VIEWS: 260 PAGES: 31 POSTED ON: 3/25/2011
Introduction to EDF (Electric Ducted Fan) Model Flying Jim Shima AAM Meeting 1/4/2011 Apropos to RC Model Flying “Aviation in itself is not inherently dangerous. But to an even greater degree than the sea, it is terribly unforgiving of any carelessness, incapacity, or neglect.” — Captain A. G. Lamplugh, British Aviation Ins Group, c. early 1930's. “There are two critical points in every aerial flight - its beginning and its end.” — Alexander Graham Bell, 1906. EDF Overview With the advance of battery technology and brushless motors, EDF offerings have exploded and gained popularity in the past 3-4 yrs. Foam molding has allowed almost any plane/military jet in EDF form to come to market. Larger 15+ lb. fiberglass/composite EDFs have also gained traction in the hobby – even rivaling turbine performance (BVM/Tamjets). Li-Po battery technology allows for larger planes and more powerful fan units (sourcing several hp). EDF units vary from 50mm small fans to over 120mm. Some sizes are “standard”, but there are also manufacture specific sizes. EDF Basics Brushless motors used due to their high efficiency. Motors are rated with “KV” spec. This denotes the motors unloaded RPM per volt. Ex: 4000KV is 4000 RPM/volt. With 10V going to the motor, the RPM would be 40,000. EDFs max out around 50-65k RPM. Must scale the motor and battery to match the EDF unit. More blades -> lower KV motor, less blades->higher KV motor. Static thrust is governed by fan diameter, motor RPM, number of fan blades. Stators on the back of the EDF housing straighten out airflow. Inlet lip/flange has great effect on static thrust – keep ducting and inlet smooth! Typical EDF Setup Fan unit (rotor, housing, collar, rotor plug) Brushless motor (size/KV depends on fan diameter) Brushless ESC - max amperage depends on fan size+motor (30- 100A) Battery pack size (2s-12s lipo) and capacity (1300-10,000mAh) depending on above Optional BEC (most ESCs have built in BEC circuit, 2-3A) Thrust tube Any 5 to 9 channel RC radio and Rx (2.4G preferred but not necessary) Flying an EDF/Turbine Model Anyone can fly one if you abide by simple rules On takeoff/launch let the model get “on step” before giving it large control surface input. Thrust is not immediate, think 2 sec ahead. Make wider turns, remember you don’t have a prop pushing air over the wings. Military jet models have higher-wing loadings and stall easier – don’t expect to glide it in. Land with some power! Allows you to get out of situations. I like at least ¼ throttle to touchdown. Set your timer conservative. First flight should be short so you have little chance of going into battery LVC. In short, fly it like a jet and things will go well. EDFs at Altitude What Combo is Right? Some stock RTF planes will be sluggish at our altitude. Typically a motor/ESC upgrade will solve the problem. Nowadays some larger 90mm and up RTFs will do ok stock – upgrades are an option to get better performance. Thinner air can increase RPM/current draw compared to sea-level data. EDF combos I’ve used at altitude with great success: XF 55mm 3-blade fan w/ Don’s wicked extreme 5400kV on 4s - easy 100+ mph (Phase 3 F-16) 64mm “EDO” type or SF/Eflite w/ Don’s wicked 4000-4800kV motors on 4s lipo (Eflite F-15, FW SU-34) 70mm HET 6904 w/ Typhoon 2W-20 on 4s (Xflight A-7, HL F-5). 90mm HL stock setup on 6s (F-18, EF2000). 69mm Eflite Delta V on 4s: 5s possible with new ESC (Habu) . www.donsrc.com has lots of eagle tree power/current data on motor-fan combos in different sizes. Use as a good starting point. Experimenting yourself will also give you invaluable data (simple thrust stand can be built). Advanced EDF Info EDF does not compress air like a turbine, just forces it through the fan. Fan housing mitigates blade tip losses and allows higher operating RPM. Not as much unloading in the air like a normal prop. Clearance between blade tips and housing is important. Less clearance = more thrust. Centering the fan rotor is also crucial. At high RPM the blades will actually stretch out. Efflux/exhaust velocity governed by the thrust tube’s area versus the FSA (fan swept area). Smaller thrust tube diameter sacrifices thrust for higher max speed. Typical thrust tube/tailcone is about 80% FSA (more speed) to 90% FSA (more thrust). Anything impeding exhaust airflow will result in turbulent flow and greatly reduce thrust. Some EDF airframes do not have sufficient inlet ducting to “feed” the fan. In this case the plane has “cheater” holes – these allow enough air flow into the fan so it is not starved. The holes increase static thrust but should not be made too large. What Else? Many models today have built-in thrust vectoring for aerobatics (high alpha, Cobra, flat spins, Harrier) If