Quote Originally Posted by FBW View Post I don’t always calculate RCS. But when I do, I prefer to use Google

I prefer to use a good textbook, such as Knott, Shaeffer, and Tuley’s classic ‘Radar Cross Section’. -Mercurius

Bit of an off color joke from a popular beer commercial in the states. Not a slur aimed at you Mercurius, I find your posts to be amongst the most even handed and informative. It was more a incredulous reaction to trying to compare highly classified RCS numbers with any certainty.

Regarding the RCS comparisons to a steel marble or golf ball, I was always under the impression that the DoD used these analogies for media consumption. An explanation that RCS of the aircraft varies greatly on the angle presented to the radar would result in op-eds on how “stealth” is a waste of money. One recalls the articles claiming that stealthy aircraft could be detected when it rains.

My question is whether these new articles from Russian news and Sukhoi interviews about the Pak-fa RCS reflect a change from their original position that they were not aiming for that level of LO seen in the F-22 for cost/ performance trade-off issues? Pravda ran this back in 2010 (Russia’s T-50 PAK FA Not Fifth-Generation Fighter Jet Yet – English … Pravda.ru)
cannot find the source, but remember a Russian official making a comment to the effect that the Pak-fa’s goal was better maneuverability, range, and a price below 100 million U.S., at cost of a slightly higher RCS

Recent comments,
“In the F-22 (U.S. fifth generation fighter – IF-AVN) – 0.3-0.4 meters We have similar requirements for visibility, “- said Davidenko, are of a different nature. Was there a change in requirements? Or are the recent comments reflecting ongoing developments, future changes?

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Idea admittedly plagiarized but apropos considering the current F-22 / Pak-fa RCS debate

“PAK FA will have 0,0035 sq m ( maybe much lower?) frontal RCS, while side RCS will change and grow up to 1sq m. In results the average total rcs will be ~0,4 sq m.”

“according Sukhoi PAK FA will achieve similar RCS level as F-22 (we don’t know it’s a bit better or worse than magic F-22A golf ball).
” My point was that even if PAK FA will have two times greater minimal frontal RCS than F-35, it’ll have a lot of other advantage ( kinematics, radar range, maneuverability) against US light /medium multirole fighter – F-35 ( especially in a-a combat)”

I would find it very hard to believe that Russia had any accurate measure of the RCS of the F-22 or F-35. I would also find it hard to believe that Sukhoi has a very accurate idea of the PAK-FA RCS. They probably have a rough idea from computer modeling (indoor RCS Model testing?), and only RCS measurements based on shape of the aircraft. This does not take into account the RAM, any issues with production tolerances with the airframe, issues that may come up from fitting the various radar, antennae, OLS. Unless there is a model or prototype not yet seen publicly, Sukhoi probably has a lot of testing still left to do in certifying the true RCS of the Pak-fa.

That’s probably one reason that Russia is building (upgrading) an RCS range:http://www.janes.com/article/31716/former-soviet-pvo-centre-to-conduct-rcs-tests-on-t-50-and-pak-da, http://russiandefpolicy.wordpress.com/2013/12/10/

I spent much of my youth living near the RCS range for the US and was able to see the RAH-66, early JSF models, and others upside down on their stands for months at a time while in RCS testing. It is apparently a slow process in going from a computer model, to a rcs mock-up, to a production representative vehicle. I’ve read that Sukhoi has completed some RCS testing (indoor range?), but recent prototypes are just being fitted with the radar and other systems for testing. It does not seem that there is a prototype fitted with all systems and RAM coatings that would provide production representative testing. (Anyone who has seen an outdoor RCS range knows what I mean, think huge distances, miles between radars and the test stands)

One would expect this testing to reveal issues with traps or hotspots that need to be addressed by Sukhoi or sub-contractors. Many of these changes may not be visible. Production tolerances on LO airframes are rumored to be very tight. F-22 assembly workers reported hearing an audible “click” as parts were fitted together.

I am not denigrating the Pak-fa, just find any hand wringing or pronouncements a bit premature.

[QUOTE=aurcov;2103049]You got it wrong!

