Aerodynamics Discuss the physics of flight revolving around the aerodynamics and design of aircraft.

How can asymmetrical planes fly?

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Old 11-26-2013, 06:50 AM
  #1
Lnewqban
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Cool How can asymmetrical planes fly?

While this forum has been so quiet, I have been studying Rutan's designs, finding the asymmetrical Model 202 Boomerang (1996).



http://stargazer2006.online.fr/aircr.../boomerang.htm

"It was designed by Burt Rutan to be a safe and efficient twin-engine aircraft that would not become dangerously difficult to control in the event of failure of a single engine.
..............In the Boomerang, all of the asymmetry is there to eliminate the asymmetry experienced during an engine failure. If an engine were to fail, the pilot doesn’t need to do much to maintain control. The airplane continues flying straight.
..............Rutan calls the Boomerang his greatest accomplishment in general aviation. He pretty much created the aircraft to be his own personal machine, and flew the plane for six years before hangaring it as other projects took his focus."


Here is my question for us to discuss:
How can asymmetrical planes fly?

I wonder how many aerodynamic challenges Rutan had to face during design and trim.

I know of one successful model of this design, which was awarded in the 2009 Toledo show:
2009 Non Military Sport Scale Plane Winners
Third Place
Mike Fritz
Waterloo, Ontario



The model is 1/5th scale with an 88 inch wingspan and is powered by two Saito 72 four stroke engines.

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Old 11-26-2013, 07:43 PM
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At a quick guess, by flying straight I'm guessing that means any roll induced by yaw is minimised.

With forward swept wings, the wing that's yawed forward would tend to produce less lift. There also may be carefull attention paid to the angles the engine are pointing in so that the airstream from the props strikes certain parts of the airframe that they wouldn't normally strike when both engines are running. Free flight guys have tweaked with how everything interacts in designs for years, from full power to glide, and all powers in between, they don't have the luxuary of just sticking and engine into a basic shape and havig some mug wiggle controls to make it fly properly.
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Old 11-26-2013, 10:07 PM
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The major advantage with this design is that the engines can be much closer together without having a fuselage in the way. This reduces the asymmetric thrust issue following an engine failure. Supposedly the aircraft requires zero rudder input in an engine out situation.

The original plan was to use radial Diesel engines running on Jet A1 (cheaper and widely available). Once the engines reached their life they would be exchanged for new ones at a cost well below the cost of reconditioning. The engine company would then use the used engines to power generators offsetting the cost of the new engines.

Somewhere on the net there is a series of sketches starting with a Beech Baron that is slowly modified one step at a time till it becomes the Boomerang. Rutan explains the reasoning, advantages, and performance increases of each step.

BTW there's no such thing as a symmetrical propellor aircraft. The torque and p factor make a symmetrical design fly crooked.

Dave H
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Old 11-27-2013, 12:11 AM
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Have a look at the German BV-141 from WWII: http://en.wikipedia.org/wiki/Blohm_&_Voss_BV_141

First flown in 1938.

The concept is far from new.

Bedford
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Old 11-27-2013, 08:49 AM
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Quote:
Originally Posted by beepee View Post
...........The concept is far from new.
Thanks, Bedford !!!

Different reasons and number of engines (one radial BMW in this case), but a pioneer asymmetrical design indeed.



Quote:
Originally Posted by gerryndennis View Post
.............Somewhere on the net there is a series of sketches starting with a Beech Baron that is slowly modified one step at a time till it becomes the Boomerang. Rutan explains the reasoning, advantages, and performance increases of each step..............
Thanks, Dave !!!

Here is Rutan's reasoning:
http://www.rutanboomerang.com/multim...g-step-by-step

"In trying to explain how Burt Rutan developed the idea of the Boomerang, he used a step-by-step comparison of a "traditional" twin-engine aircraft (Beech Baron BE58) and his design."



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Last edited by Lnewqban; 11-27-2013 at 08:59 AM.
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Old 11-27-2013, 06:31 PM
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Yep that's it, although the version I saw gave the theoretical performance increase and reduction of Minimum Control Speed at each step.

Clever bloke, I've flown the Varieze, Quicky, and Q2 designed by him.

Dave H

Last edited by gerryndennis; 11-27-2013 at 06:37 PM.
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Old 02-25-2014, 08:46 PM
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Quote:
Originally Posted by Lnewqban View Post
Here is my question for us to discuss:
How can asymmetrical planes fly?
How about this short answer to your question:

They can't. Asymmetrical looks doesn't mean asymmetrical forces. Same way a 767 can fly with one engine.

Kurt

Last edited by Bozarth; 02-25-2014 at 08:49 PM.
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