January 10, 2010

Developing a Soaring Model in Flight

This post was inspired by an email from a local pilot that files out of Mountain Valley Airport here in Tehachapi, Ca. An excerpt is provide below.

**************
Mark Grubb says:
You need to build a model of the airmass + wind +
terrain + sun angle and then test the model by putting your airplane
in the regions you define (based on your model) as good energy lines.
Based on the evidence you collect, you adjust the model and re-test.
Do this efficiently for 8 hours and you have flown 1000 km.

The most dangerous place to get into, IMO, is bumbling along, having
no idea of what is going on around you. Most of those "I flew into
massive sink / turbulence/Hand of God" are completely predictable if
one is acute enough to pick up on the many signals the world gives us.
Secondly, one must be skeptical and constantly testing the model.
Complacency is what has almost killed me twice. You must have
evidence that your model reflects reality or you are living in a
fantasy.
**************

The concept is easy to describe but very difficult to master. I have been thinking about it more and more because I recently read this article by Gavin Wills on page 16 of Soaring-August 2002 (SSA membership required to access the article). The article wasn't written with the same intent as the quote from Mark, however the basic idea of building a picture of the sky ahead is at the crux of the article. Reading the article in this way has allowed me to extract a specific method for building a model accompanied by a very nice case study of it's implementation.

To build an atmospheric model you need to ask yourself a series of questions covering 3 basic topics: (I use the acronym ATE)

The state of the Airmass
The nature of the Terrain ahead
Where is the Energy going to be

Airmass
To understand the airmass you are flying in you need to know the wind at all altitudes, and the height, stability and moisture content of the boundary layer. Here are some examples of questions you might be asking while determining the state of the air mass.

What indications do I have for wind?
What has been the height of my past 3 thermals?
Is the day building or dying?
Is it a pre-frontal or post-frontal day?
How long until the day dies?
Are there Cu's ahead?

Terrain
Terrain is more critical in mountain flying than for a day of flying in the plains, but it is always important to search for order in the chaos of a cu riddled sky, or worse yet a blue sky, over a flat seaming featureless surface. Here are a few examples of questions you should be asking to understand the terrain (hopefully) far below you.

What is the general direction of the most predominate terrain features (along track/cross track)?
Are there tall peaks, low ridges or a mix?
What is the surface like (Read Reichmann pg 4 - different heating rates of cereal crops vs trees etc)?
Are there options on you route (high ground vs low ground)?
Are there wind shelters to collect warm air on windy days?

Energy
Knowing where the atmosphere will have more or less energy is really the end goal of developing our model. The following questions require some additional information gathering but more so synthesis of the data collected in the Airmass and Terrain sections. Here are the questions you should be asking when thinking about Energy.

Where has the sun been hitting the ground?
Are there obvious thermal triggers around (peaks, rocks, tractors, etc)?
is there Ridge lift, wave lift?
Can you stay up wind?
Can you stay to the high ground?
Are there large bodies of water near that such energy?
Is there smoke that will limit solar heating and energy reaching the atmosphere?

You should be able to get to the point where this process takes only 30 seconds and requires minimum effort and minimum additional information gathering; because presumably you should have been paying attention to these things all along. I use the term, "you" collectively because this is specifically something I need to work on. Once you have built your atmospheric model use the tricks (stay up wind, run ridge lift, etc) you have learned previously to exploit the energy available in the air. And continuously recheck you model to make sure things haven't changed.

The next post will be to support my presentation at the SSA convention in Little Rock, Arkansas. I will be presenting on using Google Maps as a tool for cross country prep and also how to share tribal knowledge with the My Map utility. Until then...

Keep soaring,
Michael

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