ARTICLES

 

         
Redundancy

 

Most of us have flown on commercial airliners and have noticed that all of them have at least two engines. These aircraft are designed in such a way that should one engine fail, the other engine would be able to get the aircraft to a safe landing. Many of the larger helicopters also have more than one engine both for power and safety. Our little helicopters do not have the luxury of twin engines for safety so we must insure that the systems that have been designed to keep our one engine running smoothly, even in the event of a fuel pump, ignition, fuel injection system, or computer failure. Rotorway has included backup systems for these critical systems but many of us have been flying these machines with a fatal flaw that can take out all primary and back up systems simultaneously. WILL YOUR HELICOPTER BE NEXT? Now donít panic, there is a simple fix to this problem and I wanted to get the word out to all Rotorway owners that without this fix, they may be next, complete engine shutdowns have happened twice that I know of in just the past 12 months.

Over the years of my involvement with Rotorway helicopters I have experienced a number of component failures. As I look back on each of these failures, the majority of them could have been prevented either by improved maintenance procedures or by carefully looking at the design of each system on the helicopter. A big factor in preventing failures is to have as thorough an understanding of your helicopterís systems as possible and that is the primary reason that I take the time to write these articles. My goal is to pass along the knowledge and experience that I have gained from flying literally hundreds of different experimental and certified helicopters over the years including the two Rotorway helicopters and one Ultrasport 496 that I have personally built and flown.

My helicopter experience began with the purchase of a basic Exec152 that came standard with an automotive-style distributor that ran off a little wimpy V belt that was about 1/8Ē wide. We called it a sewing machine timing belt at the time and that is most likely what itís origin was. This system never impressed me as being reliable and eventually supported that suspicion by failing resulting in an autorotation to the ground.

Back then those of us who were builders mostly networked by phone calls and group meetings since we did not have the internet with which we could network and share our ideas. The Rotorway factory did not encourage builders to interact with each other and often builders in close proximity to each other were unaware that there were other builders nearby. Through clubs like the Sierra Rotorcraft club that many of us belonged to we were able to compare notes, meet other builders, and encourage those that were in the building process.

The main problem that we all were concerned about was that the ignition system did not have any backup system. If any part of that system failed, the engine would shut down. Some folks figured a way to install dual electronic ignition with a set of diodes both firing the same set of spark plugs. The heads only had one plug per cylinder and I know of at least one builder who filled in the spark plug hole and then drilled and tapped in a dual set to allow for the redundancy of dual plugs.

My very first auto occurred on April 29th of 1993 while providing autorotation training to a student pilot Dan VanDuesen who was getting ready to take his check ride at the Rotorway factory. We had completed several practice autos and were climbing through 250 feet AGL heading for 500 feet AGL for another one when the engine quit. Dan was on the controls and I realized quite quickly the benefit of the flight instructor keeping his hands on all controls at all times. Dan was not fast enough to react on the controls for me so I immediately lowered the collective into the pocket and began a turn into the wind. We later discussed the incident and decided that we both lowered the collective at the same time. The lowering of the collective actually took place in less than a second from the time the engine quit so it was understandable that both of us would not wait for the other to drop the collective.

I had received autorotation training from several flight instructors by this time and practiced power recovery autos most times that I flew. In what seemed to be only about 5 seconds but was actually more like 10 we were sitting on the ground realizing that we were still upright and the helicopter was intact. When we got out to inspect the helicopter we found that the tail rotor end cap was polished and there was a small rock directly behind the little Scorpion that had a streak of aluminum on its surface.

Further investigation showed that the single coil on this single ignition engine had failed resulting in a complete engine shut down. If this helicopter had been equipped with a dual ignition system, this failure would not have resulted in the engine quitting. While I hiked the 3 miles back to my hangar to take the coil out of my Exec152, Dan used his permanent marker to memorialize that momentous event. I now have a rock that sits on my desk to this day as a reminder that things can and will go wrong with these helicopters but with proper training and good judgment, we can get through them in one piece.

Since that first auto in 1993, I have had to do several more in Rotorway helicopters. Each one was a learning experience and looking back on each one, the failures that precipitated those autos could have been avoided had I known what to look for.

One of those failures was caused by an old fuel pump. This one was at least 10 years old and should have been replaced. This Exec had redundant fuel pumps but one of them failed in a manner that I had not anticipated. Over time the ďOĒ ring that sealed the two components of one of the pumps had deteriorated and cracked to the point that all at once while I was out flying I was engulfed in fuel vapors and mist and could not even breathe. All I could think about was those fuel vapors finding their way to the sparking points of the distributor and the entire helicopter exploding into a ball of flame.

Fortunately I was able to hold my breath and auto the helicopter safely to the ground and shut down all electrical before a fire was able to start. I was sure that I was going to be the first person arriving at the scene of the accident and that I would beat the paramedics there by at least 15 minutes. Once the helicopter was firmly on the ground I bailed out and ran but thankfully no fire ensued. It is important to remember that components age with exposure to the elements, including the air that they are in. A component like a drive belt or water hose can age prior to being installed onto the helicopter and may need replacing if your kit is of the older vintage.

I have always thought that the 162F wiring was redundant as it comes from the factory and is installed on the helicopter. About a week after providing flight training to one of my students he called to tell me that he had experienced a complete system shut-down while flying his 162F. He did an auto and the only damage was a couple of bent skids. The cause of the problem was a solitary short in a wire that shorted out against the fuel pump inertia switch bracket. As you can see from the photo, the wire rubbed on the bracket until the insulation was rubbed through and the short occurred. The owner cut out the damaged section and then soldered the wire together followed by properly insulating the repair. On my next visit to the studentís location we removed the wiring bundle and then rewired and secured the wiring to prevent a future short, as shown in the following photo. I had a difficult time believing that a single short in the electrical system would actually shut down all of the helicopters systems at the same time, after all, we had full redundancy for all critical systems didnít we?

