I'm not an expert in jet engines or fighters engines but it's better to have an engine capable of flying at mach 2.5 than mach 1.6 because, even if those speed won't be reached, it means that your engine is much more solid and the limit is far away from your cruise speed or some top speed you could reach during a fight.
I am not engine expert either, but we are talking about what you need and not what you want.
If you want a fast car you can simply put the biggest engine you can make into it... leading to a very big and very heavy car that burns fuel faster than you can fill it... even when not accelerating.
Another approach is to get a standard sized car and fit the biggest engine you can but then you look at the weight of everything and try to shave off as much as you can to reduce the amount of weight the vehicle has to carry around.
Formula one sports cars don't even carry a full tank of fuel if it does not require it to minimise weight.
The point is that different engines prefer different speeds... if you are only ever going to be subsonic then a turboprop is the best option... if you need some supersonic capability turboprops are not an option at all.
Most subsonic transports and bombers use high bypass turbofans for efficient high subsonic flight relying on weight of airflow for thrust rather than velocity of airflow.
For supersonic speed you need a turbojet or a low bypass turbofan, or a ramjet or scramjet.
Most modern jet aircraft that are supersonic like modern fighters and interceptors are low bypass turbofans... to get supersonic they dump a lot of fuel into the after burner to generate the thrust to go fast... but it is very inefficient.
Even a ramjet is more efficient even though it is only an afterburner driven engine.
Back to your comment that having a really big powerful engine is better than not... do you think the car you drive to work at 100km/h or less would be better if it had a V8 700hp engine in it?
Especially when that means removing the front seats and shifting everything to the back seats with enough fuel in the fuel tank for 2 minutes at full throttle?
A long range bomber would benefit from high speed... anything that avoids stuff benefits from higher speed.
The problem is that more power means more fuel needed for every flight which means bigger aircraft, shorter range, inflight refuelling tankers all the time.
Conversely if the new PAK DA is a low drag flying wing design then new low bypass turbofans could allow supercruising, which means mach 1.4+ flight, which would actually be as much use as mach 2 flight.
Let me explain.
In an F-15 you can either fly subsonic and fly decent distances at that speed for interception, or you can fly supersonic, but it is like a car... depending on whether you are on the flat or going up a hill you don't just change speed with a push of the pedal... in top gear on a hill you might find sitting at 100km to be easy with moderate revs, or on the flat you might find 130km/h is a good speed... what you might find is that without changing down a gear or trying to run at huge revs that 100km is not a good speed to run at.
Back to the F-15... a subsonic target would need supersonic flight so ABs would be engaged, but ABs means a certain speed is possible but the speed range is not huge... in other words against a subsonic target the F-15 is going to comfortably catch up easily which gives them control of the interception. With a supersonic target the closing speed is much lower and against a fast target like a Tu-160M2 it might be a case of giving up and letting an F-15 closer to where the Blackjack is going to have a go.
Mach 1.4 will be a real challenge for the F-35 to intercept and with supercruising that means the bomber is not rapidly burning through its fuel like the F-15 is to try to catch it.
The extra few years the PAK DA is taking means scramjet potential is becoming real... a ramjet is a very simple engine... air goes in one end and is compressed... fuel is added and burned and it all goes out the rear at high speed meaning thrust. A scramjet means the air can flow through the engine at any speed because the fuel is burnt at supersonic speeds. All current jet engines are limited because the fuel burnt has to be at subsonic speeds... so at mach 2.83 the air going into the engine of the MiG-31 has to be slowed to subsonic speeds and then fuel added and burned and exited out to produce thrust.
In a scramjet engine you don't need to slow down the airflow or restrict it in any way... meaning higher air speed for the exhaust and more volume of air too...
The SR-71 used bypass air like a ramjet to achieve mach 3.5 flight speeds.
While having mach 1.6 max limit means your engine is more suceptible to damage if you reach accidently mach 1.5 or mach 1.6 in afterburners in a dogfight.
It is not about a speed limit.
The best example is the bomber Sukhoi was developing... the T-4.
It was a mach 3 bomber. It was going to be very expensive to make and to use, but the US had the Valkyrie so the USSR had to have one too.
Sukhoi got busy so the bomber design was handed to Tupolev who knew a mach 3 bomber would be a complete waste of time and money... he convinced them that mach 3 was excessive and mach 2 would be good enough.
It all comes down to the law of diminished returns... and applies to stealth as well.
A mach 3 bomber would only be slightly more safe than a mach 2 bomber but the cost of building and operating a bomber that could fly mach 3 was 1,000 times the cost of making one to fly at mach 2.
What I am trying to say is that when scramjet technology is mature then high speed flight will be much easier and cheaper... it is like during WWII faster than the speed of sound could not be performed by propellers... only rockets... but it was expensive and very unsafe.
