F-4F Wildcat BNF

ParkZone Park Pilot Fighter
By: Frank Granelli

By 1936 the U.S. Navy’s Grumman F-3F biplane fighters were getting outdated. Germany was already flying its Me-109 prototypes (9/35) while Japan’s A5M monoplane fighter (2/35) and Britain’s famous Hurricane (11/35) were then entering squadron service. Their performances were all far superior to the Navy’s biplane fighters.

Maybe even more importantly, the U.S. Army Air Forces had been flying monoplanes since the early 1930’s (the P-26 from 1933) and had several new, higher performance designs in the works. There was no way the Navy was going to let those “bleeping” Army guys get away with that!

Grumman was working on the Navy’s newest biplane fighter, the F-4F-1, but quickly realized that they just couldn’t repeal the laws of aerodynamics enough to allow their biplane to outfight the newest monoplanes then flying. Besides, Brewster was already working on a Navy monoplane fighter called the Buffalo.

The “legend” is that the Grumman designers simply erased the bottom wing on the plans, moved the top wing down to the middle of the fuselage and squared the wingtips. They also “X’d out” the 800-hp Wright engine and drew in the 1,050-hp Twin Wasp instead. The F-4F-2 was created. (It wasn’t that simple but it does make for a good legend.)

However, even this radical redesign was not enough for the Grumman to beat out the Brewster Buffalo in competition. So, Grumman installed the now legendary 1,200-hp R-1830-76 engine and raised the stabilizer to the fuselage mid point to match the wing. The resultant F-4F-3 prototype flew the wings off the Buffalo in subsequent informal flight tests.

This was fortunate for Navy and Marine pilots as the Brewster Buffalo had to have been one of the worst fighters the U.S. flew in WW II. It was retired from frontline service very soon after its disastrous performance in the defense of Midway Island during that battle (June 4-6, 1942).

Photo courtesy of Wikipedia

While superior to the Buffalo in every way, the F-4F Wildcat (“Wildcat” was adopted October, 1941) was not quite the fighter that the Japanese Zero was. Even so, U.S. pilots held their own against this deadly adversary while newer designs, like the F-6F Hellcat, were being developed. The Wildcat held the line at Wake Island and the Coral Sea, attacked at Marcus and Marshall Islands and then defeated the Japanese at Midway and the Eastern Solomon’s.

The Wildcat was a tough, resilient fighter that protected its pilots above all else. It was heavily armed with 4 or 6 50-cal heavy machine guns. 7,885 Wildcats served throughout WW II with the U.S. and British Navies. Even though it could not climb or turn with the Zero, its pilots found ways to defeat the Japanese fighter using dive and zoom tactics and the effective Thach Weave.

One of those pilots, LT Edward “Butch” O’Hare, won the Medal of Honor in the Wildcat when he attacked 8 Betty Bombers, shooting down 3 and damaging the others which spoiled their attack on the USS Lexington. And yes, Chicago’s O’Hare airport is named after Butch O’Hare and even has a Wildcat on display in his honor. The ParkZone Wildcat is modeled after the F-4F-3 flown by Lt. O’Hare (known as “White 15”) on his Medal of Honor flight.

This ParkZone Wildcat is the BNF (Bind N’ Fly) version. There is also a PNP (Plug N’ Play) version. The BNF Wildcat includes all servos installed, the receiver installed plus flight battery and charger. All that the pilot supplies is a DSM2 or DSMX transmitter. The Spektrum DX 6i was used for this F-4F. The servos are mounted in the PNP version but the airplane needs a receiver, flight battery and charger to fly. The BNF version sells for $190 while the PNP Wildcat is $160. Unless you already have plenty of 3S, 1800 to  2100 mAh Lithium Polymer batteries, a suitable charger and extra receivers, the $30 up charge for the BNF version is a very good deal.

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The colorful box contains the carefully packaged Wildcat parts. Both versions are almost completely assembled but the PNP does need the receiver to be added and connected. The BNF’s receiver is already installed and connected to the servos.

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The airframe is constructed of Z-Foam™ which has proven durable and dent resistant during flight tests. The  dual aileron servos are ParkZone’s PKZ SV 81 units while the elevator and rudder servos are PKZ SV1080 models. The BNF’s receiver is the Spektrum AR500 2.4 GHz 5-channel, full range unit. It is compatible only with Spektrum or JR DSM2 or DSMX transmitters. If you like the Wildcat as much as I do but prefer other brand radios, then the PNP version is best for your application. The servos work with just about any receiver.

