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Elite 1K Joined: Jul 22, 2005 Posts: 1012 Status: Offline

Corsair1963 wrote:

dwightlooi wrote:

Somehow, I doubt that the F-35A's in total drag is more than 2.4 times higher than the F-104 at low supersonic speeds (Mach 1~1.3). That is how much more thrust the F135 has over the J79 -- 28,000 lbs vs 11,800 lbs. Aerodynamic performance at Mach 2~2.5 which can really benefit from the rocket shaped profile of the F-104 is largely irrelevant. Hey, the F-35 is 8% lighter with 20% more thrust than the F-4 Phantom while having the capacity to carry 65% more fuel, 5750 lbs of weapons in internal bays and presenting an RCS the size of a golf-ball.

Truely, impressive when put in that context! As for Super Cruise we will likely have to wait for more data to become public.......I wonder what the max military power is on GE's forthcoming F-136? As rumor claims it make about 5,000 lbs more in A/B than its PW F-135 cousin. (i.e. 48,000 vs 43,000 lbs) So, even without "Super Cruise" the F-35 is going to be one hot fighter! Wink

This should have a sticky. Want to talk impressive? The varient of F135 in the X-32 put out 52,000lbs of thrust in afterburner and 34,000 dry. RR was quoted in AvWeek stating that the F136 would be capable of 56,000lbs in afterburner. That later figure has since been not repeated which could mean A) the guy being quoted didn't know WTH he was talking about, B) that it would have the potential to be developed into a 56k engine (like the F100 is up to 37,500 now), or C) he accidently let the cat out of the bag. I'm guessing it was B.

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where do people get this stuff? I have a hard time believing the LIGHTER JSF X-plane with the VASTLY MORE POWERFULL engine would have had such a hard time with the hovering part of the program. Likely someone looked at the weight of the X-32 and said "Oh wow, with fuel it weight X so its dry thrust for hovering must by X+. So that means its afterburning power is X*Y=Z This is a hell of an engine!!" No. X-32 could only hover after having several thousand pounds of STRUCTURE and SURFACE removed and on light fuel loads. Thats why X-32 could not do the "Hat Trick"

Elite 1K Joined: Jul 22, 2005 Posts: 1012 Status: Offline

sprstdlyscottsmn wrote:

where do people get this stuff? I have a hard time believing the LIGHTER JSF X-plane with the VASTLY MORE POWERFULL engine would have had such a hard time with the hovering part of the program. Likely someone looked at the weight of the X-32 and said "Oh wow, with fuel it weight X so its dry thrust for hovering must by X+. So that means its afterburning power is X*Y=Z This is a hell of an engine!!" No. X-32 could only hover after having several thousand pounds of STRUCTURE and SURFACE removed and on light fuel loads. Thats why X-32 could not do the "Hat Trick"

Wow, wish I was as smart as you think you are. Doesn't take a brain surgeon to come up with the numbers. Got the X-32's engine thrust from International Airpower Review. And of course the dry thrust has to be at least equal to the X-32's VTOL weight or it won't go anywhere. Pretty simple eh? Rolling Eyes

sprstdlyscottsmn wrote:

where do people get this stuff? I have a hard time believing the LIGHTER JSF X-plane with the VASTLY MORE POWERFULL engine would have had such a hard time with the hovering part of the program. Likely someone looked at the weight of the X-32 and said "Oh wow, with fuel it weight X so its dry thrust for hovering must by X+. So that means its afterburning power is X*Y=Z This is a hell of an engine!!" No. X-32 could only hover after having several thousand pounds of STRUCTURE and SURFACE removed and on light fuel loads. Thats why X-32 could not do the "Hat Trick"

Well, the afterburner thrust is IRRELEVANT. The X-32 was a direct lift SVTOL. That means that it vectors its engine thrust downwards to provide lift without the aid of an additional vertical liftfan. Without the additional fan, the lift thrust is essentially the maximum dry thrust rating of the engine -- ala Harrier. In this case, it was 34,000 lbs by working the engine extra hard. This is about 5,500 lbs less than the F-135 is able to put out with the additional airflow from the vertical fan. If you think 34,000 lbs is a lot, think again. That is 15.4 tons. The X-32 itself is probably about 13 tons which doesn't leave much for fuel, instrumentation and everthing else.

