THE FIRST internal-combustion engine used to power a model airplane in flight was British engineer David Stanger's 1906 four-stroke V-4—spark ignition, of course. Its 6.75-cubic-inch displacement is like that of some of today's Giant Scale power plants. However, it weighed 51/2 pounds, and its output of approximately 1 1/4 horsepower was surpassed years ago by competition two-stroke .15s (glow and diesel types). Model-engine design has progressed a long way since 1906—to the point where it's now extremely difficult for anyone to come up with further significant improvements. However, improvements are possible, and Norvel's new Russian-made Revlite™ AME R/C engines are proof. At first I hesitated to acquire any of the new AME R/Cs. That's because I fly model airplanes strictly for personal enjoyment, and Norvel's original AME engines had become well-known primarily for their high-rpm performance in Free Flight competition. But I've been misled before about a model-engine type; e.g., the Webra Speedy. I assumed that any engine with such a name had to be a racing special, and twice I passed up chances to obtain one. But one day a friend gave me a Webra Speedy .12 R/C. I mounted it on my test stand and ran it with various-size propellers, just to see what it could do—and its "friendliness" and adaptability astonished me. Therefore, I've just bought "on spec" two of the new Norvel AME R/C engines: a .15 and a .25. They arrived only a couple of days before I wrote this, and I've had no chance to run them yet. However, they're loaded with major and minor "newsworthy ; features" and provide plenty of topics to write about. Norvel's major innovation (used in all its engines) is the Revlite™ piston and cylinder. Both are aluminum alloy, with the cylinder "hard anodized" inside and out. (Norvel also refers to this type of piston/cylinder combination as AAO: Aluminum Aluminum Oxide.) Model engines with an aluminum piston running in an aluminum cylinder are far from new. The first ones (incredibly Besides Revlite™ construction, Norvel's AME .15 R/C features snap-in-place muffler, 45° swept-back needle to maximize safety. The Norvel AME .25 R/C's flat-topped look is deceiving; it provides better top-end cooling than average finned-head engine. cheap designs mass-produced in 1946 called Thor, Genie, and Ram) ran—but just barely. Some 45 years later, K&B came out with its Sportsman series of glow engines, which featured pistons and cylinders made from high-silicon aluminum alloy. These ran quite well once they were properly broken in. 1 used a Sportsman .45 to power a 900-square-inch Radio Control (RC) trainer, for teaching teenagers how to fly RC. The more that engine ran, the better it performed. However, K&B's Sportsman series (.20. .45. and .60) never became popular. "It feels funny," one owner told me—and he sold me his almost-new Sportsman .20 for $10. The new AME R/C engines are different! Norvel calls the hard-anodized Revlite™ cylinder surface a "ceramic." That's not quite accurate; true ceramics (such as porcelain) are kiln-fired materials. Hard anodizing is a "conversion coating." Like case-hardened steel. hard-anodized aluminum's outer surface is an integral part of the metal, specially treated to convert it into a hard and durable skin. It's not an added-on coating like plating! Chrome plate can sometimes peel off; hard anodizing's sapphire-hard surface cannot. (Sapphires, rubies, and hard-anodized aluminum are chemically identical; they're aluminum oxide.) Besides providing extreme resistance to wear, the AME's Revlite™ cylinders optimize heat transfer. The outer fins and the inner bore are a single piece of metal, providing an uninterrupted conductivity path for disposing of surplus combustion-chamber heat. AME R/C engines use standard glow plugs, installed in an unusual two-piece removable head. (You need a special Norvel "spanner tool" to remove and replace the head retainer ring. It costs roughly $7 and fits the .15 and the .25.) I can see an advantage to this removable head design that Norvel doesn't specifically mention; the ability to change the compression ratio to suit various-size propellers. The lower part (Norvel calls this a "Glow Plug Adapter") seals to the cylinder with a thin metal ring gasket like Cox uses for sealing its glow heads. Adding extra gaskets reduces the compression and permits flying with larger propellers without suffering preignition and overheating problems. The new AME R/C engines feature double ball bearings, a positive-keyed propeller drive, and a gasketless rear cover. The .25 has a bolt-on, adjustable-outlet muffler; the .15 uses an ingenious spring-clip muffler attachment with an inner