I went to Melbourne air show last weekend. It was my first ever air show and it was awesome.

The only sonic boom I have ever experienced was generated by the space shuttle upon re-entry when landing in Titusville. That landing strip for the space shuttle is about 35 miles as the crow flies from my house. And that boom would rattle the whole darn house. One time I was in the garage and about messed my shorts because I thought the garage door was being blown off the rails by the boom. Those booms were really, really loud and powerful.

At the airshow, one of the jets was a F-18, and I snapped this pic while in flight.


I posed this pic on Facebook along with some others and a whole bunch of my friends have said, "That is so cool you caught the pic as the jet broke the sound barrier." I keep replying that the jet did not break the sound barrier, that the announcer mentioned multiple times that the jets would get close to the speed of sound, but not break it, and that I heard no sonic boom.

I assume sonic booms differ in intensity? The space shuttle was large and started out traveling at over 10,000 mph, so the boom was huge. But I also assume that if I was 2,500 feet away from a F-18 that broke the sound barrier, there would be no missing the boom created?

I agree with you. That's not a sonic boom.

Our cabin was near a MOA (training area) for a fighter base. Back in the late 60s early 70s you'd occasionally hear a sonic boom. They were miles away and thousands of feet above ground and it sounded like a very sharp lightning/thunder clap. I'd imagine it would be extremely uncomfortable to be at airshow distance from one.

There would be no mistaking it. He was likely close, but did not exceed the sound barrier.

Intensities can vary; think of a subsonic round going off versus a super sonic round going off. Although the muzzle blast obscures a lot of it, you can typically discern the crack.

Some other pics I took;

F-16



F-16 and P-51 Mustang



Blue Angels


Blue Angels

quote:

Originally posted by holdem:


my friends have said, "That is so cool you caught the pic as the jet broke the sound barrier." I keep replying that the jet did not break the sound barrier

I bet we have SIGforum members who have flown the F-18 and other aeronautical experts who can comment conclusively (I'm not in either bucket), but I believe you are correct, and that your photo (great shot, by the way) shows condensation, rather than having to do with breaking the sound barrier.

I can't see the picture, but it sounds like you've captured a vapor cone

Yes, that is a vapor cone, but it doesn't mean the jet broke the sound barrier. It does mean that the place is transonic, which means it is close to breaking the sound barrier. In fact, because the speed of sound varies with many factors, including air pressure and temperature and because those conditions can vary at different parts of the airplane, parts of a plane can be supersonic and other parts may not be. That is transonic flight.

You would know it, without doubt, if the plane went supersonic.

While attending grade school in the fifties we often experienced sonic booms during flyovers here in the flyover MidWest..One of the most severe ones cracked a couple of the large windows of the school building. The booms are pretty distinctive. I would put them somewhere between a lightning strike without the longer roll afterward, more closely to an artillery shot concussion. Either way, they are always unexpected and definitely get your attention.

It depends on how close you are. I was stationed at Holloman when they had F-22s, German Tornadoes, T-38s, and F-4s (drones). They were all supersonic, and for the first (and only) time in my life, I heard routine sonic booms. Some were like distant thunder. Some literally shook the house or my office building so that dust settled from the ceiling. Some of the bigger ones scared the ever-living crap out of me (it's literally like an explosion going off right over you entirely at random).

At the Air Force Academy, a famous incident had an F-105 do a flyover - where it 'accidentally' broke the sound barrier (they could never *prove* the pilot did it on purpose).

Now, those familiar with USAFA know there is a LOT of glass in the architecture. Well, thousands of windows were shattered by that fly-over, just from the effect of the boom.





No (responsible) pilot would EVER do a sonic boom over an airshow. It would shatter windows, damage other property, scare the crap out of people, likely resulting in injuries and/or deaths from the panicked herds of people, and maybe even result in permanent hearing damage to some people.


Over in A-stan and Iraq, we would sometimes schedule 'show of force' missions. We would have a B-1 bomber fly low over an area at night, all darked out except for the open bomb bays (those were lit up with all the lights they had in there). Imagine being a terrorist (or whatever), camping out way out in the 'stan, suddenly being over-flown by such a HUGE plane (not sure if supersonic or not, but I guess they did that, too) at night with those huge lights on would be enough to convince many people not to screw with the USA. . .

Watched many a plane fly past the carrier(s) at faster than the speed of sound.

If you don't know it's coming, it'll scare the shit out of you!!

And yes, you can feel the concussion as the plane does it fly-by.

quote:

Originally posted by bettysnephew:
While attending grade school in the fifties we often experienced sonic booms during flyovers here in the flyover MidWest..One of the most severe ones cracked a couple of the large windows of the school building. The booms are pretty distinctive. I would put them somewhere between a lightning strike without the longer roll afterward, more closely to an artillery shot concussion. Either way, they are always unexpected and definitely get your attention.

I remember those! More Like early 60's when I was in grade school. We were told it was the SAC practicing bombing Chicago. Planes were probably B-58 Hustlers as this was the only supersonic bomber we had at the time. The booms were alway unexpected and shook the whole school. No glass damage that I could remember. All us kids thought it was pretty cool.

