Reference / Paper · 2000
Peak of Flight #1: How are your flying skills
Apogee Components' Peak of Flight newsletter, issue 1 (2000-04-16).
- peak-of-flight
- apogee-components
- model-rocketry
Reference / Paper · 2000
Apogee Components' Peak of Flight newsletter, issue 1 (2000-04-16).
Apogee Components' Peak of Flight newsletter, issue 1 (2000-04-16).
N I S S U E 0 1 , A P R I L 1 6 , 2 0 0 0 E S W L E T T E R How are your flying skills? By Tim Van Milligan It is pretty simple to judge building skills of a modeler. You can physically look at the rocket and tell by the quality of the craftsmanship. Are the balsa fins airfoiled, or are they just rounded off. Is the model bare, or painted?Are the fins glued on straight, or are they crooked. Are they evenly spaced around the perimeter of the rocket? Are the grooves in the tube filled? Is the rocket multi-colored, or just a solid color? Are there fillets along the edges of the fins? But judging a person’s flying skills is much harder. One way that I can tell is how a modeler chooses a motor for the rocket. Do you know how to select a proper motor for your rocket? Or do you ask someone else for assistance? Being able to choose the right motor for the rocket, is just part of what I call “flying skills.” I’m often asked by competition modelers for advice on selecting motors for different competition events. They’ll often say: “what is the best motor for such-n-such event?” To me, this question lets me know the person is lacking in their flying skills. Because if they had sufficient flying skills, the question would be phrased much differently. They’d first tell me about the physical size of the rocket: how big in diameter, how much does it weigh, how many fins, what airfoil shape is used on the fins, the predicted drag coefficient, the engine mount size, and then stability margin. Then, they’d tell me about the wind conditions of the launch site, and how they plan on launching the rocket. Such as: launch rod, rail launcher, and piston launcher. Finally, they’d let me know the purpose of the flight. Do they want to gain maximum altitude, or maximum speed. Do you want highest reliability, or is the model going for broke? Wow! Look at all these factors are used to determine what motor should be selected. And that is just one portion of “flying skills.” The other big “flying skill” that I am concerned about is how a rocketeer preps the model for flight. Is it a race against the clock, or do they prep the model as if the rocket was worth a million dollars? Does the modeler carefully inspect his own rocket for defects? Do they pull out the shock cord fully and give it a good hard tug? Do they inspect ejection baffles? Do they wiggle the motor mount to see if it has come loose on the last flight? Do they wiggle the fins to see if any hairline fractures occurred the last launch? Does the nose cone fit properly? Does the person carefully fold the parachute before inserting it into the tube, or do they wad it up and jam it in? Once the chute is in the tube, do they check it to see if it will eject easily? How is the motor installed. Is it securely fastened so that it doesn’t move either forward or rearward? Finally, the last flying skill is what I call “good judgment.” Does the modeler know enough about the flight characteristics of the rocket to judge whether or not it should be flown? I often see modelers arrive to the range after not having launched a rocket in a couple of months. They show up with a brand new rocket; and they are determined to fly it under any circumstances; because they know that they won’t be able to launch again for another couple of months. So they want it to fly “TODAY.” Even if the wind is blowing 20 miles per hour. Not flying that rocket takes a lot of guts, and is a great measure of a modeler’s flying skills. So how do you acquire flying skills? The only way is to practice, practice, practice. It could take hundreds of launches before you feel comfortable. Because larger rockets can be expensive, I recommend that new modelers stick with low power rockets for a long time before graduating up to the bigger ones. In my opinion, it takes a lot of bravery for these people to fly the smaller rockets while there is a lot of peer pressure from others to launch the bigger ones. In the long run, this patience will pay off. When they launch their rockets, they will be more successful, 1130 Elkton Drive, Suite A Colorado Springs, CO 80907 USA www.ApogeeRockets.com orders @ApogeeRockets.com phone 719-535-9335 fax 719-534-9050 Page 1 P E A K O F and they’ll get them back to fly again another day. The newer way to gain experience is to run computer simulations. In my opinion, the best program to use is RockSim. It will allow you to design a variety of models and test them under different launch conditions, and with different motors. What I suggest you do is to download some of the designs of other modelers, and erase the simulations that they’ve run. Then, look at the model, and make a guess as to what motor you think would give it a good flight. You can do this with dozens of different designs. The more you play with it, the faster you’ll acquire good flying skills. In a future article, I’ll try to give you some guidelines and criteria for what makes a “good” flight. F L I G H T About the Author: Tim Van Milligan is the owner of Apogee Components (http://www.apogeerockets.com) and the curator of the rocketry education web