New O.S. Alpha .56 four-stroke engine
Joe Wagner | [email protected]
O.S. never seems to run out of improvements to its already superb line of engines. The new four-stroke .56 demonstrates that nicely. O.S. calls this engine "Alpha" because it's the first in a series of single-cylinder, overhead-valve four-strokers.
Externally you can see the Alpha design approach in a new, more compact muffler, shortened pushrod tubes, a different carburetor assembly, and the absence of a crankcase breather. The latter is because of a novel internal system for lubricating the shaft, ball bearings, gears, and cam/follower assembly.
Earlier four-strokers depend for lower-end lubrication on the small amount of oil that combustion-chamber pressure forces through the tiny clearance gap between the piston and cylinder sleeve. The Alpha .56 uses a much better system.
There's a small hole through the head alongside the intake valve. It allows crankcase vacuum on the intake stroke to draw a minute amount of fuel-and-oil mixture downward and into the region surrounding the shaft and cam assembly. From there a hole in the shaft and a cross-port between the bearings delivers oil to those parts—but not a lot. The Alpha .56 doesn't spit oil from behind the propeller driver. Nevertheless, enough is forced into the front bearing to provide the lubrication it needs for long service life.
There are two major differences between the Alpha's new carburetor assembly and earlier types, one of which may be because O.S. engineers read this column. I claim that because the Alpha uses an intake extension with a well-radiused "bell mouth." I've added that feature to my customized model engines for years and have shown it several times in column illustrations. The other carburetor change is a "reversed layout." The Alpha .56's needle is on the same side as the muffler, with the throttle arm on the other side. That makes for a compact arrangement. However, it does mean a long extension is needed for the needle valve, to prevent fingers from getting burned by contact with the muffler. The .56's needle has a neat provision for that: a hole in the end of the needle knob, with a setscrew to lock onto the extension.
O.S. offers a needle-valve extension-cable set as an accessory. It has a semiflexible wire cable and a knurled knob. I found that 1/16-inch wire works nicely for a homemade extension. I form the outer end into a full loop because I'm tired of snagging things on the usual "bent angle" end of needle-valve extensions.
O.S.'s Alpha .56 owner's manual advises using only an electric starter with this engine. It has no manual "choking" provision. But especially with a new engine I prefer hand starting (with a leather glove on in case of a backfire). I can get a much better feel for what is happening during startups that way. The Alpha .56 gave me no problems. Instead of choking the inlet I just blocked off the muffler outlet with a fingertip as I hand-flipped the propeller. The resulting back pressure to the tank via the muffler pressure tubing forces enough fuel into the carburetor for a prompt start-up. The Alpha .56's snappy compression helped there.
For break-in I used a wooden 13 x 6 propeller. After following O.S.'s recommended "running-in" procedure (I always read the instructions), I hit 6,500 rpm at full throttle. That was using 10%-nitro fuel, with extra castor oil to ensure a minimum 20% lubricant content. I'll have more about this topic later in the column.
After a couple more tanks of fuel I managed to get a reliable idle at just more than 1,800 rpm. With a heavier, reinforced plastic propeller I think I can reduce that to approximately 1,650 rpm.
The O.S. Alpha .56 runs smoothly. Its short stroke—only 86% of the cylinder bore—and lightweight ringed aluminum piston contribute greatly to that. I'm sure the engine's sturdy, compact design helps too.
1/2A engines and fuels
Plenty of modelers still fly with 1/2A power. However, fuel for those little power plants has become hard to find. They need special fuel that has high nitro content and lots of castor oil.
At least 23% nitro is needed because small model engines have more cooling area in proportion to their displacement. A high castor content is needed because of the high stresses, especially at the piston end of the rod.
Several readers have asked where to find 1/2A fuel. Byron makes a 25%-nitro, all-castor-lubed blend that works well (I use that). However, Byron's fuel is not available everywhere. Therefore, I found an alternative: Tower Hobbies' Tower POWER 30%-nitro helicopter fuel, with added castor oil.
