engineering

NOTAR

NOTAR is a engineering topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand NOTAR rather than just read about it. In short: NOTAR ("no tail rotor") is a helicopter system which avoids the use of a tail rotor. It was developed by McDonnell Douglas Helicopter Systems (through their acquisition of Hughes Helicopters).

Key takeaways

NOTAR belongs to engineering; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect NOTAR to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of NOTAR from memory before moving on to harder problems.

Reference excerpt

NOTAR ("no tail rotor") is a helicopter system which avoids the use of a tail rotor. It was developed by McDonnell Douglas Helicopter Systems (through their acquisition of Hughes Helicopters). The system uses a fan inside the tail boom to build a high volume of low-pressure air, which exits through two slots and creates a boundary layer flow of air along the tailboom utilizing the Coandă effect. The boundary layer changes the direction of airflow around the tailboom, creating thrust opposite the motion imparted to the fuselage by the torque effect of the main rotor. Directional control is gained through a vented, rotating drum at the end of the tailboom, called the direct jet thruster. Advocates of NOTAR assert that the system offers quieter and safer operation than a traditional tail rotor.

Development

The use of directed air to provide anti-torque control had been tested as early as 1945 in the British Cierva W.9. During 1957, a Spanish prototype designed and built by Aerotecnica flew using exhaust gases from the turbine instead of a tail rotor. This model was designated as Aerotecnica AC-14. The Fiat 7005 used a pusher propeller that blew against a cascade of tail vanes at the rear of its fuselage. Development of the NOTAR system dates back to 1975, when engineers at Hughes Helicopters began concept development work. On December 17, 1981, Hughes flew an OH-6A fitted with NOTAR for the first time. The OH-6A helicopter (serial number 65-12917) was supplied by the U.S. Army for Hughes to develop the NOTAR technology and was the second OH-6 built by Hughes for the U.S. Army. A more heavily modified version of the prototype demonstrator first flew in March 1986 (by which time McDonnell Douglas had acquired Hughes Helicopters). The original prototype last flew in June 1986 and is now at the U.S. Army Aviation Museum in Fort Novosel, Alabama. A production model NOTAR 520N (N520NT) was later produced and first flew on May 1, 1990. It collided with an Apache AH-64D and crashed on September 27, 1994 while flying as a chase aircraft for the Apache.

Concept Although the concept took over three years to refine, the NOTAR system is simple in theory and works to provide some directional control using the Coandă effect. A variable pitch fan is enclosed in the aft fuselage section immediately forward of the tail boom and driven by the main rotor transmission. This fan forces low pressure air through two slots on the right side of the tailboom, causing the downwash from the main rotor to hug the tail boom, producing lift, and thus a measure of directional control. This is augmented by a direct jet thruster and vertical stabilisers. Benefits of the NOTAR system include increased safety (the tail rotor being vulnerable), and greatly reduced external noise as tail rotors on helicopters produce much of the aircraft's sound. NOTAR-equipped helicopters are among the quietest helicopters certified by FAA.

Applications

There are several production helicopters that utilize the NOTAR system, which are produced by MD Helicopters:

MD 530N: a 2025 NOTAR variant of the Hughes/MD500 series helicopter powered by the Rolls-Royce C30 engine MD 520N: a NOTAR variant of the Hughes/MD500 series helicopter MD 600N: a larger version of the MD 520N MD Explorer: a twin-engine, eight-seat light helicopter

See also Coaxial rotors Fenestron Intermeshing rotors (synchropter) Tandem rotors Transverse rotors Multirotors Quadrotors Tiltrotors Tip jet rotor Youngcopter Neo

Notes

References

Illustrations

Worked examples

Example 1 — a first encounter with NOTAR

Start with the simplest possible case. Write down what NOTAR claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In engineering, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to NOTAR before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about NOTAR ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of NOTAR

In research: NOTAR appears in engineering research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses NOTAR in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: NOTAR is common in secondary-school and first-year university syllabi. It links to neighbouring topics Aerospace engineering, Helicopter components, so understanding it makes those chapters shorter.
In everyday life: Look for NOTAR outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study NOTAR in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what NOTAR means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain NOTAR out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is NOTAR in simple terms?

NOTAR ("no tail rotor") is a helicopter system which avoids the use of a tail rotor. It was developed by McDonnell Douglas Helicopter Systems (through their acquisition of Hughes Helicopters).

Why does NOTAR matter?

Because it connects several engineering ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study NOTAR?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on NOTAR.