For Questions That Don't Merit Their Own Thread

[magnemoe]

5 hours ago, DDE said:

It wasn't. The initial ascendancy of jet engines was driven primarily by material science limitations - their turbines are exposed to a particularly harsh operating regime, and are still at the forefront of metallurgy, ceramics, and compounds my high school chemistry teacher thinks not possible. Perhaps the two significant leaps would be the straightforward axial flow compressor design - which shrunk the frontal area of the engine - and the turbojet, which counterintuitively routed some/most of the compressed air past the combustion chamber, with some examples being essentially ducted turboprops with a different propeller design.

The lack of axial compressors, however, did not present much of a challenge for the initial designs, and the turbojet increased efficiency but was developed after the birth of civilian aviation.

This the WW2 German jets had an engine lifespan of around 20 hours. Yes Germany was critically short on tungsten and other high temperature materials but it was issues. 

One other problem with the early jet engines was the high fuel use, this is why the B36 had both jet and piston engines and they was experimenting with parasite fighters on them as fighter jets had way to short range to escort the B36. 
Noway pretty much all commercial propeller planes are turboprops. Piston engines are popular on personal planes as they are much cheaper so use in bush planes and similar but not for flight routes. 

This might well have slowed down the allies interest in jets, they wanted long range fighters to follow the slow bombers.
An engine who ate lots of fuel and was likely to fail forcing the pilot to bail out over enemy land was not very interesting. 
Other role was tactical air support but here speed was not very important.

Germany on the other hand needed interceptors who did not need range but needed superiority over the enemy. 

[mikegarrison]

11 hours ago, ARS said:

What's the main problems of the early jet engines?

The turbines would be destroyed by the heat.

7 hours ago, DDE said:

 the turbojet, which counterintuitively routed some/most of the compressed air past the combustion chamber, with some examples being essentially ducted turboprops with a different propeller design.

You mean: "turbofan".

[StrandedonEarth]

7 hours ago, DDE said:

turbojet, which counterintuitively routed some/most of the compressed air past the combustion chamber

I believe you meant turbofan. 

oops, ninja'd, didn't see the new page...

[mikegarrison]

ps. There's no "one revolutionary solution" for keeping the turbines alive. Lots of solutions working in concert.

1. better temperature distributions from the combustor
2. better turbine materials
3. active cooling
4. TBC (thermal barrier coating)

[ARS]

Two materials of different heat conductivity are joined into a single bar, with connection point in the middle. Material A has very good heat conductivity, while material B has very bad heat conductivity. A heat source then make a contact directly on the connection point, heating the bar equally on A and B side on the small area on the connection point. My question is does it makes B's heat intake lower by allowing A to divert some of the incoming heat due to it's better conductivity?

[wumpus]

On 8/24/2019 at 4:29 PM, magnemoe said:

This the WW2 German jets had an engine lifespan of around 20 hours. Yes Germany was critically short on tungsten and other high temperature materials but it was issues. 

One other problem with the early jet engines was the high fuel use, this is why the B36 had both jet and piston engines and they was experimenting with parasite fighters on them as fighter jets had way to short range to escort the B36. 
Noway pretty much all commercial propeller planes are turboprops. Piston engines are popular on personal planes as they are much cheaper so use in bush planes and similar but not for flight routes.

Oddly enough, the turbo-compound engine were also in considerable use in WWII.  The idea was that you used the exhaust from your piston engine to drive a turbine, which helps drive the propellers.  This increased gas efficiency and ("brake specific horsepower") and thus range, at a cost of extreme complexity and maintenance costs. Simplifying the whole structure into a turboprop was a big driver in that direction.

My understanding is that the real driver for buying a turboprop over a piston engine are the maintenance costs (A&R mechanics are expensive).  Increased fuel efficiency is great, but you save more on longer time between overhauls.

10 hours ago, ARS said:

Two materials of different heat conductivity are joined into a single bar, with connection point in the middle. Material A has very good heat conductivity, while material B has very bad heat conductivity. A heat source then make a contact directly on the connection point, heating the bar equally on A and B side on the small area on the connection point. My question is does it makes B's heat intake lower by allowing A to divert some of the incoming heat due to it's better conductivity?

I would assume so,  at least until Material  A was heated to a uniform temperature.  Until then, the rest of the bar on material A's side will act as a heatsink drawing heat away from the connection point.  As material A's temperature increases this effect will get less and less (to the point the effect may switch, as material B's side will remain cold but is a lousy heat sink).

Warning: I have no formal education in thermodynamics beyond learning enough in physics class to understand the Carnot cycle.  On the other hand, One blue three brown (a great youtube channel devoted to explaining math) is doing a multipart series on the equation that governs the topic you are asking about

[kerbiloid]

If put at one side of the heater a silver spoon, at another side - vacuum, the spoon gets hot, the vacuum not.

So, almost everything goes into spoon.

[mikegarrison]

14 hours ago, kerbiloid said:

If put at one side of the heater a silver spoon, at another side - vacuum, the spoon gets hot, the vacuum not.

So, almost everything goes into spoon.

This is because of heat capacity. Vacuum, having essentially no mass, has essentially no heat capacity. All the heat has to go somewhere, so it goes to the spoon.

The original problem is not really very well-posed.

If you glue a sponge to a rock and set it in some water, which half is most of the water going to end up in? The sponge, because sponges have a capacity to absorb a lot of water while rocks generally do not.

Edited August 29, 2019 by mikegarrison

[kerbiloid]

24 minutes ago, mikegarrison said:

This is because of heat capacity. Vacuum, having essentially no mass, has essentially no heat capacity. All the heat has to go somewhere, so it goes to the spoon.

