GIANT SCALE RACING
GETTING STARTED AND AIRPLANE DESIGN
By: Ed. E. Rankin
This will be a series of articles focused on Giant Scale Racing. The articles will be directed toward the beginner in racing and also for experienced pilots who want to improve his skills.
In the technical articles Aeronautical Engineering technology information will be presented and how it can be applied and made useful and understandable to the modeler. However, the reader will require a fundamental understanding of the laws of physics, mechanics, and math. If you don’t have those skills ask a friend to explain it to you. In helping people, I have found that most experienced modelers have this knowledge, through their study, building and flying model airplanes. You will not require a degree in Aeronautical Engineering to understand this information, just dedication, willingness and patience to learn.
In addition to a “Getting Started” article approximately eight to nine technical subjects will be discussed in this series: propeller design, engine tuning/fuel systems, configuration design, aerodynamics of the airplane, stability and control, airplane performance, structural design/building/finishing, and racing strategy. The order may be changed or some subjects may be combined as development progresses.
Especially, subjects will be modified as a result of comments from the reader. I have asked Fred Sattler to help me by reviewing my articles prior to publication to assure that my goals are achieved. Fred is one of the top-winning pilots in the USRA and is well respected by all of us. He has made a study on airfoils for Giant Scale Racers, and has had good success with the application of his study results. In addition, Ken McSpadden, USRA president and one of the top-winning pilots in the USRA will have final review and approval before publishing.
You should attend several races to determine if you are interested in participating in Giant Scale Racing.
Some things to do at the races are:
Consider your skills and attitude to determine if you are qualified to build and control these fast models, and if racing fulfills your desires. You should be an experienced pilot with large scale models, have quick responses and reflexes, be able to avoid accidents (6 airplanes are flown in each heat), have good depth perception (take off and landing, pylon turns), have good eye to hand coordination (control the airplane properly), and have a good attitude and reaction to others.
You must understand that Giant Scale Racing is a form of risk just like any racing sporting events. Considerable cost is involved in travel, and entry fees, constructing the model, engine purchase, and equipment required. You must consider if you can afford these costs for the class you choose. Make sure you can handle the tremendous stress involved in competition pylon racing, and that you can handle the possible risk of crashing your airplane and destroying the model, engine and radio systems.
Another consideration is to make a self-examination of what type of competitor you are. Are you one who likes competition and fly for fun regardless if you win or not? Are you a very serious competitor and think you must win to continue. Believe me, you will probably not be successful the first few races. However, you will be successful if you have dedication to improve regardless if you don’t win or lose your airplane. Remember, emotions are high and the competition is tough.
To race in a sanction event you must join the AMA and USRA. The Unlimited Scale Racing Association (USRA) was created in 1994 and is the international special interest group representing all of giant scale racers and races. The USRA’s purpose is to promote the sport in a professional manner with a democratic organization. The USRA represents the best interest of its members and the sport by setting organizational by-laws, class specifications, the conduct of the races and regulations. Also, the USRA controls the sanction race points that are accumulated during the year to determine and reward individual racing class champions. The USRA’s web site is http://www.usrainfo.org.
The following information can be obtained: about USRA, rules and specs., constitution and by-laws, contact USRA, Join USRA, manufacturer list, media relations, World Championship Point standings, President’s report, prior year’s races results, race workers, racing links, R/C Excellence magazine containing the latest USRA news and reports.
You would be wise to find an experienced race pilot as a mentor. He could advise you on every step of preparations, organizing a team, financing, selecting a class, and purchase of your model and race engines/propeller/fuel systems. Several people are needed on the team:
There are six classes to choose from and a new F-I class is being formulated to reduce the cost to new race pilots. There is no so-called entry-level class; all of these airplanes require a high level of pilot skills and are very competitive. However, in 2004 several of the race promoters have offered a non-sanctioned USRA entry-level class called the Dominator class. It is a low cost easy to fly, one airplane/engine type airplane class that has had considerable success.
Fiberglass/foam kits, or ARF airplanes are available from many manufacturers (refer to USRA website). Observe what airplane/engine combination is the most popular being used. You may want to choose this airplane for the class you have selected. However, you may want to choose something different that is competitive. In either case you should consult your mentor or other active race pilots.
The six classes available are: AT-6, BIPLANE, THOMPSON TROPHY, FORMULA-I, UNLIMITED, and EXPERIMENTAL. Each class has different parameters of speed, different requirements in pilot skills, and different options and costs. All of the airplanes are scale replicas of airplanes flown in full-size airplanes races such as Reno and Cleveland. Airplane size, requirements, engines, weight are covered in the USRA’s Specs. Race course speeds vary from approximately 120 mph for the AT-6 to 230 mph for the Experimental Class. Costs not including radio systems will vary from around $ 2000 to as high as $ 6000 depending on the class and whether you build a kit or buy an ARF model, or have your engine tuned by a specialist. The following is a brief description of each class. Refer to the USRA web site for manufacturers list:
§ AT-6 CLASS- This is a one-model, one–engine class using the AT-6/SNJ and the stock Zenoah 62 ignition engine running on gasoline/ prop furnished by the Race Management. Speeds range from 100-120 mph. Costs for the airplanes range from $1500 to $3000. (Wood kit, fiber glass, foam kit, or ARF) Engine cost about $800. Weights vary from 25-28 pounds.