While I was providing flight training in another studentís 162F recently, we had a very unexpected failure of the helicopters electrical system.

This student had built an elevated helipad that was around 5 feet higher than the surrounding terrain so we would lift into a hover and then execute a max performance take off to attain ETL (effective translational lift) as quickly as possible so that we would not settle toward the high weeds surrounding the helipad. On one of our lift-offs all at once the engine quit, and the helicopter settled back onto the helipad. In the deafening silence we immediately noticed that both FADEC displays were off, all warning lights were off, the fuel pumps had shut off, and both ignition systems had quit.

This was not only very puzzling but maddening as well. I had, up until this time, felt that the 162F electrical system provided for true redundancy of all critical systems that keep the helicopter running. Isnít that what we check during our run-up? We fault FADEC one system by turning off the FADEC 1 toggle and the back-up system, FADEC two, takes over the engine operation tasks. We turn off one fuel pump and the other fuel pump maintains adequate fuel pressure and keeps the engine running. There are two ignition systems providing independent spark for the dual plugs on each cylinder so if one system were to fail the other ignition system would be there keeping the engine running,,,, right?

I remembered that my student Joe had experienced the same problem in his 162F and that it was caused by a short in a single electrical wire, could this most recent failure have been caused by the same type of short?

What could cause both FADEC systems to simultaneously shut down at the same time that both fuel pumps quit working and both ignition systems stopped firing? What happened to the redundant back up systems that are always there giving us such a warm and fuzzy sense of security? In both of these incidents, all primary and backup systems quit simultaneously causing complete and instant engine stoppage.

Obviously something very major had happened and if it had happened 20 seconds later, you would most likely have been reading about a crash and rollover involving this flight instructor instead of this article warning you of the potential danger. Fran and I pulled the helicopter back into the hanger and began taking it apart. We first removed all of the access panels so that we could get a good look at everything. The overhead panel has 10 fuses that come pre-wired as a unit from the factory. It was apparent that two of the three 30 amp battery fuses had blown.

How could that happen? These fuses are supplied with power from the battery on one side and then the other side sends power to the ignitions and the FADECS as well as the fuel pumps. Investigating further we found that the 30 amp fuse on the single wire that comes from the alternator, is routed along the passenger side frame and then up to the battery switch in the overhead panel was also blown. With all three fuses blowing at one time, this shut off all power to the FADECS, the fuel pumps, and the ignition systems. There actually was a degree of redundancy but no independence from one system to the next.

If you look at the diagram (posted under HINTS AND TIPS) you can see that the factory has wired the fuses and switches so that power from the battery fuse 1 comes from the battery, through the 30 amp fuse, hooks up with the 30 amp lead from the alternator and then supplies electrical power to Ignition 2, Ignition 1, FADEC 2, and then FADEC 1 before daisy chaining back up to the second 30 amp battery fuse. These critical systems and not independently wired at all but are all wired together in such a manner that allowed one electrical short circuit to take them all out at the same time. These two incidents that I am referring to are just the two that I am aware of. Were there others that caused complete engine shut downs where the cause was never discovered?

There is a photo of the overhead fuse panel as viewed from the top side under HINTS AND TIP on this forum. The wires with the red marking are the ones that are feeding all of the engine systems as outlined in the diagram above. After the photo was taken, we rewired the panel to separate the primary systems power from that of the back up system with no interconnection between the two.

We found the precipitating cause of the trouble to be one of the fuel tank supports. I have seen a number of different ways of attaching the fuel tanks on the exec 90 and 162F. The factory plans call for fabricating clamps that wrap around the frame and then attach to the tank straps with bolts.

There is a photo in HINTS and TIPS that shows how the wrap around fuel tank support strap has slid down the frame over a period of 20 hours. I drew a line on the frame where the strap was originally and the arrow shows where the tank slid causing the tank and tank strap to settle approximately one inch,


In many of the 162Fs that I have flown the builder has opted to weld fuel tank support brackets to the frame that the tank straps bolt onto. The wisdom of using the welded brackets is that the fuel tanks cannot slip down the frames as they can when using only wrap around straps.

In the case of this second failure, the builder used the factory method of securing the tank straps to the frame with wrap-around clamps.

With time and the weight of full fuel, the tank on the passenger side had settled enough that the tank strap crushed the 30 amp feed wire that runs from the alternator to the overhead panel. This wire then shorted out to the tank strap blowing all three fuses that powered all engine systems.

If your Rotorway Exec 90 or 162F has the factory supplied wiring installed then you most likely do not have the redundancy that you thought. To date I have helped the owners of several 162F and Exec 90ís to rewire those critical systems to allow for true redundancy.

We then separated the wires feeding the critical components as follows. One 30 amp circuit that runs from the alternator ties into one 30 amp battery fuse, then FADEC 1 and Ignition 1. The other 30 amp battery fuse powers the backup system. Now if a short circuit occurs in one of these systems, it will blow the fuses or pop the breakers of the associated FADEC and ignition without taking out the backup systems. Now we have true redundancy of these critical systems and can fly with a greater degree of reliability.

I would encourage everyone that has one of these helicopters to trace out your wires and insure that you have true redundancy and not just a false sense of security.

Fly safe and enjoy your these amazing machines.

Orv Neisingh R/H CFI
Sho-Me Helicopters, LLC