Max Q
Topic Author
Posts: 7488
Joined: Wed May 09, 2001 12:40 pm

How important is top speed to a fighter these days ?

Sun May 19, 2019 11:09 pm

In the past top speed was always seen
as a priority for jet fighters and they steadily increased this capability with
newer generation aircraft


Contemporary fighters have top speeds
varying between 1.6 all the way to 2.5 Mach



Point is, does it matter ? I can see how good acceleration is beneficial but you can’t outrun modern missiles
The best contribution to safety is a competent Pilot.


Guns and the love of them by a loud minority are a malignant and deadly cancer inflicted on American society
 
Ozair
Posts: 3942
Joined: Mon Jan 31, 2005 8:38 am

Re: How important is top speed to a fighter these days ?

Sun May 19, 2019 11:36 pm

Max Q wrote:
In the past top speed was always seen
as a priority for jet fighters and they steadily increased this capability with
newer generation aircraft

If you consider jet fighter generations speeds haven’t really increased past gen 3. The gen 4 aircraft, F-15,16,18 etc all had speeds similar to the century series 3rd gen. Same for Soviet aircraft of that time period.

Max Q wrote:
Contemporary fighters have top speeds
varying between 1.6 all the way to 2.5 Mach

Correct. 4th gen aircraft almost always fly with external fuel tanks and payload, generally limiting their top speed to below those given above, hence the top speeds are often not representative of actual combat performance.

Max Q wrote:
Point is, does it matter ? I can see how good acceleration is beneficial but you can’t outrun modern missiles

Note that acceleration and top speed are two different metrics to judge aircraft by. The current speed of aircraft may be equivalent or slower but a lot of them are powered by high performance engines that provide excellent acceleration. Therefore in WVR combat acceleration, or P sub s, is important as it provides the ability to add energy quickly. Top speed plays little to no role in this situation.

Speed, and altitude, can be a factor in weapons employment especially in BVR engagements. An F-22 flying high and fast can launch an AIM-120 with more velocity/energy and thereby increase the missile’s range, same with for example a MiG-31. With the advent of more stealth aircraft detection ranges are reducing, even with AESA radars, and therefore the longer range shots may not be as necessary. The other side is the proliferation of longer ranged missiles and especially the Meteor which is able to stay at a high energy state for a significant portion of its long range flight profile.

So does top speed matter? For an interceptor yes, for a general multi-role airframe less so. Given interceptors are almost gone from most Air Forces then that probably shows where the cost/capability decision is being made. Stealth is also a factor in that Air Forces recognise it is better to remain undetected than be detected and be high and fast.
 
checksixx
Posts: 1218
Joined: Wed Mar 09, 2005 11:39 pm

Re: How important is top speed to a fighter these days ?

Sun May 19, 2019 11:53 pm

Top speed isn't important. Most pilots fly their entire careers without ever seeing the top speed their aircraft is capable of.
 
RJMAZ
Posts: 1452
Joined: Sat Jul 09, 2016 2:54 am

Re: How important is top speed to a fighter these days ?

Mon May 20, 2019 12:41 am

Sustained high speed is more important than peak speed. Sustain speed allows you to escape the enemy and avoid getting chased down. It also gives the enemy less warning time.

The maximum speed a fighter can sustain for say 30 minutes with a basic air to air load is the most important.

Most fighters while reaching mach 2 will burn through their fuel in 15 minutes.

The F-22, F-35 and Suhkois are very evenly matched in this regard. All three can maintain around mach 1.5 for 30 minutes. The F-22 will not need afterburner but it has a very small fuel capacity so it actually has no advantage. The Suhkoi and F-35 would need a very low afterburner setting to maintain that speed but they both have a huge fuel capacity allowing them to keep up with the F-22.

The Eurofighter, F-15 and Rafale would all need light afterburner to hit that speed with a few air to air missiles but as their fuel capacity is quite small they will not be able to average a speed as high. If they tried to match the speed of the Suhkoi, F-22 and F-35 they would run out of fuel first.
 
Planeflyer
Posts: 1391
Joined: Fri Mar 14, 2014 3:49 am

Re: How important is top speed to a fighter these days ?

