REFLECTOR: Engine Selection

Thu Jun 17 14:05:53 CDT 2004

Doug, you're no fun!

-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of Douglas Holub
Sent: Thursday, June 17, 2004 10:44 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 <mailto:ALVentures at cox.net>  

To: 'Velocity Aircraft <mailto:reflector at tvbf.org>  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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