martinbayer
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You got it exactly backwards...Rule-of-Cool because Props look better than jets?
Randy
Jet engine development fails - what would aviation look like?
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Faster speeds produce runtime and rendering flaws. That's why the simulation has introduced wacky new plot elements ever since the A-12 demonstrated practical Mach 3 flight... too many SSTs flying about and the servers will overheat. SpaceX introducing the Starship with plans for point-to-point hypersonic passenger transport is why cities have recently burst into flames.
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What about an SR.53 with rocket engines and a "get-you-home" piston engine? In general it's hard to see what you can do with the propellers when mixing with rockets.
Deltafan
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Thanks.
In 1939 Lockheed presented the Army a proposal for Jet-fighter aircraft by Kelly Johnson
The L-133 with axial-flow L-1000 turbojet engine of their own design
sadly the L-133 was to advance for it time and Army consider this more Buck Roger
until they encounter Me232 and Arado 234 and hell got the British Jet engine fast and Kelly Johnson had build P-90 around it...
The Lockheed L-133
I can blame this one on this website (http://www.secretprojects.co.uk/forum/index.php/topic,3636.0.html). LOL! I had never before heard of Lockheed's L-133 design until visiting this website several years ago. When I saw the drawings and illustrations (also thanks to Mr. Lowther and his...www.secretprojects.co.uk
I knew L-133, but I didn't know that it was a project of 1939.
Edit : it seems that if the work on the L-133's design began in 1939, the project with the engine came later as proposals for Air Force :
Lockheed J37 - Wikipedia
Lockheed L-133 - Wikipedia
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Folding stowable propellers is probably more difficult than a jet engine....
Dunno about that. Mechanically? Maybe. But materials-wise? Doubtful. They are clearly feasible for low-power applications:
For high performance systems using rocket boosters, you'd either keep the props turning (it's not like a rocket is going to run *that* long) or feather them:
But the more adventurous of our parallel-world aeronautical engineers might go for a true foldable high performance prop...
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Yeah I meant mechanically not materials-wise. Reliability of high speed flight with large piston engines would be bad enough without having folding propellers to worry about.
Maybe something like this would be the logical endpoint of high speed piston engine development:
Maybe something like this would be the logical endpoint of high speed piston engine development:
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Many moons ago I came up with a what-if HTP-fuelled steam turbine driving propellers, based on the German coal dust-fuelled steam turbine designs drawn up for heavy bombers.
My thought was if you used HTP you would get masses of steam without the weight of a boiler. Maybe you could even direct-drive the turbine from the HTP exhaust itself? A crazy idea but one that passed my mind years ago.
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A world without the jet airliner from the late 50s would be a very different place.
If airliners had been limited to propellers (even turboprops) the emphasis on luxury rather than coach air travel would have continued.
A Western equivalent of the Tu114 would have been the flagship of the airlines. It would have been derived from the big USAF prop bomber..
Britain would have produced the Britannia and then?
Rocket powered fighters based on the Me 163 would have fought in Korea.
The institutional mindset would make developing jets complicated, but they would come eventually.
If airliners had been limited to propellers (even turboprops) the emphasis on luxury rather than coach air travel would have continued.
A Western equivalent of the Tu114 would have been the flagship of the airlines. It would have been derived from the big USAF prop bomber..
Britain would have produced the Britannia and then?
Rocket powered fighters based on the Me 163 would have fought in Korea.
The institutional mindset would make developing jets complicated, but they would come eventually.
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The problem with aircraft like the Me 163 is that they are not fighters but interceptors which would take on larger aircraft. Fighter would still need a much better range than you can get with a workable interceptor. Much more development of piston types and further use of marginal designs such as the MB series etc. Marginal in the traditional timeline due to the advent of the gas turbine rather than their being no good.
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There is still the motorjet option.
Where the jet engine compressor is driven - NOT by itself (a turbine in the exhaust) but by a separated piston engine. Henri Coanda had imagined and build it (although NOT flown it) by 1910.
Now that would make a strange alt-history... what if Coanda succeeded, somewhat, with motorjet in 1910, triggering a "proto jet age" 30 years in advance ?
(I do know that motorjets are shit compared to turbojets, it is more for the sake of coolness. Imagine - motorjet powered Zeppelins, motorjet powered SPADs, motorjet powered Sikorsky Illia Muromets bombers...)
Where the jet engine compressor is driven - NOT by itself (a turbine in the exhaust) but by a separated piston engine. Henri Coanda had imagined and build it (although NOT flown it) by 1910.
Now that would make a strange alt-history... what if Coanda succeeded, somewhat, with motorjet in 1910, triggering a "proto jet age" 30 years in advance ?
(I do know that motorjets are shit compared to turbojets, it is more for the sake of coolness. Imagine - motorjet powered Zeppelins, motorjet powered SPADs, motorjet powered Sikorsky Illia Muromets bombers...)
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Haven't read all the posts but, assuming the energy density for storage ever gets there, you could have an electric turbojet. Superconducting motor starts the compressor turning and you use electrical elements to heat the air. Like Project Pluto or a direct cycle nuclear jet engine but using electricity to produce the heat.
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Given a single turbine blade on the latest generation of gas turbine absorbs as much power as a Formula 1 engine at max chat, I’m trying to picture how big the electric motor will be to drive typically compressor. I mean there’s between 300-400 turbine blades and this is before you do the air heating thing, actually why do that? In gas turbine (chemical or nuclear) it’s done to release the fuels potential energy which is unnecessary in this hypothetical electrical engine. I guess heating the air will give an increase in exhaust velocity due to the higher temperature but is this an advantage? Whatever. all that energy you’re adding to the air then simply pushing it out the back will give a dreadful cycle efficiency.
Piston engines can't run turbine like blade.
