Navigation

[Acestick]

Does anybody know exactly what pressure pattern navigation is?

I came across a brief mention of it but I have not been able to find any text that can explain what it is...I'm sure its as obsolete as celestial navigation is, what with GPS and FMS and glass cockpit displays showing up everywhere today; but it never hurts to stay sharp. If anyone can help me I would greatly appreciate it.


Acestick

 

[onthebeach]

This is an extremely interesting subject.

In the days before organized track systems, etc., etc., PP was employed to save time & therefore fuel on long range operations...primarily oceanic, but it works over land as well.

Here it is, in a nutshell:

Everybody knows the shortest distance between two points is a straight line...on the earth, this is a great circle straight line, of course. However, when you factor in a changing wind, the straight line course may take *longer* than flying some other way.

If you can arrange the flight path so that you have more favorable winds, you may get there sooner than flying great circle. Such a route is called a *minimum time route* and takes into account the atmosphere's pressure pattern...hence, "PP Navigation."

It's hard to do this without diagrams, but let's take a simple example: You are flying from L. A. to Boston. There is a Low pressure area aloft centered around Denver. There's a High pressure area aloft centered around Chicago. Let's say both areas are pretty intense, so that the winds aloft are significant. ATC permitting, the great circle route would take you generally along the route DEN - ORD - BOS. However, you would encounter severe crosswinds all the way, cutting down groundspeed.

If, however, you could fly something like Flagstaff - Amarillo - Wichita - MKE - BUF, you would be south of the Low and North of the High, and thus have tailwinds all the way! Therefore, although you flew a longer path, you would be airborne less time, saving fuel.

This is a very simplified explanation of the way this works. The military and the airlines actually did this back in the "old days." In fact, probably the people who used this the most were the Zeppelins...when you only have an airspeed of forty knots or so, wind makes a big difference!

If you want a better, very technical explanation, try to get hold of an Air Force manual called "Air Navigation." Some of the aviation bookstores might sell it.

The routes were planned on the ground by meteorologists and give to the crews by dispatch.

There is a way to plan & employ it in flight, but it involves sophisticated radar altimeters...stuff that only the transport planes carried.

A simplified type of PP is called "single heading flying." Believe it or not, there is a way to calculate a single heading which, if held from takeoff to landing, will result in flying the minimum time route...and all you need are the altimeter settings at the departure and destination airports! Barry Schiff's book *The Proficient Pilot* has an article about it.

Enjoy.

 

[aero99@home]

nice reply beach. thanks for the lesson.

And celestial navigation isn't obsolete.

When the gps and gadgets go out on the sail boat 800 miles from land you better start shooting stars.-but thats another message board.

 

[TurboS7]

LR23

I once flew a LR23 from Toledo, Ohio to Ogden, Utah doing just that. By swinging north almost to MSP with a upper air Low around MLI I landed at Ogden with 1100lbs of fuel with a full load of freight. We didn't have a GPS either

 

[Rvrrat]

Great circle plotting

Just found this thread while doing a search for great circle nav. Thanks for the PP nav reminder.

Is there text that covers calculating great circle routing & plotting said route on a map? Is there by chance a flight planning program that will do so?

 

[pilotyip]

How it works

To fly pressure pattern, you had an extremely sensitive radar altimeter, at FL290 it would read +- 20' or something like that. You found the baro reading at your destination and set that in your altimater at the nav station and then as pressure changed you flew left or right of your course and stayed on the same pressure pattern line across the ocean and hopefully arrived at your destination, cross checked with Cel nav and DR. It was out of popular use by the mid 60's when I when through Nav school at VT-29 at NAS Corpus Christi, but we were thaught the theroy. P-3 pilots had to qualiifed Navigators in the 60's

 

[JimNtexas]

Re: How it works

To fly pressure pattern, you had an extremely sensitive radar altimeter, at FL290 it would read +- 20' or something like that. You found the baro reading at your destination and set that in your altimater at the nav station and then as pressure changed you flew left or right of your course and stayed on the same pressure pattern line across the ocean and hopefully arrived at your destination, cross checked with Cel nav and DR. It was out of popular use by the mid 60's when I when through Nav school at VT-29 at NAS Corpus Christi, but we were thaught the theroy. P-3 pilots had to qualiifed Navigators in the 60's

That's what they taught in USAF Navigator school in 1975. We also used CONSOLAN and manual Lorans. I was on the very last student flight of the T-29 (Convair twin radial), and may have been the last student navigator to use a driftmeter.

Jim

 

[TurboS7]

First thing that you need is a slow moving platform, 7 miles a minute doesn't give enough time to get an accurate fix.

 

[JimNtexas]

First thing that you need is a slow moving platform, 7 miles a minute doesn't give enough time to get an accurate fix.

Speak for yourself . Back in prehistoric days, Nav students in the T-43 (B737) were expected to perform a 3 star fix or a sun line every 30 to 45 minutes, with only the use of a mechanical sextant, celestial almanac, paper, pencil, and watch.

I understand that a lot of the B747 classic models still have a sextant port, and I myself have an aeronautical sextant. So I'm ready when celestial nav comes back.

Jim

 

[Skyliner]

Celestial navigation

FlyChicaga wrote:
Anyone have a suggestion on the best way to learn celestial navigation? I'd be interested in becoming proficient, since I both sail and fly. Might be something cool to try out.

Hey FlyChicaga, there's actually someone in our area whos been trying to put together a class or do some instruction on that. Check with me, I might be able to dig up his name for you.