140 MODEL AVIATION
IS EVERYBODY enjoying winter? Yeah,
right! This issue will come out sometime in
January, smack in the middle of winter. I’m
writing this in October, so I have no idea
how the winter is going to shape up. I do
know one thing: there’s not much outdoor
helicopter flying going on in February and
March in the North.
Now is a good time to think about getting
radios out for repair and tuning. I used to
work for a small Radio Control radio-repair
shop, and I know for a fact that people don’t
think about getting their equipment tuned
right now. The first warm day in spring or
late winter usually brings them out in
droves. The backlog goes out several
months. If you don’t want to get caught up
in the rush, do it now!
Earlier this year I took my Intrepid 46
out for a spin. I hadn’t touched it in quite
awhile. Sure, I did the once-over with the
mechanics and I had freshly charged the
batteries (Ni-Cds). After approximately 30
seconds into the flight, things started to go
wrong. I was getting tail-rotor twitching, and
then the engine was going to idle. It was
going into “fail-safe.”
I still had enough control to auto the
helicopter and shut off the engine. I went
over and moved the controls and was getting
sluggish response. I checked the battery
pack and, lo and behold, it had lost a cell.
That was close!
I went home and cycled all of the
installed batteries in my shop. I also found a
failed cell in one of my 9Z transmitters. The
moral of that story is, Do some battery
Dan Williams, 27 Treeline Dr., Liverpool NY 13090; E-mail: [email protected]
RADIO CONTROL HELICOPTERS
The YS .91 in a Vigor CS, showing the stock YS head. The fan
shroud is removed in preparation for the modification.
Shown is the ViperHead compared to the stock YS head. The shim that comes with the
dual-plug ViperHead for the YS .91 engine is thinner than a stock shim.
In combustion-chamber view of ViperHead (left) and stock YS .91 head, notice offset
location for main plug and extreme angle for secondary plug.
Nice marking on the ViperHead! Each head is serialized. The
ViperHead has more cooling area than a stock YS .91.
cycling during the winter months. It won’t
guarantee a failure-free season, but it’s
better than doing nothing.
There are several good battery cyclers
out there. I used an ACE Digipace for many
years; that’s what we used at the shop. It
discharged at roughly a 500 mA rate and
then charged again at the C/10 rate. It also
had an auto-trickle rate for pain-free cycling.
I used the FMA Direct Supernova 250S
(from www.fmadirect.com) most recently,
and it is my current favorite.
I have an even better suggestion: if the
battery is more than three years old, replace
it! Helicopters are expensive and batteries
are cheap.
I recently had the opportunity to fly with a
ViperHead-equipped YS .91 engine installed
in a Vigor CS helicopter. Ray Stacy of
Performance Hobbies (Webster, New York)
just started getting ViperHeads in stock.
This is a result of Curtis Youngblood’s visit
and his success with it.
We decided to make a head swap in
Ray’s Vigor CS and compare the power and
flying characteristics before and after. The
day we picked for the experiment was nice;
the temperature was in the 70s with low
humidity (which is unusual in this area), so
we weren’t unduly influencing the test with
extreme weather conditions. The engine was
tuned correctly for the conditions.
The YS .91 had a Youngblood Muscle
Pipe II for exhaust, and we were using
Morgan Cool Power 30%-nitromethane
March 2004 141
ViperHead-equipped YS .91 is installed in the Vigor CS. Notice
the modified plug cutout to accommodate both plugs.
Kyle Stacy (who just turned 8), with his proud dad Ray, is an
accomplished helicopter and fixed-wing-model pilot.
helicopter fuel. Ray had modified the
cooling shroud to accommodate the glowplug
location(s) on the ViperHead.
Each of us made a flight with the Vigor.
It’s great to be able to experiment on
someone else’s helicopter—especially when
he buys all of the parts to do the testing! We
wanted to get a good feel for the power
characteristics and especially find a point
where we could load the engine down with
a maneuver and use that as the benchmark
for the modification.
We both played around with some
maneuvers and found that a good, solid
“rainbow takeoff” (take off and climb out
with a lot of pitch while rolling to inverted,
and immediately upon flying inverted, pull
full negative pitch to do an inverted
climbout) causes a slight reduction in
engine rpm.
It was subtle since there was tremendous
power coming from the YS .91. Bogging
from a maneuver with this engine usually
means that you’ve done something wrong or
are doing something more extreme than I’m
capable of right now.
I proceeded to do the changeover to the
ViperHead. I was able to gain good access
to the head without dropping the engine. We
just removed the fan shroud, and all of the
head bolts were accessible from the rear of
the model.
142 MODEL AVIATION
When we removed the head, I noticed a
distinct odor of cotton candy. Apparently
someone had put some cotton candy fuel
fragrance in Ray’s fuel. I don’t know what
that stuff is made from, but I don’t think I
want it in my fuel.
The shim that comes with the ViperHead
is slightly thinner than the stock YS shim. I
don’t know if the new shim and the
ViperHead would raise or lower the
compression ratio, but I followed the
instructions and used the shim that came
with the head.
