Is this considered a rotary winged aircraft?

[vladshulman]

I am trying to determine if a particular aircraft design would be considered rotary winged, as there is no direct definition of what's considered rotary winged:

If one was to take, let's say, a helicopter, and replace the top rotor with a ducted fan, would this still be considered rotary winged? In this configuration, the thrust produced by the ducted fan will be the force that's keeping the aircraft hovering / flying. That is, the pressure increases produced by the fan and nozzle are the significant causes of thrust (not necessarily the velocity increase).

I've heard some people say no to this question simply because a ducted fan isn't "called" a rotor, however a fan consists of blades that rotate about an axis, thus they are rotors in the same way the blades inside an axial compressor are referred to as rotors.

I highly appreciate your input on this confusing matter!

[JEFF TIPTON]

I would think it would be considered a powered lift much as the VT-22 Osprey.

[Alan_Cheatham]

Read this: http://en.wikipedia.org/wiki/Powered_lift

.

[vladshulman]

But that wikipedia article states:
"Powered lift or powered-lift refers to a type of aircraft that can take off and land vertically and functions differently from a rotorcraft in horizontal flight."

Does this mean that a powered-lift device can be considered rotary-winged if it never flies horizontally?

Also, it puts compound rotorcraft under the category of powered lift, and states:
"...in the USA, the term "compound rotorcraft" officially refers to a mixed powerplant system). Some types have a ducted rotor design..."

and uses the V-22 as an example. Would putting ducts around the V-22's rotors turn it into a different class of aircraft? Or would it still be considered compound rotorcraft? (if it's still a compound rotorcraft, why aren't compound rotocrafts / powered lift vehicles a subcategory of rotorcrafts?)

I apologize for the in-depth look, but I am really trying to determine if my original design falls under the rotary winged category!

[hillberg]

It's more like a Hawker Herrier powered lift-jet thrust to hover

[vladshulman]

But I thought the Harrier was considered a powered lift-jet because it used the exhaust gases produced by combustion to ultimately provide the thrust. Would it still be considered a powered lift-jet if instead the Harrier used a turboshaft engine to spin a rotor for thrust? Or simply powered lift?

Because in this case I am wondering where the line is drawn between something being a rotary wing aircraft and powered lift aircraft.

[Alan_Cheatham]

FAA Federal Aviation Regulations 14 CFR 1.1


Rotorcraft means a heavier-than-air aircraft that depends principally for its support in flight on the lift generated by one or more rotors.

Helicopter means a rotorcraft that, for its horizontal motion, depends principally on its engine-driven rotors.

Powered-lift means a heavier-than-air aircraft capable of vertical takeoff, vertical landing, and low speed flight that depends principally on engine-driven lift devices or engine thrust for lift during these flight regimes and on nonrotating airfoil(s) for lift during horizontal flight.

.

[hillberg]

The pegasus in the AV 8 is a Fan engine,Front nozzles "cool" rear nozzles "hot"
A Turbo fan has a core engine driving a fan section.

[vladshulman]

Originally Posted by Alan_Cheatham

FAA Federal Aviation Regulations 14 CFR 1.1


Rotorcraft means a heavier-than-air aircraft that depends principally for its support in flight on the lift generated by one or more rotors.

Helicopter means a rotorcraft that, for its horizontal motion, depends principally on its engine-driven rotors.

Powered-lift means a heavier-than-air aircraft capable of vertical takeoff, vertical landing, and low speed flight that depends principally on engine-driven lift devices or engine thrust for lift during these flight regimes and on nonrotating airfoil(s) for lift during horizontal flight.

.

Great! Thanks for the FAA classification!

Then if I understand correctly, the only difference between a rotorcraft and powered-lift is the use of nonrotating airfoils for lift during horizontal flight!

Going back to the design idea I wrote in my first post; if the ducted fan produced thrust for vertical flight, and likewise for horizontal flight (with control surfaces keeping the aircraft stable and not attributing anything to lift, such as the apache AH-64, then it would be classified as a rotorcraft?

[hillberg]

????AH-64?????The AH 64 is all helicopter What are you thinking???????

[vladshulman]

Originally Posted by hillberg

????AH-64?????The AH 64 is all helicopter What are you thinking???????

I was referring to the "stub wings" that an AH-64 has.
http://www.boeing.com/rotorcraft/mil...-2_375x300.jpg

Clearly they produce some lift, thus can act as control surfaces. But the AH-64 is still considered a rotorcraft because that amount of lift is relatively small compared to that of its rotors.

So I was thinking that if an AH-64 is considered a rotorcraft, then a ducted fan with control surfaces that impact lift minimally (purely for stability and control), is also considered a rotorcraft.

[PW_Plack]

Originally Posted by vladshulman

...In this configuration, the thrust produced by the ducted fan will be the force that's keeping the aircraft hovering / flying. That is, the pressure increases produced by the fan and nozzle are the significant causes of thrust (not necessarily the velocity increase)...

Whoa, time out. In a hovercraft, the pressure can provide a force which lifts the craft above the ground, but pressure does not provide thrust. Thrust is created by the acceleration of a mass of air, (as in, measurable in pounds,) not just by pressurizing it, or by moving an unspecified mass of air at a certain velocity.

The FAA can't win on this one. The distinction is semantic. Under the FAA's definition, a hovercraft which uses flat fan blades is a powered-lift, but if the fan blades are shaped like an airfoil it's a rotorcraft. This is one of those "know it if I see it" definitions which is tied to how the aircraft is used, but can't be framed that way without opening a bunch of gray areas.

[vladshulman]

Ahh I see! So then how exactly does the FAA look at an aircraft and determine its classification? Or does the designer rather put a case up as to what he believes the aircraft is classified as, and then the FAA "approves or denies" his request?

Originally Posted by PW_Plack

... but pressure does not provide thrust. Thrust is created by the acceleration of a mass of air, (as in, measurable in pounds,) not just by pressurizing it, or by moving an unspecified mass of air at a certain velocity.

And in regards to this, you're absolutely correct in stating that thrust is created by acceleration of mass air, however when you break it down further, thrust (in a duct) is determined from the velocity and pressure leaving the nozzle before it interacts with ambient conditions. (Thrust = massflow*(velocity exit - velocity ambient) + NozzleArea*(Total pressure exit - total pressure ambient)). In, for example, conventional turbofans high and low, it has been found that they produced more thrust when their nozzles were choked; that is, so total pressure exiting was greater than ambient conditions. Unlike previous designs that relied on the greater velocity increases to provide thrust while the flow expanded to ambient pressures.
So that's where I was going with talking about pressure. But regardless of which method is most efficient for thrust, my primary concern was if this idea could pass as rotorcraft, so thank you very much PW_Plack!

[PW_Plack]

Vlad, you'd probably be at the mercy of your local FSDO and inspector if you built something which looked like a hovercraft and tried to register it as a "rotorcraft." It's simply a gray area that has to stay gray to accommodate innovation. If you built something that looks like an R22 with non-airfoil blades, could make it fly, and called it a powered-lift, you'd raise eyebrows, but I don't know whether they'd have to give it to you or not.

"Hmmm...it walks like a duck, quacks like a duck. Probably better be registered as a duck."

This is one reason the loophole exists that allows pilots with a private certificate in any category/class to fly solo in any experimental, provided the operating limitations require only category and class, but not a specific category and class. Otherwise, there would be no way to test-fly new inventions that blurred the lines.

[cleatus99]

Sounds Similar in fuction to this, which I would consider Powered-Lift Aircraft.