What is specificall about D-30F6 engine and Mig-31 inlet

Cold war, Korea, Vietnam, and Desert Storm - up to and including for example the A-10, F-15, Mirage 200, MiG-29, and F-18.
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garrya

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Unread post25 Dec 2015, 13:44

People say mig-31 and mig-25 fly much higher and faster than others aircraft even though they have high wingloading and draggy airframe because of its variable inlet and it's engine is specifically designed for high speed operation
but Su-27, F-15 also have variable inlet so why cant they fly as high and as fast?
and D-30F6 is a turbofan engine with high bypass value so how can it still operating effective at high altitude?
p/s :
i made my original thread in keypublishing but people told me that if i come here a guy name TEG can give me the answer :D so TEG can you please help me with my question?
http://forum.keypublishing.com/showthre ... -turn-rate
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Unread post25 Dec 2015, 17:46

Other smaller details:
For such large jet as Mig-31, both the relativt small wings have thin airfoil for less drag. Meaning it cant turn very well but its not part of its designed requirement.
Other details, even the Vertical Stabz is quite thin, and fairly sweeped back angle. A stark kontrast to the F-15, Su-27 and F-22 vertical stabz.

And the cockpit glass..
You say the Mig--31 has a draggy airframe..??
Compaired cockpit section and what I mention above with other jets, then you'll find the Mig-31 quite sleek ;)

The whole cockpit section of Mig-31 looks like it belong on a orbital Rocket.
A stark contrast to the F-22 cockpit section, with its bathtub design and fragile bubble cockpit glass.
Last edited by borg on 25 Dec 2015, 19:14, edited 3 times in total.
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KamenRiderBlade

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Unread post25 Dec 2015, 18:08

If you look at the MiG-25 & MiG-31, they're literally designed to be dragsters in the sky.

Meant for straight line speed and wide turning radius.

So they were designed to intercept US aircraft at range and to spy on targets.
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That_Engine_Guy

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Unread post26 Dec 2015, 21:01

garrya wrote:People say mig-31 and mig-25 fly much higher and faster than others aircraft even though they have high wingloading and draggy airframe because of its variable inlet and it's engine is specifically designed for high speed operation but Su-27, F-15 also have variable inlet so why cant they fly as high and as fast?
and D-30F6 is a turbofan engine with high bypass value so how can it still operating effective at high altitude?
p/s :

The MiG-25 an MiG-31 have very different engines.

The MiG-25 is powered by twin Tumansky R-15BD-300 afterburning turbojet engines. These engines also included a water/methanol injection system within the inlet for added mass-flow (increasing thrust) during takeoff. Some sources list the R-31 as the 'newest' engine being flown in the MiG-25. I'm going to assume the R-31 is a newer or export variant of the R-15BD with greater power and reliability, but the facts and figures here are for the R-15. It's interesting to note the R-15 engine was the first Soviet military engine to have electronic controls.

The MiG-31 is powered by twin Soloviev D-30F6 augmented turbofan engines of 'medium' (0.57) bypass.
(In comparison the F100-PW-100/200/220(E) engines have a 0.70 BPR, and the newer F100-PW-229 has a 0.36BPR or the AL-31F at 0.57)

The R-15 engines were very failure prone in early versions, and have VERY limited life (150Hrs). High-speed dash (over Mach 2.5) would further reduce the life if not kill the engines during the dash. Lieutenant Viktor Belenko said after his MiG-25 defection, that Maximum speed speed of his Foxbat-A was Mach 2.5, and speeds above Mach 2.8 would cause the engines "to run out of control and burn up."

Remember both of these engines are massive; the D-30F6 is 4.8' (1.455m) in diameter and 15.8' (4.836m) long and 5081lbs (2305kg). The R-15/31 is even larger/heavier.

You ask; "D-30F6 is a turbofan engine with high bypass value so how can it still operating effective at high altitude? "

The bypass ratio on the D-30F6 isn't very high as we've found.

You are correct saying variable inlets are key to Mach 2+ flight. The inlets must slow the air to subsonic speeds and provide supersonic pressure recovery. They must do so without the sonic shock wave reaching the compressor blades and without causing excessive distortion (turbulence) to the air. They all have the same basic function and are fairly well understood.

While it's true that a Turbojet is more efficient at high-altitude or high-speed flight, an afterburning turbofan can still go fast. Exhaust gas velocity is the driving force. Just because a large BPR commercial turbofan makes 100,000lbs of thrust doesn't mean it can go Mach 2, but an F-104 with a 16,000lb thrust engine could! Why? Thrust is force x mass. You either accelerate a small mass to a high velocity, or a large mass at a lower velocity. Fighter engines with afterburners are the former and it's that high velocity supersonic afterburner thrust that translates into high speed. Depending on the variables for it's operation, it's the afterburner in these engines that make them capable of this high Mach number flight.

