Mach 6.70
Chloe Sarnoff
I talked with older pilots who have had flight experiance with the airframe and they broke it down for me. They said it was pretty tough for the 111 to get past mach 2 compared to most jets. It was explained that the engines (I'm not sure if this differs from other countries or if they use the same engines) but as far as the US version was concerned the engines were designed for low level flight. Down low the F-111 ws said to be "wicked fast" and there wasn't a fighter that could keep up with it.
I heard the following numbers from one colonel and a major with whom the 111 was thier first jet earlier today. It could reach 1.7 mach at 100 feet or 30 meters Above Sea Level. Most fighters like the F-15 are designed to perform well at high altitudes and so they were outpaced down low in thicker air. This limitation is largely based on engine design and not the airframe.
Playing a bit of devils advocate on my behalf I asked if it were possible to max out at high altitude then dive and reach mach 3. They hesitated and said maybe, and they were sure the airframe could take it, but they didn't know of anyone who tried. 111s went up high to get fuel or for ferry flights, but for mission training it was mostly low level NOE type flying staying within the engines designed performance envelope.
If you were wondering where I got mach 3 number from my first supervisor recieved a ride in the 111. He described a scenario where the pilot maxed out at 30,000 feet about 9100 meters rolled inverted and pulled into a dive. He explained watching the mach needle hit three and how the pilot laughed at him when he freaked out. He was a man who never indulged in embellishment so I believe him, but I was still wrong about the 111 being a mach three jet.
Even in the F-15, going up above mach 2.3-2.4 is a 'time limited' operation where you're allowed to exceed this speed for a minute or so before requiring engine replacement. Keep it there a bit longer and they'll fry on you in flight - we're talking engine fire.
The F-111 is certainly among the contenders for the fastest aircraft ever a low level, but I do have to be very sceptical about the 1.7 mach number. What I've seen other places is from about 1.2 to 1.3. And other aircraft which are designed to be really fast at low level (like the Tornado, Su-24 and F-104) max out at around 1.2. That the F-111 should be able to do 0.5 faster than anything else at that low level where the drag is immense sounds unreasonable.
Also the official world record at low-level was set by a modified F-104 at 1,590.45km/h, which is around mach 1.3. Of course millitary aircraft don't always compete in such contests, but if they had something which shattered the record then I'm sure they would...
After having read quite a bit about the designs of the SR-71 and XB-70 and how they were designed around flying at mach 3, and all of the problems they had to overcome and build into the design to achieve it, it seems really implausible that other aircraft that weren't designed for it can just accelerate or dive to mach 3, just because they have the engine power for it.
If that was supposed to happen, it probably would need another type of design to withstand the temperature contraction and expansions, like the SR-71. Such a design of airframe may be more flexible, and logically less robust.
Yes the stress on an airframe at mach three is significant, but not impossible. The jet wouldn't explode and neither would the engine. Its not like going past the redline with a car engine. Doing 1.7 mach at 100ASL is mighty tough on an airframe, much more so than mach 2 at high altitude.
To my understanding one of the Mig-25's problems was couldn't control its shockwave properly which would cause the damage from high speed flight. Around mach three the shockwave from the sound barrier would start to angle down the intake and contact the engine blades creating severe turbulence in the compressor stage and damaging the engines. Not all aircraft had this problem. The cone protruding from the SR-71 engine intake is on a track that allows it to manipulate the shockwave. The F-15 intake changes shape for this same reason.
For that speculation we'd have to know the temperature difference of the speeds mentioned. An object traveling at mach at sea level is going to be hotter than an object at 50K ASL traveling at the same speed. More air molecules at lower alt. means more friction, and that means more heat...doesn't it?
The SR-71 uses an unusual design but was also designed a long time ago, and much has been learned from its weaknesses. Looking at the technology available and the design of the airframe from an aeronautic point of view it probably maxed out closer to mach 6. (There's my speculation) The X-15 A2 achieved 6.2 mach before the space race began and it didn't use the corrogated design style that the SR-71 did to the same extent. Alloys have become more advanced since then, so maybe a maybe is appropriate.
The F-111 has an aluminium airframe, aluminium starts to deform from the physics of creep at mach 2.61, this is the reason why the SR-71 has a titanuim alloy airframe. The F-111's performance will be limited to the very maximum of mach 2.61.
And in one exceptional circumstance one F-111F pilot told about doing 890 kts at 3500 ft (i.e. not quite low level, but still low), which was mach 1.37. That was so exceptional that he took a photo of the instruments to have proof that he went that fast. That the ones you talked to went 25% faster at lower altitude in the same aircraft doesn't seem very likely to me...
That's not to take anything from the F-111, it's certainly one of the fastest aircraft ever at low level. But exageregating its performance doesn't help, and isn't necessary, it's impressive enough as it is.
