Flying The V-22
The V22 Osprey model produced by Mr. Tom Mast is the only one in the world I am aware of which can successfully hover, perform conversion flight with the rotor nacelle at different tilt angles, and then convert into airplane mode for forward flight. Tom is very knowledgeable about tilt-rotors because he is also an engineer at Bell Helicopter in Texas, where the full-size V22 is designed and built.
Having flown the V22 for many flights now, including one crash, I can now provide you with Part Three of the V22 review. The emphasis this time will be on tips for tuning and flying the model.
The Rotormast V22 relies on three separate heading lock gyros to maintain stability and controllability. Rotormast recommends using only Futaba GY-401 or GY-520 gyros. That is because these are the gyros that Tom has tested and found to work for him. I asked Tom if it is possible to use other gyros and he said it would be at your own risk. It is important to use three separate gyros instead of a single 3-axis gyros system, such as a Futaba GY-750. The reason is most 3-axis gyros do not permit setting the feedback gains differently for elevator and aileron. The three GY-520 gyros that I used worked out extremely well. On a totally calm day, the V22 model will sit in a hover perfectly still and is almost as easy to hover as any 450-size electric helicopter.
Until you get used to hovering the V22, I do not recommend flying it in the wind. When there is even a slight wind, the V22 becomes very sensitive and the controls can become tricky.
The V22 is more sensitive to wind than most RC helicopters. During hover, the nacelles do not have to be perfectly vertical, it is possible to use the rotary knob to change the nacelles to 85-degrees or 95-degrees and the model will still hover fine. Check the center of gravity before flying. The ideal CG position should be exactly in line with the center line of the two rotors. I had to move the two 4S 2700mAh LiPo batteries slightly aft to get the CG perfect.
The trick to get into forward flight is to master hover first. It is important to be comfortable hovering the V22 from any azimuth angle; including a nose-in hover. Practice doing some figure-8 maneuvers in helicopter mode. Basically, fly it like a helicopter. Once you become very comfortable, the next step is to start exploring conversion mode. Conversion mode means the nacelle is tilted at less than 90-degrees. It is important to use the auxiliary channel rotary knob on your transmitter to control the nacelle tilt angle. I am using a Spektrum DX8 transmitter; however, the rotary knob on the DX8 is located too far aft and is difficult to reach with the right index finger. I recommend relocating the rotary knob to the front right. Practice and become comfortable at spinning the knob with your right index finger during flight. Initially, try only to change the nacelle from 90- to 80- and then 70-degrees, so you are not totally in the airplane mode. Fly the model around until you get used to it. Remember, you only have about six minutes of battery, so it is important to save some time to bring the nacelle back to 90-degrees and come back for a landing.
Once you are completely comfortable at flying in the conversion mode, pick a huge empty field for your first forward flight trial. A huge field is needed because the V22 is quite fast in forward flight airplane mode and can cover a lot of airspace quickly. Similar to a full-size V22, the aircraft has a small wing with minimal surface area, leading to high wing loading. This requires the model to maintain relatively high airspeed to generate sufficient lift to stay afloat. The full-size V22 is designed to fly in airplane mode from 200 to 300mph. The V22 model has the wing trailing edge flap permanently taped in a downward position to help generate additional lift.
The smart electronic board included in every V22 kit performs many functions. It interprets the pilot™s commands for pylon tilt angle and then it rotates the rotor pylon nacelle at a constant speed. It takes 11-seconds to completely rotate the pylon from vertical to horizontal or vice versa. With the channel rotary knob on the transmitter, you can stop the pylon at any angle. In forward flight mode, the smart electronic board automatically changes collective pitch angles so the motors are not overloaded. If rotor rpm becomes unbalanced, the controller will adjust the collective pitch of both rotors to allow the slow rotor to recover and maintain a balanced system. Furthermore, when the aircraft is at high power settings during conversion flight the controller has a built in pitch governor and adjusts the collective pitch as necessary to prevent slowing of the rotor. This will set the proper collective pitch for any given airspeed and allow collective pitch to increase as airspeed increases, improving the top speed of the model.
The Spektrum DX8 rotary knob has been relocated further to the right to permit easy access of the knob by index finger during flight to change rotor pylon angle.
The first time getting into airplane mode is the scariest because it is something you have never experienced before. You only have six to seven minutes flight time to go from hovering to conversion flight in order to build up airspeed to about 20mph, then you can rotate the nacelle to horizontal and you are now committed to flying it around like an airplane without slowing down. Once it is in airplane mode, you cannot fly too slowly or it will stall and fall out of the sky. To get back to hover, pull back on throttle to slow down to approximately 20mph and start rotating the nacelle back to vertical while slowly bleeding off forward flight speed. Once the nacelle is vertical and you are back in hover mode, you can stop shaking. To prepare yourself for the first forward flight, I recommend that you get your hands on a V22 simulation model on the Great Planes RealFlight simulator. The V22 simulation is an add-on to the standard RealFlight simulator and it is very realistic.
