Some definitions "Stealth" and "Supercruise"

[Mike_NZ]

Got two terms I'm not too sure about how to define:

1. Stealth
I realise this is not a black and white thing, just because you don't look like an oddly shaped dice doesn't mean you don't have some aspect of stealth technology. Also it's a relative term, if the enemy has some means of detecting you, then you're not really stealthy then are you?
Classical stealth aircraft I know of are the F117A nighthawk, B2 bomber, the F22 and the JSF. What defines stealth? Is it a cut off in RCS? If so how much?

The concept I have in my might atm is that stealth incorporates the whole emission spectrum, from human eye to radar to IR to wave length-undefined.

2. Super-cruise
From some sources I've seen that super-cruise is simply the ability to cruise at supersonic speeds (ie over mach 1) without the use of afterburners, but you're allowed to use it to get supersonic. Others have stated it's more like mach 1.4 where "all flow is supersonic" which I don't really understand.
Lockheed Martin have defined supercruise as a unique ability currently only the F22 can do and thats cruise at mach 1.7 without augmentation.

Can anyone enlighten me on better ways of looking at these two innocent looking words?

 

[rjmaz1]

There is no set level where an aircraft can be classified is "stealth".

All forms of emissions can be reduced to make the aircraft more "stealthy". So again it is not black and white at all nor is it directly targetted at one form of emission.

Most current fighters have some form of radar cross section reduction.


Now regarding supercruise as an aircraft nears Mach 1 drag increases above a linear rate.

To give you an idea, i'll make an example. Going from Mach 0.6 to Mach 0.8 is a 33% increase in speed and drag increases also 33%. However travelling from Mach 0.8 to to Mach 1.0 is only a 25% increase in speed, drag should increase by 25% also but in real life drag increases by nearly twice as much as expected. This is called the "transonic region". When travelling from Mach 1 to Mach 1.3 is a 30% increase in speed yet drag would increase by only 15%. This is because the aircraft is now completely supersonic and is now travelling faster than the transonic region.

The size and length of the transonic region depends on the aircraft design however it is still significant.

So basically if you had a fighter such as the F-22 that could travel at Mach 1.6 without afterburning if you plotted the maximum range acheivable at any speed you'll find the F-22 can travel just as far at say Mach 1.3 as compared to Mach 1. So you'd be crazy to cruise at Mach 1 when u can travel faster for free. Some aircraft can cruise at Mach 1.1 and 1.2 without afterburners however its range will be so much less than cruising at Mach 0.8.

Lockheed martins definition is that the aircraft must travel faster the the transonic region. This means only the F-22 can supercruise and the Eurofighter can also with a light load. As cruise usually is related to effeciency travelling at a high drag mach 1.1 is not supercruise is their opinion.

Hopefully this helps.

 

[Feanor]

It does. A few more questions, so what determines the ability to supercruise? From what you explained it sounds like any aircraft will have reduced drag for speed increase ratio at over mach 1.1 Is it the ability to go over mach 1.1 while still travelling efficiently in terms of fuel?

 

[МиГ-23МЛД]

Supercruise currently is a capability used by at least six aircraft:

F-22, MiG-31, Eurofighter, Su-35BM, Gripen and Rafale.

Supercruise is the ability to fly supersonically without afterburner

Accroding to the Russian specialists in the field the MiG-31 is the aircraft with the closest supercruise ability to the F-22.

An only recently the Su-35BM has achieved similar speeds.

The MiG-31 can fly at Mach 2.3 for 30 minutes, but the russians say it can fly at supersonic speeds without afterburner.

 

[gf0012-aust]

Mike, if you do a search for "LO" and "Stealth" in the aviation threads you'll find a post I made on the history and definition of stealth. Fundamentally "Stealth" is a term thats been abused from here to eternity. The correct term is Low Observable/ity

http://www.defencetalk.com/forums/showthread.php?t=2972&highlight=taube+gf0012-aust&page=2

Start at Post Number 52

There is also a comment from NASA Dryden (I emailed them as I was getting sick of everyone making up their own to fit their own personal beliefs ) about the definition of Supercruise.

 

[Scorpion82]

Supercruise currently is a capability used by at least six aircraft:

F-22, MiG-31, Eurofighter, Su-35BM, Gripen and Rafale.

Supercruise is the ability to fly supersonically without afterburner

Accroding to the Russian specialists in the field the MiG-31 is the aircraft with the closest supercruise ability to the F-22.

An only recently the Su-35BM has achieved similar speeds.