I spoke with James O’Neals after our
initial testing, and he said that the required
shim thickness might vary with the type of
fuel, engine, and age of the engine. We may
have to experiment with the shims,
depending on the situation.
When we closely examined the
ViperHead, we noticed some unique
characteristics. The combustion chamber
appears similar in shape to the stock head
(well, sort of; it was basically round).
There are two glow-plug locations on the
head. The normal center-located (main)
glow-plug hole is moved slightly forward
toward the front of the engine. It’s not in the
center of the combustion-chamber dome.
This is the reason why the fan shroud had to
be slightly modified.
The second glow-plug location is quite a
bit to the rear of center and is tipped toward
the rear at quite an angle. This doesn’t pose
a problem for access in the Vigor because
the rear skid mount is not in the way. I
imagine that the glow-plug location in some
helicopters could cause accessibility
problems.
The instructions recommend using a cool
plug in the main location and a hot plug in
the rearmost location. This caused quite a
search exercise in all of the flight boxes
because most fliers use O.S. #8 or Enya #3
plugs—all of the hot variety. O.S. #A-5,
Enya #4, and Enya #5 are cool plugs.
Nobody had a cool plug, so we used two
hot plugs instead (one O.S. #8 and one Enya
#3). During his visit Curtis Youngblood
commented that it didn’t seem to make
much of a difference whether a hot or cold
plug was used.
When I spoke with James O’Neals later,
he said that the cool plug/hot plug
combination is more for Fédération
Aéronautique Internationale (FAI)-style
flying and it smoothes out the hover. We ran
with what we had and buttoned things up
for a test flight. Who hovers in 3-D flying
unless you’re putting grass stains on the
blades while inverted?
After a good preflight and a refueling,
we prepared for a start. There is no need to
connect both plugs to the glow starter at the
same time for starting. The main plug can
be used for starting by itself. We hooked the
glow starter to the main plug and started the
engine. It had a completely different exhaust
note. We then touched the glow starter to
the second plug. Immediately the exhaust
note changed again and the idle rpm rose! It
had a great sound, even at idle.
At the flightline the engine spooled up
the blades with no trouble, although the
engine seemed to be running a bit richer than
before. Up in a hover, it was definitely a bit
richer but had a vastly different exhaust tone
than before the modification. It probably
could have used some needle tweaking, but
that didn’t detract from the performance so
we left it alone for the time being.
After a couple of circuits, all seemed
well. Ray launched the Vigor into a rainbow
takeoff, and as soon as it was inverted and
got negative pitch, the engine rpm went up!
It was obvious that there was much more
power available! The engine wasn’t loaded
by anything we threw at it. I’m sure someone
could have, but we didn’t. The model was
definitely peppier, the engine performance
was extremely crisp, and it was even more
responsive.
It was my turn. I haven’t flown much
with one of the 90-size big-block (rat)
engines. My machines are still outfitted with
60-size small-block (mouse) engines. I took
off and flew some circuits with the usual
airplane-type maneuvers. (I’m a wimp.) The
model was definitely more responsive. I had
to get used to the extra power that I don’t
have available with my machines, but this
was impressive!
I flipped the model inverted and took off
vertically with it, and it launched without
changing a note! I did some stationary flips
with it, and the Vigor climbed as I was doing
them. When I get one of these I’m going to
have to relearn my timing because the
response was instantaneous. It seems to
change everything for the better. With every
maneuver I did, the helicopter seemed to
dance in the sky with the extra power. I gotta
get me one of these!
All too quickly, the fuel was almost gone.
As I noted, the engine probably could have
been tweaked a little more lean and the
economy may have picked up some. I
imagine that the fuel mileage may still end
up going down a bit from this new head, but
I may be wrong. It’s too early to tell; I will
need more time (with Ray’s machine, of
course).
Since the initial testing was completed
the helicopter was tested using the
recommended hot plug/cool plug
combination. There was no noticeable
difference in performance; we’re 3-D pilots,
and we don’t end up concentrating on the
FAI maneuvers.
I highly recommend talking with James
O’Neals, especially if you’re having
difficulty getting your particular setup to run
properly. With the different kinds of fuels,
plug preferences, and various ages of engines
out there, he can help with plug and shim
combinations to get you going. He has a
wealth of knowledge to share. For more
information, contact James at OMI at (256)
776-0879 or www.oneals.com/
Viperhead.html.
In all, the ViperHead modification is a
worthwhile improvement at a reasonable
March 2004 143
cost. It definitely complements the Muscle
Pipe II, and with the gearing and setup of the
Vigor, now I understand why Curtis flies
with it and recommends it. I give it the
“Dan-o thumbs up”!
A club sent me a letter and some pictures
describing some of its activities, so next
month I’ll do a short club profile. I also got
to take a first look at the new Hirobo
Sceadu 50 EVO, so I’ll pass along some
information about that as well.
