@tomo pauk Do you have any more details on that 2-stage turbo-supercharger design? It sounds like a good way of eliminating the power sapping engine driven second supercharger.
How to properly turbo-supercharge the P-39 Airacobra.
- Thread starter Draconis
- Start date
IMO that was certainly a good idea. Both impellers were of the 'mixed flow' variety, with wide chord blades, the air entering the impeller axialy (ie. paralel to the impeller axis) and compressed air leaving at approx 45 deg into the collector. Second stage also fed the air to the hollow blades of the turbine, thus making possible attaching it next to the engine with it's hot exhaust gasses not representing the problem.
I'm surprised that they could build hollow blades for the turbine using the 1940s era metallurgy. Sounds like a good idea though. Do you know how the second stage was designed? Did it kick in after the first stage compressor reached max.RPM? Or were both stages linked together to the turbine which increased both their RPM with the throttle setting? I guess both stages running together makes more sense if the second stage is always supplying cooling air to the turbine.
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Wow, I have missed a lot. For some reason I had missed notifications on this thread.
In any case, the Ford engine seems promising if it could actually achieve the projected performance reliably. The same could be said of the Continental and Chrysler engines of the era though and neither of those ever quite got "up-to-snuff" during the war so I am in doubt of Ford's ability to get theirs running any better. The overall design seems a great improvement but the added complexity and tighter tolerances--while improving performance--may have a detrimental impact on the serviceability of the engine in the real world. It is like the difference between a BMW S54B32 inline 6 (E46 era M3 engine) and an AMC/Chrysler 4.0L I6 (as found in 80's/90's Jeeps). The BMW has great power density and phenomenal performance but that AMC is indestructible.
In any case, the Ford engine seems promising if it could actually achieve the projected performance reliably. The same could be said of the Continental and Chrysler engines of the era though and neither of those ever quite got "up-to-snuff" during the war so I am in doubt of Ford's ability to get theirs running any better. The overall design seems a great improvement but the added complexity and tighter tolerances--while improving performance--may have a detrimental impact on the serviceability of the engine in the real world. It is like the difference between a BMW S54B32 inline 6 (E46 era M3 engine) and an AMC/Chrysler 4.0L I6 (as found in 80's/90's Jeeps). The BMW has great power density and phenomenal performance but that AMC is indestructible.
Continental and Chrysler engines, along with the Lycoming, Wright, Pratt & Whitney et al, failed. The Ford engine didn't fail. As an aero engine, it was not called upon and developed, but as a tank engine in V8 and V12 configurations, it was largely successful, and remains a highly tuned tractor-pull engine today. The added complexity and tighter tolerances remark may require explanation. Merlins made at the Trafford Park facility were made to revised tolerances for what Ford deemed to be proper mass production, as they were at Packard, and Ford's Merlins were noted for reliability. Improvements to the valve gear and con-rods may seem complex, but were just modern improvements accepted as quite normal today. The turbo and fuel injection systems remain of conjectural nature, and you can think any way you want one way or the other, without validation of any sort, but the Bosch fuel injection system to be used did function in German engines.
Apologies for digressing on behalf of other readers, but I think a lot of confusion is caused by tolerances vs clearances. As I understand it the first is how much the dimensions are allowed to vary before they fail quality control, the second is how much of a gap there is between the parts.
A 'tightly fitted' or 'precision' engine as is discussed will have very small clearances and be desperately vulnerable to overheating, damage, oil quality, etc etc etc. But you can make such an engine out of quite mismatched parts if you have enough of them and can just micrometer everything and assemble the big pistons in the big bores, small pistons in small bores etc. This was OTL 'the British way". Easier to make the parts, a pig to assemble.
Alternatively if you can manufacture to good tolerances, effectively every approved part is identical and you can put any piston in any bore and still get the right clearances. This was how Ford, GM, Packard etc did business - 'proper mass production'. Much harder to make the parts but easier to assemble.
