'maximising the effort'- how technology keeps the gas turbine surging forward

[tartle]

Following on the Camm comments in 'increasing the charge' thread:
There are many interacting technologies that make the development of the gas turbine possible; we can explore the technologies here. It is interesting how politicians etc that are not experts seem to think technology can be grabbed and applied easily to solve a problem.. perhaps we can do some myth busting in this thread! We should still discuss engines separately and here just do compressors, turbines, materials, computation, etc that can be regarded as the enabling tools, techniques and skills we need to 'do the product'.
tbc

 

[Delta Force]

How about the titanium engine technologies developed by Orenda in the late 1950s? It allowed the Iroquois to be the most powerful engine in the world when tested and gave it thrust and weight characteristics on par with (and in some cases better than) engines developed in the 1970s and 1980s.

 

[tartle]

Definitely... a pioneering effort...I'll put it on the technology list! Thanks for suggestion ... the Canadians did some great stuff in the post-war period.

 

[charleybarley]

The only 'first-hand' thing I can offer is the introduction of engine usage monitoring systems (EUMS) as a means of saving costs without compromising flight safety. The day the tapes were processed from 2 Red Arrows Gnats (leader and wingman) was a big revelation.
The wingman had accumulated 25X (IIRC) the LCF damage of the leader during a practice display flight....the effect of throttle excursions to maintain position. This replaced the previous intuitive method.... "oh, about 5X".

Mini cassette tapes were the recording medium with (IIRC) time, T1 and rotor speed at about 1 Hz. They had to be processed with a stress program to calculate how many stress cycles had been used up on the discs.

 

[tartle]

charleybarley,
Absolutely fascinating... the consumption of Low Cycle Fatigue Life first came to my attention when the fatigue life of hp turbine discs on the bigfans was used up much faster than our calculations derived from Conway and Avon practice... the use of monitoring was only an idea then... it is really interesting to hear how it is helping to help people understand how their flying practices actually has a measurable affect on the engine.
The philosophy at RR for engine health monitoring is here; there is a paper to show how complex the systems can get and the benefits below.
It is interesting reading of the efforts of Spitfire (and Hurricane) pilots using up their 'fatigue life' trying to follow the flight leader in the Vic formation the RAF started with (especially the weaver) and how going to finger 4 helped that situation.

 

[charleybarley]

tartle,
I had not heard of the vic/finger 4 story. I really like those different scenarios which illustrate the same underlying basics.
thank you for those links on the status of monitoring today at RR. It reminded me of doing it all by hand in the past...manual plotting of trends during endurance runs..performance..oil press, temp, consumption..gearbox pressure..vibrations..time to light..time to idle..rundown times..accel times..SOAP sample concentrations. And of course the one thing the automatic monitoring can't do ..the visual checks.
And despite the sophistication of vibration analysis I'm sure there's still no substitute for visually assessing the waterfall plots.
And also, as reminded by the RR EHM 'Acquire' section, the grabbing of data around an exceedence or interesting event like a surge.

Delta Force,
the Iroquois lives on..in British Columbia.
Not sure if you've seen this great footage

http://www.youtube.com/watch?v=_qms6vCS3Dw
pristine titanium LPC http://www.youtube.com/watch?v=vzP29E_P_Yo


http://www.youtube.com/watch?v=f1NpX-tqqKk

The videos above, posted by Robin Sipe http://www.pipelinenewsnorth.ca/article/20120127/PIPELINE0118/301279983/-1/pipeline/
are complemented by even more-instructive ones on the J79 for example.


tartle,
One possible thread that came to mind was something along the lines of
'features on yesterdays engines that are no longer required'
and one example is shown on this amazingly instructive footage, again from Robin Sipe
http://www.youtube.com/watch?v=s5UdobEQi3A

 

[charleybarley]

An enabler on the computing front (in common with CAD, etc in every other industry of course):
Physical mock-ups once produced in the model shop, for example , are no longer needed for trial fits....
Engine installations are assessed with wrench-wielding manikins...

