Solid state propulsion: a ramjet aircraft WI

Hendryk

Banned
The theory behind the ramjet dates from the early years of powered flight, when French engineer René Lorin first thought of applying the compression-combustion-expansion thermodynamic cycle to aircraft propulsion in 1908. The problem was that such a jet engine required a minimum speed to kick in that was unattainable at the time, and the idea was shelved until its rediscovery by another Frenchman, René Leduc, in 1935.

Ramjet_operation.png


Leduc was a firm believer in the potential of ramjet propulsion for fighter aircraft, and proceeded to develop prototypes. The first one, the Leduc 0.10, finally flew in 1949. Further prototypes were assembled in the following years, the 0.16, 0.21 and finally the 0.22, which used a dual propulsion system--a classic turbojet engine to reach the required speed threshold, and the ramjet itself. Some 30 test flights took place, but in 1956 the cash-strapped French government stopped funding the project.

But what if the ramjet concept had generated more interest both in France and abroad? Could it have successfully competed against the classic turbojet concept for fighter aircraft? Would it have found a niche, perhaps for interceptors?

Here's what the 0.22 looked like. Note the cockpit located in the inner wedge.

leduc_022.jpg


leduc_022_1.jpg
 

Hendryk

Banned
Something worth mentioning is that, while the first experimental flight of the 0.10 only took place in 1949, Leduc's research was actually pretty advanced before the war, and the prototype was almost ready by 1940. At that point, German advance required the Breguet facilities (where Leduc was working) to be hastily moved from Villacoublay to Toulouse, and once there a bombing raid destroyed the prototype--on the plus side, this prevented its falling into German hands. In other words, the ramjet suffered from poor timing and/or location, and if one pushes forward the beginning of Leduc's work by a year or two, this may have made a significant difference.

Had a complete prototype been ready in 1940 and shipped off to Britain to continue development, what could have happened?

Here's a French website on Leduc.
 

MrP

Banned
That's rather a delightful design, I must say. I can't but wonder if some of the '60s Dan Dare spaceships were based on it.
 

Thande

Donor
Interesting WI. I suspect ramjets of that type would be too specialised to compete with turbojets - they're closer in concept to rocket-powered aircraft. I do wonder if a design like the prototype shown here could have formed the basis for an unmanned missile, though...
 

Hendryk

Banned
That's rather a delightful design, I must say. I can't but wonder if some of the '60s Dan Dare spaceships were based on it.
I wonder whether it might look even better with the type of delta wings that Dassault was putting on its Mirage series at the time.

s022-2.jpg


Interesting WI. I suspect ramjets of that type would be too specialised to compete with turbojets - they're closer in concept to rocket-powered aircraft.
If there's one type of aircraft that could use the ramjet, I believe it's an interceptor. In theory, it's possible to push the ramjet up to Mach 5, though that was never attempted with Leduc's prototypes, as the structural stress of hypersonic flight would have certainly torn them apart.
 

Thande

Donor
If there's one type of aircraft that could use the ramjet, I believe it's an interceptor. In theory, it's possible to push the ramjet up to Mach 5, though that was never attempted with Leduc's prototypes, as the structural stress of hypersonic flight would have certainly torn them apart.

Well yes, but I think it would have to be a fairly specialised interceptor, again similar to the rocket ones of OTL - the German Me 163 Komet or the (cancelled by one of our idiotic governments) British Saunders-Roe SR.117.
 
this TL can work !
had René Lorin better support, France had Ramjet or Pulsjet plane in World War One

but Ramjets (Pulsjets) start to work on speed of 150 mph (240 km/h)

launch from a catapult or Aircraft is need
maybe launch from Big gun for Ramjet Grenade ?

but major problem is the building materials !
the Aircraft from WW1 are build from wood frame labels with textile and stabilizes by wire !
imagine a so build Ramjet or pulsjet Aircraft with speed of 373 mph (600 km/h)

they have to change to duralumin fuselage !

wat about that ?
a French V-1(Fieseler Fi 103) like Aircraft used on front against germany troops.
 

