is an abbreviation for Vertical Take-Off and Landing. VTOL describes
fixed-wing aircraft that can lift off vertically. This classification
includes only a very few aircraft like helicopters, autogyros, jump
jets, and tiltrotors. Helium-filled balloons and airships are not
normally considered VTOL. The following project was dedicated to
our passion for making a functional VTOL design for the hobbyist
using conventional components available at multiple vendors.
seems that some people currently working on a VTOL project
are getting hung up on making a functionally true to scale
model (like a V22
Osprey) which makes the cost and complexity of the project
extremely high. Other successful projects have been contracted
by commercial or military organizations where cost is not
a major focus.
have also seen successful VTOL projects that end up looking
like spiders from outer space. While I suspect that these
"spiders" are good low-cost designs, they do not
look or fly like a scale plane.
VTOL was inspired by the Bell/Augusta BA609
Civilian Tiltrotor. This multi-part article details my design
that has vertical take-off capability but looks and flies
like a twin turboprop plane.
focus in this month's issue of AMP'D will be in making a VTOL
design that is a repeatable project for the advanced R/Cer;
one that is easy to repair and looks like a real model plane.
By using some of the key concepts revealed in this multi-part
article, you can create your own VTOL design inspired by your
Selecting a Host
initially looked into making a V22 Osprey for my VTOL project.
I discovered that this model did not exist in a .60-.90
size kit or ARF so I then planned to use an existing heli
body to cover my framework. The model that seemed closest
to the V22 Osprey body was the Century Airwolf
fuselage that cost around $200?unpainted
decided that my host airframe must be inexpensive, readily
available in ARF form, and, easily repairable. After discovering
the full scale Bell/Agusta BA609 Tiltrotor, I realized that
my host design could take on the form of a more conventional
plane instead of the military heli-like V22 Osprey.
choose the Multiplex Magister ARF for my host plane due to
its size, low cost, and, my previous experience from first
it and then modifying it for brushless
power. The Elapor foam can be assembled quickly and repaired
with regular CA and kicker (accelerator). The nice thing about
using the Magister as a host is that I already know it flies
great and it is available from trusted vendors like Hobby
Lobby , Horizon
Hobby, and Tower
Hobbies. The CG was not critical for normal flight and
could deviate +- 10mm without issue. l will simply be using
twin motors instead of a single one in the nose.
Key Component Selections
key components, my goal was to design the project so that it may be
reproduced easily by others using commonly available parts and low-cost
components available through multiple vendors. To date, most designs
I have seen are making military-sized VTOL projects, spending thousands
of dollars. These projects often used custom machined parts that were
not readily available to others.
transmitter with 8 or 9 channels is a must for this project as it
makes mixing the spare channels easy to coordinate. I will be using
a Futaba 9C transmitter with a dual-conversion receiver. At the
very least, an 8 or 9 channel receiver and Futaba 9C transmitter
will provide a good start.
it comes to gyro performance, you basically get what you pay for.
The better performing gyros cost more money. To help me select the
right gyro for my VTOL project, without breaking the bank, I solicited
help from heli experts, Ray and Kyle
felt that using an inrunner motor would be easier to mount and swing
90 degrees without having to deal with a rotating can. My plan was
to use two Jeti
Phasor 30-3 inrunner brushless motors, Jeti
40-amp ESCs, and 12" props on a single 3-cell (20C) 5000mAh
LiPo pack. The single 14oz 3-cell 5000mAh pack can deliver 100amps,
if needed, and keep the cost and weight of the model down. By using
12" props, I could theoretically obtain about 8lbs of thrust
on my target 5lb plane.
