03Birdy.jt1.doc
SPECIFICATIONS
Model Type: Sport/Old-Time Pattern Competition ARF
Skill Level: Intermediate builder/intermediate pilot
Wingspan: 64.5 inches
Wing Area: 690 square inches
Wing Loading: 24.2 oz. / sq. ft. (fixed gear)
Airfoil: Symmetrical
Length: 56 inches
Weight: 7.25 pounds (fixed) 7.6 pounds (retract/pipe)
Engine: .60 to .65 two-stroke
Radio System: 4-5 channel, standard size servos
Construction: Fiberglass/Foam
Retail Price: $299.97
TEST MODEL DETAILS
Engine: O.S. Max 65 AX muffler or MACS Products #1060 quiet pipe
Propeller: APC 12x6 (muffler) or Zinger 11x7.5W (pipe)
Radio System: Futaba T7C transmitter; Futaba R617FS receiver; four Futaba S3151 servos on flight controls; two S3004 throttle/nose retract and Hobbico CS-63 main retracts. “Y” cord on retracts.
Flight duration: 11-12 minutes
Center of Gravity: 5 7/8 inches
Control Movements: Ailerons - ½ in. 35% Expo; Elevator – 9/16 in. 30% Expo; Rudder 2 in. 60% Expo.
Pluses:
Very fast, very accurate build.
Everything fit well and is competition grade.
Extreme precision aerobatic performance.
Very gentle but outstanding sport airplane.
Hardware included for sport, SPA or CPA versions.
Fun and impressive to fly.
Detailed instruction manual.
Minuses:
This excellent ARF was not available in 1980!
The following is going to be an in-depth review of the Dirty Birdy. During the last 37 years, this airplane has earned its place as a competition aircraft and how it fits into today’s complex RC sport/aerobatic world also needs exploration.
Since this ARF version has few parts and assembles quickly, the building portion will also be shorter than usual. The Dirty Birdy was meant to out-fly anything in the air, then or now, making the flying part of this review longer than usual.
Joe Bridi designed this airplane for Precision Aerobatics (Pattern) competition in the mid-1970s as an improvement on his winning Kaos series. The most obvious improvements included increased wing sweep and area, a straight trailing edge, retracts, increased frontal fuselage side area and an airfoil stabilizer.
The result was an aircraft that rolled precisely, flew straight in knife-edge, required less rudder correction all around and had few bad habits. The Dirty Birdy was an easy to manage Pattern airplane which sport pilots could make truly perform on any level.
It remains so today. Unlike many of its contemporaries, the Dirty Birdy will not snap out of tight turns when flown slowly, must be forced under protest to tip stall, goes precisely where directed and will gracefully perform any Pattern maneuver asked of it. It always was, and is, a pilot’s airplane.
The new Great Planes ARF version is also a pilot’s airplane in an easier to build fiberglass/foam format. It should be as its airframe is almost identical to my 1976 wood kit. A comparison showed that the wing root airfoil and airframe dimensions are identical with some improvements.
The engine is side mounted on a modern fiberglass mount for easier tuned pipe installation and better looks. The fiberglass cowling is removable rather than being part of the fuselage, making engine and nose wheel installation far less painful. Twin aileron servos are used for more precise aileron control.
While the original Dirty Birdy was primarily designed for Master Class AMA Pattern competition, my guess is that most served as one of the better sport airplanes at many local flying fields. Choose it for everyday flying and the Dirty Birdy will quickly become your favorite. Even with fixed landing gear the airplane’s precision, smoothness, piloting ease, great looks, and sheer gracefulness will keep your other sport airplanes gathering dust in the hangar.
The airplane will precisely snap roll and spin on demand yet exhibits none of the “snappiness” so common with scale aerobatic airplanes in this size range. While higher than “Hershey Bar” low-wing sport aircraft, its landing speeds are slow enough that any sport pilot will hardly notice the difference.
The Dirty Birdy is also an extremely capable competition aircraft in both modern “old time” or “non-turnaround” style Pattern classes. The two, very different, forms of such Pattern competition are the Senior Pattern Association (SPA) and the Classic Pattern Association (CPA).
Aircraft in SPA competition must have fixed landing gear and cannot use a tuned pipe. While the Dirty Birdy was designed for retractable landing gear, it will fly the wings off any Hershey Bar (constant cord) 1960’s SPA Pattern aircraft. Because of its inherent precision, great slow-speed performance and gentle handling, it is one of the better flying 1970’s airplanes even with fixed-gear. CPA rules allow the Dirty Birdy to fly as conceived using both retracts and a tuned pipe.
As the rules for each organization are so different, now might be the time to choose whether your Dirty Birdy will fly for Sport, SPA or CPA competition. Or, maybe do all three versions in one? But first, we have to assemble the airplane. As the Dirty Birdy arrives with fixed gear, the SPA version will be detailed.
