--- Anker Berg-Sonne <[EMAIL PROTECTED]> wrote: > Flying at max L/D is great when looking for thermals in relatively still air. > However, where flying at best L/D is really, really important is when you > are trying to return to the field from downwind in a stiff breeze, or a > howling hurricane. > The problem is that flying at max L/D isn't optimal. Some higher > speed is.
Right. For the math of this, see http://www.mvsaclub.com/articles/penetrate.htm As you feed in downtrim, airspeed, ground speed, and sinking speed all increase. The sinking speed is airspeed / (L/D), and the ground speed is airspeed - wind velocity. An easy way to figure out how far upwind you can fly from a given altitude at a given speed is to calculate the associated sinking speed, then figure out how long the plane can stay in the air; once you know that, you can get how far the plane can fly over the ground by multiplying time in the air * ground speed. To do this, you need the plane's polar. As Anker points out, best penetration typically occurs at a lower CL (i.e. at a faster speed) than does max L/D. For my simulated 3M plane loaded to 13 oz., best penetration comes at a CL of 0.5 if the wind is 10 mph, 0.4 if it's 15 mph, and 0.3 if it's 20 mph. __________________________________________________ Do You Yahoo!? Send FREE video emails in Yahoo! Mail! http://promo.yahoo.com/videomail/ RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED]
