high-bypass turbofans and military aircraft

[tflash]

I was flying some FSX airplanes lately, like the Airbus A-321 with the truly magnificent CFM56-5 133 kN or 30.000 lbs class high-bypass turbofans.

 

Even in FSX, you can already feel the tremendous power of current generation turbofans. It is exactly in this area that military airplanes are lagging horribly behind. A whole fleet of Boeing-707 based aircraft need replacement in the USAF, not to speak about the outright tragedy surrounding the Nimrod fleet in the UK.

 

Lets face it: even the current arms race with Typhoon, Rafale and Mig-35 aircraft involves fighters with engine designs dating from the stone-age eighties; many of them conceived in the pre-digital age. The end of the cold war effectively halted necessary investments, and we wittness the consequences today.

 

I think F-35 will be the first to sport a TRULY modern, higher bypass turbofan. I think we should not be fooled by the high specs of some engines that in fact are eighties technology.

 

One can only dream of an A-10A sequel with the kind of fuel-efficient turbofans we see on todays commercial fleets. I will not even go into the Tumansky R-195 turbojets that "power" the Su-25T.

 

So what's your opinion: will modern engine technology revolutionize military aviation further?

[rogue_blade]

wow i never thought of that. quite insightful!

engine technology and fuel efficiency has a longg way to go as we are in the early stages of using more efficient yet powerful fuels such as bio-diesel. yet im sure all of the effort being put into commercial jet engine technology is having its fare share of use in military research

[GGTharos]

Fuel efficiency = range.

 

Obviously for the modern fighter, you also want raw power ...

[Pilotasso]

I was flying some FSX airplanes lately, like the Airbus A-321 with the truly magnificent CFM56-5 133 kN or 30.000 lbs class high-bypass turbofans.

 

Even in FSX, you can already feel the tremendous power of current generation turbofans. It is exactly in this area that military airplanes are lagging horribly behind. A whole fleet of Boeing-707 based aircraft need replacement in the USAF, not to speak about the outright tragedy surrounding the Nimrod fleet in the UK.

 

Lets face it: even the current arms race with Typhoon, Rafale and Mig-35 aircraft involves fighters with engine designs dating from the stone-age eighties; many of them conceived in the pre-digital age. The end of the cold war effectively halted necessary investments, and we wittness the consequences today.

 

I think F-35 will be the first to sport a TRULY modern, higher bypass turbofan. I think we should not be fooled by the high specs of some engines that in fact are eighties technology.

 

One can only dream of an A-10A sequel with the kind of fuel-efficient turbofans we see on todays commercial fleets. I will not even go into the Tumansky R-195 turbojets that "power" the Su-25T.

 

So what's your opinion: will modern engine technology revolutionize military aviation further?

 

 

The reasons behind the existence of low bypass engines on military aircraft such as fighters or fuel tankers AWACS etc are different. For these last, simply theres a huge amount of surplus arround to carry other engine types for some time yet. This is called Technological Inertia and is further agravated by means of support living off the same experienced enginners, technical procedure and facilities for eons.

 

For fighters is extremely difficult to have high bypass engines because they are much bulkier, just take alook at an airliners jet and try figure out where such monsters would fit in. The solution would have to be like in the A-10. They would have to be sticking out of the airframe. Furthermore a jet cant be very fast with large compressors. They would desintegrate and/or limitate acceleration to max speed above mach 1. Military engines for supersonic jets may be based on old designs but the lates gen engines implement exoctic technologies such as powder metalurgy wich does allow higher operating temperatures and even higher bypass ratios (not as high as airliners of course).

 

Engines for F-35 and F-22, Superhornet, Typhoon and Rafale are only loosely based on experienced gained with engines from previous gen F-15/16's, tornado, mirages (even these have been highly MOD'ed by now)and immensly improved on power and efficiency. You would be tremendously understimating the technological prowess behind that by saying they are pre digital era lol

[D-Scythe]

I think F-35 will be the first to sport a TRULY modern, higher bypass turbofan. I think we should not be fooled by the high specs of some engines that in fact are eighties technology.

