Author: Jim Hiller
Edition: Model Aviation - 2009/08
Page Numbers: 120,121
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Radio Control Jets

Jim Hiller

[email protected]

An all-in-one system for pneumatic sequencing

I obtained a valve system that I like for actuating gear doors. Through the years I’ve tried many solutions to program gear-door actuation, from air-bleed timed systems to electronic. Some were of good quality and some were questionable — you know, the ones that let you down on the test flight?

A new actuation system, which I greatly appreciate so far, is on my bench. It is an AirPower Smart Multi-function Valve EVSD-5U-PRO. I got the unit with a Skymaster ARF; the company is licensed to sell these systems with its products.

This valve unit is electronic and programmable, with air valves that are built in for the landing gear retraction and gear doors. There is also a separately programmed output channel to which you can attach a servo and valve. One more thing: the brake valve is built into this unit. All our pneumatic systems in one block — sweet!

The EVSD-5U-PRO is housed in an aluminum case that weighs a healthy 166 grams (approximately 6 ounces) with the mounting bracket, air fittings, and servo wires attached, which is not much different from the weight of the three servos and valves it replaces. The unit is 2 3/4 inches long, 2 inches wide, and roughly 1 1/4 inches tall. It’s compact for what it does.

The system has a 1 3/8 x 3/4-inch LCD for program information and only three input buttons for programming. Four LEDs indicate which valve is open during the sequence, to aid in programming. Operating voltage is 4.8–6.0 V, and it can draw up to 650 mA maximum.

So what does the EVSD-5U-PRO really do? Let’s start with the gear-door functions: its main purpose. The unit has four basic operating modes.

  • Mode 1: Basic gear-door open with struts extended. Gear-extension sequence: gear doors open, gear extends, and gear doors remain open. Retract cycle: gear retracts, then gear doors close.
  • Mode 2: All gear doors closed with struts extended. Extension sequence: gear doors open, gear extends, and gear doors close. Retract sequence: gear doors open, gear retracts, then gear doors close — basically what is used on an F-86 Sabre.
  • Mode 3: Combination of Mode 1 and Mode 2; requires adding a servo and valve plugged into the Mode 3 port. Mode 3 can simplify setup on multifunction door arrangements, such as those on the F-18; all timing and sequence are handled in one place.
  • Mode 4: Fully customizable; intended for users to tailor the setup. The EVSD-5U-PRO walks you through all programmable values with each push of the setup/enter button. You set parameter values in up and down increments. These values are displayed on the LCD on the front face of the unit; the active parameter for adjustment blinks.

Another EVSD-5U-PRO retract feature is a programmable pressure setting at which to extend the landing gear before you run out of air. The default setting is 50 psi, but you can change it to suit your needs. Since the unit is monitoring air pressure, it shows the pressure on the LCD screen for both the brake and landing gear systems.

The system also prevents gear-up when the transmitter is turned on, keeping those embarrassing moments to a minimum. Pressure values can be displayed in one of three modes: psi, kg/cm2 (kilograms per square centimeter), or bar.

The brake function is the pulse type, which is an alternative to air-pressure regulators and has proven to be acceptable. My BobCat has a traditional pressure-regulator valve on the brakes, and my T-33 uses a pulse brake-function actuator. I prefer the pressure-regulator valve because it uses less air when light braking is applied, but that alone hasn’t motivated me to change out the T-33 valve, and that jet has many seasons of flying on it. Pulse-type brakes work exceedingly well when set up properly. The EVSD-5U-PRO solves the ongoing problems we create for ourselves as we complicate our aircraft. Whether you fly turbines or propeller models, this item is worth checking out; it is a cool way to set up your airplane.

Scale A-10 and Experimental-class operation

Craig Gottschang flies a large, gorgeous scale A-10. He lives in Georgia, so how he found time to build such a beauty with all that warm flying weather is beyond me, but he did.

His A-10 is from a wonderful Mibo Generation 3 kit, and he loaded it with detail. Craig is uniquely qualified to know A-10 details; he flew the full-scale version 20 years ago.

Craig finished his model in the colors of "Killer Chick," as Kim Campbell flew in Baghdad, Iraq, in April 2003 during Operation Iraqi Freedom. Craig's attention to detail needs to be seen to be appreciated.

The big smoking gun that the A-10 is built around looks great sticking out of the nose, ready to light them up. Craig flies his jet with ordnance in place hanging from the wings; this model is ready to do battle. The cockpit is another work of art; it is complete, full depth, and looks incredible.

Craig's A-10 is powered by two JetCat P120-SE turbines — big power for a big aircraft. The model weighs 55 pounds empty, which qualifies it for the Experimental Radio Controlled Aircraft class. This is where it gets interesting.

Our AMA opened up the Experimental class to include turbine-powered models, so now those aircraft that weigh more than 55 pounds (ready-to-fly) can be piloted at any AMA-sanctioned model event when certified.

The Mibo A-10 is marginally close to the 55-pound limit, but once it is fully detailed, large turbines are installed, and ordnance is added, it won't stay under the limit, so the Experimental class is the way to go. Craig shared some of his knowledge about flying in this category.

He applied for the Experimental-class waiver with all the required documentation. He put all of it in his aircraft-documentation book, so reviewing it with him was a great education.

This book is a great help to contest directors when he shows up at an event to fly; many of us are unfamiliar with the Experimental waiver and what information we should be checking. Craig's documentation is complete; it includes his flight log, aircraft waiver, and other items that are required to obtain and maintain the waiver.

The details of applying for an Experimental waiver, documentation requirements, and aircraft requirements are covered in AMA Document 520. Turbines are specifically covered under Appendix A. Read that information carefully if you intend to build a turbine-powered model to operate within the Experimental class. These aircraft have different airframe requirements, pilot-experience necessities, general setup requirements, and required documentation, including calculated servo power necessary for each control surface.

A turbine-powered model is allowed a heavier wing loading — up to 100 ounces per square foot. But the maximum takeoff weight is limited to 75 pounds, so don't get carried away.

The maximum power-to-weight ratio is limited to less than 1-to-1. Depending on the model, you might be left in a marginal situation for power — especially on a twin-turbine setup when one engine shuts down. This twin-turbine power-to-weight ratio is normally okay for straight-wing jets, but some scale models with highly swept leading edges and low-aspect-ratio wings can be a handful when one turbine shuts down and you have to bring it home.

Kudos to Craig Gottschang for the professional job he is doing operating his A-10 in the Experimental class. I hope he motivates others to follow suit. Let's get some big jets up there!

Sources:

Transcribed from original scans by AI. Minor OCR errors may remain.