'Increasing the Charge' - how piston engine technology provided the power to fly

[tartle]

Why the fascination with piston engines history: simply they are very important. Sidney Camm wrote in his 1966 article 'A Lifetime of Design':
"Looking back over the development of aircraft one is struck by the number of factors that have to be considered --aerodynamics, materials and structures are the main categories and it is fascinating to notice how from time to time, just as we had seemed to reach a stage when progress was slowing down, some new discovery would raise the horizon again. The classic case of this, of course, was the jet engine that was being developed by Frank Whittle. From 1930 it had been obvious that we were approaching the limit of speed with the airscrew engine combination, as in spite of all we could put into airscrew developments, any extra power developed by the engine was wasted due to tip speed losses of the airscrew, and it looked as though speeds between 450-500 mph were about as far as we could go with this arrangement.. Almost overnight the Whittle engine changed this and although we are again approaching a limit due to what may be called the heat barrier, I am sure this will be surmounted.
The point which emerges from this is the dependence of the aircraft design on the production of improved powerplants. This was obvious, even in the days of the Wrights. They first flew, not because their aircraft had any great merits, but because they produced a powerplant-airscrew combination able to lift the somewhat cumbersome machine off the ground. The introduction of the rotary Gnome engine in 1911 was responsible for a tremendous surge forward until the arrival of the Hispano Suiza in line engine which more or less eclipsed the rotary type of engine, although it was still used on a number of aircraft with some success until the arrival of the Rolls-Royce Kestrel in 1927."
This seems a good reason for a technology thread.. this one on piston engines.
A successful technology is only 'successful' if it impacts on an engine in one or more of these categories:
New types and power increases
Changing operational requirements
Environment
Flight operations
Aircraft installations
Repair capability
Life development
Manufacture and suppliers
All these need to move forward if a new technology is to be successfully adopted... it is interesting how the RR racing 'R' engine which gave vast power increases in a short space of time ,,, but only for a life of 1 hour at max output was emulated by the progress of the Merlin, ten years later- but for 100 hours plus life.

 

[Tailspin Turtle]

Thanks for the excellent chart and introduction. Another area of discussion is the rivalry between liquid-cooled and air-cooled engine for dominance and the continuous improvement in both that basically resulted in a standoff. (The often repeated statement that the U.S Navy abandoned the liquid-cooled engine in the 1920s is at best a simplification; the Bureau continued to fund liquid-cooled engine development right up to the point where the jet engine made propeller-driven fighters obsolete.) I covered this at some length in my monograph on the XFL-1 Aerobonita published by Steve Ginter since it was central to the Navy's decision to contract with Bell for an Allison-powered fighter in competition with the Vought F4U and the Grumman F5F.

 

[tartle]

Tailspin Turtle,
Thanks for the feedback... it can be challenging to know... I am writing because I like to put my thoughts 'out there' but it is useful to know sometimes that 'out there' is not a vacuum!
The aircooled vs liquid argument is fascinating as it weaves together Capital and Innovation in so many different ways that change with time. What looks obvious to us now is not so obvious in the context of the technical, political and personalities of the date we are focusing on. We tend to underestimate the affect a 'personality' can have on 'distorting' the way things unfold.... hopefully we can tease out some of that as a group.... 'Together We are Better'.
There are incidents that happen where engineers decide to ignore the rules of political etiquette... I remember being told of an 'incident' in the 1930s involving two senior engineers, British and American aircooled radial experts, who met aboard the Staten Island Ferry, I believe, and by 'accident' took each other’s brief cases as they got off. It so happened each engineer had been carrying blueprints and technical reports on how they had solved a problem that the other engineer was faced with at that time. They did not compete with each other so felt there was no need to feel concerned about giving away trade secrets.... and I would not be surprised if it still goes on ... I certainly had similar experiences in the early 80s.

 

[AeroFranz]

Tartle, thanks for the chart - definitely stored in my archives in the 'keeper' folder!

 

[J.A.W.]

Camm's team tried all 3 big Brit piston engines in their 40's Fury prototype.

The RAF was of course jet-bent by then & didn't order any of the top performing Sabre powered jobs,
but the RN picked up the lesser performing Centaurus powered version for their Sea Fury.

