I think the F-117 may be supersonic - good reason.

This may sound far-fetched, but when I was about 7 years old, a mere 8 years ago, I attended an airshow at the Chicago Lakefront. I was there with my father, and I was intrigued with the maneuvers. I plugged my ears during the sonic booms but only during the sonic booms, everything else wasnt loud enough.

I remember being along lake shore drive when the strangest aircraft I had ever seen went by. It made a boom so loud I had to cover my ears. It was about a half mile out, banking and making a sharp left turn into the lake.

The point - I saw the F-117 and heard a sonic boom about 8 years ago.

I know it sounds far-fetched - but it could have been a pilot error - accidentally went over the speed limit - I know its hard to believe, but I DISTINCTLY remember it.

They don't go supersonic at airshows. First of all it's illegal, secondly if they did they'd be footing the bill for some SERIOUS glass replacement. They'd shatter every window within a huge distance. There's a story about an SR-71 that went supersonic coming in on a record setting flight from England. He started to decelerate over Phoenix and blew out windows in Beverly Hills.

As for the F-117 there's no way that it can go supersonic. The shape of it, and the way they vent the exhaust prevent it. Until the F-22 you had to have afterburners to get supersonic, and the F-117 can't use afterburners. Because of the way the exhaust vents you have a very low thrust to weight ratio, and if you used afterburners you'd set the RAM on fire. Once that stuff lights up you aren't getting it out.

Not in level flight, but transonic?
Going supersonic in a dive?

However that would not be possible at low altitudes for obvious reasons!


Does a sonic boom occur on transonic a/c when they exceed the barrier on dives?

Originally posted by Daedalus3
Does a sonic boom occur on transonic a/c when they exceed the barrier on dives?

Yes, a sonic boom happens however the aircraft breaks the sound barrier.

Originally posted by Daedalus3
Does a sonic boom occur on transonic a/c when they exceed the barrier on dives?

A sonic boom occurs when the nose of the aircraft is travelling faster than the local speed of sound.


Even though your average 747 is in transonic flight, the only supersonic flow is localised above the wings, so no sonic boom in that case.

BAC Lighning was also supersonic without afterburners (reheat). In the 1950's this is nothing new to the F22

Enjoy

Originally posted by BlackWidow23
This may sound far-fetched, but when I was about 7 years old, a mere 8 years ago, I attended an airshow at the Chicago Lakefront. I was there with my father, and I was intrigued with the maneuvers. I plugged my ears during the sonic booms but only during the sonic booms, everything else wasnt loud enough.

I remember being along lake shore drive when the strangest aircraft I had ever seen went by. It made a boom so loud I had to cover my ears. It was about a half mile out, banking and making a sharp left turn into the lake.

The point - I saw the F-117 and heard a sonic boom about 8 years ago.

I know it sounds far-fetched - but it could have been a pilot error - accidentally went over the speed limit - I know its hard to believe, but I DISTINCTLY remember it.

I wouldnt be surprised at all. the actual top speed would be top secret.
as the sr 71 top speed is still classified.

What at the chicago airshow? Almost EVERY aircraft goes supersonic. I remember seeing a Tomcat zoom in at mach 2 over the lake making a boom so loud the ground shook. It was definately supersonic, full afterburner. I remember seeing a pair of B-1s fly overhead and not hearing them until they were way out over the lake.

When I saw the F-117, it made a roar so loud the ground shook. I am SURE it was a sonic boom.

In the book F-117 Stealth in Action there are pilot interviews. F-117 pilot Steve Paulson sat down for an interview with Author Jim Goodall. Here's a quote of what he said on the F-117's top speed:

Jim: I understand that the F-117A's top speed is limited to Mach .82 to .84. Can it go faster?

Steve: Yes, there is an artifical limit we set that is just a little higher than that just so we wouldn't go too fast.

Jim: Is it capable of supersonic flight?

Steve: It is capable.

Jim: Are you limited by delamination of the RAM?