If it’s sitting on the shelf looking pretty,
it’s just getting dusty. I’ll be back next
month. MA
Edition: Model Aviation - 2004/03
Page Numbers: 140,141,142,143
Edition: Model Aviation - 2004/03
Page Numbers: 140,141,142,143
140 MODEL AVIATION
IS EVERYBODY enjoying winter? Yeah,
right! This issue will come out sometime in
January, smack in the middle of winter. I’m
writing this in October, so I have no idea
how the winter is going to shape up. I do
know one thing: there’s not much outdoor
helicopter flying going on in February and
March in the North.
Now is a good time to think about getting
radios out for repair and tuning. I used to
work for a small Radio Control radio-repair
shop, and I know for a fact that people don’t
think about getting their equipment tuned
right now. The first warm day in spring or
late winter usually brings them out in
droves. The backlog goes out several
months. If you don’t want to get caught up
in the rush, do it now!
Earlier this year I took my Intrepid 46
out for a spin. I hadn’t touched it in quite
awhile. Sure, I did the once-over with the
mechanics and I had freshly charged the
batteries (Ni-Cds). After approximately 30
seconds into the flight, things started to go
wrong. I was getting tail-rotor twitching, and
then the engine was going to idle. It was
going into “fail-safe.”
I still had enough control to auto the
helicopter and shut off the engine. I went
over and moved the controls and was getting
sluggish response. I checked the battery
pack and, lo and behold, it had lost a cell.
That was close!
I went home and cycled all of the
installed batteries in my shop. I also found a
failed cell in one of my 9Z transmitters. The
moral of that story is, Do some battery
Dan Williams, 27 Treeline Dr., Liverpool NY 13090; E-mail: [email protected]
RADIO CONTROL HELICOPTERS
The YS .91 in a Vigor CS, showing the stock YS head. The fan
shroud is removed in preparation for the modification.
Shown is the ViperHead compared to the stock YS head. The shim that comes with the
dual-plug ViperHead for the YS .91 engine is thinner than a stock shim.
In combustion-chamber view of ViperHead (left) and stock YS .91 head, notice offset
location for main plug and extreme angle for secondary plug.
Nice marking on the ViperHead! Each head is serialized. The
ViperHead has more cooling area than a stock YS .91.
cycling during the winter months. It won’t
guarantee a failure-free season, but it’s
better than doing nothing.
There are several good battery cyclers
out there. I used an ACE Digipace for many
years; that’s what we used at the shop. It
discharged at roughly a 500 mA rate and
then charged again at the C/10 rate. It also
had an auto-trickle rate for pain-free cycling.
I used the FMA Direct Supernova 250S
(from www.fmadirect.com) most recently,
and it is my current favorite.
I have an even better suggestion: if the
battery is more than three years old, replace
it! Helicopters are expensive and batteries
are cheap.
I recently had the opportunity to fly with a
ViperHead-equipped YS .91 engine installed
in a Vigor CS helicopter. Ray Stacy of
Performance Hobbies (Webster, New York)
just started getting ViperHeads in stock.
This is a result of Curtis Youngblood’s visit
and his success with it.
We decided to make a head swap in
Ray’s Vigor CS and compare the power and
flying characteristics before and after. The
day we picked for the experiment was nice;
the temperature was in the 70s with low
humidity (which is unusual in this area), so
we weren’t unduly influencing the test with
extreme weather conditions. The engine was
tuned correctly for the conditions.
The YS .91 had a Youngblood Muscle
Pipe II for exhaust, and we were using
Morgan Cool Power 30%-nitromethane
March 2004 141
ViperHead-equipped YS .91 is installed in the Vigor CS. Notice
the modified plug cutout to accommodate both plugs.
Kyle Stacy (who just turned 8), with his proud dad Ray, is an
accomplished helicopter and fixed-wing-model pilot.
helicopter fuel. Ray had modified the
cooling shroud to accommodate the glowplug
location(s) on the ViperHead.
Each of us made a flight with the Vigor.
It’s great to be able to experiment on
someone else’s helicopter—especially when
he buys all of the parts to do the testing! We
wanted to get a good feel for the power
characteristics and especially find a point
where we could load the engine down with
a maneuver and use that as the benchmark
for the modification.
We both played around with some
maneuvers and found that a good, solid
“rainbow takeoff” (take off and climb out
with a lot of pitch while rolling to inverted,
and immediately upon flying inverted, pull
full negative pitch to do an inverted
climbout) causes a slight reduction in
engine rpm.
It was subtle since there was tremendous
power coming from the YS .91. Bogging
from a maneuver with this engine usually
means that you’ve done something wrong or
are doing something more extreme than I’m
capable of right now.
I proceeded to do the changeover to the
ViperHead. I was able to gain good access
to the head without dropping the engine. We
just removed the fan shroud, and all of the
head bolts were accessible from the rear of
the model.
142 MODEL AVIATION
When we removed the head, I noticed a
distinct odor of cotton candy. Apparently
someone had put some cotton candy fuel
fragrance in Ray’s fuel. I don’t know what
that stuff is made from, but I don’t think I
want it in my fuel.
The shim that comes with the ViperHead
is slightly thinner than the stock YS shim. I
don’t know if the new shim and the
ViperHead would raise or lower the
compression ratio, but I followed the
instructions and used the shim that came
with the head.