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The Wildcat’s R-1830 engine hides a 480-size, 960Kv brushless outrunner motor. The propeller is a flexible 9 x6 E. This is the same motor and propeller as used on the ParkZone P-51 Mustang. Maximum rpm is just about 7,375. The wide-blade propeller does provide a lot of thrust for the 25.5 oz. airframe. There is a significant amount of right thrust built into the motor mount to compensate for this power.

The rpm’s are slightly higher than the ParkZone Mustang’s 7,300. So we checked the numbers. The Mustang’s 480 motor is working at 10.17 Volts producing 130 Watts while drawing 13.17 Amps. The Wildcat’s motor used 10.3 Volts to produce 147 Watts of power while drawing 14.5 Amps.

It seems that, just like glow engines where one can be slightly faster than an identical engine, electric motors and batteries can also vary a little. In this instance, the Wildcat’s battery was able to deliver a slightly higher voltage under load than was the Mustang’s. This extra voltage translated into more power and higher rpms. It also seems that the Wildcat’s motor was a bit more efficient as well. This information will come in handy during the test flights.

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The servos and receiver fit well inside the “tubby” fuselage (“tubby” and “Wildcat” are often used in the same paragraph for obvious reasons). The elevator and rudder pushrods are carbon.

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The flight battery fits into a forward compartment and is held in place using a single hook and loop strap. The ParkZone PKZ 18A BL 18-Amp Electronic Speed Control (ESC) also fits into a separate fuselage slot as shown. The ESC has a Battery Eliminator Circuit (BEC) that powers the on-board radio system to save weight.

CONSTRUCTION?

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There isn’t much construction on this airplane. What construction there is involves installing the stabilizer and elevator. Photo 9 shows all the parts required for the installation. . That “near yellow” strip is actually the four pieces of clear tape used to permanently mount the stabilizer to the fuselage.

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The two elevator halves are factory installed into the stabilizers. These stabilizers slide over a carbon spar. The control horns are factory installed as are the two composite elevator joiners.

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Before installing the stabilizer, it is a good idea to bind the BNF receiver, or install and bind the PNP receiver. Elevator operation is required to test the final installation so the receiver and transmitter need to be communicating now. NOTE: Remove the propeller before binding the receiver. This is a good practice to follow on any electric powered airplane. Test that the elevator and rudder servos are working and that the motor (NO PROPELLER) also responds to throttle.

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Slide the carbon spar into the left stabilizer half and insert the assembly into the fuselage. Then slide the right stabilizer half over the rod as it protrudes from the fuselage. Make sure the elevator joiner is correctly hooked up. Carefully slide each stabilizer half into the fuselage fillets. They do fit but be careful to do it right the first time. Make sure the stabilizer halves fit snuggly against the fuselage. Then secure the stabilizer using the four clear tape pieces top and bottom as shown. The tape installation can only be done once as trying to reposition the tape will lift the paint.

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Connect the clevises to the outer holes on the elevator and rudder control horns. Again, with the propeller removed, power up the airplane and transmitter. Check the elevator control direction. If you are using DSM2 or DSMX equipment, you will note that the elevator travel direction is reversed. Moving the transmitter elevator stick back for up results in the elevator’s moving down. Not good. The rudder also moves in the “wrong” direction. Use the transmitter reversing function to correct both controls. While you are at it, go ahead and reverse aileron direction as well since that is also required.

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The wing halves install just as did the stabilizers except that the wings are removable. Slide each wing half onto the carbon spar and insert fully into the fuselage fillet. Make sure that the aileron wire is pushed through the slot and into the fuselage interior as shown (photo 17).

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When properly installed, the hole in the blue tab will line up with the hole in the fuselage nylon bearing. Use one of the supplied screws to “bolt” the wing half in place. Install both wing halves and then connect the aileron extensions into the “Y” cord that is connected to the aileron port in the receiver. Check that both ailerons move in the correct directions. As stated, most transmitters will require reversing aileron direction for proper operation.

Make sure the battery is disconnected and install the propeller. Insure that the propeller is firmly against the thrust washer. Follow the directions carefully. The instruction booklet is very complete and goes into great detail using many photographs.

Total construction time does not exceed 30 minutes. Juts how little work is required for the BNF Wildcat version was illustrated at a recent trade show. The Academy of Model Aeronautics (AMA) was exhibiting at the New Jersey Council of Mayors Convention in order to sign up towns for new airfields. For some reason, the display aircraft did not arrive as scheduled (missing items seem to be the rule at all trade shows).