A propeller must impart momentum to the passing air. Viscosity results in a serie of helicoïdal vortex around the prop. To minimise recirculation drag, the goal is to impart the minimum momentum change on each blade, hence to run them at low pitch, imparting the minimum momentum per blade, something that you compensate by augmenting the number of blade and disk rows.
With a turbine, this is natural since the rotating speed of a fan is identical or nearly identical to the rotation speed of its shaft at every moment.
A piston engine would be unable to provide torque and rotation speed at the same time. And when it does it won't do it efficiently.
Hense pistons engines must impart a high momentum from each of their blade and compensate the effect of recirculation drag and momentum change with an elongated geometry (high chord ratio). Obviously variable pitch is there to adapt the rotation speed of the shaft engine to the need of the aircraft instead of increasing the regime in a turbine.
Electrique turbines in big airplabe would work obviously but IMOHO their design must adapt to their specificity in term of performances. Instead of simply copy pasting turbine design in term of bypass ratio and section span, a new core architecture could ease their general use in aviation with a larger distance b/w each disk, no go throught shaft etc...
A propeller must impart momentum to the passing air. Viscosity results in a serie of helicoïdal vortex around the prop. To minimise recirculation drag, the goal is to impart the minimum momentum change on each blade, hence to run them at low pitch, imparting the minimum momentum per blade, something that you compensate by augmenting the number of blade and disk rows.
With a turbine, this is natural since the rotating speed of a fan is identical or nearly identical to the rotation speed of its shaft at every moment.
A piston engine would be unable to provide torque and rotation speed at the same time. And when it does it won't do it efficiently.
Hense pistons engines must impart a high momentum from each of their blade and compensate the effect of recirculation drag and momentum change with an elongated geometry (high chord ratio). Obviously variable pitch is there to adapt the rotation speed of the shaft engine to the need of the aircraft instead of increasing the regime in a turbine.
Electrique turbines in big airplabe would work obviously but IMOHO their design must adapt to their specificity in term of performances. Instead of simply copy pasting turbine design in term of bypass ratio and section span, a new core architecture could ease their general use in aviation with a larger distance b/w each disk, no go throught shaft etc...
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Okay, I want to jump in here with some thoughts;
First of all, I think many of you guys are so fixated on reality that you miss the whole point of "Alternate History" especially pertaining to questions. I know I am new to this forum, but not to Alt-history.
I think what the O.P. is wanting to do is get some people thinking about how piston engines might have pushed the limits of technology for WHATEVER reason. Make a reason up, or just POOF jet turbines cannot exist because the universe says so.
The REASON is irrelevant, the idea is "HOW FAR COULD PISTON ENGINES HAVE GONE IF JET ENGINES NEVER HAPPENED?".
Or; "HOW FAR COULD PISTON ENGINES HAVE TAKEN AVIATION IF THEY REMAINED THE ONLY FORM OF TECHNOLOGY AVAILABLE."
This does not limit piston engines to not having superchargers, I think really, it just eliminates the turbine. In reality, the turbine was inevitable, because Steam turbines existed, it was only a matter of time before gas turbines also existed. But lets say turbines never exist because reasons. This does however restrict supercharging to mechanical only. Or, just allow turbos anyway. I suggest we allow turbos anyway since they don't require mechanical transmissions to change gear at various altitudes.
.....................
The first thing is that, like mentioned earlier, piston engine aircraft reach the point of diminishing returns around 5000hp for a single engine. With a sharp decline supposedly at about 7500hp for a single engine.
Looking at the pace and direction of engine development through the war, you get the idea that they could have reached the 5000hp limit by 1946 and the 7500hp limit by 1948. Air-cooled radial engines would find their limit around 5000hp just because you cant cool more than 4 rows deep in any meaningful way. Inline air-cooled engines could use cowling design to more effectively cool more rows of cylinders, drawing in air separately for rear-most or even individual cylinders; but radials reach a realistic limit at 4 rows without secondary ventilation.
Lycoming ran the XR-7755 in 1944; a liquid cooled radial consisting of 9 banks of 4 cylinders each, ad displacing 7,756cu-in, the 6,000lb engine made 5,000hp for takeoff/military power and 4,000hp for cruise. With a diameter of just 61 inches, it was quite compact.
The Pratt & Whitney R-4360-51VDT was 61 inches diameter, displaced 4362 cu-in, weighed 3,720lb and produced 4,300hp.
The Napier Sabre with a width of 40 inches, a height of 46 inches, displacing 2240cu-in and weighing in at 2360lb, started production with an already impressive 2200hp and had final prototypes making 3500hp by the end of development.
The Yakovlev M-501 was a 8760cu-in, 7-bank, liquid cooled radial with 6-cylinders per bank. It weighed 6500lbs with no turbo and 7500lbs with a turbo. Without a turbo it produced 4750hp and with a turbo it produced 6205hp. Oh, and did I mention it was a diesel? The turbocharger alone produced 551lb-ft of thrust. (Although, the engine was very good, it ended up powering ships since gas turbines happened.)
The designer felt the engine could produce 7000hp if fully developed. And proving him more than right, a modern example was modified for tractor-pulling and produces over 10,000hp.
The Napier Nomad managed to make 3150hp and weighing 3580lbs while being 56 inches wide and 40 inches high, it also produced 320lbf thrust from the jet portion of the engine.
The Napier Nomad gets dangerously close to being a jet engine in it's efforts to produce massive power with great fuel efficiency, basically it unknowingly becomes a motorjet but uses most of the power to drive a propeller like a turboprop rather than making thrust via ducted thrust (with or without expanding gasses; ducted fans are simple motorjets), as with a typical motorjet. Since it IS a motorjet by definition, I am allowing it. Maybe bending the rules a little, since it does have a turbine section that recoups power, but, since the turbine section operated as a turbocharger, (89psi boost!!!) it just barely fits I think.
