

Oct 10, 2008, 02:59 AM  
Joined Jul 2008
92 Posts

Quote:
Your Easy Star, is like my two RTF Harbor Freight 3ch 55" Wild Hawks. My first rc buy was a new $65 WH last July 2008, and bought a 2nd used $16 WH a month later. Both operating, and enjoying flying both, ... one with faster flying lighter 6 cell nica battery packs, the other with a longer flying 7 cell nimh pack. So, I'm still new to rc, and found I enjoy the beauty of glide fight, when its so high it's barely visible, or on landing approach, or anywhere in between. Thanks for your discussion of "with and without" the ailerons. I have not yet had ailerons, and thought, maybe, it would be an interesting new addition to my next rc experience and plane. If you were at my stage, never having ailerons, new to rc for 3 months, and all your experience had been only with your 3ch Easy Star, (like me with the 3ch 55" Wild Hawk), ... knowing what you know, about the "Easy Glider" with ailerons, but pretending you had not yet experienced the Easy Glider and ailerons yet, and knowing what you know so far, about the Radian, would you tend to go next for the Easy Glider with ailerons (having not yet experienced ailerons, like me, now), or the Radian without ailerons? Second, could you compare, the $249 brushless/lipo 3ch Radian, with an on sale $192 free ship 4ch with ailerons bushless/lipo Grand Distribution Icon Hawk, ... as if you had never yet experienced ailerons, like me, but knowing what you do know now, about planes with ailerons like your Easy Glider, ... and without ailerons, such as the Radian. On a final note, my Wild Hawks fly so well, at the smaller of the two fields I fly, its sometimes hard to land without running out of runway, and nearly hitting trees at either end and sides. So, at the smaller field, maybe flaps, or spoilers, or ailerons in a flap position, could slow it down some for landings? Thanks. 

Oct 10, 2008, 11:52 AM  

Wow, that Icon looks exactly like the easy glider!
So, which should you get? I'd say get the one that most attracts you. I'd also say that you probably shouldn't expect any one plane to be your final perfect design though (although there's always the possibility!). There's probably going to be a process (might take a few years) of trying a few different things out and seeing what you like. You might end up wanting to keep a few different models on hand. Obviously that can get expensive [especially when you choose the wrong model  it sure sucks to make expensive mistakes!]. But you don't have to do it all at once  and you already know you enjoy the Wild Hawk. You can keep coming back to it. But anyway, get the one that most attracts you, the one that's going to get you jazzed to go flying. If the main thing you want to do next is explore ailerons, get some kind of aircraft with ailerons. If the main thing you wanted to is explore thermalling, well ailerons can certainly be a part of that, but ailerons do make it a bit more complicated (and expensive) than just learning to thermal with an RE ship. But either way will be fine. An aileronequipped glider like the Easy Glider Electric (or, I'm sure, the Icon) is fine for learning to catch thermals. 
Oct 10, 2008, 05:04 PM  

I definitely agree that ailerons aren't needed on a sailplane. I've seen many people learn to fly/thermal without them. I'm not sure though whether or not to just buy the RTF or PNP.... I already have the DX7 , yet to buy the $60 AR500 and 1 or 2 1320 3S from hobbycity.com is probably over $250... What's everyone else doing?

Oct 10, 2008, 05:39 PM  

Could Wing Flutter ever become an issue on the Radian..?
Now I fully realize that the Radian is neither a Hotliner, nor a Warmliner.
But since the foam Multiplex Blizzard has been experiencing significant wing flutter on rapid decent/dives...I just thought I would ask... Is it safe to say that flutter should never be an issue with the Radian...even in high altitude dives. So far there are no video's showing any type of altitude dives. What would happen if you tried it....nothing..something. Just curious... Thanks, mike 
Oct 10, 2008, 07:58 PM  