The X-32 could not and was never intended to be able to light its afterburners in vertical hover flight. The aft nozzle has to be straightened out for the burner can to be geometrically in place.

But if the assertion is that the F-135 engine core has significant extra power to spare for either future thrust growth, superior performance at high altitudes, or that it may have been considerably derated for exceptional life at current thrust levels, I think that is probably true. This is a core with the horsepower to generate 39,400 lbs of DRY THRUST with the lift fan engaged. Of course, the extra working area helps and this may not be possible with the airflow limitations of the 51" engine diameter, but it does tell you that the core is significantly overpowered and has tons of untapped reserves.

The F136 (if it retains the F120 core dimensions) has an even larger core. Not by much, but enough to make a difference in the YF-22/23 applications.

Why is the P&W F-135 and GE F-136 making so much more power than the P&W F-119 in the Raptor. Seem like the reverse would be true. As the F-22 is made for Super Cruise and High Speed flight in general.........

Corsair1963 wrote:

Why is the P&W F-135 and GE F-136 making so much more power than the P&W F-119 in the Raptor. Seem like the reverse would be true. As the F-22 is made for Super Cruise and High Speed flight in general.........

Well, the F119 is officially rated at 35,000 lbs, but the current consenses is that it is really a 39,000~40,000 lbs thrust engine. Of this, about 26,000~30,000 is available dry.

The F135 is a more powerful engine than the F119. It uses the an updated version of the F119 core with an larger diameter fan and low pressure spool (51" vs 46~47"). This allows it to move more air and do so more efficiently. Bypass ratio also went from about 0.2:1 to 0.56:1 probably yielding a small improvement in TSFC numbers.

The F135 does not make "so much more" power. It makes slightly more power. The official rating is 28,000 lbs dry and 43,000 lbs with reheat. The engine makes 39,400 lbs dry only when it is driving the lift fan in addition to roll post and downward vectored engine thrust. The lift fan adds much larger area with which to move air allowing for more of the engine core's power potential to be harnessed. In theory, you can put an even larger fan on the F135 and have it make ~40,000 lbs dry. But if you do so, you'll end up with a very fat engine which doesn't fit into the F-35 or any reasonable fighter airframe. Nonetheless, the untapped power of the core is still useful because it means that the engine will have a lot of core power to overcome the performance loss with altitude and it probably also indicates at least a good potential for future thrust growth without changing the core design. With no additional fan area, it was possible to get about 34,000 lbs of dry thrust (maybe not for more than for the limited duration -- 1~2min -- of a vertical landing attempt) out of the design to support direct lift in the X/F-32 proposal. This is a reasonable estimate for thrust growth in the F-135 if pursued in the near future -- up to about 34,000 lbs dry, 52,000 with A/B without changing the engine diameter or intake area.

Enthusiast Joined: Mar 13, 2007 Posts: 98 Status: Offline

Corsair1963 wrote:

Why is the P&W F-135 and GE F-136 making so much more power than the P&W F-119 in the Raptor. Seem like the reverse would be true. As the F-22 is made for Super Cruise and High Speed flight in general.........

Want a simplied answer: look at a Boeing 747 engine which has "a lot" of thrust and look at the F-5A which is a flee in comparison. Thrust and velocity are related to one another, but not in a 1:1 relationship... too many variables to be 1:1.

Just because a 747 engine has a lot of thrust does not imply that the same engine on a smaller and lighter and slicker airplane would be able to hit supersonic airspeeds (the engine aint designed for that as should be obvious). And as such, the F-35 may have more thrust "per capita" than an F-22, but that does not imply greater airspeeds. It just means that it carry more crap under the wings than an F-16 w/o falling out of the sky since there is more energy in reserve to out-muscle the penalties of carrying sh*t under your wings.

The F-35 simply ain't optimised for "speed" as is the F-22.

fox100 wrote:

Want a simplied answer: look at a Boeing 747 engine which has "a lot" of thrust and look at the F-5A which is a flee in comparison. Thrust and velocity are related to one another, but not in a 1:1 relationship... too many variables to be 1:1.

