January 2004 65
NEW AND TRULY practicable advances in model-airplane engines
don’t come along often. Some major advances I remember are when
model “diesels” were developed in Europe during the World War II
years, when the glow plug came out in 1948, and when the first 1⁄2A
engines came out the year after that.
In the half century since then we’ve seen significant detail
improvements in model-engine design, such as mufflers, Radio
Control (RC) carburetors, and ABC (aluminum brass chrome)
construction, but nothing especially radical and practical. (The Wankel
was radical all right, and possibly practical, but it never became
popular.)
However, the recent British-made RCV engines are a major
departure from general practice. Calling the RCVs “revolutionary” is
an obvious pun because they’re four-stroke engines that use rotating
cylinder sleeves instead of poppet valves to open and close their intake
and exhaust ports. (RCV stands for Rotary Cylinder Valve.)
Earlier RCV engines used the rotary cylinder itself to drive the
propeller. This had the advantage of a small frontal area since the
cylinder axis—located fore and aft—was also the engine’s thrustline.
But that design had the disadvantage of being, in effect, geared down
2:1. That “in turn” (another pun I couldn’t resist) required largediameter,
high-pitch propellers.
The new-this-year RCV58-CD is different! Externally it looks
conventional enough, with its cylinder vertical and its propeller drive
via the crankshaft. (“CD” stands for crankshaft drive.) But it’s far
shorter than any other four-stroke engine of similar displacement; it’s
even shorter than most two-stroke .60s! (Comparing the RCV58-CD
with a two-stroke .60 another way, an O.S. .60 FP weighs 24 ounces;
the RCV weighs only 19.)
The RCV58-CD’s beam-mounting width (11⁄2 inches) is also less
than that of most two-stroke .60s. But the length of its mounting
lugs—almost 2 inches—means that it wouldn’t fit any of my test-stand
mounts. However, I made a pair of sheet-aluminum “extension wings”
to adapt the RCV58 to my PSP Engine Break-in Stand. Bolted firmly
to the RCV’s mounting lugs, these wings solved the test-stand problem
nicely.
One further test-mount modification proved necessary. I had to
Joe Wagner
T h e E n g i n e S h o p
212 S. Pine Ave., Ozark AL 36360
This RCV58-CD offers much more than a different look for fourstroke
model-engine design.
The RCV’s compactness is evident when placed next to the
author’s two-stroke O.S. Max .61 FP.
Only the long extension of its muffler mars the sleek contours of
the RCV58-CD engine.
RCV on the test stand; notice the raised fuel tank position. The
acorn propeller nut isn’t an RCV part.
01sig3.QXD 10/27/03 9:52 am Page 65
66 MODEL AVIATION
raise the height of the PSP’s fuel tank 13⁄8
inches before I could start the RCV58. (With
only one intake stroke in two revolutions of
the propeller, single-cylinder four-stroke
model engines lack the strong fuel suction of
two-strokes.)
However, installation of the RCV58 in an
airplane won’t present fuel-tank-location
difficulties. “Standard procedures” will put
the model’s tank at the proper height.
Following is how the RCV58-CD works.
It has a bevel gear on the crankshaft just
ahead of the crank web. This meshes with
another bevel gear on the base of the cylinder
sleeve. As the crankshaft turns (and drives the
propeller), the cylinder sleeve rotates—at half
the shaft speed.
The top of the RCV’s cylinder sleeve has a
smaller-diameter protrusion. This contains the
combustion chamber and a radial passageway.
As the cylinder rotates, this passageway aligns
with the intake port, then the glow plug, then
the exhaust port.
This unusual engine design presents four
distinct advantages compared to poppet-valve
types. First, its simplicity eliminates pushrods,
cam followers, rocker arms, springs, valves,
and valve guides. In fact, the only
reciprocating part in the RCV58 is its piston
assembly.
Second, since the RCV has no valve
springs, the “valve crash” speed limitation of
poppet-valve four-stroke engines doesn’t
apply.
Third, the cylinder’s intake and exhaustport
gas flow benefit greatly from their large,
unobstructed, almost straight-through
passageways.
Fourth, the RCV’s massive design and its
lack of “fiddly bits” make it quite resistant to
damage from “unplanned landings.”
The RCV58-CD comes with an exploded
parts diagram (which shows everything
numbered, but nothing is named) and an
eight-page manual containing all of the breakin
and operating instructions. Since this
radical engine was so new to me, I followed
the manual’s directions meticulously. They
worked for me!
