REFLECTOR: Engines and High DA

Al Gietzen ALVentures at cox.net
Sat Feb 5 22:58:59 CST 2005


 

 

-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of Scott Derrick
Sent: Saturday, February 05, 2005 7:05 PM
To: Velocity Aircraft Owners and Builders list
Subject: Re: REFLECTOR: Engines and High DA

 

 

>I'd expect the most effective way to reduce takeoff roll would be going to
a

>variable pitch prop, no?

>

Maybe, maybe not.  There are wins and losers for an MT, the only prop 

with a history  and its checkered.  You do gain in a reduced take off 

roll.  You lose in a 65-85 lb CG demon on the end of the engine.  I've 

been told to expect at least a 100 lb loss in net weight once you add 

weight up front to get the cg in line.  They break easily & often.  They 

are horribly expensive to get fixed.  They take forever to get fixed.  

Many on this list have more time on there spare fixed pitch then there 

MT.  You also loose 5 to 10 knots on the top end, something I don't want 

to do.  And of course there is the added complexity for flying and 

maintenance.

 

Yeah; I was thinking purely from the standpoint of translating power into
thrust - not all those other things.  I don't want one of those on my
airplane either.

 

>  For a fixed pitch cruise prop a good portion of

>the blade is in stall condition until the speed gets up, and adding more

>power would mostly just make more noise.  I'm just guessing here; have no

>data.

>

The data I  have gathered says your wrong.  Its not just noise.  Its 

called Horse Power.  The density altitude alone  here in Grants reduces 

my HP by 20 %.   I've been taking to a fellow with an E-Racer with a 

TIO540, using a Catto Prop.  He breaks ground in less than 1000 feet at 

gross weight.  With his old IO360 it was 2500 ft.  Sounds like a goodly 

portion of those 300+ HP are pushing it along down the runway. 

 

I just meant that the stalled portion of the produces mostly noise and
little thrust, so more power into the stalled portion makes more noise.
Clearly the unstalled portion, and the power converted as the speed picks
makes a big difference.  That's good to know.

 

Craig has done a marvelous job with the prop design.

 

Al

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