What is Speeed To Flybasicaly it's a theory how fast -how much speed bar- should you fly in order to get
- furthest(highest) possible given the wind/sink you're facing
- fastest possible to the destination given the amount of lift you expect to get when you get there (McCready)
1. Glide angleGlide angle is relation between lost height and flown distance. That is how far can we fly with certain height. Glide ration of 8 means we fly 8000m from 1000m of height. Glide angle is the relation between the speed you fly and the sink(vario) you're facing. Different sink rates at different speeds are drawn in a graph called POLAR function.
- Glide = speed(m/s) / sink(m/s)
- Speed(m/s) = Speed(km/h) / 3.6;
- Glide = speed(km/h) / 3.6 / sink(m/s)
- Yellow is flying with min sink speed and will land last
- Violet is flying with best glide speed will land fist but will get further
When on transition you want to get as far as possible and be there as high as possible. So you want to fly with best glide. But what about thermaling? When you're thermaling you care only about finding the best lift. In this case you're trying to minimize your sink rate. That's when you should fly with min sink speed!
2. How does wind affect Glide angleWe see from the previous example that the best glide angle is at 39km/h. This measurements are always reffering to speed of glider through the air. When there is no wind, speed of glider moving through the air is the same as the speed of glider moving over ground. But when there is some wind component the wing is still moving through the air with same speed but the speed of moving over ground is different. If we're facing 10km/h head wind the glider is moving 39km/h through the air but only 29km/h over ground.
We said before that the best glide is at 39km/h in no wind. Let's make now an assumption that we're facing a head wind of 39km/h. We will be standing still over ground. Our glide ration would be 0! If we push just a little bar to go faster we would move forward and would improve our glide ration. So we see that in head wind we should fly faster to obtain the maximum glide. But how fast is this? That's what we're trying to figure out with our analysis!
3. How does sinking air affect glide angleThe air we're flying through is never still and this affects the speed we should fly at. Similiar as with the head wind we should fly faster if flying through the sinking air. The more it goes down, faster we should fly. Again we will not go into details of mathematics but you can check it in the analysis!
4. McCreadyMcCready gave a theory that we should fly faster than optimal glide speed if we know we will face lift when we arrive at the destination(next thermal, ridge...). How much faster should we fly depends on the average of lift we'll face when we get there. Average of lift should include time to center thermal and average thermal lift once in it.
- Blue is flying with best glide and will get higher into the next thermal
- but Red is flying faster with optimal McCready speed and will gain more height thermaling in mean time
Check out in the analysis how expected lift dictates our speed.
Hope this helps you and feel free to comment or contact me at firstname.lastname@example.org