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 Mikoyan MiG-25 Foxbat |
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From: toro@inforamp.net (Thomas Rodriguez) EXPH24A@prodigy.com (Joe Barrington) writes:
Your source was right when it said the MiG-25 engine(s) was a derivative of an engine somehow related to a large high speed cruise missile, but the engine was not originally designed for a missile. The original engine, Mikulin/Tumans- kiy R-15-300, was designed to serve, together with the MiG E-150 test bed aircraft, as the basis for a new generation of interceptors. Initially it was tested in a remotely piloted aircraft (they had no test beds capable of flying at the intended speeds, I suppose), and from there the idea to use it in a missile was born. The E-150 with this engine was rolled-out in December 1958. Eventually they reached M2.65 at 73 800 ft. For its use in the MiG E-155 (the MiG-25 prototype) the engine was further developed, but this time the designers used as a basis the R-15K, the variant tested in the cruise missile, simply because it had been tested at speeds higher than those attained by the original. To control the exact fuel/air ratios for quick thrust changes, the typical for those days hydromechanical fuel metering valves were replaced by an electronic fuel control unit. This unit automatically compensates for any throttle mishandlings. I think it can be agreed that it would be totally absurd to design a highly sophisticated a/c, employ 11 pounds of pure silver(!!) to insulate its engine compartments and not employ a relatively inexpensive device to avoid overspeeding the engines. I cannot understand why your source would accept such an apocryphal tale as good. The MiG-25 was originally designed to counter the A-11, not the B-70 as we all believed. It is a well designed aircraft that satisfactorily complies with its design goals. With the Cold War over, there is no need anymore to paint the Soviet designers as inepts, void of ideas, who did not care about their pilots lives. It is simply not true. I read an article in which this a/c was called a "dud". I think it is dangerous to underestimate the opponent. Unfounded overconfidence is not the best way to win battles and, unfortunately, countries like Libya and Irak have this aircraft. The Mig-25 is by no means a dud. It is true that, with external stores, it can only reach M 2.8; but what other known aircraft can do that (except the MiG-31)? It is also true that its max. operating limit load factor is only 4.5g: but how many other aircraft can do that a M2 + ? This limit is misleading if you do not know how Soviet designers use this characteristic. This load factor is not the maximum that a pilot can use in combat. This is the everyday limit to preserve at 100% the structural safety margins required by regulations( yes they have military a/c safety regulations which are very tough due to their operational environment). According to these, this a/c can sustain up to 6.75g (supersonic) without danger to suffering plastic (i.e. permanent) deformations, and probably 8.4g before catastrophic destruction of any component. In combat a pilot will only remember the 6.75g limit. But the Mig-25 is not a dogfighter. (I cannot imagine an SR-71 pulling anything beyond 2-3g at M 3. It would have been irrational to design if for much more than that: first, because it is so slender that the weight penalty for stiffen- ning it would have been be too high; and second, because it does not need more for its mission). It is also true that its service ceiling is "only" 67 900ft, but then again.... This a/c once held 16 aviation world records and four specifically female world records. Some still stand unbeaten. I think it is reasonable to assume that an aircraft strong like a boxcar (steel, titanium plus the shape of a soap-box) and powerful enough to fly at M 2.83 with full external stores load, can perfectly reach M 3+ in a clean reconnaissance configuration. That was what the Israelis clocked a few times as reported by Aviation Week years ago. In this respect, the USAF was not wrong, and IMHO, they were correct in the evaluation of this aircraft as an interceptor/recce aircraft, never considering it a fighter or dogfighter, which it never was intended to be. What I cannot understand is the fixation with the MiG-25, an a/c "deja passe" and not with the MiG-31, its more capable stablemate. But well, that is a theme for another thread. Thomas Rodriguez
From: mbovanko@orlando.loral.com (Anonimous)
Victor Belenko, the Foxbat pilot who defected in 1976, stated that the top speed of the MiG-25 was Mach 2.8, but flight above Mach 2.6 was difficult because of a tendency of the engines to overspeed. Victor related that MiG-25 pilots were in fact restricted to flying below Mach 2.5 except with special permission.