Replace the vacuum with air and take a silver spoon of infinite size.
Now you have two accumulators with infinite capacity, but most part of heat withh pass into the spoon due to high conductivity.

[mikegarrison]

21 minutes ago, kerbiloid said:

Replace the vacuum with air and take a silver spoon of infinite size.
Now you have two accumulators with infinite capacity, but most part of heat withh pass into the spoon due to high conductivity.

Eventually, all the heat will be distributed such that the temperature is even everywhere. How the heat is initially distributed depends on the details. It is relatively hard to put heat into air, while it is relatively easy to put it into silver. However, it is also relatively hard to take heat out of air, while it is relatively easy to mix air. So if you are adding heat using a hot air gun, you may heat the air up faster than the silver.

So it depends on how much heat you are adding, how quickly you are adding it, whether there is forced convection or natural convection or no convection at all (if there is no gravity), etc.

The question is mixing rates and capacities and does not specify some important parameters and is just generally not really well-posed. Generally speaking, if you give the heat an easy path and a hard path, it will take the easy path. But as more and more heat goes to the easy path, unless you have an infinite sink then the temperature will eventually get hotter, which will divert more and more heat to what was originally the harder path. You will eventually reach an equilibrium in which the heat flow is split such that the rate of temperature rise in both paths becomes equal.

Edited August 29, 2019 by mikegarrison

[kerbiloid]

Forward windows to look when docking.

***

Gemini, Apollo, Shuttle, TKS FGB, designed Zarya have forward windows to see where they dock.
Soyuz due to its specific shape has a periscope and cameras. (TKS FGB also had cameras).

But all of them are old-style.

***

Modern ships:
Orion and CST-100 have forward window(s).
Crew Dragon and PTKNP afaik don't.

Say, Orion has specific tasks, PTKNP has specific origin.
But CST-100 and Dragon have exactly same task: to make a short trip to the station and dock.

Why CST has a window, why Dragon doesn't?
Does Dragon have better cams? Are these windows really needed?

P.S.
As Kerbals have low-sitting eyes, it makes a headache to have them properly windowed.

[DDE]

3 hours ago, kerbiloid said:

TKS FGB also had cameras

Did it? AFAIK it had a Soyuz-MS-style blister included into its aft rim, for direct line of sight.

[kerbiloid]

10 minutes ago, DDE said:

Did it? AFAIK it had a Soyuz-MS-style blister included into its aft rim, for direct line of sight.

It has two windows above the docking port and 2 camera-looking objects captioned as "TV camera", below and aside from the port.
And pdf "СОИ комплекса Алмаз" shows a videoindicator on the Jupiter control panel.
So, probably the pilots and the ground operators could use them.

[ARS]

Is it practical to use chainsaw as weapon during zombie apocalypse if it has (somehow) infinite fuel and you're strong enough to wield it?

Edited August 31, 2019 by ARS

[kerbiloid]

Zombies get attracted by loud sounds, not frightened.

[DDE]

16 hours ago, ARS said:

Is it practical to use chainsaw as weapon during zombie apocalypse if it has (somehow) infinite fuel and you're strong enough to wield it?

No. It's bad at chopping, gets easily fouled up (ask tankers what driving over infantry does to their tracks) and likes to rebound into your face.

[mikegarrison]

CST-100 may have a window, but their docking is done autonomously via computer. And if it does have to be done manually, it's done by joystick and screen.

 

 

Edited September 1, 2019 by mikegarrison

[ARS]

6 hours ago, DDE said:

rebound into your face.

How it's going to rebound to my face?You could just grind up the zombies with it

[kerbiloid]

28 minutes ago, ARS said:

How it's going to rebound to my face?You could just grind up the zombies with it

(Can't find out right now that student slashing movie when one guy plays with chainsaw, hits a branch above head, and it bounces back right into his girl head).

***

But basically, yes. A chainsaw is a great tool against zombies.

You hype somebody with the idea of chainsawing the zombies, give him a chainsaw, and hide aside with a silenced gun.

Edited September 1, 2019 by kerbiloid

[mikegarrison]

1 hour ago, ARS said:

How it's going to rebound to my face?

"kickback"

 

[Nightside]

21 hours ago, mikegarrison said:

"kickback"

 

That would make a good dynamics problem.

[KG3]

On 8/31/2019 at 2:14 AM, ARS said:

Is it practical to use chainsaw as weapon during zombie apocalypse if it has (somehow) infinite fuel and you're strong enough to wield it?

Yes, although I wouldn't use it directly on the zombies.  Putting felled trees in the path  of oncoming zombies is a great strategy.  Zombies would have a difficult time navigating through the crowns of the trees and get impaled on branches and stuck in crotches.  If you can find a thorny tree such as Black Locust or Hawthorn all the better.   

[magnemoe]

On 8/31/2019 at 8:14 AM, ARS said:

Is it practical to use chainsaw as weapon during zombie apocalypse if it has (somehow) infinite fuel and you're strong enough to wield it?

Chainsaws are horrible weapons as they are heavy and slow, the only good thing about them is the intimidation effect, i would prefer an axe. 
A bit better fighting zombies as you need to inflict heavy damage and they don't use weapons or tactic. 

Still this would be way more effective, longer reach, the weapon part is light and much more cutting damage as its 3 fast rotating knives on the end of an pole. 

[kerbiloid]

A team spirit. A command work.

And halberds.

Spoiler

Two are are fixing a zombie and holding away.
The third one slashes.

[DDE]

Picture a suborbital mission with an apogee of barely above 100 km.

At apogee, the pilot exits the vehicle, and never gets back in.

Is the parachute jump from near space survivable?

Does the situation change if were's talking 80 km above Kerbin?

Edited September 5, 2019 by DDE