The Secret Horsepower Race by Calum Douglas (and piston engine discussion)

[F119Doctor]

I keep wondering why the early gas turbines failed to accelerate as quickly as late model piston engines and, why the hybrids failed to bridge the gap. I understand materials were a problem until quite late on but I reckon a lot of it came down to political decisions and strategic investment.

To accelerate a gas turbine engine, you have to add fuel to the combustor to generate the additional energy to the turbine necessary to turn the compressor faster to increase airflow.

When that additional fuel is first introduced at the low power setting, it increases the combustor temperature, which challenges the turbine heat resistance, and the combustor pressure, which challenges the compressor stall margin at the low airflow condition. Early engines had low stall margin and low turbine temp capability, so they were limited on how fast the fuel flow could be increased for acceleration.

 

[Foo Fighter]

Thank you, Sir. Got it.

 

[steelpillow]

I keep wondering why the early gas turbines failed to accelerate as quickly as late model piston engines and, why the hybrids failed to bridge the gap. I understand materials were a problem until quite late on but I reckon a lot of it came down to political decisions and strategic investment.

Gas turbines are at their best at high speeds and altitudes. When stationary on the ground, they are less effective. On the other hand a piston engine is far more at home at zero feet, while a variable-pitch prop is equally at home with zero airspeed. Result; the jet takes time to build up full thrust.
Jeremy Clarkson once raced a Eurofighter from a standing start (can't recall what supercar he was driving, a McLaren or Bugatti Veyron or something like that). He shot ahead at the gun, but the jet overtook him comfortably before it reached rotation speed.

 

[Calum Douglas]

They were getting there its just that the development curve was quite behind the USA, as we had pretty much ignored turbochargers in the 30`s. Fedden was very keen on turbos, going back a long time, but - as Fedden also had a talent for annoying almost everyone he was dealing with, I suspect this may have retarded their development in Britain to some extent.

Also, I think we probaby didnt really have the capacity to really develop more than one engine with full national effort at a time, so its also probably a case of us having all our eggs in the "Merlin" basket.

 

[Calum Douglas]

This provides some contemporary background to that general discussion about gradual development vs new
ideas.

 

[Calum Douglas]

Feb 1945

 

[Calum Douglas]

Feddens review of the Bristol wartime period, written in 1945.

 

[Foo Fighter]

I keep wondering why the early gas turbines failed to accelerate as quickly as late model piston engines and, why the hybrids failed to bridge the gap. I understand materials were a problem until quite late on but I reckon a lot of it came down to political decisions and strategic investment.

Gas turbines are at their best at high speeds and altitudes. When stationary on the ground, they are less effective. On the other hand a piston engine is far more at home at zero feet, while a variable-pitch prop is equally at home with zero airspeed. Result; the jet takes time to build up full thrust.
Jeremy Clarkson once raced a Eurofighter from a standing start (can't recall what supercar he was driving, a McLaren or Bugatti Veyron or something like that). He shot ahead at the gun, but the jet overtook him comfortably before it reached rotation speed.

With a car, you lose massively in transmission and drivetrain. While those so called tests are interesting to some I have to admit to boredom.

 

[Hobbes]

I keep wondering why the early gas turbines failed to accelerate as quickly as late model piston engines and, why the hybrids failed to bridge the gap. I understand materials were a problem until quite late on but I reckon a lot of it came down to political decisions and strategic investment.

Gas turbines are at their best at high speeds and altitudes. When stationary on the ground, they are less effective. On the other hand a piston engine is far more at home at zero feet, while a variable-pitch prop is equally at home with zero airspeed. Result; the jet takes time to build up full thrust.
Jeremy Clarkson once raced a Eurofighter from a standing start (can't recall what supercar he was driving, a McLaren or Bugatti Veyron or something like that). He shot ahead at the gun, but the jet overtook him comfortably before it reached rotation speed.