The MiG-31 can fly at Mach 2.3 for 30 minutes, but the russians say it can fly at supersonic speeds without afterburner.

The MiG-31 uses afterburners to achieve and hold such speeds. Just the huge amount of fuel allows it to operate with such speeds for quite some time. Though this is essentially a form of supercruise its not the "modern" kind of supercruise which means achieving and holding supersonic speeds without afterburners.

 

[winnyfield]

Supercruise currently is a capability used by at least six aircraft:

F-22, MiG-31, Eurofighter, Su-35BM, Gripen and Rafale.

That's certainly a capability that is advertised. Most fighter aircraft have the ability to fly supersonic without afterburners particularly when they're lightly loaded. Whether or not they can sustain that is where the definition of supercruise is made. The F-22 is unique in that its a big aircraft with a heck of a lot of fuel but few ordnance.

 

[Feanor]

So you can use afterburners to get supersonic, as long as you can hold the speed without them? Also, just supersonic? So all you need is past mach 1.0? Not mach 1.7?

 

[МиГ-23МЛД]

That's certainly a capability that is advertised. Most fighter aircraft have the ability to fly supersonic without afterburners particularly when they're lightly loaded. Whether or not they can sustain that is where the definition of supercruise is made. The F-22 is unique in that its a big aircraft with a heck of a lot of fuel but few ordnance.

Well the Su-35BM and Eurofighter probably supercruise at speeds of Mach 1.2 or Mach 1.3, the Rafale and Gripen are also close to that speed, the MiG-31 is an aircraft optmised for high speed high altitude but i have no idea how fast it can fly at its more economical supercruise.

But certainly the F-22 if detected by a modernized MiG-31 is not going to survive, it can fly faster and has missiles of longer range, in my humble opinion the F-22 is the best but as the Russians affirm the MiG-31 is the closest supercruiser to the F-22

 

[cobzz]

The Su-35BM could supercruise?

 

[Aussie Digger]

In relation to Supercruise, WHO cares?

F-22 has demonstrated an ability to "supercruise" at Mach 1.7 according to publicly reported accounts.

Excellent. Now over what RANGE can it do it? The F-22 might be more fuel efficient because it's not using an afterburner to achieve supersonic flight but the faster you go, the faster you burn fuel, irregardless of afterburner usage or not.

Even the F-22 (which I acknowledge is probably the most capable "supercruiser ever) is going to spend the majority of it's flight time, flying subsonically.

It's a "fan boy" concept that the F-22 will be flying supersonically everywhere...

Would you guys care for an F-22 to "supercruise" over your house for instance?

 

[Scorpion82]

But certainly the F-22 if detected by a modernized MiG-31 is not going to survive, it can fly faster and has missiles of longer range, in my humble opinion the F-22 is the best but as the Russians affirm the MiG-31 is the closest supercruiser to the F-22

No because detection is one thing, to launch a missile you have to acquire the target and to destroy the target the missile seeker must be able to lock on the target as well and that's the most difficult part.
The Russian claim a lot when the day is long...

 

[rjmaz1]

I think the last of fighters that can break the sound barrier without weapons or the user of afterburners is quite long.

Approximately 30 aircraft i think was posted previously.

So obviously Mach 1 without afterburners is NOT the definition of supercruise.

If an aircrafts range is a reduced to a quarter when travelling at Mach 1.3 opposed to Mach 0.8 then it is not supercruise

Su-35BM and Mig-31? Some crazy people here.nfloorl:

 

[МиГ-23МЛД]

I think the last of fighters that can break the sound barrier without weapons or the user of afterburners is quite long.

Approximately 30 aircraft i think was posted previously.

So obviously Mach 1 without afterburners is NOT the definition of supercruise.

If an aircrafts range is a reduced to a quarter when travelling at Mach 1.3 opposed to Mach 0.8 then it is not supercruise

Su-35BM and Mig-31? Some crazy people here.nfloorl:

The MiG-29 and F-15 can not fly at Mach 1 without the use of afterburner.

A supercruiser has to have an engine that compresses air to the degree it also generates thrust.
The SR-71 is a good example of a supercruiser, in fact it is the best supercruiser of all times in terms of speed and supercruise it can fly at mach 3.2 for several hours, however at Mach 1.7 the F-22, has not the advantages of flying at Mach 3 where air is compressed by the inlet and air speed the aircraft is flying.

The MiG-31 does fly at Mach 2.3 for more than 25 minutes and the Su-35BM has already been flown at supercruise speeds without afterburner, read about it in the Sukhoi press releases.