Did the lowest performing (Griffon powered) Fury prototype feature an R-R designed 'power-egg'
of/similar to the type productionised for use in the Shackleton?

AFAIK the Sabre & Centaurus installations were in-house Hawker types, but did Napier ever fit a
Fury airframe with their annular radiator Sabre 'power-egg' set-up?

 

[J.A.W.]

Here are a couple of interesting period articles from 'Flight', which give comparisons between
air-cooled radial & liquid cooled in-line piston engine installations.

Apart from power-to-weight & cooling considerations, one advantage of in-lines for high speed use
is in exhaust jet thrust, note the ejectors utilized by the high boost ADI equipped Sabre Tempest F6..

http://www.flightglobal.com/pdfarchive/view/1946/1946%20-%201443.html

http://www.flightglobal.com/pdfarchive/view/1946/1946%20-%201455.html

 

[tartle]

Thrust augmentation was possible on radials just not as easy#;
"THE exhaust thrust augmentor developed for the Convair 240 airplane overcomes cooling drag and adds enough thrust to increase level flight 10 mph and take-off payload 2000 lb."

 

[J.A.W.]

True, T, the way the BMW radial powered FW 190 arranged its exhaust pipes in a thrust enhancing group
was of interest to Bristol ( Kawasaki & Grumman , too) for their Centaurus/Tempest II installation, but they were never able to offer the several hundred lbs thrust in a positive aero-package that in-lines could achieve.

Was that Convair running a turbo-compound radial?

Other issues for hi-po engines using air-cooling included cylinder head temp control (under & over cooling)
& the difficulty with siting large oil coolers & air-to-air charge inter-coolers.

Funny that many of them ended up running de-facto liquid cooling internally as ADI, either extra fuel,
as per BMW, or Methanol/Water injection..

 

[tartle]

This particular Convair 240 model was an early (1948) one with Pratt & Whitney R-2800 Double Wasp.
NACA was investigating radial engine thrust, reporting in 1940 on test bed results.. see below. It references two reports, the Oestrich one that started the thinking about thrust augmentation and the Hive's one about RR's use of augmentation.

 

[J.A.W.]

Thanks, T, I have seen a similar NACA test done on an early Spitfire,
where they swapped the paired ejector stacks for individual pipes,
& which of course - was done in service, later.

As for their '550 mph' thrust rating, that would surely be, as Capt Mainwaring was wont to say..

"Delving into the realms of fantasy, Jones."

The smoothly faired big-bore ejectors fitted to the 2,200+hp V-1650-9 Merlin powered Mustang H
always impressed me as sculptural art & potent thruster nozzles both.

 

[tartle]

Sculptural art?.... I see what you mean!
and 550 mph...in a dive perhaps!

 

[J.A.W.]

& Here.. http://www.youtube.com/watch?v=HfPOVWOIL8M

550mph in a dive? any radial doing that would've been throttled well back, I'd reckon..

Sabre was cleared for 4,000rpm diving though, & Tempest dive limitation in pilots notes was ~550mph..

 

[J.A.W.]

Jet thrust from in-line exhaust had inherent advantages over radial arrangements.

The in-line row of ejector pipes gave a low frontal area penalty for the grouping,
& also enabled equal length pipes for optimum tuning/back pressure values.

Certainly it was noted as one of the positive factors in FW swapping to a Jumo V12 engine for their 190D.
& by R-R, as part of their reasoning for favouring mechanical supercharging over turbos..

The even spacing of induction system manifolds & even firing orders inherent to in-lines was another advantage,
particularly in high boost applications, whereas uneven mixture/pressure distribution in radials could be
problematic..

The dynamics of radial crankshaft reciprocation & heavy valve-gear also meant that the sudden, large
movements in revs/boost required in fighter combat manoeuvres were also problematic for radials.

Len Setright wrote about the Napier Sabre being able blip up & down the rev meter like a car engine..

 

[tartle]

I read an article about 'Tubby' Sielle yesterday; the strapline was 'A centenarian who helped develop the technology to take the fight to Hitler....'
It reminded me of Kranzberg's First Law (of Technology):

• Technology is neither good nor bad; nor is it neutral.

