The Model 250 began in 1958 as a simple, low-cost engine for both turboshaft and turboprop applications. By the time the -C28B variant arrived, it had become the dominant powerplant in the light helicopter market, powering the Bell JetRanger, Hughes 500, and a generation of training and utility rotorcraft .
250-C28B Architecture and Impact
The primary subject of this technical guide focuses on the Allison 250-C28B engine, engineered specifically for Turboshaft applications. Below is an essential digest of this powertrain configuration.
• 500 shp turboshaft
• 104 kg weight
• Powered JetRanger and Hughes 500
• Single combustion chamber
Allison 250-C28B Specification Data
500 shp output; single-stage centrifugal compressor; single combustion chamber; two-stage gas generator turbine plus two-stage free power turbine; weight 104 kg .
The 250’s single combustion chamber was unusual for a turbine engine—most designs used multiple chambers or annular combustors—but it simplified maintenance and reduced cost. The free power turbine allowed the rotor system to operate independently of the gas generator, a crucial safety feature in helicopters. The -C28B powered the Bell 206 LongRanger that set an around-the-world helicopter record in 1982, demonstrating the engine’s reliability over extended operations .
| Type | Turboshaft |
|---|---|
| Power | 500 shp |
| Compressor | Single-stage centrifugal |
| Combustor | Single chamber |
| Turbine | 2-stage gas generator + 2-stage free power |
| Weight | 104 kg (230 lb) |
| Fuel | Jet fuel |
Aircraft Powered by the 250-C28B
This engine model is deployed across various operational frameworks. Here is a breakdown of the typical machine or vehicle applications using this unit:
Bell 206A JetRanger, Bell 206 LongRanger, Hughes 500, Fairchild-Hiller FH-1100, Hughes OH-6A, Bell OH-58A
Pros & Advantages
Lightweight; simple single-chamber combustor; free power turbine for rotor independence; proven reliability.
Cons & Disadvantages
Modest power output; single combustor limits growth potential.
Frequently Asked Questions (FAQs)
Q1: What was the Allison 250 originally designed for?
A1: It was designed as a simple, low-cost engine for both turboshaft and turboprop applications, first running in March 1959 .
Q2: Which helicopters used the 250-C28B?
A2: The Bell 206A JetRanger, Hughes 500, Fairchild-Hiller FH-1100, and military OH-6A and OH-58A .
Q3: Why is the 250’s single combustor unusual?
A3: Most turbine engines use multiple chambers or annular combustors; a single chamber simplifies maintenance and reduces cost but limits power growth .
A Bell 206 LongRanger powered by the 250-C28B set an around-the-world helicopter record in 1982 .