Mon May 20, 2019 4:04 am

What speed does an AC need to outrun or avoid missiles?
 
Ozair
Posts: 3942
Joined: Mon Jan 31, 2005 8:38 am

Re: How important is top speed to a fighter these days ?

Mon May 20, 2019 4:45 am

Planeflyer wrote:
What speed does an AC need to outrun or avoid missiles?

Aspect is generally more important for outrunning a missile than speed. If the target is flying towards the missile then the potential intercept range increases significantly. If the target is flying away from the missile then the range decreases significantly. The below graphic shows how a missile has a shorter range from rear aspect than head on.

Image

Missiles typically have a “No Escape Zone” which is dependent on a number of conditions such as launch altitude, launch speed, missile speed, etc. For the set parameters if the missile is launched within this zone then it has the kinematic ability to intercept the target. That doesn’t necessarily mean it will as the NEZ doesn’t factor in EW or other countermeasures but the missile has the energy to make the impact. And no manoeuvre or expected target speed will prevent the missile from reaching the target (again not necessarily intercepting…).

Outside the NEZ an aircraft could launch a missile at long range on a target that is coming directly towards it, potentially further than the missile can fly becuause it is using the closing speed of the target aircraft and missile to close the range. In that scenario the missile will potentially intercept the target at long range from the launch aircraft. What happens though if the target aircraft flows cold, turning in the opposite direction? In that scenario the missile has to play catch up and runs out of energy long before it reaches the target.

Below is a graphic of a generic missile velocity profile. The missile while under boost from its rocket motor increases speed rapidly until the motor burns out, at which point the missile will glide towards its target losing velocity as it goes.

Image

Obviously not all missiles have that type of velocity profile, for instance a short range AAM may have a boost only motor while a long range AAM may have a boost and sustain section before gliding. Meteor for example will have a boost and then long sustain section given it is an air breathing ramjet.

The trajectory of the missile also impacts range. A long range missile may use a lofted trajectory to increase range by initially under boost gaining altitude into thinner air before gliding towards the target. A larger, heavier or aerodynamically dragger missile may have a faster initial speed but also lose speed more rapidly when it glides. A shorter range AAM will fly essentially directly towards the target using various navigation techniques to effect an intercept.

In the end the answer to your question is "it depends...".
 
YIMBY
Posts: 584
Joined: Tue Sep 20, 2016 4:32 pm

Re: How important is top speed to a fighter these days ?

Mon May 20, 2019 5:44 am

RJMAZ wrote:

Most fighters while reaching mach 2 will burn through their fuel in 15 minutes.



In 15 minutes you fly 500 km which is more than from border to border in most European countries.

You can even make a strike to St Petersburg: The distance from Nato border is about 200 km.
 
User avatar
cpd
Posts: 5932
Joined: Sat Jun 28, 2008 4:46 am

Re: How important is top speed to a fighter these days ?

Mon May 20, 2019 10:05 am

Planeflyer wrote:
What speed does an AC need to outrun or avoid missiles?


Not just speed, but altitude as well and probably backed up by stealth features. I think you'd be looking at M3.2+. If a plane can sustain that kind of speed (or more) for decent amounts of time and also fly extremely high it will make the thing very hard to shoot down. Even more so if it is stealthy. By the time you've locked it, if you can, it might be too late and then the plane is gone.

But really, those speeds were done ages ago by the SR-71 and its related aircraft. With all the years gone by and extra research - it's a pretty safe bet something has gone faster than that and has probably already been retired and replaced by something faster still.

But fighters aren't going to do that. Those things are generally strategic/recon aircraft that are large machines, certainly not fighter plane material.
 
duboka
Posts: 50
Joined: Sat Feb 27, 2016 12:07 pm

Re: How important is top speed to a fighter these days ?

Mon May 20, 2019 12:35 pm

RJMAZ wrote:
The Eurofighter, F-15 and Rafale would all need light afterburner to hit that speed with a few air to air missiles but as their fuel capacity is quite small they will not be able to average a speed as high. If they tried to match the speed of the Suhkoi, F-22 and F-35 they would run out of fuel first.


