What is HLG/SAL/DLG?

By Chris Adams

Hand Launched Gliders (HLG), Sidearm Launched Gliders (SAL) and Discus Launched Gliders (DLG) are models gliders with a number of variations that are propelled aloft only by the initial power of a human throw.

Initially, gliders, as defined, are airplanes that do not have a motor to power the airplane in any sort of sustained or slowly descending flight. All airplanes can be considered gliders once no power is applied to keep the airplane aloft. In modeling, there are many classes of gliders, from simple paper airplanes to very complex and high performance sailplanes. All gliders or sailplanes extract energy form the air and the properties of the air through which they fly. Model sailplanes can use forms of energy extraction that cannot be used by full sized, man carrying airplanes, due to the size or maneuverability of the airplane itself.

For the purposes of Radio Control (RC or R/C) modeling, this article will address the progress of RC glider flying in the designs of Hand Launched Glider through their evolution to Discus Launched Gliders. We invite you to visit the article on “History of Hand Launched Gliders” written by Paul Clark here on the Field Guide to Modeling. Additional descriptions of hand launched and discus launched gliders can also be found in the article on Wikipedia here (a) and on FatLion.com here (c).

Gliders which are launched by the power of the human arm or body are classified based on their style of launch. The sections below describe these methods. However, all gliders which are launched or even test flown or glided prior to their main flights, can be considered hand launched gliders. It is only when these gliders are launched high enough such that the energy required for them to increase altitude after their initial flight are considered to technically be hand launched.

Hand Launched Gliders (HLG)

R/C hand launched gliders can be initially characterized by the grasping a glider under the CG of the plane and throwing the plane as if it was being thrown like a ball. The method is generally an overhand motion. This method was later called javelin launching, as it mimicked the throwing of an Olympic javelin. Energy and flying speed imparted by the person is a combination of both running to develop speed and then throwing overhand to impart the remaining energy of the throw into the speed of the flying plane. Plane speed (kinetic energy) is converted to altitude (potential energy) and it is the potential energy that is used as the glider descents. The ability to impart speed into the plane depends upon the ability of the pilot to launch the plane without their hand slipping off or releasing prematurely from the plane. To increase the solidarity of the hold, a number of features were added to the underside of the plane. These features include holes in the underside of the fuselage that permitted a finger to be inserted, or cross peg dowels to mimic the grip of throwing a baseball. In some instances, the launchers finger used the trailing edge of the wing to act as the cross peg. Designers often added sandpaper to either side of the fuselage to increase grip strength and reduce hand slippage from the fuselage.

The disadvantages of the overhand/javelin launch is the potential destruction or damage to the throwers arm, shoulder or another part of the anatomy. Pilots were often know to take excessive amounts of pain killers or anti-inflammatory drugs, e. g. aspirin, in order the permit the continued exertion during the throwing motion. The potential physical harm to the body limited the number of participants in contests, or the heights of launches during normal flying activities.

Overhand launches still remain in use, often only when the pilot needs to test fly a plane for trimming purposes or when launch height is not a criteria for flight time duration.

Side-Arm Launched Gliders (SAL)

Side arm launched gliders are a variant of discus launched gliders. Side-arm launches are often equated to discus launches primarily due to the holding location of the glider during the launch. Side-armed launches require the launcher to grasp the wing of the glider at the tip and swing the glider through a reduced radius under 360 degrees of rotation or via an underhand type motion force the plane from under to an upward motion of the plane prior to release. Side-arm launches cannot impart significant speed to the plane and thus exhibit reduced launch height. Side-arm launches also reduce the rolling action of planes, especially planes of smaller wingspans. Planes with smaller wingspans often exhibit significant rolling action which is undesirable as it reduces launch height. For those pilots that have difficultly spinning or are more susceptible to dizziness during launch rotation, the use of side-arm launches permits the pilots to participate in non-competitive hand launch flying. Side-arm launched planes often do not have wing pegs like standard discus launched gliders. Without pegs launches are not affected by the delayed release of the peg that causes launch rotation issues. In some cases, wingtips are coated with a rosin or another substance that increases gripping action but does not suffer from release issues.

Discus Launched Gliders (DLG)

F3K

F3K is a classification of gliders as limited by wingspan and not by their method of launch.

References:

a) Wikipedia: http://en.wikipedia.org/wiki/Discus_Launch_Glider

b) Hip Pocket Aeronautics: http://www.hippocketaeronautics.com/ff_ou_hlgliders.htm

c) Fatlion: http://www.fatlion.com/sailplanes/hlg.html

d) RCGroups: http://