Design and Testing
initial testing purposes, I saw two independent engineering
goals. One is the ability for Vertical Take Off and Landing
(VTOL). This testing will lift the plane up and set it down
with the props pointed up. There will likely be a need for
an additional stabilization tail motor to keep it level on
a third axis. The second goal is to simply make a flyable
plane when the props are forward. This should be a normal
plane design with dual motors. My previous experience with
the Multiplex Magister proved it to be an excellent stable
flyer. The final goal would be the transition from VTOL to
flying (and back) where the plane starts moving forward from
hover to flight.
problem to deal with will be roll control. The electronic
speed controllers (ESCs) may not be fast enough to control
roll using a gyro. I may need a basic rate gyro to dampen
out roll during the hover mode.
control is another issue. If the aircraft uses gravity for pitch
stabilization, it will be become unstable. Perhaps a small motor
and prop in the tail pointing up or down might work if the aircraft
is made tail heavy. The pivot on the main motors could be made to
shift the center of gravity back so that the tail fan can be more
effective. When the motors are shifted forward in normal flight,
the CG can be moved forward again. These type of design issues were
mulled over, again and again. I knew that it would likely take some
testing before finding out if a particular technique worked or failed.
I also wanted to keep things simple.
Wiring would be simple plug and play. It should allow for easy disconnect
of the main motors and various control stages. The Futaba 9C transmitter
and receiver will control everything using mixes, knobs, and switches.
An inexpensive gyro on the tail fan could be used for pitch dampening.
The two main motors could be mixed in the transmitter to provide
manual roll control. There could also be gyros on each speed control
in the roll direction, if needed.
not to worry too much about regular flight mode since I knew the
plane flew well so my initial concentration would be on hovering
and stabilization. Did I even have enough thrust to hover? What
if the plane weighed more than I had anticipated? These questions
were often thought about during the initial design phase. I saw
the transition from vertical hover to forward flight as the tricky
are some key points that I considered to reduce the cost and complexity
of the project.
Does not need to be functionally scale
2) Use a computer transmitter for mixing functions, 8 (or more)
3) Use gyros for hovering stabilization
4) Motors only swing on one servo-driven axis (perhaps only
90 degrees for up and forward
5) Use a tail fan somewhere on aft fuselage for pitch stabilization
6) Use inexpensive rate gyros for low level hovering stabilization
7) Break problem into basic steps
Vertical Takeoff and hover
Test vertical lift to verify thrust/weight level (correct
2) Initial tail stability control can be done manually
3) Use gyros and tail fan for final hover stability
Normal flight with normal gear landing (fly it like a normal
c) Transition from take-off to flight
d) Transition from flight to landing
steps 7c and 7d to be the most difficult and will address them in
a future part of my article. One possible solution is to rely on
advanced piloting skills. Proper hovering stabilization may also
prove to be a challenge.
my first test for VTO (or thrust level) the dual Jeti Phasor 30-3
motors will use the throttle stick for master ESC control and I'll
have a mix set up in the 9C transmitter to use aileron stick to
slightly offset the speed of the ESC for simple roll control. This
offset mix will help during the test as the gyro will not be set
up yet. A simple string tied on the tail will let a human control
the pitch for the initial thrust test. I don't expect to take the
plane more than 4' off the ground on this test. It will qualify
my choice of motors, props, and 3-cell 5000 pack as valid components
on the Magister...or maybe it won't qualify them.
to Motocalc 8,
I can expect 4lbs of thrust at 43 amps using an 11x5.5 APC prop
on my Jeti 30-3 motor. That's 8lbs total thrust and 86amps full
throttle for both motors on my expected 5lb airframe. Since the
generally accepted practice is a minimum thrust to weight ratio
of 1.1:1, it was a good start.
Multiplex Magister host plane and other key components had all been
selected. I had also broken the complex VTOL plan into more basic,
easier to achieve steps that could be tested independently. It was
time to start building!
Building and Stabilization Planning
decided to try the following techniques for my initial VTOL
project stabilization and control. A single JR DS8611 digital
servo (260oz/in on 6v) will control both outer wing thirds
from not only swinging up and forward but providing additional
pitch control in the hover mode. The servo easily mounted
in the stock area meant for the standard aileron servo. I
will be using smaller HS-55 servos on 6v for each aileron
which provides about 1/2 the torque of a standard stock servo
on 5v. Just about a perfect torque replacement for the stock
requirement. By rotating a large portion of the wing up during
hover mode, it keeps the motor thrust very efficient.