In the article he talks of horrific pieces of technology that did not work and lives were lost. He did not put this down to incompetence but sabotage. He mentioned two people at Farnboro' who had left leaning politics..... Ben Lockspeiser and F W Meredith (later Managing Director of Smiths -aircraft instrument makers). Both were monitored by security services but not enough evidence to dismiss them. There was a 3rd man, Jack Richards head of instrument dept. He dissented from the decision to fit American Sperry autopilots in RAF bombers, insisting on F'boro's design.... this never worked! etc.
Fascinating stuff in the context of our discussions.
The link only gives a summary so I've scanned my paperr.

 

[J.A.W.]

T, does it date from the time that ol' Adolf & uncle Joe were 'thick as thieves' prior to Barbarossa?
& is the Meredith mentioned - the same bloke who did the coolant matrix (radiator) as thrust duct work?

 

[Basil]

J.A.W.,
the exhaust stubs of an liquid cooled inline are far too short to add the scavenging of the engine They are only optimized for thrust an do nothing to help gas exchange in the cylinders - in contrary - this arrangement adds work to the piston to expell the gases. To support gas exchange from individual cylinders you have to combine different exhaust headers depending on the firing order of the engine (a good example is the "bundle of snakes" exhaust of a Ford GT endurance racing car).
You are right - the firing order of a radial with its master rod and slave rods is not elegant and adds vibration and other engineering tasks. It's a pity that true motion connecting rods (see several Curtiss Wright patents of the 1940s - google patent) did not make it to production.
Regarding the drag of radials I do not agree with you - several of the fastest fighters were powered by radials. Also look at Reno. Of course fuel consumption is usually a little higher compared to liquid cooled engines to regulate cylinder head temperature under high power settings. At least from beginning of the 1940s cooling was arranged in a way that the heated air from engine, oil cooler and charge cooler added a significant net thrust to the total propulsion package. For example, BMW, a leader in providing complete power packages to airframe manufactureres calculated that total cooling drag (including fan power consumption) was more than offset by the additional heat thrust of the powerplant (the calculation I know was done for the stillborn BMW 802). Besides, there are very nice examples of exhaust thrust headers for radials - BMW 801 an the FW 190 (you mentioned it), Bristol Centaurus on the Sea Fury, etc (they also add to expel the hot cooling air from the engine).

 

[tartle]

The same fellow...brings new meaning to the 'Meredith effect'. Vielle is publishing a book 'Almost a Boffin' in June so details might be better in that.
Amazon' s description is:
To continue to live life to the full at 100 years old is quite amazing! In this exhilarating, exciting and at times emotional book EE (Tubby) Vielle takes us through a life which involved several different careers. His early childhood memories draw you into a forgotten world. The threat of hunger during the Great Depression led him away from university to the RAF and flying 150 types of aircraft, not without incident! He guides you through an unexpected account of WW11 which includes mysterious happenings between scientists and some, to date unpublicised, treacherous acts with far reaching implications. His optimism, purpose and enthusiasm are what he sees as the markers for his long and fulfilling life. At age 43, having survived and thoroughly enjoyed 25 years of flying and then being faced with having to serve in desk jobs, "Tubby" Vielle accepted the offer of twice the salary of an Air Marshal, to retire from the RAF and become Managing Director of a company set up to develop and commercialise his invention of an airborne anti-collision system for aircraft (and ships). He also wrote two novels which were based on his own flying experiences. Both, were world-wide best sellers and translated into over 20 languages. That, and the sale of the film rights for the first, resulted in Tubby taking up residence in Switzerland, writing more novels and engaging in other interesting pursuits - including becoming involved in trying to recover the Rommel Treasure from the bottom of the Mediterranean Sea and inventing a method of investing which, in ten years, turned £32,000 into over £7,000,000. Now again resident in UK, he still normally gets up at around five o'clock and enjoys working 10 hours a day!

 

[J.A.W.]

Basil, if you look at high boost supercharged top-fuel dragsters, you will note short individual
dump tube pipes directing high energy exhaust gasses in a useful thrust path..
Forced induction 4-stroke mills do not require the '5th element' cycle of 'extractor'
type tuned-group exhaust manifolding..

At Reno, 'little Limey' Merlins - of a fraction of the capacity of the lazy monstrosity radials - have
dominated in recent years, being able to hack far higher pressures, for longer..

What prodigious feats could a hot-rod Sabre unleash? Plenty - according to Len Setright..

