Home Help Search Login Register
Do you want your ads here? Contact me.
Home | Forum | Results | Articles | FAQ | Competition archive | Media Gallery | Store
www.baggressive.com provides information for boomerang throwers and interested parties. You will find all the info you need to successfully throw a boomerang over 100m and have it return over your head.

 
 
ld book | Popular T-Shirts | Store overview
The classic B_AGGRESSiVE Shirt. Find it, and lots more designs in our shop.

Don't forget to check out our ld book, the best offline reference for long distance boomerangs.
BAGGRESSiVE forum  |  Long Distance  |  Articles  |  Topic: Wheel Radius
Pages: [1] Print
Author Topic: Wheel Radius  (Read 11358 times)
Hard Knox
Member

Offline Offline

Posts: 11



« on: Mar 14, 2007, 16:44 »

This is a good starting topic.  It may be obvious, but its implications may not be.  Wheel radius is a term I came up with to relate spin velocity to forward velocity.  Wheels come to a complete stop as they come in contact with the ground.  At a certain radius a boomerang will also come to a complete stop in midair.  That radius is what I refer to as the wheel radius (Rw).  At this radius the tangential velocity (Vs) due to the rotation is equal to the forward velocity (Vf).   Vs and Vf line up and cancel each other out when a point on the boom is at the wheel radius and at the lowest point of rotation.



View picture full screen

This means that the flow on the outside of the wheel circle is generally flowing in one direction, while the flow inside the circle is in all directions.  Knowing the Rw helps to determine what foil shape to use for each section.

Rw constantly changes during flight.  On the way out the forward velocity decreases until the boom reaches its highest point then it increases on its way back.  The spin velocity slowly decreases over the entire flight.  This means the wheel radius gets smaller as the boom goes out and gets bigger again on the way back.  The wheel radius will be zero if the forward velocity is zero. 

At launch the wheel radius is very close to the grip radius.  This is because the boom is moving forward very fast and the thrower must stay behind.  Remember that the wheel circle is where the forward velocity and spin velocity can cancel each other out.  Since the grip point is nearly standing still at the release point then the wheel circle should pass thru the grip point.  For this reason the distance between the grip point and the CG will determine the spin rate.  If you grip a boom closer to the CG then the spin rate will be higher. 


* wheel radius illustration.jpg (52.98 KB, 871x594 - viewed 3678 times.)
« Last Edit: Mar 14, 2007, 18:30 by Tibor » Logged
Tibor
136 m
BAGGRESSiVE
Member

Offline Offline

Posts: 226


B AGGRESSiVE


« Reply #1 on: May 28, 2007, 00:39 »

I have been going through this several times now and I still cannot make sense of this:
Quote
If you grip a boom closer to the CG then the spin rate will be higher.

Shouldn't it be the closer you grip to lower the spin rate?
Logged
Hard Knox
Member

Offline Offline

Posts: 11



« Reply #2 on: May 31, 2007, 13:11 »

The closer you grip to the CG the lower the forward velocity, but the spin rate is higher.

The best way to explain it is to continue the wheel analogy.   Consider two wheels rolling on the ground side by side at the same forward velocity.  One wheel is half the size of the other and will have to spin twice as fast to keep up with the larger wheel.  The grip point on the boom is like the point where a wheel meets the ground.   When you release, the boom “rolls” out of your hand.  Therefore, if the grip point is closer to the center of rotation (which is also the CG) then it will spin faster. 

Throw two similar boomerangs: one weighted on the leading wing, and the other on the trailing wing.  The one with the weight near the grip point will spin faster but have a slightly lower forward velocity at release.  The one with the weight further from the grip will spin slower but have a slightly higher forward velocity.  You may need to do a tandem throw to be able to see the two flying side by side for comparison.

Compare any two booms of equal weight but with very different grip-to-CG distances, and this will hold true.
Logged
Tibor
136 m
BAGGRESSiVE
Member

Offline Offline

Posts: 226


B AGGRESSiVE


« Reply #3 on: May 31, 2007, 14:38 »

I know it holds true. The effects of distance between grip and COG are very noticeable.

I always imagined that right at the time of release, the boom rotates around the grip point, and the center of rotation works its way to the COG in a few revolutions. Basically transferring rotational and forward velocity in some mystic ratio I cannot understand.

It has been shown in a high speed camera study (I can give you a citation but the study was done in German) that spin of a boom right after release is already around 10 Hz. The study does not disprove my theory of movement of the rotational center from grip to COG but it renders it less likely.

OK, check this out then and tell me if it makes sense:
If your rolling wheel theory is right and the boom rotates around the COG immediately after release, then you can deduct that you have to throw the same boom harder if you hold it closer to the COG to achieve the same forward velocity.
Or in other words: If you hold the boom at the elbow, you'll have to throw it harder to get the same forward velocity than if you would hold the boom at the trailing wing tip. Because, thrown at the elbow, more of the "throw energy" goes into creating spin than forward motion, compared to the throw gripped at the trailing wing tip.

You basically say that spin is inverse proportional to the distance between grip and COG and forward velocity is proportional to the same distance. It would be interesting to learn if it is a linear relationships (knowing boomerangs, probably not) and if there is a way to at least approximate how the ratio between spin and forward velocity is affected by the distance between grip and COG. Do I make any sense at all here? (I am a chemist, not an engineer or physicist, so way out of my league)
Logged
Pages: [1] Print 
BAGGRESSiVE forum  |  Long Distance  |  Articles  |  Topic: Wheel Radius
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1 RC3 | SMF © 2001-2006, Lewis Media Valid XHTML 1.0! Valid CSS!