REFLECTOR: Engine Selection

Thu Jun 17 18:16:57 CDT 2004

yes this is true, but even though you have the centrifugal forced balanced
with the counterweight, you still get asymmetrical thrust from only one side
of the prop hub so it really is not feasible- many years ago when I used to
race RC aircraft, there was a guy with a tiny .049 powered bird running 90%
nitro methane and he used a single bladed prop, it was about 50% larger in
diameter than the normal 2 blade- that little plane probably did about
120mph, the engines did not last long at 20,000 rpm, but he said that they
were cheap, so he did not care.........
  -----Original Message-----
  From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org]On
Behalf Of J.P. Brooks
  Sent: Thursday, June 17, 2004 12:00 PM
  To: Velocity Aircraft Owners and Builders list
  Subject: Re: REFLECTOR: Engine Selection

  most efficient blade would be a single blade with a
counter-weight.....yes?

  At 10:43 AM 6/17/2004, you wrote:

    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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