Comments on: NOTAR

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By: Ehud Gavron

Ehud Gavron — Sun, 13 Sep 2009 03:26:03 +0000

Without a tail rotor, the two rotors will cancel the torque of the engine and transmission, and to a certain point will provide lift on opposite sides. After the blade-stall point an increase in airspeed means that each rotor’s dissymmetry of lift meant it was LESS effective on its retreating-blade cycle (and conveniently this was made up by the other blade’s advancing cycle) so in effect there ended up being ONE rotor blade at any given time ADVANCING and providing lift.

So yes, this helps eliminate retreating blade stall, since the other rotor’s blade makes up for it, and also makes up for dissymmetry of lift across the entire “rotor zone” (when we include the two counter-rotating rotors).

However, whereas before the blade stall on each 1/2 of 2 rotors there was sufficient lift and power, now there’s less… so if you have a super power-available aircraft where you can pile on the turbines and bring more power to bear, than yes, after such loss of lift (speed greater than blade stall per rotor) you can now function with “1 effective rotor” and continue to have 100% lift and 100% thrust (requiring somewhere >100% normal power). If you don’t have that power, you’re still limited.

I look at it from an engineering standpoint. My mechanic and pilot friends just shake their heads and walk away slowly. Sometimes they call me for beers. I hope Tim explains it better

Ehud

By: mick fincher

mick fincher — Sat, 12 Sep 2009 03:31:49 +0000

Around 1942, a german aircraft designer, Anton Flettner, perfected the FL282 “Kolibri” a helicopter with side-by-side, counter-rotating, intermeshing rotors. It had a rudder bot no tail rotor. Further, I suspect that, provided the rotors where advancing outboard of the fuselage, this arrangement would go a long way to eliminating retreating blade stall, one of the speed limiting factors faced by conventional rotorcraft. Comments?

By: Fritz Cripe

Fritz Cripe — Fri, 11 Sep 2009 18:03:03 +0000

The NOTAR system is not only more costly, it also eats away at the cruise speed by approx. 10 knots. According to the MD website, the 500E cruises at 135, the 530F at 134 and the 520N at 123 (lowering the gross weight by 350 lbs. will get you up to 128). This is one of the main reasons the military stayed with the conventional tail rotor system on the MH-6/AH-6 platforms. MD also offers the Quiet Knight tail rotor system, a 4 -bladed system turning at a slower RPM, which greatly reduces the noise footprint.

Tim, keep up the great articles. It’s nice to see us rotor-heads represented so well.

By: Kevin

Kevin — Fri, 11 Sep 2009 16:54:53 +0000

Disadvantages of NOTAR? Mainly, it’s more expensive to order an MD ship with NOTAR, and some buyers are still opting for the conventional bladed tail in the 500 series (go to the MD helicopter website for more info). Power demand? A conventional tail rotor also feeds off the main engine, but the NOTAR loses some energy pushing all that air. I agree with a previous poster, thanks for the history lesson on the company.

By: Chris

Chris — Fri, 11 Sep 2009 08:35:42 +0000

Any disadvantages to a NOTAR? Is it as responsive as a conventional tail rotor, and how does it compare with respect to power demand?

By: Paul Lisowski

Paul Lisowski — Sat, 05 Sep 2009 02:27:09 +0000

There is a kit helicopter under development in Europe using a NOTAR antitorque system. Check out http://www.youngcopter.com/ for interesting details.

By: Dale Long

Dale Long — Sat, 05 Sep 2009 00:00:14 +0000

Thank you, Sir. Loved the history listen.