Jet engines run better in cold environments?

[159th_Viper]

....or moving stairs....

 

Stairs moving Up, Down, or alternating between Up and Down at a preset, determined frequency?

 

:P

[Bucic]

Stairs moving Up, Down, or alternating between Up and Down at a preset, determined frequency?

 

:P

The answer is: Freakin' ORRRR . . . :disgust:

;)

[kimkiller]

More Oxygen...more power...

[Beagle One]

Hey folks.

 

Simple and quick:

Why do jet engines run better in a cold environment? That seems to be the common opinion and I can't quickly find an answer on google.

 

Thanks in advance.

Not only, jet engines, all combustion engines run better and have more power in cool and dry air.

 

That's why the power of a car engine is rated at sealevel and 15°C with 0% humidity...add humidity and tmperature and power output will decrease.

E normal car engine can have up to 15% power rate deviation just through climate conditions.

Edited January 1, 2012 by Beagle One

[sobek]

This was in the first couple of days of commercial flight school.

 

You might want to go over that again. ;)

 

Edit: Because this special part hasn't been dissected:

It gets colder the further apart the air molecules are

 

Temperature has nothing to do with how the particles are spaced. By definition, temperature is the mean kinetic energy of the particles if uniform movement speed of all particles is subtracted.

Edited January 1, 2012 by sobek

[Krebs20]

*Disclaimer* I've only just started reading this thread, so this will most likely already have been written. *Disclaimer*

 

 

 

Which is wrong. It gets colder the further apart the air molecules are (the higher you get). Think of it this way:

 

The closer the molecules (higher air density), the more friction is needed, thus you need more engine power to sustain a given airspeed.

 

Which is why airliners travel at high altitudes. To save fuel, and the passangers' money, and to maximize distance travelled.

 

This was in the first couple of days of commercial flight school.

 

 

Double check this.

 

I know what you are trying to say. But what we are talking about is Colder Air the the same altitude will give better performance to your engines than hot air.

 

The closer the molecules (higher air density), the more friction is needed, thus you need more engine power to sustain a given airspeed.

Not only will the engines produce more power in cold air to overcome the greater density, But your wings are more effective in the denser air and you will climb to your cruise altitude faster.

[kimkiller]

Cold air can contain more Oxygen.

More oxygen is needed to burn more fuel.

 

Think of it as the cheapest turbocharger ever...... :)

[Bucic]

your wings are more effective in the denser air and you will climb to your cruise altitude faster.

What? :)

[BlackRazor]

What? :)

 

I think what he wanted to say is that the lift generated by wings is directly proportional to air density, the more dense the air is the more lift is produced by wings.

[Cougar12dk]

n = pV/(RT), or "the amount of air molecules (i e density) in a given volume is proportional to the inverse of the temperature (1/T)". Double the temperature, half the density.

 

The rest, well, don't think you know anything just since it was taught in ground school. I'm afraid they teach just enough to let people sit up front and drive without screwing up too badly, and simplify to make it understandable enough after a very short time in the classrom and without a background in physics, maths or engineering. Unfortunately, "enough" in this case is often far from "correct". I'm often horrified by just how little you really are required to know and understand to hold an ATPL, leave alone a CPL. Fortunately, most pilots know more... or we'd have an AF447 every few weeks.

 

Double the temparture, half the density. That is just not logical at all. Maybe on the southern hemisphere, that is correct? A high pressure area on the southern hemisphere equals a low pressure on the northern. (And no, I never completed my training because I was nearly killed in a car-accident before I could finish and get some real flying experience), it did leave me unable to fly for the past 9 years, so....

 

And, yes, I should've read the whole thread before writing anything, but I didn't this time.

[Bucic]

I think what he wanted to say is that the lift generated by wings is directly proportional to air density, the more dense the air is the more lift is produced by wings.

Soo, I guess we'll just ignore the fact that drag is described by the same equation (for aerodynamic force) and that it is too directly proportional to air density? ;)

 

Long story short when density decreases you just fly faster. Also when you fly faster in a climb the vertical component of your speed is greater compared to the one for higher pressure / lower speed. And so Rate of Climb is higher in lower air density.

 

Notes:

* assumption: you retain your engine power with increasing altitude

* you might consider some efficiency changes related to density changes but you'd probably have to dig into Reynolds number

Edited January 2, 2012 by Bucic

[effte]

Double the temparture, half the density. That is just not logical at all.

 

One way to visualize it: Consider the temperature of the air in a container as the speed of the air molecules. Pressure is created as the molecules bump into the walls of the container. Increase the speed of the molecules, and you need fewer to create the same pressure. Same pressure, same volume, fewer molecules - lower density.

 

Cheers,

Fred

[effte]

You'd think aircraft would get lighter with more advanced avionics. Interestingly, they usually don't. We rip out one clock and put in two elecronic boxes and a display/control head... and it all just got heavier. More capable, but heavier.

 

Bit of the same with UAVs. Rip out the pilot, ejection seat, life support, pressurization, presentation etc etc. Allright. Lots of space, lots of weight saved. Now, add advanced comms gear (with encryption worth the name this time around), sensor suites, automation... whooops! Back where you started. Humans are amazingly space and weight efficient sensor suites and infomation processors. Then you want HALE and can't AAR (yet - I'm sure we'll see it), so you end up filling every nook and cranny with fuel. Where's that 18 kilometer runway when you need it?

 

Still don't see UAVs in the A/A role either, or in the near future.