As it happened, I had received the Wildcat “kit” just before leaving for the show so it was still in my car. I went to the parking lot and assembled the Wildcat on the tailgate of my Suburban in just 3, yes just 3, minutes. 10 minutes later, it was hanging in the AMA booth and was the center of attention by the Mayors and Councilmen present. The airplane was a huge hit at the show and helped us get several potential new flying field leads.

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The instruction booklet provides recommended “low” rates for all the control surfaces but frankly, the Wildcat is so easy to fly, positive and smooth in the air that low rates are not really required. But if you insist, low rates are 8 mm for aileron, 9 mm for elevator and 11 mm for rudder. These settings are good for a newer pilot just out of a trainer. But I am willing to bet a soda that an advanced pilot will never use low rate aileron.

Similarly, increasing the elevator’s control deflection from 13 mm (.55 in.) to 16 mm (.66 in.) does the same. The ailerons are fine at the factory 11 mm (.45 in.) setting. Increasing rudder deflection from the factory 14mm (.58 in.) to 18 mm (.75 in.) does not do much for knife edge (we’ll see why later) but does help the spin. For the first flights, use the factory settings and CG location

Make sure that all control surfaces are neutral when the transmitter trim tabs are centered. The airplane’s airfoil rudder and stabilizer makes control response very positive, not sensitive but effective. So make sure these controls are neutral before flight.

AT THE FIELD

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If you purchased this airplane, then you have to love the Wildcat’s distinctive looks. For some reason, I always have. This is one very attractive fighter with lots of molded in panel lines, rivets and scale details. No matter the angle, the F-4F looks “cute” but with a certain menacing appearance. Many pre-war Wildcats sported roundels on each wing half, top and bottom. If you want this look, order the Wildcat decal sheet, PKZ1902, from Horizon Hobby. “White 15” had only one roundel as shown.

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Since the Northeast was snow-bound this year (all 6 of my flying fields were closed) I was “forced” to test fly the Wildcat from Florida’s Markham Park field. This Broward County field features a700 ft long paved runway and wide open flying vistas with some very friendly pilots. Joel Cimmino of the Broward County RC Society was kind enough to give the Wildcat its first push skyward.
It is a good practice to get an assist from a friendly pilot like Joel on the first flight as the airplane could be out of trim requiring the pilot to be on the controls from the very start. Thanks Joel!

The Wildcat has only simulated landing gear in the retracted position. Considering the full-size airplane’s narrow, complicated retractable landing gear, this is a huge plus. Takeoffs are easy and grass landings are slow and gentle. If you fly from a paved runway like this field, just land in the grass next to the runway.

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Joel gave a gentle shove and the Wildcat was airborne and climbing rapidly. The hand launch angle was on the conservative side (about 20 degrees up) as noted in photo 23 and just as the instruction booklet recommended. But the airplane accelerated so rapidly that it was obvious that there was a lot more climb potential in this fighter.

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The nose was raised up to about 45 degrees and the climb rate skyrocketed. As photos 24 and 25 prove, the Wildcat was able to hold this steep climb angle right from the takeoff. This was no zoom climb that would quickly run out of “zoom”!

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Photo 26 was taken immediately after photos 24 and 25 and shows that the steep climb was maintained. The climb would have continued as long as I wanted it to but climbing a light blue, 38-inch span airplane too high and far away against the blue Florida sky is not always a good idea.

All the concern over the first-flight trim was needless. The F-4F required two beeps of right aileron trim and that was it. The airplane is very stable in the air. After the landing, I found that the ailerons were both perfectly centered after the trim was added. So somehow, they must not have been neutral before launch. Make sure yours are and you will most likely never need trim adjustments.

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Subsequent hand launches proved so easy that the pilot has no problem with a DIY launch. Tracking is positive even under full power. The airplane leaves your hand flying straight and level allowing lots of time to make the switch back to the sticks. The best hand hold area is as shown in photo 26A.

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The first flybys for the camera tracked well despite a small crosswind of about 5-7 mph. There is a good amount of dihedral built into the ParkZone Wildcat as it was into the full-size aircraft. The full-size Wildcat had a reputation as being fun and easy for an experienced fighter pilot to fly. The ParkZone flies much the same. It is easy to fly and honest but does require its pilot to have some experience on the sticks.

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Rolls to the right were predictable and quick enough for any pilot. Left rolls were a little quicker but needed minor pilot corrections to stay on line. The roll rate averaged about 3 rolls in 6-7 seconds. Multiple rolls needed only small amounts of down elevator to remain level while inverted.

Loops were surprisingly large, averaging about 50 feet in diameter from full power level flight and about 70 feet from a slight dive entry. The Wildcat tracked extremely well requiring no aileron correction whatsoever during the entire maneuver. Guess the dihedral is working.