Construction
The 45-page instruction booklet has 155 photos detailing standard and optional construction steps. That’s quite an improvement over 1976’s 16-page, text only, directions (although they were better than the usual “here’s the box photo, make it look like this” directions of the day). Both sets of directions start with building the wing.
Before installing the aileron servos, cut out a small groove in the foam around the servo opening for the wire as the fit is very tight.
The spar is constructed by laminating two plywood pieces to an aluminum center using 30-minute epoxy. Mark the spar’s center. Insert the spar (no adhesive) and the nylon anti-rotation pin (glue first with thin CA or it sinks into the wing) in one wing half and test assemble. When satisfied, apply 30-minute epoxy inside each spar slot, the open anti-rotation pin hole and on one wing root. Join the wing halves as shown.
The ailerons are factory hinged. Make sure the servo arms are on the outside when installing the control horns as that is where the plywood mounting plates are located. There is some extra space for the fixed landing gear mounts. Use the front block for alignment when drilling the screw holes.
The entire wing mounting system is factory installed and perfectly aligned. Some covering must be removed before mounting the two “belly pans”. Use the scraps to protect the area around the visible bolt holes which are slightly exposed under the fairing.
There is very little work to do on the fuselage. The supplied adjustable mount fits about every .60 size two-stroke engine made. Eight brands were tested and they all fit. The engine chosen is the O.S. Max .65. This engine is well suited to both SPA and CPA competition and is great for sport flying. The firewall mounts are already factory made. Fit your engine with its thrust washer 4 5/8 inches from the firewall and drill the mounting holes.
The cowling must be cutout to fit the engine and nose wheel strut. Since they are straight openings they do not require any special techniques.
Position the cutout cowling 1/8 inch behind the spinner backplate, aligned with it, and drill the four mounting screw holes. The fixed nose wheel mounts inside the motor mount and Great Planes has already filed the “flats” in the strut for both steering and mount retention security
The stabilizer mounts onto two carbon fiber spars and is glued to the fuselage using 30-minute epoxy. The all-important stabilizer incidence and wing alignment are therefore achieved. This is a great feature whose importance cannot be overstressed.
The vertical fin is part of the fuselage and the rudder and elevators are factory mounted. The only real work required is mounting the control horns. Control rod installation is simple and Great Planes even provides full-size templates where needed.
While standard servos (Futaba S3004) will work, a competition Dirty Birdy will benefit from the true precision performance of Futaba S3151 digital servos on the control surfaces. Before mounting the servos, reinforce the servo tray/fuselage mounting joints with fillets made from 5-minute epoxy and micro-balloons.
Mounting plywood servo trays to curved fiberglass fuselage sides can prove problematical over time making this precaution is a good idea.
Completing the model with fixed gear will take about ten hours. The retract version requires three extra hours. The small difference is due to Great Planes having included all the extra parts needed for retract installation including axles and servo mount. Great Planes has also installed a plywood mounting plate in the wing for tuned pipe installation.
Flight Tests
The Dirty Birdy is a versatile airplane that can perform three separate missions; sport, SPA competition and CPA style. How you equip yours depends on the mission you choose. This airplane flew many (54+) test flights. Most were flown in sport/SPA configuration, the rest with retracts and tuned pipe (CPA style). When laterally balancing this airplane (a must), leave any balance nails protruding from the wingtip until flight tests are complete.
Sport flying this airplane is nearly a dream come true. The sport configuration is the same as SPA- muffler and fixed gear. Several propellers were tested in this setup but the best was the APC 12x6 inch (11,600 rpm max). The 11 x 7.5 inch, standard and wide propellers reached 11,900 rpm but climb suffered.
A 13 x 5 inch (10,900 rpm max) provided the highest airspeeds but with reduced climb performance. The 13 x 5 inch propeller produced excessive torque requiring rudder correction in the climb.
The 12 x 6 inch APC provided the most climbing ability while needing the least amount of rudder correction in either takeoff or verticals. The airplane just flew more smoothly with this propeller.
There isn’t any non-3-D maneuver you can ask of the Dirty Birdy that it won’t fly with a smooth grace that will surprise even its pilot. When this airplane was designed, having computer transmitter mixing would have meant you were from outer space. The airframe itself was designed for good flight characteristics.
Knife edge flight is straight in both directions. The airplane has little, if any, tendency to pull out of vertical dives. Point it anywhere and it goes, straight and true. There is even some tendency to lock onto a 90° vertical up line should the pilot be 2-3 degrees off during the initial pull up (if throttle is slowly applied during the upward ¼ loop).
The airplane is faultless in its sport handling ease. Hold full up elevator in low-speed, steeply banked turns and the airplane just flies slow circles with absolutely no tendency to snap out in either direction.
Inverted flight does require some down elevator. Full aileron and rudder must be used for inverted spins or the airplane will stop rotation. It just doesn’t get any easier to handle than that!
Landing places about the only demands on a sport pilot. Landings are faster than the usual low-wing sport ship but are much slower than needed by most scale aerobatic aircraft. Keep the airplane in a level attitude during the approach with speeds in the 25 mph range. The airplane will land itself, slightly nose high.