That shows the mismatch between the high-speed exhaust from the jet and the surrounding air, making power transfer inefficient. That's what makes jet engines sluggish from a standstill. High-bypass turbofans and turboprops are better in this regard.

 

[steelpillow]

That shows the mismatch between the high-speed exhaust from the jet and the surrounding air, making power transfer inefficient. That's what makes jet engines sluggish from a standstill. High-bypass turbofans and turboprops are better in this regard.

Most authorities regard bypass turbofans as a form of jet engine, and for that matter ramjets too. What you are thinking of is more correctly described as a turbojet. And of course all those early jets were turbojets.
But one must be careful over the velocity mismatch; a rocket generally creates the highest thrust of all, yet has the greatest velocity mismatch - in fact, the bigger the mismatch the higher its thrust. So the issue is about more than just thermodynamic efficiency.

 

[Nicknick]

Turbomachineries have high rotational energy and low torque, this will make tham less responsive (even if variable guide vans were used). The Chrysler turbine car suffered from slow response despite it was really optimized for reacting quickly. In aircraft application, the response time is not as important as in road vehicles, so this drawback was simply accepted.

 

[Pasoleati]

What low torque? E.g. the gas-turbine of the Abrams tank has the highest maximum torque and torque rise among its power class's tank engines.

 

[Trident]

In a car vs. fighter jet drag race, the reason why spool up time comes into play at all is the lack of a "clutch", so to speak. The brakes cannot hold the jet on the line at full thrust if T/W approaches (let alone exceeds) 1.0, so it can only throttle up to full reheat after brake release. Even in static condition a EJ200 engine develops 90kN, so a lightly loaded Typhoon (empty weight 11t, say 2t of fuel) would otherwise accelerate at almost 1.5g straight off the line, comfortably beating any car short of a top fuel dragster.

This is the reason why in time-to-climb record attempts the aircraft is tied down until the engines achieve full thrust.

 

[Nicknick]

Let’s take a look on the PT6 112:

https://www.easa.europa.eu/downloads/16560/en

The PT6 112 has a shaft horsepower of 373 kw at a shaft speed of 31914 rpm (power turbine); this can easily used to calculate the torque:

M = P/(2*Pi*n) = 111.6 Nm

This is about the torque of a natural aspirated engine from a small car (1,2 L displacement). Of course, shaft torque is nothing you can feel and it shouldn’t be overestimated, but this example makes clear, that turbines have high rotational energy (due to the high rpm) and little torque to spool them up, so they are needing a lot off time for changes in power output

 

[Pasoleati]

Let’s take a look on the PT6 112:

https://www.easa.europa.eu/downloads/16560/en

The PT6 112 has a shaft horsepower of 373 kw at a shaft speed of 31914 rpm (power turbine); this can easily used to calculate the torque:

M = P/(2*Pi*n) = 111.6 Nm

This is about the torque of a natural aspirated engine from a small car (1,2 L displacement). Of course, shaft torque is nothing you can feel and it shouldn’t be overestimated, but this example makes clear, that turbines have high rotational energy (due to the high rpm) and little torque to spool them up, so they are needing a lot off time for changes in power output

Take a look yourself of real torque curves.

 

[Nicknick]

these are torque curves behind the gearbox, they give no indication of the amount of torque on the shaft. All it takes is just a simple calculation (P=M*n*2Pi)

 

[Pasoleati]

these are torque curves behind the gearbox, they give no indication of the amount of torque on the shaft. All it takes is just a simple calculation (P=M*n*2Pi)

The torque available on the turbine shaft is irrelevant as a reduction gear is always fitted in turboprop/turboshaft installations. And for vehicle installations you miss the key point, torque rise (maximum torque available at the turbine shaft is irrelevant as one can manipulate it by reduction gear ratio). Torque rise is the key figure because it affects the number of speeds in the gearbox required for a given speed range. The higher the torque rise, the less gear shifting is required to accelerate/drive.