If an F 15 goes 0.8M-1.2M in 65 sec. at 40.000 feet, you can be sure that at 30,000 feet, it will take less.
Look at the F 18 C flight manual that Sintra mentioned. At 30,000 feet (2 Sparrows +2 Sidewinders) the Hornet needs 3 min. to reach 1.5M (page 328/346). At 40,000 feet (same load) it needs 5 min. (page 336/346)!

So. if an F 15 (8 AAMs) needs 65 sec. at 40,000 feet, you can bet that it will need less than 40 sec. at 30,000.

And BTW, an F 15 will go faster than an F 35 at all altitudes. It is a fighter not a striker.[/QUOTE]

Yeah, you are partially right. The F-15 would accelerate faster at 30,000 feet (when I clicked back on the chart I was looking at the acceleration chart with a centerline tank), but the f-18 takes 90 sec ( .8 to 1.2) not three min at max weight 30,000 ft, at 40,000 feet it takes around 3 min.
Your quote “And BTW, an F 15 will go faster than an F 35 at all altitudes”, that very much depends on the stores. As I was trying to point out, the F-15 does not reach Mach 1.2 with 8 missiles and a centerline tank (not surprising)at 10,000 feet. Aerodynamic Drag is higher at lower altitudes, the F-15 carrying a centerline fuel tank shows this when comparing acceleration at 10,000ft and 40,000 ft.
As far as the F-15 being “faster”, clean yes, with weapons, even just missiles? Well, again look at the charts at 39,000 pounds carrying 4 aim-7 and 4-aim-9, the F-15 will reach mach 1.82 at 36,000 feet, at 36,000 pounds without the missiles it will reach mach 2.1 on a standard day. Take your f-35 carrying roughly 4,600 pounds internal weapons, it will reach speeds in excess of mach 1.6. Don’t really think there is a huge difference in max speed of the F-15 or F-35 carrying similar weapon loads, except when the F-15 is just carrying 4 aim-7 class weapons (an no other pylons), see for yourself. http://www.scribd.com/doc/94648410/TO-1F-15A-1-Flight-Manual-USAF-F-15-Series-A-B-C-D-Block-7-and-Up-Change-5-01-Mar-1986 (figures A9-1b a through g)

As far as acceleration, the F-35 appears to have decent acceleration at 30,000 feet. It won’t match an F-15 with an air to air load, but again it’s not an air superiority fighter, it’s a multi-role fighter and should be compared to an f-16c, f-18, gripen, etc.

“Bordering on the Ridiculous”? “Respectfully”?!

You have a very interesting way of showing “respect”…

The USAF F-15A/B/C Flight Manual has enough credibility?

http://pt.scribd.com/doc/94648410/TO-1F-15A-1-Flight-Manual-USAF-F-15-Series-A-B-C-D-Block-7-and-Up-Change-5-01-Mar-1986

The numbers that you´ve asked, (an F-15C with four AIM-7, four AIM-9P and a central external tank) are on page A9-16, more specificaly “Figure A9-12”.
The exact numbers for the three Dave versions are not public we only know that the KPP´s were designed around the F-16 and the F/A-18A/C (clean), we also know that Dave A failed the KPP´s (Mach 0.8 to 1.2 at 30K) by eight seconds, the B failed by 17 seconds and the C for whooping 43 seconds. Now if we pick the F-18A/C numbers (public) and add these “failed seconds” above and compare with the charts on that manual… You can figure it out by yourself. If we pick the Viper numbers then its a more rosy scenario.
On top of that we actually know, from LM themselves, that there´s another Western aircraft (i am not talking of the Raptor,) with dynamic performances not dissimilar to the F-15C, that outruns a F-35A while being “combat loaded” (i would imagine that this means 8 AAm´s and 2 external 1000L fuel tanks, but again that was not stated in the paper), its the same aircraft that goes to mach 1.8 with three external fuel tanks, you can figure it out what aircraft i am talking about; by the way this LM presentation was made before the FY2012 Director of Operational Test and Evaluation (DOT&E) report recommended reducing the F-35’s performance requirements.

