RADIO CONTROL JETS
Jim Hiller 6090 Downs Rd., Champion, OH 44481
The KingCat (BVM)
The latest jet model from Bob Violett Models (BVM), arriving in the hands of modelers this summer, is the KingCat. This is a large sport jet, best described as a bigger, distant brother to the BobCat.
Key specifications and features:
- Length: 94 inches
- Wingspan: 80 inches
- Wing area: more than 11 sq ft
- Typical finished weight: can be built as light as about 26 lb
- Fuel capacity: large Kevlar fuel tanks plus a 16-ounce header tank; total ~4.8 liters (more than 1 gallon)
- Recommended turbine: at least 27 lb thrust for comfortable performance
Design and construction:
- Pod-and-twin-boom layout, similar to the BobCat but larger.
- Exposed turbine installation to simplify construction, reduce components, and reduce weight.
- Painted canopy (no cockpit details required) to reduce complexity and weight.
- All-composite construction with the airframe painted in the molds — a technique common in high-end ARFs.
- Available color schemes range from sport/aerobatic to military styles.
Control-surface and landing-gear details:
- Control-surface hinging uses flex hinges; the model skin flexes to provide hinging for a smooth surface transition from wing to aileron.
- BVM supplies a solid retract landing-gear unit with wheels and brakes sized for this large aircraft.
- Inner struts are heat-treated and ground to fit outer gear down tubes for a slop-free fit.
- Nose-gear yoke is a precision steel casting for durability.
Fuel and endurance:
- Large fuel capacity reflects the fuel consumption of big turbines; expected to provide comfortable 10+ minutes of flying time under normal throttle usage.
- This follows the trend in jet modeling toward fuel systems that allow reasonable flight times comparable to piston-powered aircraft.
Flight characteristics:
- The KingCat is a large, slow-flying jet with low wing loading and generous wing area and airfoil design.
- Wing design and washout provide gentle stall characteristics, making the approach and landing benign.
- It handles tight aerobatics comfortably without fear of a high-speed stall; top speed is moderate rather than extreme.
- Offers a wide speed range for aerobatic enjoyment, including low, slow, tight routines with snap rolls and spins.
- Landings require a different technique: because it flies final approach slowly and the flare takes time, you must treat it more like a sailplane than a typical jet. With proper airspeed control on final, the KingCat delivers very short, smooth landings and encourages touch-and-go practice.
Overall:
- The KingCat expands available jet models that emphasize low-speed handling and aerobatic capability over pure speed.
- It is a higher-end, higher-cost model, but BVM provides quality components and construction.
- For the latest information, see www.bvmjets.com.
Proportional Brake Systems
Understanding proportional brakes and how to use them is key to smooth, effective stopping on jet models. There are two common types of proportional brake control for pneumatic brake systems: pulsed-air control and pressure-regulation control. Both have pros and cons; I fly both and like them each for different reasons.
Types and how they work:
- Pulsed-air valves (examples: Jet-Tronics unit, MiniHobby ATL)
- These are simple on-off valves that are pulsed at a rate proportional to the brake slider switch position.
- At full travel the valve is held on and full air from the tank is supplied to the brakes. In partial positions, the valve is pulsed on and off; air is bled from the brake lines during valve-off time and supplied during valve-on time.
- The average pressure in the brake lines (and thus braking force) is determined by the ratio of on/off time.
- Pros: very simple to set up — plug into the receiver like a servo, hook up air lines, ready to go; little routine maintenance (author notes Jet-Tronics valves have been reliable without regular service).
- Cons: air is continually bled from the tank during partial braking, so you have limited total time available for partial braking before the tank is depleted.
- Regulated-pressure valves (examples: BVM Smooth Stop, Ultra Precision U.P. 6)
- These valves regulate the pressure applied to the brake system. A servo positions a floating piston that acts as a pressure regulator and controls the air pressure to the brakes.
- Pros: very efficient with air usage — each brake application cycle uses roughly 3–5 psi from the tank, and holding partial positions does not continually bleed air. Allows techniques such as applying light brake pressure prior to landing.
- Cons: setup requires careful adjustment of servo linkage to get correct brake release and actuation. Valve O-ring seals must be airtight but allow free movement; occasional lubrication of O-rings may be necessary. The servo does not need high torque — a microservo is typically adequate. Also, the supply tank pressure must be relatively high (typically higher than ~65 psi) for the regulator valve to function properly.
Practical notes on usage and technique:
- Full-brake application typically results in a 3–5 psi loss of pressure in the air tank but can be held for extended periods (for example, when holding short awaiting takeoff clearance).
- A popular landing aid is to apply a small amount of brake pressure prior to touchdown. Light braking on the mains at touchdown helps pull the nose gear down and prevents the model from skipping back into the air if landing slightly fast. This reduces the chance of destructive bounces and can shorten rollout on short runways.
- Important: pre-applying brakes before touchdown works only with regulated-pressure valves (Smooth Stop, U.P. 6). A pulsed-air valve will have bled off the brake air during the approach and may leave you with no brake pressure at touchdown.
- Each brake application cycle consumes roughly 3–5 psi; with regulated valves the duration of partial braking does not consume additional air, whereas pulsed systems continuously bleed air during partial application.
Summary:
- Pulsed-air systems are easy to install and reliable but consume air during partial braking and require monitoring of available tank pressure.
- Regulated-pressure systems are more air-efficient and enable advanced techniques (like pre-applying brakes), but require careful setup and occasional maintenance (O-ring lubrication, proper linkage adjustment) and a higher supply pressure.
- Choose the system that fits your aircraft, flying style, and willingness to perform setup and maintenance.
Transcribed from original scans by AI. Minor OCR errors may remain.
