The "Flat Rate" Concept in Turbine engines

[Turbine Cowboy]

Hello all,

I need a little more than basic* explanation of the "Flat Rate concept" in Turbine engines.


*Limit it at SL to get it's most at higher levels

Thanx a bunch

TC


:confused: :hmm:

[Tinstaafl]

Start with a 'standard' turbine. It will be rated for a certain amount of thrust at SL on a standard day. As soon as the air temperature increases or pressure reduces (eg at altitude) then so does the thrust it can produce. It's possible to get more thrust from the engine by supplying more fuel however various bits of the engine won't stand up to the strain due to the increased temperatures inside the engine & the strain on the moving parts.

Change those limiting parts so that the engine now has the capacity to run hotter &/or faster. You now have a choice:

1. Supply the extra fuel at SL on a standard day = higher thrust engine, or

2. Leave the extra capability in reserve for a hot day or high altitude and use the ability to burn some extra fuel to maintain the original thrust capacity ie delay the normal altitude/temp. thrust reduction. Only works to point though. Eventually some part of the engine will reach its limit & thrust will reduce with increasing temp &/or altitude.


Now go beyond #2 and design the engine from the outset so that it has this reserve capacity. Certify it at whatever lower capability you choose. You now have an engine that can maintain its output up to some higher than normal air temperature before its performance starts reducing. It's 'flat rated' to whatever that particular temperature is.