Although I have been flying Masters turn-around Pattern, I was competing in non-turnaround AMA Pattern back in 1980 and did so until it was phased out. I remember those days and look forward to flying this Pattern style once again.
As a test, I flew the Dirty Birdy through the Expert SPA Pattern. Flying the slow roll, 4-point, 8-point and multiple horizontal rolls was simple as the airplane stayed on line needing very little piloting.
The Dirty Birdy maintained axial horizontal rolls (they must be slightly off axial but I couldn’t see it). However, it did politely ask for retracts during the Top Hat, Figure M and 180 Degree Turn vertical rolls by being slightly out of true axial rotation. This was not due to aileron differential as the entire airframe was ever so slightly off axial due to the fixed gear. (The airplane exhibited no adverse yaw during slow-speed tests showing that differential isn’t the problem.)
Even with fixed gear, the Dirty Birdy maintained sufficient airspeed such that no special handling was needed when flying the Double Immelmann or Running Eight maneuvers. The airplane’s excess rudder authority made Stall Turns beautiful. This airplane should be very popular in SPA events in the coming years. Its performance is a generation ahead of the 1960’s aircraft yet, due to its minimal wing sweep and low wing loading, its aerobatic abilities at medium, fixed gear airspeeds is amazing.
Low airspeeds are not a factor in Classic Pattern competition. CPA aircraft usually fly in the 100+ mph range using fixed gear and tuned pipes. When equipped with $20 Hobbico mechanical retracts (HCAP400), the Hobbico Command CS-63 retract servo ($28) and an extra Futaba S3004 servo ($14), the Dirty Birdy becomes a totally different performer.
Add the MACS Products #1060 Quiet Pipe and the #2861 Long Header, (providing an extra 1,000 to 1,500 rpm), to convert the Dirty Birdy into the world-class precision aerobatic performer it was designed to be. The instruction booklet contains detailed instructions for the conversions.
The results are amazing. On takeoff, the airplane actually leaps ahead as the gear is retracted. It has to be gaining at least 20 mph in the climb, maybe more. When leveled out with the engine turning more than 13,500 rpm (Zinger 11x7.5 Wide propeller) on the pipe, the airplane not only exceeds 100 mph but grooves on its flight line as if it were riding a monorail.
Rolls are perfectly axial in all attitudes, especially the vertical. At these aerobatic airspeeds, the airplane actually climbs in knife edge while holding a perfectly straight line.
Any maneuver, especially loops, all rolls, Vertical Eights, stall turns and all snaps, becomes effortless.
Maneuvers can be as large, or small, as the pilot commands. They are always on track and need little correction. The 6 ounce weight penalty goes unnoticed by the airplane as stall and landing airspeeds seem about the same. The Dirty Birdy always maintains its great slow-speed handling.
As a CPA airplane, the performance is as outstanding as it was in the 1970s and flying the current CPA Master’s Pattern is enjoyable. Now, here’s the problem. SPA competitions are extremely popular and a lot of fun. The same is true for CPA events. What is a budding old-time Pattern pilot to do? If you know me, you already know the answer is to do both! Great Planes has made this an easy task by supplying all the equipment needed for both configurations.
Instead of cutting up the supplied fiberglass nose hatch cover for the retractable gear, copy its shape and make a 1/32-in. plywood version with the necessary cutouts. Make both a screw-on installation as shown in the photos. Make a template from cardboard and create two 1/8-in. light plywood covers for the wings retract wheel openings and screw into ¼ x 3/8 inch spruce blocks. The Dirty Birdy’s red matches Top Flite Monokote True Red so cover the three “hatch” covers in it.
I timed it, removing the wings retract gear and replacing it with fixed struts took 17 minutes. Extending the nose gear and installing the stock fixed gear hatch required another 4 minutes (cut a small notch to clear the nose strut). Replacing the pipe installation with the muffler required another 9 minutes. Changing props (12x6 to11x7.5W) was another 8 minutes. Total conversion time is 38 minutes.
With just 38 minutes work, my Dirty Birdy can fly as one of my very best sport aircraft and also be a world-class SPA competitor. Or, it can again become one of the best non-turnaround Pattern airplanes of all time as CPA events grow in popularity.
Only one real question remains. Why the heck wasn’t I smart enough to be flying a Dirty Birdy in my early competition days like everyone else was? I don’t know, but hopefully I have become smarter now. I am really going to be enjoying this gentle high-performer in the years ahead.
Frank Granelli
[email protected]
MANUFACTURER/DISTRIBUTOR:
Hobbico
Box 9021
Champaign IL 61826
(800) 637-7660
www.greatplanes.com
Sources:
O.S. Max Engines
www.os-engines.com
MACS Products
(310)539-2313
www.macspro.com
Zinger Propellers
(310)539-2313
www.zingerpropeller.com
APC Propellers
(530) 661-0399
www.apcprop.com
Futaba Products
www.futaba.com
Hobbico Products
www.hobbico.com