((Aviation kinda forgot about the diesel piston engine and is worse off for it. With 30-60% less fuel consumption and only 30% more mass in early designs, it stands to reason that further development could have yielded some fantastic engines. Particularly since diesels seem to take increases in boost pressure and convert it to pure power without loss of cruise efficiency, I think that 2-stroke, turbo-diesel piston engines would likely have been the direction engine designers would have had to turn eventually to get both the power and efficiency needed to keep gaining ground.))
There are more examples that could be cited, but I think the point we see is best shown with the two US fighters. The P-47 and F4U. Both originally built with 1800hp, and later 2300hp R-2800 radials. Both had been prototyped with the new R-4360 engine. The F2G "Super Corsair" getting the "-4" variant with 3000hp and the XP-72 getting the "-13" variant with 3500hp. Both eventually could have been fitted with the final "-51" variant with made 4300hp. It should be assumed that if development continued, it is claimed (can't find the source) that the engine could possibly have been tuned up to 4700hp before a completely new, larger engine would need to be built.
The need for not only counter-rotating props but props with 5, 8, 15 blades would also be needed to both keep tip speeds as low as possible and bite enough air to put that much power into play. We see this development later (1960s-1990s) with the prop-fan, being driven by turbines producing more than 10,000hp, We also see development of ducted fans being driven by turbines with upwards up 100,000hp, in our hypothetical world they would be driven by piston engines. Of course, our piston engines will never make that much power. So, it would stand that aircraft would need more, smaller engines or aircraft would be smaller or both. However, breaking the sound barrier without the use of rockets is theoretically possible using motorjets.
While the realm of the supersonic would initially fall to rocket powered or at least rocket boosted aircraft, the motorjet could be developed to make enough thrust to push an aircraft past the sound barrier. Lets look at motorjets a bit;
In 1910 Henry Coanda made a motorjet with "cold" thrust. He later claimed that he intended to add an afterburner, and then later claimed that he HAD an afterburner and that the afterburner is why he crashed, it produced so much thrust that he stalled and crashed just above the runway. The drawings he used to prove his claim was reworked from the original copies and his claims are understood to be dubious at best. He claimed a thrust of 240lbf but modern engineers have calculated it to be 36lbf without the afterburner and 54lbf would be required to fly out of ground affect. He likely flew within ground affect, pulled up to fly and simply stalled and crashed. So, enough of his design, it was never developed to a working level.
Next we have the FW-44J (the "J" may not have been given to the test aircraft with the intention of calling it a "jet" in modern terms, as it is a ducted fan with engine heat added) The design reportedly worked but was just abandoned for reasons I can't find. The idea would have eliminated the need for large diameter props with long landing gear and timing gears for machine guns. Plus the design would have opened new aircraft designs to possibility. With the fan being embedded into the airframe.
Next major motorjet is the Caproni-Campini N.1 Motorjet. The Wikipedia page is full of errors and disorganized information. There was two prototypes built, but both had exactly the same name. The aircraft is cited by seemingly everyone for failing to produce performance on par with then current propeller driven fighters. However, since it is known that there was two N.1s built. And from what I can find, it appears that the first one used a 3 stage axial compressor driven by a 700hp piston engine. This aircraft only managed 233mph. Lets call this the N.1a for simplicity. The N.1a and N.1b were 9,200lb aircraft with a nearly 52 foot wingspan. 700hp, even with the rudimentary afterburner, was just not enough power. The other (I'm assuming second) aircraft (we will call it N.1b) but had a three stage axial compressor and a 900hp engine. It also had a redesigned secondary combustion (afterburner). This produced a maximum speed of 320mph. Still only par for the fighters at the time. But it was a comparatively large aircraft for 900hp.
Especially in 1940 when fighters like the BF-109E had a max take off weight of 5875lbs, a wingspan of just 32.5ft and had 1175hp and had a top speed of 348mph.
The N.1a and/or N.1b might have also recorded the 233mph speed at "sea level" and the 320mph speed at a more efficient altitude of around 15,000ft. However, I don't think this is the case as the speed disparity is too high. The other possiblility is that 233mph was without afterburning and 320mph was with afterburning. This seems a more likely case, but doesn't explain why the two models have a difference of power ratings. Unless both aircraft used the same 900hp engine and the 700hp listing is a mistake.
Given the last possibility, where both aircraft were in-fact, identical, then the speed ratings must be with and without afterburning. If the engine ratings are correct, where one aircraft had 700hp and the other had 900hp, then the ratings seem to be based on power differences between the two. That said, it is evident that the thrust from the afterburner DID provide extra thrust, as the aircraft was too heavy and too big to manage such high speed with only 900hp.
Another aircraft with comparable performance was the Macchi C.200 with 34ft-9in wingspan and weighing 4850lbs, the 870hp engine gave the aircraft a top speed of 313mph. Compared to the N.1b with 900hp pushing a 9200lb aircraft with a huge 52ft wingspan to 320mph. It suddenly isn't such a failure. But also, the powers that be probably didn't see the potential and only saw the "same" performance.
Had the N.1 series included another craft with a more fitting 1500hp engine and further improved afterburner, the big N.1 could have been pushed into the 380-410mph range. Which in 1940 still wasn't very impressive, since the P-47 and P-38 already had those speeds. However, where the motorjet would begin to shine is when that 1500hp engine and better afterburner get shoved into a smaller airframe. Also, the compressor design was not as efficient/effective as it could have been with more development than the original that had only 6 blades per row.
The Germans worked on motorjets as well but the war ended before any significant milestones were made.