Per the regs, you can’t go supersonic over land for civilian aircraft. I would assume the reasons they don’t allow it would be the same logic why you wouldn’t do it at an air show next to a large crowd of people.

We had an event a few years ago where someone busted the Presidential TFR and they had to scramble F-15s out of PDX. They broke the sound barrier to get to the target.

I've heard the sound barrier be broken 3 times and it is unmistakable. You hear a clap but the cool part is the pressure wave that you feel head-to-toe.

The first time I heard it I was in the Navy and I was hosting my grandmother and aunt on a family day cruise. I had watch afterward and when I went down into the plants, all the dust that had previously been accumulating in the air vents and elsewhere was now suspended in the air like a giant dust cloud.

Fun times!

JP

We were staying at Edwards Air Fore base when the (at the time) YF-22 was doing flight testing. It broke the sound barrier, and so did it's chase plane. Double sonic booms Every car alarm on base was blasting!

Those are mach compressibility effects.

There is no such thing as a sound a barrier. That was a popular press invention to dramatize and simplify the effort at the time to exceed speeds at which compressibility factors began affecting aerodynamic control. The aircraft in the picture is in a transonic state.

The reference used is the speed of sound, but that doesn't actually mean anything so far as the "boom" or a "barrier." It's a function of air temperature and density. The reference point is Mach 1.0 or M1, which is equivalent to the speed of sound at a given temperature. The actual speed through the air, or over the ground varies; close to the ground, at lower altitudes, the aircraft can fly high indicated airspeeds and still be at a relatively low mach number; at higher altitudes the aircraft can be close to it's limiting mach number of Mach 1.0, yet will be at a low airspeed.

The transonic range, at which the aircraft is flying in the picture, is roughly .8 to 1.2 M1.

The effect of the mist around the airframe is one defining an area behind the shock wave, or the area of compressibility that is occurring. The aircraft is pushing through the air at a speed fast enough to plow or force the air ahead of it to create a wave or layer. Subsonic air isn't considered compressible for aerodynamics, but as M1 is approached, the airflow does compress, and forms typically two (or more) angled waves of air that form a sort of "V", with the apex at or ahead of the aircraft.

As the aircraft goes faster and faster, the shock waves pass aft, and occur farther and farther back on the wing. This changes the area where lift is centered, which changes the control of the aircraft and it's "trimmed" state. In the early years of the "sound barrier," as aircraft approached higher and higher speeds, this shock wave movement caused flight control problems that included "mach tuck," in which the center of lift and center of pressure moved aft, causing a nose-down pitching moment that made control difficult or impossible. It also caused fluttering of some flight controls, leading to an inflight breakup, or the locking up of flight controls due to the location of the shock wave, and wing design. The swept wings you see on most jet aircraft today were developed to overcome this problem, and a few others (and created some more in the process).

If you've ever ridden a motorcycle near a semi truck on the freeway, you've probably felt the "bow wave" as you passed the semi, as you approached the cab of the truck. Once you passed through that and moved ahead, the buffeting and the way you manipulated the bike changed a little. That's similar to the shock wave you see around that aircraft.

Your car air conditioning system works by compressing a gas, then rapidly expanding it. As it expands, temperature drops. In the picture of the F-18, you see air being compressed against the shock wave or bow wave of air, and then rapidly expanding behind it (think of the draft behind the semi truck when you're riding your motorcycle on the freeway). The air behind the shockwave is expanding, cooling, and as it cools, the temperature of the air reaches the dewpoint, or saturation point of the air, and when that happens, cloud forms, or mist forms, which is what you see. It's not breaking the "sound barrier," but you're seeing evidence of the shock wave.

Regardless of the science behind it, it's cool to watch. You can see it on humid days when airliners take off, especially as they begin to climb; vortices of mist form at the wingtips and behind the wing above it, and around propeller tips on some airplanes. You'll see it occur in the intake of some turbine engines in certain cases, too.

So far as exceeding mach domestically, there are places set aside where that can happen, but for the most part it's not allowed over land in the US, unless in those specific locations (MOA's, or military operating areas). The "boom" is the collapse of the shock wave as it passes the aircraft, and the effect for the aircraft once beyond that point is a reduction in drag (there's a big drag rise as one approaches mach in the transonic range, where large increases in power may be required for very small gains in speed).

If the semi-truck were a bit more pointed in shape and could go a lot faster, something similar would occur with the truck...but the tires would come apart well before that.

quote:

Originally posted by sns3guppy:
Those are mach compressibility effects.

Good summary.

quote:

There is no such thing as a sound a barrier. That was a popular press invention to dramatize and simplify the effort at the time to exceed speeds at which compressibility factors began affecting aerodynamic control. The aircraft in the picture is in a transonic state.

I'm not sure the term 'sound barrier' was an invention of the press. A lot of pilots of the faster aircraft from the middle of WWII onward encountered compressibility, and I believe they coined the term. I do know that in Tom Wolfe's book The Right Stuff, the pilots (allegedly) spoke about it as if it were a concrete wall in the middle of the sky (I'm not a fan of Wolfe, so I can't be 100% certain).

