Student needs help with pilotage

[cwyckham]

But this method seems to require knowing ahead of time what the pressure will be at the destination. As we know, weather forecasting can be a bit of an art! I don't have Schiff's book. How does he address this?

Well, winds are due to pressure differences, and both change all the time. So if you do your planning based on wind triangles or pressure differences, you're equally at the mercy of the forecasts. I would think the main difference is that if you're flying a straight line, you can keep track of these changes more easily en route.

Goes to bookshelf and digs up volume 1...

Barry says that you use the pressure difference at cruise altitude between the airports. Therefore, if they're both going up or down at roughly the same rate, nothing changes. It's only when one's going up and the other's going down that you could have issues. He says that this would only be an issue on flights greater than a few hundred miles.

The advantages are that you're flying the minimum time route and you only have to hold a single heading the whole time. Most of us only fly legs of a few hundred miles at a time anyhow. I'd think that if you had a really long leg, you could simply get an updated weather forecast mid-flight and recompute a new heading based on your current pressure and current locatation.

I'd like to try it some time.

Chris

 

[Dwight B. Van Zanen]

I think it would depend more on time enroute than distance. Highs and Lows move, so a location on the other side of the low could be the same pressure as the departure point at launch, but if it is a while getting to it it may be more in the middle of the low and with a much lower pressure. Which is what really confuses me about the Lindbergh example. He was something like 40 hours enroute. If they were the same at launch, it was just luck if they were the same on arrival. And all I know about the flight was the Jimmy Stewart movie, in which he did look at the wave tops for wind correction. Don't know how accurate that was. Good movie though.

 

[tonycondon]

He described checking out wave tops in the book "Spirit of St. Louis"