I spent the last several days providing flight instruction to
two students in PA in a new Jet Exec built by Steve Walton. Steve
has built 2 Jet Execs so far and I have had the privilege of providing
the initial and subsequent flight training to the proud new owners
in each of them.
One of the first things that I discovered about the flight characteristics
of the of the Jet Exec is that the original rigging must be changed
to account for the different weight and CG of the helicopter.
If one is converting an existing Rotorway that has previously
flown, the rigging may be quite different following the JE conversion.
Normally when I instruct in a new helicopter we remove all of
the panels and covers off the helicopter from the fuel tanks back
to the tail. This allows us easy viewing access to monitor for
oil and coolant leaks, belt tensions, and any needed adjustments.
Since this Jet Exec conversion had only 5 hours on it we removed
all of the cowling from the rear portion of the engine compartment
as shown in the photo.
The hover testing went well and we needed to only make a few rigging
adjustments to get the helicopter airworthy. Jake buckled into
the pilots position and I occupied the flight instructor seat.
I found that the following sequence worked best for starting the
turbine. After the normal control checks were completed and with
the throttle in the fully closed position, we turned on the master
and instrument switches, turned the starter lockout key to the
start position, and after announcing “CLEAR”, with one hand on
the governor switch (off position) engaged the starter. At around
11% rpm the burner ignites with a low rumble and when that sound
is heard the governor switch is engaged.
The pilot keeps his fingers on the governor switch throughout
the start sequence so that it can be rapidly switched to the off
position should a hot start occur. It is crucial to monitor the
turbine outlet temperature(TOT) gauge during the start procedure
because this gauge will indicate that a hot start is occurring
by a rapid rise in the TOT. If a hot start is allowed to continue
the turbine can burn itself up in a matter of seconds.
On Jake’s ship we found that it worked best if the starter button
is held in the engaged position up to around 56% rpm before releasing
the button. Idle on this particular engine was set at 52% and
if we released the starter button near that speed, the governor
would give a surge of fuel and we would hear a very unsettling
sound that experts have explained as compressor stall. If we allowed
the starter to spool the turbine up to 56% prior to releasing
it, the governor would slightly reduce the fuel input and the
engine would settle into a very smooth idle. The engine that most
are using on the Jet Exec does not have a bleed air line to help
relieve the excessive back pressure on the compressor turbine
if too much fuel is introduced into the burner can at one time
so advancing the throttle must be slow and smooth.
After the normal checks the throttle was brought up to 102% and
then rolled off enough to get needle separation as we checked
the sprague clutch for disengagement. If the throttle was rolled
back to 102% too quickly we would get that annoying bark from
the engine as the governor would dump too much fuel into the burner
and the compressor would again experience compressor stall. This
is one area that I feel needs to be addressed by the Jet Exec
community. More on that later in this article.
Once the engine was running smoothly at 102% it easily picked
us up into a 2 foot hover. The power of these little turbines
is surprising! I am sure that it is capable of performing a vertical
takeoff to 100 ft. AGL with no effort but that is not a safe or
recommended maneuver in any experimental helicopter so we did
not test that theory. The Jet Exec has very good tail rotor authority
compared to it’s piston powered lineage. (Now several years later
I experienced a control lockup covered under HINTS AND TIPS section
of this web site. The Jet Exec that it happened on went straight
up at least 100 feet before I was able to reduce the throttle
enough to settle it back to the surface. This was not a fault
with the Jet Exec design, see the write up for a full explanation).
After several hours of hovering trials, we decided that it was
time to go to altitude and see how Jake's Jet Exec handled in
forward flight. We were in for a surprise!
I discovered that the forward flight aerodynamics of the Jet Exec
without it’s cowlings installed were extremely unfavorable, to
put it mildly. The Jet Exec needs the cowling on during forward
flight or the helicopter encounters dramatic porpoising and yaw
oscillations that can really get your attention and under gusty
conditions could be very dangerous. Take a look at the photo of
Jake’s ship (under GRADUATES) and notice how much engine and transmission
are hanging up there in the helicopters slip stream. There is
a lot of surface for the wind to interact with, and interact it
The airport in PA that we were training at is on a knoll bordered
by canyons on each side. Since the wind was a 90 degree crosswind
to the traffic pattern we experienced dramatic up drafts as well
as down drafts during our flight around the pattern. The winds
were gusty and flying the pattern initially required abundant
fore and aft cyclic movement to keep the helicopter from pitching
up or diving. Remembering that unloading your main rotor system
and experiencing a low G condition can be deadly, it took a lot
of discipline to s-l-o-w-l-y and smoothly apply opposite cyclic
to keep us upright.
When an updraft pitches the helicopter nose up 60 degrees the
first impulse (especially for a fixed wing pilot) is to rapidly
push forward on the cyclic to bring the nose level. Flight training
and discipline teach us to slowly and smoothly apply enough forward
cyclic to regain pitch control without unloading the rotor system.
Remember that the helicopter is most stable in an autorotation
so if you experience dramatic gusts that cause you to question
the safety of the flight, slow down to the best maneuvering speed,
use smooth control inputs, and enter an auto and land if you feel
that the safe outcome of the flight is in question. Unloading
the semi-rigid rotor on the Rotorway helicopter can be fatal.
You need to get the proper training to avoid becoming a victim
of Low G.
