REFLECTOR: Engine Selection

[Alex Balic]

Larger props are generally more efficient, and because of their diameter,
they need to be swung at lower RPM
  -----Original Message-----
  From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org]On
Behalf Of Douglas Holub
  Sent: Thursday, June 17, 2004 11:44 AM
  To: Velocity Aircraft Owners and Builders list
  Subject: Re: REFLECTOR: Engine Selection


  To each his own.  You can always go faster with a bigger engine, but to me
the weight and fuel consumption penalty for anything over 200 hp in a plane
this size isn't worth it.  That's just me.  A lot of guys like to build the
biggest, baddest airplane they can.  I love it.  More power to them
(literally.)  It takes all kinds of people to make up a world.  I'm one of
those "less is more", "think smarter not harder" kind of guys.  I'm shooting
for 180 mph and 25 mpg at 9,000 feet with my top door, short wing, fixed
main gear, retractable nose gear Velocity.

  I'm disappointed to hear that propellers are not more efficient at lower
RPMs. I was hoping that extra efficiency would give my diesel a little free
speed boost.

  Doug
    ----- Original Message -----
    From: Al Gietzen
    To: 'Velocity Aircraft Owners and Builders list'
    Sent: Thursday, June 17, 2004 11:22 AM
    Subject: RE: REFLECTOR: Engine Selection


    Just a couple of comments on this power, efficiency and speed thing.
Torque is a measure of force; HP is a measure of work; force times time – or
acting through a distance.  So it is the HP that does the job.  Hp is simply
torque times rpm.  You can have high torque a lower rpm but if it gives you
the same HP you’ve gained nothing; unless the prop was more efficient at
lower rpm.  I thought this was true as well – until I studied some prop
performance charts and found it wasn’t true.



    160; 180; or 200hp – IMHO, these are all low for a fixed gear 173.
Getting 161 mph at 5500 ft with 160 hp translates to 173 mph with 200hp
(remember; speed goes as the cube root of power).  That’s 153 kts.  Hardly
impressive.



    Al



    Subject: Re: REFLECTOR: Engine Selection



    Plenty of power. He's got a 173 RG. The Velocity was originally designed
for 160 hp.  The DH180A4 is 180 hp up to 18,000 feet. The DH200A4 is 200 hp
at 18,000 ft. Plus, the diesel has better torque at lower RPMs than a
Lycoming, and propellers are more efficient at lower RPMs. Plus it weighs
less if you take into account that it is 30% more fuel efficient, so you
don't need to carry as much fuel weight to get the same range. A DH160V4 is
in the factory's test airplane.  With the 160 hp engine they clocked it at
202 mph at 15,500 feet, and 161 mph at 5,500 feet. And that is with a fixed
pitch propeller.



    The DeltaHawk has half the moving parts of a Lycoming, no spark ignition
to interfere with the radios, and burns readily available and slightly
cheaper Jet A.  It is much smoother because it's a two-stroke. Plus, since
the DeltaHawk test platform is a Velocity Std RG, the firewall foreward
package is pre-designed.



    No, I don't own stock in the company. Just excited about the first
significant improvement in general aviation powerplants in 50 years.



    Doug Holub

    Std Top Door, 50% done, 80% to go

      ----- Original Message -----

      From: NMFlyer1 at aol.com

      To: reflector at tvbf.org

      Sent: Tuesday, June 15, 2004 9:18 PM

      Subject: Re: REFLECTOR: Engine Selection



      nice idea Doug... but not enough power scotty


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