MAT strategy – wind and options

Contest corner

John H. Cochrane

On a MAT (Modified Assigned Task) you have to pick where to go, and this choice makes a huge difference in the outcome. Point spreads are larger on MAT days, so they count a lot in the final standings. Alas, there are no easy answers. Picking the right course means putting together a lot of ingredients and balancing a lot of pros and cons.  Here are a few you might not have thought of.

• Upwind/downwind or crosswind?

The usual advice is to go upwind/downwind, but that’s not always right. If your speed through the air is the same, crosswind can be better. Imagine yourself rowing a boat in a river that is flowing just a bit slower than you can row.  If you row a mile across and back, you’ll make it, albeit slowly.  But it will take basically forever to go a mile upstream.

Of course, everything else isn’t the same.  If you go up and downwind, you can work streets, so your speed through the air should be larger.  You face a classic tradeoff: can you fly enough faster by using streets to offset the inherent advantage of going cross-wind?

Here’s an example. Suppose you can average 50 mph through the air. The table tells you what you’ll average going up/down wind vs. crosswind, and how much slower you could go through the air by flying crosswind to achieve the same result as the upwind/downwind pilot. (Formulas below)

 Wind 5 10 15 20 25 Up/down average 49.5 48 45.5 42 37.5 Crosswind average 49.7 49 47.9 46.5 45.1 Required extra speed 0.2 1 2.1 3.5 4.9

In a light 10 mph, wind has very little effect on your cross-country speed, so other considerations are more important. You only need to go 1 mph faster by working thermal streams or streets to make upwind/downwind better, so that’s the right strategy. As the wind picks up, though, this conclusion is harder. In a 25 mph wind, you have to go 5 mph faster through the air to make upwind/downwind a winning proposition. On a day with clouds and well-marked streets that probably still is right. But on a ragged blue day when you’re having trouble staying in the elusive “blue streets”, and (with me) having good luck locating the rivers of sink, a crosswind course might be a better option.

I like to split the difference on blue windy days.  I work upwind in a street or stream as long as I can. When I lose it and it turns in to a river of sink, I head directly crosswind. This also helps to find the next street and get quickly out of the river of sink. It ends up about 45 degrees into the wind.

• Upwind low, downwind high

We all know it’s faster to turn upwind turnpoints low and downwind turnpoints high (see “Upwind and Downwind” in the October 2006 contest corner).  If you can do it, the more low-upwind and high-downwind turnpoints you can take, the better.  Ideally, you would take a turnpoint at the bottom of every thermal, and another one at the top of the thermal, thus counting fully all the distance you drift while circling. This isn’t possible of course, but it’s a model worth keeping in mind. If you find yourself low near a turnpoint, it might be worth taking it and drifting downwind. If you find yourself high near a turnpoint, it might be worth taking it and going upwind.

• Finish upwind

The natural tendency is to head upwind at the beginning of the day, and then plan a nice easy downwind final glide. That makes sense for distance and fun days, but not for speed. Since you want to do all your thermaling going downwind, it’s best if everything else is equal to turn one last point downwind at the very top of the last thermal and then glide back upwind to the airport.

• Stay close or go for the big one?

There are always a few turnpoints near the home airport, that are useful for fine-tuning the end of the flight. It’s very tempting to head back towards the home airport early and run many trips around these close-in turnpoints. There will be lots of markers, and if the day really falls apart and you can dump into the home airport, avoiding the points disaster of a real landout.

I try to avoid this temptation. It’s usually better to take fewer turnpoints rather than more.  Going to a turnpoint always seems to involve a few minutes of inefficient flying or flying through poor air.  The “markers” will be goofing off in poor thermals. And the home airport is too tempting. I find it psychologically hard to resist the call of a landing and a beer if I’m in glide range of the airport. The cure is, stay out of glide range!

Many stunning MAT victories come from pilots who choose a daring turnpoint and go for it. Once committed you have to keep going.  Of course, some stunning contest-ending landouts have happened the same way!

• Options

Contest strategy overall is a game of managing your options.  Other things equal, it’s good to head to an area with many turnpoints, so you’re not forced to cross a big blue hole or other problem area if it should develop. Also, especially on weak days, it’s good to have a string of turnpoints so you can easily retreat without losing too much distance.

Psychology can argue against this however. If you commit to one far off goal and then go for it, you often end up turning in a faster flight than flitting between too many options.

• Ridge

Of course, you want to spend as much time on the ridge as possible, and cross as few gaps or make as few upwind transitions as possible. Ridge also can upend the usual rule to finish  as close to minimum time as possible. On ridge flights, you want to add as much ridge flying in as possible, so the fast ridge flying dilutes the mandatory gap crossing or transition, even if that means finishing overtime. Last year at Mifflin, a few pilots took flights hours over the minimum and did quite well. The longest flights were nearly 1000k.  Quite a few pilots cut the flight short after the minimum time, and were surprised to see late arrivals do much better.

Formulas

Writing = average cross country speed through the air and  = wind speed, the average cross country speed over the course  is given for upwind/downwind flight by

.

For cross-wind flight it’s given by the standard wind triangle

.

With these two formulas, you can find the speed through the air going upwind and downwind Vup needed to equal a given speed through the air going crosswind Vcross. The answer is to a very good approximation

The squares in these formulas give the key: up/downwind has the advantage in weak winds, but crosswind has the advantage in strong winds.