Alternator failures are an unpleasant fact of life for aircraft owners. In most instances, theyre not a big deal. The undervolt or ALT light blinks on, you dump some electrical load and land as soon as you can.
Its not so easy at night, in IMC and 100 miles from the nearest airport. Nightmare scenario: An alternator diode fries and you dont notice the failure until the battery voltage drops to the point where the avionics give up all at once.
Newer airplanes have a second alternator option but most older aircraft dont have a spare accessory pad to mount another alternator, even if an STC exists to add one. One solution we recently flight tested is a stowable ram air turbine alternator from Basic Aircraft Products, an Evans, Georgia accessory builder. (See Aviation Consumer, March 1996 for our first mention of this product.)
The BAE-14 (for 14-volt) RAT alternator is designed purely as emergency back-up, not supplemental power. It remains stowed inside the airframe-wing, fuselage or baggage compartment-until needed, at which point its popped into the breeze via a cable release.
The installation we tested was in our friend Brian Pecks TurboSaratoga. On the Saratoga, the turbine is installed inside the front baggage compartment door, as show in the photos at right. When the cable is tugged, a small gas-cylinder spring pushes the door open and deploys the turbine into the slipstream.
Basic Aircraft has STCs for the Saratoga and the Cessna 210, with approvals planned for the Bonanza, Cessna 206 and Piper PA28 series. In the Cessna 210 and Bonanza, the turbine is mounted under the right wing. In the Cherokees, it will go under the fuselage, below the baggage compartment.
To try out the turbine, we simulated an alternator failure by switching off the aircrafts alternator and monitoring the voltage on the Stormscopes battery monitor. Surprisingly, the aircraft alternator delivered voltage between 11.9 and 12.2 volts, with everything in the panel on.
When we deployed the turbine at 110 knots with the panel equipment turned off, the voltage soared to 13.1. Flipping the boxes on one by one, and adding the high-drain pitot heat, the voltage decreased only slightly, never dipping below 12.5 volts, except when we slowed for landing.
Because of its mount behind the prop, the turbine voltage is quite sensitive to engine power setting. Even at slow airspeeds, a high engine power setting will maintain sufficient voltage. (The wing-mounted models dont benefit from the prop blast and require higher airspeeds.)
Power output for both 14- and 28-volt models depends on airspeed, but its nominally given as 12 to 14 amps, at 150 knots. Ron Cox, who owns Basic Aircraft and builds the devices himself, tells us the turbines have been deployed at speeds of 170 knots. At 110 knots, we noticed no noise, yawing or loss of airspeed when the turbine was deployed. In fact, except for the in operation light alongside the T-handle, we wouldnt have known the turbine was humming away outside the airplane.
To control electrical load effectively, Cox recommends that the system be wired into the avionics, rather the main bus, thus allowing the master switch to turned off to isolate the rest of the electrical system. Turning the master on then ties the turbines output into the entire system, allowing the gear to be lowered or the battery to be charged, if necessary.
Cox told us the system has not been significantly tested in icing conditions. It has a plastic turbine wheel, thus theres no way to heat it. (Nor is there sufficient power to do so in any case.) Wax or Ice-X on the turbine blades may help, but no promises. That shortcoming notwithstanding, we think this is one of the best-made products weve seen in a while, performing even a bit better than the maker claims it will.
At $1595 for the kit, plus another $400 to $600 to install, this is not a cheap accessory. But in many single-engine airplanes, its the only choice for reliable electric back-up, thus we think its worth the asking price. Basic Aircraft also makes wind-driven alternators for aircraft which have no electrical system, such as Cubs, Champs and Taylorcraft.
Contact Basic Aircraft Products at 4474 Hickory Dr., Evans, GA 30809, phone 706-863-4474.