Pressure pattern navigation

[Luscombe Driver]

I have forgotten everything I used to know about pressure pattern navigation. Can anyone direct me to a good publication or web site that might bring me back up to speed? For those who don’t know what this is, it’s the fastest way to get from point a to point b, using wings.

[Capt Claret]

Luscombe Driver,

Sorry I can't help with your request but the thread title reminded me of a story which I thought I'd share with you. I believe it pertains to Qantas in the days when PP Nav was the way to go.

The story revolves around a rather pompous Captain who didn't get on with his Navigator too well.

In order to agravate the navigator one time, the Captain plonked his almost empty coffee cup onto the Navigator's chart, on the track that the Navigator was plotting, so hard that some of the coffee splashed out of the cup onto the chart.

When the Navigator registered his displeasure, the Captain refused to remove the cup, so the Navigator gave heading corrections to steer 'around' the cup. (I don't know the chart scale so don't know the extent of the 'diversion'.)

The story goes, that whenever the pompous Captain and Navigator were crewed together over that route (across the Pacific), the Navigator would give heading corrections around the coffee stain!

Revenge is so sweet! :)

------------------
bottums up !

[Feather #3]

LD - Can't help as I'm in the same boat. A bloke knocked off my Howse computer with the PP formula on it!!

However, if you need some help in counting Consol, let me know.


CaptC - Only happened once to my knowledge. the Chief Nav was rightly p'd off!

G'day

[GulfStreamV]

Errrmmmm, What is Pressure Pattern navigation?

[Tinstaafl]

Instead of flying a straight line across a pressure system, it can be quicker to fly a curved track that follows the air flow around the pressure system.

Gives greater tailwind component for that part of the flight which in turn compensates for and overcomes the slightly longer track distance.

[This message has been edited by Tinstaafl (edited 15 September 2000).]

[NIMBUS]

Luscombe Driver,

The magic formula and factors devised by Dr. J. Bellamy, Chicago give the net drift , in nautical miles:

(P1-P2)*K /TAS

Where;
P1= Pressure at Departure
P2= Pressure at Destination
K = Factor for average latitude between departure and arrival points.
TAS = True airspeed (knots).

Latitude - K Factor
22-25 - 540
25-28 - 480
28-31 - 440
31-34 - 400
34-38 - 360
38-43 - 330
43-50 - 300
50-55 - 270

(P2-P1)is positive= Left drift
(P2-P1)is negative= Right drift

When you have the net drift worked out,use flight computer (E6-B or whatever!)to figure out the drift angle. True heading + magnetic variation +/- drift angle gives single-heading to fly the route. As you probably know already, this is useless for flights at 2000" AGL or less, due to surface friction.

I’ve used this for fun, and found it to be no more than 1 or 2 miles off on trips of about 200 nm!

Hope that helps!



[This message has been edited by NIMBUS (edited 16 September 2000).]

[Luscombe Driver]

Thanks for the information. I’m amazed that more people aren’t aware of this very handy navigational aid. It is especially useful when having a “who’s plane is fastest” race between yourself and a friend flying identical iron. You both agree upon an rpm and manifold setting and then sit back and see whose bird is fastest from your home base to were ever your going for dinner that day. I used to pull out every trick I knew like moving the seats back and making the passengers sit in the baggage compartment, holding trim and navigating by pressure rather then radio, to get every last bit of speed out of my bird. The other guy could never figure out why his plane was so much slower. The longer the flight, the more effective this type of navigation is. The down side is that your not able to fly a strait ground track so it might be more difficult to find the pieces should something expensive happed along the way.

[Checkboard]

Also discussed previously here on Tech Log:

Anyone know about "Pressure Pattern Flying"? (http://www.pprune.org/ubb/NonCGI/Forum3/HTML/000151.html)