 

Considering that the F-35's engine is based heavily on the F-22's F119 technology, this statement seems a bit silly don't you think?

[rogue_blade]

oh yea and we can super cruise now :D

[MiGMadness]

oh yea and we can super cruise now :D

 

What do you mean we can supercruise NOW?

 

This badass MoFo was supercrusin' from the 11th of August 1954 (3rd flight).

 

 

Did a lot more besides that. A truly amaizing aircraft for it's time.

 

Probably one of the reasons behind the f-35's name. ;) :P

 

The Lightning’s speed and climb performance were excellent not just by 1950s or 1960s standards but even compared with modern operational fighters. Its initial rate of climb was 50,000 ft per minute (15 km/min). The Mirage IIIE climbed initially at 30,000 ft/min (9 km/min), the MiG-21 managed 36,090 ft/min (11 km/min), and the Tornado F3 43,000 ft/min (13 km/min).

The official ceiling was a secret to the general public and low security RAF documents simply stated 60,000+ ft (18 000 m), although it was well known within the RAF to be capable of much greater heights. Recently the actual operating ceiling has been made public by the late Brian Carroll, a former RAF Lightning pilot and ex-Lightning Chief Examiner, who reports taking an Lightning F53 up to 87,300 feet (26 600 m) at which level "Earth curvature was visible and the sky was quite dark".

 

In 1984, during a major NATO exercise, Flt Lt Mike Hale intercepted an American U-2 at a height which they had previously considered safe from interception. Records show that Hale climbed to 88,000 ft (26,800 m) in his Lightning F3. Hale also participated in time-to-height and acceleration trials against F-104 Starfighters from Aalborg. He reports that the Lightnings won all races easily, with the exception of the low level supersonic acceleration, which was a "dead heat."

Carroll reports in a side-by-side comparison of the Lightning and the F-15C Eagle (which he also flew) that "acceleration in both was impressive, you have all seen the Lightning leap away once brakes are released, the Eagle was almost as good, and climb speed was rapidly achieved. Takeoff roll is between 2,000 & 3,000 feet [600 to 900m], depending upon military or maximum afterburner-powered take-off. The Lightning was quicker off the ground, reaching 50 feet [15m] height in a horizontal distance of 1,630 feet [500m]".

 

In British Airways trials in April 1985, Concorde was offered as a target to NATO fighters including F-15s, F-16s, F-14s, Mirages, F-104s - but only Lightning XR749, flown by Mike Hale and described by him as "a very hot ship, even for a Lightning", managed to overtake Concorde on a stern conversion intercept

[rogue_blade]

wow im so glad im british!

[GGTharos]

Other supercruising aircraft include the F-104, the SR-71, and likely the B-58 also.

The reason that you hear all this 'supercruising' hype is that the F-22 and F-35 can do it 'without afterburner' ... that in and of itself isn't a huge feat - turbojets were pretty efficient in afterburner at high speeds and altitudes anyway.

[MiGMadness]

The reason that you hear all this 'supercruising' hype is that the F-22 and F-35 can do it 'without afterburner' ...

 

Exactly how the English Electric Lightning did it as well.

[Brit_Radar_Dude]

not to speak about the outright tragedy surrounding the Nimrod fleet in the UK.

Huh?? What tragedy? Did I miss something?

[p_o_d_2_2]

Other supercruising aircraft include the F-104, the SR-71, and likely the B-58 also.

The reason that you hear all this 'supercruising' hype is that the F-22 and F-35 can do it 'without afterburner' ... that in and of itself isn't a huge feat - turbojets were pretty efficient in afterburner at high speeds and altitudes anyway.

 

I thought I read somewhere that the F-15E and the Eurofighter could as well.

[ericinexile]

I fly the CFM56 for a living and agree that it's a very nice engine. Fortunately for the engine I am unable to fly faster than M.82. Approaching transonic and beyond, all the high-bypass advantages begin to erode. That's why we see comprimises with fighters that have less concern for fuel efficiency and even less for noise footprint.