I spoke with James O’Neals after our
initial testing, and he said that the required
shim thickness might vary with the type of
fuel, engine, and age of the engine. We may
have to experiment with the shims,
depending on the situation.
When we closely examined the
ViperHead, we noticed some unique
characteristics. The combustion chamber
appears similar in shape to the stock head
(well, sort of; it was basically round).
There are two glow-plug locations on the
head. The normal center-located (main)
glow-plug hole is moved slightly forward
toward the front of the engine. It’s not in the
center of the combustion-chamber dome.
This is the reason why the fan shroud had to
be slightly modified.
The second glow-plug location is quite a
bit to the rear of center and is tipped toward
the rear at quite an angle. This doesn’t pose
a problem for access in the Vigor because
the rear skid mount is not in the way. I
imagine that the glow-plug location in some
helicopters could cause accessibility
problems.
The instructions recommend using a cool
plug in the main location and a hot plug in
the rearmost location. This caused quite a
search exercise in all of the flight boxes
because most fliers use O.S. #8 or Enya #3
plugs—all of the hot variety. O.S. #A-5,
Enya #4, and Enya #5 are cool plugs.
Nobody had a cool plug, so we used two
hot plugs instead (one O.S. #8 and one Enya
#3). During his visit Curtis Youngblood
commented that it didn’t seem to make
much of a difference whether a hot or cold
plug was used.
When I spoke with James O’Neals later,
he said that the cool plug/hot plug
combination is more for Fédération
Aéronautique Internationale (FAI)-style
flying and it smoothes out the hover. We ran
with what we had and buttoned things up
for a test flight. Who hovers in 3-D flying
unless you’re putting grass stains on the
blades while inverted?
After a good preflight and a refueling,
we prepared for a start. There is no need to
connect both plugs to the glow starter at the
same time for starting. The main plug can
be used for starting by itself. We hooked the
glow starter to the main plug and started the
engine. It had a completely different exhaust
note. We then touched the glow starter to
the second plug. Immediately the exhaust
note changed again and the idle rpm rose! It
had a great sound, even at idle.
At the flightline the engine spooled up
the blades with no trouble, although the
engine seemed to be running a bit richer than
before. Up in a hover, it was definitely a bit
richer but had a vastly different exhaust tone
than before the modification. It probably
could have used some needle tweaking, but
that didn’t detract from the performance so
we left it alone for the time being.
After a couple of circuits, all seemed
well. Ray launched the Vigor into a rainbow
takeoff, and as soon as it was inverted and
got negative pitch, the engine rpm went up!
It was obvious that there was much more
power available! The engine wasn’t loaded
by anything we threw at it. I’m sure someone
could have, but we didn’t. The model was
definitely peppier, the engine performance
was extremely crisp, and it was even more
responsive.
It was my turn. I haven’t flown much
with one of the 90-size big-block (rat)
engines. My machines are still outfitted with
60-size small-block (mouse) engines. I took
off and flew some circuits with the usual
airplane-type maneuvers. (I’m a wimp.) The
model was definitely more responsive. I had
to get used to the extra power that I don’t
have available with my machines, but this
was impressive!
I flipped the model inverted and took off
vertically with it, and it launched without
changing a note! I did some stationary flips
with it, and the Vigor climbed as I was doing
them. When I get one of these I’m going to
have to relearn my timing because the
response was instantaneous. It seems to
change everything for the better. With every
maneuver I did, the helicopter seemed to
dance in the sky with the extra power. I gotta
get me one of these!
All too quickly, the fuel was almost gone.
As I noted, the engine probably could have
been tweaked a little more lean and the
economy may have picked up some. I
imagine that the fuel mileage may still end
up going down a bit from this new head, but
I may be wrong. It’s too early to tell; I will
need more time (with Ray’s machine, of
course).
Since the initial testing was completed
the helicopter was tested using the
recommended hot plug/cool plug
combination. There was no noticeable
difference in performance; we’re 3-D pilots,
and we don’t end up concentrating on the
FAI maneuvers.
I highly recommend talking with James
O’Neals, especially if you’re having
difficulty getting your particular setup to run
properly. With the different kinds of fuels,
plug preferences, and various ages of engines
out there, he can help with plug and shim
combinations to get you going. He has a
wealth of knowledge to share. For more
information, contact James at OMI at (256)
776-0879 or www.oneals.com/
Viperhead.html.
In all, the ViperHead modification is a
worthwhile improvement at a reasonable
March 2004 143
cost. It definitely complements the Muscle
Pipe II, and with the gearing and setup of the
Vigor, now I understand why Curtis flies
with it and recommends it. I give it the
“Dan-o thumbs up”!
A club sent me a letter and some pictures
describing some of its activities, so next
month I’ll do a short club profile. I also got
to take a first look at the new Hirobo
Sceadu 50 EVO, so I’ll pass along some
information about that as well.