Heinkel developed engines called the HeS 50z and the HeS 50d. Little is known about them and almost no info exists in the west online. I was able to find some information about the HeS 50z on a Russian website that stated that the engine was a X pattern 4 bank design with 4-cylinders per bank. The engine was almost completely embedded into the engine cowling, with just the valve covers exposed outside. The engine drove a 3-stage compressor and used some of the compressed air flowing around it to feed a small supercharger that fed the engine's fuel injection. The engine was air-cooled, allowing the heat to be added to the flow to increase thrust, and the exhaust was also added to the flow stream. From what I found the 50z had 1200hp. Unknown thrust rating.
The HeS 50d had a horizontal H piston layout with 4 banks of 6 pistons. Reportedly designed to 1500hp, it was liquid cooled and had a radiator in the airflow stream to add heat to the compressed air and cool the engine. The entire engine was within the air stream; probably in an attempt to recover as much heat as possible. The heat normally wasted by an engine can be recovered by a motorjet and is then added to the efficiency, further boosting overall efficiency.
Last in the HeS motorjet series was the HeS 60. The engine was reported to be powered by a 2000hp, air cooled, 32 cylinder radial and produced 2,753lbf thrust with afterburning. The intent was to use them for the Amerika Bomber since they would be more reliable than the jet engines then available. And while the engine was slightly less efficient than a comparable piston engine when running "cold" (without afterburning), it was far more efficient than jet engines at cruise speed. It also was slightly more efficient than turbojet engines of the same thrust at full power. Also, since the engine produced about 40% of max thrust when cruising "cold", it had lots of take-off power but ran efficiently at a slower cruise speed.
In the 1990s NASA worked on a motorjet that was designed to operate at 90,000ft. They wanted the efficiency of the piston engine but needed a compression-thrust system to operate that high.
The MiG-13 used a hybrid motorjet similar to the design of the Napier Nomad. With the aircraft capable of 440mph with propeller alone and 508mph with the motorjet engaged.
..........
Moving back to the what-if.
I think that piston aircraft would continue to push the boundary of 550mph using increasingly ludicrous amounts of power. And while top speed would see a significant diminishing return, rate-of-climb would continue to improve as massive amounts of power became available.
The P-47D had a RoC of 2050-2850fpm without water injection and up to 3260fpm with water injection. The XP-72 had a RoC of up to 5280fpm.
As fighters got slightly larger to accommodate the larger more powerful engines, the need to get traction would become the primary issue. The design of propellers would be the hot ticket area of science. With curved blades, more blades and wider blades eventually growing from the research. Eventually the prop-disc is no longer able to be seen through and the propeller cannot be mounted in front of the pilot. Single engine fighters would need to switch to pushers or twins to maintain visibility.
Meanwhile you would have very small fighters with rocket boosters and/or motorjets trying to make 1250hp engine equipped aircraft faster. The gap between heavy fighters and slight fighters would increase. With light aircraft being used for long range escorts and close air support. While the heavy fighters are focused on interception using their powerful engines to climb up to meet bombers with ever increasing altitudes and speeds. Eventually bombers will be able to fly at 55,000ft at speeds of nearly 500mph. Catching them relies on heavy interceptors with 5,000hp engines with 12, curved, wide-bladed propellers in pusher configuration with rockets on pods that are dropped right after takeoff and initial climb and internal rockets that allow for maximum climb performance upwards of 10,000-15,000fpm. The heavy interceptors level off near the bombers at the same extreme altitude and pursue at 550mph, the tips of the propellers scraping at 0.99 mach.
Eventually ducted fans are used to improve the limits of performance but they still can't break about 550-580mph. Motorjets and rockets are the only way to move forward. 5,000hp air-cooled engines stuffed into big fuselages with 4 or 5 stage compressors and a powerful afterburner. Possibly with small rocket motors inside the afterburner to further improve thrust expansion would finally give level speeds over mach 1. Very small, very thin, swept wings mean very high take off and landing speeds. The gap between fighters and interceptors continues to increase with fighters being nimble and small and interceptors getting quite big to house ever more powerful engines to drive the compressors in ever increasing efforts to catch the bombers. Rocket boosted afterburners and eventually ramjet style afterburners allow for further increased speed. But it would seem that the single engine would reach its limit at 7500hp driving a ducted fan style axial flow compressor. Probably making almost 10,000lbf thrust. Next the interceptors would need two of them in order to keep up with bombers that are already using probably 6 to 10 of these powerful engines to fly up to 70,000ft at speeds of 700+mph. Aircraft would use either multiple motorjets or multiple engines driving a single motorjet compressor.
Rocket powered interceptors would eventually be the only vehicles fast enough to catch the speedy, high-altitude bombers and spy-planes. Using smaller motorjets purely to save fuel on their route and using rockets to zoom to the enemy. The only other method of defense from them would be dirigibles with long range guns and radar hovering at 75,000-80,000ft and forming a defensive line of firepower shooting down at the approaching bombers and spy-planes. Spy-planes soon use rockets once within range to push them to mach 3 for a few minutes. While rocket interceptors are launched from the dirigibles to attack from airborne runways. Aircraft would rely on lots of wide, curved blades, usually in ducts (ducted fans) to get every ounce of tractive force from their every more powerful piston engines. And since a ducted fan creates a jet of thrust, that jet can be augmented by adding heat; afterburners, ramjet augmenters, rocket boosters and other creative methods of making more power would become a race of technical performance. Something we did with turbojets in less than a decade would probably take two decades to even get close. Diesel engines would supplant gasoline when the boost levels got too high for gasoline to cope. Alcohol and diesel would become the more popular fuels. With diesel engines likely boosted well past 100psi and making close to 3hp per cubic inch per pound. Piston engines with close to 10,000hp would emerge being only 60 inches wide but likely more than 200 inches long to make room for so much engine and turbo equipment. The Allison V1710 made 1200hp back in the day, but today tractor-pullers manage to get 3,000-3,600hp from those same engines just with improved fuel injection and modern turbocharging. Imagine a P-51 with 3000hp & an 8 blade prop. Performance would be awesome. But range would not. If the Allison can be made to make so much power, imagine what would happen with other engines. Like the Lycoming XR-7755. It made 5000hp then, today it could probably be pushed to nearly 12,500-15,000hp.
