Vocal Voices

Mirror headline

Russian military jet 'accidentally shot down by Syrian defences'

The picture.



Yes, really, those are propellers….

Head in hands muttering about why he never listens to a thing they say.....

It is pretty bad.
Interestingly other sources are saying that it was shot down by the Israelis.

Confusing, isn't it?

Yes, those are propellers, but the engine is, technically, a jet, a gas turbine. It has a single shaft containing intake fan, compressor, combustion chamber, turbine and exhaust. It works to the same basic principles as what we more commonly call "jets" except that the thrust comes from a propeller mounted front or rear, unlike a turbojet or turbofan. In the trade it is known as a turboprop.

The Russians claim if was a "friendly-fire" incident caused by Israeli F-16 attacking Iranian posts near Latakia and it reserves the right to "take action".

Well technically it's a TurboProp, just a propeller plane driven by a more efficient engine. A jet is reserved for planes driven by the air flow through the inside of the engine and not from the air flow over propellers driven by the engine, but outside of the engine.

Ok so I'm a pedant. But they should know better.

Bunch of numpties.

Yes that's going to cause a bit of kerfuffle. If they do attack the Israeli planes, we'll find out just how good the Israeli F16's are. We do know that Israel updates the tech in the equipment they buy from America so it will be an interesting exercise.. We also know that Israel follows the US model of sending in SAM hunting aircraft first, to kill the missile systems, before attacking in force. So far Israel has been working on the basis that the SAM systems are nothing to worry about. If they decide that the SAM systems are a problem, they'll destroy them first.

Ah, pedantry. I can do that.

Suff, you are right about an axial flow jet where everything is contained in what is like one big venturi tube. It gets all its thrust from the exhaust gases exiting the turbine. However, not all fuel is burnt so some have afterburners for extra thrust, and this can also be increased by adjusting the diameter of the exhaust tube outlet. A pure 'jet' if you will.

Now, let's look at a turbofan. It also has an axial flow jet at its core, but it also has a separate outer casing, which holds the core. At its intake it has a huge centrifugal impeller which funnels air into the outer casing. This air by-passes the axial flow core hence why they are sometimes known as by-pass turbines. The by-pass air meets the exhaust gases as it exits the chamber and becomes a super-heated gas, which expands very quickly to create thrust. It is never ignited. Turbofans offer economy over long distances at speeds below Mach.

Turboprops, the propeller jobs, also have an axial flow jet at their core. It works similar to standard except that its fuel burn and turbine are more efficient. This allows for greater torque than thrust to allow a propeller to turn through a reduction gearbox. The propeller differs from tradition in that it has variable pitch blades to alter their thrust at constant revs from the jet engine. This provides a stable platform at speeds of ~350kt (400mph) and at altitudes of ~ 6,000m (20,000ft). Their endurance time is longer for the same amount of fuel making them ideal for recon aircraft like the Il-20M.

In all cases they are jets (gas turbines) of some description just like most common Diesel and petrol engines are reciprocating I.C.Es. even when they are super or turbocharged.

Yup, pedantry...

Jet engine..

A jet engine is a type of reaction engine discharging a fast-moving jet that generates thrust by jet propulsion. This broad definition includes airbreathing jet engines (turbojets, turbofans, ramjets, and pulse jets). In general, jet engines are combustion engines.

There essentially is the difference. The propeller aircraft pulls itself forward through the air using the blades, a Jet pushes itself through the air using a fast moving jet of gasses coming out of the back of the jet engine.

Now, of course, if we want to really start splitting hairs, a turbofan is both a jet and a prop, sort of....

Confused?

It's simple really. Jets don't have propellers stuck on the outside front of the engine.... So the picture does not satisfy the title. Kind of normal for some press..

I think that in the modern day there is quite a bit of semantic crossover between rockets, jets and gas turbines and also between the different ways propellers are driven.

Rockets: they do not breathe air, they are driven by an exothermic reaction between binary (or more) agents. Think Saturn 5 or Ariane. They carry their own fuel or in disposable tanks.

Jets: "real" jets are ramjets (scramjets, pulse jets. Air is necessary for them to work, but they have few, if any, moving parts. Think doodlebugs. They also carry their own fuel payload.

Gas turbines (jets): are a sort of hybrid. They have a rotating shaft containing all the parts.... except the fuel.

It matters not whether an aircraft relies on its forward momentum due to the direct thrust of a gas turbine or the thrust converted to torque to the shaft provided by a gas turbine in order to drive another means of forward momentum, a propeller, they are all gas turbine driven = "jets" for want of a better word.

I'll get the ex to dig out my old APs from my RAF fitter's course, if she still has them. They have some interesting figures from compressor pressure, to fuel flow in the combustion chamber, to turbine pressure and temp, to "thrust" at the exhaust nozzle. It is all pertty boring, but also interesting, if you are that way inclined.

Next up: Theory of flight. Anhedral and dihedral wings and leading edges. Book your seats now.

From a purely pedantic point, yes that is true. But people tend to differentiate between "jet" and not "jet" by whether it has propellers or not. Truboprops, when they first came out were certainly not Jet.

But agree that it's all jet propelled nowadays, just different ways of using the jet.

Very true.

Ask an ordinary person if that is a jet when they see it has propellers and they will say "no". Ask an aeronatics engineer like myself and we will want to know the power source.

If it's gas turbine powered it's a "jet".