If it’s sitting on the shelf looking pretty,
it’s just getting dusty. I’ll be back next
month. MA
Edition: Model Aviation - 2004/03
Page Numbers: 140,141,142,143
140 MODEL AVIATION
IS EVERYBODY enjoying winter? Yeah,
right! This issue will come out sometime in
January, smack in the middle of winter. I’m
writing this in October, so I have no idea
how the winter is going to shape up. I do
know one thing: there’s not much outdoor
helicopter flying going on in February and
March in the North.
Now is a good time to think about getting
radios out for repair and tuning. I used to
work for a small Radio Control radio-repair
shop, and I know for a fact that people don’t
think about getting their equipment tuned
right now. The first warm day in spring or
late winter usually brings them out in
droves. The backlog goes out several
months. If you don’t want to get caught up
in the rush, do it now!
Earlier this year I took my Intrepid 46
out for a spin. I hadn’t touched it in quite
awhile. Sure, I did the once-over with the
mechanics and I had freshly charged the
batteries (Ni-Cds). After approximately 30
seconds into the flight, things started to go
wrong. I was getting tail-rotor twitching, and
then the engine was going to idle. It was
going into “fail-safe.”
I still had enough control to auto the
helicopter and shut off the engine. I went
over and moved the controls and was getting
sluggish response. I checked the battery
pack and, lo and behold, it had lost a cell.
That was close!
I went home and cycled all of the
installed batteries in my shop. I also found a
failed cell in one of my 9Z transmitters. The
moral of that story is, Do some battery
Dan Williams, 27 Treeline Dr., Liverpool NY 13090; E-mail: [email protected]
RADIO CONTROL HELICOPTERS
The YS .91 in a Vigor CS, showing the stock YS head. The fan
shroud is removed in preparation for the modification.
Shown is the ViperHead compared to the stock YS head. The shim that comes with the
dual-plug ViperHead for the YS .91 engine is thinner than a stock shim.
In combustion-chamber view of ViperHead (left) and stock YS .91 head, notice offset
location for main plug and extreme angle for secondary plug.
Nice marking on the ViperHead! Each head is serialized. The
ViperHead has more cooling area than a stock YS .91.
cycling during the winter months. It won’t
guarantee a failure-free season, but it’s
better than doing nothing.
There are several good battery cyclers
out there. I used an ACE Digipace for many
years; that’s what we used at the shop. It
discharged at roughly a 500 mA rate and
then charged again at the C/10 rate. It also
had an auto-trickle rate for pain-free cycling.
I used the FMA Direct Supernova 250S
(from www.fmadirect.com) most recently,
and it is my current favorite.
I have an even better suggestion: if the
battery is more than three years old, replace
it! Helicopters are expensive and batteries
are cheap.
I recently had the opportunity to fly with a
ViperHead-equipped YS .91 engine installed
in a Vigor CS helicopter. Ray Stacy of
Performance Hobbies (Webster, New York)
just started getting ViperHeads in stock.
This is a result of Curtis Youngblood’s visit
and his success with it.
We decided to make a head swap in
Ray’s Vigor CS and compare the power and
flying characteristics before and after. The
day we picked for the experiment was nice;
the temperature was in the 70s with low
humidity (which is unusual in this area), so
we weren’t unduly influencing the test with
extreme weather conditions. The engine was
tuned correctly for the conditions.
The YS .91 had a Youngblood Muscle
Pipe II for exhaust, and we were using
Morgan Cool Power 30%-nitromethane
March 2004 141
ViperHead-equipped YS .91 is installed in the Vigor CS. Notice
the modified plug cutout to accommodate both plugs.
Kyle Stacy (who just turned 8), with his proud dad Ray, is an
accomplished helicopter and fixed-wing-model pilot.
helicopter fuel. Ray had modified the
cooling shroud to accommodate the glowplug
location(s) on the ViperHead.
Each of us made a flight with the Vigor.
It’s great to be able to experiment on
someone else’s helicopter—especially when
he buys all of the parts to do the testing! We
wanted to get a good feel for the power
characteristics and especially find a point
where we could load the engine down with
a maneuver and use that as the benchmark
for the modification.
We both played around with some
maneuvers and found that a good, solid
“rainbow takeoff” (take off and climb out
with a lot of pitch while rolling to inverted,
and immediately upon flying inverted, pull
full negative pitch to do an inverted
climbout) causes a slight reduction in
engine rpm.
It was subtle since there was tremendous
power coming from the YS .91. Bogging
from a maneuver with this engine usually
means that you’ve done something wrong or
are doing something more extreme than I’m
capable of right now.
I proceeded to do the changeover to the
ViperHead. I was able to gain good access
to the head without dropping the engine. We
just removed the fan shroud, and all of the
head bolts were accessible from the rear of
the model.
142 MODEL AVIATION
When we removed the head, I noticed a
distinct odor of cotton candy. Apparently
someone had put some cotton candy fuel
fragrance in Ray’s fuel. I don’t know what
that stuff is made from, but I don’t think I
want it in my fuel.
The shim that comes with the ViperHead
is slightly thinner than the stock YS shim. I
don’t know if the new shim and the
ViperHead would raise or lower the
compression ratio, but I followed the
instructions and used the shim that came
with the head.