I've read something different about the Eurofighter and the F-35. The Eurofighter has even the ability to supercruise at Mach 1.21 with a combat load load. And official published numbers are even saying that it has the ability to supercruise Mach 1.5 with an air superiority missile load. And the F-35 engines are not even designed to for this task with my knowledge... Does someone knows more?

And does supercruise means that the aircraft is able to reach Mach 1 or more without the afterburner or does it means that it can use the afterburner to reach Mach 1 but then keep it without it?
 
RJMAZ
Posts: 1452
Joined: Sat Jul 09, 2016 2:54 am

Re: How important is top speed to a fighter these days ?

Mon May 20, 2019 1:28 pm

duboka wrote:
I've read something different about the Eurofighter and the F-35. The Eurofighter has even the ability to supercruise at Mach 1.21 with a combat load load. And official published numbers are even saying that it has the ability to supercruise Mach 1.5 with an air superiority missile load. And the F-35 engines are not even designed to for this task with my knowledge... Does someone knows more?

And does supercruise means that the aircraft is able to reach Mach 1 or more without the afterburner or does it means that it can use the afterburner to reach Mach 1 but then keep it without it?

No you have not read something different. What I said is 100% accurate. You either misread or misinterpreted what has been written.

The best way to work it out would be to determine the maximum level of thrust that can be produced by each aircraft at sea level for 30 minutes.

With a modern and typical fuel consumption of 0.80 lb/(lbf·h) the Eurofighter at full dry thrust will run out of fuel in 30 minutes and 33 seconds.

The F-35 at full dry thrust will last a massive 49 minutes and 32 seconds. This is well above the 30 minutes, the F-35 could use a light afterbuner setting and still reach the 30 minute target.

Dry thrust versus dry thrust the Eurofighter is indeed slightly faster than the F-35. But the F-35 can fly at 25% afterburner setting and travel much faster than the Eurofighter.

The F-22 at full dry thrust will run out of fuel in only 25 minutes. So the F-22 would actually have to use a 90% dry thrust setting to last for 30 minutes. So the supercruise thing is quite overrated as the F-22 lacks the fuel to make the most of it.

The F-35 can actually fly the F-22 supercruise mission profile at the same speed. The F-22 and F-35 are both in a speed class above the Eurofighter. You must ignore peak speeds. It is the fuel load that determines the speed of an aircraft.

The Su-35 at full dry thrust can fly for nearly 40 minutes as it has a large fuel capacity. So it can use a low afterburner setting and still last 30 minutes. So the Su-35 can keep up with the F-22.

Fuel burn becomes less at altitude this is just to compare the data to show how the F-35 can use afterburner in an apple to apple comparison.
 
Planeflyer
Posts: 1391
Joined: Fri Mar 14, 2014 3:49 am

Re: How important is top speed to a fighter these days ?

Mon May 20, 2019 8:17 pm

So is it fair to say that top speed is not critical unless and until an AC can achieve mach 3.2 and maybe not until mach 3.5( margin of error) for sustained periods of time?
 
Ozair
Posts: 3942
Joined: Mon Jan 31, 2005 8:38 am

Re: How important is top speed to a fighter these days ?

Mon May 20, 2019 9:48 pm

Planeflyer wrote:
So is it fair to say that top speed is not critical unless and until an AC can achieve mach 3.2 and maybe not until mach 3.5( margin of error) for sustained periods of time?

Again, speed is close to meaningless if the aspect is wrong. If an aircraft is flying towards you at M3.2-3.5 and your aircraft has the ability to detect it from a long enough distance then the missile intercept geometry is pretty simple. At those speeds there is little manoeuvrability, you are just barrelling straight and fast and become an easy target. Even high I expect most lofting missiles such as AIM-120 if given the time can gain the altitude required, especially something like the D model that has a two way datalink.

Obviously if you’re flowing cold at that speed then nothing is going to catch you but the question would be asked what is the point. At those speeds you are a flying IR beacon and become a target from long range for all to see.
 
checksixx
Posts: 1218
Joined: Wed Mar 09, 2005 11:39 pm

Re: How important is top speed to a fighter these days ?