you are a speed junkie, EDFs can easily satisfy your speed appetite (foam up to 160 mph, glass up to 200+ mph) Scale flight is overlooked. Look ma, no prop! EDFs allow you to fly in short order w/o going through time-consuming fueling, assembly, and starting procedures (convenience factor). If you are looking to advance into turbines, EDFs offer an economical way to “fly-before-big-buy” (EDF=$100’s, turbines=$1000’s) Most EDF planes (even small ones) have flight characteristics like their larger turbine counterparts. Beginner Foam EDF Models Phase 3 F-16 – www.hobbypeople.net Phase 3 U2 – www.hobbypeople.net ParkZone Habu – www.horizonhobby.com Hobby Lobby - Executive jet (SFM), EF2000 eurofighter (FreeWing), F-35. Others include C-17, F-86, Twister, etc Accessories for Getting Started ESC programming card (set up LVC, motor timing) Wattmeter (check motor current draw) LiPo batteries – 30 to 40c if available LiPo balance battery checker (field check batts) LiPo battery balance charger Real-time battery monitor (Quanum, Hitec, Weatronics). Helps you monitor battery voltage and avoid surprise LVC. Eagle Tree logger (for more advanced testing) Some Web Sites Don’s RC: www.donsrc.com Everything EDF up to 70mm Wicked motors are some of the best. Hobbywing ESCs and dynamically-balanced fans. Hobby Lobby: www.hobby-lobby.com Mostly ARF/RTF planes. HobbyCity/HobbyKing: www.hobbycity.com Tons of fans and motors to choose from. Turnigy ESCs, Lipo batteries, chargers, etc. Also has wattmeters, Quanum telemetry unit. Economical way to get into EDFs. Turbo Fan Electrics: www.turbofanelectrics.com Lots of planes, HET fans and motors. Philip’s workshop: www.pw-rc.com Great customer service and offers newest jets at a discount, Hobbywing ESCs. Electric Jet Factory: www.ejf.com Good selection of different-size and type of EDFs, motors, planes. Tamjets: www.tamjets.com Example for getting into larger (and more expensive) EDF planes 100mm+. Have Fun! (Q&A after Sid) Introduction to Turbine Model Flying Sid Gates AAM Meeting 1/4/2011 Turbine Engine Components Most current production engines are Single Shaft with an annular combustor. The Single Stage Centrifugal Compressor is driven by a Single Axial Flow Turbine Wheel. The shaft is supported by two lubricated, pre- loaded angular ceramic ball bearings Turbine Engine Disassembly Compressor and turbine wheel installed on the shaft No bearings shown. Turbine Combustor Annular Combustor – The combustion chamber is made out of stainless. The hole pattern is designed to control the size and shape of the flame in the chamber. Side View Combustor with Injectors Fuel feeds in through the small tube shown on top and goes into a fuel manifold that goes around the back of the combustion chamber. Twelve stainless fuel injector needles are silver soldered into the fuel manifold. The ends of the needles are placed into the rear of the twelve vaporizer tubes. The vaporizer tubes are soldered to the back of the combustion chamber and run approx. ¾ of the way to the front of the combustion chamber. Side View Vaporizer tubes atomize the fuel for sustaining “well-behaved” flame Turbine ECU An Electronic Control Unit (ECU) monitors exhaust gas temperature, RPM, ambient pressure and controls the fuel pump voltage. The miniature fuel pump in turn controls turbine speed (thrust) by varying its RPM and the fuel flow rate. The ECU acts as an electronic speed control so that fuel pump speed is proportional to the transmitter throttle stick position. Turbine Compressor The spinning compressor pumps air into the case. Air is compressed (density increased) and passed to combustor for fuel/air mix. The diffuser shown below straightens the air flow as it goes into the case. The sleeve that houses the shaft is shown attached. Turbine Engine Disassembly 6 The diffuser is shown on the front (left) of the combustion chamber and the Nozzle Guide Vane (NGV) on the back (right) of the chamber. Turbine Engine RAM 500 engine disassembled (~12 lb thrust) Turbine Operation Test stand with engine and all components necessary to run. The engine can be run from the data terminal or the transmitter. The start/run sequence to be described is for the RAM 500, others vary slightly. Start Up Sequence The start up sequence can be initiated by the Data Terminal or the Transmitter. First the electric starter motor spins the engine up to approximately 6,000 RPM then cuts off. The engine is allowed to coast for a short time and then the ECU pulses the propane (gas) solenoid and lights the glow plug. Start Up Sequence (cont) The propane lights and the engine accelerates to approx. 