Just because a 747 engine has a lot of thrust does not imply that the same engine on a smaller and lighter and slicker airplane would be able to hit supersonic airspeeds (the engine aint designed for that as should be obvious). And as such, the F-35 may have more thrust "per capita" than an F-22, but that does not imply greater airspeeds. It just means that it carry more crap under the wings than an F-16 w/o falling out of the sky since there is more energy in reserve to out-muscle the penalties of carrying sh*t under your wings.

The F-35 simply ain't optimised for "speed" as is the F-22.

Let's put it this way, the F-135 engine makes more thrust than the F119. But there is only ONE on the F35 whereas there are TWO F119s on the F-22. The F135 is also larger in diameter and heavier than the F119. In addition, the F-35 while roughly 2/3 of the weight of the F-22 has roughly 75% the frontal area. For these, it has roughly 61% the thrust. In other words, the F-22 has more thrust per unit weight and/or cross sectional area. Assuming similarly aerodynamics, the F-35 will be slower than the F-22.

How much slower is the interesting question. Because 61% the thrust with 75% the area, 68% the weight and a very similar layout in general does not add up to an aircraft half as fast, there are many who believe -- not without good reason -- that if the F-22 is a Mach 1.7+ supercruiser, it is highly unlikely that the F-35 maxes out at Mach 0.85 on dry thrust.

Elite 1K Joined: Aug 19, 2004 Posts: 1090

Why do you think cross sectional frontal area is a figure of merit for either the F-35 or F-22 or any other aircraft for that matter? If you really wanted to do a simplified drag analysis, you wouldn't use cross sectional frontal area, okay? If memory serves, you would use "wetted area" for certain drag component calculations... like skin friction drag. Thrust per unit of cross sectional area... it has no meaning or analytical value in aeronautical engineering. You can come up with a bunch of "common sense" notions like these, but that doesn't mean they're actually meaningful. Either hit the books way harder or resist the urge to sound like you're knowledgeable in these non-trivial subject matters.

Raptor_One wrote:

Why do you think cross sectional frontal area is a figure of merit for either the F-35 or F-22 or any other aircraft for that matter? If you really wanted to do a simplified drag analysis, you wouldn't use cross sectional frontal area, okay? If memory serves, you would use "wetted area" for certain drag component calculations... like skin friction drag. Thrust per unit of cross sectional area... it has no meaning or analytical value in aeronautical engineering. You can come up with a bunch of "common sense" notions like these, but that doesn't mean they're actually meaningful. Either hit the books way harder or resist the urge to sound like you're knowledgeable in these non-trivial subject matters.

The idea was never to arrive at an accurate calculation at all. What I was saying is that the F-35 is an aircraft that is substantially lighter (~68% the weight) and somewhat smaller (~75% the frontal cross section and a little smaller than that in planar area) and hence require less power to push it through the air. This along with the known installed thrust of the engine being roughly 61% that of the Raptor does not suggest 50% the cruise performance; it suggests more than that.

The reason I cite the frontal area is because it gives a good reference to the size of the aircraft and it is easy to see and compare. Calculating the wetted area is very complicated and it still won't give as an accurate prediction of drag anyway so I am not going to bother. If you think that it doesn't yield any kind of an accurate estimate? I never said it does. If you think that it is beneath your standard of approximation, well I am sure it is. If you don't agree with my very rough methods, well I guess thats just too bad!

Elite 1K Joined: Aug 19, 2004 Posts: 1090

Your very rough methods, as you call them, are not methods at all. You're just rambling off numbers that don't support your conclusions. Your conclusions may be in the ballpark or may not. Even if some of your conclusions are correct in a very general sense, the methods you've used to reach them are completely bunk. It's like someone doing a math problem wrong, but getting the right numerical answer by chance.

Raptor_One wrote:

Your very rough methods, as you call them, are not methods at all. You're just rambling off numbers that don't support your conclusions. Your conclusions may be in the ballpark or may not. Even if some of your conclusions are correct in a very general sense, the methods you've used to reach them are completely bunk. It's like someone doing a math problem wrong, but getting the right numerical answer by chance.

Well, that is YOUR opinion. Mine is that the weight, frontal area (which gives a rough reference to overall size) and thrust of the F-35 in comparison to that of the F-22 gives an indication to its performance differences between the two. It's OK if you don't agree!

