Reviewed by: Ivo Almuli - Harrison, NY, USA
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The Cermark Pitts S2B is the first 1/4 scale replica of this well-known aerobatic two-seater in ARF form on the market. As such, it really caught attention when it was announced late in 1999. This kit was received as a Christmas gift and arrived in two large boxes containing the wings and fuselage. Although building from kits is normally preferred, time is scarce commodity these days. The prospect of having a large scale biplane ready with only a few days is really exciting. A new Saito 150 was on-hand so expectations regarding performance were very high, especially since this particular plane was penned by Dave Patrick, the noted aerobatic designer responsible for most of Carl Goldberg's aerobatic planes. The plane has an all-wood airframe covered in Ultracote, which will facilitate eventual maintenance and repairs. The covering was very well applied and the scale sun burst design is very attractive. After a couple of days in the workshop, several wrinkles appeared in the covering. These, however, were easily removed with a heat gun. The fuselage, other than the balsa sheeted turtle decks is mostly light plywood. The engine mount is a sturdy-looking 1/4" plywood slab reinforced by two aluminum back up plates. The tail feathers are open framework 3/8" balsa supported by rigging, which given the tail group's construction method, should not be omitted. In fact, the most notable characteristic of the fuselage, is its low weight derived from the extensive use of lightening holes and a generally "less is more" approach to the design. The wings are completely built right out of the box, requiring only hinging of the ailerons, installation of the interplane struts mounting lugs, and installation of the aileron servos and related harware. The cowl and wheel pants are painted fiberglass units requiring minimal additional work. While the wheel pants were well made, the cowl had a couple of rough spots in the paint and was deformed along one of the sides. The hardware provided was mostly very good. A Dubro 16 oz. tank and 3" wheels are standard, as is a Prospin 3" aluminum spinner. Because the stock mounting hardware of the spinner does not allow for the installation of a jam nut, a Tru Turn spinner was substituted for added safety. The stock spinner would, however, work well with a two-stroke engine. The supplied pull-pull hardware for rudder and elevator works well, but a small piece of fuel tubing must be used to secure the nylon snap links, which might otherwise open under load. As the completed plane needed some tail weight, a Sullivan tail wheel bracket was installed instead of the stock unit. The Sullivan unit does not transfer shocks from the tail wheel directly to the rudder, which will considerably extend the life of the rudder servo. Since the fields from which this model is to be flown are quite rough, 1/4 scale Dubro Cub style wheels and tires with a diameter of 4.25" were install. The resulting appearance with hubcaps painted to match the covering, was quite good. Initial hopes of getting the Pitts in the air quickly were dashed, however, by several problems that needed to be corrected in order to make the airplane airworthy and at least minimally durable. The glue joints of cabane struts seemed inadequate. Since a failure there would have catastrophic consequences, this joint was reinforced by sanding the cabanes down to the bare wood where they meet the top wing mounting blocks and adding 1/32" plywood gussets to the joint. The fuel tank compartment was not fuel proofed. The covering was removed from the bottom of fuselage and thinned epoxy was applied. Modelers who purchase this kit should consider ordering a roll of "Deep Red" Ultracote in order to patch those areas that require modification or repairs. The plywood was delaminating in several spots in the fuselage including the servo mounting area and just behind the firewall. Glue was squirted in the split areas as much as possible and the areas were clamped securely and left to cure. These area were also reinforced areas with 1/32" aircraft grade plywood or 6 oz. fiberglass cloth. One of the blind nuts used to secure the bottom wing was installed too deep in its hardwood block, which did not allow the nylon wing mounting screw to engage it. This was particularly annoying as it required filling the hole in the mounting block with an epoxy/milled fiberglass mixture and re-drilling and tapping for standard size 1/4" nylon screws. The landing gear mounting blind nuts were too thick and protruded through the bottom of the fuselage restricting the screws from being tightened sufficiently. A layer of 1/16" plywood was laminated on the fuselage bottom so that the blind nuts remained recessed. Several of the interplane strut lug mounting holes were too large to allow the self-tapping lugs to install securely. The inside of the holes were coated with a layer of epoxy to improve the fit and using a Dremel cutoff