One More Thing
to Work On
Cog Belt Break
In my previous article that appeared in the November issue of EH, I made
the following statement: “I would like to state that this year I
have had fewer in-flight failures than in any of the past 10 years.”
Up to the time that I wrote that article I had experienced one engine
failure due to a valve rocker falling off of the valve and push rod (this
has been about a once a year event for me and is an issue that we solved
in the new VPHelo, LLc engine that we are now testing. NO MORE VALVE ROCKER
FAILURES!!!!!!!
In the case of that engine failure I was able to auto the helicopter
safely to the ground, we had a short walk back to the hangar to get some
tools, repositioned the rocker and adjusted the valve lash, and then continued
my student’s flight training.
I experienced another engine failure this year while instructing in Texas
when the crank sensor failed. The FADEC computers faulted from FADEC 1
to FADEC 2 which activates the secondary fuel injectors in the manifold.
This a not the best design because the engine can only run for a short
time on these secondary injectors before the spark plugs foul with carbon
to the point the engine looses power and quits.
In this instance I was with my phase 2 student Mike Sidler as we turned
final for an approach to a hover over a very muddy area about a mile from
the airport, in fact, everything in that area of Texas was muddy with
standing water due to the recent rains. When the computers faulted to
FADEC 2 I told my student that I was going to try to make it back to the
airport where the ground was firm so that we would not have to try to
find a way to recover the helicopter from the mire we were over. All I
could think of was trying to convince a farmer to let us tear up his pastures
as we would attempt to traverse his property with recovery vehicles.
Knowing that I had about 500 feet of altitude and a mile to fly to get
to the airport where there was some firm ground, I thought that my student
and I had a good shot at making it there safely. As we neared the airport
the engine began to run progressively rougher as the spark plugs were
getting fouled up with carbon. I kept the ship over open areas for the
inevitable autorotation that I knew I would need to execute at any time.
The extremely rich mixture of the FADEC 2 injectors was causing quite
a reduction in the engine power. I needed to maintain 70 mph so we continually
lost altitude as the airport area got closer. By the time we were adjacent
to the taxiway of the very busy airport where Mike’s ship is based,
I informed him that we would keep the ship over the grass next to the
taxiway so that when we set down, we would not block the taxiway. By this
time we were down to about 100 feet AGL with full throttle, and descending.
Mike was ready, I told him to let me have all of the controls because
we were about to run out of engine power as we neared our intended landing
spot. We were just about 100 yards from our normal landing area when the
engine coughed and died. At this point we were about 30 ft. AGL and still
traveling at around 70 mph airspeed. Mike and I had been practicing quick
stops for the past few days so I informed him that we were going to just
do one now. We were all set up, proper altitude, proper air speed, extended
reinforced front skids with flipped front landing gear bow, what more
could we ask for (other than an engine system that would not be so prone
to failure)?
When the engine quit, all that was needed was to drop the collective,
haul back on the cyclic for a nice 70mph flare, settle, level the ship,
and slide it onto the soft grass that borders the taxiway, very nice and
really not a big deal if you are all set for it. Following the rotor spin
down, we walked to the hangar, which was just about 100 yard further than
we would have had to walk if we had made it back to our intended landing
spot. We got his car, a rope, the ground wheels, and returned to the helicopter.
In a few minutes we were pulling the ship down the taxiway to the hangar.
It took a few minutes to isolate the problem, one of the crank sensors
had failed. Mike called Rotorway and Robin sent a new set to us by overnight
currier. The next morning we had the new crank sensors, installed them,
and continued Mikes training with over 200 autorotations (practice ones
only as his ship flew flawlessly from then on). Mike told me that those
autos now had new meaning seeing that if done correctly, and if equipped
with the proper landing gear and skid configuration, a touchdown autorotation
was not such a big deal or something to be feared.
I would like to add that if anyone is not flying with the longer aluminum
skids with the steel reinforcement on both sides, they need to check out
the VPHelo, LLc web site at http://www.vphelo.com . Andrew is making very
nice skids with stainless steel skid shoes and to date we know of at least
6 ships that have been saved by the owner installing these extended skids.
The new VP engine also has shaft-mounted roller rockers that cannot fall
off of the valves and two redundant fadec computers that both operate
identically and at the same time. This way if one computer fails, the
second one continues to run the engine with no interruption or change,
and the pilot gets a warning light to indicate that he is now flying on
only one computer. VP has also eliminated the secondary fuel injectors
that foul the spark plugs. Once the VP engine is ready for public use,
we will be presenting it here in Experiemental Helo magazine.
Only days after writing the November article I was flying with a student
here at my training center in Missouri. He was beginning his phase one
flight training and was very excited to begin practicing autos. As we
were beginning our take off from my helipad, we were accelerating through
about 10 to 12 mph and were about 5 feet skid height when all at once
the engine raced, the ship did an immediate rotation to the right and
dropped. This one was a real surprise and happened in a hear-beat.
I informed Larry “I have it” at which time he let go of the
controls. Larry had just installed the extended reinforced skids with
the front gear leg reversed and it was what saved the ship. As the ship
dropped and the spun 90 degrees to the right, chopped the throttle, applied
full up collective, cyclic opposite to the direction that we were traveling,
and full left anti-torque pedal. The helicopter dropped onto the front
of the left skid, where the stock skid will snap off, and pivoted around
to the 180 degree position of our original take off direction of travel.
We were then sliding backwards and the ship rocked back onto the tail
rotor and slid to a stop. We surely would have rolled over had it not
been for the extended reinforced skids which allowed the ship to pivot
the 180 degrees to where the tail boom acted as an outrigger preventing
the ship from rolling over backward.
Upon inspection we found that the new factory cog belt with only 21 hours
on it had snapped. This was the first instance of a ship equipped with
the tensioned cog drive that I was aware of the cog belt breaking. When
the belt broke, the power to the main rotor was disconnected so all of
the engine power went to the tail rotor, snapping the nose of the ship
90 degrees to the right. We were very fortunate to have not experienced
a rollover but we sure came close.
I have included several photos of Larry’s ship following the belt
break. There is some damage but not nearly as much as would occur from
a rollover. The belt manufacturer engineers stated that the break was
most likely from the belt being run with too little tension allowing the
cogs to ride up the driving cog wheel which can hyper extend the reinforcing
fibers causing a belt failure. This may happen when the engine is starting
but there is insufficient oil pressure to properly tension the belt until
the engine is running.
Shortly after this incident I received a call from Bruce in Main. He
told me that the exact same thing happened to his AP cog drive belt as
he was in a hover and setting down. He told me that the hard set down
also damaged his ships tail rotor and tail boom as well as the landing
gear and skids but he was also able to keep the ship upright.
Once again, Andrew at VPHelo, LLc is working on a solution to the potentially
dangerous problem and we will publish his findings when they are complete.
As always, only fly your ships over areas that are safe to auto into.
If this should happen at altitude, it would give the pilot more time to
get to the ground safely with no damage.
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