radars, wings, engines etc

[Halibut]

Please could someone explain to me in basic terms how radars, wings, engines actually work? Also how long have planes been using the GPS system?

[gaunty]

Phew here goes!
Interesting exercise Halibut in 25 words or less???

Radar bounces pulsed radio waves off objects and times the return. The result is displayed on a Cathode ray tube as an image

Wings are structures that have an convex shape on the top surface over which air passes and is made to accelerate, this causes a drop in air pressure over the surface which causes the surface to be lifted.

Piston Engines are reciprocating air pumps into which fuel is introduced and ignited by spark plugs then burnt to increase the total energy. This process is not continuous and has to work in a cycle intake, compress, combustion (power), exhaust. The amount of air allowed into the engine determines the amount air/fuel burnt and power produced. Hence the term throttle. Throttle the engine reduce the air and power and vice versa. Instead of energy being required to turn it, it turns itself with enough excess power available to hopefully drive a propellor. The propellor is itself a rotating wing, see above, and the lift it produces pulls the aircraft along.

Turbine engines use the principle od action reaction and are rotary air pumps, the compressors, into which fuel is introduced, a combustion chamber to increase the energy of the air which is then passed through a divergent duct which accelerates it and increases the velocity. This process is continuous and does not require spark plugs except to start. This invokes Newtons Third Law of motion ie. action/reaction and produces thrust, that is it pushes the engine forward.
In a jet engine it is the compressors that do the actual work the turbines are there to drive the compressors. It gets a bit more complicated when a compressor is made big enough at the front of the engine and outside of the main gas path they are then known as Fans which are like shrouded propellors except they produce thrust not lift by accelerating the air to the rear.
In a turboprop the turbines drive the propellor (they produce lift see wing above) with whatever energy is left used as thrust.
There is many times more air produced in a turbine than is actually used for combustion, some of which is used for cooling but mostly there to be accelerated for thrust.

GPS I suppose more than 10 years.


Thats as simple as I can make it anyone else want have a go, correct, refine etc.

[pjdj777]

Good one Gaunty.

Reminded me a bit of one of those modern plays where they fit the entire work of Shakepeare into two minutes.

[WX Man]

pjdj, have to agreee the RSC (Reduced Shakespeare Company) rule. They are the dons!

Gaunty, maybe I'm wrong, but I thought that planes don't use GPS as far as I know. People use GPSs, planes (at least, the big ones) use INS (Inertial Navigation System). It's a bit like an electronic gyroscope that measures acceleration in all axes (I'm sure you know what it is, but I'm explaining it to Halibut as it was explained to me by a Maersk captain).

If it [the INS] knows your start point on the ramp (which one of the pilots enters into the FMC: it's written on the aerodrome info. pages of the Aerads under 'Ramp INS positions' for each stand), it can calculate your position later on based on what your starting point was.

Indeed 'tis a cunning device. I believe it's more reliable than GPS at lower altitudes.

[The twin]

Then maybe a fringe interpretation could be

1 Radar is about bouncing - at all times

2 Wings are about bouncing - at landing

3 Engines are about big bouncing - at failure

[Snigs]

Well done Gaunty, but if I may correct a few minor details.

In a gas turbine the compressor compresses the air, it is mixed with the fuel and ignited (burnt) in the combustion chamber.

The turbines do all the work in a jet gas turbine engine (they turn the compressor), in a Turbine Prop (as you correctly said) they have to turn the propeller as well as the compressor.

Halibut, what a great way to get everyone else to do your research for you !!!! :)

[McD]

Wx Man: Planes most definitely use GPS. Nearly ALL the new models have it, and many older models are being modified with GPS receivers. Our B757/767s have GPS and INS (IRS, really).

[McD]

Also, jet engines summarized in 4 words:

Suck, Squeeze, Bang, Blow

For those that think I'm just being crude, think about it....it's true:

Suck: Intake of air

Squeeze: Compression

Bang: Combustion

Blow: Exhaust/Thrust

:)


[This message has been edited by McD (edited 08 September 1999).]