Time 4:06, on this clip shows removal of engine starter and air supply tube

http://www.youtube.com/watch?v=SAKLjJ99Dmw

 

[tartle]

Great stuff! Just found this, with a pic (below) of A Boeing B-47 with Iroquois side mounted. This engine will be worth the archeology! dug up another pic!... from here.
Also video here.
An informative Flight magazine article starts here. It has a pic of the B-47 in flight and discussion of titanium.
Another to Robin Sipe's restoration project,
and a book of Iroquois Rollout photos by Peter Zuuring is here ... there is also an Arrow book. Peter's story is here.
The book is online here. Page 21 is a cutaway.

 

[tartle]

It is worth remembering that titanium had been used before in gas turbines; almost a decade earlier Rr had incorporated titanium blades in the final stages of the Conway hp compressor. However this was the first time the material had been used for all stages and the discs.... quite an achievement!
The photo below shows an hp turbine blade, note it is solid but does not carry a shroud at the tip; the extra mass can add some 40 or 50% to the critical section centrifugal stress so it is a trade off between blade life, turbine efficiency and manufacturability to decide the design parameters.
This ref may be worth looking at if anyone has access:
‘Fifty years of Structures and Materials Technology in Canada — An NRC Perspective’ by William Wallace in Canadian Aeronautics and Space Journal, 2004, 50(1): 33-48, 10.5589/q04-002

 

[Trident]

If I may interject a somewhat trivial question, but I wonder how many other 7-engined aircraft there were?! Can't be many!

 

[JFC Fuller]

Wasn't the original Arrow design powered by Rolls Royce RB.106's?

 

[charleybarley]

Wasn't the original Arrow design powered by Rolls Royce RB.106's?

Yes, read it only the other day in Jim Floyd's "The Avro Canada C102 Jetliner", as well as further details...
Then came the Wright J67, only to be cancelled by the USAF. Only then after foreign engines had fallen by the wayside was it decided to fit the PS13 Iroquois, which incidentally gave better performance than spec.

 

[charleybarley]

If I may interject a somewhat trivial question, but I wonder how many other 7-engined aircraft there were?! Can't be many!

and also unique as the only foreign-operated B-47?

 

[charleybarley]

Testing in the B-47 was limited by it's flight envelope, about Mach 0.84 and 40,000ft.
The engine was also tested to M2.3 and 66,000ft in an altitude test chamber at the NACA Lewis laboratory. This testing investigated an HP compressor stall problem at high altitudes.
Various potential fixes were evaluated...HPC IGVs, increased turbine areas, reduced compressor tip clearances with plastic abradable shrouds.
The problem had not been predicted by the HPC rig results (ample surge margin) because of the in-engine distortion from the LP compressor.
This, in all its excruciating detail, in on-line NACA RM SE58E26.

Other altitude testing .. including relights up to 63,000ft and heat soaking at high inlet temperatures, eg 34 min at M2 and 4 min at M2.3 detailed in NACA RM SE58F17.

 

[charleybarley]

there is also an Arrow book

"The Arrow Scrapbook" It is viewable on-line http://issuu.com/tikit/docs/scrapbook

 

[tartle]

Wasn't the original Arrow design powered by Rolls Royce RB.106's?

