No jet class,,,CONFIRMED

[Randy Haskin]

Re: No jet class,,,CONFIRMED

I think they reported vapor shockwaves coming from the airframe exactly-prior to the boom

That's not meaningful, unfortunately. I can get vapes off my jet at 250 knots in the pattern...it all depends on temperature, baro pressure, humidity, etc.

Randy, is it remotely possible that a P&W compressor stall could release enough sound-energy to even begin to approach the dB level of a sonic boom?

No, of course not. I just think that the sound of an actual sonic boom is a lot louder than people think, AND it's accompanied by a noticeable pressure change on the eardrums at that close of a distance.

Again, just my opinion.

I'll be happy to go buy beers and admit I'm wrong if someone can show otherwise.

And why would the compressor stall during a normal low-pass down the show line?

My biggest compressor stall occurred on takeoff at about 330 knots, 1500' MSL and full military power. There wasn't any strange throttle movement, any high AOA or maneuvering, or anything else other than a 10-degree nose high wings-level climb. It literally sounded like a .45 being shot right next to my left eardrum.

Happens all the time with the big Pratts and GEs, but fortunately because of the digital electronic engine controls they have it's not a big deal (aside from the pilots crapping their pants).

It would not surprise me at all to see a compressor stall during a high-speed pass like this.

[matt]

Re: No jet class,,,CONFIRMED

so in other words randy, a sonic boom from that distance could have hurt someone.

[RandyGoss75]

Re: No jet class,,,CONFIRMED

If I could get my Grumman Yankee thru the wall at .02 mach I would tell you! RG

[Eric]

Re: No jet class,,,CONFIRMED

When I was TDY to Cold Lake back in 96 I heard a Dutch F-16 compressor stall on T/O. I heard that through double hearing protection while driving on the flightline. Made a few people jump wondering what was going on.

[Air Race Addict]

Re: No jet class,,,CONFIRMED

Happens all the time with the big Pratts and GEs, but fortunately because of the digital electronic engine controls they have it's not a big deal (aside from the pilots crapping their pants).

So Randy, is that a reportable event? Or do you let it ride? Just curious. They can be induced. I have done it in an F-28 with RR Speys. It is pretty impressive to be sitting there minding your own business doing a power assurance run at night and have this big flash accompanied by a big bang. Usually happens when you do a slam test. Either forward or to idle. I have experienced it once in a CRJ with GE fans. It happened with a fairly strong crosswind and the APU running with a misconfig in the bleeds. Really a weird thing. But, it really gets your attention. And it happened a lot further back than in an F-15 or T-38! We had to do a visual inspection of the LP blades, (bending or locking). I hear Airbus and 737 compressor stalls occasionally when they reverse thrust on landing. Generally not a good thing, but not THAT unusual.

[TWD]

Re: No jet class,,,CONFIRMED

Excuse my ignorance but "costly to produce"
????

Steve Dilda told me that it was going to cost $18,000 for race week insurance for his wife to race in the jet class in 05.

[MRussell]

Re: No jet class,,,CONFIRMED

Steve Dilda told me that it was going to cost $18,000 for race week insurance for his wife to race in the jet class in 05.

But, unless I'm mistaken, that is a cost to the teams, not the RARA producers.

[MRussell]

Re: No jet class,,,CONFIRMED

You can see such vapor patterns from high-subsonic/near-transonic aircraft. Many photos claim supersonic flight because a visible cone of vapor becomes visible around the plane. I've seen them myself at airshows without any trace of a sonic boom.

You clipped what I said. The rest of my quote states:

(I realize that's not proof of any kind, but it still counts as "evidence").

It still counts as evidence, because there is some correlation between the transonic range and the visible shockwaves.


Randy, when you said you could get vapor at 250KIAS, did you mean the "vapor pillow" that forms on-top of the wings during vacuum, or the vapor "rings" from the nose and other parts of the a/c associated with shockwave formation?

