Stupid Weather Facts

[ramcharger]

I recently inherited a really nice German made barometer, hung it up and realized it wasn't working. The mechanism is easily seen and I could tell it was pegged at it's lowest setting (wrapped all the way down passed 28" and back up to 30.5"". Duh, I realized that I had transported this from near sea level so I had to re-adjust it. I did a bit of research and found that a weather barometer is set like an aircraft altimeter, to the corrected barometric pressure. So, there are three pressure readings that have to be taken into account:

1. Station pressure, which is the actual pressure reading at any given place on the globe.

2. Altimeter Setting, which is the corrected pressure shown on nationwide/worldwide weather maps.

3. Mean Sea Level Pressure which is the baseline "average" pressure.

Now for some stupid facts:

Air pressure at sea level is approximately 14.7 psi at a barometric reading of 29.92, here in Denver it's 12.1 psi 24.63 (which corrects to 29.92, no wonder that needle on the barometer was wrapped around). That's 2.6 less psi pushing the air/fuel mixture in when the piston drops... :bootysha: no wonder my junk seems to haul *** when I drive east, lol.

The boiling point of water is directly related to true barometric pressure. Water boils here @ 202 F.

The highest correct pressure ever recorded was in Siberia in 1968 @ 32.01" and temperatures were in the -50 F range. The lowest corrected pressure was in a typhoon over the Western Pacific Ocean @ 25.69".

Just thought I'd post this as the correlation between true barometric pressure and power produced is substantial. 8)

 

[mullinax95]

That's interesting Joe..... I have a little house that sits on a table or shelf. It has a boy (bad weather) and a girl (good weather) that comes out one of the two doors. There is a little rock there in the middle that keeps it from spinning 360 degrees. You might know what I'm trying to explain but it works off of some type of spring inside the little house. Probably works on the bases of exactly what you described above. It's adjustable so sometimes when I think it is incorrect I will spin it so each boy and girl are lined up with the doors. Right now the little boy is just about to come out of his door. The weather here is partly cloudy, hot, and 30% chance of rain. Makes since I guess lol

 

[ramcharger]

That's interesting Joe..... I have a little house that sits on a table or shelf. It has a boy (bad weather) and a girl (good weather) that comes out one of the two doors. There is a little rock there in the middle that keeps it from spinning 360 degrees. You might know what I'm trying to explain but it works off of some type of spring inside the little house. Probably works on the bases of exactly what you described above. It's adjustable so sometimes when I think it is incorrect I will spin it so each boy and girl are lined up with the doors. Right now the little boy is just about to come out of his door. The weather here is partly cloudy, hot, and 30% chance of rain. Makes since I guess lol

Yep, I bet there's some sort of sealed diaphram that pushes the spring somehow and if there is, it certainly is reading barometric pressure.

 

[She Devil]

Cool info! I have a major interest in weather systems, mostly I like knowing how different clouds are formed and what the weather is doing to make them that way.
I figured I'd share a pic of my favorite weather station ever

 

[memike]

I have a pair of barometer's that I use to use for fishing, and the info you shared with us here is something I like to learn about :read2: I am going serfing today and learn more, If I remember right when the barometer is on the rise the fish close there mouth, it's sorts like the old saying if the winds out of the east the fish bite the least, and when it's out of the north stay on the porch, but when its out of the west it's the best and out of the south they open there mouth, Thank you for sharing Joe :happy10:

 

[inkjunkie]

Interesting stuff, never would have guessed boiling point of water is directly related to true barometric pressure, nor that the boiling point of water where is 202....

 

[ramcharger]

Cool info! I have a major interest in weather systems, mostly I like knowing how different clouds are formed and what the weather is doing to make them that way.
I figured I'd share a pic of my favorite weather station ever

I dig the weather station and I'll bet it's 100% accurate. :-D Weather has always fascinated me too.

I have a pair of barometer's that I use to use for fishing, and the info you shared with us here is something I like to learn about :read2: I am going serfing today and learn more, If I remember right when the barometer is on the rise the fish close there mouth, it's sorts like the old saying if the winds out of the east the fish bite the least, and when it's out of the north stay on the porch, but when its out of the west it's the best and out of the south they open there mouth, Thank you for sharing Joe :happy10:

Your welcome Mike. I agree that the fishing is always best before a storm. Right now I'm watching River Monsters and the guy is going after the Giant Nile Perch in Africa. They get to be 8' long!

Interesting stuff, never would have guessed boiling point of water is directly related to true barometric pressure, nor that the boiling point of water where is 202....

I have to cook rice another 5 minutes over the package time. Weird, 'aint it? This would also mean that with the pressure cap off, water in a auto radiator would boil sooner here too.

 

[memike]

Your welcome Mike. I agree that the fishing is always best before a storm. Right now I'm watching River Monsters and the guy is going after the Giant Nile Perch in Africa. They get to be 8' long!

Seen that one :cheers: And the one on catfish and how they set out trot lines and get pulled in buy the giants when the hooks get hooked to them in Africa I think. That ol guy has allot of cool and scary shows, He is one brave fellow 8)

 

[C130 Chief]

OK, these are not stupid weather facts, nor is it just gee-whiz weatherman and pilot stuff. This is stuff every hotrodder should know, and every drag racer must know if they want to be consistent. Indulge me a long rambling post as I endeavor to explain.

A barometer and an altimeter are basically the same instrument. We just read them different depending on what we want to know. In either case, they are typically constructed of a sealed bellows connected to an indicator on a scale, which indicates atmospheric pressure. In an aircraft we want to know our altitude, so we correct our altimeter to the current atmospheric conditions. With a barometer, we want to know pressure so we correct to our actual MSL altitude.