This said, your assessment that the MiG-25 has no real requirement to pull high g's at supersonic speeds is probably correct. In a high Mach intercept mission, the MiG-25 should be using its excess thrust for climb, not for turning. The GCI should ensure that the Foxbat is positioned so that it can complete the intercept without violent maneuvers. You might note that the A-12/YF-12/SR-71 is limited to 45 degrees bank at design speed and altitude. It is also limited to 1.5g under these conditions. Furthermore, the Blackbird is only cleared up to 400 KEAS at high Mach, a far cry from the (often ignored and exceeded) Foxbat's 650 KEAS limit. Compared with the SR-71, the MiG-25 is quite agile at speed.
An isolated incident? How about the single Iraqi Foxbat-E that eluded eight sweeping F-15s then tangled with two EF-111As, firing three missiles at the Ravens and chasing them off station. Unfortunately, the Ravens were supporting an F-15E strike, and the EF-111's retreat led to the loss of one of the Strike Eagles to a SAM. Oh BTW, the Foxbat easily avoided interception and returned safely to base. There's more. When F-15 pilots were fighting for the chance to fly sweeps east of Baghdad late in the war, itching for a chance to get a shot at an Iraqi running for Iran, they weren't expecting the fight that a pair of Foxbats put up. Two Foxbats approached a pair of F-15s, fired missiles before the Eagles could get off shots (the missiles were evaded by the Eagles), then outran those two Eagles, four Sparrows and two Sidewinders fired back at them. Two more Eagles maneuvered to cut the Foxbat's off from their base (four more Eagles tried, but were unable to effect an intercept), and four more Sparrows were expended in vain trying to drop the Foxbats. The Iraqis had a total of twelve MiG-25PDs at the beginning of the war, of which maybe half were operational at any given time. Imagine what trouble they would have caused if there had been more. The Foxbats, when well flown, proved capable of engaging allied fighters and avoiding them at will. Only the limitations of their weapons proved a problem.
We had a counter for the Foxbat: the F-12B. The Eagle should have remained a multi-role aircraft. The Strike Eagle has proven the airframe's abilities in this role.
From: topwop@magicnet.net (Anonimous) The MiG-31 has two 34,200 lbst Soloviev D-30F-6 turbofans (bypass ratio is 0.5). The MiG-25P has two 22,500 lbth Turmanskii R-15B-300 turbojets, whereas the MiG-25R varaints, the MiG-25PD/PDS and the MiG-25BM have 24,700 lbth Turmanskii R-15BD-300 turbojets. The MiG-31's official top speed limit is Mach 2.83, but this can be exceeded if the mission requires it.
From: topwop@magicnet.net (Anonimous)
In response to Dave Sutton, Kristan Roberge wrote: > >I don't know about the F-15 but I do know a bit about the MiG-25. > >It's supposed capability of Mach 3 is vastly overrated. When I was > >in Europe training on the MiG 21 and 23 I spoke with a few pilots > >who had flown the 25 and they without exception stated that in > >order to go Mach-3 the engines were subsequently scrap. Serious > >overtemps. In operation, the 25 was used to about 2.3 or so, with > > It has been published that the Mach3 plus speed is a DASH rating, > not continuous cruise. The reason the engines need to be overhauled/ > replaced is that the EARLY Mig-25s used stainless steel in the airframes > instead of the Titanium being used in the A-12s/YF-12As of the time. > > The Mig-25 was designed as an interceptor to counter the US XB-70A > valkyrie (then in testing) which had a cruise speed of Mach-3.The MiG-25 was designed as a counter for the A-12, not the XB-70. It had been widely held that the MiG-25 was a counter to the XB-70, but recent revelations by the MiG OKB (notably by R.A. Belyakov, the OKB's current head) have dispelled this myth. All MiG-25s (not just early models) are built primarily of a nickel steel (not stainless steel) alloy. Although MiG-25s do contain some titanium components, the Soviets were smart enough to realize that Soviet Ti manufaturing technology was not mature enough in the early '60s to consider building an entire airframe from the metal. Steel, particularly nickel steel, is a viable substitute for titanium in a high speed aircraft. In a standard structure, nickel steel carries a weight penalty, but not a strength penalty. Consider the fact that the B-70's primary structure was a stainless steel honeycomb while the X-15 was made of Inconel-X (a nickel alloy). The MiG-25's airframe was designed from the outset to heat soak at Mach 3+. The engine overspeed problem at Mach 2.6+ is entirely unrelated to the airframe.
