Symmetry

[Dave Jackson]

Man is symmetrical, in that his right side is a mirror image of his left side. I think women are symmetrical also. <img src="eek.gif" border="0"> In fact, all mammals are symmetrical. All birds, fish and insects are symmetrical. The only exception being crabs and tennis players, which have bigger right arms. <img src="smile.gif" border="0">

Man's inventions are founded in nature. The car, the boat, the plane are all symmetrical. The lowly bicycle and tricycle are even symmetrical.

Why was the helicopter made asymmetrical? <img src="confused.gif" border="0">

[john du'pruyting]

On the basis that one counterexample will disprove your theory, I find that my scrotum renders your proposition on mans symmetry incorrect <img src="cool.gif" border="0">

[Nick Lappos]

Dave,. .I believe you champion for bi-lateral symmetry, which only demands purity about one axis. Why discriminate against bi-horizontal or bi-vertical symmetry? Only a few people and creatures look the same upside down, and almost none of our machines do. What do we have that looks the same front-back?

It could be that you are looking, like those tortured 12th century philosophers, for metaphysical reasons to design a device, rather than good old fashioned practicality. Do I see a synchropter in this somewhere??

I myself would like to be sure that ships had their hulls on the bottom, airplanes had their wheels on the bottom, helicopters had their rotors on the top, sandpaper that is rough on only one side, and pens with ink only at the tip. This all seems quite nice to me, symmetry be damned! <img src="wink.gif" border="0">

[Dave Jackson]

handysnaks;

Perhaps you might try sleeping on the other side <img src="wink.gif" border="0">

. .Nick;

Too True. I do champion for symmetry, but like nature, only lateral symmetry. How cruel to suggest that this might have something to do with the synchropter. <img src="smile.gif" border="0">

Might it be fair to say that a strong argument for fly-by-wire in helicopters is that of providing ease of control electronically; whereas it could have been there by design from the beginning?

PS Only the Aussies, Kiwis and South Africans look OK upside down.

[ 26 January 2002: Message edited by: Dave Jackson ]</p>

[Lu Zuckerman]

To: Dave Jackson

The first operational helicopters had symmetrical airfoils in that the camber above and below the chord line was the same. When the designers departed from that philosophy and made helicopter blades like airplane wings they started to have problems. What I was taught in tech school and on the job at various helicopter firms the cambered blade as opposed to the symmetrical blade will try to climb when cyclic pitch is increased and tend to dive when cyclic pitch is decreased. This would lead me to believe that this condition precipitated the inclusion of dynamic vibration suppression systems on some helicopters. One helicopter that suffers from this phenomenon is the Apache. On the Apache the blades are attached to the head by a strap pack in the form of the letter “A”. The blade is attached to the apex of the A and the two legs of the A are attached to the rotorhead. This in itself is a very flimsy attachment so the only rigid attach point is the pitch horn / pitch link attachment to the swash plate. As mentioned previously the blade will try to climb and dive with the respective inputs of the pitch horn. Because the pitch link and the forward attach point of the A to the rotorhead are forward of the pitch axis, the two points tend to stabilize the blade but the rear attach point does not provide any stability other than the centripetal / centrifugal forces acting on the attach point. When the blade tries to dive the rear portion of the strap pack will lift up and then will be forced down when the blade climbs. This banging against the lower plate of the rotorhead causes the outside elements of the strap pack to fatigue and eventually fail resulting in a very high maintenance item.

[Dave Jackson]

Hi Lu

You may be moving off topic by bringing up blade symmetry; but for the fun of it ......

Rotor blades and their airfoils appear to be a very complex subject. A subject that entails art, theory, experimentation, computer modeling and a Ouija board. Some airfoils will pitch down when the angle of attack is increased, others will pitch up. Some blades are now produced which combine these opposing features in the same blade. Composite construction has allowed the helicopter blade to have varying attributes along its span.

Even carbon and Kevlar fibers may be replaced by silk. Just this week it was made public that man-made silk has finally been produced. It is 10x the strength of steel.

Your point about the lack of torsional stiffness in rotor blades is another sound argument for rotor rigidity. Mind you, all this torsional, in-plane and out-of-plane stiffness is going to play hell with the feathering bearings.

[heedm]

Dave, nature is only superficially symmetric. Some aren't even that, that girl in my senior year was 34A/C. weird. I don't recommend trying this at home, but if you cut open someone's abdomen, you'll find that we are very assymetric. And functionally so.

Don't want to flog a dead horse, but you live on the west coast and still think that fish are symmetrical? Go Halibut fishing.

Of course, airplanes aren't symmetrical, at least those with one engine and a prop aren't. Racing canoes with an outrigger are assymetrical. My bicycle has a chain only on the right side, my tricycle a bell only on the left. The Porsche 959S, which by all accounts is a fine example of an automobile, has a rearview mirror only on the driver's side.

. .Even the most simple of the building blocks of matter (subatomic particles) are assymetrical. Likely the most basic is the neutrino which by all proven accounts has only spin as an attribute. Chirally assymetric, just like a conventional helicopter.

(edited to add a happy face, <img src="smile.gif" border="0"> )

[ 26 January 2002: Message edited by: heedm ]</p>

[Dave Jackson]

heedm

You may be loosing sight of the forest because of the trees. Your perspective is too focused on detail. This is obvious, because the localized attention you gave your girlfriend resulted in her breast imbalance. . . <img src="eek.gif" border="0"> ~ :)

[ 27 January 2002: Message edited by: Dave Jackson ]</p>

[nucleus33]

Dave, people aren't very symmetrical. For instance your Lymph system is very different left and right, not to mention organs and innervation.

As for breasts, most women on the planet have a larger left breast than right. One theory as to why is that babies over the ages have prefered the left breast because it is closer to the soothing sound of their mother's heart, leading to it's developement evolutionarily.

Now I want all you guys to go and conduct some field research to verify this factoid.

Hans Conser :)

[baranfin]

I volunteer to do my best to collect as much information on FBS as I can. Women love it when you ask them if they want to participate in a survey. (actually I wouldn't know) <img src="frown.gif" border="0"> <img src="mad.gif" border="0">

[RW-1]

I would love to interview the women of the SoFla for this.

BTW, you didn't take into account which way one "hangs". If you are one way or the other, you are not purely symmetrical :) . (Some day's it's to the left, others ....)

[ 30 January 2002: Message edited by: RW-1 ]</p>