US Army Hyper Engine

Zipper730 · Jul 30, 2018

From what I recall, the hyper-engine started out of two things

Basically: Basic efforts to improve engine power by decreasing weight and increasing power.
Immediately: A paper in the 1920's that stated it would not be possible to achieve one horsepower per cubic inch without sleeve valve

The engineers at Wright Field felt that was incorrect and planned to show it was wrong by having S.D. Heron modify a Liberty Engine cylinder and running it at increasingly high pressures and achieved the benchmark figures.

They then got Continental Motors to build the engine, with the engineering work being done by the Army. The actual engineering development was Army only.

While I know there weren't pay-as-you-go contracts: Was this how most engines were developed at the time?

I would have figured the buyer (the government) sets the specs, and the designer builds the design with the agreement of the buyer, and budget, but using their own engineers with either government test facilities or their own.

wuzak · Jul 31, 2018

Ricardo had written a paper espousing the virtues of the sleeve valve and Diesel type engines as the future for aero engines on the basis that the fuel quality was insufficient to support engines of higher power. That was written in 1927.

Meanwhile in the US, tetraethyllead was being adopted as a way of increasing the octane rating of fuels, and Sam Heron had invented the sodium cooled exhaust valve.

These developments overcame some of the issues of poppet valve engines with regards to knocking and pre-ignition.

So Heron was able to run the engine hotter with higher pressures.

The contract with Continental was basically because the Army didn't have its own manufacturing facilities, so they needed a sub-contractor to build their design.

Allison built the X-4520, air cooled X-24 engine to the Army's design in the 1920s. Allison X-4520 24-Cylinder Aircraft Engine

But in general, the engine manufacturers would design their own engines, to a design spec (for the military or for commercial aviation) or as a private venture.

Zipper730 · Aug 1, 2018

wuzak said:
The contract with Continental was basically because the Army didn't have its own manufacturing facilities, so they needed a sub-contractor to build their design. . .
But in general, the engine manufacturers would design their own engines, to a design spec (for the military or for commercial aviation) or as a private venture.

Why in this case didn't they just do that with the Hyper-Engine and X-4520?

GrauGeist · Aug 1, 2018

Another engine to examine, was Chrysler's IV-2200, which did exceed that 1:1 criteria.

kmccutcheon · Aug 2, 2018

Zipper730 said:
From what I recall, the hyper-engine started out of two thing

Basically: Basic efforts to improve engine power by decreasing weight and increasing power.

Immediately: A paper in the 1920's that stated it would not be possible to achieve one horsepower per cubic inch without sleeve valve

The engineers at Wright Field felt that was incorrect and planned to show it was wrong by having S.D. Heron modify a Liberty Engine cylinder and running it at increasingly high pressures and achieved the benchmark figures.

They then got Continental Motors to build the engine, with the engineering work being done by the Army. The actual engineering development was Army only.

While I know there weren't pay-as-you-go contracts: Was this how most engines were developed at the time?

I would have figured the buyer (the government) sets the specs, and the designer builds the design with the agreement of the buyer, and budget, but using their own engineers with either government test facilities or their own.

kmccutcheon · Aug 2, 2018

Robert Schlaifer said:

Development of American Liquid-Cooled Engines
The Hyper cylinder was to have the same 4 5/8-in. bore as the air-cooled Liberty which had been used in the experiments, but to permit higher speeds of rotation the stroke was to be shortened from 7 in. to 5 in., giving a displacement of 84.0 cu in., or a total of 1008 cu in the 1000-hp 12-cylinder vee-type engine which was to be built around it. The Army also decided that in order to operate satisfactorily with ethylene glycol at 300° F, which was considered desirable in order to minimize the weight and drag of the radiator,[4] the cylinders would have to be constructed individually, not en bloc, despite the contribution of rigid block construction to the reliability of an in-line engine with its long, flexible crankshaft, and despite the greater length of an engine with individual cylinders.[5]