[WX Man]

Apple-ogies, I stand corrected. Does this mean that the CAA may be coming around to accepting that signals received from geostationary satellites are an acceptible form of navigation? I don't know much about the accuracy of INS (or IRS) but the principal strikes me as (on balance) being an inferior one to GPS.

[Wee Weasley Welshman]

Huge round of applause to gaunty.

WWW

[gaunty]

Snigs,

You're right about the first bit should have edited the post a bit better, of course the fuel is burnt in the combustion chamber.

Now about what is doing the work, this is how I understand it and I am the first to admit I'm no PhD. on this.

You are right about the turbines converting some of the energy to drive the compressors and this is where IMHO it gets a bit complicated/esoteric.
Its a definition of whats producing the resultant thrust that is in play here. The compressors or the turbine. This is the ultimate chicken and egg scenario.

Again in 25 words or less!!

The turbines by definition are actually EXTRACTING energy from the gas path to use elsewhere in the engine.
Not in themselves producing any thrust.
On their own they are incapable of doing anything.
The energy in the accelerated higher energy air THATS LEFT is converted to thrust through that divergent duct or nozzle at the back end.

In a straight no bypass turbojet the job of the turbines is simply to provide energy to the compressors to pump, or accelerate, add energy to the air thus produce thrust this requires an external energy input (fuel) to become self sustaining and hence my comment on the compressors actually doing the work.

Its much simpler in a fan engine as almost all of the energy not required to directly drive the compressors is provided to the fan which produces around 80% or more of the actual thrust, sometimes refered as cold thrust as it does not pass through the hot part of the engine core.
The fan is like a big shrouded propellor but produces thrust by accelerating the air not as lift. That's not so simple either however..

Turboprops are an even simpler example of this concept.
Almost all of the energy not used to drive the turbines goes to the prop with only a small amount of residual thrust from the jetpipe.

Perhaps as an example that might illustrate the whole.
A fixed shaft Garrett turboprop for example might have a shaft horsepower of say 800HP... that is what is available or left over from the total energy produced in the engine after the compressors have taken their bit out. Their bit in this instance if it were reduced to HP is around 1200HP. In simple terms if you wanted to drive just the compressors at the operating RPM required from an external source you would need a 1200HP engine to do so.
Ergo the total thermodynamic production of the engine is actually around 2000HP. Similar ratios apply to straight turbine.
Its a whole lot more complex but I think I've got it right in simple terms
Usually if the engine is down on power or running hot the cause is usually found in the compressors.

Snigs help me here in case I lead anyone astray.

Any one ????

[This message has been edited by gaunty (edited 09 September 1999).]

[This message has been edited by gaunty (edited 09 September 1999).]

[Snigs]

Gaunty, I think that the only thing that we differ on is the definition of "work done"

You said The turbines by definition are actually EXTRACTING energy from the gas path to use elsewhere in the engine. Not in themselves producing any thrust.
On their own they are incapable of doing anything.

I totally agree, the energy extracted is used to drive the compressors

You said The energy in the accelerated higher energy air THATS LEFT is converted to thrust through that divergent duct or nozzle at the back end.

Agree, but the energy (by which I refer to as thrust) is producted by the combustion and subsequent expansion of the "exploded" air. This explosion accelerates the air backwards (through the turbine) at a high rate of knots. The "thrust" at the combustion chamber outlet, minus the energy extracted (work done) to turn the turbine blades leaves the engine thrust figure that is quoted by the engine manufacturers (simplistic summary I know!)

You said In a straight no bypass turbojet the job of the turbines is simply to provide energy to the compressors to pump, or accelerate, add energy to the air thus produce thrust this requires an external energy input (fuel) to become self sustaining and hence my comment on the compressors actually doing the work.

Just our terminology is different!

You said Its much simpler in a fan engine as almost all of the energy not required to directly drive the compressors is provided to the fan which produces around 80% or more of the actual thrust, sometimes refered as cold thrust as it does not pass through the hot part of the engine core.

Correct, a fact born out by the fact that the Rolls-Royce Trent family of engines (all quoted at different thrust) have the same core (intermediate and high pressure modules) but different fan diameters.

