Here's what I came up with. Let's say my two split fingers are 1/4" apart 22" from my eyeball. I'll need an angular measurement for that so the circumference around my eye would be 2piR = 138.16". That divided by my 1/4" finger spread = 552.64. This must be converted to degrees so 552.64 / 360� = 1.535�. This is the angular measure from my eye to my outstretched fingers. Now the formula I got from http://www.astro.lsa.umich.edu/users/emiller/astro125/geom/geom.html#smallangle looks like this d = a / 360� x 2piR = aR / 57.3�. In our case d = wingspan, a = angular measurement, and R is the elusive distance to glider (altitude AGL if the plane is directly above our heads). So, solving for R, if my glider has a 100" span: 100" / 1.535� x 57.3 = 3732" or 311 feet. If I plug in your plane and antenna dia. of .34" and distance from eye = 26" we have 78" / 1.33 x 57.3 = 3360" or 280 feet. I did these over and over and can't find fault. This, however, does not mean I'm sure I'm right. I can't find any text with the formula you give. Can you point me in the right direction? Am I all screwed up here? Thanks, Pete --- [EMAIL PROTECTED] wrote: > On Tue, 18 September 2001, "Pete S." wrote: > > > How do I solve for R? > > Assuming you are asking how to make a cheap > rangefinder for judging how far away a glider is: > > Several convenient, no cost rangefinders are > available to you now. > > The basic principle involved is that a small opject > held at arms length can visually cove a much larger > object at a distance. > > For example the Tx antenna diameter can be used as a > distance gauge. There is some distance that allows > you to just barely cover the wingspan of your glider > with the diameter of the antenna. A "no math" way to > do this is to have a buddy hold up the glider near a > straight section of road. Then you just drive down > the road a bit and see how far you need to go before > the antenna diameter can just barely cover the > wingspan. (hold out the Tx at arms length). You can > do the same thing with other objects on the Tx such > as the handle diameter. > > If you want to calculate the distances to get an > idea of what kinds of range you will be working at > you can do some small math as follows. > > distance_to_glider = wingspan / antenna_diameter * > eye_to_antenna_distance > > The antenna diameter on my airtronics Tx is 0.34". > The eye_to_antenna distance is 26". Wingspan is 78" > > So when the antenna just barely covers the wingspan > it is > > 78 / 0.34 * 26 = 5965 inches which is 497 feet > away. > > Be advised that the eye_antenna distance changes > with angle of veiw. Horizontally for me it's 26" and > vertically it's 22". > Also on my Tx the antenna button is also 0.34" and > if I point the antenna directly at the ship the > eye_to_antenna_button distance is about 72". The > distance that the ship would be at when the antenna > button just covers the wingspan would be 1376 feet. __________________________________________________ Terrorist Attacks on U.S. - How can you help? Donate cash, emergency relief information http://dailynews.yahoo.com/fc/US/Emergency_Information/ RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED]