There are several choices in this class; you can build a wood kit from plans or build a model from a fiberglass fuselage and foam wing/tails kit or buy an ARF. Building an AT-6/SNJ model from a wood kit/plans requires a very high degree of building skills. The stock Zenoah 62 should be disassembled and “Blue Printed” by an engine tunning specialist. Remember no reworking can be made other than substituting factory parts to make better fits, or some hand lapping.
§ BI-PLANE- these models are scale replicas of the Reno Sport Biplane race planes, and use an engine with a maximum displacement of 4.8 cu. in. They weigh from 25-30 pounds and speeds range from 120-150 mph. Costs of the model are from $1000 to $3000, engine $800 to $1200.
USRA rules state that the lower wing should be no less that 30% of the total wing area of 1475 sq. in. The fastest models in this event are the biplanes that have more wing area on the top wing than the bottom. The technical reason for this is that interference drag is reduced for biplanes by a smaller lower wing/upper wing, and/or negative wing stagger. The new Mong design with the very small lower wing, the Sundancer, or the Soceress with negative stagger wings are popular. The Mong Special versions and the Knight Twister are also very competitive. You can choose either a single or twin cylinder 4.8 cu. in. engine, but it is recommended that an engine tuner rework it for maximum power.
§ THOMPSON TROPHY-These models are scale representation of the fuel-size airplanes that raced in the Thompson Trophy Races between 1929 and 1939. Speeds range from 150-170 mph. Maximum engine displacement is 6.0 cu. in. for fixed gear airplanes, and 4.8 for retractable gear airplanes. They weigh between 25-30 pounds, and the cost of the model is from $1000 to $2000, engine costs are $800-$1200.
Plans for wooden kits, and fiberglass/foam kits are available for this class. Retractable landing gear models are usually chosen with a reworked 4.8 engine. However, fixed gear models can be chosen with a reworked 6.0 engine. Choose one with a wing area of 1100-1300 sq. in. to keep the wing loading down because of the model weight. Good choices are the Caudron, Eight Ball, and Miss Los Angeles. (Fixed or retractable landing gear)
§ FORMULA I –These airplanes are a 42% replica of the Reno Class Formula I full size airplanes using a maximum displacement engine of 4.8 cu. in. Costs for the model range from $1500 to $3000, engine cost about $1000-$1500; speeds range from 150-180 mph and weight from 25-30 pounds. A new low cost F-I event is being created for this class using a stock 4.8 ignition engine with fuel and prop furnished by the race management that should weigh 27-32 pounds. Airplanes should cost the same but the engine should cost $800-$1000. Speeds should be 130-140 mph.
This class is the fastest growing event in Giant Scale Racing, and many choices are available (see web site). You can build wooden models from scratch or fiberglass/foam kits, or buy ARF’s. Midwing models are generally lower drag than low wing airplanes due to the lower wing interference drag. This is especially true in the straightaway where skin friction drag and interference drag are predominating. However, midwing models are usually heavier that low wing models. This is due mainly to wing/fuselage structural attachment requirements. Wing aspect ratio will be examined in future technical articles. Popular models to choose from are the GR-7, Polecat, Nemesis, Shoestring, Kelly F1-D and the Proud Bird. Have your single or twin cylinder 4.8 engine reworked and tuned for maximum power.
§ UNLIMITED- All airplanes must be scale replicas of the full size aircraft that raced in the Unlimited Class at Reno or other races such as Phoenix 500. They cost between $2000 and $4000, engine cost $2500-$3000, speeds can range from 200-220 mph on the race course. They weigh approximately 32-50 pounds. Engine limit is 14 pounds.
Several manufacturers offer plans, fiberglass/foam kits, ARF models, or you can design your own within the USRA specs. All models require retractable gear. Popular models are P-51 clip wing variants, Vendetta, Miss Ashley, Corsair, Sea Fury, Bearcat, and Tsunami. Twin cylinder engines are necessary to meet the horsepower requirements to power these models. The Herbrandson 280 & 290, A3 8.8 &11.4, and Aerrow 200 are good engine choices but need heavy rework to be competitive.
§ EXPERIMENTAL- these models are scale representations of the full size airplanes raced in the Reno Sport Class, or any of the full size Experimental Class airplanes that have flown. They are approximately the same cost as Unlimited Models. Speeds range from 210-240 mph and weigh 28-35 pounds.
