Introduction to EDF (Electric Ducted Fan) Model Flying

1
Introduction to EDF (Electric Ducted Fan)Model
Flying

• Jim Shima
• AAM Meeting
• 1/4/2011

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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.

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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.

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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 -gt lower KV motor, less blades-gthigher 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!

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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
  sizemotor (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)

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EDFs at AltitudeWhat 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 Ive used at altitude with great
  success
• XF 55mm 3-blade fan w/ Dons wicked extreme
  5400kV on 4s - easy 100 mph (Phase 3 F-16)
• 64mm EDO type or SF/Eflite w/ Dons 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).

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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
  tubes 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.

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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 dont have a prop
  pushing air over the wings.
• Military jet models have higher-wing loadings and
  stall easier dont 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.

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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
  (EDF100s, turbines1000s)
• Most EDF planes (even small ones) have flight
  characteristics like their larger turbine
  counterparts.

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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

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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)

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Some Web Sites

• Dons 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.
• Philips 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.

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Have Fun! (QA after Sid)