Mon May 20, 2019 10:42 pm

RJMAZ wrote:
The F-22 will not need afterburner but it has a very small fuel capacity so it actually has no advantage. The Suhkoi and F-35 would need a very low afterburner setting to maintain that speed but they both have a huge fuel capacity allowing them to keep up with the F-22.


You do realize the F-22 and F-35 share nearly identical fuel capacities...? The F-22 can carry even more with external tanks.
 
Max Q
Topic Author
Posts: 7488
Joined: Wed May 09, 2001 12:40 pm

Re: How important is top speed to a fighter these days ?

Mon May 20, 2019 11:18 pm

Thanks for the great responses


They clarify how top speed is helpful in certain scenarios


But as far as escaping from the enemy?


If you turn tail and run aren’t you just presenting a super bright heat source for your attacker and a clear target for his missiles that far eclipse your own top speed?
The best contribution to safety is a competent Pilot.


Guns and the love of them by a loud minority are a malignant and deadly cancer inflicted on American society
 
Ozair
Posts: 3942
Joined: Mon Jan 31, 2005 8:38 am

Re: How important is top speed to a fighter these days ?

Mon May 20, 2019 11:54 pm

Max Q wrote:
Thanks for the great responses


They clarify how top speed is helpful in certain scenarios


But as far as escaping from the enemy?


If you turn tail and run aren’t you just presenting a super bright heat source for your attacker and a clear target for his missiles that far eclipse your own top speed?

If you are in a tail chase Max the missile has to overcome the fleeing target’s speed with its own. That is why in the first graphic I posted above the distance is typically so short for a rear aspect shot. The missile rocket motor generally doesn’t burn forever, it has a finite limit and speed it will reach after which the missile glides, losing energy. Meanwhile the fleeing fighter jet is likely increasing or maintaining its speed away from you. The second graphic shows how the missile loses velocity over its flight time. What it doesn't show is how much of an impact a manoeuvre may have on missile kinematics. During the glide phase the missile loses energy every single time it has to change its direction while the fleeing aircraft is continuing to apply thrust.

The big IR target is less of an issue given most long range missiles are radar guided. If you’re talking post a WVR engagement, where the fleeing aircraft is trying to break the engagement, then perhaps a short range IR missile will work but as the range increases a longer ranged radar guided missile is typically best.

Again the Meteor is an exception to the above as the missile has a very long sustainment burn and so maintains a high energy state for longer and is probably an excellent missile for a tail chase scenario.
 
Planeflyer
Posts: 1391
Joined: Fri Mar 14, 2014 3:49 am

Re: How important is top speed to a fighter these days ?

Tue May 21, 2019 12:28 am

Sorry, I was not clear at all. My working assumption Is that any all new AC has stealth Incorporated into it so at what speed in a stealthy ( let’s F35 like) platform are all current missile defense systems obsolete?
 
Ozair
Posts: 3942
Joined: Mon Jan 31, 2005 8:38 am

Re: How important is top speed to a fighter these days ?

Tue May 21, 2019 1:42 am

Planeflyer wrote:
Sorry, I was not clear at all. My working assumption Is that any all new AC has stealth Incorporated into it so at what speed in a stealthy ( let’s F35 like) platform are all current missile defense systems obsolete?

I doubt there is an IR stealth technology with the ability to hide a Mach 3+ aircraft so any decent IR sensor and sensor fusion should be able to spot that airframe a long way away. If you really want to stay stealthy across the entire spectrum, IR and radar and EM, then slow is better than fast.

I don’t think anyone can give you an indicative speed at which a missile system becomes obsolete, there are just too many variables and missile systems continue to advance alongside the aircraft. For example the Israeli Stunner missile has a dual seeker head that incorporates both EO-IIR and active radar homing. In that context going fast lights you up to the EO-IIR sensor. It is better against that system to stay sub-sonic and rely on the IR stealth features built into the aircraft. If the adversary only has traditional homing such as semi-active/active radar or command guidance then high speed in an RCS stealth airframe works well.
 
Planeflyer
Posts: 1391
Joined: Fri Mar 14, 2014 3:49 am

Re: How important is top speed to a fighter these days ?

Tue May 21, 2019 2:21 am

Thanks for the explanation. Very helpful.
 