site: http://www.apogeerockets.com/education. He is also the author of the books: "Model Rocket Design and Construction," "69 Simple Science Fair Projects with Model Rockets: Aeronautics" and publisher of the FREE ezine newsletter about model rockets. You can subscribe to the e-zine at the Apogee Components web site, or sending an email to: [email protected] with "SUBSCRIBE" as the subject line of the message. About this Newsletter You can subscribe “FREE” to receive this e-zine at the Apogee Components web site (www.ApogeeRockets.com), or sending an email to: [email protected] with "SUBSCRIBE" as the subject line of the message. that they add strength to your rocket s body tube. Fig 1-13 Equipment Pods and Air Scoops: Equipment pods are used to store and protect delicate cargo, and air scoops allow air inside the aircraft. Adding either of these features to your rocket can dramatically change its appearance. Construction of these components is fairly easy, as they can be made out of cardboard, plastic, or balsa wood. What thickness of wood should you use for fins a rocket powered by a D motor? What are the nine types of fin construction? What are the other five different recovery methods besides: parachute, streamer, glider, and helicopter recovery? What size wing do you need for a rocket glider? How does high power construction differ from small rockets? Forward Fins and Stabilizing Vanes: In addition to having fins at the rear of the rocket, they can be added to the nose, middle, or tail of the rocket. Vanes are the same a fins, but are usually much longer. Although they add a distinctive look to the model, forward fins and vanes should be small in size because they can cause the rocket to become unstable. Always perform a stability check before flying the model equipped with forward fins or vanes. Fin Geometry and Shape: By changing the geometry, the number, or the size of the fins, you can completely change the overall appearance of the model. Fins are usually made out of flat balsa sheet, but you don t Fig 1-17 Forward fins Forward fin should be kept small Fig 1-18 Vanes Vanes are similar to tunnels except that they are made from thin sheets of wood Fig 1-14 Scoop Air scoop made from flat cardboard Scoop Air scoop made from short body tubes Fig 1-15 Fig 1-16 Fig 2-11 Fig 2-11 Pod Simple pods can be CP constructed from body tubes Scoop Frontal air scoop is a great decoration for missiles CP Old CP have to limit yourself to that material or to New CP CP a flat shape. You can make stabilizing fins out of plastic, paper, wood dowels or even hollow body tubes. The model does not even have to use any fins if you use cone stability. This is described in Chapter 2. Fig 2-12 centerline of the model, the fins will have to Extraneous Details:beLike a differmuchadding larger to provide the restoring force ent paint pattern or using a to lot of decals, needed overcome the unbalanced force of the engine. adding three dimensional components the This is to why you outside of the rocketkeep can the enhance look of should always thrustthe forces concentric around the centerline a basic rocket. These details orof the components model. Otherwise, the model can be simple pieces of wood, they can be may or become unstable as soon as it extra plastic parts you have a the plastic clears thefrom top of launch rod. airplane kit. Adding them to the rocket is as Besides moving the location of the CP or thetoCG, easy as gluing them the side the body you of might be able to correct instability by causing the tube. rocket to spin on the Canted motor Keep way up. This is called motor causes rotation spin stabilization. The straight spinning Body Tube Shape: You can vary not only action creates angular momentum , which the diameter but the shape of the body tube provides inherent stability (think of a as well. Why nottoy change the top shapeorfrom a spinning a gyroscope). The spinning also cancels but there is a photo out any unbalanced on page (18). forces acting on a rocket, Fig 1-19 The drawback to spinning such as that is the amount produced by one fin of drag it produces. creating more lift that This increase in drag the other fins. will reduce the overall height that the model Spinning the rocket rocket is capable of can be accomplished achieving. in three ways. You Rockets with small can cant the fins on fins have a harder the body tube at some time producing the small angle; you can necessary forces to add small canted tabs toA model s appearance restore the model to the bottom of existingis the correct flight path. fins; or you can sand easily anged by modifying To help increase these each of the forces you can fins so they have a cambered airfoil increase the velocity. fin shape geometry shape.and More air flowing over Another way of inducing a spin to the fins will produce the rocket is to use larger restoring a 15 You can spin tower-launcher. increase speed by reducing forces. These are very rare, drag or Fig 2-13 selecting an engine that produces more Fig 2-14 Fig 2-15 Spin tabs Canted fins Cambered airfoil on each fin 22 How did you do? If you couldn’t answer them, you’ll be happy to know the answers are in the book Model Rocket Design & Construction. It was written for modelers that want to build their own designs. For more information, or to order your own copy, see our web site at: www.ApogeeRockets.com/design_book.asp A P O G E E Page 2 Call Us at: 719-535-9335 R O C K E T S PAGE 2