In 1932 an agreement for the engineering and development of this cylinder and of the engine employing it was reached between the Army and the Continental Motor Company. Continental had been in the 1920.s the most successful manufacturer of engines for automobiles and trucks built by other makers. It had entered the aviation field in 1928 with a medium-power air-cooled radial, and in October 1931 had received a Navy contract for a radial air-cooled engine with single-sleeve valves.[6] The company had earlier had an unimportant contract with the Army for a single-sleeve-valve liquid-cooled engine, which was dropped because of poor performance at the time the Hyper project was undertaken.
Continental's role in the Hyper project was essentially to be nothing but routine engineering and testing. The Army not only had decided upon the basic principles and the size of the Hyper cylinder but also had laid down the main lines of the complete engine in which it was to be used, and the first two years of work were actually done in a special office set up by the company in Dayton to be near Wright Field.

The original cylinder, Hyper No. 1, was tested in 1933. Its intended power, 1.00 hp/cu in., was extremely high for the time - the Rolls Royce Merlin was designed in this same year for an initial rating of 750 hp or 0.46 hp/cu in.[7] - and for the fuel of Performance Number 75 [8] on which the Army intended to obtain this rating. Wright Field soon began to worry also about the possibility of obtaining a supercharger adequate to give this very high specific output. Finally, it became known that foreign liquid-cooled engines were being based on considerably lower specific power. In 1934 the Army instructed Continental to proceed with a cylinder of somewhat larger size [5.500" x 6.500"] (118.8 cu in. instead of 84.0) and reduced performance, Hyper No. 2.[9] The output aimed at from what was then a 1425-cu in. engine was still 1000 hp, amounting to 0.70 hp/cu in. This goal seems to have been reasonable enough: the Rolls Royce Merlin was type-tested in 1936 at 0.62 hp/cu in. on 68-PN (87-octane) fuel, and as far as detonation was concerned this rating could have been raised to about 0.70 hp/cu in. by the use of the 75-PN fuel the Army planned to use in the Hyper engine.

At this time the first design studies were made of a complete engine in which the new type of cylinder was to be tried out. The Army's original intention had been a 12-cylinder vee, and both the power-plant branch at Wright Field and the company would have preferred for mechanical reasons to adhere to this plan. The airplane branch at Wright Field, however, was then absolutely convinced that the engines of virtually all future airplanes, including even fighters, would be buried in the wings for the sake of higher speed, and at their insistence the Army specified that the new cylinder be the basis of a "flat" or opposed engine. This was the origin of the Continental O-1430.

As far as ability was concerned, it is true that since 1930 the company had been losing money at a rate of $2,000,000 or more per year, and that between 1929 and 1934 its working capital had shrunk from nearly $10,000,000 to $300,000, but it had nevertheless continued during this period to invest in a single-sleeve-valve automobile engine, $753,000 being written off as a loss in 1935. The real difficulty was simply the company's lack of faith, not in the technical soundness of the project, but in the prospect of sales of even a successful product. Even though some engineers at Wright Field believed that engines based on the Hyper cylinder might prove best for all types of combat planes, no one at all foresaw any commercial use, and the company thought of it as purely a fighter engine and did not believe that the probable market for fighter engines was large enough or sure enough to warrant the risk of any company money. It was the huge prospective market which encouraged heavy investment in an automotive engine despite all financial difficulties.

Thus the entire burden of financing the development was left to the Army's experimental funds. All Continental's contracts with the Army were of the fixed-price type, each individual contract specifying in detail the work to be done in the "phase", i.e., the portion of the whole job, which it covered, and management insisted on a signed contract for every expense, however small. The formalities made necessary by the laws governing Army procurement meant that there was considerable delay in negotiating a new contract as each new phase was begun, and work virtually stopped during these intervals. Since the Army's experimental funds were so slight that it could not afford to give a contract unless a need were conclusively demonstrated, even such obvious precautions as the provision of spare parts to provide for breakage in test were not made by either side. Test facilities were at least an equally serious problem, since the company would not buy special ones and the Army's procurement rules prevented Army payment for them as a cost of development; on occasion they were lent by the Army.

