Introduction to EDF
(Electric Ducted Fan)
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.
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
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.
Brushless motors used due to their
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
Static thrust is governed by fan
diameter, motor RPM, number of fan
Stators on the back of the EDF
housing straighten out airflow.
Inlet lip/flange has great effect on
static thrust – keep ducting and inlet
Typical EDF Setup
Fan unit (rotor, housing, collar,
Brushless motor (size/KV
depends on fan diameter)
Brushless ESC - max amperage
depends on fan size+motor (30-
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)
Any 5 to 9 channel RC radio and
Rx (2.4G preferred but not
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
Fan housing mitigates blade tip losses and allows higher
operating RPM. Not as much unloading in the air like a normal
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
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.
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”
Most EDF planes (even small ones) have flight
characteristics like their larger turbine counterparts.
Beginner Foam EDF Models
Phase 3 F-16 –
Phase 3 U2 –
ParkZone Habu –
Hobby Lobby - Executive jet
(SFM), EF2000 eurofighter
Others include C-17, F-86,
Accessories for Getting
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
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)
Turbine Model Flying
Turbine Engine Components
production engines are
Single Shaft with an
The Single Stage
is driven by a Single
Axial Flow Turbine
The shaft is supported
by two lubricated, pre-
loaded angular ceramic
Turbine Engine Disassembly
Compressor and turbine wheel installed on the
No bearings shown.
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.
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
The ends of the needles are placed
into the rear of the twelve vaporizer
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
An Electronic Control Unit (ECU)
monitors exhaust gas
temperature, RPM, ambient
pressure and controls the fuel
The miniature fuel pump in turn
controls turbine speed (thrust) by
varying its RPM and the fuel flow
The ECU acts as an electronic
speed control so that fuel pump
speed is proportional to the
transmitter throttle stick position.
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.
RAM 500 engine disassembled (~12 lb thrust)
Test stand with engine
and all components
necessary to run.
The engine can be run
from the data terminal or
The start/run sequence
to be described is for the
RAM 500, others vary
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
The engine is allowed to coast
for a short time and then the
ECU pulses the propane (gas)
solenoid and lights the glow
Start Up Sequence (cont)
The propane lights and the
engine accelerates to approx.
If the RPM and temperate are
rising the ECU starts pumping
fuel (Kero or Jet-A).
The Data Terminal will then
When the engine reaches
50,000 RPM the Terminal will
display “RUNNING” and you
have transmitter control of the
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
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
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
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
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
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
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.