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
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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
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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
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Fan unit (rotor, housing, collar,
rotor plug)
Brushless motor (size/KV
depends on fan diameter)
Brushless ESC - max amperage
depends on fan size+motor (30100A)
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)
EDFs at Altitude
What Combo is Right?
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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:
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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
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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.
Flying an EDF/Turbine Model
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Anyone can fly one if you abide by simple rules
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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.
What Else?
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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
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Phase 3 F-16 –
www.hobbypeople.net
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Phase 3 U2 –
www.hobbypeople.net
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ParkZone Habu –
www.horizonhobby.com
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Hobby Lobby - Executive jet
(SFM), EF2000 eurofighter
(FreeWing), F-35.
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Others include C-17, F-86,
Twister, etc
Accessories for Getting
Started
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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
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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 differentsize 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)