wheel, tap of sorts was made by cutting a vertical grove in one of the lugs. Following the recommendation of an associate of Cermark, Hitec 525 servos were used on ailerons while higher torque Hitec 545 servos were chosen for rudder and elevator. To get a little extra power from the servos, a 1700 mah 5 cell pack was installed. Due to its inverted installation, the Saito's stock muffler/header would not allow for a good fit inside the cowl. The solution was to order a coupler and flex tubing kit from Macs Products which allowed placement of the stock muffler right in the opening at the bottom of the cowl. This results in a neat and trouble-free installation. Reaching around and under a spinning 16 inch APC prop to disconnect a glow driver did not seem such a good idea, so a remote glow driver was installed in the firewall. In using this setup, care must be taken so that the muffler does not come in direct contact with the covering. A small 1/8” plywood plate can be used to slightly raise the muffler. The Saito 150 was given about 30 minutes running time on a test stand before installation in the Pitts. Test flights were performed on break-in fuel consisting of 5% nitro, 20% oil (5% castor 15% synthetic) and a APC 16X8 prop. In order to avoid backfires and to give the engine additional break-in time, initial flights were performed at a rich needle valve setting. Test flights were performed under near ideal conditions during March, 2000, and proved surprisingly uneventful. The control throws were set exactly as recommended and to be safe, low rates were used for the initial flights. The center of gravity was, however, left in the slightly nose-heavy condition at about 1/4” ahead of the suggested location resulting from assembly. After reading horror stories about ground handling of the full-scale Pitts, there were expectations of trouble keeping the Pitts on a straight line. The first takeoff run was begun by slowly advancing throttle while holding about half up elevator. At about 1/3 throttle the tail seemed to want to rise, so some back pressure was released to allow it to run on its main gear while the throttle was advanced. At about 3/4 throttle, all the Pitts needed to become airborne was some additional back pressure on the stick. Virtually no rudder input had actually been required to keep the Pitts on track, which is remarkable for a relatively short-coupled biplane. Three clicks of right rudder and two of up elevator had it trimmed out for hands-off flight. Although the forward center of gravity was probably responsible for the up trim, it did tone down the plane's reactions, which can be a benefit during the first flights. The first flying session was cut short when one of the metal 3 mm. top wing mounting bolts was found to be missing after the second flight although everything was checked for tightness after the first flight. Since there were no metric size spares in the fieldbox, addition test flights had to be postponed. Considering what would have happened had both wing bolts loosened led to modifications the top wing mounting method. The blind nuts were removed from the cabane struts and, using the same method as for the bottom wing, the installation was modified to accept standard size hardware. This allowed for the use of 1/4" nylon screws, which install under sufficient friction not to vibrate loose. The second test session was performed using 15% nitro fuel and with two (2) ounces of lead weight added to the tail. Vertical performance is very good and snap and spin maneuvers can be executed with ease. Opposite aileron mix of 25% was programmed into the radio to neutralize the strong rudder roll coupling that was noted during initial tests but the plane still pulls to the belly on knife edge. Towards the end of the Pitts’ third flight, aileron response became sluggish. One of the aileron servos was loose inside the wing due to its hardwood mounting blocks having separated from the plywood plate. Close inspection revealed that the plywood had delaminated. The servo mounting hardwood blocks were glued back on and small self-tapping screws were installed to secure the blocks to the plywood plate permanently. Further flight testing revealed that the cause of the servo mount failure was aileron flutter. The manufacturer is aware of the problem and recent, March 2000, releases of the kit have included a fix. Those who assemble older versions should be advised to not use the stock aileron horns. By replacing these with large Dubro 1/4 scale horns and using the next to last mounting hole, the angle and the leverage of the connection between the control surface and the servo is changed in a manner that eliminates the fluttering of the ailerons at high speed. Overall, the Cermark Pitts S2B flies very well, attracts a lot of attention at the flight line and despite requiring many modifications, it can still be put in the air in a fraction of the time it would take to build this plane from a kit. |
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