The RCV58 requires somewhat special
fuel with limited castor content. Wildcat Fuel
makes a blend specifically for these power
plants. Since my local hobby shops didn’t
carry Wildcat-brand fuel, I settled on
Morgan’s Omega 10%-nitromethane blend. It
contains 17% oil, of which 12% is synthetic
and 5% castor. That meets the RCV58-CD’s
fuel specifications.
The RCV manual proved especially
helpful to me in setting the carburetor’s two
needles. They required careful adjustment to
achieve optimum idling and full power. After
approximately an hour’s break-in and some
judicious needle tweaking, my RCV58 turned
a 12 x 6 Master Airscrew at just more than
10,000 rpm, with a reliable idle at 2,200.
Starting the RCV was easy enough once I
learned that the engine preferred “wet
choking”: two through-compression flips
while a finger seals off the carburetor’s intake
opening. After that, a mere touch of the starter
set the RCV58 going.
On the underside of the RCV58’s main
bearing housing is a tube fitting that is larger
than either the carburetor fuel-line nipple or
the muffler pressure port; this is the
crankcase breather. Although the RCV58
runs cleanly, with negligible oil coming from
the muffler outlet, I found that the crankcase
breather emits a considerable amount of
oil—while running and afterward.
This proves to me that the RCV’s rotating
cylinder sleeve is adequately lubricated. The
oil flowing into the case must have been
forced down between the sleeve’s outside
diameter and its mating cylinder bore during
the compression and power strokes. Its flow
path after that provides lubrication for the
gears and all three ball bearings.
When I install this extraordinary new
engine in a model, I’ll make sure to connect
a length of Tygon tubing to the crankcase
breather and out through the fuselage
bottom. That will expel the bypassed oil
overboard rather than into the engine
compartment.
As regular readers of this column probably
know, I much enjoy slaughtering “sacred
cows.” I’ve done it again—this time to the
“moisture in the glow fuel” belief.
For decades we model fliers have been
warned about the horrid effects of leaving our
glow-fuel containers open. “Methanol is
hygroscopic! It will suck water vapor out of
the atmosphere like a sponge. If you don’t
keep your glow-fuel cans sealed tightly,
water will sneak into the fuel, ruin your
engine’s performance, and cause rust inside!”
More than 10 years ago I tried to produce
rust in model-engine ball bearings by
purposely adding water to glow fuel and
splashing that onto the bearings every day or
two—for four months! I used seven brands of
fuel: Red Max, Byron, Fox, K&B,
PowerMaster, Cool Power, and Cox. In those
four months I was never able to generate a
single speck of rust in a model engine, even
with as much as 20% water added to these
fuels.
(Eventually I learned that rusting inside
model engines is caused by fuel
decomposing into acetic acid, and that is
caused by the catalytic effect of brass
components inside the fuel tank.)
But because the results seemed so
obvious, I never did investigate watercontaminated
fuel’s evil effects on modelengine
performance. I’ve done that now,
though, and I’m still surprised by what
happened.
I test-ran one of my most reliable
Control Line (CL) engines (a 1956 Johnson
.29) on 15%-nitromethane fuel (with 23%
castor-oil content; lapped-piston CL Stunt
engines need that much) with a 10 x 5
Graupner gray propeller. The results were
11,300 rpm max.
Rather than add water gradually to my
Johnson .29’s fuel and make a series of test
runs, I went whole hog. I added a full fluid
ounce of tap water to four ounces of my
stock fuel, resulting in a “fuel blend” of
20% water, 18% castor, 12% nitromethane,
and 50% methanol.
Did that make a difference to the
Johnson? Yes, it did! I had to open the
needle valve another half turn, leave the
glow-plug lighter connected for roughly 30
seconds, and flip the propeller five or six
times to start instead of the usual three. As
for speed, the Johnson spun up 11,400 rpm!
What happened? Could I have achieved a
power boost from something similar to the
“water injection” used in World War II
fighter-airplane engines?
True, my Johnson .29 has a bit higher
compression than “the average” CL engine
of its time. It’s also a lapped-piston engine,
thoroughly broken in and with minimal
internal friction. That may have made a
difference from, say, “the average” modern
RC engine.
But the intriguing fact remains that using
glow fuel containing more water than nitro,
my Johnson .29 started almost as easily as—
and ran a trifle faster than—it did 15
minutes earlier on its “usual fuel.” MA
Running steadily at 11,400 rpm, 1956 Johnson .29’s test fuel has 20% water!