Going by the math that the HeS 60 was 2000hp and made 2750lbf thrust, that means it could manage 17,180lbf - 20,625lbf thrust. But unline turbojets that make that kind of power, it would be a much larger, heavier engine making the power. And if not a motorjet, or even a ducted fan, you would have many-blade, counter-rotating props or rather prop-fans with wide, swept blades. Non-motorjet and non-rocket aircraft would use either ducted fan type cold-motorjets or unducted fans a.k.a: prop-fans.
I know I have rambled on for a while, but it seems that unless you take away rockets and afterburners and even ducted fans, you still end up with a form of jet engine eventually emerging. If you force the world to only use propellers, then you end up with unducted fans with many huge swept blades and almost exclusively counter rotating in order to capture that immense power.
First of all, I think many of you guys are so fixated on reality that you miss the whole point of "Alternate History" especially pertaining to questions. I know I am new to this forum, but not to Alt-history.
I think what the O.P. is wanting to do is get some people thinking about how piston engines might have pushed the limits of technology for WHATEVER reason. Make a reason up, or just POOF jet turbines cannot exist because the universe says so.
The REASON is irrelevant, the idea is "HOW FAR COULD PISTON ENGINES HAVE GONE IF JET ENGINES NEVER HAPPENED?".
Or; "HOW FAR COULD PISTON ENGINES HAVE TAKEN AVIATION IF THEY REMAINED THE ONLY FORM OF TECHNOLOGY AVAILABLE."
This does not limit piston engines to not having superchargers, I think really, it just eliminates the turbine. In reality, the turbine was inevitable, because Steam turbines existed, it was only a matter of time before gas turbines also existed. But lets say turbines never exist because reasons. This does however restrict supercharging to mechanical only. Or, just allow turbos anyway. I suggest we allow turbos anyway since they don't require mechanical transmissions to change gear at various altitudes.
.....................
The first thing is that, like mentioned earlier, piston engine aircraft reach the point of diminishing returns around 5000hp for a single engine. With a sharp decline supposedly at about 7500hp for a single engine.
Looking at the pace and direction of engine development through the war, you get the idea that they could have reached the 5000hp limit by 1946 and the 7500hp limit by 1948. Air-cooled radial engines would find their limit around 5000hp just because you cant cool more than 4 rows deep in any meaningful way. Inline air-cooled engines could use cowling design to more effectively cool more rows of cylinders, drawing in air separately for rear-most or even individual cylinders; but radials reach a realistic limit at 4 rows without secondary ventilation.
Lycoming ran the XR-7755 in 1944; a liquid cooled radial consisting of 9 banks of 4 cylinders each, ad displacing 7,756cu-in, the 6,000lb engine made 5,000hp for takeoff/military power and 4,000hp for cruise. With a diameter of just 61 inches, it was quite compact.
The Pratt & Whitney R-4360-51VDT was 61 inches diameter, displaced 4362 cu-in, weighed 3,720lb and produced 4,300hp.
The Napier Sabre with a width of 40 inches, a height of 46 inches, displacing 2240cu-in and weighing in at 2360lb, started production with an already impressive 2200hp and had final prototypes making 3500hp by the end of development.
The Yakovlev M-501 was a 8760cu-in, 7-bank, liquid cooled radial with 6-cylinders per bank. It weighed 6500lbs with no turbo and 7500lbs with a turbo. Without a turbo it produced 4750hp and with a turbo it produced 6205hp. Oh, and did I mention it was a diesel? The turbocharger alone produced 551lb-ft of thrust. (Although, the engine was very good, it ended up powering ships since gas turbines happened.)
The designer felt the engine could produce 7000hp if fully developed. And proving him more than right, a modern example was modified for tractor-pulling and produces over 10,000hp.
The Napier Nomad managed to make 3150hp and weighing 3580lbs while being 56 inches wide and 40 inches high, it also produced 320lbf thrust from the jet portion of the engine.
The Napier Nomad gets dangerously close to being a jet engine in it's efforts to produce massive power with great fuel efficiency, basically it unknowingly becomes a motorjet but uses most of the power to drive a propeller like a turboprop rather than making thrust via ducted thrust (with or without expanding gasses; ducted fans are simple motorjets), as with a typical motorjet. Since it IS a motorjet by definition, I am allowing it. Maybe bending the rules a little, since it does have a turbine section that recoups power, but, since the turbine section operated as a turbocharger, (89psi boost!!!) it just barely fits I think.
((Aviation kinda forgot about the diesel piston engine and is worse off for it. With 30-60% less fuel consumption and only 30% more mass in early designs, it stands to reason that further development could have yielded some fantastic engines. Particularly since diesels seem to take increases in boost pressure and convert it to pure power without loss of cruise efficiency, I think that 2-stroke, turbo-diesel piston engines would likely have been the direction engine designers would have had to turn eventually to get both the power and efficiency needed to keep gaining ground.))
There are more examples that could be cited, but I think the point we see is best shown with the two US fighters. The P-47 and F4U. Both originally built with 1800hp, and later 2300hp R-2800 radials. Both had been prototyped with the new R-4360 engine. The F2G "Super Corsair" getting the "-4" variant with 3000hp and the XP-72 getting the "-13" variant with 3500hp. Both eventually could have been fitted with the final "-51" variant with made 4300hp. It should be assumed that if development continued, it is claimed (can't find the source) that the engine could possibly have been tuned up to 4700hp before a completely new, larger engine would need to be built.