Multiplex Magister design provides a carbon rod and channel
meant to hold the two wing halves together. The plane was
designed for easy removable wing halves. I will create a
one piece wing as the span is only 64"...still very
stock channel cover can be cut and then sealed with the
carbon rod to the outer 1/3 wing half but let the tube swing
inside the channel on the center 1/3 portion. This technique
allows a single DS8611 servo to control the wing pitch and
will perhaps be stabilized by a single gyro.
Since the outer third of the wing on each side will swing
up, the ailerons can be used for yaw control as the air
from the main motors will flow right over them. A gyro in-line
with the aileron channel will provide automatic yaw control.
An additional transmitter mix from the rudder stick into
the aileron channel (during hover mode only) will allow
the pilot to also perform manual yaw compensation.
ground level, I expect hovering to take place by pilot and
gyro control. Higher up, I expect the pilot to control most
of the movement. The unique side trim controls on the 9C
transmitter may allow for easy mode or gain changes on the
gyro. When the wing is swung down for normal flight, I will
use leading and trailing edge stops to keep the wing properly
positioned. I may also need a servo driven latch to help
lock the wing position for normal flight.
initial flight mode testing would use the following control
Take-Off and Landing
- moves ailerons for yaw
Elevator - moves elevator but has no effect
Aft Pitch Control Motor - On with gyro stabilization, manual
gain adjust using knob
Wing swing servo - up position, has mix for manual pitch control
using elevator stick
Rudder - moves rudder but has no effect, transmitter mix adjusts
yaw by ailerons
Motor ESC mix on aileron stick for manual roll control
- moves ailerons for roll
Elevator - moves elevator for pitch
Aft Pitch Control Motor - Off
Rudder - move rudder for yaw
Speed 600 motor
mount used on the Hobbico Superstar EP can be unscrewed
as well as shimmed to vary the thrust line, if needed. I
tested the power system using a 12x6 APC e-prop to draw
44amps (440w) at full throttle on a 3s 3200mAh (20C) pack.
This should work well with a single 3s 5000mAh (20C) pack
on two motors. I expect to hover at around 30-35amps per
The linkage on the JR DS8611 servo used stock Hangar 9 1-1/2"
Titanium Pro-link (HAN3550), 4-40 hardware (HAN3616), and,
a 3D servo arm (HAN3578) from Horizon Hobby. Note the carbon
rod for locking the leading edge into position. For the
trailing edge, I used a small rectangular piece of lite
I misjudged my control horn position on the carbon bar before
CAing it. It was too far forward making it difficult to
achieve full vertical position for hover take-offs. The
metal bracket "fix" is a Sullivan 5/32" (#888)
wheel pant bracket with one arm removed. It is an attempt
to correct the swing range. I will keep these lessons in
mind for a second wing build.
was somewhat concerned about the strength of the 10mm carbon
tube for supporting the weight and thrust of the outer wing
thirds. I will look into using an aluminum tube for my second
wing build. By using a ½" aluminum tube for
my second wing build, I could then utilize a regular Hangar
9 (HAN3614) 8-32 Swivel Clevis Horn. The 8-32 screw will
easily fit through the tube without weakening it as it would
be bolted in place. I should still be able to make this
initial version work and gain valuable experience from it.
I could not find an APC 12x6 pusher e-prop, the Zinger 12x6
normal and counter-rotating (pusher) wood props (ZINQ1260
were used to cancel the torque of each motor. These props
are available at Tower Hobbies. The brushless motor can easily
be reversed by swapping any two of the three wires going to
6v 10-amp Power Force Regulator (VRLI2) from FMA
Direct was used to power the receivers, gyros, and servos.
With all the electronics, I was concerned that the 3-amp UBEC
would not be able to supply sufficient enough current. Further,
the 10-amp Power Force Regulator uses noise-free linear regulation
for a clean 6v output.
found a new use for my old chin-up bar in the garage as it will
help me balance the VTOL plane and perform stabilization tests.
