REFLECTOR: Engine Selection

[NMFlyer1 at aol.com]

In a message dated 6/17/2004 10:25:59 AM Mountain Standard Time, 
ALVentures at cox.net writes:
You can have high torque a lower rpm but if it gives you the same HP you’ve 
gained nothing
Well Al, I have to disagree on that aspect. If you have higher torque at a 
given RPM, Then you can turn more pitch at that RPM. If you have an adjustable 
prop, that should relate to a change. Either lower RPM setting for the same 
cruise speed (more pitch) or a higher cruise speed for the same RPM. Unless I am 
totally hosed (sometimes I wonder). 

For me, the goal was to get to rotation speed as quickly as possible. All 
else is a bonus. 
The 173 FGE is speced to cruise at 162KTS on a 200 HP powerplant. I did a 
little more shadetree work to guesimate the speed of my aircraft, here's what I 
came up with: 

The SR-20 is a slick, composite 4-seater with about the same gross weight as 
the 173FGE. 
It was powered with a 200HP IO-360. Cruise speed was 160 kts. 

They built the SR-22 with 300 HP. It gained weight due to the bigger engine, 
and gross weights stayed similar.  It cruises at 180 kts. 

So, 20 Kts increase in cruise speed for 100HP. expensive :)  Take off roll 
also went down by over 25% and climb increased by over 25%  

I have similar numbers. 125-140 extra HP, but I still have the same weight as 
an IO-360. 
No protruding scoops should help a little... couple of knots. 
So.. If my crayons are close... I should be able to cruise easilly at about 
180 kts. Of course, I'll have to find that sweet spot between power 
setting:cruise speed:fuel burn. 

Only time will tell. I have either convinced myself into buying a Packard in 
a dragster suit... 
Or built a decent performing machine.  Wish me luck. 

 Kurt Winker
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