15,000 RPM. If the RPM and temperate are rising the ECU starts pumping fuel (Kero or Jet-A). The Data Terminal will then display “RAMPING”. When the engine reaches 50,000 RPM the Terminal will display “RUNNING” and you have transmitter control of the engine. Model Suggestions You have the best chance of success if you start with a A slightly higher performance choice and the lowest initial cost is trainer jet such as the the Tornado package offered Boomerang Sprint ($795.00) by Modellbau USA for the 12-22 lb thrust engine. If you start with a larger engine the Boomerang Elan or XL are very good choices. Slower landing speed and lighter wing loading. If you are only interested in a military scale model I Tornado Sport Jet Comb Package Model is recommend the Top Gun F-15 a redesign of a model that re- quired a lot of mods for turbine operation. Engine is a or any F-15 available (Yellow, proven design. Fei Bao, Avonds) Choosing the Right Engine 1. Decide on your budget. Purchasing New vs Used: 2. Decide what size models and There has been rapid whether Sport or Scale. improvement in engine design 3. Your model choice will dictate the past few years. Faster acceleration, lighter the size of Engine. weight and better fuel 4. Chose the brand of Engine. economy. Main Stream Brands: Make sure you know the engine designs short comings if Jet Cat buying an older used engine. WREN ASK/CONFIRM used engine Jet Central has not been in crash or if was Newcomer: serviced afterwards Web searches are a good Kingtech place to research an engine. AMA Turbine Waiver Summary Turbojets and Turbofan single engine models shall not exceed static thrust of 45 lbs. & multi engine shall not exceed 50lbs combined RC fixed wing aircraft: The maximum velocity will be 200 mph. All radios must be equipped with fail safe and the ECU shall be configured to shut down the engine within 2 seconds of fail safe activation. An experienced turbine pilot is defined as a pilot who has completed 20 or more turbine flights during the preceding 24 months and who has a current turbine waiver issued by AMA. For confirmation purposes, the pilot is required to keep a written log of all flights and will provide copies to AMA upon request. An AMA member may be permitted to fly a turbine powered model on the slave transmitter of a buddy box as long as the master transmitter is operated by an experienced turbine pilot. All turbine waiver applicants should have accomplished at least 50 flights on a high performance model. Fixed wing: Model should be capable of sustained speeds of 100 mph or higher. AMA Waiver Flight Demo The purpose of the flight test for the turbine applicant to demonstrate their skills, knowledge, and understanding of how to safely operate and fly a turbine model aircraft. Key Elements: The following elements are to be demonstrated through action along with verbal discussion of the element where appropriate. 1. Demonstration of proper turbine ground operations a. Discuss the need to keep the tailpipe area clear of people and flammable items during start, shutdown, and all ground operations. b. Explain the response plan for dealing with an aircraft fire similar to one resulting from a hot start. Fire extinguisher to be present per AMA safety regulations. c. Explain the potential for a post crash fire and the response plan to deal with the situation. Explanation to include local fire department contact number and fire fighting equipment immediately available for the modeler to respond to the fire. d. Explain and demonstrate typical turbine startup and shutdown procedures. AMA Waiver Flight Demo (cont) 2. Flight Skills a. Takeoff, to be held within 10 feet either direction of centerline, with smooth, controlled corrections as necessary. b. Horizontal Figure 8. Pilot to hold altitude to within +/- 50 feet during the Figure 8. This demonstrates skills at both left and right hand patterns and the ability to control the models flight path. c. Perform two aerobatic maneuvers with combined looping and rolling elements to be selected by the turbine applicant. Examples include Cuban 8, Humpty Bump with ½ roll, or similar maneuvers. This demonstrates the general flying skills of the modeler. d. High Speed Circuit of the field performed at a safe high rate of speed. This demonstrates the ability to control a model aircraft at speed. e. Square Traffic Pattern including a missed approach go-around. This maneuver to be in the opposite direction of the takeoff and landing if conditions allow. This demonstrates the ability to control a model aircraft in the landing approach mode. f. Landing to a complete stop. Again, smooth, controlled corrections to the aircraft’s path after touchdown are required. The landing must be completed on the runway. * At no time during the flight shall the aircraft pass behind the designated safety line. Thanks! Q&A
"Introduction to EDF Electric Ducted Fan Model Flying"