For Questions That Don't Merit Their Own Thread

[p1t1o]

1 minute ago, YNM said:

I'm not sure, but on a flat road you can leave the engine on idle (no throttle), press the clutch, engage the first gear (manual) and let the clutch off - it'll roll on itself.

Indeed that is the optimal situation. The lurching seems to be prevalent at those awkward speeds where you need to go 1-2mph faster than that threshhold.

[YNM]

5 minutes ago, p1t1o said:

The lurching seems to be prevalent at those awkward speeds where you need to go 1-2mph faster than that threshhold.

I don't think there's any way around that -you either go at this idle speed or have a bit of throttle every now and then.

Though with more experience you'll be able to control it better. My father can even start off from stop in 2nd gear (usually in start-stop traffic as the 1st gear often gets harder to engage).

Edited December 12, 2018 by YNM

[p1t1o]

8 minutes ago, YNM said:

Though with more experience you'll be able to control it better. My father can even start off from stop in 2nd gear (usually in start-stop traffic).

Been driving for 17 years now! Starting in second is not difficult but its not great for the clutch.

But its not even a clutch thing. You could have the clutch fully engaged in gear and moving slowly and smoothly at some speed, then if I carefully slow down, at a certain (>idle) slow speed, the lurching begins. Im talking 1st or 2nd gear here. In higher gears you can slow down to the point where the engines is not turning sufficient revs to maintain operation and stalls, without ever experiencing the "lurching" effect - apart from if the stall is particularly "jerky" but I think that is a different phenomenon.

I dont know anything about a combustion engine that could explain a mechanical cause for the lurching, the power train should be capable of smooth operation through a large range of revs, right down to almost the point of stall, right?

Like I said Im guessing its a human factor but I've tried like, holding my foot perfectly still on the pedals and the lurching still manifests, seemingly out of nowhere. 

[YNM]

2 minutes ago, p1t1o said:

You could have the clutch fully engaged in gear and moving slowly and smoothly at some speed, then if I carefully slow down, at a certain (>idle) slow speed, the lurching begins.

I was thinking that one way to counter this is just to half press the clutch (or somewhere inbetween unpressed and half pressed).

Could it be due to the synchromesh, so it tries to disengage but failing (as the clutch isn't pressed) ?

My father have done 30+ years in manual (and some years having automatic).

[p1t1o]

7 minutes ago, YNM said:

I was thinking that one way to counter this is just to half press the clutch (or somewhere inbetween unpressed and half pressed).

Could it be due to the synchromesh, so it tries to disengage but failing (as the clutch isn't pressed) ?

Think that would work, but riding on a half-clutch wears it out quite rapidly, generally bad practice.

Its easily avoided by just coasting in neutral periodically, Im just at a loss as to the cause.

[Aquaticfantastic]

11 minutes ago, p1t1o said:

I dont know anything about a combustion engine that could explain a mechanical cause for the lurching, the power train should be capable of smooth operation through a large range of revs, right down to almost the point of stall, right?

This is mostly correct but there is a lower limit to this in each gear (1st is usually about 900rpm),  the lurching/juddering you feel when in a high gear/lowspeed is the engine beginning to stall, No cylinder or barrel is perfectly identical so not all combustion chambers will stall at the same rpm. What you are feeling is essentially the same as a mis-firing engine - one or more cylinders cannot compress/ignite the fuel properly because of the resistance caused by trying to turn a larger gear at too low speed, basically the extra resistance prevents the piston from rising back to the top of the cylinder with enough force to 'squeeze' the fuel air mixure this leads to less or no 'bang' from that cylinder this will slow the engine rpm further leading to a stall or if not quite enough judder. All this is also effected by engine temperature.

4-stroke cycle - Suck (inlet valve opens to allow fuel and air in) Squeeze (the fuel and air above the piston) Bang (spark plug ignites compressed fuel/air forcing the piston back down) Blow (exhaust valve opens to allow exhaust gasses to escape). Suck, Squeeze, Bang, Blow! All in one revolution, beautiful if you ask me.