 

[Nicknick]

You shouln't forgett, we are talking about the amount of torque which can spool up the turbine. For simple reasons, there is no free torque given in any chart for the free spinng gas generator shaft, so we have to use the torque of the the drive turbine to get the right magnitude. The surpluss torque on the gas generator shaft will be even lower than that of the drive shaft. How much torque we have in the final drive is abslolutly irrelevant, the load change depends soley on the spool up time of the gas generator shaft.

 

[Pasoleati]

You are making absolutely no sense. By your logic the lowest throttle response (in piston engines) would be in high-revolution engines with light crankshafts while the fastest response would be in large marine diesels because their crankshafts have the highest torque.

 

[Nicknick]

The engine load in natural aspirated Diesel engines (and lean burn Otto engines) can be increased from one cycle to the next, just the speed increase takes some time (not much). In turbocharged engines, the load changes depend on the turbocharger which needs some time to spool up.

 

[Jemiba]

Just as a reminder, this thread principally is about "... piston engine discussion". So, comparisons
to turbine engines are ok, I think, but discussions shouldn't stray too much into the field turbine
engines only.

​

 

[Nick Sumner]

Calum, Any thoughts on a way for English only readers to get hold of the new information in the Italian edition?

Can I just 'bump' this question?

 

[Calum Douglas]

Calum, Any thoughts on a way for English only readers to get hold of the new information in the Italian edition?

Can I just 'bump' this question?

Umm you either get an Italian Dictionary and get very clever, VERY fast.

Or you can wait for us to make a heavily revised ACTUAL 2nd edition (instead of just reprints with typo fixes) of The Secret Horsepower race in English which will incorporate a lot of the new Italian materials.

Option 2 is being discussed at present with the publisher (potential allowance for another 40,000 words) but a few line-items to tick off before that is solidified into reality. If it goes ahead I`d be hoping to get that done in... 5months ish?
Said 2nd edition would not be just new Italian material, but there have been quite a few "bits and bobs" I`ve found since which probably need to go in, I`ll have to go back to Germany for a bit to get documents.

 

[Pasoleati]

Even though I have the current edition, I would gladly buy the revised 2nd edition.

 

[Calum Douglas]

Even though I have the current edition, I would gladly buy the revised 2nd edition.

Providing i can find funds for a German research trip, it should be possible.
Travel (and indeed everything) has got insanely expensive in the last year.
I can see why many people dont bother and just write a load of "I reckon this probably happened"
stuff and just give some very vague bibliography at the end....

 

[edwest4]

Gosh, I sure hope not...

 

[steelpillow]

...potential allowance for another 40,000 words...

With accompanying illustrations, no doubt. 600 pages of A4 is a helluva monster. Bindings get a bit stressed about it, apart from anything else. Sounds to me like a two-volume edition might be called for, split appropriately enough somewhere around Chapter 6: The Turning Point?

 

[elmayerle]

Even though I have the current edition, I would gladly buy the revised 2nd edition.

I will second that!!

 

[Dagger]

Calum, Any thoughts on a way for English only readers to get hold of the new information in the Italian edition?

Can I just 'bump' this question?

Umm you either get an Italian Dictionary and get very clever, VERY fast.

Or you can wait for us to make a heavily revised ACTUAL 2nd edition (instead of just reprints with typo fixes) of The Secret Horsepower race in English which will incorporate a lot of the new Italian materials.

Option 2 is being discussed at present with the publisher (potential allowance for another 40,000 words) but a few line-items to tick off before that is solidified into reality. If it goes ahead I`d be hoping to get that done in... 5months ish?
Said 2nd edition would not be just new Italian material, but there have been quite a few "bits and bobs" I`ve found since which probably need to go in, I`ll have to go back to Germany for a bit to get documents.

Calum,
I was always under the impression that so far the many reprints of your book only had typos corrected, but in your tweet of Aug 11 you show a photo (attached below) of pages 94 & 95 of TSHR which are completely different from those (or any other) pages in my very first printing. Also the title of the chapter (top left page on the photo), which is either 'May 1939 - May 1945' or 'July 1939 - May 1945' is not a chapter in my book.
Is this one of the later English reprints with more than just typos corrected?
Or is this your English draft for the Italian printing?
Or part of your draft for the new 2nd edition?
Or what?

