REFLECTOR: To Turbo or Not

Jeff Barnes jcbarnes411 at sbcglobal.net
Sat Apr 18 16:43:40 CDT 2009


Hi Scott, 
 
    To Chuck's point, or to restate/paraphrase Duane Swing: Turbo is fine if you do a lot of west to east, but not so good if you do a lot of east to west.  Chuckle aside, no sense using the jetstream as a headwind.  
 
    High DA GW takeoffs: More is better, period.  The IO-540 300hp guys who have flown 260hp's is high DA will tell you the 300hp is way better. You only have to overrun an airstrip a few feet to hit a drainage ditch, runway lights, etc. 
 
   Another Duane Swing point: You can throttle back a 300hp to match the 260hp's best cruise: you'll get the same fuel economy.  I'm thinking other than full-on takeoffs & climb,  
if you slow your superHP tsio-520 down to 170kts, you should be getting really good fuel economy as well.
 
   If you build it out and it's a good runner, then change your mind as to whether it's right for your airplane - I'd think the higher HP would have much better resale value.
 
   Good luck !
 
Regards,
 
Jeff Barnes
        

--- On Sat, 4/18/09, Scott Derrick <scott at tnstaafl.net> wrote:

From: Scott Derrick <scott at tnstaafl.net>
Subject: Re: REFLECTOR: To Turbo or Not
To: "Velocity Aircraft Owners and Builders list" <reflector at tvbf.org>
Date: Saturday, April 18, 2009, 10:09 AM

I think part of my indecision is the question, "Does turbo charging make
my airplane more efficient?". 

Last years fuel prices  were an indication of  what we will see  in the
near future.  Once the world economy gets back to burning fossil fuels
at a greater and greater rate, prices will rise again. 

The Velocity is a very efficient airframe once airborne, though it has
its  problems.  For me that was  using way too much runway at  the
airports a frequented. 

Taking Chuck's question about mission to the problem.  Do I really need
325 HP vs 285 HP at takeoff, to solve the problem that initiated  this 
engine upgrade.   Getting off the ground at high elevation airports in a
reasonable amount of runway, in the summer at gross weight.

Am I sacrificing efficiency  for a Tool Time Velocity?   The  IO360  was
definitely  deficient at take off at elevations above 4,000.  Above 6500
it could get downright scary.   But is a TSIO520 going overboard when a
IO520 would do the job.

I was fairly happy with the cruise speed of 170 ktas that the io360
produced.  Especially at 9 gph.  With higher fuel prices a future drop
dead certainty that is a huge plus.  I've been told an optimal turbo
system uses 10% of the HP just to support itself.   Thats 33 HP for this
520.  Meaning the engine is actually producing 350HP to get 325 to the
prop.  I wonder how much in gph that costs. Seems like its going to
raise my cost to 10.5 gph, to go 170 ktas. 


Scott

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