Tower doesn't specify the oil type or percentage used in its helicopter fuel. Since engines used in helicopters run hot, I assume that the oil content is roughly 18%. I add 3 fluid ounces of Sig's castor oil to a quart of Tower POWER 30% helicopter fuel.
Fuel-mixing calculation:
- A quart contains 32 fluid ounces.
- 18% of 32 fl oz = 5.76 fl oz (assumed original oil).
- Adding 3 fl oz of castor brings the oil volume up to 8.76 fl oz.
- Total fuel volume becomes 32 + 3 = 35 fl oz.
- 8.76 / 35 ≈ 25% oil — perfect for my 1/2As.
The added oil brings the nitro content down to about 27%, but that hardly matters for sport flying. An empty half-gallon juice bottle makes a good mixing container for this special 1/2A fuel-blending process; it's fuelproof and has a big enough opening to easily accept a piston-type fueling syringe.
Wooden muffler and simple custom exhausts
I have done another offbeat model-engine experiment, this time with a wooden muffler. It seems like almost all model-club flying fields require mufflers—and have for a long time. Even the tiny G-Mark .031 of long ago came with a muffler. Yet many perfectly usable older engines lack mufflers.
Nobody ever seems to throw those old power plants away, and I get regular queries from readers about where to obtain a muffler to fit, say, a 30-year-old Enya or the like. Those are difficult to find, and I know of no sources anymore.
I've made several custom mufflers for my older engines, and it's not that hard if you have metalworking machinery. Through the years I've built and flown several models with closely cowled engines. In those the exhaust outflow passes directly over wooden surfaces. The dope finish there sometimes blistered, but the wood itself never showed heat damage.
Therefore, I made a wooden muffler to test on an old Fox .36X. I used pine to ensure failure—if failure was possible (pine ignites easily). I ran three full tanks of fuel through the mighty Fox at full throttle and then took the muffler off to see what its insides looked like.
The interior was blackened, but only on the surface. Shaving off a little wood from the insides showed that the black went no deeper than a few thousandths. The outside of my pinewood muffler showed no sign of scorching.
I'm sure a model-engine muffler made from rock maple would work as well as an aluminum muffler. Aluminum isn't that much harder to work with than hard maple.
For another test, using only a hacksaw, a drill press, and files, I made an "exhaust diverter" from stock aluminum bar and tubing to fit an old O.S. .15—one of the early RC types with a pivoting exhaust restrictor coupled to its carburetor. The whole job took roughly an hour.
I made this diverter to connect to a Fly Quiet muffler system from Bayou Production. They are amazingly effective at cutting down engine noise and cost little. The Fly Quiets are bulky, but they don't weigh a great deal and can be installed inside the fuselage. One built into a P-47 would let the exhaust come out from the scale location.
Fix for gummy crankshaft bearings (glow engines)
A problem that plagues many modelers is gummy crankshaft bearings. There's an easy fix for glow engines:
- Inject approximately a teaspoonful of Marvel Mystery Oil or Tower Hobbies' After Run Oil into the crankcase.
- Hold the engine pointing downward.
- Flip the propeller vigorously.
The idea is to make crankcase compression force the thin new oil out through the main bearing clearance and flush away the sticky oxidized oil from that passageway. When you hold the engine nose-down, the After Run Oil (or Marvel Mystery Oil) pools against the inside front of the case. Then when you flip the propeller, crankcase compression forces the oil out through the shaft clearance, washing all the thick, sticky goo out with it.
I've used this technique many times with older engines I've handled. It always works—and I'm often amazed by the amount of brown gunk that's pushed out into the gap behind the propeller driver.
The reason for hand flipping is that using an electric starter presses the propeller driver backward, which might block the exit of sticky goo.
—MA
Sources
- Bayou Production
Box 15182 Baton Rouge LA 70895 www.flyquiet.com
Transcribed from original scans by AI. Minor OCR errors may remain.
