Afterburning Sabre comment & a Big Opportunity 

To allow expansion of the sonic speed but elevated pressure exhaust, you need a divergent section after the end of the convergent section. This allows expansion and further acceleration of the gases to supersonic speed. Without a so called Con-Di nozzle, all that extra fuel just makes more heat and more noise, as the gases expand in all directions after leaving the engine. In a rocket engine, the -di part of the con-di nozzle, is that bell shape...

I believe a plane can exceed Mach 1 despite the exhaust traveling subsonic by increasing the mass of air it propels backwards. Increasing momentum can only be done two ways. You either increase velocity or you increase mass. I'm probably oversimplify, and hopefully I'm not to out of the ballpark, but let's assume the simplest model of a a jet moving forward only due to the exhaust sent backwards. Every action has a reaction. To move the mass of the plane forward faster you have to increase your momentum going forward and you do that by sending air backwards with enough momentum so that you accelerate. Any momentum change of the exhaust changes the momentum of the plane here, no matter what the velocity is at a particular moment. Momentum (p) = mass (m) times velocity (v). Since we assume the plane only gains momentum from the exhaust we can say that the momentum of the plane moving forward is equal and opposite of the momentum of the exhaust jet moving backwards. So, momentum (plane) = -momentum (exhaust). Since momentum is equal to mass times velocity we can say that p(plane) = -p(exhaust) and since p=mv so then get m(plane)*v(plane)=-m(exhaust)*v(exhaust). To simplify we can just assume here that the mass of the plane doesn't change, so any increase in momentum will increase it's velocity. We can see from the equation that it doesn't actually matter what the velocity is of the exhaust gas moving backwards, any momentum sent backwards will increase our momentum forwards. We can increase the momentum of that exhaust (which creates the plane's momentum) by either increasing the velocity of the exhaust gas moving backwards or increasing the mass or amount of exhaust gas moving backwards. There are physical issues with attempting to move exhaust gas at supersonic speeds, so the only way to efficiently and effectively move the plane faster is to increase the amount or the mass of exhaust you are moving backwards (assuming we're exhausting the gas backwards at some constant and ideal subsonic speed). Even if the exhaust is going 100 mph, as long as I can move enough of it backwards at 100 mph, I can go as fast as I want. So if my exhaust is stuck moving at Mach 1 and I want to go Mach 2, I'll have to move double the mass or amount of air going Mach 1 out the back. So you'll have to accelerate 4 tons instead of 2 tons. Additionally, it does not matter what speed you are moving mass backwards, you'll still gain speed. If I'm stuck on a barrel full of apples in space I can change my velocity and momentum by throwing. Even if I'm already going 100 km/s, if I throw an apple backwards at 1 kph I'll still travel ever so slightly faster in the forwards direction. Your momentum will change no matter how slow I'm throwing it. In fact, I could travel forwards at half of light speed by only throwing apples backwards at 1 mph, as long as I had enough apples. Even if the apple is still moving forward after I throw it, I'm still pushing off and slowing down that apple when I throw it. So if I'm traveling 1000 mph forward and I have an apple with me that means it's also moving forwards at 1000 mph. After I throw it backwards at 1 mph, that means the apple is now moving forward at a slightly slower speed of 999 mph and I'll be moving forward a little faster at 1000.000000000001 mph. I changed the momentum of the apple, so my momentum will also change no matter what the speeds are and even if the vehicle and exhaust are still traveling in the same direction after combustion. Edit: This is just to explain how something can go faster than velocity of gas sent out the back. Obviously, things get way more complicated than I could understand and jet engines have complex interactions with changing temperatures, pressures, volume, velocity, mass for rate, etc that is even more complicated as it also interacts with the atmosphere. From my understanding the speed comes from moving has backwards and it's not created by the exhaust pushing off of the air. You do have to consider exhaust pushing off the atmosphere in that the outside air affects and changes how much as how fast you move exhaust gas at the nozzle. To maximize and optimise the thrust you send backwards you have to get the exhaust to the optimum parameters so that the atmosphere doesn't steal to much energy from the exhaust. You want the energy of combustion to only go into changing the exhaust momentum, but they every can get to it increasing temperature or changing volume or pressure instead of going into overall momentum change. I hope I'm not to far off here.

Herewith a short answer to gettinsmeegy. What most people don't get is the fact that the speed of sound in the hot exhaust is much higher than the speed of sound at ambient atmospheric temperatures. So, even with a convergent final nozzle, where the gas velocity at the nozzle exit plane cannot exceed Mach 1, the aircraft can fly at supersonic speeds. UK subscribers will understand if I say, "Simples!"

@@zlm001 Herewith an edited comment. A jet aircraft can't go faster than the velocity of the hot gas from the jet exhaust in controlled, sustained flight, with the engines continuing to produce useful thrust: that would be a physical impossibility. It could happen in a dive, but then the engines would effectively be causing drag. A rocket vehicle in space can travel faster than the rocket engine's exhaust velocity,, but an air-breathing jet engine in earth's atmosphere can't, while continuing to produce useful thrust. I've now provided more detail in another comment. PS At risk of labouring the point, to produce thrust, a jet engine must always have an exhaust velocity greater than the forward speed of the aircraft. If in an extreme case, such as in a dive where the speed of the aircraft is greater than the jet velocity, the engine (if it is still running) will not be producing useful thrust.

