All entries for March 2009

March 06, 2009

Flight testing

Today I began doing some preliminary tests on my paper airplanes (or gliders). I just want to 1) try a few small things like folding the wing tip up/down, changing the wing area, to see what effect they have on flight time. I was actually quite surprised at the result especially when some of the modifications I made produced unexpected results (like when I expected not to fly, it did, when I expect it to fly, it crashes etc). Some of the more consistent finding I observed were

1) The way I throw launch the plane has a significant impact on the flight time/ distance

Initially I did not expect this to make much difference because I thought after the launch phase, the plane will just glide according to its aerodynamic properties conferred by its design. But I noticed sometimes on the same plane I get different results. When I tried to make my throw consistent, I noticed a relatively horizontal throw (very little angled throw) will produce much better flight distance than a more vertical throw (aimed higher say around 30 degrees from horizontal).

This finding made me reconsider whether to use throwing angle as my 'noise' factor in my Taguchi experiment. Initially I thought from a customer's view , one may not pay careful attention to the way he/she throws the paper aeroplane, so a 'robust' plane could be something that could be thrown at any angle and still produce good flight results. But since any throwing angle of above 20 degree or so may potentially reduce flight performance significantly, there may not be much point changing the angle of flight throw (i dont know...) .

Then I read about several different launch method. One is to throw the plane vertical as high as possible and let it decend through gliding. The second is to launch it from a high place. The second method is better for me because I don't think I could get my throw consistently high every time. But both methods require a large space such as the basketball court in the sport centre. This availability of space could be a potential constraint for my experiement. This means I may end up throwing it horizontally allowed by my height in a large classroom, or in a long corridor (such as the corridor in Claycroft).

2) The flight result of two identical planes are surprisingly similar

This is a result I wanted but I didn't expect the flight result of two identifical planes to be so similar to each other. Initially I thought the variation in my throw could have significant impact on the result, but to my surprise, when I perform the same throw on two planes with identical design (with a little practice to get consistent throw), they both landed at the exact same location! This is good news because it suggests with a careful attention to my throw, I could actually eliminate or reduce the influence of my throw on the flight result. This means the changes in flight result will likely be attributed to the design changes.

3) Somtimes it hard to determine whether improved flight is due to deliberate change in design or unknown factor

This is something I observed when I tried to throw a randomly folded plane (still maintain the basic design but has its wing tip folded down for no particular reason), I noticed the plane actually 'glide' quite nicely (slow descent)  but in an upside down manner. But when I fold another plane properly with a much larger wing surface, it didn't glide but rather flies like a dart (very fast, no gliding) and descend very quickly. This suggest to me that for the first plane it wasnt the wing that was producing lift but when it turned upside down, the whole plane upside down was producing lift (confusing).

That's for now, I will think more about what control factors I will use for the Taguchi experiment to influence flight performance. I also need to think about the location where I perform the experiment. Initially I thought about doing this outside, but now I think the wind will have too much influence which could make my experiment invalid. So indoor is probably better option for now. But as mentioned before, there are also multiple options for indoor location.

principles of flight

Principles of flight
This is a simplisitic summary of how I understand paper airplane aerodynamics


How does plane fly?
Plane flys because when it flys lift is created on its wings.

How is the lift created?
This lift is created because when the air pressure is smaller above the wing and greater underneath the wing.

Why is airpressure different above and under the wing?
This happens because when wings travel through air, the air travels faster above the wing and slower underneath the wing.

Why air travels faster above wing?


(Fig 2a)
The ways airfoil is designed (curvature on the top) means the distance to travel from the front end to the rear end is greater on the top surface than on the bottom surface (more distance to travel at the top, less distance underneath). When to bottom air reaches the rear end of the airfoil, the top end is still 3/4 of the way (see fig 2a), this creates a vacuum of air (vortex) at the rear end that pulls the top air to make it go faster (like how a vacuum cleaner pulls air) to meet the bottom air at the rear. (Note as of 16:40 06/03 a mistake in the description about the 'distance difference as a cause of lift generation' is recongised and will be corrected in a future entry)

How is air pressure difference related to lift?
Consider this; a motionless object is simply in a state where all forces applied to is equal in all directions. Pressure difference creates unequal balance in force. As the pressure above the wing lessens, the downward 'push' by gravity and weight of atomphsphere is overcomed by the upward 'push' of a denser under-wing air (like a hydrogen balloon, air inside ballon is 'lighter' (less pressure) than the 'heavier' air outside the ballon (higher pressure), therefore the plane rises up.