O-ring which provides a seal. (Imperfect sealing at the muffler-to-engine joint has no adverse effect on anything except cleanliness of the engine area.) AME's clever carburetor design impresses me. It's a double-needle, cam-action type with a central "annular orifice" fuel-delivery nozzle. The main needle is swept back at a 45° angle. That positions the needle-adjustment end more than two inches aft of the propeller. When I received these two AME R/C engines, both carburetors were installed with their main needles swept back considerably more than 45°. Evidently, this was done to minimize the overall width of the assembled engines in their packages and lessen the risk of anything getting bent in "handling." Resetting the AME carburetor angle for straight fore-and-aft action of the throttle arm required cautious work with a precision open-end wrench. The clamping nut is small, thin-walled, and made from brass. Don 'l use long-nose pliers on this nut! (Or on anv nut or bolt.) One further advantage of Norvcl's Revlite™ engine design is light weight. The AME .25 R/C is more than an ounce lighter than the K&B Sportsman .20, even though that's also an "all-aluminum" design —and 20% smaller in displacement. Now I'm wondering who will be first to use an aluminum crankshaft in a model-airplane engine. Some aluminum alloys are as strong as steel — and with hard anodizing to provide an almost invulnerable surface, why wouldn't an aluminum shaft work? Dale Dutt (Norco LA) wrote about "sudden stop" troubles with his Saito 65 four-stroke. Shown are the AME .25 R/C's head components and the spanner tool used to remove and Install them. Metal ring gaskets allow easy compression changes. "... No problems for years, just a pleasure to run ... Saturday at the field it would start, no problem—idle perfectly—transition up to 3Xt throttle, then stop abruptly as if someone grabbed the crank." That sounds serious! And for a while it seemed so to Dale. He and his friends tried everything they could think of. but nothing helped. Eventually someone suggested changing the propeller, and the source of the trouble stood revealed; an insufficiently tightened propeller slipping on its shaft. This isn't a new problem. I've experienced it myself from time to time, first with a spark-ignition Forster .29 (in a Control Line Fireball) back in the Good Old Days. My Forster started easily; when I tried speeding it up (by advancing the spark timer), it suddenly quit. It did the same thing repeatedly. One of the "older fliers" came over and told me, "Your prop nut isn't tight enough." That was the problem, all right! The Forster had smooth-faced prop washers, and only friction drove the propeller. It was probably sufficiently tight when I first installed it. but after a while the wood at the prop hub compressed just enough to allow it to slip. This same thing has happened to me with engines that lack a positive connection between the shaft and the propeller. They use a tapered shoulder on the shaft and a mating conical hole in the back of the propeller drive washer. Friction does the whole job of connecting the engine shaft to the propeller—and model-airplane engine shafts are normally oily. Here is why a slipping propeller causes trouble. As I mentioned in a recent column, model-airplane engines use the propeller as a flywheel. On power strokes, the crankshaft turns the propeller; but on the "upstrokes," the propeller's rotating energy is the only thing that drives the shaft and keeps the engine running. If the propeller-driver interface slips, the flywheel action suffers. At higher rpm, the problem worsens —and the engine quits. This is even more of a problem with four-stroke engines. On two-strokers the crank drives the propeller on every downstroke. and the propeller drives the shaft on every upstroke. But on a four-stroker, the propeller momentum has to rotate the shaft through three complete strokes (two up and one down) for each of the power strokes from which the propeller acquires its energy. It's a good idea (though nobody I know actually does this) to loosen the prop nut after every flying or engine-operating session. Retighten the nut firmly the next time you need to run the engine. That way. the propeller hub material (wood or plastic) doesn't have to withstand a constant crushing pressure all the time it's not in use. Any slippage whatever between a propeller and its driver will hurt performance. A minute amount of slippage may not stop the engine, but it will reduce the power output. If this persists, the resultant "burnishing" action on the propeller's rear face will soon make things worse. AH
Edition: Model Aviation - 2002/09
Page Numbers: 50, 51