I spoke with James O’Neals after our
initial testing, and he said that the required
shim thickness might vary with the type of
fuel, engine, and age of the engine. We may
have to experiment with the shims,
depending on the situation.
When we closely examined the
ViperHead, we noticed some unique
characteristics. The combustion chamber
appears similar in shape to the stock head
(well, sort of; it was basically round).
There are two glow-plug locations on the
head. The normal center-located (main)
glow-plug hole is moved slightly forward
toward the front of the engine. It’s not in the
center of the combustion-chamber dome.
This is the reason why the fan shroud had to
be slightly modified.
The second glow-plug location is quite a
bit to the rear of center and is tipped toward
the rear at quite an angle. This doesn’t pose
a problem for access in the Vigor because
the rear skid mount is not in the way. I
imagine that the glow-plug location in some
helicopters could cause accessibility
problems.
The instructions recommend using a cool
plug in the main location and a hot plug in
the rearmost location. This caused quite a
search exercise in all of the flight boxes
because most fliers use O.S. #8 or Enya #3
plugs—all of the hot variety. O.S. #A-5,
Enya #4, and Enya #5 are cool plugs.
Nobody had a cool plug, so we used two
hot plugs instead (one O.S. #8 and one Enya
#3). During his visit Curtis Youngblood
commented that it didn’t seem to make
much of a difference whether a hot or cold
plug was used.
When I spoke with James O’Neals later,
he said that the cool plug/hot plug
combination is more for Fédération
Aéronautique Internationale (FAI)-style
flying and it smoothes out the hover. We ran
with what we had and buttoned things up
for a test flight. Who hovers in 3-D flying
unless you’re putting grass stains on the
blades while inverted?
After a good preflight and a refueling,
we prepared for a start. There is no need to
connect both plugs to the glow starter at the
same time for starting. The main plug can
be used for starting by itself. We hooked the
glow starter to the main plug and started the
engine. It had a completely different exhaust
note. We then touched the glow starter to
the second plug. Immediately the exhaust
note changed again and the idle rpm rose! It
had a great sound, even at idle.
At the flightline the engine spooled up
the blades with no trouble, although the
engine seemed to be running a bit richer than
before. Up in a hover, it was definitely a bit
richer but had a vastly different exhaust tone
than before the modification. It probably
could have used some needle tweaking, but
that didn’t detract from the performance so
we left it alone for the time being.
After a couple of circuits, all seemed
well. Ray launched the Vigor into a rainbow
takeoff, and as soon as it was inverted and
got negative pitch, the engine rpm went up!
It was obvious that there was much more
power available! The engine wasn’t loaded
by anything we threw at it. I’m sure someone
could have, but we didn’t. The model was
definitely peppier, the engine performance
was extremely crisp, and it was even more
responsive.
It was my turn. I haven’t flown much
with one of the 90-size big-block (rat)
engines. My machines are still outfitted with
60-size small-block (mouse) engines. I took
off and flew some circuits with the usual
airplane-type maneuvers. (I’m a wimp.) The
model was definitely more responsive. I had
to get used to the extra power that I don’t
have available with my machines, but this
was impressive!
I flipped the model inverted and took off
vertically with it, and it launched without
changing a note! I did some stationary flips
with it, and the Vigor climbed as I was doing
them. When I get one of these I’m going to
have to relearn my timing because the
response was instantaneous. It seems to
change everything for the better. With every
maneuver I did, the helicopter seemed to
dance in the sky with the extra power. I gotta
get me one of these!
All too quickly, the fuel was almost gone.
As I noted, the engine probably could have
been tweaked a little more lean and the
economy may have picked up some. I
imagine that the fuel mileage may still end
up going down a bit from this new head, but
I may be wrong. It’s too early to tell; I will
need more time (with Ray’s machine, of
course).
Since the initial testing was completed
the helicopter was tested using the
recommended hot plug/cool plug
combination. There was no noticeable
difference in performance; we’re 3-D pilots,
and we don’t end up concentrating on the
FAI maneuvers.
I highly recommend talking with James
O’Neals, especially if you’re having
difficulty getting your particular setup to run
properly. With the different kinds of fuels,
plug preferences, and various ages of engines
out there, he can help with plug and shim
combinations to get you going. He has a
wealth of knowledge to share. For more
information, contact James at OMI at (256)
776-0879 or www.oneals.com/
Viperhead.html.
In all, the ViperHead modification is a
worthwhile improvement at a reasonable
March 2004 143
cost. It definitely complements the Muscle
Pipe II, and with the gearing and setup of the
Vigor, now I understand why Curtis flies
with it and recommends it. I give it the
“Dan-o thumbs up”!
A club sent me a letter and some pictures
describing some of its activities, so next
month I’ll do a short club profile. I also got
to take a first look at the new Hirobo
Sceadu 50 EVO, so I’ll pass along some
information about that as well.
