UNIVERSITY

HandLaunch UNIVERSITYAerobatics

Welcome to the Hand Launch Aerobatics UNIVERSITY. Be sure to add this page to your "Favorites" in the menu at the top of your screen so that you can always find your way back to this web site. Some of the links presented here take you to other web sites. An excellent place to start your studies of Flight Sciences, the NASA Glenn Research Center has created the Beginner's Guide to Aeronautics (BGA) as a Web-based "textbook." The creation of the BGA is a research project to explore the use of the personal computer and the Internet to present educational materials to students, teachers, and lifelong learners in a more interactive way than a printed, bound textbook. This excellent basic reference for all students of Flight Sciences has a Beginner's Guide to Aerodynamics which includes sections on Newton's Laws of Motion, The Forces on a Falling Object and the Three Forces on a Glider. The basic concepts explained in these references are the governing principles of Hand Launch Aerobatics, as well as other forms of flight.

It is important to realize while you study and learn this material that Hand Launch Aerobatics is a very specialized form of radio controlled flight. It is also an extremely small category in the much larger world of model aviation, and the even larger world of full scale flight. In HLAerobatics we are able to use the general flight science references such as NASA's Beginner's Guide to Aeronautics (BGA) because aircraft flying through our atmosphere are all subject to the same laws of physics and flight science. It is important to realize that the goals of Hand Launch Aerobatics, high maneuverability and relatively slow speed low altitude aerobatics, are not usually the goals of most other forms of model or full scale aviation.

Although this section may sometimes sound like a textbook, HLAerobatics is a somewhat unconventional application of flight science, and therefore it is optimized toward unconventional goals with respect to most other forms of flight. With that said, however, HLAerobatics does represent a somewhat classical form of flight vehicle optimization problem, even if the optimization goals of low aerobatics and survivability when hitting things not typical goals of aircraft design. The artistic goals of the Hand Launch Aerobatics performance and interaction with the human animal are also not typical of most other forms of model or full scale aviation.

The classical flight science aspect of HLAerobatics, in the form of a flight vehicle optimization problem, is presented on this web site in a rather informal manner. The reader, or the legal guardian(s) of the reader, should realize that such an informal presentation of a technical topic is by no means rigorous or exact. The NASA BGA pages referenced above are a wonderful learning resource and a detailed presentation. The explanation presented below takes a large degree of artistic liscense to greatly simplify a vast and detailed area of science into a few short paragraphs. If you really want to learn about this topic in datail, you should consider a formal institution of learning to do so properly. If you just want to have fun with model airplanes, read on....

An Object In Motion

Newton's First Law states that an object in motion remains in motion unless acted upon by an externally applied unbalanced force. This is the law that governs Basic Object Motion, or "translation" and "rotation", of any object INCLUDING HLAerobatic airplanes. These two types of motion, straight line and rotational, are the key to how our airplanes maneuver. We give our models a straight line or translational motion when we throw them. We do this by applying a force to the model to accelerate it to it's launch velocity. In other words, we throw the model.

The velocity imparted to the model by throwing it results in the flow of air over the control surfaces and lifting surfaces of the aircraft. By deflecting the control surfaces with the radio control, aircraft rotations may be produced by aerodynamic forces acting on those control surfaces of the vehicle. The rotation of the aircraft to some new orientation changes the direction and amount of Lift acting on the airplane, which change its direction of flight. So aerodynamic forces are used by the pilot to change the orientation and direction of the airplane. These changes in the airplane's orientation and direction are what make up the aerobatic maneuvers that we want to achieve. The more change in the airplane's orientation and direction during a single flight, the better! That is the goal of Hand Launch Aerobatics - lots of maneuvers per flight. Back to top of page.

All About Energy

To reach our goal of MAXIMUM AEROBATIC MANEUVERING from hand launch (HL), we want the losses due to drag to be as small as possible, so that our airplane stays up as long as possible. We also want to throw our airplane with as much speed as we can to give it as much energy as possible. When we throw the HLAerobatic model we are imparting kinetic energy to it in the form of velocity. The speed, or kinetic energy, may be traded for height, or potential energy, during the flight. Other factors effect the energy of the glider in flight as well. Maneuvering and even straight flight both take away energy from the glider.