By the time the O-1430 had got through its development test in 1939, if not still earlier, the Army had decided that 1000-hp engines were obsolete for all purposes. As will be explained directly, they had also concluded that the power needed for large airplanes could not possibly be obtained from an engine of the displacement of the Continental even if its power was pushed to the limit of development. Wright Field hoped, however, that the output of this engine could be increased enough over the original aim to suffice for a fighter. Fighter wings were then much too thin to make a submerged installation, and since the opposed engine was an inconvenient type to install in the nose of a single-engine fighter it was decided to develop the engine as a vee. The company would have much preferred a vee of the standard upright type, but the tactical officers of the Air Corps had become convinced that they wanted an inverted vee for improved visibility, [11] and early in 1939 instructions were given to Continental to drop work on the O-1430 and begin work on an inverted IV-1430.

Shortround6 · Aug 2, 2018

Continental had been a major supplier of engines to the car, bus, truck and industrial markets during the 20s. With the Great Depression cutting heavily into the numbers of small manufacturers who contracted their engine production out Continental was looking for new markets.
However Continental didn't seem willing to gamble it's own money on a large/expensive military engine. Both Packard and Curtiss were getting out of the liquid cooled large aircraft engine market with P & W and Wright dominating the Civilian market (and by extension, most of the contermory military market even if not quite what the military wanted).
Continental was quite definitely on a "pay as you go" basis with the US Army.

Zipper730 · Aug 6, 2018

kmccutcheon said:
The Hyper cylinder was to have the same 4 5/8-in. bore as the air-cooled Liberty which had been used in the experiments, but to permit higher speeds of rotation the stroke was to be shortened from 7 in. to 5 in., giving a displacement of 84.0 cu in., or a total of 1008 cu in the 1000-hp 12-cylinder vee-type engine which was to be built around it.

I didn't know the displacement was so little at first

The Army also decided that in order to operate satisfactorily with ethylene glycol at 300° F

What temperatures were seen in coolant in WWII engines?

In 1932 an agreement for the engineering and development of this cylinder and of the engine employing it was reached between the Army and the Continental Motor Company. Continental had been in the 1920.s the most successful manufacturer of engines for automobiles and trucks built by other makers. It had entered the aviation field in 1928 . . .
Continental's role in the Hyper project was essentially to be nothing but routine engineering and testing. The Army not only had decided upon the basic principles and the size of the Hyper cylinder but also had laid down the main lines of the complete engine in which it was to be used, and the first two years of work were actually done in a special office set up by the company in Dayton to be near Wright Field.

Why did they do that? Why not just dictate the basic principles, and horsepower specs and let the contractor do it's job?

The airplane branch at Wright Field, however, was then absolutely convinced that the engines of virtually all future airplanes, including even fighters, would be buried in the wings for the sake of higher speed, and at their insistence the Army specified that the new cylinder be the basis of a "flat" or opposed engine. This was the origin of the Continental O-1430.

I'm confused about this: The V-1710 wasn't an opposed cylinder...

The real difficulty was simply the company's lack of faith, not in the technical soundness of the project, but in the prospect of sales of even a successful product. Even though some engineers at Wright Field believed that engines based on the Hyper cylinder might prove best for all types of combat planes, no one at all foresaw any commercial use

The same problem that other inline manufacturers of the time seemed to run into if I recall.

The formalities made necessary by the laws governing Army procurement meant that there was considerable delay in negotiating a new contract as each new phase was begun, and work virtually stopped during these intervals.

Did this apply to the US Navy as well?

By the time the O-1430 had got through its development test in 1939, if not still earlier, the Army had decided that 1000-hp engines were obsolete for all purposes.