If it’s sitting on the shelf looking pretty,
it’s just getting dusty. I’ll be back next
month. MA
Edition: Model Aviation - 2004/03
Page Numbers: 140,141,142,143
140 MODEL AVIATION
IS EVERYBODY enjoying winter? Yeah,
right! This issue will come out sometime in
January, smack in the middle of winter. I’m
writing this in October, so I have no idea
how the winter is going to shape up. I do
know one thing: there’s not much outdoor
helicopter flying going on in February and
March in the North.
Now is a good time to think about getting
radios out for repair and tuning. I used to
work for a small Radio Control radio-repair
shop, and I know for a fact that people don’t
think about getting their equipment tuned
right now. The first warm day in spring or
late winter usually brings them out in
droves. The backlog goes out several
months. If you don’t want to get caught up
in the rush, do it now!
Earlier this year I took my Intrepid 46
out for a spin. I hadn’t touched it in quite
awhile. Sure, I did the once-over with the
mechanics and I had freshly charged the
batteries (Ni-Cds). After approximately 30
seconds into the flight, things started to go
wrong. I was getting tail-rotor twitching, and
then the engine was going to idle. It was
going into “fail-safe.”
I still had enough control to auto the
helicopter and shut off the engine. I went
over and moved the controls and was getting
sluggish response. I checked the battery
pack and, lo and behold, it had lost a cell.
That was close!
I went home and cycled all of the
installed batteries in my shop. I also found a
failed cell in one of my 9Z transmitters. The
moral of that story is, Do some battery
Dan Williams, 27 Treeline Dr., Liverpool NY 13090; E-mail: [email protected]
RADIO CONTROL HELICOPTERS
The YS .91 in a Vigor CS, showing the stock YS head. The fan
shroud is removed in preparation for the modification.
Shown is the ViperHead compared to the stock YS head. The shim that comes with the
dual-plug ViperHead for the YS .91 engine is thinner than a stock shim.
In combustion-chamber view of ViperHead (left) and stock YS .91 head, notice offset
location for main plug and extreme angle for secondary plug.
Nice marking on the ViperHead! Each head is serialized. The
ViperHead has more cooling area than a stock YS .91.
cycling during the winter months. It won’t
guarantee a failure-free season, but it’s
better than doing nothing.
There are several good battery cyclers
out there. I used an ACE Digipace for many
years; that’s what we used at the shop. It
discharged at roughly a 500 mA rate and
then charged again at the C/10 rate. It also
had an auto-trickle rate for pain-free cycling.
I used the FMA Direct Supernova 250S
(from www.fmadirect.com) most recently,
and it is my current favorite.
I have an even better suggestion: if the
battery is more than three years old, replace
it! Helicopters are expensive and batteries
are cheap.
I recently had the opportunity to fly with a
ViperHead-equipped YS .91 engine installed
in a Vigor CS helicopter. Ray Stacy of
Performance Hobbies (Webster, New York)
just started getting ViperHeads in stock.
This is a result of Curtis Youngblood’s visit
and his success with it.
We decided to make a head swap in
Ray’s Vigor CS and compare the power and
flying characteristics before and after. The
day we picked for the experiment was nice;
the temperature was in the 70s with low
humidity (which is unusual in this area), so
we weren’t unduly influencing the test with
extreme weather conditions. The engine was
tuned correctly for the conditions.
The YS .91 had a Youngblood Muscle
Pipe II for exhaust, and we were using
Morgan Cool Power 30%-nitromethane
March 2004 141
ViperHead-equipped YS .91 is installed in the Vigor CS. Notice
the modified plug cutout to accommodate both plugs.
Kyle Stacy (who just turned 8), with his proud dad Ray, is an
accomplished helicopter and fixed-wing-model pilot.
helicopter fuel. Ray had modified the
cooling shroud to accommodate the glowplug
location(s) on the ViperHead.
Each of us made a flight with the Vigor.
It’s great to be able to experiment on
someone else’s helicopter—especially when
he buys all of the parts to do the testing! We
wanted to get a good feel for the power
characteristics and especially find a point
where we could load the engine down with
a maneuver and use that as the benchmark
for the modification.
We both played around with some
maneuvers and found that a good, solid
“rainbow takeoff” (take off and climb out
with a lot of pitch while rolling to inverted,
and immediately upon flying inverted, pull
full negative pitch to do an inverted
climbout) causes a slight reduction in
engine rpm.
It was subtle since there was tremendous
power coming from the YS .91. Bogging
from a maneuver with this engine usually
means that you’ve done something wrong or
are doing something more extreme than I’m
capable of right now.
I proceeded to do the changeover to the
ViperHead. I was able to gain good access
to the head without dropping the engine. We
just removed the fan shroud, and all of the
head bolts were accessible from the rear of
the model.
142 MODEL AVIATION
When we removed the head, I noticed a
distinct odor of cotton candy. Apparently
someone had put some cotton candy fuel
fragrance in Ray’s fuel. I don’t know what
that stuff is made from, but I don’t think I
want it in my fuel.
The shim that comes with the ViperHead
is slightly thinner than the stock YS shim. I
don’t know if the new shim and the
ViperHead would raise or lower the
compression ratio, but I followed the
instructions and used the shim that came
with the head.