The invention and perfection of jet engines has made it relatively easy to go supersonic, but going faster than mach 2 for any period of time is still not with us yet. Sure you can load in huge amounts of fuel, but for a strategic bomber that already needs lots of fuel there is no choice but to make the biggest bomber in the world... no something that will be cheap or easy to use.
Moreover, for bombing mission mach 2.0 is very usefull to get away from the target once destroyed because you can outrun fighters coming to you. Remember the 10 AMRAAMs shot and failed to a Mig-25 in Irak or Pakistani uncapable to intercept Indian Mig-25 near Islamabad. No need to use it all the way long, just to put some distance.
Cheaper and simpler to use 5,000km range cruise missiles and not let those fighters get anywhere near you.
Closing on the target at mach 2 to avoid interception means any SAM system could detect and shoot you down easily, let alone fighters sent up as you approach with heat seeking missiles from the front...
Then we can agree that your comparation of the speed of the Su-PAK-FA with the speed of the MiG-31 was not right, being both aircrafts of different role.
My comparison was to show that not all aircraft benefit from very high speed... in fact only a very few aircraft need high speed. Very high speed would be useful for many types but the cost means only those that seriously need it actually get it.
In the case of the fighters, the speed is also important, in lower measure than in the case of the interceptors, but it is also important.
In the 1970s the US realised that top speed for fighters is not that important because except the odd aircraft used as an interceptor (ie MiG-25/31) they will never achieve such speeds, so the aircraft that replace the F-15 and F-14 have top speeds less than mach 2. The F-16 and F-18 are both sub mach 2 aircraft. This saves in weight and cost but has really not made them ineffective in their primary roles as fighter bombers.
Like I said and have said several times top speed is almost never achieved.
At mach 2.4 or so the Su-27 appears to be rather fast, but it would take a full 20 minutes at full AB at medium to high altitude to actually get to that speed so it almost never actually does it... you burn up most of your fuel and you can't manouver properly at that speed.
For a MiG-31 it pretty much accelerates all the way to its target so the time spent is not such an issue and it is basically a fuel truck.
Being a better aircraft, the Tu-160 totally killed the procurement of the Tu-95. It is obvious why. Same size, same range, higher speed that leads to a more effective compliance of its main mission, but that also helps in almost every other mission with use of conventional armament over land or sea. The replacement was done and was effective in terms of procurement.
In terms of active service, Russia has been building the number of Tu-160 that considered necessary until now, and plans to build more in the future because they consider necessary to have more of them. And this need is not based only in the analysis of the needs for the compliance of its role with nuclear weapons, also the needs for operations with conventional armament are being considered.
The Tu-160 is a very good aircraft... but it is expensive to buy and to operate and up until now they didn't really have enough aircraft for a really viable force. The decision to make more is great... I remember suggesting they build more in the 1990s and being told that the technology to make them was gone... recently read that it has been tested and is working fine now.
The Tu-95 has remained in service all this time because there were never enough Tu-160s to replace them. Now that they are making at least 50 Tu-160M2s it makes you wonder why bother with the PAK DA.
The Tu-160 is very capable, but it is expensive to operate.
Having a more stealthy subsonic bomber/cruise missile carrier makes the problems of the defences much more difficult.
More importantly unless these aircraft are expected to be first strike weapons even at supersonic speed they will not reach their missile launch positions until several hours after the ICBMs and SLBMs have impacted the enemy.
This means little to no enemy air defences to penetrate and no interceptors active.
In conventional conflicts against countries like terrorist forces in Libya or Syria or Yemen or Somalia for instance... long range cruise missiles seem to get the job done.
One thing is to have T-95s in the arsenals since the 1960s and the 1970s and use them, and other thing is to order in the 2020s aircrafts that have the same flaw.
The current Tu-95s are actually Tu-142s and were built in the 1980s and 1990s. For what they do there is little you could do to improve their design or performance... they are still the worlds fastest propeller driven aircraft on the planet and can move at 950km/h.
At low altitude they are actually rather faster than most subsonic jets... the large propellers are rather more efficient down there...
PS: Between the Tu-95 and the Tu-22, I would say that the Tu-22 can remain longer in the Russian Armed Forces than the Tu-95, because it remains more actural as military concept than the Tu-95. Lower speed means today a bigger problem than lower payload at the time of the compliance of the missions vs well armed enemies.
I am sure the Russian AF has noted the efficiency of using Tu-22M3s with dumb cheap bombs and will now likely keep them for some time, but much of their role is now being eclipsed by the Su-34, which is part of its replacement.
I was thinking the Tu-160 was going to replace the longer range role of the standard strike aircraft with a heavy payload, but the Tu-160s after upgrade seem to have lost their bomber optics under the nose...