The RB106 engine was one of the engines considered for the Arrow... not sure if it was the lead engine in design. I wrote a little about the RB106 here. The RB106 preliminary studies started in 1951 when a requirement for a jet engine larger than the Avon was required for the next generation of fighters arose. Much titanium is involved. The previous post I refer to above was using RB106 technology in 1953 so pretty serious work had been undertaken by then. More work was done on combustion chamber... maybe this is where the annular Avon design came from? ... and a complete 5-stage transonic LP compressor was rig tested by 1956 when Duncan Sandys speech stated that it was the end of fighters for RAF (may have got that prediction wrong!), and the engine died... it is said in the press that the sole beneficiary from the cancellation was Canada who acquired expertise and experience to drive the Iroquois programme

 

[Trident]

there is also an Arrow book

"The Arrow Scrapbook" It is viewable on-line http://issuu.com/tikit/docs/scrapbook

Thanks for sharing that! Was a very pleasant evening's reading, and I was surprised at the number of remnants (both engine and airframe) that appear to have survived - for some reason I was under the impression that practically no hardware of the Iroquois power plants still existed!

 

[tartle]

I think the trick is to hide things where people will probably forget about them, and where the 'bean counters do not venture to see if they can clear out and sell off! When RR went bankrupt (4 February 1971... I was there!) Mike Evans who created the RRHT identified the safest place to be the financial strongroom in the basement of the newest building to be built for RR. There is a legal obligation to preserve company financial documents so the official receiver knew that what was in there needed to be there... cunning man was Mike... much of what we can unearth comes from that 'archeological site' plus what went home for safekeeping! copy it, hide the original and take the copy home was the mantra... long may it continue. I have a book of small drawings of the Cosmos Jupiter engine that came from a trash can...etc, etc.

 

[JFC Fuller]

The RB106 engine was one of the engines considered for the Arrow... not sure if it was the lead engine in design. I wrote a little about the RB106

I have seen it mentioned in a number of books and articles that prior to 1954 the RB.106 was the engine around which the Arrow was being designed. The story then goes along the lines that RB.106 development was delayed resulting in the decision to pursue an alternative engine.

In the UK I have only ever seen the RB.106 as having been proposed for developed versions of the Supermarine Type 545 (supersonic Swift development) though the RB.106 was apparently scaled up to be come the RB.122 for the Fairey OR.329/F.155/Delta III. An uprated version was supposedly the RB.128 and was the engine in the final Fairey OR.329 design. It was reported by Flight that only £100,000 of government money had been spent on the RB.106 which further suggests little work was done...?

 

[tartle]

As I said above.. the RB106 design must have advanced pretty quickly as the transonic compressor design was being adapted for the Conway and reports issued by Dec 1953.
Avro submitted the C105 proposal to the RCAF in June 1953.
This is an extract from the rollout news release via this site which is full of Arrow info!

"In less than one month the "Go-Ahead" was received from the government authorizing a design study of the C105 to meet the RCAF requirements.
First step in the design study was to adapt the new concept to Rolls Royce RB106 engines which were then in an advanced stage of development. From that point things progressed rapidly and the first tests of the wind tunnel development program were run in September 1953, only two months after the "gun was fired"....
Powerplant Changes
Later in 1954, powerplant problems arose which required major changes in the proposed program. The Rolls Royce RB 106 engines which were incorporated in the design, would not be available in time for the CF-105, and were replaced by two Curtiss-Wright J67 engines. Then, in early 1955, the U.S. Air Force disclosed that the J67 also would be too late to meet the Avro schedule. At this point, the program now in effect was laid on-the installation of Pratt & Whitney J75s as an interim measure, and Orenda PS13s (Iroquois) when they become available. Although the Iroquois development was well advanced, and its specifications more than met Avro's requirements, the combination of an untried engine and an untried airframe was considered not practical on an aircraft development flight test program."

 

[tartle]

Interesting article in Flight starting here. It has some numbers that contrast the use of steel vs. titanium, etc.
Also a report here that has a section on Iroquois testing in US facility. The refs are interesting too. They highlight the surge problem on the engine compressors that had not been resolved by the time of cancellation... not an unusual problem then (or now!). Also a turbine failure... also not unexpected at the engine's maturity phase.
There is also stuff on the Arrow firsts... Number 12 is:
"First by-pass engine design. (all current fighters have by-pass engines)."
The Iroquois is of course a non-bypass engine so that does not apply. I wonder if the term is used within the air intake system that probably 'spills' air at some point on the flight envelope in order not to 'overstuff' the engine and cause choke/stall issues.
There is an Arrow/Iroquois timeline here.