 

[Artie Bob]

I would like to make a few comments having flown a litte bit in a/c with early generation US turbine engines, which had fixed geometry compressors. But I believe the real problem was the relationship between engine speed and power output. If I remember correctly, it was not at all linear. Again it has been over 60 years since I flew with those engines , but it was a real effort to just get away from a dead start on the ramp. I believe 90% RPM was 80 % power, 100%-100%, 101%-102%, 102%-105%. Engine spool-up time from idle was pretty slow, so all of those a/c I flew had speed brakes, which were deployed in the pattern which then required a higher engine power setting. If you had a go-around, you immediately retracted the speed brakes as you pushed the throttle forward, which in effect, instantly gave you more usable power to accelerate. I believe one of the smaller turbine engines had a max rotating speed around 10,000 rpm. Even retracting speed brakes, the decision to bolter had to be made as soon as your wings were level on final, or you were going to make a touchdown. You might have made it a touch and go, but it wasn't a certainty. Max endurance was around 1 hour, but if you had done several touch and gos at the end of a 45 minute flight you were at low fuel state and I know of several instances of flame-outs on the ramp before reaching the chocks. Very good training to make you aware of the importance of fuel state.

There is a book on engine and fuel development published in the late 1940s, "Development of Aircraft Engines" by Robert Schlaifer with a section on fuel development by S.D.Herron. If one has not read it, it may have some different perspectives on some of the issues discussed here.

ArtieBob

 

[fightingirish]

The cover of the German edition of the book is a mirror image of the cover of the original English edition.

View attachment 678085

As a consequence the air intake of the FW 190 D is now shown on the port side instead of the starboard side.

Maybe this has already been noticed by Calum or the editor or the publisher and will be corrected before the book is released, but I thought I mention it anyway, just in case

I`ll forward on that concerm.

The good news is that my Uncle did the translation work under my guidance, so the text inside will be grade A.

Many greetings from Speyer and Sinsheim.
I just noticed, that the German publisher has changed the front cover.

Looking forward to October this year. Source: https://www.motorbuch.de/index.php?...w99900Z0ofGYxO5pD7aZhmZkD20220825185034&navid

 

[Calum Douglas]

It will be mid November now for release, as (like all the other publishers discovered) it is a rather large and complicated book to get right.
However, I have a full draft copy pdf of the German language version in final layout with all images and refernces in place, we`ve just got about... fifty or so small bits to tidy and a couple of images to tweak.

 

[sienar]

Roy Fedden mentions a couple neat ideas in "The First 25 Years of the Bristol Engine Department" from the Journal of Royal Aeronautical Society.

"These failures, for which I took full responsibility, were naturally a great disappointment to me. Some most promising new design work was undertaken by the Design and Development Departments on an improved copper cylinder head and a double entry blower, both of which would have paid good dividends, and I believe could have easily been brought into Production during the war. Resulting, however, from a close liaison with the Ministry of Aircraft Production officials and the Production side of the Company, born of contacts made
in connection with the Shadow Industry, over which at that period I had very little influence, these obvious improvements which, in my view, should have gone into the sleeve valve family of engines post-haste, were re-buffed. We were therefore not able to show the rapid development on the Hercules that was provided by the Rolls-Royce Merlin under a wholehearted single control."

And;

"I remember well a folder I sent to the late Chairman in 1942 strongly advising against gearing two engines together or an 8 engine installation of any sort, and pressing for the 6^ in. bore, 4,140 cubic inch, 18-cylinder engine to be proceeded with, having new copper heads and cylinder porting turned round to provide a new exhaust, which I believed would have made a fine engine of about 3,500/4,000 h.p. Both Arthur Gouge and Rex Pierson gave me full support on this, and were anxious to prepare designs for this engine."

