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<<3) I have been told to expect cruse speeds in the 225 knot area with the
normally aspirated, 260hp IO-540. Does that seem about right?
>>

Ron,

The Lancair web site lists the following speeds for the Legacy:

310 hp Cont IO550 - 276 mph @ 8,000 ft

200 hp Lyc IO360 - 250 mph @ 12,000 ft -AND- 280 mph @ 18,000
I'm guessing the figures for the Lycoming are a turbocharged installation.


75% power cruise for your Lyc IO540 is 195 hp
75% power cruise for the Cont IO550 is 232.5 hp

The "engine power ratio" between these two engines is 232.5hp/195ph = 1.19

I believe speed varies with the cube of power for propellor aircraft so:

"speed power ratio" = (276mph/258.7mph)^3 = 1.21   (note 258.7 mph = 225 kts)

225 kts seems reasonable if the figures claimed on the website are correct.


A question for you:
You have some experience with flying turbocharged (Cont. TSIO360) aircraft.
What are your thoughts on a turbo IO360 Lycoming vs non-turbo IO540 Lycoming?
I've noticed, as you have, that the used IO540s are not more expensive than
the used IO360s. I'm wondering if the extra weight and complexity of turbo
makes the IO540 the better choice.
What do you think?
Paul Klusman


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