 

[Trident]

I think that list needs to be taken with a grain of salt... whoever compiled it appears to be mixing tentatively planned and even merely potential (i.e. not planned for, but possible with hindsight) upgrades with historical fact. #11, 12 and 13 seem to refer to one and the same thing, as described here:

"The fuel system and other accessories are all shrouded under
the engine inside a large accessory tank. This has been done not
merely to keep the engine tidy but in order to provide a closed
bay of the type normally produced by the employment of radial
firewalls. The latter cannot be used with the Iroquois since
they are impossible in the supersonic installation of the engine
in the Arrow intercepter. The fixed aircraft intake is designed
for correct performance at one flight condition only (probably
acceleration of the aircraft at maximum power at a speed just
above Mach 1). As the engine works up
into the high-supersonic range it finds it
cannot swallow all the air coming in at
the aircraft intake, and, were nothing
done to alleviate the condition, high
spillage-drag would ensue. What Avro
and Orenda have done is to employ
ejector nozzles so designed that they
generate a huge airflow over the outside
of the engine to reduce intake drag and
improve nozzle performance. This naturally
prohibits the use of any transverse
firewalls. As a result the fuel system and
other accessories are enclosed in a box
through which the airflow is restricted
to a level at which methyl bromide firesuppression
bottles can still meet the
specified requirements of concentration."
(http://www.flightglobal.com/pdfarchive/view/1957/1957%20-%201325.html)


I'm having difficulties grasping how that worked, possibly ejector nozzles drawing air not from the external slip stream as normal, but from the interior space between the inner engine bay wall and the outer casing of the engine itself, into which excess intake air was discharged at supersonic speed (rather than dumped overboard)? If so that does sound fairly unique and quite neat, although it is obviously not a by-pass engine/turbofan in the accepted sense (actually, it seems more like a primitive take on the J58). It might also provide a pointer regarding the hitherto unexplained source of air for the mysterious IR suppression technology on Rafale/M88 claimed by some, where a cold stream between the external nozzle petals and the internal convergent nozzle is supposed to shroud the hot exhaust.

 

[tartle]

I made a mislink which I have corrected above and repeat it here:
The 'Iroquois Rollout' book by Peter Zuuring is here.
...and yes the list seems to be a fantasy wishlist rather than factual one! Made me think though!

 

[aim9xray]

I'm having difficulties grasping how that worked, possibly ejector nozzles drawing air not from the external slip stream as normal, but from the interior space between the inner engine bay wall and the outer casing of the engine itself, into which excess intake air was discharged at supersonic speed (rather than dumped overboard)? If so that does sound fairly unique and quite neat, although it is obviously not a by-pass engine/turbofan in the accepted sense (actually, it seems more like a primitive take on the J58). It might also provide a pointer regarding the hitherto unexplained source of air for the mysterious IR suppression technology on Rafale/M88 claimed by some, where a cold stream between the external nozzle petals and the internal convergent nozzle is supposed to shroud the hot exhaust.

Well, I don't quite know how it was done, but we can look to the J79 as a useful analogue, as it represents the state of the art for a period several years earlier than the Iroquois.

Firstly, excess airflow is removed by a circumferential "bellmouth" just ahead of the engine. This is part of the aircraft and is not governed by the engine control systems. Air flows through the engine bay around the engine and is discharged through the annular ejector nozzle. The aircraft structure forms a seal to the outer ring on which are mounted the secondary [outer] flaps (generally known as "turkey feathers").

It should be noted that as the airflow at the engine face is subsonic (hopefully!) the air drawn from the inlet just slightly ahead of the engine face would be subsonic as well as the engine bay airflow.

HTH!