As you discovered, on a "Standard Day" at sea level the atmospheric pressure is 29.92" Hg (inches of mercury) and the temperature is 15 degrees Celsius (59 Fahrenheit). Using this as a standard point of reference we not only have a pressure altitude of 0' MSL, but a Density Altitude of 0' MSL as well. As you also noted, atmospheric pressure decreases (less air above you pushing down) as altitude increases. Temperature also decreases (approx 2 degrees C per 1000 feet), which is equally important. Density Altitude is what we are concerned with.

So to recap this far, Pressure Altitude is where you are, corrected for barometric (weather) conditions, and Density Altitude is Pressure Altitude corrected for temperature. Or more simply, Density Altitude is the actual amount of air (specifically oxygen) available for our engines or lungs.

As Density Altitude increases, engine performance decreases in a basically linear and predictable fashion (assuming correct fuel mixture). Horsepower ratings (SAE net) are based on standard atmospheric conditions, and good dyno operators should either correct to standard day conditions or publish their numbers as "uncorrected". This way we can compare apples to apples.

Most race tracks have a weather station, and many serious racers have their own. This way they always know what the Density Altitude is. By keeping good notes, a racer can look at Density Altitude, make an informed prediction regarding jet choice and dial-in. Really handy if you travel to different tracks. Also nice for keeping an eye on the general health of your race car.

 

[ramcharger]

C130,

I was trying to grab some attention to this stuff and find a fun way to enlighten those that were not aware of this, hence the title and I agree with you 100% in regards to "This is stuff that every hot rodder should know", plus everything else you stated. My mom was a teacher and I learned pretty quick that if information is presented in a fun way, people pay attention and keep interested.

All,

I would also like to point out that density altitude also takes into account "grains of water per pound of air". Water molecules take up space that normally oxygen would occupy so the more grains per pound equal a higher density altitude (which is bad).

I'm going to be at the Mopar Mile High NHRA Nationals this Sunday and if anyone cares to watch this on the TV, they'll see an awfull lot of talk about density altitude. The Pro-Stock class will loose about .7 of a second on average but the Funny Car and Top Fuel classes can overdrive their blowers to compensate some for "natures anti-supercharger". Wing angles for downforce are increased as there is less air to push the rear end down but on the plus side, the coeffient of drag at speed is decreased (that's why there are so many home runs at the Coors Field ballpark).

Although I'm not a pilot, I would imagine that that control surfaces become less responsive as altitude increases. Anyone got any feedback on this? I'm curious.

Ever wonder why your car seems so quick one day and not so quick on another? Check your barometer..... and your jetting. Like C130 pointed out, most drag strips have a weather station and you may be able to get a density altitude report from their website. Local airports may have information readily availible too.

 

[ramcharger]

Your welcome Mike. I agree that the fishing is always best before a storm. Right now I'm watching River Monsters and the guy is going after the Giant Nile Perch in Africa. They get to be 8' long!

Seen that one :cheers: And the one on catfish and how they set out trot lines and get pulled in buy the giants when the hooks get hooked to them in Africa I think. That ol guy has allot of cool and scary shows, He is one brave fellow 8)

He certainly has balls, lol. He even had a show that featured a weird fish that'll jump into your pecker and stick there with spines if you pee in a river. Thank God that fish is only in South America. :-D

 

[John Morrow]

too much for the small space in my head.......brain overload...Where's my Tylenol? lol J/K Thats some cool info. never thought about it and its necessity for use in drag racing.

 

[C130 Chief]

Almost any airport has an ATIS (Automated terminal Information Service) or AWOS (Automated Weather Observation Service) which broadcasts weather and other relevant info over VHF and UHF radio frequencies. The machine can also be reached by phone. (Denver Int'l is 303-342-0838 ).

Yes, changes in density altitude will effect control surface response. This is exhibited by the difference between Indicated Airspeed and True Airspeed. The difference increases as Density Altitude increases. All else being equal, aircraft performance and response will be the same at any given Indicated Airspeed, regardless of True Airspeed. One advantage to higher Density Altitudes is the reduction in Parasitic Drag (wind resistance) because the air is thinner. So although engine performance drops as you climb, the airplane itself gets faster. A commercial jet airliner's sweet spot is typically 35-40,000 feet, a C-130 likes 22-28,000, depending on weight, and most piston singles do best between 8,000 and 15,000.

OK, enough gee-whiz pilot stuff, this is a car forum. If you think this stuff is interesting, I highly recommend adding "Learn to Fly" to your bucket list.

 

[ramcharger]

too much for the small space in my head.......brain overload...Where's my Tylenol? lol J/K Thats some cool info. never thought about it and its necessity for use in drag racing.

It's amazing the effect that this stuff has on all facets of a persons life.

Almost any airport has an ATIS (Automated terminal Information Service) or AWOS (Automated Weather Observation Service) which broadcasts weather and other relevant info over VHF and UHF radio frequencies. The machine can also be reached by phone. (Denver Int'l is 303-342-0838 ).

Yes, changes in density altitude will effect control surface response. This is exhibited by the difference between Indicated Airspeed and True Airspeed. The difference increases as Density Altitude increases. All else being equal, aircraft performance and response will be the same at any given Indicated Airspeed, regardless of True Airspeed. One advantage to higher Density Altitudes is the reduction in Parasitic Drag (wind resistance) because the air is thinner. So although engine performance drops as you climb, the airplane itself gets faster. A commercial jet airliner's sweet spot is typically 35-40,000 feet, a C-130 likes 22-28,000, depending on weight, and most piston singles do best between 8,000 and 15,000.

OK, enough gee-whiz pilot stuff, this is a car forum. If you think this stuff is interesting, I highly recommend adding "Learn to Fly" to your bucket list.

Thanks for the Denver number C130! I never thought about the sweet spot balance between drag and engine power.