Hot News Projects V-22 Osprey — 21 August 2012

The World’s Only RC V-22 Tiltrotor

V-22 Osprey model produced by Mr. Tom Mast is the only one in the world that I am aware of which can successfully hover, perform transitional flight with the rotor nacelle angle at different tilt angles and convert into airplane mode for forward flight. Tom Mast invested four years into the engineering and testing his V-22 scale model and then formed Rotormast, LLC to distribute this machine. Toms knowledge of tilt rotors comes from his career as an engineer at Bell Helicopter in Texas, where the full-size V-22 is designed and built.

Thanks to using three GY-520 gyros to keep the model steady, the V-22 can hover almost hands-off when properly set up. In airplane mode with rotor pylons in the horizontal position, the V-22 is very fast because similar to a full-size V-22, the aircraft has a small wing with minimal surface area which results in a very high wing loading. This high wing loading requires the model to maintain a fast airspeed to generate sufficient lift to stay afloat.

Here with all the major components disassembled for travel.

In a conventional airplane, a larger wing area is required to generate sufficient lift to permit airspeeds that are slow enough for landing. With a tiltrotor, the V-22 takes off and lands in hover mode; the wing is only used when in forward flight. The full-size V-22 is designed to fly in airplane mode from 150 to 250 knots. To fly slower, the rotor pylons on the V-22 are tilted at an angle, this is called transitional flight or conversion mode. Another reason why the wing on a tiltrotor is smaller than that of a conventional airplane is during hover, the rotor downwash is impinging on the wing. If the wing is too big, there will be a reduction in thrust. On the model, the wing flaps are permanently deployed in a 40 degree down angle to help increase lift and to reduce downwash.

The Spektrum DX8 Aux three rotary knob has been relocated further to the right to permit easy access of the knob during flight to change the rotor pylon angle.

For the V-22 model, it is best to use a transmitter with a rotary knob or slider to control the pylon angle which will allow an infinite adjustment from full vertical to full horizontal positions, and any angle in between. I used a Spektrum DX8 transmitter and relocated the rotary knob on the top of the transmitter to the top right corner position. I always hold the transmitter stick with my thumb and index finger. This allows me to easily reach the knob with my middle finger. This worked out very well. Alternatively, it is possible to use a transmitter with a slider on the side. Using a rotary knob gives better resolution than a slider because a slider only rotates through a 45 degrees angle, while a knob usually rotates through 200 degrees hence a rotary knob offers finer adjustment for controlling pylon angle.

The Rotormast V-22 uses a modified Hitec HS-5085MG servo, which they include, to operate a rack and pinion system to rotate the rotor pylon. The potentiometers in the modified servos are used to measure the pylon angle. The information is fed back to a special electronic board within the model which monitors and controls the two pylons so they operate in unison.

The pylon in the hover position. Amazingly, the servos, swashplate, electric motor, and ESC all hide inside the fiberglass nacelle like the real McCoy.

Unlike a conventional helicopter, when in a hover, a left/right cyclic command to roll the aircraft results in raising one swashplate on one rotor and lowering the swashplate on the other rotor which causes a differential thrust change to roll the aircraft. When in airplane mode, the differential thrust causes the aircraft to yaw instead of roll. To roll the aircraft during airplane mode, the swashplate tilts one rotor upward and the other downward. In hover mode, tilting one rotor forward and tilting the other backward yaws the aircraft. But the pilot does not have to worry about this as it is all automatically controlled by the electronic controller board that comes with the kit.

The controller board is mounted inside the V-22 model and it interprets the pilots commands for pylon tilt angle, and then it rotates the rotor pylon nacelle at a slow speed. The board sends commands to the servos according to the flight mode and it automatically adjusts blade collective pitch angles during forward flight so the motors are not overloaded. It monitors each rotors rpm to prevent the system from bogging and resulting in an overload power system.

This is the smart electronic controller board that comes with each kit. The text explains the wonderful capabilities of this board to make the model V-22 easily flyable.

When the aircraft is at high power settings during conversion flight the controller has a built-in pitch governor which adjusts the collective pitch to prevent slowing of the rotor. This sets the proper collective pitch for any given airspeed and allows the collective pitch to increase as airspeed increases, improving the top speed of the model.

With the landing gear down, it looks just like the real V-22 coming in for a landing.

The Rotormast model is available in two versions: a profile version and a scale fuselage version. With the profile version, the electronics, wings, and horizontal tail are all attached to a 10mm thick composite board, which has the profile shape of a V-22. You can buy the V-22 as a scale kit or you can start with the profile version and add the scale fuselage at a later date. For an additional $99, you can add a scale retractable landing gear kit to the V-22.


At 6 pounds, the model has plenty of power for climbing and handles wind well. It is very fast, shown here with landing gear retracted.

