>From: "Mark Langford" <n5...@hiwaay.net> >The KR1B motorglider may not be such a bad idea after all. Maybe not for >Sport Pilot, but registered as a motorglider.
Here is a series of cut and pastes from the following website that addresses various gliders and motorgliders. While it does not address the glide or wing loading requirements (if there are any) to be classified as a motorglider. I'm sure it's out there somewhere to be found. http://vansaircraft.com/public/rv-11int.htm The term motorGLlDER implies that it is typically of lower performance, thus a GLIDER rather than a SAILPLANE. Later in this discussion the performance distinction will become more obvious Sailplanes: Simple; they just fly through air which is rising as fast or faster than their descent rate. If this parcel of rising air is of a size and shape that requires no turning (such as slope lift or wave lift), it is a simple process of comparing sailplane sink rates to the lift rate of the rising air. However, since the vast majority of lift used in soaring is thermal lift, sailplane circling performance must also be considered. Thermals are rising columns of warm air, and since columns are finite in diameter, one must circle in order to stay within them. More often than not, the diameters of thermals are so small that bank angles of 30-45° or greater are required to remain with their strong lift core areas. A sailplane which flies slower can circle tighter and thus remain in the stronger lift core of the thermals. In Figure 6 below, I have superimposed the sailplane sink rate drawing over a drawing showing relative lift rates within a thermal. From this it is easy to see that the low performance (slow) sailplane has a smaller turning diameter, and can more easily stay with the stronger lift. Often these slower sailplanes can climb as well or better than the higher performance ships with lower (level flight) sink rates. On the other extreme is the classic motorglider which has both a high sink rate and a high glide speed. It is relegated to the outer regions of the thermal where lift is less, yet it needs more lift than the other sailplanes charted here. The result is that, in marginal lift, the classic motorglider cannot soar and thus must either land or start its engine and look around for stronger lift. On the other hand, the self-launch sailplane soars nearly as well as its unpowered counterpart. It has a slightly higher sink rate because of the weight of the engine it is carrying around, but its drag is essentially the same as its pure sailplane equivalent. Statistics show that only 20 percent of the active glider/sailplane pilots in the US engage in cross-country flying. That means that 80% of them never venture farther than gliding distance of their home airport. There is nothing inherently wrong with that. Each pilot finds his rewards in different places. The pure joy of sustaining motorless flight is reward enough. For this majority, a sailplane of limited performance would suffice. Back in the 1950s, the international soaring community chose a 15-meter (49.2 ft.) span as a practical size for competition and sport sailplanes. Thus, the majority of single seat sailplanes today are 15-meter ships, and they have become the standard of comparison. Recently, we have seen the establishment of an 18meter (59 ft) class, largely inhabited by self-launch sailplanes. The added span helps carry the weight of the retractable engine and still offer very good minimum sink rates. Thus, lets think in terms of a minimum 15-meter span as a basis for motor glider design concept. The best 15-meter fiberglass sailplanes achieve L/D ratios of 45 or slightly higher. The best of the 15 meter aluminum sailplanes can attain around 40:1 L/D. By rule of thumb, we might assume that the same basic wing used on a motor glider with a fixed tractor engine, a drag optimized cowl, and a feathering (or folding) prop, would achieve an L/D of 33-35. Sink rates of the better 15 meter ships come in at just under 2 ft/sec. (120 fpm), so we can hope for as little 2.5 fps (150 fpm) for the motor glider equivalent. These are numbers which translate into what should be a very acceptable sport sailplane. Dana Overall 1999 & 2000 National KR Gathering host Richmond, KY i39 RV-7 slider, Imron black, "Black Magic" Finish kit 13B Rotary. Hangar flying my Dynon. http://rvflying.tripod.com/aero1.jpg http://rvflying.tripod.com/aero3.jpg http://rvflying.tripod.com/blackrudder.jpg do not archive _________________________________________________________________ Optimize your Internet experience to the max with the new MSN Premium Internet Software. http://click.atdmt.com/AVE/go/onm00200359ave/direct/01/