From: topwop@magicnet.net (Anonimous) > i have a magazine around here that says the MIG-25 has the altitude > record for a jet at 125,000 feet. Is this correct? > i do not have the article convenient.... > > > to the Ye-266's absolute altitude record. You might also consider that > ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ > What is this record???Among other records, the Ye-266 set the world's absolute altitude record for a ground-launched aircraft at 118,867 ft. on 25 July 1973. After the Streak Eagle broke many of the Ye-266's time-to-climb records (but not its absolute or payload-to-altitude records), the modified Ye-266M reclaimed its records over a two year period starting in 1975. Some of the Ye-266M's records have since been broken by the Sukhoi P-42, but six still stand. Among these is the absolute altitude record of 123,492 ft. and the altitude record with a 2,000 kg payload, 121,622 ft. "Ye-266" is actually a invented name. The designation was used to cover three aircraft, the Ye-155R-1, Ye-155R-3 and Ye-155P-1. The former two were modified prototypes of the MiG-25R while the latter was a modified prototype of the MiG-25P. The P-1 was powered by R-15B-300 engines while the R-1 and R-3 used the more powerful R-15BD-300s. The "Ye-266M" was actually the Ye-155M, a technology demonstrator for the MiG-31. It retained the airframe of the MiG-25P but used the very powerful R-15BF2-300 engines. It should be noted that the A-12, the F-12 or the SR-71 could all have easily broken the absolute altitude records set by the Ye-155 series, but any such record attempt would be a one-way trip in a Blackbird. The Blackbird has strict AoA limitations which would undoubtedly be exceeded during a zoom to an altitude in excess of 100,000 ft. If the AoA limits are exceeded, a pitch-up results, leading to a structural break-up at supersonic speeds.
From: topwop@magicnet.net (Anonimous) Michael Colangelo wrote: >Of course the use of stainless steel, as opposed to titanium, will compromise >the performance of the MiG-25. Aircraft made of stainless steel will >almost always be heavier than those made of titanium, assuming similar >structural design methodologies. It's safe to say that a heavier >structure will result in reduced performance than a lighter one. ...and Matthew Saroff replied: > It is not necessarily true that a stainless steel structure will be >lighter. Carpenter Steel has an alloy, Airmet-100, which has a higher >strength to weight ratio than Titanium (At least that's what the pamphlet >says It has a yeild of about 240KPSI, and it's about as tough as spring >steel). I'm looking to make mideval armor out of the stuff. > You must machine to much tighter tolerances and thinner structures >to get similar weights though, and this can make fabrication more difficult.From an elevated-temperature strength:weight perspective. Ti is tough to beat. If it were not for the elevated temperature factor however, alloy steels would stomp Ti. In order to make steel structures competitive with Ti structures for high speed aircraft, you've got to use exotic designs like the B-70's honeycomb. Kelly Johnson knew enough about the nightmares NAA was having with fabricating SS honeycomb to write off this option for the design of the A-12. One has to wonder however, if Kelly knew how much trouble he was going to have with the Ti manufacturing, would he have reconsidered the SS honeycomb? The Soviets rejected SS honeycomb for the same reasons that Kelly did. I'm sure they would have loved to make the MiG-25 out of Ti, but this was impractical given the current level of Soviet Ti technology, the imposed schedule and the required number of Foxbats to be built. Nickel steel was a compromise, but not nearly as much of one as the aviation press would suggest. The Western press was used to seeing Al and Ti airplanes (they conveniently ignored the X-15, B-70, F-103, F-108 and other high Mach designs) so a steel airplane was a foreign concept to them. Perhaps the USAF was still sore that they seriously screwed-up the F-X design by requiring it to combat super-Foxbats (the CIA had miscalculated the weight of the Foxbat by incorrectly assuming it was made from Al), so they went along with the Foxbat bashing. Yes, the Foxbat would have better performance if it were made of Ti. At high Mach, however, the difference would be minor. A Ti Foxbat would perhaps have a ceiling a few thousand feet higher. You could also probably tack another couple thousand feet onto its already amazing climb rate. Lest we forget however, nothing made of Ti has come anywhere close to the Ye-266's absolute altitude record. You might also consider that the Ti F-12B was limited to 1.5g at high Mach, while the steel MiG-25P is cleared for 4.5g maneuvers at high Mach. For the curious, most fighter airplanes are not made primarily of Ti or alloy steel not because of cost, manufacturing, or even survivability considerations. From a _stiffness:weight_ perspective, aluminum beats all other metals at normal operating temperatures. Composites are even better than Al, and you see lots of composites because it's stiffness, not strength, that is usually the primary design constraint for aircraft structure design.
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