 

[Trident]

Excellent explanation, thanks for the effort! I didn't realize the J79/F-4 did this as well. By supersonic, I meant aircraft speed (there would probably be no mass flow mismatch at lower speeds), not air velocity at the engine face.
EDIT: Now that I think about it some more, the D30-F6 in the MiG-31 looks as though it probably does the same thing, except it is of course a genuine turbofan.

 

[aim9xray]

Thanks! Not to beat this into the ground, but I found some graphics that tell the story fairly well for the F-4 Phantom.

 

[charleybarley]

Thanks for the YJ79 nozzle photos. I just happened to be looking for something like that the other day.

Well, I don't quite know how it was done, but we can look to the J79 as a useful analogue, as it represents the state of the art for a period several years earlier than the Iroquois.

1957 state of the art in handling bypass air would probably be the J79 installation in the B58 with its translating inlet spike.

 

[charleybarley]

Can I offer another enabling technology?

The use of radiographic imaging to troubleshoot and understand what's going on inside a running engine.
Peter Stewart at Bristol with Derek Pullen at Harwell did pioneering work. I remember watching playbacks of the Olympus 593 turbine moving during transients. Something you always wanted to do...see with your own eyes rather than interpret/guess from instrumentation readings or condition of disassembled parts.
There are stills on this link which show an HPT blade seal coming out of engagement (593?). Also, oil starvation in the Gem.
http://www.shawinspectionsystems.com/library/dawpullen/dawpullen.htm

 

[charleybarley]

Tartle

Also a report here that has a section on Iroquois testing in US facility

Can you confirm this link? I couldn't find anything in the listing.

 

[tartle]

Charleybarley,
Another mislink!... it should have pointed to 'Pursuit of Power' ... you can download pdf or other format here.
I have corrected original link too. The report is 'data rich' but I think the concluding remarks are fascinating (we must spend some time on compressor stall). I've cut and paste them:
CONCLUDING REMARKS
An investigation of the prototype Iroquois turbojet engine in an
altitude t e s t chamber disclosed a severe stall problem in the high-pressure
compressor at low Reynolds numbers and low inlet-air temperatures.
Consequently, the operating range of the original engine configuration
was severely restricted below Reynolds number indices of 0.45 at
moderate and high corrected rotor speeds. The reduced operating range
resulted in high thrust penalties. For example, at standard conditions
at an altitude of 56,000 feet and Mach number of 0.9 the maximum possible
net thrust was 26 percent below that available without compressor s t a l l .
In contrast, the engine exhibited a large operating margin at simulated
Mach numbers of 1.5 and 2.0 at altitudes of 50,000 to 60,000 feet (inlet air
temperatures between 100O and 250° F and Reynolds number indices of
approximately 0.4) .
Examination of the component data of the original engine configuration
revealed that the s m a l l stall margin of the high-pressure compressor,
when it was operating as an integral part of the engine, was basically
due to the radial flow distortion at its inlet. This and an accompanying
Reynolds number effect on the high-pressure compressor resulted in the
curt ailed engine operation at altitude.
As a consequence, the manufacturer produced engine modifications
that included variable high-pressure compressor inlet guide vanes, increased
turbine-stator areas, and other modifications of a lesser nature.
The effect of these modifications was, in general, beneficial but inadequate
as far as engine operating limits were concerned. These modifications
were incorporated without penalizing the engine performance,
The analysis of the component performance of the three engine configurations
disclosed that of the modifications employed, opening the
turbine-stator areas was the most effective modification and the one
requiring the least amount of development, In addition, a practical
reduction of the flow distortion entering the high-pressure compressor
still appears to offer profitable stall margin improvement.
Lewis Flight Propulsion Laboratory
National Advisory Committee for Aeronautics
Cleveland, Ohio, June 13, 1958

Also an afterburner report can be downloaded here

 

[tartle]

The next technology generation on from Iroquois was the A-12 and SR-71 aircraft; the SR-71 was given the go-ahead in Aug 1959; its nacelle functions as shown in figure below (from US Air Force).

