CaptainPanic

IT HERE!!!! http://www.etotheipiplusone.net/?page_id=700

This thread is ancient (it started in 2008), but it appears this is the first actual Air trecks built... even though their name is Razerblades, rather than airtrecks. Congrats to the creator (named Charles).

Check out that website, it is worth it.

It would be a pretty low-maintenance defensive line.

imatfaal, thanks for the link. It is the best explanation (and the only one with a link) so far.

As I was taking a little summer holiday in Russia by browsing on google maps, I found some weird features in the Russian landscape that I cannot explain. There are triple or quadruple rows of trees (or other types of green), which extend for hundreds of kilometers through the landscape.

Here's an example of a triple line.

Here's an example of a quadruple line.

Here's one that crosses through a town, to give a sense of scale.

Finally, here's one just outside of Volgograd (formerly Stalingrad), which seems to give a possible hint about what this is...

These lines seem to have little to do with the borders of the oblasts or other governmental regions. The line just outside Volgograd suggests to me that this is a line that indicates the furthest advance that the German forces made in WWII (even though it is outside the city, and I thought that the battle took place inside the city)? The scale of these lines (hundreds of meters wide, stretching hundreds of kilometers) is quite mindboggling.

I've searched the internet for quite a while now, but I haven't been able to find a single reference to what these are. Guesses are welcome, but links and sources are what I am really looking for!

When was the last time there was a flying elephant landing near you?

Last Saturday at about 2:00 AM, I swear I saw it. I was walking home from the pub... in a very straight line too, I may add.

This made me chuckle...

cixe has been suspended for 1 week because of continuous personal attacks despite several warnings. Focus on the contents, not the people.

(Funny all 10 minutes, but my favorite bit is after 3 minutes until the end).

Hi there,

 

Sorry, I didn't find an introduction section, so I'll do it here.

You must have overlooked The Official "Introduce Yourself" Thread, which is a pinned thread in The Lounge. I moved your post and its reply into it.

Also, welcome to the forum!

spacevudo was banned for spamming. The rules say: We don't mind if you put a link to your noncommercial site (e.g. a blog) in your signature and/or profile, but don't go around making threads to advertise it. When you do the exact opposite, and make threads with the sole purpose of advertising your site, you get yourself banned.

wlad was banned for posting discussions from elsewhere on our forum, for continuing such discussions in absence of the other participants of that those discussions, for repeatedly ignoring warnings about that, for not learning from his suspension less than 2 weeks ago, and for soapboxing.

burgess has been banned for spamming: posting content on our forum that appears on hundreds of other websites across the internet.

Also, posting wiki-style posts without indicating the purpose of the thread (discussion, question, debate) is undesirable behavior. This was in itself not sufficient for a ban, but since warnings did not help, it was added to the list of charges, and it made our decision just that much easier.

md2 was suspended for 3 days for failing to engage in a two-way discussion and for writing incomprehensible or incomplete posts. Failure to engage in a two-way conversation will trigger a one-way response from the moderators, as happened right here.

I think he might be a chemist also

Apologies for a serious remark in the jokes thread, but I would just like to state that chefs are indeed chemists, and cooking is a form of (organic) chemistry.

To compensate for being so serious, here's a lolcat:

Have a good weekend!

Right, so the velocity has no direct relation to any process going on inside the rocket. Rather, the relative differences between the velocities of these propellants is what is interesting.

Hello everybody!

 

The gas generator cycle is widely used on rocket engines, but some variations are still possible and desireable. For instance, the Falcon launcher burns the derived flux with much kerosene and little oxygen to limit the turbine's temperature, but the resulting soot complicates the reuse of the engine.

 

One alternative, similar to Ariane's Viking, would add water to a tuned mix of RP-1 and oxygen, injected in two steps. 107:10:34 results in 873K=600°C; expansion from 50bar to 5bar gives 1133m/s. Good solution with one pump more.

 

If accepting additional propellants, (yuk!) hydrazine or MMH, hydrated for 600°C, give 2004m/s and 1696m/s - not fully useable by a turbine. Methylamine (yuk as a volatile amine, not carcinogenic like hydrazines) gives 400°C and 1552m/s if its decomposition is even. Hydrogen peroxide, 84% for 600°C, gives 1099m/s but can detonate.

I'm not much of an expert in rocketry, so can you explain some of the jargon here? What do you mean when you say that a particular fuel (or rather probably its combustion) "gives a certain temperature and velocity"?

I thought I understood that the temperature is the temperature you reach in the turbine due to the decomposition of the fuel (a temperature which is limited, so you don't break the turbine)? But what then do you mean with that velocity? What is going that fast, and where? And wouldn't that velocity depend on some more design parameters that you did or did not introduce here?

Laptop manufacturers will claim that the battery will last 5 hours, but that is at minimum usage. You may want to look up the Whr (watt-hours) of the battery. Then you want to look up the power usage of your motors. And then you can calculate how long that battery will last in your skates. (Hint: not 5 hours).

If you want a simple system that has a battery, a motor and a power throttle, get a cordless drill. It has everything you need already. This will have a motor of about 100W.

A more expensive (but probably better) system is found on an electric bike. Electric bicycles have a 250 W motor which can get those bikes up to 25 km/h (with the cyclist having to pedal too). But although their motors are designed to be lightweight and small, they're probably too big for a skate.

Author is Gary Larson. I am not sure this is the original source of the picture (i found it on some blog).

 

Your Hayabusa will do a mile in about 27 seconds and continue to accelerate for a bit more and given a nice empty road continue at damn close to 200 miles per hour. The fastest horses in the world take around 95 seconds to do a mile. Those speed gains are not linear - double the power does not double the speed.

That's not funny!

(as in, that's way too serious for this thread)

Now, this is funny:

Welcome to the forum, everyone.

Disenssio, if your native language isn't English, don't worry about any spelling mistakes. Just make sure to ask good questions, or give good answers.

Davidivad, ducttape is your friend for putting things together.

Noise of construction workers outside.

From XKCD. Made me chuckle.

p.s. Yes, this is the same text as at the top of the Homework Help forum.

Dear all,

Recently the amount of spam on the forum has increased. We are aware of this, and we are working on a solution (we know what caused it).

The spam is generally of the crappiest quality and easy to recognize. Generally, we patrol the forum and remove any spam quite soon after it was posted, but if you think a particular spam message has been missed by the staff, please report it.

Best regards,

SFN Staff

Seriously though, I've tried for a day or so to figure out the drag at 60mph in a tucked position and I can't do it.

Here's a list of drag coefficients (wikipedia). I'd go with the value for the cyclist or the skier.

It enables you to calculate that the drag force is about 300 N (rough back-of-the-envelope-calculation). At 60 mph, you're going about 27 m/s.

Power = Force * velocity = 300 * 27 = 8.1 kW, or about 11 hp.

Please note: this calculation is very rough... I did some rounding of the numbers. However, I still stand by my point of several years ago: I think you'll all struggle to get that kind of power in a shoe on wheels.

I am leaning towards Chemistry, but the more I learn, the more I realize I have no idea what I want to do.

 

I am terrified and excited at the same time.

 

Cheers!