Why didn't they just double the O-1430 into an H-2860? That was done with the V-1710 in the V-3420...

Shortround6 said:
Continental didn't seem willing to gamble it's own money on a large/expensive military engine.

So Continental was the primary decision maker to just build to spec and let the Army do everything?

Continental was quite definitely on a "pay as you go" basis with the US Army.

Okay

wuzak · Aug 7, 2018

Zipper730 said:
I didn't know the displacement was so little at first

I'm shocked!

Zipper730 said:
What temperatures were seen in coolant in WWII engines?

Less than 300°F.

Around 250-260°F for WEP, maybe 220-230°F for continuous.

Zipper730 said:
Why did they do that? Why not just dictate the basic principles, and horsepower specs and let the contractor do it's job?

Because the contractor did not want to do that job.

Lycoming would design its own engine around the Hyper cylinder, but they invested their own money.

Zipper730 said:
I'm confused about this: The V-1710 wasn't an opposed cylinder...

The V-1710 program predated the whole "bury it in the wing" concept.

Zipper730 said:
Why didn't they just double the O-1430 into an H-2860? That was done with the V-1710 in the V-3420...

Continental weren't spending their own money.

The Lycoming O-1230 to H-2470 is better match to your scenario. But the H-2470 was a failure as well.

wuzak · Aug 7, 2018

From de Havilland Mosquito FBVI Pilot's notes (available at wwiiaircraftperformance.org):

Max Climbing (1 hour): 125°C/257°F
Max Continuous: 105°C (115°C)/221°F (239°F)
Combat (5 minutes): 135°C/275°F

The temperature in parentheses for max continuous was fro short periods only.

Shortround6 · Aug 7, 2018

Zipper730 said:
What temperatures were seen in coolant in WWII engines?

They thought that 300 degree temp would allow for smaller radiators due the greater difference between the temps of the coolant and the air flowing through the radiator. What happened was more heat went into the oil and they wound up needing bigger oil coolers that canceled out the smaller radiators.
Don't forget they were using 87 octane fuel (if they were lucky) and low boost too.

Why did they do that? Why not just dictate the basic principles, and horsepower specs and let the contractor do it's job?

Because the contractors didn't want to do the job. The Army was looking for 1hp per cubic inch. The last Curtiss Conquerors built did 700hp for 1570 cubic inches and had a turbocharger (even if it didn't do much at sea level.) but no engine supercharger. The Army "concept" was too far in advance of what was actually going on to make it a good gamble for the private companies. Please remember that this was going on in the middle of the Great depression. Not a good time for risking large amounts of money on experimental projects.

I'm confused about this: The V-1710 wasn't an opposed cylinder...

as mentioned by Wuzak the V-1710 predated the Army hyper project and was started with private funds.

The same problem that other inline manufacturers of the time seemed to run into if I recall.

Sort of. There were only two inline manufactures, Packard and Curtiss. Both had the same problem, their in-line engines (both had two) dated from the earlier/mid 1920s and were becoming obsolete. They were lightly built and would not stand up to the powers desired without substantial redesign (money). Packard had the additional problem of their chief designer dying in an air crash and Curtiss and Wright had merged, the new corporation was quite happy to sell Wright Cyclones and saw no reason to compete with itself.

Why didn't they just double the O-1430 into an H-2860? That was done with the V-1710 in the V-3420...

Timing, if you stack the flat engines they become too fat (high) to stick in the wing anymore and if you flip to vertical they sure won't fit. Lycoming did the stacking and flip to vertical once the army had given up on sticking the engines in the wing. It was also an attempt to salvage some of the money they had poured into the project because the O-1430 was no longer powerful enough to compete. The P & W R-1830 radial had started out as a 750hp engine in the early 30s. it was over 1000hp near the end of the 30s and closing on 1200hp in 1940/41. Same with the Cyclone and the V-1710 not to mention the R-2600 and the R-2180 (which went nowhere but was rated at 1450hp).