Steve: No, there is a limit, and there is a reason for it, but it has to do with the way you get inputs to your flight control system.

So there's your answer on F-117's and supersonic speed.

Tim

Why yess, indeedy, when Chuck Yeager helped find it. It became the standard for military aircraft.

The Eagle, a staple of the 70's war birds, was in fact...duh...duh...FASST!

Originally posted by Ghost01
So there's your answer on F-117's and supersonic speed.

Tim

That could mean anything.


Stick it in a nose dive for long enough and you'll get most things to supersonic speeds.

An aircraft can be almost supersonic and still be incredibly loud, and pass by you before you hear the sound. They can SOUND like they're supersonic, when they aren't. The simple FACT of the matter is that a sonic boom would shatter HUGE amounts of glass in Chicago. Why do you think that the Concorde would have to fly 30-60 minutes off the coast before they could go supersonic? If they could go supersonic over land then the Concorde would have made a lot more sense.

Studies have shown that a few panes of glass could withstand repeated sonic booms, but you're talking MILLIONS of panes of glass around the area of this airshow. And the effect is cumulative. The more sonic booms, the more chance of structural damage. And sonic booms can travel very large distances. We used to have minor "earthquakes" when HANG F-4s went supersonic 100+ miles offshore.

www.globalsecurity.org...

As for going supersonic, as kilco said, dive long enough and you'll go supersonic. They were getting close to supersonic speeds from P-38s in WWII. Even a 747 hit Mach 0.9 in a dive in flight testing.



[edit on 5/21/2007 by Zaphod58]

Originally posted by Zaphod58
Studies have shown that a few panes of glass could withstand repeated sonic booms, but you're talking MILLIONS of panes of glass around the area of this airshow. And the effect is cumulative. The more sonic booms, the more chance of structural damage. And sonic booms can travel very large distances. We used to have minor "earthquakes" when HANG F-4s went supersonic 100+ miles offshore.

At one point, didn't they fly supersonic over an area to find out what an acceptable altitude for supersonic flight over land was? I think it was in America, but I can't remember where or when exactly.

It was several experiments actually. One was the White Sands Missile Range, another was Edwards AFB, there was Oklahoma, and another over a forested area to determine the effects of sonic booms on animals.

Here's an interesting page of sonic boom effects.

Overpressure in pounds per square foot is used to measure sonic booms. Overpressure is the amount of pressure above normal atmospheric pressure.

* Normal air pressure is 2,116 psf or 14.7 psi.
* At 1 psf of overpressure, no damage to structures occurs.
* 1 to 2 psf of overpressure occur at ground level from aircraft flying at supersonic speeds at normal operating altitudes. Overpressure above 1.5 psf is irritating to people.
* At 2 to 5 psf some minor damage can occur to structures.
* As overpressure increases, the chance of structural damage increases. Structures in good condition can withstand overpressures of up to 11 psf.
* 20 to 144 psf are experienced at ground level when aircraft fly at supersonic speeds at altitudes of less than 100 feet. Such levels of overpressure have been experienced by humans without injury.
* At 720 psf damage to eardrums results. At 2160 psf lung damage occurs.

The following over pressures at ground level have been measured for several aircraft:

* 0.8 psf for the F-104 at Mach 1.93 and 48,000 feet.
* 0.9 psf for the SR-71 at Mach 3 and 80,000 feet.
* 1.25 psf for the Space Shuttle at Mach 1.5 and 60,000 feet during landing approach.
* 1.94 psf for the Concorde SST at Mach 2 and 52,000 feet.

library.thinkquest.org...

Notice that an SR-71 at 80,000 FEET has a psf of 0.9. That's at HIGH altitude. As they come down lower, the psf would increase.

