Two Stroke

2021 Engine Buyer’s Guide

4

Aircraft Engine Buyer's Guide 2021

Hirth

Recreational Power Engineering (RPE) in Ohio distributes powerful, precision-built two-stroke engines built by Hirth in Germany to the North American market. For 2020 Hirth has discontinued some larger engines—namely the 3502, 3702 and 3703—to concentrate on its best-selling small and midrange displacements. Otherwise, there are no model or technical changes to the Hirth lineup. And while international currency fluctuations require checking with RPE for the latest pricing, there are no price increases.

Hirth engines are typically offered with or without a gearbox (with many gear ratios to choose from) and could have other important ordering options such as adding a centrifugal clutch to the drive, an electric starter, oil injection or electronic fuel injection.

Concentrating on their best-selling midrange engines means Hirth has dropped their three-cylinder offerings for 2021. That still leaves up to 70 hp available from their two-stroke, two-cylinders at barely over one pound per horsepower.

For this guide, we’re displaying the base engine for each model in our charts. Furthermore, there can be tuning differences within an engine model line, meaning power and torque peaks can be selected between high and low options depending on if maximum peak power or maximum cruise fuel efficiency is more valued. Lower power Hirth engines are air-cooled; larger engines are water-cooled.

Because Hirth engines are manufactured in limited, noncontinuous runs, there can be a four- to six-week lead time when ordering, so planning ahead is a must. Warranty terms from RPE are good and include prepaid shipping when returning an engine for service.

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Rotax

The short version of the contemporary Rotax two-stroke story is the 65 hp 582 UL remains in production and is used in several LSAs. That means complete 582 engines, parts and service are readily available. Once past the 582, however, the extensive legacy of Rotax’s two-stroke engine line is fading into history. The 503 is the Rotax two-stroke most recently out of production, but there’s still some support. Lockwood has 503 short blocks in stock—at least for now.

The 582 is available in direct-drive form or with one of two gearboxes. The B gearbox (“drive” in Rotax speak) is suitable for smaller diameter, lighter three-blade propellers, while the E gearbox is larger and includes an electric starter at its bottom. The other 582 engines place the starter at the rear, or the other end, of the engine. The E box can handle roughly twice the inertial mass at the propeller as the B drive. For 2021, Rotax has not made any technical changes to the 582 line.

Engine ModelDrive TypeHorsepowerWeightPrice
BRP Rotax
582 UL
inline WC twin
geared65 hp @ 6500 rpm carbureted104 lb w/o radiator, w/ E gearbox and exhaust$5378 w/o gearbox,
$6428 B drive,
$7373 E drive
Hirth also: recpower.com
F-23
opposed twin
belt50 hp @ 6150 rpm71 lb free air w/starter, exhaust$6312 electric start
3202
inline twin
geared55 hp @ 5500 rpm79 lb fan cooled w/starter, exhaust; opt. gearbox adds 19 lb$6218 recoil start
3203
inline twin
geared65 hp @ 6300 rpm79 lb fan cooled w/ starter, exhaust; opt. gearbox adds 19 lb$7045 recoil start
3503
inline WC twin
geared70 hp @ 6500 rpm79 lb wo/radiator, w/ starter, exhaust: opt. gearbox adds 19 lb$7876 recoil start
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Pumping avgas and waxing flight school airplanes got Tom into general aviation in 1973, but the lure of racing cars and motorcycles sent him down a motor journalism career heavy on engines and racing. Today he still writes for peanuts and flies for fun.

4 COMMENTS

  1. ROTAX USED UL 2 STROKES 185UL/185F, 277UL/277F, 377UL/377F/380F, 447UL/440F, 462UL/470 LC, 503UL/503F, 532UL,/521 LC 582UL/580 LC/582 LC/583 LC, 618UL/617 LC, 670 LC, ARE WIDELY STILL AVAILABLE, AND CHEAP TO REBUILD! THE SAME UL ENGINES WERE ALSO USED IN SKI-DOO SNOWMOBILES!
    HIRTH
    SIMONINI
    POLINI
    COMPACT RADIAL MZ34

    THERE WERE AT ONE TIME 32+ DIFFERENT BRAND NAME SNOWMOBILE ENGINES THAT MANY COULD BE USED ON AIRPLANES. JLO ALONE MADE 14 DIFFERENT SINGLES FROM 100cc to 395cc!