The Lycoming project really got started when a few Continental engineers got frustrated with slow progress of the Army/Continental project and jumped ship. They went to Lycoming and got them to drink the kool-aid, They did get government money but Lycoming had dumped over 1 1/2 million dollars of their own money into the project by the end of the 30s.

The Allison was always seen by the Army as the "back-up" plan. The low risk temporary substitute for the hyper engine rather than a true competitor.

Zipper730 · Aug 8, 2018

wuzak said:
Less than 300°F

Had a hunch

From the de Havilland Mosquito FBVI Pilot's notes (available at wwiiaircraftperformance.org):

Max Climbing (1 hour): 125°C/257°F
Max Continuous: 105°C (115°C)/221°F (239°F)
Combat (5 minutes): 135°C/275°F

Was the 300F figure based on combat, max continuous, etc?

Because the contractor did not want to do that job.

Why did they hatch a deal with Continental motors and not just look for another engine contractor if they didn't want to produce the engine?

Lycoming would design its own engine around the Hyper cylinder, but they invested their own money.

Lycoming joined the fray because they knew that their
biggest competitor was working on the hyper-engine. I'm curious if the USAAC knew that Lycoming was Continental's biggest competitor?

Shortround6 said:
They thought that 300 degree temp would allow for smaller radiators due the greater difference between the temps of the coolant and the air flowing through the radiator.

I would have honestly thought that the higher temperature would have required a bigger radiator because you're dispelling more heat into the same air-temperature unless you had a very high airflow rate through the system. And the fact that the oil temperature going up required bigger oil-coolers seems to be an example of this.

Because the contractors didn't want to do the job. The Army was looking for 1hp per cubic inch. The last Curtiss Conquerors built did 700hp for 1570 cubic inches and had a turbocharger (even if it didn't do much at sea level.) but no engine supercharger.

Was the technology developed on the hyper-engine ever planned to be used for civilian aircraft?

The Army "concept" was too far in advance of what was actually going on to make it a good gamble for the private companies.

And Lycoming only was interested because Continental was involved right?

Sort of. There were only two inline manufactures, Packard and Curtiss. Both had the same problem, their in-line engines (both had two) dated from the earlier/mid 1920s and were becoming obsolete. They were lightly built and would not stand up to the powers desired without substantial redesign (money). Packard had the additional problem of their chief designer dying in an air crash and Curtiss and Wright had merged, the new corporation was quite happy to sell Wright Cyclones and saw no reason to compete with itself.

Plus the NACA cowling. That started seeing routine use since 1932 right?

The Allison was always seen by the Army as the "back-up" plan. The low risk temporary substitute for the hyper engine rather than a true competitor.

That makes more sense, but one also needs to know that the first hyper-concept was V-cylinder too. The flat-cylinder thing seemed to have taken hold around the early 1930's.

Did the RAF have a similar interest in flat cylinders?

wuzak · Aug 8, 2018

Zipper730 said:
Was the 300F figure based on combat, max continuous, etc?

It was the maximum temperature, so it would have been at the engine's highest rating.

The downside was that more heat was rejected to the oil, which, consequently, required a larger radiator for cooling. This negated the gains on the coolant raidator.

Zipper730 said:
Why did they hatch a deal with Continental motors and not just look for another engine contractor if they didn't want to produce the engine?

Perhaps because Continental was scratching around for work and other manufacturers weren't.

It wasn't that they didn't want to make the engine, it was that they didn't want to spend their own money on the engine.

Zipper730 said:
Lycoming joined the fray because they knew that their
biggest competitor was working on the hyper-engine. I'm curious if the USAAC knew that Lycoming was Continental's biggest competitor?

Can't speak to that.

The USAAC probably did not give a shit about who was Continetal's biggest competitor.