This data shows why shock waves are so destructive to buildings. Each high pressure region of a shock wave is followed by a rarefaction. The greater the initial pressure rise, the greater the rarefaction and the more negative the overpressure. At ground level usually only two shock waves are experienced. The rapid change in air pressure from positive overpressure to negative overpressure and back to normal air pressure caused by a sonic boom causes a series of imploding forces followed by exploding forces to be applied to a building, since the air pressure inside the building remains at 1 atmosphere while the pressure outside rapidly fluctuates. This causes the walls and windows of a building to be pushed in and out by the changing forces exerted by rapid changes in air pressure. This causes the structure to resonate at destructive frequencies. At 31,000 ft, the temperature is about -43°C. The speed of sound at this altitude is 287 m/s or 941 ft./s (Mach 1). At this altitude Mach 1.25 is 1,442 ft./s, or 983 mph, and the length of the sonic boom signature at ground level is about 200 ft. Thus at this speed and altitude, it takes only 0.14 seconds for the entire sonic boom signature to sweep over a point on the ground. During this short instant in time the rapid fluctuation in air pressure occurs at ground level.

library.thinkquest.org...


[edit on 5/21/2007 by Zaphod58]

Originally posted by kilcoo316

That could mean anything.


Stick it in a nose dive for long enough and you'll get most things to supersonic speeds.

Ok, I was just trying to help! If my answer don't suit you, there is another option:

File a Freedom of Information Act Request with the US Air Force and the Department of Defense asking them for what you want. However, don't hold your breath, we're still waiting on one related to Groom Lake from 2004!

Tim

The faceted shape of the F-117A does not lend itself to supersonic flight. The inlets, covered with fiberglass composte screens are not designed for supersonic airflow. The plastic and rubber radar-absorbent material (RAM) coatings would melt from aerodynamic heating (assuming they didn't just peel off, which they sometimes do anyway). The air data system is not designed for use at speeds above Mach 1.

Finally, the F-117A Utility Flight Manual (T.O. 1F-117A-1) gives the aircraft's maximum speed as 525 knots calibrated airspeed (Mach 0.9).

The F-117A that crashed near Bakersfield, California, may have been traveling at supersonic speeds at the time of impact, as it was in a steep dive at the time. The pilot, already spatially disoriented, would have also been reading erroneous airspeed data on his instruments. This may have been a contributing cause of the accident.

Originally posted by Shadowhawk
The faceted shape of the F-117A does not lend itself to supersonic flight.

The facited shape of the F-117A does Not lend itself Flight Period! Back when it was origionally design, Skunkworks chief aerodynamicist Dick Cantrell had doubts about if the design would fly.

The F-117A that crashed near Bakersfield, California, may have been traveling at supersonic speeds at the time of impact, as it was in a steep dive at the time. The pilot, already spatially disoriented, would have also been reading erroneous airspeed data on his instruments. This may have been a contributing cause of the accident.

I've read that! Do you think supersonic speed may have been a contributing factor in the crash?

Tim

[edit on 5/22/2007 by Ghost01]

Originally posted by Ghost01
The facited shape of the F-117A does Not lend itself Flight Period! Back when it was origionally design, Skunkworks chief aerodynamicist Dick Cantrell had doubts about if the design would fly.


I've read that! Do you think supersonic speed may have been a contributing factor in the crash?

Tim

Subsonic and supersonic lift is generated by two fundamentally different mechanisms - the F-117 is not shaped to generate supersonic lift, it would more likely produce a helluva lot of supersonic downforce.

Take the F-117 nose, and compare the amount of body above the nose to say, the B1B, or the Tu-160, or even the F-22. Its alot more for the F-117, and the slender ratios don't really work out either.

Actually at airports around where I live the air national guard trains quite a bit and the entire airport is made out of glass and it doesn't shatter most of the panes in the lobby are thin and the planes go well past supersonic just a few minutes into the air.

Originally posted by Anonymous ATS
Actually at airports around where I live the air national guard trains quite a bit and the entire airport is made out of glass and it doesn't shatter most of the panes in the lobby are thin and the planes go well past supersonic just a few minutes into the air.

Ahem, utter rubbish.

I'm starting to think that most people don't actually know what a sonic boom sounds or feels like...