Valin,

I have a TSIO-550 powered Legacy. I’m assuming you have a standard IO-550 engine. The compression ratio for my engine is 7.5:1. I think your engine is probably 10:1. If you don’t install intercoolers for the turbos the IAT (inlet air temperature) will probably be in the neighborhood of 30 to 40 degrees F above a non turbocharged engine. That being said, I don’t think that would be a problem as long as you keep the MP at 30”.

As far as high density altitude performance is concerned, You will be happy with what a turbocharger can do for you. Though there is slight increase in ground speed/true airspeed for the same indicated airspeed as altitude is increased the turbocharger will allow you to only give the factor little consideration. The engine will produce sea level as long as you maintain 30” of MP. This also allows you to not have to make constant changes to the mixture during the climb.

The turbos will certainly reduce the density altitude restraints to only a minor consideration. Just remember the compression ratio and don’t start pushing the throttle to where the MP is much above 30”.

Lynn Farnsworth

Super Legacy #235

TSIO-550 Powered

Hey LML gang,

With an eye toward practicing instrument approaches, I downloaded the RealAir Lancair Legacy airplane model for Flight Simulator X.  I’ll send a separate LML post asking about its accuracy to focus that particular discussion.  I was impressed, though, with its apparent flight performance fidelity in general.

With our Legacy still under construction, it was interesting to fly the simulated Legacy out of our new airport base in Colorado at the Rocky Mountain Metro Airport (KBJC) near Boulder (former Jeffco) with a field elevation of about 5673 ft MSL.  Fortunately the longest runway is about 9000 ft long.  Even with that, if the Legacy sim model is fairly accurate, it has me concerned about takeoff performance especially during summers with density altitudes as high as around 9000 ft.  With a naturally aspirated engine we’ll be looking at only about 24“ of manifold pressure at full throttle and the thinner air for the prop and wings...

So my question is, what kind of takeoff performance are Legacy pilots seeing at high elevation airports – take off rollout, climb rates, etc.?  This has us thinking about at least turbo-normalizing our IO-550 engine…  For those with turbo-chargers, what kind of improvement in performance are you seeing at high elevation airports?

Also, how are pilots adjusting their takeoff technique at high elevations.  In comparing the sim Legacy at sea level and in Colorado, and being on the back side of the power curve below about 120 kts, it helps to delay take off rotation speed at high elevation in the sim.  Real world…? 

Thanks,

Valin Thorn

Legacy Project

Boulder, Colorado