The Tu-95s don't really have bomb capacity, so that means the Backfire will likely soldier on even though the Tu-22M3 is a theatre strike bomber and the Tu-95 is a strategic cruise missile carrier.
The new engines for the PAK DA could be made to also fit the Tu-22M3 and further improve its performance hopefully.
The Tu-22 is an strategic bomber
No it is not. It is a theatre bomber... think of it as two F-111s fused together and not needing inflight refuelling.
And it means the survability of the Tu-22 properly used is higher than the survability of the Tu-95.
Neither plane would have been flying at supersonic speed so if they might as well have used the much cheaper subsonic bomber... actually the Tu-95 doesn't carry bombs so using the Tu-95 would have made it cheaper as it would have used cruise missiles instead of bombs and not gone any where near Georgia for the attack.
Its range is not very important. It can't reach US mainland neither western europe by flying through the north. In Syria it did nothing military important, just show of force. Its strikes could have been done by any plane from Hmeimin air base. I f you keep it just for operations like in Syria thats wasting money.
It is good for the Tu-22M3 regiments to get bombing practise... especially as they are using the same cheap dumb bombs they would use for bombing practise... the fact that the accuracy is up there with cruise missile attacks but without the cost is amazing. Something the west gladly ignores... imagine the effect on the bottom line if the western taxpayers found dumb bombs can be made as effective as expensive guided ones for the price of one upgrade.
The Tu-22 would reach the US coast, at least Seattle, the problem would be the return. Likely would need two refueling operations, one going and other returning. I would have to think about which would be the best option (Tu-22 with refueling or Tu-95 without).
The Tu-22M3 has never been and cannot be fitted with inflight refuelling equipment...
Despite it there are lots of missions in Eurasia and over the sea that the Tu-22 can do. In this area the range really reachs until the areaas where the adversaries have high density of air defenses.
The purpose of the Tu-22M3 is theatre strike... that means China/Japan/South Korea, plus Middle East (ie Syria), plus Europe... that was and is its job.
The Russian Navy no longer has any Backfires AFAIK.
The Tu-22M (quite different than Tu-22) is a cruise missile carrier. So that would mean it could launch a salvo of cruise missiles at long enough ranges where it wouldn't get hit. But I noticed as of recent years how much they use it to drop dumb bombs.
The Tu-95 and Tu-160 are cruise missile carriers. The Tu-22M3 is a long range strike... as I said above... two F-111s fused together with one inflight refuelling topup built in.
I always had a soft spot for the Tu-22M and think building more of those with modern systems like composite materials, modified engines, newer avionics package, etc would be really ideal. I know they once planned to use Irbis-e radar on it. It would be huge and be the most powerful radar used on such an aircraft. But it was too costly with little benefit.
I have always liked it too... an interesting MiG-31 replacement... cut back to two crew but put a huge radar in the nose and extend the internal bomb bay and carry a dozen S-400 or S-500 missiles...
New engines from the PAK DA should allow it to super cruise around the place which should greatly increase its flight range, and of course the new light metals that are heat resistant and any composites you like and you have a much lighter much more powerful aircraft....
If it was a situation the Tu-95 never would have been in, neither the Tu-22 should have been in a situation like this.
The Tu-22M was bombing... which is one of its roles. The Tu-95 is not a bomber... it is a cruise missile carrier.
I would not completely remove supersonic bombers from the fleet,
Having a mix of high speed bombers and more stealthy slower bombers makes the forces rather more flexible and the slower bombers should be much cheaper to keep operational.
More importantly while the Tu-160s are being built to can withdraw some of the Tu-95s and with the upgrades of the engines of the Tu-160s they could develop new high energy engines able to make super cruising bombers a possibility which offers the best compromise of higher flight speed but without enormous fuel consumption.
China was claimed few years ago as possible customer for new-built Tu-22Ms however it never came to be.
They only wanted two of them... yeah... I know who blinked first...
Two different aircraft actually.
The photos you posted show the Tu-22M3 and the Tu-22... the Tu-22M0, Tu-22M1, and Tu-22M2 had different nose shapes to the M3 model, but all had their engines internally rather than in pods at the base of the tail fin like the Tu-22.
Every source says that the Tu-22M was developed from the Tu-22. Being for the same role it means the Tu-22M is a variant of the Tu-22.
They are from scratch different designs. Tupolev was not supposed to be making a new aircraft design... he was supposed to be making the Sukhoi T-4 mach three bomber... he knew it would be too expensive to buy and operate but could not get permission to build the bomber he wanted to build so he called the bomber he wanted to build Tu-22M so it sounded like a version of the Tu-22. It was nothing of the kind.
He got away with it though.
And the Tu-22M is a much better aircraft than the Tu-22 ever could be.
They give it the name Tu-22M because it would have been baned by the START threaty.
Nothing to do with any treaty... everything to do with the politics of the time...