The need for not only counter-rotating props but props with 5, 8, 15 blades would also be needed to both keep tip speeds as low as possible and bite enough air to put that much power into play. We see this development later (1960s-1990s) with the prop-fan, being driven by turbines producing more than 10,000hp, We also see development of ducted fans being driven by turbines with upwards up 100,000hp, in our hypothetical world they would be driven by piston engines. Of course, our piston engines will never make that much power. So, it would stand that aircraft would need more, smaller engines or aircraft would be smaller or both. However, breaking the sound barrier without the use of rockets is theoretically possible using motorjets.
While the realm of the supersonic would initially fall to rocket powered or at least rocket boosted aircraft, the motorjet could be developed to make enough thrust to push an aircraft past the sound barrier. Lets look at motorjets a bit;
In 1910 Henry Coanda made a motorjet with "cold" thrust. He later claimed that he intended to add an afterburner, and then later claimed that he HAD an afterburner and that the afterburner is why he crashed, it produced so much thrust that he stalled and crashed just above the runway. The drawings he used to prove his claim was reworked from the original copies and his claims are understood to be dubious at best. He claimed a thrust of 240lbf but modern engineers have calculated it to be 36lbf without the afterburner and 54lbf would be required to fly out of ground affect. He likely flew within ground affect, pulled up to fly and simply stalled and crashed. So, enough of his design, it was never developed to a working level.
Next we have the FW-44J (the "J" may not have been given to the test aircraft with the intention of calling it a "jet" in modern terms, as it is a ducted fan with engine heat added) The design reportedly worked but was just abandoned for reasons I can't find. The idea would have eliminated the need for large diameter props with long landing gear and timing gears for machine guns. Plus the design would have opened new aircraft designs to possibility. With the fan being embedded into the airframe.
Next major motorjet is the Caproni-Campini N.1 Motorjet. The Wikipedia page is full of errors and disorganized information. There was two prototypes built, but both had exactly the same name. The aircraft is cited by seemingly everyone for failing to produce performance on par with then current propeller driven fighters. However, since it is known that there was two N.1s built. And from what I can find, it appears that the first one used a 3 stage axial compressor driven by a 700hp piston engine. This aircraft only managed 233mph. Lets call this the N.1a for simplicity. The N.1a and N.1b were 9,200lb aircraft with a nearly 52 foot wingspan. 700hp, even with the rudimentary afterburner, was just not enough power. The other (I'm assuming second) aircraft (we will call it N.1b) but had a three stage axial compressor and a 900hp engine. It also had a redesigned secondary combustion (afterburner). This produced a maximum speed of 320mph. Still only par for the fighters at the time. But it was a comparatively large aircraft for 900hp.
Especially in 1940 when fighters like the BF-109E had a max take off weight of 5875lbs, a wingspan of just 32.5ft and had 1175hp and had a top speed of 348mph.
The N.1a and/or N.1b might have also recorded the 233mph speed at "sea level" and the 320mph speed at a more efficient altitude of around 15,000ft. However, I don't think this is the case as the speed disparity is too high. The other possiblility is that 233mph was without afterburning and 320mph was with afterburning. This seems a more likely case, but doesn't explain why the two models have a difference of power ratings. Unless both aircraft used the same 900hp engine and the 700hp listing is a mistake.
Given the last possibility, where both aircraft were in-fact, identical, then the speed ratings must be with and without afterburning. If the engine ratings are correct, where one aircraft had 700hp and the other had 900hp, then the ratings seem to be based on power differences between the two. That said, it is evident that the thrust from the afterburner DID provide extra thrust, as the aircraft was too heavy and too big to manage such high speed with only 900hp.
Another aircraft with comparable performance was the Macchi C.200 with 34ft-9in wingspan and weighing 4850lbs, the 870hp engine gave the aircraft a top speed of 313mph. Compared to the N.1b with 900hp pushing a 9200lb aircraft with a huge 52ft wingspan to 320mph. It suddenly isn't such a failure. But also, the powers that be probably didn't see the potential and only saw the "same" performance.
Had the N.1 series included another craft with a more fitting 1500hp engine and further improved afterburner, the big N.1 could have been pushed into the 380-410mph range. Which in 1940 still wasn't very impressive, since the P-47 and P-38 already had those speeds. However, where the motorjet would begin to shine is when that 1500hp engine and better afterburner get shoved into a smaller airframe. Also, the compressor design was not as efficient/effective as it could have been with more development than the original that had only 6 blades per row.
The Germans worked on motorjets as well but the war ended before any significant milestones were made.
Heinkel developed engines called the HeS 50z and the HeS 50d. Little is known about them and almost no info exists in the west online. I was able to find some information about the HeS 50z on a Russian website that stated that the engine was a X pattern 4 bank design with 4-cylinders per bank. The engine was almost completely embedded into the engine cowling, with just the valve covers exposed outside. The engine drove a 3-stage compressor and used some of the compressed air flowing around it to feed a small supercharger that fed the engine's fuel injection. The engine was air-cooled, allowing the heat to be added to the flow to increase thrust, and the exhaust was also added to the flow stream. From what I found the 50z had 1200hp. Unknown thrust rating.
The HeS 50d had a horizontal H piston layout with 4 banks of 6 pistons. Reportedly designed to 1500hp, it was liquid cooled and had a radiator in the airflow stream to add heat to the compressed air and cool the engine. The entire engine was within the air stream; probably in an attempt to recover as much heat as possible. The heat normally wasted by an engine can be recovered by a motorjet and is then added to the efficiency, further boosting overall efficiency.
Last in the HeS motorjet series was the HeS 60. The engine was reported to be powered by a 2000hp, air cooled, 32 cylinder radial and produced 2,753lbf thrust with afterburning. The intent was to use them for the Amerika Bomber since they would be more reliable than the jet engines then available. And while the engine was slightly less efficient than a comparable piston engine when running "cold" (without afterburning), it was far more efficient than jet engines at cruise speed. It also was slightly more efficient than turbojet engines of the same thrust at full power. Also, since the engine produced about 40% of max thrust when cruising "cold", it had lots of take-off power but ran efficiently at a slower cruise speed.