March 05, 2009

An amazing Discovery

Think you are paying too much for your international calls?

Then you should read about my 'amazing discovery'!

It's for all the people who make international calls to their family, friends

If you usually talk on the phone with someone from one country

You can pay GBP 2 something and talk as much as you like from your skype to their landline

The voice clarity is much better than Skype-2-Skype, or MSN-2-MSN

What's more!

You can select a landline number in any country, so your friend and family can use their landline to call you on a local number and pay only the local rate! It's great if your friend or family does not have good internet connection, just ask them to call their local landline number !

In New Zealand, local phone calls are capped, so now I have a virtual New Zealand phone number. My girlfriend  and family can call me from their landline phone and pay nothing !

I put this information here because before my 'amazing discovery' I paid like GBP 5-8 a month on international calls T.T

March 04, 2009

Inventory Management

After spending sometime reading the content page on KBAM (Knowledge based asset management) homepage. I realise Knowledge management and Asset management is only an umbrella term for a huge number of other management ideas/tools. For example, asset management alone has 7 separate ideas from facilities management, security management to resource utlisation, all of which are important in ensuring that, resources (such as building, knowledge, man power, machines, raw materials etc etc) are used in the most efficient manner. This high level of effciency is important for successful companies because being highly lean, effcient means less wastage, and product and services can be produced/provided at lower cost.

I am particular interested in one area - inventory management. Inventory exists in companies (esp in manufacturing) because it is often difficult to predict how much demand there will be at a future time. If we do not have some spare stock sitting in our warehouse, we risk losing sales and make disatisfied customers. Inventory, which can be raw material, work in progress, and finished good , provides a buffer that balances the discontinuity between supply and customer demand. I guess the general philosophy is it is better to play safe, to have excess stock sitting in the warehouse rather than not to have enough.

But there is the JIT (just in time) philosophy which goes against the idea of inventory. It argues inventory makes the job of supplier easier but it adds no value to end customer, plus it ties up working capital which can be better utlised in e.g. investing in new technology, paying off debt. The JIT philosophy, although make good sense, seem to require a very good system of managing supply orders, fulfilling customer orders, inventory levels etc in order to avoid problem with unbalanced supply and demand. I think I would read up more about it to see how it works.

To achieve JIT philosophy, there seem to be tools that help to gather and organise supply, production , and inventory information so that they can be translated into specific orders, times of orders, times of receipts etc. Right now these tools such as MRP(Material requirement planning), MRP II (master production planning), DRP (distribution requirement planning) are just names to me, but I think they are used to manage inventory.

Right now I have no idea why this is important to me or how I may use this knowledge. It just seem interesting to me because of two reasons. First I can relate it to my previous work experience as a salesperson. At that time, I remember the many occasions when there were many customers demanding a particular Television or Fridge but we simply did not have the stock sitting in our warehouse. A sales opportunity wasted. It wasn't even our own fault because we have no say in our warehouse. So you can imagine our disappointment after successfully persuaded customer to buy something only to find out we have nothing to sell them. Since this happened so much in our job, we developed the habit to check stock before we sell something (I have a small trick for this :P). But this means we often have to, 1) only sell product that are available but not the one best suited for customer, 2) Go extra effort to convince customer to change their choice of product. I believe if the problem with inadequate supply is addressed we could have increase our turnover significantly.

The second reason comes from the business simulation we did in FACS module. In that simulation I was the commercial manager responsible for getting the right amount of contract. I remember it was quite tricky determining our production capacity and use that information so that at the end of each year we have no working capital tied up in the inventory. Then there was issue of determining how much raw material to purchase at each quarter so that we don't either have too much raw material (tied up money) or too small raw material (we have nothing to make). The general feeling I had at the time was managing supply chain is quite tricky. It seemed like if every body (production, finance, marketing directors) just try to optimise their own departments, there would be a huge problem with supply chain.

March 2009

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  • totally agree by prestige car hire on this entry
  • Again another example of people being too soft ..what wrong with working for stuff by seo london on this entry
  • WHAT ! This is totally foolish you have to work for job and work either harder to keep them.. with t… by front door on this entry
  • I agree with that too. by news on this entry
  • Good things come to those who wait sounds like the right answer. by cheap seo on this entry

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