flat rated engines

[VMC]

With regard to aircraft engines, what does the term, 'Flat-rated, mean?

[Lowtimer]

Imagine you have an engine that can put out a steady 500 hp at sea level, the power drops off in the usual way with increasing altitude.

You install a pair of them in an aeroplane originally designed for 300 hp a side. You don't want to go to the expense of installing new, bigger props, perhaps having to move the engines outboard so the new bigger props clear the fuselage, lengthening the undercarriage, strengthening the airframe to cope with the extra stresses that more than 300 hp a side puts it under, redesigning the tail surfaces and the controls so that the aeroplane can be controlled with higher power, either both at once or asymmetrically. Nor do you want to go through a gerat deal of flight testing to establish the greatly changed asymmetric fliying characteristics with 500 hp one side and zero the other.

So what can you do is flat-rate the engines - basically declare that they are not be operated above power setting X, which just happens to work out at 300 hp a side. So why bother? The big advantage is that the pilot can open the taps progressively further as he climbs, or for a high altitude departure, and still get 300 hp a side rather than struggling at high altitude.

[146fixer]

I thought flat rated meant that the engines produced sealevel power up to a given atlitude through turbo or supercharging.
Might be wrong.

[Kanga767]

Lowtimer- A superb answer!

Couldn't put it better myself.


K

[VMC]

thanks for that lowtimer, now I understand. You dont teach by any chance, do you?

VMC