I spoke with James O’Neals after our
initial testing, and he said that the required
shim thickness might vary with the type of
fuel, engine, and age of the engine. We may
have to experiment with the shims,
depending on the situation.
When we closely examined the
ViperHead, we noticed some unique
characteristics. The combustion chamber
appears similar in shape to the stock head
(well, sort of; it was basically round).
There are two glow-plug locations on the
head. The normal center-located (main)
glow-plug hole is moved slightly forward
toward the front of the engine. It’s not in the
center of the combustion-chamber dome.
This is the reason why the fan shroud had to
be slightly modified.
The second glow-plug location is quite a
bit to the rear of center and is tipped toward
the rear at quite an angle. This doesn’t pose
a problem for access in the Vigor because
the rear skid mount is not in the way. I
imagine that the glow-plug location in some
helicopters could cause accessibility
problems.
The instructions recommend using a cool
plug in the main location and a hot plug in
the rearmost location. This caused quite a
search exercise in all of the flight boxes
because most fliers use O.S. #8 or Enya #3
plugs—all of the hot variety. O.S. #A-5,
Enya #4, and Enya #5 are cool plugs.
Nobody had a cool plug, so we used two
hot plugs instead (one O.S. #8 and one Enya
#3). During his visit Curtis Youngblood
commented that it didn’t seem to make
much of a difference whether a hot or cold
plug was used.
When I spoke with James O’Neals later,
he said that the cool plug/hot plug
combination is more for Fédération
Aéronautique Internationale (FAI)-style
flying and it smoothes out the hover. We ran
with what we had and buttoned things up
for a test flight. Who hovers in 3-D flying
unless you’re putting grass stains on the
blades while inverted?
After a good preflight and a refueling,
we prepared for a start. There is no need to
connect both plugs to the glow starter at the
same time for starting. The main plug can
be used for starting by itself. We hooked the
glow starter to the main plug and started the
engine. It had a completely different exhaust
note. We then touched the glow starter to
the second plug. Immediately the exhaust
note changed again and the idle rpm rose! It
had a great sound, even at idle.
At the flightline the engine spooled up
the blades with no trouble, although the
engine seemed to be running a bit richer than
before. Up in a hover, it was definitely a bit
richer but had a vastly different exhaust tone
than before the modification. It probably
could have used some needle tweaking, but
that didn’t detract from the performance so
we left it alone for the time being.
After a couple of circuits, all seemed
well. Ray launched the Vigor into a rainbow
takeoff, and as soon as it was inverted and
got negative pitch, the engine rpm went up!
It was obvious that there was much more
power available! The engine wasn’t loaded
by anything we threw at it. I’m sure someone
could have, but we didn’t. The model was
definitely peppier, the engine performance
was extremely crisp, and it was even more
responsive.
It was my turn. I haven’t flown much
with one of the 90-size big-block (rat)
engines. My machines are still outfitted with
60-size small-block (mouse) engines. I took
off and flew some circuits with the usual
airplane-type maneuvers. (I’m a wimp.) The
model was definitely more responsive. I had
to get used to the extra power that I don’t
have available with my machines, but this
was impressive!
I flipped the model inverted and took off
vertically with it, and it launched without
changing a note! I did some stationary flips
with it, and the Vigor climbed as I was doing
them. When I get one of these I’m going to
have to relearn my timing because the
response was instantaneous. It seems to
change everything for the better. With every
maneuver I did, the helicopter seemed to
dance in the sky with the extra power. I gotta
get me one of these!
All too quickly, the fuel was almost gone.
As I noted, the engine probably could have
been tweaked a little more lean and the
economy may have picked up some. I
imagine that the fuel mileage may still end
up going down a bit from this new head, but
I may be wrong. It’s too early to tell; I will
need more time (with Ray’s machine, of
course).
Since the initial testing was completed
the helicopter was tested using the
recommended hot plug/cool plug
combination. There was no noticeable
difference in performance; we’re 3-D pilots,
and we don’t end up concentrating on the
FAI maneuvers.
I highly recommend talking with James
O’Neals, especially if you’re having
difficulty getting your particular setup to run
properly. With the different kinds of fuels,
plug preferences, and various ages of engines
out there, he can help with plug and shim
combinations to get you going. He has a
wealth of knowledge to share. For more
information, contact James at OMI at (256)
776-0879 or www.oneals.com/
Viperhead.html.
In all, the ViperHead modification is a
worthwhile improvement at a reasonable
March 2004 143
cost. It definitely complements the Muscle
Pipe II, and with the gearing and setup of the
Vigor, now I understand why Curtis flies
with it and recommends it. I give it the
“Dan-o thumbs up”!
A club sent me a letter and some pictures
describing some of its activities, so next
month I’ll do a short club profile. I also got
to take a first look at the new Hirobo
Sceadu 50 EVO, so I’ll pass along some
information about that as well.
If it’s sitting on the shelf looking pretty,
it’s just getting dusty. I’ll be back next
month. MA