@@zlm001 OK, so let's get your understanding of a jet engine sorted, in terms of the basic principles of how it produces thrust. You have a basic understanding of how a rocket engine works. It carries all the material that it ejects in its exhaust and to which it adds momentum, by accelerating it through a con-di (convergent-divergent) nozzle. So far so, good - but not good enough in respect of a jet engine. Fundamentally, what you haven't accounted for is the simple fact that a jet engine is working with air. It is the air to which it adds momentum, by burning a relatively small amount of fuel in it and accelerating it through a final nozzle. This can be convergent or, more often, con-di in the case of an engine with reheat/afterburning. So, imagine a jet engine operating at, say, 600miles/hr and the air is entering the aircraft intake at 600miles/hr. If the exhaust velocity is 600miles/hr, would it be producing any thrust? No! There would be no increase in momentum of the air passing through it. Double the mass flow with the same inlet and exhaust velocities and there would still be no thrust. So what would happen if the exhaust velocity was, say, only 500miles/hr? This would mean that the air was being slowed down (relative to the aircraft), and its momentum reduced. In other words, this would result in a drag force on the aircraft. To produce any thrust, a jet engine must have an exhaust velocity greater than its intake velocity. So am I getting my message across? There is an equation I know as the Froude Equation. This quite simply defines the propulsive efficiency of a jet engine by the difference between the velocity of the exhaust relative to the velocity of the aircraft (other Froude Equations are available). It shows that propulsive efficiency increases the lower the difference between the two (and that's the reason why big turbofans are more efficient than turbojets). However is also shows that propulsive efficiency is 100percent when the two are equal. But this must mean than when propulsive efficiency is 100percent, there is no momentum increase in the exhaust and no thrust. Yes!

I recommend NASA's educational pages for most things about jets and rockets.

Eg. 500C -> 1000C air will half it's density (it takes up twice as much room) and will raise it's speed of sound by 300mph (allowing it to go 300mph faster before it reaches Mach 1.0)

@@yousausage The increase in mass flow due to the additional fuel is second order relative to the increase in velocity of the flow.

Having read the comments that have been posted, I hope you are more clued up now. The gas flow out of a convergent nozzle can't go faster than Mach 1, but the speed of sound in hot air at 600degC is over 1,300miles/hr, so the exhaust velocity out of the jet pipe of an Orenda 14 at max thrust could be up to this speed. That same stream of hot gas could be accelerated to faster than the speed of sound by adding a divergent section to the nozzle. I'll state the basics about nozzles and diffusers flowing a gas. A subsonic nozzle is convergent: a supersonic nozzle is divergent. A subsonic diffuser is divergent: a supersonic diffuser is convergent. For anyone who isn't involved in fluid dynamics, etc, these facts may seem ridiculous - but that's the truth!

Even better that such domination is by a small town in the middle of nowhere in Canada :-)

Have a look at my vid: Jet Engine Lube System

Thanks. I'll have to check it out.

Bits and pieces of the design have been built and tested, but a complete engine does not exist.

@@AgentJayZ sadly yeah, my brain just thought of that dumb joke upon seeing the title. Jokes aside though i do really hope it gets funded and made. A Look at all it’s mechanisms, *and seeing the thing fly* would be amazing. Sadly short of maybe Military uses, it is a bit impractical with how Vertical Takeoff Vertical Landing Reusability has developed. I think the company is now mainly leaning into use of their tech for Heat Exchangers and such, and most of the rocket/jet tech related to Sabre is in an archive somewhere.

The Lightning had a much later mark of Avon, which would probably have had too much dry thrust for the Sabre. In any case, it would probably have needed major changes to the engine mountings, the engine bay and the back end of the aircraft, not to mention the aircraft systems. PS The maximum dry thrust of the Avon used in the Lightning was 12,690lb, according to Wikipedia, and for the Orenda 14, 7,500lb.

It simply limited the amount of thrust augmentation to around 10 to 15percent. Anymore than this demanded an adjustable/variable nozzle.

The J47 was a little more efficient and had slightly more thrust than the Klimov VK-1 (a reverse-engineered Nene with a few 'tweaks'). It was longer and thinner, but it was significantly heavier.

@@grahamj9101 I didn't know Rolls-Royce nene turbojet copy Russians name thanks for that When the f-86 sabre was first rolled out it was not a match for the MiG 15 until the pitched wings and the all moving elevators M2 50 BMG x6 Against Russian Canon pilots report rounds like golf balls flying by canopy Cheers fella

Show me where I can find out more.

Wiki says the F86D used a J47-17 with afterburner which was rated at 5425 lbs thrust. That's the normal thrust for a J47 without any afterburner. So they are mistaken. They say later production examples used the J47-33, with 5,550 lbs thrust. That's what they make in our test cell, no reheat anywhere to be seen. I have posted test runs of J47s that I have built. Using the general 50% boost in thrust that an afterburner provides, an output of over 8,000 lbs would be expected from a reheat-equipped J47. I have never seen any documentation of such an engine, so I would love to see some.

​@AgentJayZ The J47-GE-17B was indeed afterburning. I believe 5425 dry and 7500lbs wet was the rating. It did have a very basic electronic fuel control also. Some old movies of Saber Dogs showed actual flames out tail pipe! Great work you guys do up north! Thanks for the channel!

The J73 was developed from the J47-21. It did have an afterburner, The -17B was nothing special. Wike claims the J47-17 had a "wet" thrust rating. I have taken apart a -17, and it had water injection to the combustors, which increased the thrust. This may have been confused by some who would love to think that meant afterburning. It does not. Water injection described as wet... Afterburning described as wet... Not the same thing.

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