Help - Info for JetHawk II

On Feb 5, 6:22*pm, Bob Kuykendall wrote:
On Feb 5, 2:01*pm, MOTORCITYBADBOY MOTORCITYBADBOY.3n5...@no-

mx.forums.travel.com wrote:
I'm looking for any info on a design called the JetHawk II. Plans would
be cool, or info on the designer/company.

My rule of thumb is that if Google doesn't bring up much info about a
proposed or preliminary aircraft design, then the design probably went
nowhere and there are no plans and no prototype. I found a couple of
forums where posts suggested that there was in fact a flying JetHawk
prototype and even plans available, but digging into it shows that the
plans were not well-received.

One of the best links I found was this page, it has a cutaway view
that shows the internal configuration of the JetHawk II:

http://massflow.archivale.com/

It's kind of a neat looking little airplane, but I take it with a
grain of salt of epic proportions:

* Ducted fan installations, with almost no exceptions, have
underperformed their expected results in thrust per unit everything
including weight, complexity, fuel consumption, and cost.

* The mixing of composite shells and welded steel trusses has rarely
been a match made in heaven. There are some bright exceptions,
including the GlasStar, and the old Sequoia 300, and some marriages of
necessity such as the Stemme S10 motorgliders. But for the most part
you'd come out ahead in strength and stiffness per pound and per
dollar if you just took the weight of the steel trusses and added that
much more material in shell thickness and in reinforcements to the
composite parts to make them structural members. The mixing of steel
trusses is too often the mark of a developer who is unfamiliar with
the design and development of composite parts.

Thanks, Bob K.

There is a Yahoo group on ducted fans where the Jethawk was discussed
at length. IIRC the main objection was that the airplane was designed
for a speed well above a ducted fan's optimum "sweet spot".

The take home is DF's work well at high speeds (turbofans) where a
real propeller would have tip speed mach number problems and at low
speeds below 80 knots.

I've looked at the ducted fan issue and it looks like they can be
optimized to produce 8 -10 Lbs of thrust per HP in the 80 knot speed
range. The only airplane I know of that would benefit from that is a
glider tug.

bildan wrote:
.....
I've looked at the ducted fan issue and it looks like they can be
optimized to produce 8 -10 Lbs of thrust per HP in the 80 knot speed
range. The only airplane I know of that would benefit from that is a
glider tug.

9 lb of thrust at 60 kt takes 1.6 HP
Perhaps you had 30 kts in mind for 9 lb thrust per HP at 80% efficiency?

Brian W

On Feb 5, 9:20*pm, Brian Whatcott wrote:
bildan wrote:

....

I've looked at the ducted fan issue and it looks like they can be
optimized to produce 8 -10 Lbs of thrust per HP in the 80 knot speed
range. *The only airplane I know of that would benefit from that is a
glider tug.

9 lb of thrust at 60 kt takes 1.6 HP
Perhaps you had 30 kts in mind for 9 lb thrust per HP at 80% efficiency?

Brian W

Yeah, that sounds about right. I was looking at the acceleration of a
glider being towed.

A glider tug is one of the few airplanes where the 0 - 60 acceleration
time matters since you have to get the glider up to an airspeed where
the ailerons are effective enough to balance on a single wheel. 30
knots is in the middle of that range.

A glider tug looks like a nearly perfect application for a ducted fan.

bildan wrote:
On Feb 5, 9:20 pm, Brian Whatcott wrote:
bildan wrote:

....

I've looked at the ducted fan issue and it looks like they can be
optimized to produce 8 -10 Lbs of thrust per HP in the 80 knot speed
range. The only airplane I know of that would benefit from that is a
glider tug.
9 lb of thrust at 60 kt takes 1.6 HP
Perhaps you had 30 kts in mind for 9 lb thrust per HP at 80% efficiency?

Brian W

Yeah, that sounds about right. I was looking at the acceleration of a
glider being towed.

A glider tug is one of the few airplanes where the 0 - 60 acceleration
time matters since you have to get the glider up to an airspeed where
the ailerons are effective enough to balance on a single wheel. 30
knots is in the middle of that range.

A glider tug looks like a nearly perfect application for a ducted fan.

You set off that hunger for the likes of the Fournier RF4 which could
travel a hundred miles over water on a certified (modified) VW without
going into Auto-rough, after a take off using that one retractable
mainwheel and wing outriggers.
Memorable moments when an approach controller once queried the type
(RF-4) as a military jet :-)

Brian W

On Fri, 6 Feb 2009 07:28:04 -0800 (PST), bildan
wrote:

A glider tug is one of the few airplanes where the 0 - 60 acceleration
time matters since you have to get the glider up to an airspeed where
the ailerons are effective enough to balance on a single wheel. 30
knots is in the middle of that range.

A glider tug looks like a nearly perfect application for a ducted fan.

I think not. Ducted fans are horribly inefficient at low airspeeds.
For that matter, they're not that great at higher speeds, either.

-Dana

--
"Next year in Galt's Gulch!"

