<HTML><BODY style="word-wrap: break-word; -khtml-nbsp-mode: space; -khtml-line-break: after-white-space; ">John - You are going to get as many different answers as there are responses. The best answer is, "It depends."<DIV><BR class="khtml-block-placeholder"></DIV><DIV>It depends on how you want to fly. For doing just takeoffs, some gentle maneuvering, with very little vertical, and landing, you can use 50-100 watts per pound of total airplane weight. For more aggressive maneuvering, you'll need 100-150 watts per pound. For extreme 3D flying. you'll need 150-225 watts per pound. None of these numbers answer your question.</DIV><DIV><BR class="khtml-block-placeholder"></DIV><DIV>Average watts equals average source volts times average current. The average current divided into the pack's mah rating will tell you about how long you can expect to fly. The answer still isn't here.</DIV><DIV><BR class="khtml-block-placeholder"></DIV><DIV>Let's try an example. Suppose you assume the airplane will weigh two pounds. Flying the way I think you want to fly, your airplane should use about 250 watts (2 pounds times 125 watts per pound). With a 3S pack, your average voltage will be just under 12 volts. Since power is amperes times volts, your motor will consume about 20 amperes. With a 2100 mah pack (2.1 ampere-hour) consuming an average of 20 amperes. you flight time would be about 6 minutes (2.100 ampere-hour divided by 20 amperes then times 60 minutes per hour). Is that long enough? If not, the airplane weight is too large for that pack for fairly aggressive maneuvering. If you settle for less aggressive maneuvering, the flight time will increase for that weight.</DIV><DIV><BR class="khtml-block-placeholder"></DIV><DIV>Now, you can start out assuming that you want to fly for a certain number of minutes and work the equations in reverse to determine the required weight of the airplane for your kind of flying, but, as I used to say to my students, this is left as an exercise.</DIV><DIV><BR class="khtml-block-placeholder"></DIV><DIV>Ron Van Putte</DIV><DIV><BR class="khtml-block-placeholder"></DIV><DIV><BR class="khtml-block-placeholder"></DIV><DIV><BR class="khtml-block-placeholder"></DIV><DIV><BR><DIV><DIV>On Sep 26, 2007, at 8:27 AM, John Ferrell wrote:</DIV><BR class="Apple-interchange-newline"><BLOCKQUOTE type="cite"> <DIV><FONT face="Arial" size="2">I recently bought a heli with 2100-3s packs and I have been slowly working my way towards an airplane that uses these packs.</FONT></DIV> <DIV><FONT face="Arial" size="2"></FONT> </DIV> <DIV><FONT face="Arial" size="2">What airplanes-size-weight are you using with these packs?</FONT></DIV> <DIV><FONT face="Arial" size="2"></FONT> </DIV> <DIV><FONT face="Arial" size="2">The Vanquish and Brio 10 need more than that..</FONT></DIV> <DIV>John Ferrell W8CCW<BR>"Life is easier if you learn to plow <BR> around the stumps"<BR><A href="http://DixieNC.US">http://DixieNC.US</A></DIV></BLOCKQUOTE></DIV></DIV></BODY></HTML>