These are the fastest models, and require top skills to fly them. There is a lot of room for new airplane designs in this class. Presently the Lancair IV, Lancair 360, and Polen Special II are the popular models used. Popular engines are the Herbrandson 217, Aerrow 200, and the A3 8.8, and all require tuning for maximum horsepower.
An explanation is in order for describing the nomenclature used for the options to build your airplane. In addition the cost degree of difficulty, building hours, required and comments on structural weight will be discussed. Hopefully, these comments will help the beginner to match his skills/ time available with his lifestyle. The 42% F-I class will be used as an example for this discussion.
· This terminology is used when the modeler starts with a USRA approved 3-view. The scale dimensions are then calculated to meet the USRA class specifications. I will explain how in later articles. From these scale dimensions the total model can be drawn with fuselage frames, airfoils and construction with mechanical drafting or CAD. This requires about 40-80 hours.
· This method requires considerable model building skills, and requires approximately 600 hours to complete ready-to-fly.
· The construction usually consists of balsa/plywood for the fuselage, foam core wings and tails covered with balsa skins. However, these plans can be used to make patterns for fuselage/wing/tail fiberglass models.
· The cost usually varies from $100-$200 depending on purchase source of building supplies.
· The weight can vary considerably depending on the wood density and thickness used in the structure. I will discuss this later in the structural design article. As a general rule, this construction method is heavier than a well-designed fiberglass fuselage/foam wing/foam tail design. This is due to the minimum gage thickness required to maintain the structural stiffness.
· I use this method for the prototype for my line of Racing Plane Designs. This way, problems can be solved before commitment to the expense and time required for fabricating fiberglass models.
· A wide variety of finishing techniques can be employed.
ü Monocoat complete airplane, use paint only in engine bay area. This method is the lightest and can save up to 12 ounces over painted airplanes. It is durable and easy to repair, and will withstand the high pylon speeds contrary to rumors. I have used this method on two of my Polen Special Unlimited Pylon Racers clocked at 235 mph on the course.
ü Painting - This method is usually the most attractive, however, it takes a lot of time (40 hours) and could weigh up to 1 ½ pounds (one half ounce fiberglass cloth/primer/paint.)
· This method saves the design time required to draw the plans, design the structure, and solving development problems. In the long run using plans will save a lot of money if you have several crashes before problems are solved. Cost of construction is the same.
· Purchase plans from a well-experienced performance modeler who knows what is needed. If the experienced modeler is an Aeronautical Engineer the design credibility increases.
· This type of kit usually consist of a fiberglass fuselage/top-deck/belly pan / wheel parts, pilots canopy, landing gear, and foam wing and tail cores. Usually no wood or hardware is provided. Price is approximately $800 for an F-I airplane.
· Time to construct is approximately 400 hours. The degree of difficulty is not as high as building from plans. The advantage is that the kit is a well-proven design.
· Select kits that have a very light-weight fiberglass fuselage, usually around 3-3 ½ pounds for F-I. Some of these kits have fuselage with a gel-coat and no pinholes that weigh upward to 5 pounds. They look pretty and you don’t have to fill the pinholes, however, you started with 2 pounds overweight that can never be absorbed.
· The fuselage must be painted, however, I recommend monocoating the wings and tails for a one pound weight saving.
This terminology is widely used for various stages of pre-constructed models. Various total time-to-fly hours is required depending on the degree of pre-fabrication, and vary in price accordingly.
· A prefab kit with fiberglass fuselage and prefab wing and tails; surfaces hinged or not hinged; wings and tails not installed; no wood or hardware is the basic ARF. This type of prefab kit will save about 100hours of building time over the basic kit. Cost is usually $1300, and degree difficulty is less than the basic kit.
· An all composite model airplane with molded fuselage and tails uninstalled is usually a very good choice considering the time saved, and the high construction quality. About 100-200 hours is required to finish. This model costs around $1500-$2000.
· Ready built airplanes are a very good choice if you don’t have the time or the skills for the other choices, and are available in either fiberglass/foam or all composite molded fuselage/wing/tails. The cost varies from $2500-$3000, and only around 50-100 hours is required to finish
Wings/tails/landing gear/ engine firewell/servo mounts/pushrods/and cockpit are installed and are ready for finishing.
This is a type of model that is really ready to fly. Everything is done for you , all you do is charge the batteries and go fly. This is very costly ($4000-$5000), and is available on a limited basis.
This article has been devoted mainly to the new race pilot and hopefully serves as a “primer” and step-by-step procedure of how to get into Pylon Racing and enjoy this terrific sport/hobby. My goal is to help people and encourage more pylon race pilots. With this objective in mind, I will continue to write about subjects for beginners, however, the next series of subjects will be more technical. I have asked Fred French to write an article on engine tuning and fuel system design. Fred is one of the top pylon flyers and a specialist on this subject.
Let me hear your comments on these subjects