It is true that some worthwhile work can be achieved from a skilful radial exhaust ejector/coolant duct
arrangement, but it cannot match the in-line scheme for thrust or efficiency..

The 'red-under-the bed' Meredith, ( identified by the remarkable ton-up ex-RAF chap as cited by T)
was able to demonstrate that a high speed duct incorporating the liquid coolant matrix was capable
of negating drag penalties, & unlike a big rotund radial, site it in a location remote from the engine..

FW 190, Tempest & Fury all provide examples of airframes that could & did accommodate both radial &
in-line engines of very high output, & in each case showed the superior performance was by using in-lines..

 

[Basil]

J.A.W., thanks, good points. Especially the TA-152 was much faster with its Jumo 213 than the FW-190 but the airframe was also much refined. Not sure how it would have performed with radial (a late version of the BMW 801 was also intended for the TA 152).
Regarding dragsters - of course you do not need the extractor cycle to have a high performing engine, especially if highly blown, but nevertheless it would add some horsepower. The exhaust thrust of nitro dragsters is that high it contributes a significant downforce to the whole car (I heard about several hundred kilograms).
Of course one advantage of having a radiator is you can place it on that part of the airframe where the thrust/drag ratio is the most advantageous.

 

[J.A.W.]

Thanks B,
& this 'Flight' article may be of interest, it has a table showing cooling drag comparisons done on Tempests.

Chin, leading edge wing, annular radiator, & radial installations.

http://www.flightglobal.com/pdfarchive/view/1946/1946%20-%201441.html

Note though, they are cold ratings, so not taking into account the dreaded 'Meredith effect'..

 

[J.A.W.]

& the alternative to exhaust jet thrust from ejector exhausts was the turbo-charger, - as favoured by the USAAF..
.. as it allows a consistent altitude/hp rating, & it shows in smooth curved climb/speed performance graphs.

Here is a chart showing the proposed values of the Chrysler V16 in P-47 turbo form.

http://www.weakforcepress.com/CAE/NARAEN001.jpg

The Hemi Chrysler V16 was similar in capacity to Griffon, Sabre, DB 605, Jumo 213.

Note max allowable rpm for dives, 3,840 - close to Sabre territory - in that regard..

 

[J.A.W.]

Turbos can be fun, but airframes are also important, & woe betide/tiddlers beware..

https://www.vansaircraft.com/pdf/hp_limits.pdf

Sorry, link wont work..

 

[tartle]

Try this.

 

[J.A.W.]

Much obliged T, ta.

 

[J.A.W.]

Interestingly, the following stands as unintended empirical evidence of the 'Meredith effect'..

The A. & A.E.E. - were very impressed with the high speed available from their new Mustang,
esp' on its comparatively paltry Allison out-put - & tried blanking off the radiator for high speed tests,
- only to find it significantly reduced the speed, by ~10mph,

& this was not due to over-heating causing power-loss..

http://www.wwiiaircraftperformance.org/mustang/ag351speed.gif

 

[tartle]

Terry Hefferman, who was involved in many of the A & AEE trials stated that:
"owing to abnormally high temperatures due to coring (engine oil congealing due to overcooling) during the winter months (tests in January of 1942), tests had to be made with various types of blanks over the oil cooler and engine radiator.
The blanks had a pronounced effect on the maximum level speed:
Max level speed without blanks: 370 mph at 15,000 ft
Max level speed with blanks: 357 mph at 14,750 ft
It is not certain if this considerable difference is due to increased drag of the blanked off radiators or a loss of the 'jet' effectof the heated ram air leaving the radiator efflux- possibly a little of both."

 

[tartle]

I always felt this 'essay' was a thoughtful contribution to the Meredith effect discussions.

 

[J.A.W.]

Perhaps, but Lee Atwood surely jumps to a few conclusions that appear to ignore certain aspects..

The Mosquito & Tempest I prototypes (both with wing leading edge radiators & high altitude spec engines)
made ~440mph & ~470mph respectively, in `43..

On the brute force of well over 2,000hp, perhaps,
- but the Tempest V with chin radiator also made ~460mph on test when running the same Sabre IV..

 

[J.A.W.]

Attwood's claim of the 'Meredith effect' as the primary reason for the Mustang to be significantly faster than the identically engine/powered Spitfire is also contentious..