Your example is spot on but I think that Usually if the engine is down on power or running hot the cause is usually found in the compressors. is just a little bit too broad brush for my liking!

Halibut, you should be ready to write a thesis by now!!

http://www.platl.com/sps/small20.gif


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Cheers,

Snigs

[Squealing Pig]

Hey Snigs, I like the smilies website you found !
http://www.platl.com/mas/med61.gif

[Techman]

In basic terms radars, wings and engines actually works very well.

[PPRuNe Radar]

WX Man,

The CAA do accept GPS for some applications, notably to comply with BRNAV (Basic Area Navigation) in Domestic Airspace or MNPS (Minimum Navigational Performance Specification) in Oceanic Airspace. It doesn't permit it yet for TMA operations or approaches though.



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PPRuNe Radar
ATC Forum Moderator
[email protected]

[togaroo]

Just to throw something else into the conversation, although GPS is still being trialled as a "primary" navigation means, using satellite's to navigate is not new.

Commercially on pacific routes from west coast of USA out to NZ and Aus, FANS (Future Air Navigation System)is being used. Basically a little black box on the aircraft recieves and transmit data via satellite. The data that is transfered, such as position of aircraft, height speed is combined with weather data and sent back to the aircraft to give the best route accross the pacific and maintain aircraft separation.

[scotty.d]

So would I get a star in the BA interview if I explained the jet engine like this:

Basically severla fans or turbines at the front of the engine suck in and force air through a narrow compression chambers toward the combustion chamber. Then in the combustions chamber fuel is injected into the system in a vapour format through hundreds of tiny nozzles and ignited to cause rapid explosions forcing the expanding gas out through the rear nozzle causing thrust.

This is how I remember it from physics and seems a nice easy way to understand it!! Any comments?

[The twin]

For the sake of an interview, I reckon that's not a bad few lines to remember.

With your definition, some smart **** , who uses interviews to let you know how clever he is, will probably ask you what makes the 'fans' turn at the front. Just tell him a) 'turbines at the back driven by the expanded air', b) to get a life.

[gaunty]

Scotty.d
Close but no cigar or star. I would not risk my future career on that one.
If you are having rapid explosions in or before the combustion chamber you probably have a compressor stall on your hands. The flame front propagated in the combustion chamber is continuous (no rapid explosions) as long as there is an undisturbed air flow from the compressors and fuel available.
Beg borrow or steal
The Pratt Whitney book, the Rolls Royce book and D P Davies Handling the Big Jets read learn and inwardly digest then see if you come up with the same answer.

The twin. If you already have a career you should know better if you haven't then you probably wont get one.

[The twin]

Agree with you 100% Gaunty,

... but if I were interviewing someone who didn't have an engineering degree and who hadn't done his ATPLs and could explain jet engines as close as Scotty did, I'd be pretty impressed.

I also agree with your last sentence, the way I feel about my TECHs at the moment a career in aviation seems miles away!!!

PS Give me a break - I'm an ex arts student!

[scotty.d]

Thanx guys; big smile!!! You guys are getting 2 pints each!!!!! Superb. That's made me feel a whole lot better.
By the way I learnt that during my years in the Air Training Corps; no degree and no flying career. Only an RAF flying schol. SO I think from what you say I will change the rapid explosions to continous expansion of air/fuel mixture produsing thrust and I should be ok.

[gaunty]

Scotty.d and The twin
Onya guys keep it up, good luck and hope you can buy me the pints out of your airline pay one day.
Still reckon you should get the books I described you should blow any interview board away.

[scotty.d]

Not enough time for that I'm afraid mate; only two weeks left and I gotta concentrate my studies on BA ops and history etc rather than engines; I got the basics and hopefully that will do me. I think it is more important to learn Ba's Routes and Aircraft first!! Comment if you disagree please!!

[gaunty]

Scotty.d

good luck then!!

[AYLGR]

Now where's Halibut gone? You guys go to all the trouble to do his homework for him and he doesn't come back to class to listen!
Can anyone answer my 3 questions and tell me all about GIRLS, MONEY and BEER?