On Feb 15, 4:35*pm, Dana M. Hague wrote:
On Fri, 6 Feb 2009 07:28:04 -0800 (PST), bildan
wrote:

A glider tug is one of the few airplanes where the 0 - 60 acceleration
time matters since you have to get the glider up to an airspeed where
the ailerons are effective enough to balance on a single wheel. *30
knots is in the middle of that range.

A glider tug looks like a nearly perfect application for a ducted fan.

I think not. *Ducted fans are horribly inefficient at low airspeeds.
For that matter, they're not that great at higher speeds, either.

-Dana

--
"Next year in Galt's Gulch!"

Ignorance!

The high bypass turbofans used on airliners is a ducted fan that is
very efficient at high subsonic speeds. At speeds below 80 knots, a
ducted fan is more than 4 times more efficient than an open prop.

It's just in the middle speed range that the drag of the duct offsets
the gain in efficiency.

bildan wrote:
On Feb 15, 4:35 pm, Dana M. Hague wrote:
On Fri, 6 Feb 2009 07:28:04 -0800 (PST), bildan
wrote:

A glider tug is one of the few airplanes where the 0 - 60 acceleration
time matters since you have to get the glider up to an airspeed where
the ailerons are effective enough to balance on a single wheel. 30
knots is in the middle of that range.
A glider tug looks like a nearly perfect application for a ducted fan.
I think not. Ducted fans are horribly inefficient at low airspeeds.
For that matter, they're not that great at higher speeds, either.

-Dana

--
"Next year in Galt's Gulch!"

Ignorance!

The high bypass turbofans used on airliners is a ducted fan that is
very efficient at high subsonic speeds. At speeds below 80 knots, a
ducted fan is more than 4 times more efficient than an open prop.

It's just in the middle speed range that the drag of the duct offsets
the gain in efficiency.


It's efficient - compared to a jet...

On Sun, 15 Feb 2009 17:18:10 -0800 (PST), bildan
wrote:

Ignorance!

The high bypass turbofans used on airliners is a ducted fan that is
very efficient at high subsonic speeds. At speeds below 80 knots, a
ducted fan is more than 4 times more efficient than an open prop.

It's just in the middle speed range that the drag of the duct offsets
the gain in efficiency.

A high bypass turbofan is a very different beast than a piston powered
fan.

Max thrust at low speeds is gotten by accelerating a lot of air a
little bit (i.e. big prop, flat pitch). That's not the definition of
a ducted fan.

Also fan to duct clearances have to be REALLY small for best
efficiency... difficult to achieve with the inherent vibrations of a
piston engine without a very heavy structure.

-Dana

--
There are 3 kinds of people: those who can count & those who can't.

bildan wrote:
On Feb 5, 6:22 pm, Bob Kuykendall wrote:
On Feb 5, 2:01 pm, MOTORCITYBADBOY MOTORCITYBADBOY.3n5...@no-

mx.forums.travel.com wrote:
I'm looking for any info on a design called the JetHawk II. Plans would
be cool, or info on the designer/company.
My rule of thumb is that if Google doesn't bring up much info about a
proposed or preliminary aircraft design, then the design probably went
nowhere and there are no plans and no prototype. I found a couple of
forums where posts suggested that there was in fact a flying JetHawk
prototype and even plans available, but digging into it shows that the
plans were not well-received.

One of the best links I found was this page, it has a cutaway view
that shows the internal configuration of the JetHawk II:

http://massflow.archivale.com/

It's kind of a neat looking little airplane, but I take it with a
grain of salt of epic proportions:

* Ducted fan installations, with almost no exceptions, have
underperformed their expected results in thrust per unit everything
including weight, complexity, fuel consumption, and cost.

* The mixing of composite shells and welded steel trusses has rarely
been a match made in heaven. There are some bright exceptions,
including the GlasStar, and the old Sequoia 300, and some marriages of
necessity such as the Stemme S10 motorgliders. But for the most part
you'd come out ahead in strength and stiffness per pound and per
dollar if you just took the weight of the steel trusses and added that
much more material in shell thickness and in reinforcements to the
composite parts to make them structural members. The mixing of steel
trusses is too often the mark of a developer who is unfamiliar with
the design and development of composite parts.

Thanks, Bob K.

There is a Yahoo group on ducted fans where the Jethawk was discussed
at length. IIRC the main objection was that the airplane was designed
for a speed well above a ducted fan's optimum "sweet spot".

The take home is DF's work well at high speeds (turbofans) where a
real propeller would have tip speed mach number problems and at low
speeds below 80 knots.

I've looked at the ducted fan issue and it looks like they can be
optimized to produce 8 -10 Lbs of thrust per HP in the 80 knot speed
range. The only airplane I know of that would benefit from that is a
glider tug.

A few years ago I met a man who was flying an autogyro with a rather
nice ducted fan layout using variable pitch paddle blades at high RPM. I
don't recall exactly where he's from, I think Mariana Florida. He told
me about prop efficiency in the low 60 percentile being fairly typical
in ducted fans. It was a rather tidy layout.

Dan, U.S. Air Force, retired