Far from being “ridiculous”, based on the numbers available is entirely arguable that on part of the flight envelope an F-15C configured for the typical ATA mission (with external fuel tanks) is very, very competitive with a clean F-35A in climbing and acceleration (well, the F-35A cant even be competitive with the Eagle at the top end speeds and altitudes, it simply doesnt get there).
So yes, i dont have the charts to exactly compare the two aircrafts, the numbers for Dave are not public, but that doesnt make my statement “ridiculous”, I call it an educated deduction wich may be right or wrong.
On the other hand may I ask why you believe that I am incorrect? Do you have any type of numbers from a “credible source” that proves without a doubt that I am incorrect?

You do realize that on a standard day at 40,000 feet according to to the diagram, the F-15 accelerates from mach.8 to mach 1.2 with (4) sparrow and (4) aim-9 in 65sec http://www.scribd.com/doc/94648410/TO-1F-15A-1-Flight-Manual-USAF-F-15-Series-A-B-C-D-Block-7-and-Up-Change-5-01-Mar-1986. The acceleration numbers for the f-35 are for 30,000 feet with 2 amraam at 61 sec (http://www.military.com/features/0,15240,186349,00.html. Take the F-15 down to 30,000 feet and you are talking 70 seconds give or take. Yes it is carrying 6 more missiles, but that’s the point, the drag for the f-15 is high when carrying externals, the F-35 will not be affected as much even with 4 amraams. The difference is that the F-35’s numbers do not change much when unencumbered with stores. Your average fighter aircraft looks very impressive in clean config, when you start hanging the needed stores on, the difference dwindles. Does it not? BTW, it is the F-15 that “does not get there” at high alt + speed while carrying a tank and missiles, it won’t reach mach 1.2 according to the acceleration chart at 10,000 feet and takes 90 sec at 40,000 feet, so it does out-accelerate one f-35 in that configuration, the “C” model.

Pump the brakes, I wanted to show there has been research on PMC Blisks, I thought it was interesting. Look at the figure of the f-119 IGV. But i still see a FOD issue, you ever see a video when they shoot dead birds into an engine? PMC blades may be strong but they are not malleable, one shatters and the engine is toast.

“The US Department of Defense’s decision to relax the sustained turn performance of all three variants of the F-35
was revealed earlier this month in the Pentagon’s Director of Operational Test and Evaluation 2012 report.
Turn performance for the US Air Force’s F-35A was reduced from 5.3 sustained g’s to 4.6 sustained g’s.
The F-35B had its sustained g’s cut from five to 4.5 g’s, while the US Navy variant had its turn performance truncated
from 5.1 to five sustained g’s.
Acceleration times from Mach 0.8 to Mach 1.2 were extended by
eight seconds, 16 seconds and 43 seconds for the A, B and C-models respectively.
The baseline standard used for the comparison was a clean Lockheed F-16 Block 50 with two wingtip Raytheon AIM-120 AMRAAMs.
“What an embarrassment, and there will be obvious tactical implications.
Having a maximum sustained turn performance of less than 5g is the equivalent of an [McDonnell Douglas] F-4 or an [Northrop] F-5,”
another highly experienced fighter pilot says. “[It’s] certainly not anywhere near the performance of
most fourth and fifth-generation aircraft.”

flightglobal- David Madjumdar, again is it that hard to give credit to the journalist? You have pilots who have flown the aircraft giving positive testimony and un-named sources trashing it. A pilot said…. Dewline blog is a great blog and you once again picked and chose one piece out of context. BTW, the chart, not LM (see the est. next to f-35). Journalists have to present (in an ideal world) both sides of a story. Good effort. Oh, and the piece finishes with this: “Lockheed, for its part, maintains that the F-35 has performance superior to that of any “legacy” fighter at high altitudes. “Having flown over 4000 hours in fighter jets, I will tell you the F-35’s capability at altitude, mostly driven by the internal carriage of those weapons, as a combat airplane, this airplane exceeds the capabilities of just any legacy fighter that I’m familiar with in this kind of regime,” says Steve O’Bryan, the company’s business development director for the F-35 during a January interview”.