In the 1990s NASA worked on a motorjet that was designed to operate at 90,000ft. They wanted the efficiency of the piston engine but needed a compression-thrust system to operate that high.
The MiG-13 used a hybrid motorjet similar to the design of the Napier Nomad. With the aircraft capable of 440mph with propeller alone and 508mph with the motorjet engaged.
..........
Moving back to the what-if.
I think that piston aircraft would continue to push the boundary of 550mph using increasingly ludicrous amounts of power. And while top speed would see a significant diminishing return, rate-of-climb would continue to improve as massive amounts of power became available.
The P-47D had a RoC of 2050-2850fpm without water injection and up to 3260fpm with water injection. The XP-72 had a RoC of up to 5280fpm.
As fighters got slightly larger to accommodate the larger more powerful engines, the need to get traction would become the primary issue. The design of propellers would be the hot ticket area of science. With curved blades, more blades and wider blades eventually growing from the research. Eventually the prop-disc is no longer able to be seen through and the propeller cannot be mounted in front of the pilot. Single engine fighters would need to switch to pushers or twins to maintain visibility.
Meanwhile you would have very small fighters with rocket boosters and/or motorjets trying to make 1250hp engine equipped aircraft faster. The gap between heavy fighters and slight fighters would increase. With light aircraft being used for long range escorts and close air support. While the heavy fighters are focused on interception using their powerful engines to climb up to meet bombers with ever increasing altitudes and speeds. Eventually bombers will be able to fly at 55,000ft at speeds of nearly 500mph. Catching them relies on heavy interceptors with 5,000hp engines with 12, curved, wide-bladed propellers in pusher configuration with rockets on pods that are dropped right after takeoff and initial climb and internal rockets that allow for maximum climb performance upwards of 10,000-15,000fpm. The heavy interceptors level off near the bombers at the same extreme altitude and pursue at 550mph, the tips of the propellers scraping at 0.99 mach.
Eventually ducted fans are used to improve the limits of performance but they still can't break about 550-580mph. Motorjets and rockets are the only way to move forward. 5,000hp air-cooled engines stuffed into big fuselages with 4 or 5 stage compressors and a powerful afterburner. Possibly with small rocket motors inside the afterburner to further improve thrust expansion would finally give level speeds over mach 1. Very small, very thin, swept wings mean very high take off and landing speeds. The gap between fighters and interceptors continues to increase with fighters being nimble and small and interceptors getting quite big to house ever more powerful engines to drive the compressors in ever increasing efforts to catch the bombers. Rocket boosted afterburners and eventually ramjet style afterburners allow for further increased speed. But it would seem that the single engine would reach its limit at 7500hp driving a ducted fan style axial flow compressor. Probably making almost 10,000lbf thrust. Next the interceptors would need two of them in order to keep up with bombers that are already using probably 6 to 10 of these powerful engines to fly up to 70,000ft at speeds of 700+mph. Aircraft would use either multiple motorjets or multiple engines driving a single motorjet compressor.
Rocket powered interceptors would eventually be the only vehicles fast enough to catch the speedy, high-altitude bombers and spy-planes. Using smaller motorjets purely to save fuel on their route and using rockets to zoom to the enemy. The only other method of defense from them would be dirigibles with long range guns and radar hovering at 75,000-80,000ft and forming a defensive line of firepower shooting down at the approaching bombers and spy-planes. Spy-planes soon use rockets once within range to push them to mach 3 for a few minutes. While rocket interceptors are launched from the dirigibles to attack from airborne runways. Aircraft would rely on lots of wide, curved blades, usually in ducts (ducted fans) to get every ounce of tractive force from their every more powerful piston engines. And since a ducted fan creates a jet of thrust, that jet can be augmented by adding heat; afterburners, ramjet augmenters, rocket boosters and other creative methods of making more power would become a race of technical performance. Something we did with turbojets in less than a decade would probably take two decades to even get close. Diesel engines would supplant gasoline when the boost levels got too high for gasoline to cope. Alcohol and diesel would become the more popular fuels. With diesel engines likely boosted well past 100psi and making close to 3hp per cubic inch per pound. Piston engines with close to 10,000hp would emerge being only 60 inches wide but likely more than 200 inches long to make room for so much engine and turbo equipment. The Allison V1710 made 1200hp back in the day, but today tractor-pullers manage to get 3,000-3,600hp from those same engines just with improved fuel injection and modern turbocharging. Imagine a P-51 with 3000hp & an 8 blade prop. Performance would be awesome. But range would not. If the Allison can be made to make so much power, imagine what would happen with other engines. Like the Lycoming XR-7755. It made 5000hp then, today it could probably be pushed to nearly 12,500-15,000hp.
Going by the math that the HeS 60 was 2000hp and made 2750lbf thrust, that means it could manage 17,180lbf - 20,625lbf thrust. But unline turbojets that make that kind of power, it would be a much larger, heavier engine making the power. And if not a motorjet, or even a ducted fan, you would have many-blade, counter-rotating props or rather prop-fans with wide, swept blades. Non-motorjet and non-rocket aircraft would use either ducted fan type cold-motorjets or unducted fans a.k.a: prop-fans.
I know I have rambled on for a while, but it seems that unless you take away rockets and afterburners and even ducted fans, you still end up with a form of jet engine eventually emerging. If you force the world to only use propellers, then you end up with unducted fans with many huge swept blades and almost exclusively counter rotating in order to capture that immense power.
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I don't have a problem with alternate history, though it's not a core forum topic, but alternate physics seems to be required here, which makes it sci-fi, which is REALLY off-topic. If you don't accept the principle of minor, believable changes to history, where do you draw the line? Should we discuss the effects on aircraft production of Mars invading the UK in the 19th century?
