Fly a Der Jet Vampire model like the full-scale version
by Jim Hiller [email protected]
Overview
Many modelers enjoy flying scale models—recreating the flight of full-scale aircraft they remember so well. This article discusses setting up and flying a modern ARF jet model using my Der Jet de Havilland Vampire as an example, with insight into why it was set up the way it was.
The Vampire is a British jet first flown before the end of World War II. It is a vintage jet from the early days of jet power that served for years in several air forces. Its classic lines and distinctive sound make the Vampire instantly recognizable. The aircraft comes from an age when jets were not very powerful but still fast.
Kit and control surfaces
The Der Jet Vampire's setup is straightforward and typical for an ARF jet. It arrives painted and ready for systems installation. The ailerons and elevator are hinged with Kevlar cloth molded in, providing clean, solid hinges. The flaps, rudders, and speed brakes require hinging using the provided hardware, and all control horns must be installed.
Modern ARFs often have external control linkages—practical but less clean for a scale model. The Vampire is notable for the number of servos required in the wing: eight in total, one for each control surface. The wing includes ailerons, air brakes that rotate approximately 90°, and both inner and outer flaps.
Servo and radio choices
I set up this Vampire with a JR 12X radio and JR servos:
- Flaps and air brakes: economical JR821 servos. They provide adequate power at a good cost but require servo reversers and plenty of Y-connectors for the flaps.
- Elevator: choice depends on surface size and model speed. A JR8611 has ample power, but I opted for the higher-torque JR8711 to ensure elevator authority coming off the back side of a loop.
- Rudders: limited space requires narrow servos; I used JR8321s.
Control setup and mixing
Some optional setups make complex models fun to configure. I prefer to wire nose-gear steering to the rudder channel and put the rudder servos on an auxiliary channel (Aux 4). This allows me to turn off rudder trim to the mixed Aux 4 channel and use the rudder channel trim for accurate taxi trimming when back-taxiing for takeoff.
The downside is losing rudder trim in flight; any in-flight rudder trim adjustments require landing and sub-trimming Aux 4.
The landing gear doors are actuated with air cylinders controlled by a Jet-Tronics dual solenoid valve. This combines the valve and control in one unit and removes the need for a separate servo plus air valve.
Use a servo slow (slow-up) to control the timing of the gear doors coming up after the gear retracts—about a 3-second delay works well. No servo slow is needed for gear down, so doors open as the gear extends.
Flap-to-elevator trim
Flap-to-elevator trim mix needs to be dialed in with test flights. The Vampire typically requires about 3% down-elevator trim with full flap extension, but not all models need the same amount or direction. If no recommended values exist, fly the airplane to determine direction and amount.
On a recent new-jet test I returned from, the airplane needed significant down-elevator trim. Flaps down without elevator mix produced a slow glide speed; I made the first landing with no flaps to keep it safe, refined it on subsequent flights, and finalized adjustments after the third flight.
Power and performance
My Vampire is powered by a Jet Central Rabbit producing 22 pounds of thrust. Empty weight is 33 pounds and about 39 pounds loaded with fuel. The model's power-to-weight ratio is comparable to the full-scale aircraft, which means you must fly the model on the wing similar to the full-scale Vampire.
In the air and cleaned up, the Vampire accelerates well, reaching roughly 130 mph at top speed and full throttle. At 1/5 scale, that would equate to about 650 mph for the full-scale aircraft—obviously not a practical cruising speed for scale flying. Most flying is done at about 50% throttle for good looks and comfortable speed; more throttle is used for aerobatics.
Takeoff and climb
Takeoff procedure:
- Use half flaps and apply plenty of elevator. Transferring weight to the main gear helps keep a straight line down the runway; too much weight on the nose gear causes erratic steering.
- Raise the nose gear 1–2 inches off the ground, relax elevator slightly, roll for a couple of feet, then allow the aircraft to lift off.
- Maintain a gentle climb—this aircraft does not have the high thrust of modern fighters.
- Retract the landing gear quickly to aid acceleration and climb.
- Begin retracting flaps once airspeed and climb are established.
Using the JR12X servo slow feature, I set the flaps to retract in nearly three seconds to avoid a large bobble as the aircraft must increase angle of attack to maintain lift during flap retraction. This helps duplicate the look of the full-scale Vampire's flight.
Maneuvering and aerobatics
- Rolls: The Vampire will not perform axial, knife-edge rolls. Rolls are best flown on a light arc; carry some speed for slow and point rolls to flatten the arc. With proper rudder-to-aileron mix, point rolls are very effective—4-, 8-, and even 16-point rolls fly nicely.
- Knife-edge: Weak even with full rudder—beware descent during the last quarter of the roll.
- Loops: Require planning—pick up speed and bring throttle to full before pulling elevator. The big wing holds energy well; ease the elevator across the top to float and get rounded loops.
- Dead-stick aerobatics: The Vampire handles energy management well; loops are nice because it doesn't bleed much speed when you load the wing.
Landing
When setting up to land, fly the model much like the full-scale aircraft:
- Slow the aircraft and lower flaps to takeoff position to improve slow-flight feel and steadiness.
- Lower the landing gear and immediately add throttle to compensate for increased drag while on downwind.
- Before turning onto base, lower flaps to full position and add power.
- On final, deploy air brakes and carry 40–50% throttle to manage approach with plenty of drag.
Early jet engines were slow on throttle response from idle; mid-throttle response was better. Fly it accordingly: keep power available until main gear tires touch the ground to allow a smooth flare. On dead-stick landings I avoid air brakes, as they steepen the descent angle.
Conclusion
Duplicating the appearance and flight characteristics of the full-scale aircraft is why many of us enjoy scale models. Building, setting up, and flying a well-behaved scale jet like the Der Jet Vampire is highly rewarding.
SOURCES
- Jet Pilot's Organization — www.jetpilots.org
- Der Jet — www.derjetmodel.com
Transcribed from original scans by AI. Minor OCR errors may remain.
