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Outgrowing electric power, or staring at a .60-size airframe wondering whether to buy glow fuel or move to gasoline, is a common crossroads. Most of the confusion comes from comparing numbers that were never measured the same way. This guide sticks to what the engine makers publish: displacement, weight, recommended propellers, fuel and oil guidance, and break-in instructions. It also checks which engines are actually listed today, because several well-known names have disappeared from the catalog.
This page is a researched buyer's guide based on manufacturer specs and manuals, not on our own bench or field testing. Power and speed figures are manufacturer claims. The RC plane motors guide covers the electric alternative, and the gas versus electric guide lays out the trade-offs.
Stock Check First
Horizon Hobby's airplane engine category listed 39 results in October 2026. A few facts from the maker's structured data matter before you shop.
- Discontinued: the Evolution .46NX glow engine and the Saito FA-100 four-stroke. Both appear in many older recommendations.
- Evolution .91NX: Horizon's Evolution category lists parts for it, but no complete engine, so availability is not confirmed.
- Backordered: most O.S. glow engines, including the 46AX II, 55AX, 65AX, 75AX, 95AX and 120AX, and the Saito FA-82.
- Out of stock: the Saito FA-62B and FA-125A.
- In stock: O.S. GT15, GF30 II and GF40 gas engines, the Saito 150B and 180B glow four-strokes, and Saito FG gas four-strokes such as the FG-21, FG-30B and FG-50. Desert Aircraft's own store showed the DA-85 as available and the DA-50 as unavailable.
DLE and RCGF engines also appear in many guides. Their maker websites could not be reached, so no specs are repeated here. If one of those is on your list, get the numbers from the seller and the manual.
How Glow and Gas Engines Differ
Both are internal combustion engines, but they ignite and are fueled differently, and that drives everything else.
Glow engines burn a methanol-based fuel that contains oil and, often, nitromethane. A glow plug ignites it, and Evolution's manual notes that methanol attracts moisture, so contaminated fuel causes poor performance. Sunlight can break down nitromethane over time. Evolution suggests storing fuel in a metal can and squeezing extra air out of partly empty containers.
Gas engines run on gasoline mixed with oil and use a spark plug and an onboard ignition. That ignition needs power, so a gas setup carries an ignition module and battery that a glow engine does not.
Oil content is not interchangeable. O.S. lists at least 16% or 18% synthetic lubricant for its glow engines depending on the model, and its GT15 gas engine lists a 30:1 to 50:1 mix. Saito's gasoline four-strokes call for 20:1, and Desert Aircraft recommends 40:1 with its preferred oil. Always follow the manual for your exact engine.
Choosing a Size
Makers describe the airframes their engines suit. Use those statements as a starting point and check your plane's own recommended range.
- Evolution .46NX: Horizon said it suited .40- to .50-size airplanes.
- Saito four-strokes: Horizon's text for the Saito .91 says it fits most airplanes designed for .60-size two-strokes and can swing larger propellers.
- Desert Aircraft DA-50: the maker calls it suited to 25 to 30% aerobatic aircraft, sport flyers and scale models.
- Desert Aircraft DA-70: designed for 18 to 24 lb aerobatic aircraft, sport models and larger warbirds.
- Desert Aircraft DA-85: engineered for 35% aerobatic aircraft and large-scale warbirds.
For more on aircraft in these size ranges, see the giant scale planes guide and the warbirds guide.
Glow Engines
O.S. AX series
Search for O.S. Engines 46AX II on Amazon
O.S. is the main glow brand still on Horizon's shelf. Horizon lists a range of AX models, though many are on backorder, so check the current listing for availability.
| Model | Displacement | Engine weight | Prop range | RPM range | Oil content |
|---|---|---|---|---|---|
| 35AX ABL | 0.352 cu in (5.77 cc) | 9.88 oz (280 g) | 10x6 to 12x6 | 2,500 to 13,000 | At least 18% |
| 46AX II ABL | 0.455 cu in (7.45 cc) | 13.3 oz (378 g) | 10.5x6 to 12x6-7 | 2,000 to 17,000 | At least 16% |
| 55AX ABL | 0.545 cu in (8.93 cc) | 0.89 lb (404 g) | 11x6 to 13x6 | 2,000 to 17,000 | At least 16% |
| 75AX ABL | 0.75 cu in (12.3 cc) | 20.39 oz (578 g) | 13x8-10 to 14x6-8 | 2,000 to 11,000 | At least 16% |
| 95AX ringed | 0.949 cu in (15.55 cc) | 20 oz (567 g) | 14x8 to 16x6-8 | 2,000 to 11,000 | At least 18% |
| 120AX ringed | 1.218 cu in (19.96 cc) | 1.305 lb (592 g) | 15x10-12 or 16x8-10 | 1,800 to 9,500 | At least 18% |
Weights are without muffler where the maker says so. The 46AX II lists a break-in propeller of 10x6 and uses the ABL (advanced bi-metallic liner) construction. It is the closest current match to the discontinued Evolution .46NX in size.