The Rotormast V-22 model is extremely scale looking. In total, 29 molds are used for fabricating all the fiberglass parts. The main rotor and swashplate are aluminum. There are very few plastic parts in the kit. This is not a kit for an inexperienced builder or a beginner pilot. The model flies extremely well, has no vibration, and no air or ground resonance issues. However, because of the very light disk loading, the V-22 will not autorotate.

CONTROL METHODOLOGY

The front hatch is held on with a strong magnet. Two 4S 2200mAh LiPo batteries are connected in parallel to provide seven minute flight time.

The V-22 model is designed to work with a heli-type transmitter which has throttle and pitch curve settings. The normal throttle mode is set up just like throttle hold mode, where moving the stick only changes collective angle and the motors will not spin. Tom recommends setting up a 5-point throttle curve such as 0-70-70-70-70 for idle-up 1 mode. In Idle-Up 2, the 5-point throttle curve is set up as 70-70-70-70-70. The rpm governing mode feature in the ESC is used to keep the motor rpm constant even when collective pitch is changed. The exact value for the throttle curves depends on the ESC and battery used. In your transmitter, choose the conventional single servo swashplate mode, and not 120 degree eCCPM mode.

Other than the very basic helicopter transmitter functions such as collective pitch curves, throttle curves, servo directions and endpoints, most of the model setup is performed in the Rotormast V-22 electronic controller utilizing a USB PC connection cable and the Rotormast V- 22 configuration software.

IN HELICOPTER MODE

1 Roll is accomplished with differential collective pitch of both rotors

2 Pitch is accomplished with fore/aft tilt of both rotors

3 Yaw is accomplished with differential fore/aft tilt of both rotors

4 Vertical control is accomplished with symmetric collective pitch change of both rotors.

This is all possible using just two servos per rotor (or per swashplate). The Rotormast V-22 controller has its own CCPM mixer that allows direct drive of the swashplates to eliminate the need of a mechanical mixer.

CONVERSION FLIGHT

The V-22 controller performs all the control mixing necessary to make the ship react the same as any typical model airplane during the conversion flight. With the left stick performing speed and rudder function and the right stick performing the elevator and aileron function. The transition between airplane mode and helicopter mode is seamless, allowing the V-22 to be flown at any conversion angle with no quirks or advanced piloting skills. As the ship converts into airplane mode with the pylon in horizontal position, the V-22 controller performs several functions to provide precise continuous control of the V-22 with no additional pilot work load other than selection of the conversion angle.

Very scale looking pylon and nacelle design. Notice the rack and pinion gears used for changing pylon angle.

During a conversion the controller will:

1 Add collective pitch to allow the ship to accelerate in conversion flight

2 Swap roll and yaw controls to make pilot inputs consistent through conversion flight

3 Adjust servo volumes to keep the feel of the ship consistent to the pilot

4 Adjust gyro gains to keep the feel of ship consistent to the pilot

5 Monitor motor rpm and adjust collective pitch to match airspeed

AIRPLANE MODE FLIGHT

As a conversion takes place, the helicopter mode controls described above transform into airplane mode control.

A carbon tube is used as a wing spar. Notice the profile fuselage plate is where all the electronics are attached to; it slides into the center of the scale fuselage. Very ingenious design.

Unlike the full-size V-22, the Rotormast V-22 does not have aileron and elevator control surfaces for airplane mode flight, instead:

1 Aileron function is accomplished with differential fore/aft cyclic of rotors

2 Elevator function is accomplished with fore/aft tilt of both rotors

3 Rudder is accomplished with differential collective pitch of both rotors

4 Speed control is accomplished with symmetric collective pitch change of both rotors It takes 11 seconds to completely rotate the pylon from vertical to horizontal, and vice versa.

With a rotary knob on the transmitter, you can stop the pylon at any angle. In the next issue, I will continue with the discussion on how well it flies in various modes. Meanwhile, let me just end by saying it flies extremely well, and exceeded my expectations. The Rotormast V-22 model flies very similar to the V-22 model on the Great Planes RealFlight simulator. The V-22 is an add-on to the standard RealFlight simulator.

IN THE AIR

Here is a shot of the full-size Bell-Boeing V-22 taken by James in 2011 at an air show.

Become very familiar with hover and orientation first, and then increase the pylon tilt angle 10 degrees at a time for each flight. Once you become accustomed to conversion mode flying start to transition into forward flight. The model has no vices in hover, you just need to get used to the shape and orientation. The GY-520 gyros in heading lock mode do a fantastic job keeping the model steady in all three axes. Leave the three gyros in rate mode before taking off. Just before spooling up or taking off, flip the switch to make all three gyros go into heading lock mode. The model can fly in rate mode, I tried it, but the aircraft must be perfectly trimmed. It is much better flying in heading lock mode. The model is extremely fast in forward flight and it can perform loops and barrel rolls, despite not having aileron and elevator control surfaces.