The R-15 and D-30 both have MASSIVE afterburners, the largest I've ever seen on fighter sized aircraft. It's fairly obvious the designers created a large afterburner needed for the performance they desired from the D-30 engine. The D-30 was more efficient at MIL power flying down low, and has vastly better reliability and service life. It was also a 'common' engine with other transport aircraft in production at the time. (Tu-154M, Il-76, Il-62M)

Now to your question; "Su-27, F-15 also have variable inlet so why cant they fly as high and as fast? "

The facts/figures for an aircraft's 'service ceiling' or 'maximum speed' are highly subjective. Was the figure measured in combat configuration or clean? Was this with minimum fuel load? Was this from a production aircraft or special/prototype configuration? What were the atmospheric conditions at the time? Is this a calculated value or demonstrated? Is it propaganda based, or altered as the true value is classified?

There is not much difference between saying a service ceiling of 62,000ft or 68,000ft when you consider aircraft can 'zoom' many thousands of feet higher or the missiles being employed have ranges measured in many miles. Likewise a few degrees temperature difference, or changes in atmospheric pressure can make speeds Mach 2.5 and Mach 2.8 very subjective. Again, missiles traveling Mach 4 or 5 negate any minor speed difference between aircraft at any similar altitude.

The thing to take away from this conversation is that these numbers are subjective and not the know all/tell all of aircraft performance. If your MiG-25 dashes across a battle at Mach 3.2 but is then rendered inoperable after the flight for the rest of the conflict; what use is it? A MiG-31 with weapons needed for an intercept mission can't even approach Mach 2.83. The F-15 can fly Mach 2.5 clean but why would it even do so in combat?

Notice how maximum speeds today are lower than what they were in the 1960s or 1970s. Many aircraft that are 'capable of Mach 2' will never reach that speed. Everyone realizes that high maximum speed is unused for combat. Likewise combat aircraft will rarely fly near their service ceiling. It is better to fly where control surfaces, wings and engines work at their best. Nobody wants to fly the edge of a flight envelope where performance is near it's limit.

In the end, it's very expensive and difficult to have an aircraft fly at Mach 2+ and above 60,000. It's rarely done, and is no longer a requirement for the designers to reach.

Even though numbers look cool on Wikipedia, take them with a heavy dose of reality.

Keep 'em flyin' :thumb:
TEG
[Airplanes are] near perfect, all they lack is the ability to forgive.
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Unread post26 Dec 2015, 23:49

And THAT is what makes F-16.net better than keypubs. Thanks TEG, as always.
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Unread post27 Dec 2015, 00:06

sprstdlyscottsmn wrote:And THAT is what makes F-16.net better than keypubs. Thanks TEG, as always.

Give credit to KeyPubs though for rererring the OP to TEG... :D
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Unread post27 Dec 2015, 02:04

Guys like TEG, Spazsinbad, Gums, etc (People who have Real World Experience) will keep us common folk grounded in reality.

That's what All Military/Aviation forums need. Not fanboys, not internet Fantasy Air Force statisticians.

If you can't keep it real, can't keep it honest, then you're just peddling junk info, we need less of that.

That's why I love it here.

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eloise

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Unread post27 Dec 2015, 11:44

That_Engine_Guy wrote:. Many aircraft that are 'capable of Mach 2' will never reach that speed. Everyone realizes that high maximum speed is unused for combat. Likewise combat aircraft will rarely fly near their service ceiling. It is better to fly where control surfaces, wings and engines work at their best. Nobody wants to fly the edge of a flight envelope where performance is near it's limit.

In the end, it's very expensive and difficult to have an aircraft fly at Mach 2+ and above 60,000. It's rarely done, and is no longer a requirement for the designers to reach.

Even though numbers look cool on Wikipedia, take them with a heavy dose of reality.

Keep 'em flyin' :thumb:
TEG

IMHO, unlike f-15, su-27, F-16,
the Mig-25, Mig-31 use their high speed , high altitude fairly more frequent
60k feet, mach 2 is the edge of F-15 flight envelope, it can not even reach that altialti in standard days
Image
By contrast for mig-25 that is around it's center
Image
Image
Image
In some case it can reach around 25 km
Image
I think one of the reasons Mig-25/31 have high speed is that their intake can create 5-6 shocks wave while the like of F-15, su-27 limit to around 2-3 shocks
Image

Some source I read indicate that the turbin blade of R-15 retract at high speed making it a pure ramjet engine, not sure if that the case for D-30F6
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garrya

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Unread post27 Dec 2015, 13:07

That_Engine_Guy wrote:The MiG-25 an MiG-31 have very different engines.