Since your "accurate and correct" methods cannot be applied given the limited information on hand, and you are reluctant to give an opinion, maybe this is all we have to go on. As I have said, if you think it is beneath you, well maybe it is! And really, it doesn't matter.

Active Member Joined: Nov 22, 2004 Posts: 134

sferrin wrote:

RobertCook wrote:

The F-104 was more or less an engine case with a few minor appendages, lightly dipped in JP-4 and squeezed to remove the excess. Smile

LOL! I looked up the back end of an F-104 without its engine once and I'd have to agree. Was thinking it should say "Coors" on the outside.

dwightlooi wrote:

Well, the afterburner thrust is IRRELEVANT. The X-32 was a direct lift SVTOL. That means that it vectors its engine thrust downwards to provide lift without the aid of an additional vertical liftfan.

If I remember correctly, the forward nozzles redirected only the bypass thrust, in order to reduce the likelihood of hot gas ingestion. For comparative purposes, we could view this system as having a smaller vectored "lift fan" (possibly with a higher bypass ratio?) that works all the time, as opposed to only functioning during hover, as in the F-35. Similarly, we could view the F-35's system as having a highly variable bypass ratio with two settings: with the lift fan for hover and without the lift fan for forward flight.

dwightlooi wrote:

Without the additional fan, the lift thrust is essentially the maximum dry thrust rating of the engine -- ala Harrier. In this case, it was 34,000 lbs by working the engine extra hard.

I imagine that it might also have had a higher-output fan, a higher bypass ratio, or both. My understanding is that is would be the most feasible way to obtain greater thrust from the same engine at low speeds and altitudes without cutting substantially into its growth potential or reliability and service life.

dwightlooi wrote:

But if the assertion is that the F-135 engine core has significant extra power to spare for either future thrust growth, superior performance at high altitudes, or that it may have been considerably derated for exceptional life at current thrust levels, I think that is probably true.

The F135's core is not all that different from the F119's, which was done in order to greatly reduce risk and development time. If you optimized it for higher altitudes and speeds, you'd essentially end up with the F119, and the reverse is more or less true, as well.

dwightlooi wrote:

This is a core with the horsepower to generate 39,400 lbs of DRY THRUST with the lift fan engaged. Of course, the extra working area helps and this may not be possible with the airflow limitations of the 51" engine diameter, but it does tell you that the core is significantly overpowered and has tons of untapped reserves.

It could probably generate even more power if you made it into a turboprop, but at some point it's not going to be a good match for the type of flight performance we'd expect from a fighter, of course. I know that you know this, I'm just speaking in general.

dwightlooi wrote:

The F136 (if it retains the F120 core dimensions) has an even larger core. Not by much, but enough to make a difference in the YF-22/23 applications.

You may turn out to be right, but I'm not sure I'd make the same assumption, because at the time, the YF120 was a bit more mature than the YF119, whereas today the F119/F135 core has been through much more development.

Corsair1963 wrote:

Why is the P&W F-135 and GE F-136 making so much more power than the P&W F-119 in the Raptor. Seem like the reverse would be true.

The F-35 is not a lightweight fighter, and it only has one engine--its engine will generate as much thrust as it needs to in order to meet specifications, and development time and money will be invested accordingly.

Corsair1963 wrote:

As the F-22 is made for Super Cruise and High Speed flight in general.........

The numbers on which you are basing this assessment are only valid for the engines at sea-level atmospheric pressure, sitting still on a test stand, and with no aircraft inlets in front of them. How they perform while installed on their respective aircraft and moving at high speed and altitude are an entirely different matter. Although it would not greatly surprise me if the F119 could generate more dry thrust than the F135 under these conditions--for which both it and the F-22 in general are designed--there is still more to this subject than just engine thrust, such as the lift/drag ratios at each point in their envelopes.

dwightlooi wrote:

Well, the F119 is officially rated at 35,000 lbs, but the current consenses is that it is really a 39,000~40,000 lbs thrust engine. Of this, about 26,000~30,000 is available dry.