 

Smokin' Hole

[WhiskeyRomeo]

I think F-35 will be the first to sport a TRULY modern, higher bypass turbofan.

A "higher bypass ratio" is of course, relative.

In the 1960s the military was using the GE TF39 (later commercial variant was CF6) with a 8:1 bypass ratio on the C-5A. (You know you're onto something good when the NAVY starts dropping TF39s into it's boats!)

For the C-17 they're using the P&W F117-PW-100 (military version of the earlier PW2000 used by 767s) with a 5.9:1 bypass ratio.

Even the old 707/KC-135 JT3D/TF33 tubofan had a 1.4 bypass ratio.

 

The F-35's Pratt & Whitney F135 engine has a 0.75:1 bypass ratio (CV & STOL versions). The conventional take off and landing (CTOL) version will have a 0.56:1 bypass ratio. F135 Bypass Ratios

For comparion: Eurofighter Eurojet EJ220 - 0.4:1 / F-18 GE F404 - 0.34:1 / F-15 & F-15 PW F100 - 0.34:1.

As the bypass ratios point out all the fighter aircraft are using low bypass turbofan engines.

 

I think the military & aircraft designers/manufacturers have a good handle on when it makes sense to use high bypass or low bypass (with or without afterburner) turbofan engines.

[tflash]

The F-35's Pratt & Whitney F135 engine has a 0.75:1 bypass ratio (CV & STOL versions). The conventional take off and landing (CTOL) version will have a 0.56:1 bypass ratio. F135 Bypass Ratios

For comparion: Eurofighter Eurojet EJ220 - 0.4:1 / F-18 GE F404 - 0.34:1 / F-15 & F-15 PW F100 - 0.34:1.

As the bypass ratios point out all the fighter aircraft are using low bypass turbofan engines.

 

 

Indeed I should mean *relatively* higher bypass ratio's. It is difficult to imagine how to mount the enormous engines of todays ETOPS aircraft onto fighters. I see however promising opportunities for CAS aircraft.

 

Neither the A-10A nor the Su-25T are supersonic performers, and that is an understatement. A CAS aircraft with a higher bypass turbofan would give very good, reduced noise performance and excellent loiter/range capabilities. It would also give impressive acceleration in the lower-speed regimes these aircraft operate.

 

An engine update for A-10A was considered I think, but didn't materialise yet.

 

Anyway there will already be such a large fleet of transport, utility, tanker, awacs, observation etc. aircraft that are bound to benefit from more modern engines, that ecological demands have forced much earlier on civilian fleets.

[Yo-Yo]

You don't take in account the fact that HBP turbofans have the thrust decreasing with the speed. The more you increase BP the more skew has the thrust vs speed curve. And it is a fundamental law because big fan as a propeller processes a huge amount of air so the velocity added to the free stream is lower than turbojet adds.

[tflash]

I agree, but neither the A-10 nor the Su-25T seem to need much speed for their job; instead, the Su-25 could use a little less speed and somewhat better low-speed manoevring. I was thinking more like an S-3 Viking design, which seemed very well suited for the lower-speed loiter ASM job.

[komarov]

Hey guys!

 

The bypass ratio is an important thing for the specific fuel consumtion, but if the bypass ratio goes higher, the exhaust gas speed goes smaller, and this thing is not so good for the fighters.

The F-35's engine bypass ratio is one of the smallest in the world, because this engine came from the Raptor's F-119, the engine with the supercruise capability.

Supercruise= fly supersonic without the afterburner.

Why we use the afterburner?

Because the higher heat produce higher nozzle pressure ratio, so it's produce the higher exhaust speed.

The thrust is came from the mass of the gas and the speed of the gas.

Look the swedish JA-37 Viggen.

RM-8B engine eat 140kg air in every second at 100-104% rpm.

The MiG-21bis R-25F-300 engine eat 68kg, the Gripen RM-12 too, the MiG-29's RD-33 eat 72kg, Su-27's Al-31F eat 112 kg...