So every Merlin signed off as airworthy probably had pretty much the same gaps between cylinder and piston, between crankshaft and bearing, between head and block, etc. Just that RR and the US firms had different approaches to how that was achieved.
Digression aside, my main scepticism about the Ford engine is that firstly a lot of promising paper engines turned out to fail when truly put to the test, and secondly there is a huge but non-obvious difference between aero and ground engines, they are a whole different class of engineering. E.g. it was a fairly normal practice until recently to ignore small amounts of casting sand in car engines. What doesn't get swept out in the first few oil changes will settle in some nook or cranny and sludge out of circulation. Jeep 4.0 engines as late as 2000 built will often show sand when stripped down. But in WW2 a series of crashes that grounded the entire ETO P-47 fleet turned out to be due to Ford-built R-2800s with casting sand in the bearings. It's a huge no-no in aircraft engines.
Ford certainly made good aero engines with the help of established aero-engine firms, but I doubt their ability to just turn up with their own first-attempt engine and do better than the competition. It's not like BMW/DB/RR/CW/P&W/Allison etc etc found this stuff a walk in the park.
It's totally understandable to doubt. I've doubted the viability of Ford engines in the past. It's also fact that they built, on production tooling, an engine that worked, in a short time, and developed successful tank engines based on the design, which doesn't mean a top-notch aero engine would result, but doesn't at all mean that it wouldn't, and I believe it was a tremendous opportunity missed.
Maybe so but it may have taken too long to bring that advanced Ford aero engine to production. Like with the Allison turbo-compound engine. By the time they were nearing completion there was no longer any need for them. Someone needs to go back in time with a lot of engineering data and a suitcase full of gold. I'll volunteer.
I think you mentioned a part of this history that is usually overlooked. How difficult it was developing better reciprocating aircraft engines in the 1940s. It was cutting edge design, engineering and metallurgy. There were many failures and abandoned projects.
Hard to tell if it really was an opportunity. The R-3350 was also built on production tooling, it worked, and in a short time. It didn't turn into a tank engine, but it did turn into a top-notch aero engine. However it was also a bitch to get the bugs out of. Coincidentally the R-2800 also first ran in 1937, I believe P&W had it on tooling pretty fast, it was very good, not a huge amount of problems.
The Ford GG design was what, 3 years or so behind these engines? Maybe combat ready in 1944 if everything goes well, perhaps late 43? If it lived up to the myth then it would have been a more modern design with far more growth potential than the merlin or V-1710, but it would have missed most of the war. And really, what could it do that a Grifon, 3350 or 2800 couldn't do as well or better?
Now, if Ford were to sketch out the design a couple of years earlier it would be really interesting. Even more interesting if they (or RR for that matter) decided 36L was about the right size.
The Enginehistory site has a lovely write-up on the solution to the problem with the P&W R-2800, in the balance.
The Ford GG was neither a hit nor a myth.
The Curtiss Wright R-3350 as built between the late thirties and the termination of large scale wartime procurement was an absolute catastrophe, feared by the aircrews of the turbosupercharged variants (B-29 & B-32), and despised by the mechanics assigned to maintain any of them it.
QUOTE="b0ned0me, post: 15661799, member: 34224"]The R-3350 was also built on production tooling, it worked, and in a short time. It didn't turn into a tank engine, but it did turn into a top-notch aero engine. However it was also a bitch to get the bugs out of.[/QUOTE]
The post war commercial versions of this "top-notch aero engine" did not, to the best of my knowledge, share a single major component with the wartime product- even the spacing between cylinder rows had to be changed.
There is abundant information on the web detailing how reliance on this engine virtually ended long range high altitude precision bombing of Japan (in favor of low altitude incendiary raids). -and how much modified "silver plate" versions were necessary for the nuclear missions.