 

[charleybarley]

An interesting history "The Pursuit of Power". The demolition photos in ch 8 reminded me of the demise of Pyestock in these photos
http://www.dailymail.co.uk/news/article-2270038/Goodbye-Pyestock-Haunting-images-iconic-home-British-engineering-tested-Concorde-engines-2-000mph.html

Things were no different in Russia

http://englishrussia.com/2012/12/13/the-place-where-aircraft-engines-were-tested/#more-115515

The report is 'data rich'

I was pleasantly surprised to find this sort of detail available. The Iroquois does well (3 reports). Not much else on other whole engines from that era altho J57 and XJ79 (interesting with its variable stator mapping) are there.

 

[tartle]

Charleybarley...
These NASA (and DTIC) archives are most useful for unearthing 'hidden histories' of our technical past. When I was looking at how creativity played out in industrial design and development processes it always struck me that official definitions of 'creative industry' in the USA had engineers at its core, along with musicians, etc; in the UK 'c i' excludes engineers... listening to this years Reith lectures made me ask... who could speak and inspire today's kids to feel engineering is great too?
...leaping off hobbyhorse, I think accessibility is what stops us getting at so much UK stuff (Kew is underfunded on the digital side relative to the weight of papers).
If we keep plugging away here we will uncover a lot of this stuff... as we are demonstrating!

 

[robunos]

Before we leave the Iroquois, this from 'Avro Arrow', The Arrowheads, Boston Mills Press, 1980, ISBN 0-919822-35-5, pp. 122-3 :-

"When installed in the Arrow, the Iroquois had it's own cooling system; the automatic intake gills immediately adjacent to the compressor inlet opened up when a speed greater than Mach 0.5 was attained. This allowed air to by-pass around the engine for cooling purposes and to minimise spillage at the intakes at supersonic speeds, and still produced good performance with fixed geometry intakes in the subsonic, transonic, and supersonic ranges.
This by-pass air, cooled the [engine]compartment walls and the afterburner duct and gave additional thrust by the use of ejectors on the exit nozzle."

cheers,
Robin.

 

[charleybarley]

Before we leave the Iroquois

The origin of the Arrowheads' words seems to be Jim Floyd's lecture here (lengthy)
http://www.avroarrow.org/AvroArrow/RAeS.asp

An interesting apples to apples narrow comparison of the Iroquios installation alone with state of the art 30 years on could be the J79 in the F-16.
Apples to apples because they are both mach2 installations of turbojets with fixed inlet ramps.
The main difference seems to be the more advanced ramp geometry on the F-16.
http://arc.aiaa.org/doi/abs/10.2514/3.22758?journalCode=jpp
A bit steep at $1420 a copy.

And comparing with a turbofan installation (eg F100 in F-16 or TF30 in F-14) the big difference would be no flow required for external nozzle cooling, etc.

 

[tartle]

charleybarley....
I agree 1420 seems a lot in any currency...but
András Sóbester is/was at Southampton University who are more enlightened.. file is too big to post so upload it here. Forgotten how odd the F-107 intake was!

 

[charleybarley]

Tartle,
thanks. A good read. It certainly holds your attention with all the photos.

Perhaps the most interesting of all is the one with no intake, the weight reduction exercise Starlifter in Fig12.

 

[tartle]

re fig 12... my first reaction was to wonder if it was April first, then a maintenance photo misinterpreted!

 

[robunos]

The origin of the Arrowheads' words seems to be Jim Floyd's lecture here (lengthy)
http://www.avroarrow.org/AvroArrow/RAeS.asp

Thanks for the link, but the pictures won't open for me...
As an aside, does anyone know who 'The Arrowheads' were/are?

cheers,
Robin.

 

[tartle]

Try this link to RAes Lecture..I could see pix.