Edition: Model Aviation - 2002/09
Page Numbers: 50, 51
THE FIRST internal-combustion engine used to power a model airplane in flight was British engineer David Stanger's 1906 four-stroke V-4—spark ignition, of course. Its 6.75-cubic-inch displacement is like that of some of today's Giant Scale power plants. However, it weighed 51/2 pounds, and its output of approximately 1 1/4 horsepower was surpassed years ago by competition two-stroke .15s (glow and diesel types). Model-engine design has progressed a long way since 1906—to the point where it's now extremely difficult for anyone to come up with further significant improvements. However, improvements are possible, and Norvel's new Russian-made Revlite™ AME R/C engines are proof. At first I hesitated to acquire any of the new AME R/Cs. That's because I fly model airplanes strictly for personal enjoyment, and Norvel's original AME engines had become well-known primarily for their high-rpm performance in Free Flight competition. But I've been misled before about a model-engine type; e.g., the Webra Speedy. I assumed that any engine with such a name had to be a racing special, and twice I passed up chances to obtain one. But one day a friend gave me a Webra Speedy .12 R/C. I mounted it on my test stand and ran it with various-size propellers, just to see what it could do—and its "friendliness" and adaptability astonished me. Therefore, I've just bought "on spec" two of the new Norvel AME R/C engines: a .15 and a .25. They arrived only a couple of days before I wrote this, and I've had no chance to run them yet. However, they're loaded with major and minor "newsworthy ; features" and provide plenty of topics to write about. Norvel's major innovation (used in all its engines) is the Revlite™ piston and cylinder. Both are aluminum alloy, with the cylinder "hard anodized" inside and out. (Norvel also refers to this type of piston/cylinder combination as AAO: Aluminum Aluminum Oxide.) Model engines with an aluminum piston running in an aluminum cylinder are far from new. The first ones (incredibly Besides Revlite™ construction, Norvel's AME .15 R/C features snap-in-place muffler, 45° swept-back needle to maximize safety. The Norvel AME .25 R/C's flat-topped look is deceiving; it provides better top-end cooling than average finned-head engine. cheap designs mass-produced in 1946 called Thor, Genie, and Ram) ran—but just barely. Some 45 years later, K&B came out with its Sportsman series of glow engines, which featured pistons and cylinders made from high-silicon aluminum alloy. These ran quite well once they were properly broken in. 1 used a Sportsman .45 to power a 900-square-inch Radio Control (RC) trainer, for teaching teenagers how to fly RC. The more that engine ran, the better it performed. However, K&B's Sportsman series (.20. .45. and .60) never became popular. "It feels funny," one owner told me—and he sold me his almost-new Sportsman .20 for $10. The new AME R/C engines are different! Norvel calls the hard-anodized Revlite™ cylinder surface a "ceramic." That's not quite accurate; true ceramics (such as porcelain) are kiln-fired materials. Hard anodizing is a "conversion coating." Like case-hardened steel. hard-anodized aluminum's outer surface is an integral part of the metal, specially treated to convert it into a hard and durable skin. It's not an added-on coating like plating! Chrome plate can sometimes peel off; hard anodizing's sapphire-hard surface cannot. (Sapphires, rubies, and hard-anodized aluminum are chemically identical; they're aluminum oxide.) Besides providing extreme resistance to wear, the AME's Revlite™ cylinders optimize heat transfer. The outer fins and the inner bore are a single piece of metal, providing an uninterrupted conductivity path for disposing of surplus combustion-chamber heat. AME R/C engines use standard glow plugs, installed in an unusual two-piece removable head. (You need a special Norvel "spanner tool" to remove and replace the head retainer ring. It costs roughly $7 and fits the .15 and the .25.) I can see an advantage to this removable head design that Norvel doesn't specifically mention; the ability to change the compression ratio to suit various-size propellers. The lower part (Norvel calls this a "Glow Plug Adapter") seals to the cylinder with a thin metal ring gasket like Cox uses for sealing its glow heads. Adding extra gaskets reduces the compression and permits flying with larger propellers without suffering preignition and overheating problems. The new AME R/C engines feature double ball bearings, a positive-keyed propeller drive, and a gasketless rear cover. The .25 has a bolt-on, adjustable-outlet muffler; the .15 uses an