Hendryk

Banned
this TL can work !
had René Lorin better support, France had Ramjet or Pulsjet plane in World War One
If you can manage that, more power to you; personally, I'd be content enough with operational ramjet aircraft in the early post-WW2 years, so the ramjet and turbojet technologies develop simultaneously.

As you say, WWI-era planes being made mostly of wood and canvas, I don't think one could realistically have a ramjet aircraft that early; for one thing, it would either have to be dual-powered with a propeller in order to reach threshold speed, or be thrown into freefall from a blimp :eek:

Incidentally, could Howard Hugues have got word of it circa 1938 and decided to develop a racing plane with it?
 
What is the liter of fuel burn rate vs kilogram of thrust for the ram jet versus the turbojet? Are ramjets throttlable? Or are they just balls to the wall? IMO ramjets are the two stroke engines of the jet engine community. Sure they are simpler but that simplicity means you give up other certain capabilities. Besides in pre WWI the metalurgy of the time was no where near what is required for a jet engine. Whittle was not the first to consider the turbojet after all.
 

Hendryk

Banned
What is the liter of fuel burn rate vs kilogram of thrust for the ram jet versus the turbojet? Are ramjets throttlable? Or are they just balls to the wall?
As a layman, I can't answer that, but this is what I found on the NASA website:

A ramjet engine provides a simple, light propulsion system for high speed flight. Likewise, the supersonic combustion ramjet, or scramjet, provides high thrust and low weight for hypersonic flight speeds. Unlike a turbojet engine, ramjets and scramjets have no moving parts, only an inlet, a combustor that consists of a fuel injector and a flame holder, and a nozzle. How do ramjets and scramjets work?

When mounted on a high speed aircraft, large amounts of surrounding air are continuously brought into the engine inlet because of the forward motion of the aircraft. The air is slowed going through the inlet, and the dynamic pressure due to velocity is converted into higher static pressure. At the exit of the inlet, the air is at a much higher pressure than free stream. While the free stream velocity may be either subsonic or supersonic, the flow exiting the inlet of a ramjet is always subsonic. The flow exiting a scramjet inlet is supersonic and has fewer shock losses than a ramjet inlet at the same vehicle velocity. In the burner, a small amount of fuel is combined with the air and ignited. In a typical engine, 100 pounds of air/sec. is combined with only 2 pounds of fuel/sec. Most of the hot exhaust has come from the surrounding air. Flame holders in the burner localize the combustion process. Burning occurs subsonically in the ramjet and supersonically in the scramjet. Leaving the burner, the hot exhaust passes through a nozzle, which is shaped to accelerate the flow. Because the exit velocity is greater than the free stream velocity, thrust is created as described by the general thrust equation. For ramjet and scramjet engines, the exit mass flow is nearly equal to the free stream mass flow, since very little fuel is added to the stream.

The thrust equation for ramjets and scramjets contain three terms: gross thrust, ram drag, and a pressure correction. If the free stream conditions are denoted by a "0" subscript and the exit conditions by an "e" subscript, the thrust F is equal to the mass flow rate m dot times the velocity V at the exit minus the free stream mass flow rate times the velocity plus the pressure p difference times the nozzle exit area:

F = [m dot * V]e - [m dot * V]0 + (pe - p0) * Ae

Aerodynamicists often refer to the first term (exit mass flow rate times exit velocity) as the gross thrust, since this term is largely associated with conditions in the nozzle.

The second term (free stream mass flow rate times free stream velocity) is called the ram drag. This term can be quite large for scramjet engines.
For ramjets and scramjets, the nozzle exit velocity is supersonic, and the exit pressure depends on the area ratio between the throat of the nozzle and the exit of the nozzle. Only for a unique design condition is the exit pressure equal the free stream static pressure. For all other conditions, we must include the third term of the thrust equation (exit pressure minus free stream pressure times the exit area). This pressure correction is usually small compared to the first term of the thrust equation. But for completeness, this term is usually included in the gross thrust.
 