The X-15 was basically a manned missile. It was built from a special heat-resistant steel alloy called Inconel-X which kept its strengt up to 650C. It only flew for a few minutes at a time, and it used liquid nitrogene for cooling that time. Still the surface temperature reached over 700C in places. But since it was just momentary it could stand it.
Regarding the service of the MiG-25RBT in Bulgaria I've never heard of any time limits regarding Mach number, except for fuel cunsumption- at that speed the engines eat the fuel like crazy. Oh yeah, one more thing- at Mach 3 the turn radius is such that my country has barely fitted that beast:D
NASA's goal for the X-15A2 was mach 8 in atmosphere and there was damage done at mach 6.7 cutting the test short however it was a relatively minor design flaw and the engineers could solve the problem. They were excited and confident that they'd reach their goal, but then the Mercury project began and NASA wasn't allowed any buget for any project out side of landing on the moon. Using the lessons learned as a stepping stone and lessons learned from the A-12 could it be that this problem had been solved to some extent?
one thing that can be said about the f111. at low level it was at the alt it was designed for and it had the most stable flightpath of all planes designed to fight low level. 2nd in line is the tornado, which has an awesome design for low level abut not quiet that good like the f111.
an tornado pilot of the german air force once said, when the eurofighter was close to compleation, that they could, after repositioning a small box in the rear of the tornado, use the new eurofighter engines, cause they were designed to fit into the tornado.
nobody ever thought that an f15c could withstand a max g of about 40 either, but it was taped and recorded by an f15 driver when he got into a no SA situation and pulled down instead of pulling up. his flight was recorded by the hudcam and the cam failed to record at about 32 or 38 gs. cannot remember, have to see if i find the video again.
The X-15 was a rocket-powered aircraft 50 ft long with a wingspan of 22 ft. It was a missile-shaped vehicle with an unusual wedge-shaped vertical tail, thin stubby wings, and unique side fairings that extended along the side of the fuselage. The X-15 weighed about 14,000 lb empty and approximately 34,000 lb at launch. The XLR-99 rocket engine, manufactured by Thiokol Chemical Corp., was pilot controlled and was capable of developing 57,000 lb of thrust. North American Aviation built three X-15 aircraft for the program.The X-15 research aircraft was developed to provide in-flight information and data on aerodynamics, structures, flight controls, and the physiological aspects of high-speed, high-altitude flight. A follow-on program used the aircraft as a testbed to carry various scientific experiments beyond the Earth's atmosphere on a repeated basis.For flight in the dense air of the usable atmosphere, the X-15 used conventional aerodynamic controls such as rudders on the vertical stabilizers to control yaw and movable horizontal stabilizers to control pitch when moving in synchronization or roll when moved differentially.For flight in the thin air outside of the appreciable Earth's atmosphere, the X-15 used a reaction control system. Hydrogen peroxide thrust rockets located on the nose of the aircraft provided pitch and yaw control. Those on the wings controlled roll.Because of the large fuel consumption, the X-15 was air launched from a B-52 aircraft at 45,000 ft and a speed of about 500 mph. Depending on the mission, the rocket engine provided thrust for the first 80 to 120 sec of flight. The remainder of the normal 10 to 11 min. flight was powerless and ended with a 200-mph glide landing.Generally, one of two types of X-15 flight profiles was used; a high-altitude flight plan that called for the pilot to maintain a steep rate of climb, or a speed profile that called for the pilot to push over and maintain a level altitude.The X-15 was flown over a period of nearly 10 years -- June 1959 to Oct. 1968 -- and set the world's unofficial speed and altitude records of 4,520 mph (Mach 6.7) and 354,200 ft in a program to investigate all aspects of piloted hypersonic flight. Information gained from the highly successful X-15 program contributed to the development of the Mercury, Gemini, and Apollo piloted spaceflight programs, and also the Space Shuttle program.The X-15s made a total of 199 flights, and were manufactured by North American Aviation.X-15-1, serial number 56-6670, is now located at the National Air and Space Museum, Washington DC. North American X-15A-2, serial number 56-6671, is at the United States Air Force Museum, Wright-Patterson AFB, Ohio. X-15-3, serial number 56-6672, crashed on 15 November 1967, resulting in the death of Maj. Michael J. Adams. Parts of the X-15-3 are on display at the Air Force Flight Test Center Museum at Edwards AFB, and the San Diego Aerospace Museum, San Diego, California. NASA Photo by: NASA Keywords: X-15; rocket-powered research aircraft; North American Aviation; XLR-99 rocket engine; Thiokol Chemical Corp.; high-speed & high-altitude flight; B-52 air launch; 4520 mph; Mach 6.70; 354200 ft (altitude); 67 miles (altitude); flight controls; reaction controls; Mercury program; Gemini program; Apollo program; Space Shuttle; hypersonic flight, heat damage Dryden Home > Collections > Photo Home > X-15 > Photo # EC67-1833 Business Education History Gallery News Room Organizations Research Search Site Index
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