An Improved Method of Aircraft Turbine Engine Starting
This System is an optional feature with most of our GCPs but is also available as a stand alone Parser Module, P/N 5-11-0010 which provides for updating existing aircraft to Parser Starting with a minimum of modification.
ParSer Start- Start is initiated with both batteries in parallael just like a normal start. At a specified point during the start, the batteries are switched into series. This reults in much faster acceleration from light off to Gnd Idle and lower peak temp.
Soft Start- Start is initiated with one battery feeding the Starter and one supports the primary bus. Just like above at some point the batteries are switched into series
3 Step Start- Same as Soft Start except a second stage is inserted briefly with the batteries in parallel before switching to series. This gives a little boost without causing undue voltage sag.
The resulting increased voltage during the later part of the start appears only at the starter and nowhere else in the electrical system. The inrush current and impact torque on the accessory gears is significantly reduced (softer), the acceleration of the engine is greater (faster) and consequently the peak gas temp during start is reduced (cooler). Our experience with this system on numerous aircraft with several make and model of engines (PT6, TPE331-10,-12&-14, Allison 250, Williams FJ33 &FJ44 and Walter) has taught us that to whatever extent starting requirements dictate the weight of the batteries and the current rating of the Starter/Generator we can reduce both significantly. Reduced battery weight and S/G rating also results in lower hardware costs. We have test data taken in the Lab, on aircraft and in Engine Mfrs test cells that lead us to the following conclusions:
The smallest 24V aircraft batteries available when used in our system will outperform two of the largest available batteries in a conventional system. To put this in perspective compare 50 lbs to 200 lbs. Actually in one instance in an engine test cell our 56 lb battery pack feeding a 200 amp S/G outperformed a 500 lb battery cart feeding a 300 amp S/G.
High inrush current (and therefore high torque and acceleration) from zero RPM to light off has nothing to do with the quality of the start. In fact it tends to be self-defeating because it causes excess heat in the starter and gassing in the battery, both of which detract from performance later in the start.
Extra torque from the starter after light off has a great deal to do with the quality of the start. A bigger battery and S/G and heavier cables can only provide marginal improvement in this critical area because what is needed is more voltage to overcome the increasing counter EMF vs RPM of the S/G.
Using smaller, lighter weight cables between the battery and the starter absolutely kills performance in a conventional system but significant reductions in wire ga are possible with our system. The reason is obvious; the critical part of the start is after light off where the extra voltage from our system largely offsets the extra resistance of the cable. But the inrush current is less, therefore a softer start. In one test in an engine test cell we introduced an extra 40 feet of 2 ga wire and still got acceptable starts.
We have observed as much as a 50% reduction in start time and as much as 180 deg C reduction in peak gas temp. It should be pointed out that thermal stress is a function of both peak temp and time of exposure and is in fact related to the area under the curve, therefore reducing both yields a second order reduction in thermal stress.
The following are some examples of the dramatic improvements we have seen:
A PT6-42 fitted with a 200 amp S/G and two 28 lb batteries starts in 10 sec (light off to gnd idle) and actually starts cooler than it idles
A TPE331-12 fitted with a 300 amp S/G and two 41 lb batteries starts in 20 sec (light off to gnd idle) with a 120 C reduction in peak gas temp.
A Walter turboprop fitted with a 200 amp S/G and two 28 lb batteries starts in 7 sec and cooler than gnd idle.
A TPE331-14 fitted with a 400 amp S/G and two 90 lb batteries starts in 22 sec.
A PT6A-60AG installed in an AT602 accomplishes the first start of the day in 12 sec, (light off to gnd idle), and 580 deg with original batteries and S/G.
An Allison 250-C20 on an engine test stand starts in 13 sec, (total start time), and peak Temp of 480 deg with two 11AH 24V bats with the Soft Start featuring significantly less in-rush current and impact torque on the accessory gear box.
Note: No Ground Power Cart used in any of the above cases.
The fully integrated Electrical Systems that we are offering are primarily intended for new designs of aircraft but could be used as an upgrade to existing aircraft. For STC applications in the aftermarket we have designed a system that consists of direct replacement GCUs, which in combination with some minor modifications to the existing electrical system will implement the Enhanced Start Feature described above. We have also supplied some kits that just implement the
Start feature without replacing the GCU. We are actively seeking launch customers who want to pursue either route as an STC.
But what are the tangible benefits to the aircraft owner/operator:
Reduced operating costs-
It is intuitive that faster, cooler starts will ultimately result in lower engine maintenance costs. One customer is claiming savings amounting to tens of thousands of dollars over a period of 6 years and four hot section inspections on two engines. He operates a spray plane operation with two Thrushs, one fitted with a TPE331-6 and one with a 10.
Starting with weak batteries-
We have solid evidence of normal starts with batteries too weak to start at all without theStart feature.
Improved cold weather starting-
For exactly the same reason as Starting with weak batteries
