

Aug 03, 2014, 08:56 PM  

Everyone is talking weight and speed, but that is not all that gives the height. If one can input speed, one has to look at what slows the plane down. Everyone has mentioned the drag of the plane, but there is more.
Additional items deal with launch technique and plane response. If we look at the Snipe it launches higher because of less drag, but it is a lot lighter than and even as light as the smaller planes. So cleanliness matter. Bigger planes fly better because they are more efficient, but so can smaller planes. Items that are not being considered is the launch "wag" of the plane as it responds to the throw. Each wag has been approximated to 1015 ft of height loss. Smaller planes are harder to keep from wagging , especially when pone tries to put extra speed and effort into the launch. As the speed increases the wing and plane has a tendency to roll more and thus one cannot get the plane to climb as straight and true as a bigger plane. The tails are shorter so there is more wing weight at the tips. Launches also experience difficulties is the release of thw wingpeg. Many tend to hold onto the peg longer and release later in the swing. I have seen the MiMi launch as high as bigger planes, even higher. So it can be done. So even though one can impart more speed because it is easier to accelerate, other factor come into play. Bigger planes, with longer wingspan just launch higher even at the same weight. 
Aug 03, 2014, 11:26 PM  

How bout airfoil shapes? We give most modern DLG airfoils a little reflex to optimize for speed (I think)...so I guess that would enter the equation as well. Also: bigger might fly better, but the reality of trying to discus launch a much bigger wingspan than 1.5 gets problematicunless you are really tall and lanky! So me at 5 ft 9 will probably never launch to the height my 6 ft 4 friend could achieve if he used a longer wingspan DLG. But even with us matched in glider size, his longer arm would likely impart more rotational speed. So there's yet another factor.

Aug 04, 2014, 07:05 AM  

I'm not talking piloting or airframe design, I wouldn't presume to teach any of you anything about that. I'm just trying to explain (as I understand it) the energy transfer from the pilot to the DLG.
Let's assume all other things are equal, eg pilot skill, pilot arm length, rotational speed, airfoil, airframe stiffness and so on; and just consider 1 meter vs. 1.5 meter DLG as the only variable. The longer wingspan plane will have it's center of mass further out from the pivot point. At the same rotational speed, the linear speed of the center of mass will be faster, thus have more kinetic energy to trade for launch height. A heavier plane will also have more energy at launch, assuming the same launch speed. Energy imparted to the DLG goes up as the SQUARE of the speed increase. If we figure an arm length from the pivot point of 36 inches and add half of the wingspan and if we use the same rotational speed, the 1.5 meter DLG leaves the pilots hand 1.18 times faster and that translates into nearly 1.4 times the energy. Now if we factor in a heavier plane, 10 ounces vs. 6 ounces, along with the faster speed, the energy we put into the plane at launch goes up 2.3 times. So, it looks to me that an average pilot with typical DLGs could easily transfer twice the energy into the 1.5 meter DLG compared to the 1 meter DLG. Dave 
Aug 04, 2014, 09:06 AM  

Quote:
SLOPE FAST  SOAR DEEP 

Thread Tools  
Similar Threads  
Category  Thread  Thread Starter  Forum  Replies  Last Post 
Discussion  Tails for a one meter DLG  racedouge1  Hand Launch  9  May 17, 2014 10:28 AM 
Discussion  Pure vs. Electric Gliders  Once launched is there a real difference?  aeajr  Thermal  36  May 16, 2014 11:46 PM 
Wanted  Buy or trade for a 1 to 1.5 meter DLG  cdninoh  Aircraft  Sailplanes (FS/W)  1  Mar 27, 2012 10:38 AM 
Cool  Appropriate wingspan for beginners' sailplane  2 meter vs 1.5 meter  Toluca Kidd  Slope  29  Oct 11, 2008 02:58 PM 
Discussion  kevlar vs. Carbonpod layup for 1.5 meter Dlg  dougmontgomery  Hand Launch  22  Aug 18, 2007 04:33 AM 