ingenious spring-clip muffler attachment with an inner O-ring which provides a seal. (Imperfect sealing at the muffler-to-engine joint has no adverse effect on anything except cleanliness of the engine area.) AME's clever carburetor design impresses me. It's a double-needle, cam-action type with a central "annular orifice" fuel-delivery nozzle. The main needle is swept back at a 45° angle. That positions the needle-adjustment end more than two inches aft of the propeller. When I received these two AME R/C engines, both carburetors were installed with their main needles swept back considerably more than 45°. Evidently, this was done to minimize the overall width of the assembled engines in their packages and lessen the risk of anything getting bent in "handling." Resetting the AME carburetor angle for straight fore-and-aft action of the throttle arm required cautious work with a precision open-end wrench. The clamping nut is small, thin-walled, and made from brass. Don 'l use long-nose pliers on this nut! (Or on anv nut or bolt.) One further advantage of Norvcl's Revlite™ engine design is light weight. The AME .25 R/C is more than an ounce lighter than the K&B Sportsman .20, even though that's also an "all-aluminum" design —and 20% smaller in displacement. Now I'm wondering who will be first to use an aluminum crankshaft in a model-airplane engine. Some aluminum alloys are as strong as steel — and with hard anodizing to provide an almost invulnerable surface, why wouldn't an aluminum shaft work? Dale Dutt (Norco LA) wrote about "sudden stop" troubles with his Saito 65 four-stroke. Shown are the AME .25 R/C's head components and the spanner tool used to remove and Install them. Metal ring gaskets allow easy compression changes. "... No problems for years, just a pleasure to run ... Saturday at the field it would start, no problem—idle perfectly—transition up to 3Xt throttle, then stop abruptly as if someone grabbed the crank." That sounds serious! And for a while it seemed so to Dale. He and his friends tried everything they could think of. but nothing helped. Eventually someone suggested changing the propeller, and the source of the trouble stood revealed; an insufficiently tightened propeller slipping on its shaft. This isn't a new problem. I've experienced it myself from time to time, first with a spark-ignition Forster .29 (in a Control Line Fireball) back in the Good Old Days. My Forster started easily; when I tried speeding it up (by advancing the spark timer), it suddenly quit. It did the same thing repeatedly. One of the "older fliers" came over and told me, "Your prop nut isn't tight enough." That was the problem, all right! The Forster had smooth-faced prop washers, and only friction drove the propeller. It was probably sufficiently tight when I first installed it. but after a while the wood at the prop hub compressed just enough to allow it to slip. This same thing has happened to me with engines that lack a positive connection between the shaft and the propeller. They use a tapered shoulder on the shaft and a mating conical hole in the back of the propeller drive washer. Friction does the whole job of connecting the engine shaft to the propeller—and model-airplane engine shafts are normally oily. Here is why a slipping propeller causes trouble. As I mentioned in a recent column, model-airplane engines use the propeller as a flywheel. On power strokes, the crankshaft turns the propeller; but on the "upstrokes," the propeller's rotating energy is the only thing that drives the shaft and keeps the engine running. If the propeller-driver interface slips, the flywheel action suffers. At higher rpm, the problem worsens —and the engine quits. This is even more of a problem with four-stroke engines. On two-strokers the crank drives the propeller on every downstroke. and the propeller drives the shaft on every upstroke. But on a four-stroker, the propeller momentum has to rotate the shaft through three complete strokes (two up and one down) for each of the power strokes from which the propeller acquires its energy. It's a good idea (though nobody I know actually does this) to loosen the prop nut after every flying or engine-operating session. Retighten the nut firmly the next time you need to run the engine. That way. the propeller hub material (wood or plastic) doesn't have to withstand a constant crushing pressure all the time it's not in use. Any slippage whatever between a propeller and its driver will hurt performance. A minute amount of slippage may not stop the engine, but it will reduce the power output. If this persists, the resultant "burnishing" action on the propeller's rear face will soon make things worse. AH