The Viggen's engine came from the commercial world, the RM-8A/B' father was the B-737-200/B-727... P&W JT-8D.

In the 60's a 1,1-1,4 bypass ratio was very big.

Now a normal commercial or transport bypass ratio is approx. 3-5.

 

But in the military world the fuel consumption or the noise are not so important.

The thrust at low altitude-low speed, high altitude-high speed, the high overall pressure ratio, the exhaust speed are much more important.

 

So, the military aircraft's bypass ratio never grown up above 1,5.

The B-1B's F-101GE100 engine b.rat. is 2.

But this is a unique thing.

 

F-15/16 (P&W F-100PW100/200/220E 0,65; F-100PW-229 0,33; GE F110GE100/129/132 0,76~0,8) Su-27 family (AL-31F 0,59) MiG-29 (RD-33 0,44~0,49) F-18 family and Gripen ( F-404/414, RM-12 0,3)

F-22A (F-119PW100 0,15!) F-35 (F-135PW100 0,25)

MiG-31 ( D-30F6 0,55)

 

YF-22-YF-23 ( GE YF-120GE100 variable bypass ratio 0,25 - 0,7 higher for the lower spedd, lower for the higher speed, higher altitude)

[tflash]

Thanks for the info, Komarov!

 

I noticed BTW that just about everything is wrong with my examples: as a matter of fact, the A-10 and S-3 Viking share the same engine (GE TF-34), which was the BASIS of the succesful commercial CF-34 regional jet high-bypass turbofans (so not really military lagging behind here ;)

 

I can be wrong though, but my guess would be that even in the military world fuel consumption and noise footprint will become a big deal.

 

Specially for the F-35 this will be an issue, even more so in F-35B.

 

There is another element gaining importance: the different way we look at military presence in the air. It is no longer a question about how many planes you can bring into the air at a given time, but how many assets ARE in the air at ANY given time. Todays battlefield are continously overflown by high-resolution sensor equipped aircraft that are sensing, targeting, relaying, observing etc. For all those assets specific fuel consumption and low noise signature are very relevant.

[Trident]

Wow, where did you get the figures for the GE F120 Komarov? I've been looking for the range of its variable bypass ratio for ages but never found any hard info. Thanks for posting that!

[D-Scythe]

I thought I read somewhere that the F-15E and the Eurofighter could as well.

 

You probably did. The F-15E with F100-PW-229 engines can supercruise without CFTs and LANTIRN. The Eurofighter can supercruise at Mach 1.3 if it afterburns to that speed first.

[komarov]

And the Tu-144D with the Koliesov RD-36-51A engines could reach the Mach 2 without any afterburner, because this engine use a unique "turbocompressor" system after the turbine.

Very interesting, but of course, very low life level solution.

Compress the exhaust gas after the turbine again.

[Yo-Yo]

And the Tu-144D with the Koliesov RD-36-51A engines could reach the Mach 2 without any afterburner, because this engine use a unique "turbocompressor" system after the turbine.

Very interesting, but of course, very low life level solution.

Compress the exhaust gas after the turbine again.

 

 

I only want to say that afterburner does not rise pressure as you have written. It heats the gas at the same pressure but its enthalpy (or should I say its ability to produce the work) gets higher so the work i.e. exhaust gas speed gets higher too. The main trick is that if you work down the pressure from P1 to P2 the power rises with the initial T of the gas.

The fuel burning in AB has higher efficience than a pair " turbine - postcompressor" so the overall effectiveness of this solution must be lower.

[rogue_blade]

Huh?? What tragedy? Did I miss something?

 

yea what tragedy?

[britgliderpilot]

yea what tragedy?

 

Well an MRA2 crashed in Afghanistan recently, but I'm not sure that's what he means . . .

 

 

There isn't a replacement aircraft for the Nimrod, it's true - however, the MRA4 upgrade (in progress, first aircraft to be delivered soon) includes new avionics, new wings, AND new engines . . .

 

It'll still only be a fleet of twelve aircraft, but hey - that just might be enough.