Zipper730 said:
I would have honestly thought that the higher temperature would have required a bigger radiator because you're dispelling more heat into the same air-temperature unless you had a very high airflow rate through the system. And the fact that the oil temperature going up required bigger oil-coolers seems to be an example of this.

The heat exchange rate increases with the temperature difference.

Though the coolant was operating at higher temperatures, it was not rejecting more heat. There is a balance between the heat in the combustion chamber, the work done by the cylinder and the heat rejected through coolant and oil.

The higher temperature in the coolant reduced the temperature difference between the combustion chamber and coolant, reducing the heat flow rate into the coolant. The heat not rejected to coolant had to go somewhere - it happened to go to the oil.

So the coolant radiator had to reject less heat to the air while the oil cooler had to reject more coolant to the air. So the oil cooler had to be bigger.

Zipper730 said:
Was the technology developed on the hyper-engine ever planned to be used for civilian aircraft?

No. It was a strictly military engine.

Highly stressed, small capacity engines were not the best for commercial aviation.

Zipper730 said:
And Lycoming only was interested because Continental was involved right?

More likely they could see the potential earnings if their engine was a success and was ordered in large quantities by the Army.

Zipper730 said:
Plus the NACA cowling. That started seeing routine use since 1932 right?

Not real sure what that has to do with the hyper engine.

Zipper730 said:
That makes more sense, but one also needs to know that the first hyper-concept was V-cylinder too. The flat-cylinder thing seemed to have taken hold around the early 1930's.

Did the RAF have a similar interest in flat cylinders?

No.

Zipper730 · Aug 8, 2018

wuzak said:
It was the maximum temperature, so it would have been at the engine's highest rating.

Makes sense

Perhaps because Continental was scratching around for work and other manufacturers weren't.

Understood

It wasn't that they didn't want to make the engine, it was that they didn't want to spend their own money on the engine.

I'm confused, I thought when a project was government funded, the government dictates the requirements (specified power/displacement, cylinder design principles, coolant temperature requirements, etc), the corporation designs it and builds it.

The heat exchange rate increases with the temperature difference.

Okay

Though the coolant was operating at higher temperatures, it was not rejecting more heat.

So it was unable to dump the heat into the airflow, and as a result the radiator had to either be made bigger, or the heat went into the oil and that made the oil hotter and needed a bigger cooler since it would only dispel so much heat?

No. It was a strictly military engine.

I was just curious because there was an entry on Wikipedia (yeah I know they're not necessarily reliable) that stated

"The hyper engine was a 1930s study project by the United States Army Air Corps (USAAC) to develop a high-performance aircraft engine that would be equal to or better than the aircraft and engines then under development in Europe. The project goal was to produce an engine that was capable of delivering 1 hp/in3 (46 kW/L) of engine displacement for a weight of less than 1 lb/hp delivered. The ultimate design goal was an increased power-to-weight ratio suitable for long-range airliners and bombers."

More likely they could see the potential earnings if their engine was a success and was ordered in large quantities by the Army.

Makes snese

Not real sure what that has to do with the hyper engine.

It had to do with the effectiveness of radials which increased their demand over inlines

No.

I guess they realized it wouldn't do any good. Interestingly they were for H-cylinders.

wuzak · Aug 8, 2018

Zipper730 said:
I'm confused, I thought when a project was government funded, the government dictates the requirements (specified power/displacement, cylinder design principles, coolant temperature requirements, etc), the corporation designs it and builds it.

The engine was designed by the Army. Continental basically operated as the Army's experimental shop. Factories were built for production of teh engine, but they were all government funded too.

Zipper730 said:
So it was unable to dump the heat into the airflow, and as a result the radiator had to either be made bigger, or the heat went into the oil and that made the oil hotter and needed a bigger cooler since it would only dispel so much heat?
I was just curious because there was an entry on Wikipedia (yeah I know they're not necessarily reliable) that stated

No, you've got it wrong.