The MiG-25 is powered by twin Tumansky R-15BD-300 afterburning turbojet engines. These engines also included a water/methanol injection system within the inlet for added mass-flow (increasing thrust) during takeoff. Some sources list the R-31 as the 'newest' engine being flown in the MiG-25. I'm going to assume the R-31 is a newer or export variant of the R-15BD with greater power and reliability, but the facts and figures here are for the R-15. It's interesting to note the R-15 engine was the first Soviet military engine to have electronic controls.

Does the D-30f6 have similar system ¿


That_Engine_Guy wrote:
Remember both of these engines are massive; the D-30F6 is 4.8' (1.455m) in diameter and 15.8' (4.836m) long and 5081lbs (2305kg). The R-15/31 is even larger/heavier.
The bypass ratio on the D-30F6 isn't very high as we've found.
The R-15 and D-30 both have MASSIVE afterburners, the largest I've ever seen on fighter sized aircraft. It's fairly obvious the designers created a large afterburner needed for the performance they desired from the D-30 engine.

Can you explain the term " massive afterburner"¿ as far as I know they are not the engine with highest thrust in after burner ( I think F-135 , F119 have far higher thrust )

That_Engine_Guy wrote:There is not much difference between saying a service ceiling of 62,000ft or 68,000ft when you consider aircraft can 'zoom' many thousands of feet higher or the missiles being employed have ranges measured in many miles. Likewise a few degrees temperature difference, or changes in atmospheric pressure can make speeds Mach 2.5 and Mach 2.8 very subjective. Again, missiles traveling Mach 4 or 5 negate any minor speed difference between aircraft at any similar altitude.

The thing to take away from this conversation is that these numbers are subjective and not the know all/tell all of aircraft performance. If your MiG-25 dashes across a battle at Mach 3.2 but is then rendered inoperable after the flight for the rest of the conflict; what use is it? A MiG-31 with weapons needed for an intercept mission can't even approach Mach 2.83. The F-15 can fly Mach 2.5 clean but why would it even do so in combat?

Notice how maximum speeds today are lower than what they were in the 1960s or 1970s. Many aircraft that are 'capable of Mach 2' will never reach that speed. Everyone realizes that high maximum speed is unused for combat. Likewise combat aircraft will rarely fly near their service ceiling. It is better to fly where control surfaces, wings and engines work at their best. Nobody wants to fly the edge of a flight envelope where performance is near it's limit.

In the end, it's very expensive and difficult to have an aircraft fly at Mach 2+ and above 60,000. It's rarely done, and is no longer a requirement for the designers to reach.

Even though numbers look cool on Wikipedia, take them with a heavy dose of reality.

Keep 'em flyin' :thumb:
TEG

Shouldn't high altitude and high speed give more energy for missiles thus allow longer range engagement ¿
and it is much harder for missiles to intercept high , fast target
Isn't that the whole purpose of supercruise ¿
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Unread post27 Dec 2015, 15:36

All aircraft are build for a mission.
=> Interceptors are build to "get there fast". That's the mission.

F-15A was build as 'the all round superior dogfighter" => That is a different mission.

Russia is LARGE.
Mig-31 has to get there FAST and with RANGE to spare and shoot "at speed and at range". Turning is NOT in its book.

Interceptors are build that way.

Remember : The clean F-104 that zoom-barrel rolled around a SR-71 at 72.000 ft?

Each aircraft is build for the mission.
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Unread post27 Dec 2015, 15:54

"Can you explain the term " massive afterburner"¿ as far as I know they are not the engine with highest thrust in after burner ( I think F-135 , F119 have far higher thrust )"

This is what "massive afterburner" means:

greg_in_mig-25_02.jpg


Also, not all engines are created equally. The Mig-25's engine for example only produces ~22,500lbs of thrust on the bench. But I guarantee you it produces more than an F100 at say Mach 2.5 and 70,000 feet. Look at the size of the Mig-25s intakes. Look at the size of the nozzles. The Mig-25 relies a lot more on inlet compression than the F-15 does. The J58, J93, and Tumansky R-15B-300 are all low-pressure engines that relied upon the inlets performing much of the compression at high speeds and altitudes.
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sferrin

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Unread post27 Dec 2015, 15:56

vilters wrote:Remember : The clean F-104 that zoom-barrel rolled around a SR-71 at 72.000 ft?


Got a source for that?
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Unread post27 Dec 2015, 17:03

garrya wrote:Can you explain the term " massive afterburner"¿ as far as I know they are not the engine with highest thrust in after burner ( I think F-135 , F119 have far higher thrust )



The question to ask would be how much thrust are they putting out at 60,000+ ft - because the thrust figures you see are normally sea level and static (not in flight) and don't really give you a clue to how much is coming out at X altitude / X speed.
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Unread post27 Dec 2015, 17:07

Yes.
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Unread post27 Dec 2015, 17:11

vilters wrote:Yes.


"Yes" in reference to what? Having a source? If so, let's see it.
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