Pilots once thought there was a 'demon' at the mach barrier that would destroy any aircraft foolish enough to approach it. It took Chuck Yeager's X-1 flight (some claim a Brit Meteor pilot did it first, but there is no solid proof of this) to prove the 'sound barrier' was no barrier at all. However, at the time, few knew this. This is why Yeager's flight is still remembered to this day as a big deal. It's the single greatest recognized aerial achievement of the 20th century between Lindbergh's solo crossing of the Atlantic and the manned space flights.

Aircraft went through fundamental changes in design, shapes, and materials to manage the mach problems. The 'coke bottle' fuselages on aircraft such as the F-102, F-106, and F-104 represent the area rule, which has something to do with cross-sectional area along the length of the fuselage (the early F-102 could not exceed Mach 1 until it was given the area rule fuselage). Swept wings helped, as did a lot of other changes. Hence, a fighter from the late 1950s looks nothing like a fighter from WWII. . .

So, 'sound barrier' is a technically incorrect term, but it goes back almost 80 years and captures the mindset of the pilots who encountered high sub-mach speed phenomena.


The P-47 and P-38 were (im)famous for compressibility problems. These were very large, very fast planes. As they dove, they would go into what they called a 'compressibility stall,' where the pilot lost control of the aircraft. The nose would typically drop downward, increasing the angle of dive and speed. The pilots (who survived) reported it felt as though their control columns were 'set in concrete.' They would plant their feet on the instrument panel and pull, but no strength could overcome the effects of the dive (Martin Caidin discussed this in his books Thunderbolt! and P-38: Fort-Tailed Devil, both of which I read about 40 years ago). The only chance the pilot had was to throttle back to idle, place the propeller(s) in course pitch (increasing drag), and ride it down to lower levels where the air was thicker, and where the controls would function again. Many aircraft literally disintegrated before the pilots could recover.

This problem hindered both aircraft (and, I believe, the P-51 as well). Pilots learned not to dive to steeply. Germans soon learned that to get away from a P-38, they just had to split-S (roll on their backs, do a quarter loop, and fly straight down). The P-38 pilot, afraid of compressibility, would seldom follow.

Finally, they introduced dive flaps on the P-38s that disrupted the airflow towards the tail, allowing the controls to take effect. This solved the problem of the P-38's compressibility issues. I'm not sure if they ever totally eradicated it from the P-47.

I was passing through a water-tight door (on a USN ship at sea) headed onto the weather deck and didn't know the carrier air wing was doing a mini end-of-deployment airshow/flyby when a pair of F-14's did a supersonic speed pass at deck level.

The door tried to slam shut on me, then jerked/flung me out onto the deck. We were trained and I always tell people even today during safety briefs, always maintain positive control over any door you are passing through on a ship. Even if it's flat calm. A smaller or weaker person than my 25 year old 6'2" 200 lb self would probably have been seriously injured by that exterior solid-steel door, They weigh around 350#.
Probably why the navy doesn't let us do fun stuff like that any more. Probably contributed to my tinnitus too along with 300 other things we routinely did without hearing protection.

There's a lot of exaggeration out there. Yeager was a master at it.

I ran into a pilot a few years ago who told me all about the mach effects on the early lears. I asked him if he'd ever been past the max mach operating speed in one, and he said no, but he knew that the controls slammed side to side and the nose pitched down such that it couldn't be trimmed up. He thought this because the simulators were modified to exaggerate the effects, to make a point. Pete Reynolds, who did much of the testing of the early series, wrote about that. I'd flown the airplanes beyond that point, as they'd exceed it in level flight if the power wasn't pulled back, and knew that the young pilot was full of bullshit.

The mach tuck on that airplane is a few ounces, actually...even though it's for the most part, a straight wing airplane with a straight trailing edge. The tuck is just outside of certification criteria, in terms of stick trim force, but nothing like what the myths would suggest.

I ran into someone a few years ago who told me about flying single engine airplanes with large horsepower (relatively speaking), how a rapid power application would take the airplane out of your hands. Yeager wrote about it. It's bullshit, but makes the P51 legendary, and other aircraft of the type. They don't really do that, though you can get them too slow and add power and have control issues. Just not what they were claimed, in lore legend.

There were a lot of lives lost trying to cross the "sound barrier," even though it doesn't exist. What do exist are aircraft type design limitations, many of which aren't the published kind that we're all supposed to respect; they're the ones that define where the aircraft departs controlled flight, or where the forces of flight exceed the structural integrity of the airframe. Those limitations are often discovered by those who learn the lesson just once.

quote:

Originally posted by Perception:
I can't see the picture, but it sounds like you've captured a vapor cone

You're right.

https://en.wikipedia.org/wiki/Vapor_cone

That's an awesome picture holdem!


Growing up just south of the Minot AFB in the 70's we heard a lot of sonic booms. They weren't close enough to break windows, but they would shake the ground pretty good.