Launching strategy for Thermals

[shockie]

Traditionally I launch my LPR directly with the wind or against the direct wind to minimize or maximize time aloft, and altitude.

First, let me say I am well aware the wind speed and direction at ground level is usually not the same at any given altitude. So lets keep this conversation restricted to the 1st 500 ft.

the NAR Launching Safely in the 21st Century safety review from 2005 basically encourages launching with the wind or into the wind. They do discourage launching cross-wind.

This is because at a 90 degree angle to the wind line is where spectators and property ( cars, tents, etc) are set up.

This is understandable.

but this got me thinking about launching safely for thermals. Thermals unfortunately don't follow a precise path right over the top of the launch site. they usually come from upwind and go downwind with the prevailing wind, but they may be off to either side of wind direction line, i.e. parallel.

so for the sake of argument let's suppose that there is a thermal on either side of the wind direction line/launch site by about 100 ft on either side.

If you launch to either side, you are launching cross-wind. I may not be a true 90 degree angle but its at some degree of right angle to the wind direction.

For those of you that are much more experienced than I am, in both NAR competition rocketry and FAI Spacemodeling competition, I would like to hear from you on this.

 

[Alan15578]

I disagree with your premise.

Don't confuse NAR best practices, with competition strategy.

I have no idea what the FAI encourages.

What was your question? The best strategy is often to avoid thermals.

I do not claim to be more experienced than you.

 

[shockie]

Alan:

What part of my premise do you disagree with. Competition strategy for duration events is to launch into a thermal, so it will stay up longer and therefore you will win. Competition 101.

Thermals don't appear magically right above your launch site. If it was just so easy. They can appear on either side of your launch site.

Normally you tilt your launch angle either with the wind(downwind) or into the wind(upwind).

This will determine your trajectory for altitude performance.

Now there's an old axiom, the higher the altitude, the longer the duration.

But when competing in duration events, if the thermal(s) are parallel to the normal line of launch tilt ( as described above) then you have to launch cross-wind in the direction that you think(or know) the thermals is located to try and take advantage of the lift the thermal provides.

The thermals can form in a 360 degree circle around you. If you are restricted to a single thermal detection pole, it's usually set upwind from your launch site.

You hope that a thermal forms and passes over this pole. Of course here's no guarantee it's going to pass over your thermal pole.

It may form to the right or left of you.

If you had the luxury of a picket line of thermal poles upwind of you then that would increase the likelihood that those thermals not in a straight line to your launch site would be discovered.

And of course, a thermal could form after the picket line on either side.

As far as the NAR safe practices, it's not illegal to launch cross-wind; its just not recommended.

Hopefully this more fully explains my premise.

 

[Alan15578]

This is because at a 90 degree angle to the wind line is where spectators and property ( cars, tents, etc) are set up.

This was the premise that I disagree with. I never have control of the wind direction, and only rarely do I have minimal control over where spectators and property is set up. It is like golf; you have to play it where it lies.

You have a good grasp of things and don't need my help. However, the return rule is a complicating factor. Thermals can be truly evil. One strategy is to fly high and establish a high enough sink rate, another is to use a dethermalizer. For thermal detection and flying try George Gassaway's website.

 

[Ez2cDave]

For thermal detection and flying try George Gassaway's website.

Yes, one must be educated to find "hot air" . . . Plenty of info there !

Personally, I think the "Bubble Machine" method is the most interesting.

Dave F.