 

[Pro'forma]

I think too here is a confusion in the context and between original message.
Anyway, take a seat and go for takeoff.

 

[МиГ-23МЛД]

I think too here is a confusion in the context and between original message.
Anyway, take a seat and go for takeoff.

You are up to a degree right, the MiG-31 and SR-71 use air speed to increase the air compression, and basicly the SR-71 has a ramjet type engine, this allows it to fly for several hours at Mach 3 besides the large amount of fuel it carries.

The F-22 uses more brute force in terms of thrust to weight ratio and an engine that has a better compression rate, similarly the Su-35BM and Eurofighter have really high thrust to weight ratios.

That is the main difference between both types of aircraft, the SR-71 works more like a ramjet, while the F-22 has a more powerful engine with better compressor stage at low altitudes and speeds

 

[Mike_NZ]

I think too here is a confusion in the context and between original message.
Anyway, take a seat and go for takeoff.

Well, the very reason I started this post was because there is a lot of confusion about the very definition of supercruise. As has come to light, lots of people have different ideas of what supercruise is. Some valid points have come up too.

1. Does supercruise incorporated an element of practicality of use of the actual ability, or is it simply a threshold which if an aircraft exceeds, it is classified as being supercruise capable?

2. In case above, how efficient does the supercruise have to be to be classified as such?

3. Finally, does an aircraft that can 'supercruise' only with clean config, and half fuel qualify to be called supercruise capable?

I don't think there will be a clear answer to be honest.

 

[МиГ-23МЛД]

Well, the very reason I started this post was because there is a lot of confusion about the very definition of supercruise. As has come to light, lots of people have different ideas of what supercruise is. Some valid points have come up too.

1. Does supercruise incorporated an element of practicality of use of the actual ability, or is it simply a threshold which if an aircraft exceeds, it is classified as being supercruise capable?

2. In case above, how efficient does the supercruise have to be to be classified as such?

3. Finally, does an aircraft that can 'supercruise' only with clean config, and half fuel qualify to be called supercruise capable?

I don't think there will be a clear answer to be honest.

Supercruise is a term to define supersonic cruising speeds without the use of afterburner, why? well flying without afterburner means great savings in fuel, almost all current and modern fighters use afterburner to achieve supersonic speeds, the F-15, F-18, MiG-29 and Su-27 are examples of that.
at military power, an engine spents around two thirds of fuel less than at full afterburner.

Military power only recently has become capable of powering a modern fighter to reach supersonic speeds.

The F-22 uses a very high thrust to weight ratio to achieve supersonic speeds with only the use of military power.

The main reason is in the 1970s and 1960s engine power was increased a lot however weight also increased so a MiG-21 barely had engines with 7000kg of thrust at max afterburner that barely could power the jet at full afterburner setting to close to Mach 2; an F-22 can yield with a single engine at military power almost twice of that thrust.

however fighter aircraft weight has also been increasing since the 1950s, so only until the 1990s the first engines that outpaced the weight growth of fighters were built.

by outpacing i mean capable of generating enough thrust to allow a fighter supersonic speeds at only military power settings.

The SR-71 has also supercruising, but in a different way, its engine generates thrust via the air speed that at mach 3 already compresses the air and makes compression superflous, also this compression generates thrust, so the SR-71 is propelled by the speed it flies.

The F-22`s Pratt & Whitney F119-PW-100 does not work in that way, niether the 117 that powers the Su-35BM these engines generate alot of air compression therefore are more economical.

 

[DarkDuke]

Supercruise is a term to define supersonic cruising speeds without the use of afterburner, why? well flying without afterburner means great savings in fuel, almost all current and modern fighters use afterburner to achieve supersonic speeds, the F-15, F-18, MiG-29 and Su-27 are examples of that.
at military power, an engine spents around two thirds of fuel less than at full afterburner.

MiG:
Sorry for ignored you rest of post.
This point posted by you also is worth to discuss.
"without afterburner means great saving in fuel", for what? for saving money because price of oil is really high recently? This will be funny enough.

So only one purpose which saving fuel for is to maximize range or combat radius. However, there are some different way to enlarge range/combat radiuse. One is carrying more fuel, especially internal fuel for reduce aero-drag. The MiG-31 loading over 16tons internal fuel could give a range langer than F-22 while both of them during supersonic flight, moreover, the supersonic MiG-31 flew is faster than F-22.

 

[Feanor]

So for all practical purposes the MiG-31 can supercruise, at least in relation to the F-22?