Leave all transmitter trims centered and all sub-trims at zero because three GY-520 heading lock gyros are used for all three flight axes. I recommend using 30- to 45-percent exponential on the pitching and rolling axes.
The 5-point throttle curve for ˜normal™ mode.
The 5-point throttle curve for ˜idle-up 1™ mode.
Assume your transmitter also uses a 5-point throttle curve. My ˜normal™ mode is set up with 0-0-0-0-0. I use the same setting for throttlehold mode; where moving the stick only changes collective angle and the motors will not spin. In ˜idle-up 1™, set the 5-point throttle curve to 0-70-70-70-70. 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 Castle ICE 50A ESC is used to keep the motor rpm constant even when collective pitch is changed. The pitch curve is simply a straight line 0-25-50-75-100 for all modes.
A Scorpion 2221-10 motor and a Castle Creations 50A Ice Lite ESC is mounted inside each pylon. Only two servos control each swashplate.
The V22 model is well thought-out. It only uses two servos to control each rotor. Unlike an RC helicopter, the V22 does not need a third servo for the swashplate because there is no lateral tilting of the rotor disk. When in 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 to cause differential thrust change to roll the aircraft. Raising or lowering of the swashplate is achieved by simultaneously moving only two servos per swashplate. By moving the two servos differentially, the swashplate will tilt to cause the rotor to tilt. Tilting the swashplate and both rotors forward at the same time will cause the V22 to fly forward. Tilting one rotor forward and one rotor back will yaw the entire aircraft.
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 V22 easily flyable.
When setting up a new V22, it is best to leave the fiberglass nacelle and the spinner off so you can easily access the two HS- 5085MG servos. By the way, Rotormast recommends only using Hitec HS-5085MG servos. The parts I bought are exactly what Rotormast recommended. Rotormast says that otherwise, you are exploring on your own.
The 3-blade rigid rotor hub design.
Before lifting off for the first flight, use a pitch gauge to check the blade angle for all six blades to ensure they are identical. The next check is to run up the rotor but, without lifting off and check the blade tracking. If everything is properly set up, the V22 model should hover level on its first flight and you can take your hands off the transmitter. The GY- 520 gyro when set properly will hold the wing level and also prevent any fore/aft nodding. If the V22 wants to roll, then the first thing I would check is the blade pitch angle. Do the left and right rotors have identical pitch angle? If the V22 rolls to the left, then it implies all three blades on the right rotor have too much collective pitch and it could be just half a degree more than the left rotor. You must mechanically increase the blade pitch angles on all three blades by adjusting the three pushrods from the swashplate to the blade grips.
The rotor pylon in the conversion flight position.
If the V22 wants to drift forward or backward, adjust the fore/aft swashplate tilting by adjusting the pushrod from the servo to the swashplate. Do this mechanically. Do not use transmitter trim because the GY-520 heading lock gyro is used. Think of it as a tail rotor on your helicopter; you would never use tail rotor trim when using a heading lock gyro.
THE LAST WORD
This V22 Osprey represents a fantastic piece of model engineering. I am still amazed that it can hover and transition into forward flight and the designer was able to maintain the exact scale dimensions. It is not an inexpensive model, but it is the only one of its kind in the world and provides tremendous pride of ownership. It is not an easy project; it should be tackled only if one is determined to put serious effort into it. Alternatively, Rotormast can build it and fly test it for you at an additional cost. Contact Rotormast for more information on this.
NEED TO KNOW
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
FLYING WEIGHT: 5.5 lb. profile version; 6 lb. 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 Thunder Power 4S 2700 mAh 25C LiPo batteries
MAIN ROTOR RPM AT HOVER AND FORWARD FLIGHT: 2,400 – 2,600
DURATION: 7 minutes
MINIMUM FLYING AREA: RC flying field
COMPONENTS NEEDED TO COMPLETE: Minimum 7-channel radio system, three heading-lock gyros, four servos, two 50-amp speed controls with BEC, and two 4S 2200-3000mAh flight batteries
Since we last examined the V22 model in the April/May 2012 issue, I have put in many more flights and now have become comfortable flying the V22 in helicopter mode, conversion mode, and forward flight airplane mode. The Rotormast V22 is extremely scale looking, but it is definitely not for beginners, nor for modelers who do not want to spend the time to carefully set up and maintain the model. It is a sophisticated and delicate model. It hovers very well in calm conditions, but becomes challenging when there is any amount of wind. In forward flight it is very fast due to the minimal wing area. I recommend that you be very comfortable with flying RC airplanes before transitioning from hover to airplane flight. The Rotormast V22 is a one-of-a-kind model and I really love mine.
www.castlecreations.com, (913) 390-6939
www.hitecrcd.com, (858) 748-6948
www.realflight.com, (800) 637-7660
www.innov8tivedesigns.com, (760) 468-8838
www.spektrumrc.com, (800) 338-4639
www.thunderpowerrc.com, (702) 228-8883