1949; Kalmbach.

Chesapeake and Ohio experimental Train X cars at the Chicago Railroad Fair, 1948.
This was the technological basis for the Turbo's wheel and articulation system.

Trains; June 1949; Kalmbach.

American Car and Foundry experimental Talgo train.
(Talgo II, to be precise)

Trains remarked on the similarity to the Train X system, above.