RJMAZ
Posts: 1452
Joined: Sat Jul 09, 2016 2:54 am

Re: How important is top speed to a fighter these days ?

Tue May 21, 2019 2:48 am

Max Q wrote:
Thanks for the great responses


They clarify how top speed is helpful in certain scenarios


But as far as escaping from the enemy?


If you turn tail and run aren’t you just presenting a super bright heat source for your attacker and a clear target for his missiles that far eclipse your own top speed?

An F-22 could indeed turn away and accelerate quickly to mach 2 and most missiles would not catch it.

The same medium range missile might have a 100 mile range in a head on engagement but only a 10 mile range in a tail chase. This is because both aircraft are still moving while the missile is in the air so you have to look at where the enemy aircraft will be and how far the missile will actually need to travel.

If a missile was fired 100 miles away in a head on engagement the missile might only fly say 70 miles as the enemy aircraft. When the missile hits the two aircraft might only be 40 miles apart of they are both supersonic. If the enemy did a 180 degree turn as soon as the missile was launched the missile has no chance of hitting the target. The missile was launched on the assumption that the enemy aircraft would keep traveling closer.

When a missile is launched within the "no escape zone" it means even if the enemy turns away the missile has enough fuel/range to hit it. The faster the enemy the closer you must get to gurantee a hit. The no escape zone is usually much closer than the maximum range of a missile.

Most engagements I have seen in the last few decade are not head on but from the 45 degree angle. So the enemy does not have turn a full 180 degrees to run. A simple 90 degree turn away could mean the aircraft is too far away to engagement. This cat and mouse game is quite common. Lots of missiles get launched at max range to scare the enemy and the enemy simply turns away.
 
YIMBY
Posts: 584
Joined: Tue Sep 20, 2016 4:32 pm

Re: How important is top speed to a fighter these days ?

Tue May 21, 2019 6:13 am

Speed is important for air policing, too. Requirements for Switzerland, Finland and Canada may be very different.
 
mxaxai
Posts: 1052
Joined: Sat Jun 18, 2016 7:29 am

Re: How important is top speed to a fighter these days ?

Tue May 21, 2019 10:12 am

Ozair wrote:
The big IR target is less of an issue given most long range missiles are radar guided. If you’re talking post a WVR engagement, where the fleeing aircraft is trying to break the engagement, then perhaps a short range IR missile will work but as the range increases a longer ranged radar guided missile is typically best.

Again the Meteor is an exception to the above as the missile has a very long sustainment burn and so maintains a high energy state for longer and is probably an excellent missile for a tail chase scenario.

Makes you wonder why so few air forces have ordered the Meteor, compared to the AMRAAM.

Also regarding rear aspect visibility, most stealth aircraft so far are optimised for attack, not for running away. The radar crosssection is almost always larger from the rear, especially if you're not using some fancy nozzles like the F-117 or F-22. I doubt that IR plays a major role in BVR situations. So top speed may be relevant to leave the radar detection radius quickly, but then you'd slow down to a more fuel efficient speed.
 
Max Q
Topic Author
Posts: 7488
Joined: Wed May 09, 2001 12:40 pm

Re: How important is top speed to a fighter these days ?

Tue May 21, 2019 10:16 am

RJMAZ wrote:
Max Q wrote:
Thanks for the great responses


They clarify how top speed is helpful in certain scenarios


But as far as escaping from the enemy?


If you turn tail and run aren’t you just presenting a super bright heat source for your attacker and a clear target for his missiles that far eclipse your own top speed?

An F-22 could indeed turn away and accelerate quickly to mach 2 and most missiles would not catch it.

The same medium range missile might have a 100 mile range in a head on engagement but only a 10 mile range in a tail chase. This is because both aircraft are still moving while the missile is in the air so you have to look at where the enemy aircraft will be and how far the missile will actually need to travel.

If a missile was fired 100 miles away in a head on engagement the missile might only fly say 70 miles as the enemy aircraft. When the missile hits the two aircraft might only be 40 miles apart of they are both supersonic. If the enemy did a 180 degree turn as soon as the missile was launched the missile has no chance of hitting the target. The missile was launched on the assumption that the enemy aircraft would keep traveling closer.