After experiencing that dramatic nose up and then nose down pitching,
we thought it prudent to land and reassess the situation. We decided
to install all of the cowling and take it up again to see if that
made a difference. The next flight was perfect. The gusts no longer
threw the little helicopter into aerial gymnastics and it just
flew like a dream. I now know that the cowling makes a dramatic
improvement in the stability of the helicopter and the Jet Exec
should not be flown without it installed. There are several after-market
engine cowls available that should improve the aerodynamics even
The wind that day was stronger than we prefer for flight training
but the Jet Exec has abundant power to handle stronger winds due
to the dramatic increase of available power and tail rotor authority.
We made hovering pedal turns both to the right and left in winds
gusting to 25mph without ever losing main rotor RPM or tail rotor
authority. In fact, we only used about 50% of the available anti-torque
pedal travel in right turns into the wind.
This doesn’t mean that if you have a Jet Exec you should go out
into a heavy or gusty wind and start doing pedal turns. Flight
experience in any helicopter is your safety margin. If you have
little experience, be very conservative in determining your personal
flight envelope. This is why flight instructors limit the students
flights to conditions that are safely within the students abilities
at the time. As the student gains experience, the instructor will
increase the flight envelope that the student can safely operate
his helicopter within.
That being said, while we were hovering back to the hanger at
the conclusion of our flight training, a gust of wind hit the
helicopter from the right side with such force that we experienced
VRS (Vortex Ring State) of the tail rotor. VRS is what the FAA
now calls what helicopter pilots know as Settling with Power.
I had never experienced tail rotor VRS before, nor do I plan on
doing so in the future.
The main rotor on the Rotorway helicopters turns to the right
as viewed from the pilots position. Remember that for every action
there is an equal and opposite reaction. The torque of the engine
and drive train cause the nose of the helicopter to turn to the
left. To counteract this torque we apply right anti-torque pedal
which applies thrust to the left at the end of the tail boom by
changing the tail rotor pitch. To produce the tail rotor thrust
to the left the tail rotor side wash is to the right. One great
thing about the Jet Exec is that it has enough power that we never
lost any main rotor RPM at anytime during our flights. There is
enough power available to get you out of trouble, should you need
As we hovered past a large hanger a very strong gust of wind
hit the side of the helicopter sending the tail rotor side wash
back into the tail rotor. Once this happened we momentarily lost
all anti-torque control and the nose of the helicopter rapidly
yawed to the left until we had turned about 90 degrees. At that
point I was able to stop the unanticipated yaw of the helicopter
and continue back to the hanger. Always be ready for the unexpected
because when it happens, you don’t have time to think about it,
only to react. We had decided that the winds were strong enough
that we would not continue altitude flight that day, we knew that
the lee side of the hangers would most likely be turbulent and
were expecting turbulence. We were not anticipating tail rotor
VRS but when it happened, we were able to handle it due to flight
experience. The more you fly your helicopter the better you become
at it as long as you had proper initial training so that you did
not develop any bad flying habits.
After instructing in these two beautiful Jet Execs I have developed
some opinions and concerns that need to be addressed by those
that are going to be flying them. My first concern is the tendency
of the engine to go into compressor stall, if that is what it
is actually doing. I am not a turbine expert and I am sure that
others with much more experience will weigh in on this issue.
I am bringing this up from the perspective of my experience to
hopefully generate dialog and a solution to what I perceive as
a potential problem.
During the engine run up the throttle must be advanced slowly.
With each increase of the throttle the governor increases the
amount of fuel entering the burner chamber. If the throttle is
advanced a bit too fast the engine falters and “barks” very loudly
indicating that something is not right. When I brought this issue
up on the msn groups rotorway fun web site, several fellows with
high turbine time replied that the turbine had experienced “compressor
stall”. They also explained that most turbines have a bleed air
line that allows excessive pressures that build up in the combustion
chamber to bleed off so that the compressor will not stall against
that back pressure. The T62 does not have this feature as it was
designed to be operated at one continuous rpm under constant load,
I am told.
In the Jet Exec the T62 runs very well at the designed flight
rpm. It is when the throttle input is changed that the governor
can supply too much fuel for the combustion chamber to handle.
This brings up a concern for practicing autos in the Jet Exec.
When the auto is entered the throttle is rolled off slightly to
allow for a small needle separation to insure that the sprague
has disengaged. I noticed that when this occurred the Jet Exec’s
engine governor would hunt for the proper rpm causing the nose
of the helicopter to yaw right-left-right as we descended.
At the bottom of the auto, you initiate your flare, level out
and roll the throttle back on. Will the governor apply too much
fuel to the combustion chamber? Will the compressor stall just
when you need the engine to produce sufficient power to maintain
a hover? With the engine and transmission up high on the frame
the center of mass is higher on the Jet Exec than on the standard
Exec. The standard Exec already has a tendency to pitch forward
and experience a dynamic rollover if a touchdown auto is not executed
perfectly. It would seem that the Jet Exec would be even more
unforgiving should the engine not come back on line when you need
I am sure that these issues are being addressed and solutions
will be found as proper procedures are developed for operation
of the Jet Exec. Just be sure that you invest the money on an
engine cowl and don’t fly at altitude without all of the cowling
Orv Neisingh Helicopter CFI