The heat of combustion has three ways to exit the chamber. Through the coolant, through the oil and through work done on the piston (ie power).

The higher temperature of the coolant lowers the heat transfer to the coolant, which means the heat difference is transferred elsewhere - and th eeasiest route out was through the oil.

The higher temperature of the coolant made for greater heat transfer rates to the air, which enabled a smaller radiator.

But the oil cooler had to reject more heat, so it had to be made bigger.

Zipper730 said:
I guess they realized it wouldn't do any good. Interestingly they were for H-cylinders.

I don't think that the RAF, Air Ministry, or whoever, was dictating the engine layout.

The Dagger, Rapier and Sabre all came from one company and one designer. The concept was for the maximum number of cylinders in the smallest space.

Then there was the Fairey P.24, which was a H engine, but essentially two separate engines in one crankcase, each half operating as an opposed 12. That went nowhere.

And there was the Rolls-Royce Eagle 22. Similar in layout to the Sabre.

I'm not familiar with any other H engines.

Notably, none of them started as an opposed 12 cylinder engine (8 in the case of the Rapier). The Fairey P.24's halves were based on the P.12, a V12 engine.

Rolls-Royce were more in favour of the X layout.

When developing the F engine (became the Kestrel), Rolls-Royce also built an X-16 engine, the Eagle XVI. It was not a flight worthy engine, and was dropped as the airframe manufacturers preferred the narrower V12 F engine.

In the '30s they built the Exe and Vulture. Late in the war they built the prototype Pennine - an air cooled, sleeve valve X-24 of 2,750 cubic inches producing 2,800hp in early development.

The government didn't dictate the shape of the engines, but they did dictate some aspects.

The original idea behind the small diameter 21 cylinder Armstrong-Siddeley Deerhound was that it would be liquid cooled. But the government wanted them to make air cooled engines in competition with Bristol. Napier and Rolls-Royce were the major liquid cooled engine manufacturers.

Zipper730 · Aug 8, 2018

wuzak said:
The engine was designed by the Army. Continental basically operated as the Army's experimental shop. Factories were built for production of teh engine, but they were all government funded too.

I'm confused, you said they didn't want to spend money to build the engine right? If that's so, why didn't the US Army just give them an outline of what they wanted and let Continental design and build it?

I think we might be running into some sort of communications gulf

No, you've got it wrong.

The heat of combustion has three ways to exit the chamber. Through the coolant, through the oil and through work done on the piston (ie power).

The higher temperature of the coolant lowers the heat transfer to the coolant, which means the heat difference is transferred elsewhere - and th eeasiest route out was through the oil.

I figure if the coolant was *hotter* there would be more heat transfer until it can't absorb anymore? Still if it got too hot, it'd probably go into the oil since the engine's being lubricated by the stuff.

The higher temperature of the coolant made for greater heat transfer rates to the air, which enabled a smaller radiator.

Of course, but I would have figured that the air would only be able to easily absorb so much heat per square foot of surface area...

I don't think that the RAF, Air Ministry, or whoever, was dictating the engine layout.

Okay, so it was a mistake for the USAAF to do this?

wuzak · Aug 8, 2018

Zipper730 said:
I'm confused, you said they didn't want to spend money to build the engine right? If that's so, why didn't the US Army just give them an outline of what they wanted and let Continental design and build it?

Continental did not want to spend Continental money on building the engine. They had no interest in the engine beyond contracting for the Army.

If the Army gave Continental an outline of what they wanted it is doubtful Continental would have proceeded with any design work.

wuzak · Aug 8, 2018

Zipper730 said:
I figure if the coolant was *hotter* there would be more heat transfer until it can't absorb anymore? Still if it got too hot, it'd probably go into the oil since the engine's being lubricated by the stuff.

There are two heat transfers at play with the coolant.

From the combustion chamber to the coolant.
From the coolant to the outside air.