The latest figure from a "reliable" source (a member of the USAF or contractors) I've heard is 39000 lbs (static, sea level), although 37000 lbs is what they generally tell the public at air shows. It's still not published as an official specification in writing, though, as far as I've seen.

dwightlooi wrote:

In addition, the F-35 while roughly 2/3 of the weight of the F-22

In terms of empty weight, that's true, although it's closer to 3/4 when loaded at takeoff.

dwightlooi wrote:

has roughly 75% the frontal area. For these, it has roughly 61% the thrust.

It's more like 55-58%, based on the growth that the F119 is said to have undergone. Dude, try to stop using slightly optimistic numbers to make your points. Wink

dwightlooi wrote:

In other words, the F-22 has more thrust per unit weight and/or cross sectional area. Assuming similarly aerodynamics, the F-35 will be slower than the F-22.

How much slower is the interesting question. Because 61% the thrust with 75% the area, 68% the weight and a very similar layout in general does not add up to an aircraft half as fast,

If this sort of reasoning were true, then technically the F-15, when totally clean, should be a lot closer to the F-22 than it actually is, yet it still doesn't live up to the numbers. The F-35 may remind us of the F-22 regarding appearance, but the devil is in the details.

dwightlooi wrote:

there are many who believe -- not without good reason -- that if the F-22 is a Mach 1.7+ supercruiser, it is highly unlikely that the F-35 maxes out at Mach 0.85 on dry thrust.

Well, I can certainly buy that and even consider it an understatement, but things like power and drag are far from linear, and it's impossible to tell without wind tunnel data (which has its own limitations) or CFD at the very least how fast an aircraft is going to fly on a certain amount of thrust (and you'd need to know the specifics of that, too). For now, it's enough that the F-35, given its requirements, still retains competitive fighter performance and has great potential in general.

Enthusiast Joined: Mar 13, 2007 Posts: 98 Status: Offline

dwightlooi wrote:

fox100 wrote:

Let's put it this way, the F-135 engine makes more thrust than the F119. But there is only ONE on the F35 whereas there are TWO F119s on the F-22. The F135 is also larger in diameter and heavier than the F119. In addition, the F-35 while roughly 2/3 of the weight of the F-22 has roughly 75% the frontal area. For these, it has roughly 61% the thrust. In other words, the F-22 has more thrust per unit weight and/or cross sectional area. Assuming similarly aerodynamics, the F-35 will be slower than the F-22.

How much slower is the interesting question. Because 61% the thrust with 75% the area, 68% the weight and a very similar layout in general does not add up to an aircraft half as fast, there are many who believe -- not without good reason -- that if the F-22 is a Mach 1.7+ supercruiser, it is highly unlikely that the F-35 maxes out at Mach 0.85 on dry thrust.

I don't have exact figures to make precise statements, but not even I (a devoted F-35 and JSF hater), believe that the F-35 cannot bust through to at least 1.3'ish mach numbers while on a strict diet of only internal aams and 23mm rounds.

But alas, most definately the surface area and weight of this F-35 makes her a pig dog for a fighter; in relative terminology as compared to what is possible with aircraft design (or was possible in the mid-90s). Everyone quotes xyz increase in wing area, and 123 increase in thrust, all over the F-16C, but no one, and I mean no one pays any attention at all to the surface area of this single engined cyclops. You also have to look at weight distribution as well, again, which is not so great for a single engined aircraft which carries an "F" designation.

If the F-35A can't bust through the mach barrier in a2a internal config then and cruise comfortably so, my god will I have lost ALL faith in the DoD, the guys at WP, the guys everywhere that had anything to do at all with this monstrosity (I still find it hard to believe they left off the Sukhoi 'styled' serpent-like tv nozzel). If 0.85 is her running speed without the burners lit, and on internal aams only... God help us because all the gee whiz bang helmets and displays and micro filled boxes will not help us outside of simulated missions.

Wow you really hate the F-35. A couple questions though:

You mention surface area and weight as detriments to performance ("pig dog for a fighter"). Are you talking about wing area or wetted area?

You mention weight distribution and I'm assuming you mean center of gravity. Are you concerned that LM has somehow picked the wrong CG for the jet?

You doubt Mach 1.3 range speeds as being possible. At what altitude? Sea level? 15,000 feet? 37,000 feet? Huge difference in drag, thrust, angle of attack, etc at those different levels.

Lot of variables out there....trying to see which ones you were using.

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Cruise speed of the F-35