Thande

Donor
As you say, WWI-era planes being made mostly of wood and canvas, I don't think one could realistically have a ramjet aircraft that early; for one thing, it would either have to be dual-powered with a propeller in order to reach threshold speed, or be thrown into freefall from a blimp :eek:
I think someone did some discussion a while ago about that Romanian bloke who tried to put an early jet engine on a WW1-era plane...

Mind you, your airship carrier freefall thing is a very AH.com solution :D And the Americans did try launching planes from airships in the 1930s...
 

Hendryk

Banned
Mind you, your airship carrier freefall thing is a very AH.com solution :D And the Americans did try launching planes from airships in the 1930s...
Well, when you want something to move at fast speed, the easiest way is to drop it from a great height. I just wouldn't want to be the test pilot, who'd be stuck in the perverse paradox of hoping his plane falls fast enough for the ramjet to start up, lest he crashes to the ground.

Leduc's early prototypes didn't have a secondary jet engine, so they had to be launched from a motherplane:

Leduc010.jpg
 
Ramjets are horribly inefficient; the _only_ time you'd ever actually want to use them is if you have a combustion temperature/velocity greater than a turbine can handle. With modern metallurgy, that effectively means at speeds greater than about Mach 3 (thus scramjets). Turbine designs are catching up, though, and I wouldn't be surprised if the first commercial hypersonic aircraft isn't a scramjet...

Simon ;)
 
A ramjet replaces the turbine in an ordinary jet with an air stream caused by the planes movement. I think that means thet the ramjet is more sensitive to quick changes in aircraft directions so it would be a huge disadvantage in a dogfight which rule it out before a efficient guided missile is developed and a lot longer due to institutional inertia. Military pilots still practice dogfighting a lot.

So the best bet is some kind of space application which way cooler anyway.
 
The Romanian fellow was that Coanda guy. The Coanda-1910 aircraft had a motorjet. It set itself on fire during the first taxi test, but at least Coanda figured out the Coanda effect as a result. (Fluid flows stick to surfaces. Put the bowl of a spoon in a narrow stream of water from the tap...)

Anyway, not really. Ramjets are suitable for some specialist applications, but they have numerous disadvantages. There's a minimum speed, many designs are prone to blow-outs during maneuevers...they were, in my opinion, about as widely used as was practical in OTL.

The SR-71's J58 engines were unique...mixed-cycle propulsion. There was a turbojet core, but a ramjet was wrapped around that, and there were some sophisticated variable-geometry intakes. At high speed the turbojet core didn't even do most of the work; the intake chines did, or something like that. (What the hell is a "chine," anyway?)

Also, there were plenty of ramjet-powered missiles. Perhaps ICBMs are delayed and there are more intercontinental strategic cruise missiles, and supersonic ones. There were several SAMs that used ramjets...the CIM-10 Bomarc, for example, and a few Soviet designs.

They're good for high-speed flight. From what I recall, though, in the wars that actually ended up being fought, that supersonic capability wasn't used that much.
 
There was no lack of ramjet-powered projects. Some were paper projects, like the German Focke-Wulf Super Lorin
jglor-3.jpg


or the British Hawker P. 1134, a mixed powerplant project with both turbojet and ramjets.

Hawker P. 1134 i1 auf der Rollbahn.jpg
 
This French aircraft, the Nord Aviation 1500-02 Griffon was actually built and flown as a prototype and was the unsuccessful rival to the highly successful (turbojet) Dassault Mirage IIIC. It also was a turbojet / ramjet mixed powerplant design.

Nord 1500-02 Griffon Flugphoto schwarzweiß 2.jpg
 
A Japanese ramjet interceptor project from World War II, the Kayaba Katsuodori - it remained a paper project.

Kayaba Katsuodori.jpg
 
Top