01sig3.QXD 10/27/03 10:01 am Page 66
Edition: Model Aviation - 2004/01
Page Numbers: 65,66
Edition: Model Aviation - 2004/01
Page Numbers: 65,66
January 2004 65
NEW AND TRULY practicable advances in model-airplane engines
don’t come along often. Some major advances I remember are when
model “diesels” were developed in Europe during the World War II
years, when the glow plug came out in 1948, and when the first 1⁄2A
engines came out the year after that.
In the half century since then we’ve seen significant detail
improvements in model-engine design, such as mufflers, Radio
Control (RC) carburetors, and ABC (aluminum brass chrome)
construction, but nothing especially radical and practical. (The Wankel
was radical all right, and possibly practical, but it never became
popular.)
However, the recent British-made RCV engines are a major
departure from general practice. Calling the RCVs “revolutionary” is
an obvious pun because they’re four-stroke engines that use rotating
cylinder sleeves instead of poppet valves to open and close their intake
and exhaust ports. (RCV stands for Rotary Cylinder Valve.)
Earlier RCV engines used the rotary cylinder itself to drive the
propeller. This had the advantage of a small frontal area since the
cylinder axis—located fore and aft—was also the engine’s thrustline.
But that design had the disadvantage of being, in effect, geared down
2:1. That “in turn” (another pun I couldn’t resist) required largediameter,
high-pitch propellers.
The new-this-year RCV58-CD is different! Externally it looks
conventional enough, with its cylinder vertical and its propeller drive
via the crankshaft. (“CD” stands for crankshaft drive.) But it’s far
shorter than any other four-stroke engine of similar displacement; it’s
even shorter than most two-stroke .60s! (Comparing the RCV58-CD
with a two-stroke .60 another way, an O.S. .60 FP weighs 24 ounces;
the RCV weighs only 19.)
The RCV58-CD’s beam-mounting width (11⁄2 inches) is also less
than that of most two-stroke .60s. But the length of its mounting
lugs—almost 2 inches—means that it wouldn’t fit any of my test-stand
mounts. However, I made a pair of sheet-aluminum “extension wings”
to adapt the RCV58 to my PSP Engine Break-in Stand. Bolted firmly
to the RCV’s mounting lugs, these wings solved the test-stand problem
nicely.
One further test-mount modification proved necessary. I had to
Joe Wagner
T h e E n g i n e S h o p
212 S. Pine Ave., Ozark AL 36360
This RCV58-CD offers much more than a different look for fourstroke
model-engine design.
The RCV’s compactness is evident when placed next to the
author’s two-stroke O.S. Max .61 FP.
Only the long extension of its muffler mars the sleek contours of
the RCV58-CD engine.
RCV on the test stand; notice the raised fuel tank position. The
acorn propeller nut isn’t an RCV part.
01sig3.QXD 10/27/03 9:52 am Page 65
66 MODEL AVIATION
raise the height of the PSP’s fuel tank 13⁄8
inches before I could start the RCV58. (With
only one intake stroke in two revolutions of
the propeller, single-cylinder four-stroke
model engines lack the strong fuel suction of
two-strokes.)
However, installation of the RCV58 in an
airplane won’t present fuel-tank-location
difficulties. “Standard procedures” will put
the model’s tank at the proper height.
Following is how the RCV58-CD works.
It has a bevel gear on the crankshaft just
ahead of the crank web. This meshes with
another bevel gear on the base of the cylinder
sleeve. As the crankshaft turns (and drives the
propeller), the cylinder sleeve rotates—at half
the shaft speed.
The top of the RCV’s cylinder sleeve has a
smaller-diameter protrusion. This contains the
combustion chamber and a radial passageway.
As the cylinder rotates, this passageway aligns
with the intake port, then the glow plug, then
the exhaust port.
This unusual engine design presents four
distinct advantages compared to poppet-valve
types. First, its simplicity eliminates pushrods,
cam followers, rocker arms, springs, valves,
and valve guides. In fact, the only
reciprocating part in the RCV58 is its piston
assembly.
Second, since the RCV has no valve
springs, the “valve crash” speed limitation of
poppet-valve four-stroke engines doesn’t
apply.
Third, the cylinder’s intake and exhaustport
gas flow benefit greatly from their large,
unobstructed, almost straight-through
passageways.
Fourth, the RCV’s massive design and its
lack of “fiddly bits” make it quite resistant to
damage from “unplanned landings.”
The RCV58-CD comes with an exploded
parts diagram (which shows everything
numbered, but nothing is named) and an
eight-page manual containing all of the breakin
and operating instructions. Since this
radical engine was so new to me, I followed
the manual’s directions meticulously. They
worked for me!