[scotty.d]

Now women; these things really are complex pieces of machinary; far harder than the corporate world of financing. Every time you think you've got them sussed they seem to stall on you!!
As for beer; I think this was invented exactly for the reason of post interview sessions; a godly object which makes interviews with BA almost worth while!!!
Finally money; a mysterious item; it doesn't matter how much you earn ; it always seems your women somehow manages to make it all dissapear; I'm still working on a solution for this one and if anyone can help I would be much obliged!!!!

[scotty.d]

Now women; these things really are complex pieces of machinary; far harder than the corporate world of financing. Every time you think you've got them sussed they seem to stall on you!!
As for beer; I think this was invented exactly for the reason of post interview sessions; a godly object which makes interviews with BA almost worth while!!!
Finally money; a mysterious item; it doesn't matter how much you earn ; it always seems your women somehow manages to make it all dissapear; I'm still working on a solution for this one and if anyone can help I would be much obliged!!!!

[pjdj777]

Aaaaaah Beer

A wonderous brew, invented to help ugly people have sex :)

[The twin]

Same as radar, wings and engines.

Girls, beer and money are all about bouncing.

[togaroo]

AYLGR
Girls - you never get enough
Money - you never get enough
Beer - you never get enough

But I like the bouncing theory tho.

[This message has been edited by togaroo (edited 13 September 1999).]

[togaroo]

Oh yeah...
My 2 bits worth...
One fan at the front only which provides most of the thrust. Air at this stage is either bypassed down the cold stream duct or into the core. Only a small percent goes through the core. B747 engine such as GE CF6-80C2 and RR RB211-524, this is approximately three to one bypass.

Compressors are next in line from the fan in the core of the engine, and there are many stages of compressor with stators and rotors. Each of these stages will be rotating at different speeds. This is achieved by having a twin or triple shaft arrangement connecting the compressor(s) to the turbine(s). ie Low pressure (fan), medium pressure and high pressure(HP)area. Early jets had single spools, but this did not allow any part of the engine to run at its optimum speed. With triple or twin spool engines, they respond faster because each module of the engine is near its optimum operating speed. When jets first came in pilot's weren't very happy about the responsiveness. Instead of getting a kick up the pants it was more like waiting for the cows to come home. I digress......

As for fuel entering the burner can, there are approximately 30 nozzles, depending upon engine type. These operate depending on the thrust setting and either spray a fine mist or dump fuel (stream) into the can. The spray is controlled by air shrouding the fuel entering the can. If the fuel was angled towards the burner can, it would burn a hole in the can and then engine fire. Temps at the furst turbine stage are in the order of 1300 deg C.

Stick with the suck, squeeze, bang, blow, theory. Its easy to remember and tells it how it is pretty simply and if you can get your hands on a Gas Turbine theory book have a quick look.


And don't panic about the interview thing. Especially don't worry about the company side of things too much. If you know too much they might offer you a different sort of job that might involve flying a desk!!!!
;)

[TBone]

The function of a woman is inheritently the same as that of a combustion engine or turbine powerplant.

To wit;

a) Suck
b) Squeeze
c) Bang
d) Blow

Unfortunately, some models, although operating to the above formula, do so in a markedly different way from that intended.

Suck - your bank account dry
Squeeze - the life out of your soul
Bang - the doors behind as they storm out
Blow - your life's savings

Make sure you have the right model fitted for the job at hand :)

Cheers

[AYLGR]

Great replies guys, especially the T's - togaroo and TBone!
Bob

[IBMR]

Why are women like aeroplanes?

Because we jump into their cockpit six times a day and take them to heaven and back!
(Captain Flash or Rik Mayall - Blackadder)

As for jet engines, wings, things etc. I'm surprised nobody mentioned "Flying the Big Jets" published by Airlife. It's a lot more user friendly than "Handling the Big Jets". I was surprised when I read it, it's like a precis of the CPL/ATPL exams plus operational stuff. I imagine it would be very useful for interviews. Transair have plenty.

As for a piece of trivia on jet engines; The JT9D burns 4 gallons a second at Take-off power. Thats a good one to impress people at parties.

[This message has been edited by IBMR (edited 18 September 1999).]