The energy of the glider is slowly lost over time to the force of drag, which acts against the direction of motion of our airplane. Drag takes away the work that we added by throwing the model in the first place, so drag is our enemy and we want to reduce the drag coefficient whenever possible. All of the energy that we put into our model by throwing it is eventually lost due to drag as the model runs out of height and velocity and ends up back on the ground, or back in our hands if we catch model instead of landing.

One of the tricks of Hand Launch Aerobatics is to carefully manage the energy that the model has in order to get the most maneuvers possible within a single flight or a single flying session. There are many ways to manage energy for maneuvering, some of which are described in detail in the Advanced Maneuvers section of the Laboratory of this web site. These tricks to maneuvering are often used by test pilots while performing flight tests in full scale aircraft. In Hand Launch Aerobatics, we get to be our own test pilots, and we get to fly high tech airplanes as described in the Lab mentioned above. Back to top of page.

Minimum Resistance, Maximum Control

Another way to help us reach our goal of MAXIMUM AEROBATICS from hand launch is to make the airplane as maneuverable as possible. To do this we would like the airplane to have low Weight. Low weight will help reduce drag too, which will help us get longer flight times as mentioned above. Ideally, the weight that is there should also be distributed as closely as possible about the Center of Gravity, or CG, of the model. We would also like our control surfaces to generate the maximum possilbe amount of torque ("moment") to change the orientation of the model.

To get the most possible torque or force out of the control surfaces of our aerobatic model airplane, we can make them very large, and give them lots of motion or "deflection" when controlled by the pilot. We would also like the model to have the minimum possible resistance to rotation about the three primary axes of Pitch, Roll and Yaw. This minimum rotational resistance, along with maximum control torque, will give us the fastest possible rotation about the Center of Gravity of the model. Quick rotations combined with the low weight of the model will allow the model to change direction very rapidly. Remember, the changes in the airplane's rotation and direction give us the aerobatic maneuvers that we want to achieve. MAXIMUM AEROBATICS FROM HAND LAUNCH is our goal. Back to top of page.

Frequency of the Pendulum

One way to reduce resistance to rotation of our models is to make them smaller. This is not always the best solution since smaller scale, or size, gives less overall efficiency in the world of airplanes. We can afford this comprimise to some degree in order to gain more maneuverability. If we are trying for the maximum possible number of maneuvers per flight, we can afford shorter flights if we gain a much higher rate of maneuvering in return. By using a smaller model such as the "Mini" or the "WingTip", the model will have much less resistance to rotation.

A good analogy of the smaller plane maneuvering faster is to look at a pendulum. The frequency at which a pendulum swings is not dependent on the mass of its "bob", or weight. A pendulum's frequency depends only on the length of the arm from the pivot to the weight. A shorter pendulum has a much higher frequency, or a higher rate of swinging back and forth. The shorter arm brings the weight of the pendulum closer to the pivot, which reduces its resistance to rotation. Likewise, if we make the size of the model smaller or "shorter", we are bringing the weight or mass of the model closer to it's pivot point, the CG of the model. With its mass closer its CG, or pivot point, our model will be able to tumble, flip and roll around in the sky much more easily. Thus a smaller model is one way to achieve our goal of MAXIMUM AEROBATICS FROM HAND LAUNCH. Back to top of page.

Conclusion

All of these details may seem overwhelming at first. Even navigating to all of the links and back can be overwhelming for that matter. It all boils down to just a few basic concepts that govern the practice of Hand Launch Aerobatics. We build a flight vehicle that has the least possible resistance to angular acceleration, or the least resistance to flipping and tumbling. We make the control surfaces of that vehicle as effective as possible at inducing such flipping and tumbling. We impart some amount of energy to the model by throwing it as hard as we can. And finally, we use that energy to make the model flip and tumble during the flight, until the energy is all used up and the model comes back down to ground level or to a catch. Its really just that simple. If you like, you can go get an engineering degree(s) in the finer details of these basic concepts. You have already been to University, however, and now it is time to get back to the HLAerobatics LAB for some applied technology of BUILDING and FLYING our aerobatic vehicles. Back to top of page.

More Links

More technical details about aircraft design can be found at the DJAerotech web site that Joe Hahn and Don Stackhouse have put together, as well as at the Links page of this site. The LAB mentioned above is just one of many Hand Launch Aerobatics topics available for browsing, all of which are listed at the top of this page. Don't miss the great FLIGHT VIDEOS featured in the first few topics. For web site feedback, contact site-admin at SiteAdmin. Be sure to leave you e-mail address if you would like a response. Back to top of page.

Tim Harris