Evolution .46NX (discontinued)
For context, the .46NX displaced .46 cu in (7.50 cc), weighed 13.76 oz (390 g) without muffler, and used a benchmark propeller of 11x6 at 12,500 rpm. Evolution's manual says each Evolution engine is test run and adjusted at the factory and ready to fly with no adjustments or break-in. That is a real convenience, and it is gone with the model. If you find one used, check its condition carefully.
Saito four-stroke glow engines
Search for Saito 180B glow engine on Amazon
Four-strokes make a scale exhaust note and swing larger propellers. Horizon lists these Saito glow engines:
| Model | Displacement | Engine weight | Prop range | Stock note |
|---|---|---|---|---|
| FA-62B | 0.62 cu in (10.16 cc) | 14.7 oz (418 g) | 11x7 to 13x7 | Out of stock |
| FA-82 | 0.82 cu in (13.44 cc) | 16.0 oz | 12x8 to 15x4 | Backorder |
| FA-125A | 1.25 cu in (20.52 cc) | 21.87 oz (620 g) | 15x7 to 17x6 | Out of stock |
| 150B | 1.50 cu in (24.58 cc) | 30 oz | Benchmark 16x8 | In stock |
| 180B | 1.80 cu in (29.10 cc) | 31 oz | 15x8 to 18x6 | In stock |
The FA-100 (1.04 cu in, 17.10 cc) is discontinued. Horizon's product text claimed it turned a 14x8 APC propeller 300 to 700 rpm faster than the Saito or O.S. .91.
Gas Engines
O.S. GT15, GF30 II and GF40
Search for O.S. Engines GF30 II on Amazon
| Model | Type | Displacement | Engine weight | RPM range |
|---|---|---|---|---|
| GT15 | 2-cycle | 0.912 cu in (14.95 cc) | 22.26 oz (631 g) | 2,000 to 15,000 |
| GF30 II | 4-stroke | 29.94 cc (1.827 cu in) | 1 lb (454 g) | 2,500 to 18,000 |
| GF40 | 4-stroke | 2.44 cu in (39.96 cc) | 2.64 lb (1.2 kg) | 1,800 to 9,000 |
The GT15 lists a total weight of 32 oz (904 g) including the ignition, a CM6 spark plug and a 30:1 to 50:1 mix. The GF40's benchmark propeller range is 18x8-12 to 20x8-10.
Saito FG four-stroke gas engines
Search for Saito FG-21 gas engine on Amazon
| Model | Displacement | Engine weight | Total weight | Prop range | RPM range |
|---|---|---|---|---|---|
| FG-21 | 1.25 cu in (20.52 cc) | 24.1 oz (0.69 kg) | 31.2 oz (0.89 kg) | 15x8 to 16x8 | 2000 to 9500 |
| FG-30B | 1.80 cu in (29.10 cc) | 31.0 oz (879 g) | 38.0 oz (1078 g) | 15x8 to 18x6 | 2,000 to 10,000 |
Saito lists a 4.0 oz ignition for each. The FG-21 recommends a 20:1 gas-to-oil ratio and Evolution's EVOX1001Q synthetic oil.
Desert Aircraft DA-50, DA-70 and DA-85
Search for Desert Aircraft DA-85 on Amazon
| Model | Displacement | Output | Weight | RPM range |
|---|---|---|---|---|
| DA-50 | 3.05 ci (50 cc) | 4.95 hp | 3.13 lb (1.42 kg) | 1600 to 7000 |
| DA-70 | 4.28 ci (70 cc) | 6.96 hp | 3.55 lb (1.61 kg) | 1400 to 6900 |
| DA-85 | 5.24 ci (85.9 cc) | 8.52 hp | 4.3 lb (1.95 kg) | 1200 to 7500 |
All three carry a three-year warranty, per the maker. The DA-85 is 5.9 in (150 mm) long, ships with a carburetor, a single ignition module, a CM6 spark plug and prop bolts, and Desert Aircraft recommends 25x10 or 26x10 two-blade propellers or 24x10 or 24x12 three-blade ones. The DA-50 recommends 22x8, 22x10 or 23x8 two-blade propellers.
