Did you know...

[Huskymaniac]

Just for fun, I wanted to start a thread about interesting and possibly little known facts which may be relevant to folks here. I will start with this tidbit I discovered today while doing actual work/research:

Did you know that Aluminum powder, especially when in the form of small/fine particles, will spontaneously combust when exposed to air? I thought I would be fine so long as I stayed away from Magnesium. I think this is usually not an issue as aluminum particles typically oxidize before we gather enough of them together for it to be an issue.

[icingdeath88]

Organic chemist here. What kind of research do you do?

[Huskymaniac]

Originally Posted by icingdeath88

Organic chemist here. What kind of research do you do?

I am an optics/laser engineer but I have found myself dabbling in organic chemistry this past week. I am particulary interested in thermally cured epoxies/plastics which are highy transparent at a wavelength of 1um, have an index of refraction of 1.49 (or slightly higher) at 1um and have a long term operating temperature of at least 150C. Any suggestions?

[BackWoodsBob]

I worked in a lab as a tech for a while. We had atomized aluminum, but never had it combust.

[wdb]

[posted in the spirit of the original thread intent]

...that Britney Spears' panties spontaneously combust upon contact with the light flash from a camera?

[icingdeath88]

Originally Posted by Huskymaniac

I am an optics/laser engineer but I have found myself dabbling in organic chemistry this past week. I am particulary interested in thermally cured epoxies/plastics which are highy transparent at a wavelength of 1um, have an index of refraction of 1.49 (or slightly higher) at 1um and have a long term operating temperature of at least 150C. Any suggestions?

Ah. You want the guys down the hall from me - polymer chemists. Sounds like interesting stuff.

Did you know that if you try to clean up lithium aluminum hydride with acetone, you make isopropanol? And also fire.

[dcarrb]

Did you know Buddy Ebsen (Jed Clampett on the "Beverly Hillbillies") lost his gig as the Tin Man on the classic "The Wizard of Oz" due to an allergic reaction to the aluminum powder in his silvery makeup?

It's important to know these things...

dcb

[svxcess]

Did you know that a banana tree is not a tree, but a herb?

And that the banana is not really a fruit at all, but a berry?

.

[Ron Mummert]

A tomato's a berry, but a banana has appeal.

[Landshark]

Cadillac CTS-V suspension could be stiffer.

[Blacky]

Originally Posted by icingdeath88

Organic chemist here. What kind of research do you do?

Hey, cool. My father had a PHD in organic chemistry.

[svxcess]

Originally Posted by Landshark

Cadillac CTS-V suspension could be stiffer.

....Then put her in a Turbo Mustang....SSDD

....


.

[injuhneer]

Originally Posted by Huskymaniac

Just for fun, I wanted to start a thread about interesting and possibly little known facts which may be relevant to folks here. I will start with this tidbit I discovered today while doing actual work/research:

Did you know that Aluminum powder, especially when in the form of small/fine particles, will spontaneously combust when exposed to air? I thought I would be fine so long as I stayed away from Magnesium. I think this is usually not an issue as aluminum particles typically oxidize before we gather enough of them together for it to be an issue.

Yes. It makes a great solid fuel for model rocketry.

-Mike O

[Stevebsy]

What are the mu ratio and the mu-1 barrier?

Mu is the English spelling of the Greek letter μ. It can be pronounced "mew" or "moo," with "mew" being the more common. It is commonly used to represent a ratio in rotorcraft engineering, sometimes called the rotor tip advance ratio. To put it about as simply as it can be put into words, the μ ratio is the ratio of the forward speed of the aircraft to the rotor tip speed relative to the aircraft. To put it into a picture, which is worth a thousand words:


where Vtip is the tip speed of the rotor, VA is the speed of the aircraft, and μ is the mu ratio.
There are a few interesting things that can be determined from the μ ratio. First, and most obviously based on how μ is defined, you can easily determine the airspeed over the tip of the rotor at the 3 and 9 o'clock positions (when the rotor is perpendicular to the aircraft). When you are at a μ of 1, the tip speed is equal to the aircraft speed. So, on the advancing blade, at the 3 o'clock position, the airspeed over the tip is twice what it is over the rest of the aircraft. On the retreating blade, at the 9 o'clock position, the airspeed over the tip is zero.

Another interesting thing that can be determined from the μ ratio is how much of the rotor is seeing reverse airflow at the 9 o'clock position. Each position on the rotor blade sees a different airspeed, which is a combination of the speed from the rotor turning and the speed from the aircraft. As you move outboard on the rotor, the rotational velocity gets higher. The μ ratio will tell you what proportion of the retreating blade is seeing reverse flow at the 9 o'clock position. For example, at a μ of 0.3, the inboard three-tenths of the retreating blade will see reverse flow, the outboard seven-tenths will see normal flow, while the point exactly at three-tenths will have an airspeed of zero. At a μ of 1, the tip of the retreating blade will have an airspeed of zero, and everything inboard of that will see reverse flow. That is the μ-1 barrier. It is the point at which the rotor first sees complete reverse flow on the retreating blade. The CarterCopter Technology Demonstrator became the first rotorcraft to achieve a μ of 1 in June 2005. The previous high of 0.92 was established around 50 years ago by the McDonnell XV-1 .


Diagram of Rotor Flow Direction for μ < 1

Diagram of Rotor Flow Direction for μ = 1

Diagram of Rotor Flow Direction for μ > 1
From a flapping stability standpoint, a μ of 0.75 is the most unstable.

[Huskymaniac]

Originally Posted by Stevebsy

What are the mu ratio and the mu-1 barrier?

Are you studying helicopters?

My father knew Igor Sikorski. Igor used to go to the club soccer games and my father played for one of the Italian clubs, back in the 50s.