THE LAST WORD

This is the only truly working V-22 tiltrotor model in the world and it flies as well as it looks. It provides a pride of ownership of a fantastic piece of model engineering.

Great attention to scale details. The wing flaps are permanently in a 40 degree down angle to increase wing lift and reduce impingement from rotor downwash during hover.

PRO TIPS

1 Before you buy this model, ask yourself if you are ready to take on this project. It is a large financial investment that requires tremendous diligence; however the final product is worth it.

2 Purchase the motors, servos, gyros, and ESC exactly as recommended by Rotormast because they have proven them in the design.

3 If you are uncertain about building, then Rotormast can build and setup the model for a fee.

4 Do not rush through building and setting up the model.

5 The website provides written and video instruction.

6 Do a flight check before each flight.

7 Carry the model carefully and do not bump into doors or tables.

8 To practice and used to get use to the pylon angle rotation knob, try the V-22 model in the Great Planes RealFlight simulator add-on.

PROS

1 Fantastic engineering and attention to technical detail.

2 Very scale looking.

3 Great looking paint job and high quality fiberglass work.

4 This is the only successful, convertible RC tiltrotor model in the world.

CONS

1 Expensive

2 Requires above average mechanical assembly skill

SPECS

HELICOPTER MANUFACTURER: Rotormast

DISTRIBUTOR: VCS Hobbies, and Rotormast.com

TYPE: Vertical takeoff and landing (VTOL) model

FOR: Intermediate to advanced

PRICE: $1,399 for the profile kit and $1,699 for the full fuselage version

FRAME MATERIAL: Composite material for the profile fuselage plate, fiberglass for the scale fuselage, wing skin and nacelle skin.

TYPE: Can be built as a simple-to-maintain profile version, or a scale fuselage version

SERVO LINKAGE TYPE: Push-pull

ROTOR HEAD GRIPS: Aluminum

HEAD BLOCK: Aluminum

LINKS: Steel pushrod

SWASHPLATE: Aluminum

CONTROL: Special control using a Smart Electronic Board included in the kit

GEAR RATIOS MOTOR TO MAIN: 15:1

FLYING WEIGHT: 5.5 lbs. profile version; 6 lbs. with scale fuselage

LENGTH: 38.6 in. (980mm)

HEIGHT: Helicopter mode: 12.6 in. (320mm); airplane mode: 7.1 in. (180mm)

WIDTH: 35 in. (spinner to spinner)

ROTOR SPAN: 25.3 in. (645mm)

ROTOR DISK AREA: 1,005 sq. in. (total for both rotors)

ROTOR DISK LOADING: 13.75 oz./sq. ft.

RADIO: Spektrum DX8

SERVOS: Four Hitec HS-5085MG servos for rotor controls. Kit includes two modified Hitec HS-5085MG servos for tilting mechanism

GYRO USED: Three Futaba GY520 gyros

POWER SYSTEM: Two Scorpion 2221-10 (3000Kv) outrunner brushless motors and two Castle Creations 50 amp Ice Lite ESC using the built-in 5A BEC

BATTERY USED: Two Turnigy 4S 2200 mAh 30C LiPo batteries

MAIN ROTOR RPM AT HOVER AND FORWARD FLIGHT: 2,400 – 2,600

DURATION: 7 minutes

MINIMAL FLYING AREA: RC flying field

COMPONENTS NEEDED TO COMPLETE: Minimum 7-channel radio system, three headinglock gyros, four servos, two 50 amp speed controls with BEC, and two 4S 2200 mAh flight batteries

Authors Opinion

A lot of engineering went into the design of the V-22 to get it to look and perform so well. It can hover, perform transitional flight, and will fly like a typical airplane. It is an impressive engineering accomplishment and the model looks just like the real Bell-Boeing V-22 Osprey. The fuselage, wing, nacelle, and tail surfaces come painted in the same color scheme as a full-size US Marine V-22. This kit is for modelers who appreciate engineering marvels and enjoy challenging projects. It requires patience and care in building and setting up. The model hovers similar to a 450 or a 500 class electric helicopter. It is extremely stable in hover. It becomes a fast airplane when rotor pylons tilt down and convert into an airplane.

Links

Castle Creations

www.castlecreations.com, (913) 390-6939

Hitec USA

www.hitecrcd.com, (858) 748-6948

Rotormast

www.rotormast.com

rotormast@rotormast.com

Scorpion Motors, distributed exclusively by Innov8tive Designs

www.innov8tivedesigns.com, (760) 468-8838

Spektrum, distributed by Horizon Hobby

www.spektrumrc.com, (800) 338-4639

VCS Hobbies

www.vcshobbies.com, (718) 921-6159

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