C-W's lack of responsiveness to AF requests for solution to R-3450 failures, resulted in their virtual exclusion from future military procurement (except for low quantity civilian variant turbo compound and trainer engines and a licensed British designed turbojet- no aircraft.) I was in the USAF sufficiently long ago to have gotten much of my opinion of C-W first hand from some of their victims.
Dynasoar
QUOTE="b0ned0me, post: 15661799, member: 34224"]The R-3350 was also built on production tooling, it worked, and in a short time. It didn't turn into a tank engine, but it did turn into a top-notch aero engine. However it was also a bitch to get the bugs out of.[/QUOTE]
The post war commercial versions of this "top-notch aero engine" did not, to the best of my knowledge, share a single major component with the wartime product- even the spacing between cylinder rows had to be changed.
There is abundant information on the web detailing how reliance on this engine virtually ended long range high altitude precision bombing of Japan (in favor of low altitude incendiary raids). -and how much modified "silver plate" versions were necessary for the nuclear missions.
C-W's lack of responsiveness to AF requests for solution to R-3450 failures, resulted in their virtual exclusion from future military procurement (except for low quantity civilian variant turbo compound and trainer engines and a licensed British designed turbojet- no aircraft.) I was in the USAF sufficiently long ago to have gotten much of my opinion of C-W first hand from some of their victims.
Dynasoar
marathag
Banned
Dodge ended up supplying many of the fixes that ended up making their production in Chicago far more reliable than the C-W production.
Oddly enough, the very earliest supercharged R-3350s seemed to be more reliable than the dual turbo setup
"marathag, post: 15663651, member: 68581"]
Oddly enough, the very earliest supercharged R-3350s seemed to be more reliable than the dual turbo setup[/QUOTE]
The above is true since the earlier versions were not operated at anywhere near the boost pressures required for B-29 takeoff power. One of the results of high induction system pressure (and corresponding high flow velocity thru the convoluted intake manifold) is a worsening of the already unacceptable variation in fuel mixture distribution at different cylinders. It was possible to have, simultaneously, cylinders misfiring lean and others fouling rich. One backfire into the induction system and the large volume of compressed air and avgas filling the several cubic feet of intake manifold would detonate and blow the back end off the engine. Lots of magnesium there to fuel a mainspar burnthrough, if the aircraft had not yet rolled inverted into the Pacific off the end of the runway.
Relatively straight forward fixes existed for many of the high boost problems, if C-W had conceded that they existed. The main problem, in retrospect, was a corporation infested with accountants at the highest levels, and far too few engineers.
After the war, when competent engineers came cheap, the R-3350 was redesigned to become an excellent (tho still not as reliable as the competition - The turbo compound Constellation was called "the fastest tri-motored airliner") engine.
Dynasoar
Oddly enough, the very earliest supercharged R-3350s seemed to be more reliable than the dual turbo setup[/QUOTE]
The above is true since the earlier versions were not operated at anywhere near the boost pressures required for B-29 takeoff power. One of the results of high induction system pressure (and corresponding high flow velocity thru the convoluted intake manifold) is a worsening of the already unacceptable variation in fuel mixture distribution at different cylinders. It was possible to have, simultaneously, cylinders misfiring lean and others fouling rich. One backfire into the induction system and the large volume of compressed air and avgas filling the several cubic feet of intake manifold would detonate and blow the back end off the engine. Lots of magnesium there to fuel a mainspar burnthrough, if the aircraft had not yet rolled inverted into the Pacific off the end of the runway.
Relatively straight forward fixes existed for many of the high boost problems, if C-W had conceded that they existed. The main problem, in retrospect, was a corporation infested with accountants at the highest levels, and far too few engineers.
After the war, when competent engineers came cheap, the R-3350 was redesigned to become an excellent (tho still not as reliable as the competition - The turbo compound Constellation was called "the fastest tri-motored airliner") engine.
Dynasoar
I love it! The Japanese pilots would have called it "one and a half planes, one pilot."
marathag
Banned
Never figured out why they didn't switch to steel, like they did with the R-2600 Twin Cyclone