Initially, I hung the plane from the two prop shafts and later
from a single point on the wing chord at the Center of Gravity.
photos show that I initially used a LensRC 17t motor from
Models for pitch stabilization in hover mode. The
thrust level was not sufficient and this motor has already
been replaced with a higher power 150 watt brushless power
system. Although the pitch control cannot be reversed,
the pilot has control over the amplitude to make the tail
settle where he wants. This seems to work well in conjunction
with a second E-flite
G90 gyro in-line with the motor's ESC. The 150 watt
at BP Hobbies) seemed to provide good pitch stabilization
also experimented with some techniques for transferring
the load from the outer wing thirds to the center portion.
The results of my experiments convinced me that what I
really needed was a stronger aluminum tube to replace
the stock carbon tube.
Initial Thrust Test
all the planning and building, it was time to perform
the initial thrust test. My final weight was close to
6lbs instead of my desired 5lb estimate. If the motors
couldn't lift the plane off the ground, I would need to
re-think my entire power system or find ways to reduce
the unwanted weight.
hope was that the low voltage drop using a single 3-cell,
20C 5AH pack combined with the efficient transfer of thrust
through the tilted wing would prove to be key areas of
the design enabling it to work.
wind was blowing about 10mph that day and it was difficult
to lift the plane off the ground without it starting to
patiently waited for a calmer day. In the Northeast, the fall
season can bring plenty of wind and rain so I had to wait
several weeks before my opportunity happened. In the interim,
I started to work on my stabilization techniques. When the
calm day finally arrived, to my surprise, the experimental
plane not only lifted off the ground, but I was only at 2/3
VTOL" was off to a great start!
Improving the Wing Design
you just have to experiment with a technique to find out what works
and what doesn't work. I did discover several valuable things on
my initial attempts. First, the 10mm carbon tube was not sufficiently
strong to handle twisting forces when crashing the plane during
the thrust and hover tests. Second, the various gyros I tested each
had their own good points and bad points. Read on as I reveal my
10mm carbon tube, although light, did not hold up to the
occasional twisting action that would occur when the plane
rolled over during the thrust and hover testing. This
type of carbon tube is not designed for twisting forces
but has great strength to withstand bending forces. Further,
the added weight of twin power systems, wires, and electronics,
put a greater load on the wing which it was not designed
Hobbies sells individual parts for the Multiplex Magister
so I built a new wing using a 1/2" aluminum tube
from Home Depot. The aluminum tube is 1/16" thick
and will be able to handle much stronger forces at a penalty
of additional weight. The 36" tube, which I cut to
a length of 31", weighed 3.5oz when finished.
help strengthen the tube channel and distribute the forces
where the wing sections separate, I added some aircraft
grade plywood braces and glued them to the center section
of the wing.
10mm wing channel was also sanded a bit bigger to make
room for the thicker ½" (13mm) aluminum tube.
This was accomplished by wrapping the 5" cut off
section of tube with #100 and #150 grit sandpaper.
mounting the aluminum tube inside the new wing channel,
I added a 6" long hardwood dowel epoxied in the center
area where the Hangar 9, 8-32 Swivel Clevis Horn will
be mounted. In this manner, drilling a hole through the
tube in that section would not weaken it very much.
entire linkage was now made from Hangar 9 giant scale
hardware. It was simple and solid. The mechanical rotation
of the new wing control provided about a 130 degree swing.
Gyros and Stabilization
some research on available gyros, it was time to try one. Basically,
what I had learned from several accomplished R/C heli pilots was
that you get what you pay for. Of course, I did not want to go out
and spend $300 for the top of the line designs so it becomes a compromise
area of the design. I decided to order three of the E-flite 9.0
Gram Sub-Micro G90
Heading Lock Gyros for initial stabilization testing. Model Aviation
columnist and heli expert, Ray Stacy, had tried one on a small electric
and said it worked fine, but they often use heavier and more expensive
JR G500T gyros on the larger T-rex brand helis.
new E-flite G90 weighs 0.3oz and the JR G500T weighs 1.0oz.
If it didn't work the way I needed, I would then try some
more expensive JR G500A or Futaba GY401 Rate Gyros.
my VTOL project, the heading lock mode is not needed. The
heading lock mode is actually an angle hold that is prefered
operation in helicopter tail control. As I later discovered,
the E-flite G90 gyro defaulted to the Heading Lock Mode
and could not be changed to the Rate Mode without using
a spare channel for control. This limitation would become
an issue later on.
consideration to keep in mind is the control speed of the
ESC. If the ESC cannot keep up with the gyro compensation,
it appears to make the gyro look like it has poor performance.