Do you know anything about this? I can't recall this being mentioned in SHR, so apologies if my memory is failing.

 

[Pasoleati]

Hmm. To me it seems that the best power/weight ratio was obtained in (piston engines) with engines in the 1000 - 2500 hp range and those projected 3500+ hp engines had actually poorer power/weight ratio. So I would be inclined to believe that coupling e.g. two V-1710s to drive a single propeller would be a better choice from many points vs. developing a single engine of twice the power.

 

[Nick Sumner]

Roy Fedden mentions a couple neat ideas in "The First 25 Years of the Bristol Engine Department" from the Journal of Royal Aeronautical Society.

"These failures, for which I took full responsibility, were naturally a great disappointment to me. Some most promising new design work was undertaken by the Design and Development Departments on an improved copper cylinder head and a double entry blower, both of which would have paid good dividends, and I believe could have easily been brought into Production during the war. Resulting, however, from a close liaison with the Ministry of Aircraft Production officials and the Production side of the Company, born of contacts made
in connection with the Shadow Industry, over which at that period I had very little influence, these obvious improvements which, in my view, should have gone into the sleeve valve family of engines post-haste, were re-buffed. We were therefore not able to show the rapid development on the Hercules that was provided by the Rolls-Royce Merlin under a wholehearted single control."

And;

"I remember well a folder I sent to the late Chairman in 1942 strongly advising against gearing two engines together or an 8 engine installation of any sort, and pressing for the 6^ in. bore, 4,140 cubic inch, 18-cylinder engine to be proceeded with, having new copper heads and cylinder porting turned round to provide a new exhaust, which I believed would have made a fine engine of about 3,500/4,000 h.p. Both Arthur Gouge and Rex Pierson gave me full support on this, and were anxious to prepare designs for this engine."

Do you know anything about this? I can't recall this being mentioned in SHR, so apologies if my memory is failing.

4140 cubic inches (67.84L) is the Orion but that had a 6.25 in bore. A single cylinder test unit was run. There's plenty about the Orion (including diagrams) in Fedden-The Life of Sir Roy Fedden by Bill Gunston, RRHT No. 26.

 

[Calum Douglas]

I have rather a lot on the Orion, but as it never really ended up as much I had to decide to not put it into the book, as if you include all the "nearly" engines it quadruples in length, and its already a telephone directory in size.. so.. anyway.

 

[elmayerle]

I've got a question Calum. My perception, from all I've read and the comments here is that the US was the only nation with a serious effort on turbochargers going on between the wars. Both German and Japanese efforts during WW II appear to be late and less than successful and Britain doesn't seem to have looked at it at all. Is this perception correct?

 

[pathology_doc]

as if you include all the "nearly" engines it quadruples in length

Yes! Release the Director's Cut!

 

[steelpillow]

Volume II: The Secret Italian Job
Volume III: The Secret Horsepower Files

 

[Calum Douglas]

I've got a question Calum. My perception, from all I've read and the comments here is that the US was the only nation with a serious effort on turbochargers going on between the wars. Both German and Japanese efforts during WW II appear to be late and less than successful and Britain doesn't seem to have looked at it at all. Is this perception correct?

Sort of, it terms of the actual "results" in aircraft thats broadly correct, but once you look at the R&D files in both Britain and Germany, it gets a bit more difficult understand at first.

There was actually a reasonable amount going in in Britain on turbos in the inter-war period. Germany too.

I have a couple of small files on Japanese turbos and I think they really did nothing at all on them what-so-ever until
they were actually IN the war.

It is more complicated than this, but the wartime turbos in Germany and Japan were basically scuppered because the casings kept cracking and the blades were only permitted a max metal temp of 600 degrees C (the gas coming out the cylinder head would be between 950 and 1080 deg C). So BMW ended up doing all that work on hollow blades with forced air cooling. This actually worked but by the time it was all done they`d lost a couple of years and "that was that".

(there were flight tests of turbochargers going on at the R.A.E. in England in 1926)