    DIFFERENT BRAND NAME ENGINES USED ON SNOWMOBILES
    1. BSE
    2. BOLENS
    3. BROOTEN
    4. BRUT
    5. CCW
    6. CHAPARRAL
    7. CHRYSLER
    8. CUYUNA
    9. JOHN DEERE
    10. HARLEY-DAVIDSON
    11. HIRTH
    12. HUSQVARNA
    13. JLO
    14. KAWASAKI
    15. KIEKHAEFER AEROMARINE
    16. KLIORITZ
    17. KOHLER
    18. LLOYD
    19. MERCURY
    20. OMC
    21. POLARIS
    22. ROCKWELL
    23. ROTAX
    24. RUPP
    25. SACHS
    26. SACHS WANKLE
    27. SCORPION BRUT
    28. SOLO
    29. SPRINT
    30. SUZUKI
    31. ZENOAH
    32. YAMAHA

  2. The Avg Cost of a used Rotax 277UL/277F with a Gear Drive is $250 to $600! Rebuild Kit, Piston & Rings, Gaskets & Seals, and Crank Bearings is less than $200.

    Version 1 277UL was rated 26hp@6250rpm, actually Dynoed 25.4hp@6000rpm!

    Version 2 277UL was rated 28hp@6400rpm! Never seen one actually Dynoed!

    Version 1 277UL with an R&D Aero Tuned Pipe Dynoed 30.5hp@6250rpm!

    Part 103 Full Power Speed is 55 knots = 63.29287 mph and probably 36 hp will Push or Pull most Part 103 55 knots!

    All Planes have a MTOW which 99% of he Part 103’s and Small kit Planes MTOW fall between 450 lbs and 660 lbs.

    If you use the Simple 1 kw for 10 kg Rule, 450 lbs = 204.1166 kg / 10 kg = 20.41166 kw to Fly Well = 27.37249 hp to Fly Well!

    Avg USA Pilot Weight falls between 180 lbs and 235 lbs. A Part 103 at 254 lbs + 30 lbs (GAS) + 235 lbs (Pilot) = 519 lbs, say 10 lbs for Bags, = 529 lbs = 239.9504 kg / 10 kg = 23.99504 kw to Fly Well = 32.17788 call it 32 hp to Fly Well!

    For a 2 Stroke to make Max hp at 6500rpm and using 11.5cr and with a Proper Sized Carb with a Tuned Pipe it takes 7cc to make 1hp! 32hp x 7cc = 224cc minimum! So a 277UL 268.8cc/7cc = 38.4hp@6500rp is possible. A +/- 1.0cr = 1hp!

    A 450 lb MTOW needs 27hp.
    A 540 lb MTOW needs 33hp.
    A 600 lb MTOW needs 36hp.
    A 650 lb MTOW needs 40hp.

  3. Anyone considering using any of the two strokes listed above should know most were very poor snowmobile engines. Therefore not good for Aviation use either.

    Example – the Bolens engine was actually Kiekhaeffer Aeromarine. The large quantity of warranty claims caused to Bolens to exit the snowmobile market and concentrate on lawn care products.

    The 14 JLO single engines were poor – they tried 14 times to produce a good snowmobile engine based on their industrial pump engines but were unsuccessful compared to the Rotax and various Japanese singles . (Yamaha, Kawasaki, Fuji, Suzuki etc).
    One of the worst examples was the JLO 372 / 380. Very overweight for the low hp produced.

    The only good JLO snowmobile engine was the twin cylinder that eventually was
    upgraded and improved into the Cuyuna UL engine family.

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