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The Wildcat was full of performance surprises. Not the least of which was its excellent outside loops. From level flight, the airplane kept its 50-foot loops and pulled extremely well over the top. Despite the dihedral, the airplane tracked well in the outside loops and needed very minor aileron and rudder corrections as the airspeed slowed over the top. Much of this performance must be due to the powerful motor as it pulled the aircraft hard over the top.

Its power made flying the Wildcat through Top hats, Immelmanns and Humpty Bumps a pleasure. But snap rolls were nearly impossible as the airplane just does not want to stall. Spins were also very difficult at the factory settings. The only way to spin was while applying power in a right spin. Left spins were impossible. Recovery was quick without requiring opposite rudder.

Increasing elevator and rudder deflection did help but snap rolls were still not truly stalled. What snap rolls happened were slow and very easy to maintain and direct. Inverted spins could be flown in the normal, power-off, manner. Inverted rotation was quick, about 1.5 to 2 turns per second, but recovery involved only releasing the “down” elevator. It was very easy to stop on point.

Moving the CG rearward by 1/8 in. also helped improve spins and snap rolls. But the maneuvers always bordered on the edge of “not quite” while remaining predictable and easy to control. This is good performance for a sport and scale airplane.

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Regular inverted flight and inverted slow rolls were about as easy to fly as were the same maneuvers upright. However, nothing is free in aviation (especially gas). The dihedral that made both large and small Wildcats so manageable and easy to fly exacts its price during maneuvers that need rudder.

The dihedral’s cost is a huge amount of roll coupling. The airplane instantly starts to roll whenever rudder is applied. Roll coupling is so pronounced that the Wildcat can takeoff, fly and land without aileron input if the pilot desires. The entire flight can be easily flown using just the rudder for directional and roll control.

The roll coupling makes stall turns difficult to fly as opposite aileron must be applied with rudder at the top of the climb. Otherwise, the airplane rolls sharply at the turn, spoiling the maneuver. The extra aileron drag significantly reduces the length of the vertical climb at the very top.
Point rolls are very difficult as the airplane tries desperately to roll into the rudder input. However, beautiful slow rolls can be flown just by holding some opposite aileron during rudder input.

In all fairness, fighters were not designed for easy and beautiful aerobatics. The Wildcat is no exception. What is surprising is just how well this airplane can fly so many aerobatic maneuvers. This is a sport airplane and a great one at that. Most sport airplanes, even some that should not, feature lots of roll coupling.

The full-size Wildcat was designed to have roll coupling to compensate for battle damage and for ease of flight. It had to takeoff and land from the tiny (by comparison) carriers of its day and get its pilot home safely. The ParkZone Wildcat follows its full-size’s example. It will get you up in the air, be fun and easy to fly, perform some excellent aerobatics and be a true joy to land.

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The Wildcat has great slow speed handling but does exhibit some, but not much, adverse yaw. This is caused by the ailerons’ being so far out on the wing. The amount is minimal but you may wish to eliminate it entirely. If do, you’ll have to use a 6-channel receiver. For PNP pilots, this is easy.

While the BNF’s AR500 receiver has a second aileron port, this seems to merely substitute for a “Y” cord. Neither Differential nor dual aileron settings seem to allow for aileron differential adjustment. The adverse yaw was so minor, I decided to ignore it and that has proven successful. However, removing the “Y” cord does save a little weight so I did do that.

It is very simple to put the airplane exactly where you want it. This is especially helpful on the landing approaches. The Wildcat landed right in front of me every time despite some crosswind. But the pilot should carry a little power through the approach and into the flair. That tubby (there is that term again) fuselage and big radial engine do produce extra drag making the airplane slow quickly when throttle is reduced. On the plus side, the extra drag also prevents the airplane from gaining too much speed in the down lines. The pilot always has time to think and plan with this airplane.

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Its great handling ease makes those picturesque fly-bys things of beauty. Control response is so positive that even low, inverted fly bys are simple. The panel and rivet detail molded into the airplane, and the factory installed pilot, make for a great scale appearance and fine looking model.

The ParkZone Wildcat is an attractive, exciting example of a very-seldom modeled fighter. Just about any sport pilot, even those just out of a Basic Trainer, can handle and fly this aircraft.

For the low price and considering all that is included, this fun aircraft is also a great buy. For more information, go to: http://www.horizonhobby.com/Products/Default.aspx?ProdID=PKZ1980 for the BNF version and to: http://www.horizonhobby.com/Products/Default.aspx?ProdID=PKZ1975 for the PNP version.

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