Desert Aircraft's FAQ recommends Red Line Racing oil at a 40:1 ratio, with Motul 800 or Stihl HP Ultra as alternatives. It also notes that every engine is test run at the factory, but that this does not mean the engine is broken in.
Fuel Guidance From the Makers
Glow fuel. Saito recommends fuel with 20% oil and 10 to 15% nitromethane, and says a high-quality two-cycle glow fuel is the next best choice. It advises against fuel made entirely of castor oil and says a synthetic-castor blend is acceptable. O.S. lists at least 16% or 18% synthetic lubricant depending on the engine. The fuel guide goes deeper.
Gasoline. Saito's gasoline four-stroke manual calls for 91-octane unleaded gasoline with 100% synthetic two-cycle oil at 20:1, says fuel with up to 10% ethanol was tested and found to work fine, and requires a filtered clunk. It also warns against silicone fuel line. Desert Aircraft's guidance differs (40:1 with its recommended oils), which is why you should follow the manual that ships with your engine.
Storage. Evolution suggests a metal fuel can for glow fuel. For glow engines in storage, Saito's manual advises using after-run oil, emptying the tank and engine, and putting a few drops of light oil in through the glow plug hole.
Break-In
The two engine families break in differently, and the maker's manual wins.
Saito glow engines. The manual says not to exceed 4,000 rpm for the first 10 minutes, then to lean the mixture slightly with each tank, and that forty minutes is sufficient before the first flight. It recommends a tachometer.
Saito gasoline four-strokes. Same 4,000 rpm limit for the first 10 minutes and the same forty-minute guideline, with a smaller propeller for the initial break-in and roughly 20 flights afterward. Saito says break-in is mainly about the conrod-to-crankshaft interface, warns "Do not skip this step," and recommends an electric starter. Valve adjustment may be needed every 1 to 2 hours of operation.
Evolution NT and NX glow engines. Test run at the factory and ready to fly with no break-in required, per Evolution's manual.
Desert Aircraft. Factory test running is not break-in, per the maker. Follow the manual that ships with the engine.
Other habits from the manuals: do not run lean, use a reliable fuel filter on gas engines, and range check your radio with the engine running and with it off. The glow plug guide covers plug wear, and the troubleshooting articles for glow and gas engines cover starting problems. For reliable radio gear in an engine-powered plane, see the transmitter and receiver guide.
Which Engine Fits
| Situation | What to look at |
|---|---|
| A .40 to .50 sport plane | O.S. 46AX II (or a used Evolution .46NX) |
| A .60-size four-stroke airframe | Saito FA-82 or a used Saito .91 |
| A scale four-stroke note | Saito 150B or 180B |
| A 15cc to 40cc gas conversion | O.S. GT15, GF30 II or GF40, or Saito FG-21 or FG-30B |
| A 25 to 30% aerobatic plane | Desert Aircraft DA-50 (check availability) |
| A 35% warbird or aerobatic plane | Desert Aircraft DA-85 |
FAQ
Q: Is gas always cheaper to run than glow?
Makers do not publish running costs, so there is no firm figure. Gas engines use gasoline and oil instead of glow fuel, but they add ignition hardware. Compare your airframe and flying schedule before assuming a saving.
Q: Do four-stroke glow engines make more power than two-strokes?
Not by displacement alone. Saito's text for the .91 describes larger propellers and more thrust than a comparable two-stroke, while many pilots choose four-strokes for the sound.
Q: Can pump gasoline go in any gas RC engine?
Follow the manual. Saito's gasoline four-strokes call for 91-octane unleaded gasoline with synthetic oil and report that up to 10% ethanol works fine. Other makers specify other oils and ratios.
Q: What is the biggest risk when breaking in a gas engine?
Skipping or rushing the process. Saito warns that skipping break-in risks seizing the conrod to the crankshaft, and recommends a smaller propeller, an rpm limit and a tachometer.