I kept this in mind when I was testing my pitch control
pitch control, I decided not to use an EDF motor as it is
not meant to run in reverse and the spool-up time may be
too long for proper stabilization. The technique I mostly
considered was to make the model tail-heavy when the tiltrotors
are pointed up so that the aft tail fan can modulate around
initial pitch control system was "borrowed" from
one of my Icarus Shockflyer models. It was a 50w brushless
power system that was meant for a 5oz to 10oz model. Initially,
it appeared that the gyro compensation into the ESC for
pitch control was rather slow but I eventually determined
that the thrust level was not sufficient. I replaced the
50w power system with a 150w brushless power system (BP-12
at BP Hobbies) spinning an 8x4 SF prop. The increase
in power provided an increase in pitch response as well
as keeping the motor and ESC cooler. The added weight was
not an issue.
until now, much of my VTOL plane control has been manual
using the transmitter sticks through various mixes. The
second E-flite G90 Gyro was added to the aileron servo for
yaw control. When the tilt rotors were pointed up, the ailerons
controlled yaw through the thrust passing over the upright
wing sections. Since the gyro was mounted on the outer moving
section of the wing, when the tilt rotors faced forward
for normal flight (a 90 degree change), the compensation
was now on the roll axis. The yaw control seemed to work
well when twisting the plane back and forth manually.
Futaba 9C Transmitter Mixes
aileron control gyro gave me another idea. I decided to
put the third gyro on the JR DS8611A
digital servo that controls the wing swing. The E-flite
G90 gyro has a digital servo mode for super fast control
response. My initial testing showed that this digital servo
control mode using the G90 gyro had excellent response time
as I could tip the plane forward and backward while keeping
the props pointed straight up! One short coming that I ran
into was that unless I connected the G90 gyro to a spare
channel on the receiver, I could not select the Rate Mode.
Further, there was no offset control (or Servo Travel Limit
Adjustment) on the gyro so I could not obtain the correct
gain I needed when the wing was properly positioned. After
wrestling with the limitations, I decided to upgrade my
wing stabilization control to a JR G500A Airplane Rate Gyro.
The JR G500A (now replaced by the G770
3D) is a more capable (and expensive) ring sensor gyro
that has outstanding holding power and drift-free operation.
It is designed specifically for airplane use and offers
a variety of settings for easy setup. The G500A has a high
rate frame selection for digital servos and separate gain
and servo travel adjustments. The JR G500A gyro allowed
me to set up the VTOL wing swing gain and position as I
wanted it. However, the G500A gyro did require using a spare
channel for gain control.
1 - Throttle -> Flap (Ch. 3 to Ch. 6 for controlling both
2 - Aileron -> Flap (Ch. 1 to Ch. 6 for manual roll control
of one motor in up position)
3 - Elevator -> Gear (Ch. 2 to Ch. 5 for manual pitch control
of wing swing in up position)
4 - Rudder -> Aileron (Ch. 4 to Ch. 1 for rudder stick control
of aileron yaw in up position)
5 - Offset -> Aux2 (Fixed offset to Ch. 8 for turning on/off
pitch control motor in up position)
6 - Throttle -> Aux2 (Fixed curve +100% offset into Ch. 8
for disabling pitch motor when throttle stick is < 10% or all
the way down)
7 - Unused
Receiver Channel Assignments
Channel 2 - Elevator
Channel 3 - Throttle for main motor 1
Channel 4 - Rudder
Channel 5 - Hover/Flight Mode Switch
Channel 6 - Throttle for main motor 2
Channel 7 - JR G500A Gain adjustment for wing swing servo
Channel 8 - Throttle for 150w pitch control motor
initial hover testing was done over a soft grassy area in
my backyard and at a local park. The transmitter mixes allowed
me to manually compensate for all three axis. The ESC gain
on the pitch control motor was controlled by a knob on the
transmitter which adjusted how the tail sat in relation
to the upright wings. After some repeated testing, I discovered
that the E-flite G90 gyro would "creep" from its
established setting making the tail go higher or lower.