[SCEPTER]

Re: No jet class,,,CONFIRMED

this is cool...F-14

[speeddemon]

Re: No jet class,,,CONFIRMED

I just think that the sound of an actual sonic boom is a lot louder than people think, AND it's accompanied by a noticeable pressure change on the eardrums at that close of a distance.

AMEN to that, Bro.

Several years ago, when I was stationed out at NAS Whidbey Island, we were sitting in the house one night and it sounded like the world exploded on us. It felt like the side of the house had just been hit by a truck, and everything shook and vibrated.

No idea what it was until the next day when it was revealed that an SR-71 had inadvertently passed through the barrier SIXTY MILES offshore....and this was what we had heard.

I was there with you for the 'barrier bump' that this thread was talking about, and though it was cool, it was not loud enough, nor enough of a shock to the body to have been one. And since the pane glass in the tower, and most of the houses in Lemon Valley and surrounding Stead area were still intact...my inclination is to believe that it was nothing more than a pressure reaction from the 'backfire'.

But hey....what do I know?

[Leo]

Re: No jet class,,,CONFIRMED

Once camping north of Sacramento we heard a boom so loud it brought evryone into the roads, most thought a ropane tank had gone off. it even brought the sheriff around checking. Found out much later it was an SR, many miles away.
When I was a kindergartner in Southern Cal, we lived near Ontario when my dad worked at Lockheed. They were constantly coming out of dives near our house on the way over the airport and we had a LOT of picture windows replaced.
The last one I heard was form the deck of the USS Ranger durinfg a pass by an F-14 in 93, it literally moved you...
I'd never heard of a compressor stall being that loud, but it makes sense as the "bom" did'nt seem as strong as I remembered.

[MRussell]

Re: No jet class,,,CONFIRMED

If it had been a compressor stall, then that totally clashes with someone's earlier suggestion that the Reno demo pilot was disciplined(although, perhaps it was erroneous info and they took no action against him at all).

[AirDOGGe]

Re: No jet class,,,CONFIRMED

Originally posted by MRussell

You clipped what I said. The rest of my quote states:

Quote: (I realize that's not proof of any kind, but it still counts as "evidence").

MRussell, apologies if leaving that line out appeared to alter the context of your text. Doing so was unintentional.


For everyone: This site has a good write-up on the topic:

http://www.wilk4.com/misc/soundbreak.htm

A few of the links on that page lead to photos of vapor cones around aircraft taken at past Moffett Field Airshows, most of which I remember well. Moffett sits at sea level and lies close to the ocean and the San Francisco bay, so we see these water vapor effects a lot during Moffett airshows.

According to the author of the photo on the main page, the F-18 in the photo just went supersonic, as he states he heard the boom.

Alternately, the F-18 in the Moffett field photos was subsonic.....No boom.

.

[FlyingTiger]

Re: No jet class,,,CONFIRMED

This came right off RARA.com HOME PAGE


3 Feb 2006: Jet Class announcement

The Reno Air Racing Association (RARA) has announced that an L-39 Jet Class will not be in the race schedule for the 2006 Reno Air Races.

"The Jet Class in its current format has struggled to acquire pilots, planes, and fans, and has turned out to be very costly to produce. We are still considering other jet racing options and we are looking forward to working with the Jet Class to revamp jet racing and to discuss other formats", said Reno Air Racing President and CEO Michael Houghton.

I've been involved with RARA since the Sport Class was created. As someone stated earlier there isn't much room for additional classes. I too believe the "Jet" class was a real snorer since they only let L39's into their minions. In 2004 they quietly put it out that any type of jet could enter (no AB usage) and they got no interest. They doomed themselves from the beginning as these "cliques" grow within the racers.

Someone mentioned that RARA (RenoAirRaceAssoc) was going to introduce the vertical Jet Canards into the races this year but I've heard nothing about that and there is nothing about it on the RARA website www.airrace.org In fact, they still have the L39's listed as racing? Plus, I don't think any of them have been built yet and if so there sure can't be many.

Tim