Thread: Mini-HowTo Beginners Guide to Motor and Prop Selection View Single Post
 Nov 18, 2009, 06:40 AM Suspended Account Joined Jul 2006 22,991 Posts Now we'll take a look at what WebOCalc is showing us about our plane. It's saying that with an APC 10x7 SF prop, our plane will be developing a top speed of around 40 mph, and developing about 29 ounces of thrust at full throttle. 29 ounces of thrust on a 25 ounce plane is a very good output! It means we'll be able to hover, and even have enough power to go vertical to some degree. It's also showing us our stall speed of about 16 mph. Shown also is our 'power to weight ratio', which is displayed as 87 watts per pound. Here's something interesting for you to consider. This "power to weight ratio" is about as useless a term as there ever was. It means absolutely nothing! We often read on RC Groups that a plane needs certain power to weight ratios to accomplish things like hovering and unlimited vertical and certain speeds. An often repeated formula is 100 watts per pound to do decent aerobatics and 150 watts per pound to go vertical. As you'll see though, we have a plane that is a powerful aerobatic performer and can go vertical on only 87 watts per pound. Watts per pound is a joke, and is totally useless as an indicator of a plane's performance. WOC is also showing us that we'll need an area of about 900' x 640' to fly our plane comfortably. Of course, we all know that the forums are rife with clowns who brag that they can fly their planes in much less space, and they can. And some go so far as to claim that they can fly their plane in a phone booth if need be. Pay them no mind. Use WOC's realistic estimate of the space you'll need to fly your plane. We also see that when we have our plane at WOT (Wide Open Throttle), our motor will be pulling around 12.6 amps from our battery. This is what is called a 'static' amp draw, or the amps it would pull on our test bench at WOT. In real life, a prop 'unloads' while it's actually flying.... which simply means that it will pull about 10% less, on average, than our static amp draw. Last edited by NoFlyZone; Nov 27, 2009 at 09:45 AM.