FlexJet Pro Turbine Conversion

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FlexJet Pro Turbine Conversion

The FlexJet Pro was designed with turbine conversion in mind. The inlet was routed down to provide ample space for a Main Fuel Tank. The Forward Equipment Tray was made removable so an alternate could be installed. The Tailcone is removable to ease component installation.
Test Stand (before Aura Pro install)

The FlexJet Pro with 4.5kg of thrust offers and excellent turbine experience. It gives an aerobatic 'fast jet' experience while never feeling heavy. Power is impressive and never lacking.

Flight time can vary depending on fuel tank install and flying style. The K-45 G3 flies about 4:20 with the 24oz main tank, and beyond 6:00 with the 35oz main tank. These times allow for startup, taxi, and ample reserves for a go around and taxi-back and shut-down.

The primary conversion involves installing the Turbine Mounts and Turbine. Installing the Tailpipe, Assembling and installing the fuel system, and equipping and mounting the forward equipment tray.

Turbine aircraft should be fitted with Wheel Brakes. These are drop in units!

NOTE: KingTech recommends test running the engine outside the model with the assembled equipment tray and fuel system. This tests all components including the electrical and fuel system while allowing inspection and easy access. Flex Innovations used this procedure and had complete success.

NOTE: Some K-45 G3 users (in general, not FlexJet Pro specific) have reported flameouts. In addition to making your fuel system perfect, consider making the 'Acceleration' and 'Deceleration' factors 1 unit 'slower' via GSU. Consult your manual and KingTech if more support is needed.

Turbine Selection

  • At the time of this writing, Flex Innovations has tested the KingTech K45 G3 and have found it to be a perfect match.
  • The Zicoy X45 has very similar specifications, and its mounting was considered in the conversion kit design. It should be easily fitted as well. You will note that there is a LOT of room in the fuselage where the turbine is mounted. Customers have flown the Zicoy X45 and the reports are very positive.
  • Flex Innovations in NO way recommends turbines with greater than 4.5kg thrust.
    • Turbines have very high exhaust gas velocities and can reach high speeds. Throttle management should be used.

Battery Selection

  • Flight Pack (aka Radio) Batteries (2S LiPo)
    • A single 2S 2000mAh 15C LiPo is a good choice when using a no-gyro setup, or when using the Aura Professional AFCS gyro.
    • Dual 2S 1400mAh+ 15C+ LiPo batteries would also be a good choice, and the Aura Professional can connect them in an ideal fashion.
  • Turbine (aka ECU) Battery (Follow your Turbine manufacturer's recommendations)
    • The KingTech K45 G3 recommends a 3S LiFe
      • Flex Innovations used this SPMX2203SLFRX from Spektrum.
      • KingTech also sells a 3S LiFe you could choose.

NOTE: The recommended CG was easily obtained with these components and no additional ballast was used.

Fuel System Components

  • Setup your fuel system in a fashion compatible with your turbine manufacturer's instructions.
  • Make sure to use Gas/Petrol compatible stoppers and clunk lines (not silicone)
  • For general fuel plumbing Flex Innovations used Tygon Large (1/8" ID) fuel line from Dubro (506).
  • Flex Innovations used this MAP 2oz UAT and the equipment tray accommodates it.
    • A UAT eliminates air bubbles going to the fuel pump/turbine. An excellent fuel system required for reliable engine operations! Take great care.
  • A 6oz Sullivan Flex Slant Tank (S738) was used as the Collector Tank (the flex allows slight deformation of the tank for a relaxed fit). The Sullivan 4oz non-flex Slant Tank (S437) could also be used.
    • The Sullivan Universal Stopper (S449) is a good Stopper choice.
    • The Collector tanks takes the fuel from the main tank before delivering it to the UAT. It adds capacity and also buffers air-bubbles from the long main tank.
  • Main Tank Choices

Flight Controller and Gyro Notes

  • The jet community has noted that vibration/sonic harmonics from the loud and high frequency turbine engine noise can get into the modern gyro MEMS sensor chips and cause unwanted control surface movements that scale up with gain.
    Aura Pro w/Remote Sensor
    • Flex Innovations has noted this with various turbines. It seems worse in Large Turbines (Louder) and Small Turbines (Higher RPM).
    • Flex Innovations specifically engineered the Aura Professional series to include a solution for this serious issue. It features a Remote Sensor Port allowing the inclusion of a Remote Sensor that includes specially engineered designs and materials to block these vibrations.
    • Flex Innovations tested with a standard Aura 8 and experienced issues using the K45. Customers also confirmed gyro sensor issues using the Xicoy X45.
    • ALL issues were cleared with the use of an Aura Pro with Remote Sensor.
  • For these reasons the only gyro system Flex Innovations recommends for the FlexJet Pro with Turbine is the Aura Professional (8 or 12) with the Remote Sensor! Combo pricing is available.

NOTE: Any turbine aircraft with any gyro can be checked for these interactions. With turbine running and aircraft restrained, set gyro gain to highest setting, sweep the throttle very slowly while watching for any uncommanded control surface jumps or movements. Do extra checking at mid and high throttles where it is most common.

General Notes and Tips

  • We have found the small turbine FlexJet Pro to operate just like any other turbine aircraft. We don't find it very different than it's larger counterparts.
  • The fuel system is smaller than a large jet. Fill the tanks at a lower rate. (Ex. Use a 2S LiPo or LiFe on the fuel jug pump instead of a 3S)
  • Always confirm fuel tank vents are open during all operations.
  • We usually set the FlexJet Pro (upright) on a table or stand when starting. This allows you to more easily monitor the start-up looking in the inlets and main landing gear doors. In the unlikely event of a start-up fire, it also allows faster and easier access to these locations for application of a fire extinguisher.
  • Make your first flights at least one minute shorter to allow for a stress free extra go-around if needed and to monitor your actual fuel system and fuel usage. Be sure to practice slow flight so you are prepared to land.
  • We find the half or fully deployed flaperons are very useful on Landing as they allow slower speeds without tail-strikes. Consider 1/2 Flaperons for landings with moderate crosswinds or high headwinds. We primarily use FULL Flaperons for calm wind landings.
  • Elevator rates for take-off and landings can be at the pilot's choice. High rates are not typically needed as they may be on other jets.
  • Takeoffs can be accomplished at half or zero flaps. It is not very different. Consider zero flaps for moderate crosswinds.
  • Extended landing flares are not required. Land at a modest speed with the nosewheel off the ground. The trailing link struts really help the model to stick to the ground. The wheel brakes are quite effective. UP Elevator will help keep weight on the main wheels/brakes!
  • As with any Jet, practice your slow flight at a safe altitude. Too-Fast or Too-Slow are common problems on landing. Once the pattern/approach speed is stabilized, some power (ex. 1/4 to 3/8) is normally required. Remember the Turbine spools up fairly slowly from dead flat Idle, it is easier to control the speed from a stabilized approach with some throttle on.
  • Turbines have very high exhaust gas velocities and can reach high speeds. Throttle management must be used.

Assembly Notes

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