 

Now, tell me where I'm mistaken as seen from a UAV driver's perspective. ;)

[Cali]

I will take a leap of faith with this statement as I think it is true.

 

All aircraft and aircraft engines perform better at lower tempertures. Provided that they are already running. It may not want to start in the 1st place.

 

I'm sure someone is about to pull out an aircraft than will make this false.

 

Had no problems starting up engines in Alaska when it was -20.

[159th_Viper]

What's the difference between a Hornet and a Hornet pilot? The Hornet stops whining when you shut the engines down.

 

Let me introduce to you myself to you........My name is Pilot I'm a Pilot that is what I do!

 

DqeURECZ8FY

[FieroCDSP]

What's the difference between a Hornet and a Hornet pilot? The Hornet stops whining when you shut the engines down.

 

Yeah, but airframes can't tell the story over and over to cage drinks (rightfully deserved, in most cases). You can take pilots out of the cockpit, but it makes the plane just another thing. You can't love a thing like you can a hero. No one grows up saying "I want to pilot drones for a living."

 

My view is as such: Take the casualties out of war, it's no longer something to avoid or fight to an end. There's no human cost, no war memorials, and no incentive to avoid other than considering it a money-pit. The day we let machines do the majority of our fighting is the day we commit ourselves to continuing it.

I don't need to go into the really important reasons AI's with weapons are a really BAD idea, do I?

[primus_TR]

@USMC_Trev

 

Do you not think latency represents an unbreachable barrier in the way of UAVs' completely replacing manned aircraft in combat roles even far into the future?

[hawk2495]

I certainly didn't. The only reason I am one today is that the Marine Corps, in it's infinite green wisdom, offered me a choice: Go to Pensacola and wait 6 months or more for an ATC school seat or go to Ft. Huachuca and be a UAV pilot right now. Being the savvy young buck that I was, I didn't want to rake rocks and stand duty for that long without accomplishing anything at all, which is exactly what would have happened, thanks to the sage advice of some of the more senior guys. That was nearly 15 years ago.

 

 

Eww, Ft Huachuca... Just Eww...:cry:

[GGTharos]

I know what you guys are saying. I have a few assertions here:

 

1 - I don't consider a buy of 100 aircraft or less much of a commitment to manned tactical aviation.

 

Which aircraft was bought in a quantity of 100 or less, other than the B-2?

 

2 - Buying a Super Tucano and modifying it for COIN for SOCOM is even less of a commitment to U.S. tactical manned aircraft design, development and production. Buying airframes from Brazil and modding them is a band-aid on a boo-boo.

 

Doesn't mean much. It's just a fact that you don't need jets for COIN.

 

3 - Air superiority does not mandate manned aircraft.

 

Actually it does.

 

NASA demonstrated in the '70s with HIMAT that an unmanned aircraft can be fast, low-observable, highly maneuverable and - since there will be a significant cost and weight savings due to the absence of a cockpit and all its' associated equipment.

 

NASA did not (and still cannot) demonstrate that such a vehicle can correctly function at least in terms of IDing bandits vs friendlies vs neutrals on its own when the ECM gets thick, IFF's fail, and both sides might be using the same type or similar looking aircraft.

 

Pilots go through years of training to be able execute their missions correctly, and the subject matter covered is pretty broad, especially in multi-ship tactics. What makes you think a UAV can do that?

 

 

no OBOGS system waiting to perniciously kill you by starving your brain of oxygen while making you giddy and sleepy until the moment you die.

 

The OBOGS didn't kill anyone.

 

Costs go up, threat aircraft development continues unabated but we make these decisions based on wars we've already fought and won. I'm not saying they're good decisions. These are the tea leaves, though.

 

Tea leaves should be considering how useless an untethered UAV is :)

[Krebs20]

From cold engine performance to unmanned UAV fighter planes. Derail...

[Ramstein]

kC-135 tankers used water injection for higher thrust for the high weight load... and as far as all angines, they all have their 'best performance range... and the fuels have ingrediants added to prevent the formation of water ice forming in the cold temps at altitude,, (you didn't think they just used pure kerosene did you?).

[Krebs20]

kC-135 tankers used water injection for higher thrust for the high weight load...

 

I thought the water injection was used to keep the TIT down to allow for a higher %RPM at takeoff. Is this incorrect?

[effte]

I thought the water injection was used to keep the TIT down to allow for a higher %RPM at takeoff. Is this incorrect?

 

But a higher RPM isn't the purpose in itself, right? What does the higher RPM (and increased mass flow) enable the engine to produce more of... ? ;)

[KLR Rico]

Both right! Water injection cools the compressed combustor air which lowers the EGT at a given fuel flow/RPM, and it also increases the mass flow in of itself.

Edited January 3, 2012 by KLR Rico
I should refresh before posting... :D

[robmlufc]

Harriers are close to the EGT limit when they are in the hover, at altitude and in high OAT it gets very close, you wont ever see them hovering with much loadout if any. Harriers also use water injection when hovering and for STOL, it gets sprayed around the combustion chambers and onto the turbine blades, which as Rico mentions lowers EGT and allows more fuel flow.

 

OBOGS has nothing to do with LOX does it? At least in the systems I have worked with they just use an MSOCS to provide the pilot with what is basically nitrogen free air from an engine under a bit of pressure...oxygen? :)

 

 

PS Dont drink de-min water its not good for you :)

Edited January 4, 2012 by robmlufc