The 'laminar flow' wing & generally aero slick airframe is very likely a stronger contender for the speed advantage, & a like comparison can be made for Typhoon & Tempest.

The Tempest - also with a 'laminar flow' wing was ~20mph faster than the Typhoon on an essentially identical
engine/radiator set-up..

 

[tartle]

...except the laminar wing on Mustang did not work that well but 'Meredith' did!

 

[J.A.W.]

Well, the Spitfire was reckoned to be built to benefit from the 'M-E' too, but was ~30mph slower..
..than the Mustang - on the same available power.

So, ~20mph for 'laminar flow' wing/slick aero & ~10mph for 'M-E' radiator efficacy?

A more likely explanation perhaps, - if extrapolation from the equivalent Hawker evolution holds true..

Esp' when the differential holds for cruise speeds, where the relative contribution from the 'M-E' is less..

 

[tartle]

Soon I will have written the appropriate chapter of a book covering the period of technology... I'll post a taster then that highlights how these technologies (i.e. tools, techniques and know-how) interplay to give the results we are discussing...tbc

 

[J.A.W.]

Jolly good, T..

& as regards the ~30mph Vmax advantage of the Spiteful over the 20 series Spitfires.

What % was due to the 'laminar flow' wing VS the redesigned radiators/'M-E' efficiency?

 

[tartle]

Some published material:

 

[J.A.W.]

& from a 'Flight' report on Napier annular radiator testing, an interesting speed/altitude graph.

http://www.flightglobal.com/pdfarchive/view/1948/1948%20-%201660.html

Note the line showing the standard Tempest F6 with chin radiator,
- higher (+17.25lb on ADI) boost levels give brute force (3,000+hp) for best speed at low level,
only to be clawed back at higher levels by the lower drag (higher 'M-E'?) annular set -up.

However the Vmax difference is ~same as between the Hawker leading edge wing & chin radiators.

 

[J.A.W.]

& for comparison - a graph showing Tempest II performance on test - Centaurus radial at +12lbs boost.

http://www.wwiiaircraftperformance.org/tempest/tempestii-cfe-appd.jpg

 

[AeroFranz]

I apologize for a quick digression from the fascinating discussion -
Tartle, the pics you posted are from Spitfire: the history (I presume). It looks like a worthwhile book to get.
I searched the book and Amazon gives a frightening price of $336 for a 2001 edition. There is also a more reasonably priced 1984 edition. Does anyone know if the 2001 edition differs significantly? Thanks!

 

[tartle]

Yes the second edition is a I borrowed mine from local library and copied a few bits!

 

[J.A.W.]

Yeah T, & good on ya, too, but do you know..is it worth the price premium data-wise?

 

[tartle]

Depends what you are after... it is the most comprehensive history of the Spit and full of technical data. I have attached what someone said about it:
How then to tell the story of such an important fighter? Many have attempted, but until Key Publishing commissioned a new work in 1987, there was nothing – in one volume – that did justice to this iconic aircraft. Here you can see the result; the front cover of the 1st edition of this book is shown (my own copy lies around 4 feet away in one of the bookcases). ‘Spitfire:The History’, Eric Morgan & Edward Shacklady, Guild Publishing (by arrangement with Key Publishing), 1988, ISBN 0946219109, is a meaty book (Quarto;634 pages) and, according to the Foreword by Jeffrey Quill, the test pilot who undertook most of the testing of the prototype, K5054,‘…it is not a book for light reading, but will be an essential on the shelves of serious aviation historians.’ Eric Morgan, who served as an Electronics Officer in the postwar Royal Air Force, and Edward Shacklady, the former Editor of ‘Air Pictorial’ and the founder of Profile Publications, were the ideal pair to deal with this important subject. Containing chapters with titles such as ‘Low Level Photography’, ‘A Useful Interim Type’ and ‘Blow The Spitfire’, this tome covers all variants, all color schemes, and every major and minor technical detail. To my amazement, I found that the book lists every single aircraft of the type, more than 20,000 of them, and what happened to them (admittedly, in very small type). I shall leave it to Jeffrey Quill – the ultimate Spitfire pilot – to give the final assessment, ‘As definitive a history of the Spitfire as is ever likely to be written’

so you pays your money if that's what you want!