Although the amount of "creep" can be minimized
by adjusting the sub-trim, it made the pitch control unreliable.
When used on a heli rotor control, the effect is minimal
as it will slowly make the tail drift in flight. On my VTOL
design, the undesired effect would sometimes make the tail
flip the plane over its nose onto its back.
The Test of Transition
first thought was to replace the E-flite G90 gyro with another
JR G500A Airplane Rate Gyro. The JR G500A ring gyro's drift-free
operation could eliminate the servo "creep" experienced
with the E-flite G90 gyro. I then realized that I had no
free channels to control the gain. I needed another solution
so I decided to try a Futaba GY401
Rate Gyro from Tower Hobbies for $140. This gyro uses a
Silicon Micro Machine (SMM) sensor that eliminates trim
changes in flight as it automatically corrects for a constant
offset like cross-wind or other unwanted axis changes.
Futaba GY401 Rate Gyro eliminated the "creep"
in trim that I was experiencing with the E-flite G90 gyro
and did not require a spare channel to set the gain or switch
to a rate mode. As mentioned earlier, this gyro benefit
came at about double the cost but it was a better fit for
that I was fairly happy with the gyro compensation on
the various axis, and, I had some success in low level
hovering, it was time to move on to step "b"
of my basic VTOL functions. Would my design still fly
like a normal plane from take-off to landing even though
it was a pound (or 20%) over the stock flying weight?
main reason for testing normal flight with a tricycle
gear take-off and landing is so that I had confidence
to fly it like a normal plane if I got into trouble
on my transitions in and out of hover mode. As it turned
out, my overweight Magister flew just fine! Although
I did not perform any aerobatics, it had plenty of power
and easily flew at only half throttle. The 5AH (20C)
LiPo pack lasted for about 7-8 minutes. The plane also
flew tail heavy so I would need to compensate by moving
the pack forward from the cockpit area and see how it
affected my hovering capability.
I was pleased with the results of my design and testing
of the Magister host plane. The power system had plenty
of thrust to hover and the heavier than stock weight did
not prevent the Magister from performing like a normal plane.
the final part, it will be time for the true test of success.
Will my VTOL design properly transition from hover to flight
and back? Will I need any additional gyros? Assuming my
design survives all the testing, what will my final scale
appearance emulate? Stay tuned for part 2 of Project VTOL
in a future issue of AMP'D.
you fly electric, fly clean, fly quiet, and fly safe!
Special thanks for contributions
"Papa Jeff" Ring and Lynn Bowerman
This section of AMP'D covers some of the
questions that our readers have sent in and I thought
would be interesting for others.
asks: "Hi Greg,
I lost my manual for the World Models 40S Ultimate and
want to know what the recommended controls throws and
CG location is?
The link for all the manuals is right near the top of
Models Web site next to the "Contact Us"
button. This link
is for the Ultimate 40S PDF.
R. asks: "Hi Greg,
just came across your Feb 2008 Amp?d article regarding
EDFs. I see you were hopping up a twister with the Ammo
28-45-3600. In one of the pictures it shows a 5/32?
tube being used as an adapter between the 3.2mm shaft
and 4mm shaft adapter. Did this work well and give a
nice snug fit? Also, is this setup performing well on
4S? Do you know the amp draw, thrust, etc by any chance?
of lead weight to the tail. See the attached photo where
I added it below the elevator and painted it silver.
I also made an exhaust ring from the bottom of a 20oz
plastic bottle of Gatorade.
far, I have had no issues with my Twister EDF
hop-up. Just rough up the motor shaft and inside
of the brass tube before using medium CA to
hold it in place. Allow a 24hr dry time before
With my 4-cell FlightPower 3700mAh pack connected,
the current draw was 55amps (about 700w) at
full throttle static testing. I never measured
the thrust but the performance change is very
noticeable over the stock setup.
Note that with the extra battery weight, you
need to add
questions by e-mailing me at firstname.lastname@example.org
7 "Project VTOL - Part