When a missile is launched within the "no escape zone" it means even if the enemy turns away the missile has enough fuel/range to hit it. The faster the enemy the closer you must get to gurantee a hit. The no escape zone is usually much closer than the maximum range of a missile.

Most engagements I have seen in the last few decade are not head on but from the 45 degree angle. So the enemy does not have turn a full 180 degrees to run. A simple 90 degree turn away could mean the aircraft is too far away to engagement. This cat and mouse game is quite common. Lots of missiles get launched at max range to scare the enemy and the enemy simply turns away.



Great explanation RJ, thanks for that and
‘No escape zone’ reminds me of a book written by Nick Richardson, a Royal Navy
Sea Harrier pilot shot down by a SAM in the
Bosnian conflict

An apt title summing up what you describe
The best contribution to safety is a competent Pilot.


Guns and the love of them by a loud minority are a malignant and deadly cancer inflicted on American society
 
RJMAZ
Posts: 1452
Joined: Sat Jul 09, 2016 2:54 am

Re: How important is top speed to a fighter these days ?

Tue May 21, 2019 11:44 pm

Another example I have previously used to describe how fuel is more important than supercruise is the following:

Take an F-22, remove an engine, plug the intake and fill the void with approx 9,000lb of fuel. Ignoring the asymmetrical thrust issue you now have an F-22 with half the thrust but 50% more internal fuel.

I would say this F-22 would have improved range and speed in 90% of missions. It could no longer supercruise but it could still reach those speeds using a higher thrust setting with the single engine.

If you took a full subsonic mission profile such as a combat air patrol the normal F-22 would be cruising with the two engines at 50% dry. The single engine F-22 would need to be cruising at 100% dry thrust to maintain speed. Both aircraft would be burning the same amount of fuel per hour but the single engine F-22 has 50% more fuel so it could fly for 50% further/longer. The single engine F-22 wins by a big margin when it comes to endurance.

Now take a standard F-22 mission with 500nm subsonic to the target zone, a 100nm supercruise dash and 500nm subsonic back to base. We can assume 40% of the fuel is used for the transit, 20% for the supercruise and the 40% for the return home. The single engine F-22 with its 50% greater subsonic range would mean it has 3.5 times more fuel available to do the supercruise section. The single engine F-22 could go full afterburner for that 100nm supercruise section. It will perform the same profile with fuel to spare despite fuel guzzling afterburners.

So in summary the F-22 is over engined and under fueled. A poor compromise for a multi role fighter that has a negative result on most missions. This was due to the F-22 being designed got air dominance which has a few very rare situations where you need extreme thrust.

The F-35 is like this single engine F-22. A much better compromise and can perform the vast majority of missions with greater range. The F-35 is two thirds of the empty weight of the F-22 yet the F-35 has more internal fuel than the F-22.

Thrust to weight ratios, max speeds or supercruise speeds are irrelevant if you have no fuel to achieve the higher thrust levels.

Penetration counter air program is going to take supercruise and fuel capacity to an entire new level.

Who is online

Users browsing this forum: DenverA330 and 8 guests

Popular Searches On Airliners.net

Top Photos of Last:   24 Hours  •  48 Hours  •  7 Days  •  30 Days  •  180 Days  •  365 Days  •  All Time

Military Aircraft Every type from fighters to helicopters from air forces around the globe

Classic Airliners Props and jets from the good old days

Flight Decks Views from inside the cockpit

Aircraft Cabins Passenger cabin shots showing seat arrangements as well as cargo aircraft interior

Cargo Aircraft Pictures of great freighter aircraft

Government Aircraft Aircraft flying government officials

Helicopters Our large helicopter section. Both military and civil versions

Blimps / Airships Everything from the Goodyear blimp to the Zeppelin

Night Photos Beautiful shots taken while the sun is below the horizon

Accidents Accident, incident and crash related photos

Air to Air Photos taken by airborne photographers of airborne aircraft

Special Paint Schemes Aircraft painted in beautiful and original liveries

Airport Overviews Airport overviews from the air or ground

Tails and Winglets Tail and Winglet closeups with beautiful airline logos