Quote:
From Wikipedia, the free encyclopedia (Redirected from Air density) Jump to: navigation, search The density of air, ρ (Greek: rho) (air density), is the mass per unit volume of Earth's atmosphere, and is a useful value in aeronautics. Air density decreases with increasing altitude, as does air pressure. At sea level and at 20 °C, air has a density of approximately 1.2 kg/m3. The density of water, which is about 1000 kg/m3 (1 g/cm³), is about 800 times more than the density of air at sea level. Contents [hide] * 1 Effects of temperature and pressure * 2 Effect of water vapor * 3 Effects of altitude * 4 Importance of temperature * 5 See also * 6 References * 7 External links [edit] Effects of temperature and pressure The formula for the density of dry air is given by: \rho = \frac{p}{R \cdot T} where ρ is the air density in kilograms per cubic meter, p is pressure in pascals, R is the specific gas constant, and T is temperature in kelvins. The specific gas constant for dry air is: R_\mathrm{dry\,air} = 287.05 \frac{\mbox{J}}{\mbox{kg} \cdot \mbox{K}} Therefore: * At IUPAC standard temperature and pressure (0 °C and 100 kPa), dry air has a density of 1.2754 kg/m3. * At 20 °C and 101.325 kPa, dry air has a density of 1.2041 kg/m3. * At 70 °F and 14.696 psia, dry air has a density of 0.074887 lbm/ft3. [edit] Effect of water vapor The addition of water vapor to air (making the air humid) reduces the density of the air, which may at first appear contrary to logic. This occurs because the molecular mass of water (18) is less than the molecular mass of air (around 29). For any gas, at a given temperature and pressure, the number of molecules present is constant for a particular volume. So when water molecules (vapor) are introduced to the air, the number of air molecules must reduce by the same number in a given volume, without the pressure or temperature increasing. Hence the mass per unit volume of the gas (its density) decreases. The density of humid air may be calculated as a mixture of ideal gases. In this case, the partial pressure of water vapor is known as the vapor pressure. Using this method, error in the density calculation is less than 0.2% in the range of −10 °C to 50 °C. The density of humid air is found by: \rho~_{_{humid~air}} = \frac{p_{d}}{R_{d} \cdot T} + \frac{p_{v}}{R_{v} \cdot T} [1] Where: \rho~_{_{humid~air}} = Density of the humid air (kg/m³) pd = Partial pressure of dry air (Pa) Rd = Specific gas constant for dry air, 287.05 J/(kg·K) T = Temperature (K) pv = Pressure of water vapor (Pa) Rv = Specific gas constant for water vapor, 461.495 J/(kg·K) The vapor pressure of water may be calculated from the saturation vapor pressure and relative humidity. It is found by: p_{v} = \phi~ \cdot p_{sat} Where: pv = Vapor pressure of water \phi~ = Relative humidity psat = Saturation vapor pressure The saturation vapor pressure of water at any given temperature is the vapor pressure when relative humidity is 100%. A simplification of the regression [1] used to find this, can be formulated as: p(mb)_{sat} = 6.1078 \cdot 10^{\frac{7.5 \cdot T2048.625}{T35.85}} IMPORTANT: * This will give a result in mb (millibar), 1 mb=100 Pa * pd is found considering partial pressure, resulting in: pd = p − pv Where p simply notes the absolute pressure in the observed system. [edit] Effects of altitude To calculate the density of air as a function of altitude, one requires additional parameters. They are listed below, along with their values according to the International Standard Atmosphere, using the universal gas constant instead of the specific one: * sea level standard atmospheric pressure p0 = 101325 Pa * sea level standard temperature T0 = 288.15 K * Earthsurface gravitational acceleration g = 9.80665 m/s2. * temperature lapse rate L = −.0065 K/m * universal gas constant R = 8.31447 J/(mol·K) * molar mass of dry air M = 0.0289644 kg/mol Temperature at altitude h meters above sea level is given by the following formula (only valid inside the troposphere): T = T_0 + L \cdot h The pressure at altitude h is given by: p = p_0 \cdot \left(1 + \frac{L \cdot h}{T_0} \right)^\frac{g \cdot M}{R \cdot L} Density can then be calculated according to a molar form of the original formula: \rho = \frac{p \cdot M}{R \cdot T} [edit] Importance of temperature The below table demonstrates that the properties of air change significantly with temperature. Table — speed of sound in air c, density of air ρ, acoustic impedance Z vs. temperature °C Effect of temperature °C c in m/s ρ in kg/m³ Z in Pa·s/m −10 325.2 1.342 436.1 −5 328.3 1.317 432.0 0 331.3 1.292 428.4 +5 334.3 1.269 424.3 +10 337.3 1.247 420.6 +15 340.3 1.225 416.8 +20 343.2 1.204 413.2 +25 346.1 1.184 409.8 +30 349.0 1.165 406.3 

Oct 10, 2008, 08:18 PM  

Dear Dr. Kiwi,
Thank you for blowing my mind on a Friday afternoon This is where my intuition was wrong: Quote:
Every so often, I'll demonstrate the Bernoulli effect to the kids with two strips of paper. It still seems pretty amazing to me. 

Oct 11, 2008, 06:41 AM  

Quote:
Yes, it's balsa and fibreglass, but the thing is a floater and extremely unlikely to need repairing unless you practice landing nosefirst into a concrete wall. I know as much about thermal soaring as a politician knows about honesty, so I won't pretend to tell you how good the Ascent is at soaring  but on the now very long Ascent thread, many experienced glider pilots will be happy to tell you so. With a lightweight brushless motor to replace the boatanchor brushed Speed 400, two small servos, a lightweight Rx, and a small lipo pack, you can build the Ascent really light  under 16 oz, at which point the wing loading drops under 7 oz/ sq ft. Charles (Everydayflier) describes one such setup: http://www.rcgroups.com/forums/showp...postcount=1306 Today you could have similar performance for much less money using a cheaper motor, ESC, and lipo pack. Flieslikeabeagle 