Higher coolant temperatures slow the heat transfer for 1 and speed up the heat transfer for 2.

Because 1 is a slower rate less heat is rejected to the coolant and thus less heat is rejected to the air, even if the rate is increased because of the temperature.

Zipper730 said:
Of course, but I would have figured that the air would only be able to easily absorb so much heat per square foot of surface area...

It depends also on the mass air flow through the radiator, the speed at which the air crosses the radiator surfaces, air temperature, humidity, coolant temperature, radiator material properties, and probably many other factors.

Zipper730 said:
Okay, so it was a mistake for the USAAF to do this?

Hindsight affords us that perspective.

At the time the wings were still thick, the nacelle designs were not the best and buried engines offered a possible aerodynamic advantage.

It proved to be negligible in practice, and the cons outweighed the pros.

Shortround6 · Aug 8, 2018

Zipper730 said:
Was the technology developed on the hyper-engine ever planned to be used for civilian aircraft?

The Army may have hoped it would be used since more engines sold would lower their own unit costs. I am not sure civilian use ever went past a few fanciful sketches/drawings.

Zipper730 said:
And Lycoming only was interested because Continental was involved right?

Lycoming and Continental were not the big rivals in the late 20s and early 30s that they would later become. Each started the 30s with a smallish (there were certainly smaller) radial, about 165hp for Continental and about 200hp from Lycoming. These engines were unsupercharged. Continental introduced the A40 flat four engine at 37hp

which was a pretty crude, if effective engine in 1931. Lycoming would not introduce a flat four until 1938. During the 30s there were several other engine makers that disappeared during /just after WW II, like Jacobs and Kinner. Franklin came in at the end of the 30s and was quite successful for a few years.

Zipper730 said:
Plus the NACA cowling. That started seeing routine use since 1932 right?

The NACA cowling was a big advance but many people tend to think it was a one shot deal, NACA cowling is introduced and presto, everything changes and then stays the same.

See; NACA cowling - Wikipedia

for starters. The original NACA cowling was up against water cooled engines, engine/radiators had to be drained and refilled in freezing temperatures if not kept warm. Pressurized cooling systems were not in use so max coolant temperature was 212 degrees at sea level, less as the plane climbed, so large radiators (and lots of heavy water) were needed.

The early NACA cowling lacked two basic things that later became standard.
1. was any internal baffles.

They didn't know it then but any air that is more than about 3/16ths of inch away from the engine does nothing to cool it. There was still a lot of air flowing though the early NACA cowling doing nothing but creating drag.
2. There was no way to regulate the temperature of the engine. it would be 1935 before the first adjustable flaps on the rear of the cowling would be used to control the airflow for different flight conditions. Cowling and airflow (drag) had to be set up for worst case condition (full power climb on a hot day).

During this time teh use or prestone stopped the need to drain radiators and allowed the higher coolant temperatures that allowed smaller radiators.

Zipper730 · Aug 8, 2018

Shortround6 said:
The Army may have hoped it would be used since more engines sold would lower their own unit costs. I am not sure civilian use ever went past a few fanciful sketches/drawings.

That wasn't the point, I was simply curious about what the intent was.

Lycoming and Continental were not the big rivals in the late 20s and early 30s that they would later become.

Okay

The NACA cowling was a big advance but many people tend to think it was a one shot deal, NACA cowling is introduced and presto

If I recall, I said that they appeared around 1932 and that many engines were fitted with it by that point.

There was no way to regulate the temperature of the engine. it would be 1935 before the first adjustable flaps on the rear of the cowling would be used to control the airflow for different flight conditions. Cowling and airflow (drag) had to be set up for worst case condition (full power climb on a hot day).

I always though that in an effort to keep the airflow moving fast through the back portion of the cowl, they wanted to keep narrowing it down but it wouldn't work at lower speeds so they'd open the cowl up to allow it through

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