The RCV58 requires somewhat special
fuel with limited castor content. Wildcat Fuel
makes a blend specifically for these power
plants. Since my local hobby shops didn’t
carry Wildcat-brand fuel, I settled on
Morgan’s Omega 10%-nitromethane blend. It
contains 17% oil, of which 12% is synthetic
and 5% castor. That meets the RCV58-CD’s
fuel specifications.
The RCV manual proved especially
helpful to me in setting the carburetor’s two
needles. They required careful adjustment to
achieve optimum idling and full power. After
approximately an hour’s break-in and some
judicious needle tweaking, my RCV58 turned
a 12 x 6 Master Airscrew at just more than
10,000 rpm, with a reliable idle at 2,200.
Starting the RCV was easy enough once I
learned that the engine preferred “wet
choking”: two through-compression flips
while a finger seals off the carburetor’s intake
opening. After that, a mere touch of the starter
set the RCV58 going.
On the underside of the RCV58’s main
bearing housing is a tube fitting that is larger
than either the carburetor fuel-line nipple or
the muffler pressure port; this is the
crankcase breather. Although the RCV58
runs cleanly, with negligible oil coming from
the muffler outlet, I found that the crankcase
breather emits a considerable amount of
oil—while running and afterward.
This proves to me that the RCV’s rotating
cylinder sleeve is adequately lubricated. The
oil flowing into the case must have been
forced down between the sleeve’s outside
diameter and its mating cylinder bore during
the compression and power strokes. Its flow
path after that provides lubrication for the
gears and all three ball bearings.
When I install this extraordinary new
engine in a model, I’ll make sure to connect
a length of Tygon tubing to the crankcase
breather and out through the fuselage
bottom. That will expel the bypassed oil
overboard rather than into the engine
compartment.
As regular readers of this column probably
know, I much enjoy slaughtering “sacred
cows.” I’ve done it again—this time to the
“moisture in the glow fuel” belief.
For decades we model fliers have been
warned about the horrid effects of leaving our
glow-fuel containers open. “Methanol is
hygroscopic! It will suck water vapor out of
the atmosphere like a sponge. If you don’t
keep your glow-fuel cans sealed tightly,
water will sneak into the fuel, ruin your
engine’s performance, and cause rust inside!”
More than 10 years ago I tried to produce
rust in model-engine ball bearings by
purposely adding water to glow fuel and
splashing that onto the bearings every day or
two—for four months! I used seven brands of
fuel: Red Max, Byron, Fox, K&B,
PowerMaster, Cool Power, and Cox. In those
four months I was never able to generate a
single speck of rust in a model engine, even
with as much as 20% water added to these
fuels.
(Eventually I learned that rusting inside
model engines is caused by fuel
decomposing into acetic acid, and that is
caused by the catalytic effect of brass
components inside the fuel tank.)
But because the results seemed so
obvious, I never did investigate watercontaminated
fuel’s evil effects on modelengine
performance. I’ve done that now,
though, and I’m still surprised by what
happened.
I test-ran one of my most reliable
Control Line (CL) engines (a 1956 Johnson
.29) on 15%-nitromethane fuel (with 23%
castor-oil content; lapped-piston CL Stunt
engines need that much) with a 10 x 5
Graupner gray propeller. The results were
11,300 rpm max.
Rather than add water gradually to my
Johnson .29’s fuel and make a series of test
runs, I went whole hog. I added a full fluid
ounce of tap water to four ounces of my
stock fuel, resulting in a “fuel blend” of
20% water, 18% castor, 12% nitromethane,
and 50% methanol.
Did that make a difference to the
Johnson? Yes, it did! I had to open the
needle valve another half turn, leave the
glow-plug lighter connected for roughly 30
seconds, and flip the propeller five or six
times to start instead of the usual three. As
for speed, the Johnson spun up 11,400 rpm!
What happened? Could I have achieved a
power boost from something similar to the
“water injection” used in World War II
fighter-airplane engines?
True, my Johnson .29 has a bit higher
compression than “the average” CL engine
of its time. It’s also a lapped-piston engine,
thoroughly broken in and with minimal
internal friction. That may have made a
difference from, say, “the average” modern
RC engine.
But the intriguing fact remains that using
glow fuel containing more water than nitro,
my Johnson .29 started almost as easily as—
and ran a trifle faster than—it did 15
minutes earlier on its “usual fuel.” MA
Running steadily at 11,400 rpm, 1956 Johnson .29’s test fuel has 20% water!
01sig3.QXD 10/27/03 10:01 am Page 66