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All good points dear zargosian,
The simplest way to delay jet engine development is too many melted turbine blades.
To fully optimize piston engine fuel consumption, you will eventually need to convert to all liquid-cooled cylinders. While air-cooled radials may have lighter empty weights, they also suffer un-equal cooling., Even the best baffling systems and supplemental fans still cannot prevent cylinders from heating to oval cross-sections. Those oval cylinders require looser manufacturing tolerances which increase blow-by which increase fuel consumption and robs power.
Liquid-cooling can also help reduce hot-spots on cylinders, specifically exhaust valves. Exhaust valves have always been the weakest/hottest part of poppet valve engines.
Also consider how much fuel injection can help even out fuel distribution to all cylinders. Conventional carburetors and induction systems can only be optimized for one rpm and manifold pressure setting.
Finally, consider how electronic ignition can help precisely advance or retard ignition to tailor ignition timing to cruise or dash modes.
And you are correct in stating that ducted fans will be needed when speeds approach trans-sonic.
The simplest way to delay jet engine development is too many melted turbine blades.
To fully optimize piston engine fuel consumption, you will eventually need to convert to all liquid-cooled cylinders. While air-cooled radials may have lighter empty weights, they also suffer un-equal cooling., Even the best baffling systems and supplemental fans still cannot prevent cylinders from heating to oval cross-sections. Those oval cylinders require looser manufacturing tolerances which increase blow-by which increase fuel consumption and robs power.
Liquid-cooling can also help reduce hot-spots on cylinders, specifically exhaust valves. Exhaust valves have always been the weakest/hottest part of poppet valve engines.
Also consider how much fuel injection can help even out fuel distribution to all cylinders. Conventional carburetors and induction systems can only be optimized for one rpm and manifold pressure setting.
Finally, consider how electronic ignition can help precisely advance or retard ignition to tailor ignition timing to cruise or dash modes.
And you are correct in stating that ducted fans will be needed when speeds approach trans-sonic.
I agree, I hope my comment was not rude in any way. Just wanted to try addressing the original question. I also agree, that its one thing to ask "what if X tech was available 6 months sooner" and something entirely different to ask about the airplane being invented during the American Revolutionary War. One is a plausible alteration, the other is sci-fi.
I did miss that. Liquid cooling will always beat air cooling except in weight. And even then, good engineering makes that difference very small.
Advances are definitely able to improve performance and reliability significantly. I suppose that is why we see 600hp 2.5L Subarus on a regular basis with modern tech.
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IOW air-cooled engines are great for short-range interceptors because their light weight allows rapid acceleration ... albeit with higher fuel consumption.
OTOH liquid-cooed engines are better suited to long-range airplanes where their lower specific fuel consumption out-weighs the higher empty weight.
OTOH liquid-cooed engines are better suited to long-range airplanes where their lower specific fuel consumption out-weighs the higher empty weight.
Hi all,
I think you all should look at it as a design-excercise instead of purely theoretical.
I think the largest change would come from improved understanding of aerodynamics and that prop-fighters would start to look like jet-fighters.
As Justo Miranda has shown us with his diagrams. So how far along the jet-design line would it be pushed? All the way up to stealth? I don't think so, but prop-fighters with LERX as an F-18? Could be possible.
How would a twin prop F18 look like? How far would you alter an P-51 to get it to fly faster then ever. You can change everything; wings, fuselage, engine or make it even multiple engines.
Let me hear your ideas
Maybe I will make a 3d model out of it..
Rob
I think you all should look at it as a design-excercise instead of purely theoretical.
I think the largest change would come from improved understanding of aerodynamics and that prop-fighters would start to look like jet-fighters.
As Justo Miranda has shown us with his diagrams. So how far along the jet-design line would it be pushed? All the way up to stealth? I don't think so, but prop-fighters with LERX as an F-18? Could be possible.
How would a twin prop F18 look like? How far would you alter an P-51 to get it to fly faster then ever. You can change everything; wings, fuselage, engine or make it even multiple engines.
Let me hear your ideas
Maybe I will make a 3d model out of it..Rob
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I gave this scenario some thought and the best way I can imagine it is simply that nobody thinks about jet propulsion until 10 or 15 years later. Perhaps Whittle dies in a plane crash and never formulates his jet engine work. Hans Von Ohain never gets to read Whittle's patents and abandons his ideas on jet propulsion. The RAE in England gets its axial turboprop designs going and everyone just sticks to building props. The war ends with no jets, and there is no immediate Cold War (maybe Stalin dies and is replaced by a less aggressive leader), so everyone just carries on refining existing aeroplane designs with no real pressure to get faster.
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Good idea Her Fluff,
We know from the Republic Thunderscreech that tractor propellers generate far more noise than thrust as they approach Mach 1.
What if you installed a ridiculously long spinner, so that a tractor prop works inside the shock cone?
How efficient would pusher propellers be if spinning inside the shock cone of a supersonic airplane?
The American Mach-Buster never did fly.
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Spinning a prop inside the shock cone won’t do anything useful as this is the slower air region;- to get a useful contribution the thrust the efflux, generally acting on a smaller mass than the aircraft. has to be higher velocity than the aircraft is flying.
The very load noise of the supersonic prop indicates a substantial energy loss. Fundamentally noise is energetic air;- The more shearing within the energised air column relative to it surrounding the higher the losses and the louder the noise. Propellers create shearing in both the efflux column and the tip eddies. I’ve never seen the figures, but I reckon it very soon becomes a law of diminishing return;- I thought the idea of supersonic prop was to provide greater low speed thrust to accelerate off of carriers ( the steam catapult had yet to be invented) but then for the prop not to impede supersonic operations;- the XF84H and XF88B experiments proved supersonic prop was useless anyway. Why did they need two concept demonstrators to prove this?
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