As a side note, its is perfectly ok to shift gear without using the clutch provide you time it right, bad timing WILL damage your gearbox so I wouldn't recommend it unless your pretty confident you know what your doing.

[p1t1o]

20 minutes ago, Aquaticfantastic said:

This is mostly correct but there is a lower limit to this in each gear (1st is usually about 900rpm),  the lurching/juddering you feel when in a high gear/lowspeed is the engine beginning to stall, No cylinder or barrel is perfectly identical so not all combustion chambers will stall at the same rpm. What you are feeling is essentially the same as a mis-firing engine - one or more cylinders cannot compress/ignite the fuel properly because of the resistance caused by trying to turn a larger gear at too low speed, basically the extra resistance prevents the piston from rising back to the top of the cylinder with enough force to 'squeeze' the fuel air mixure this leads to less or no 'bang' from that cylinder this will slow the engine rpm further leading to a stall or if not quite enough judder. All this is also effected by engine temperature.

4-stroke cycle - Suck (inlet valve opens to allow fuel and air in) Squeeze (the fuel and air above the piston) Bang (spark plug ignites compressed fuel/air forcing the piston back down) Blow (exhaust valve opens to allow exhaust gasses to escape). Suck, Squeeze, Bang, Blow! All in one revolution, beautiful if you ask me.

As a side note, its is perfectly ok to shift gear without using the clutch provide you time it right, bad timing WILL damage your gearbox so I wouldn't recommend it unless your pretty confident you know what your doing.

 

I have considered this, but - and I could be wrong - the lurching seems to appear *above* idle revs. As @YNM suggested, I could go into gear at zero (idle) throttle and let it roll on those revs. The "lurching" I am talking about occurs slightly above those revs, ergo above the stall limit.

Otherwise I might not have noticed. Rolling along at idle is easy, but trying to maintain a constant speed of 1-2mph greater than idle is where the thing occurs, making this a very annoying speed to drive, hence I notice.

Although at this point, it is as likely as not that Im mis-remembering and it is the stall limit as you say. I havnt exactly been keeping robust data logs...

[YNM]

35 minutes ago, Aquaticfantastic said:

(1st is usually about 900rpm)

Idle RPM is usually higher than this, but indeed for some reason on the first press on the throttle this goes down (rather than up).

Maybe there's more to it on the fuel regulator.

Also I don't think I'd recommend anyone to shift gear w/o clutch. Long ago before synchromesh people used double clutch technique - still seen on 18-wheelers in the US I think.

1 hour ago, p1t1o said:

Think that would work, but riding on a half-clutch wears it out quite rapidly, generally bad practice.

Well, only on the approaches to a speed bump, for instance.

Edited December 12, 2018 by YNM

[XB-70A]

1 hour ago, YNM said:

Idle RPM is usually higher than this

Not sure, but I guess it can be related to the volume and the pressure in the cylinders. I'm currently driving an Optima LX, and its 2500 cm3 can stand around 700/750 rpm in idle (still, just like the speedo', I would not trust the tachy' neither at the lowest units...)

Edited December 12, 2018 by XB-70A

[KG3]

2 hours ago, p1t1o said:

 You could have the clutch fully engaged in gear and moving slowly and smoothly at some speed, then if I carefully slow down, at a certain (>idle) slow speed, the lurching begins. Im talking 1st or 2nd gear here. In higher gears you can slow down to the point where the engines is not turning sufficient revs to maintain operation and stalls, without ever experiencing the "lurching" effect - apart from if the stall is particularly "jerky" but I think that is a different phenomenon.

 

  It's allot harder for the wheels to turn the engine in low gear.  I usually park my car in first gear without using the parking break unless it's on a steep hill.  It does help if the vehicle has good compression.  If you try parking your car in 4rth gear without the parking break on a hill the car will very easily roll away.  If you try pop starting your car (without using the starter) by getting the car rolling then taking your foot off the clutch you need to do it in 1st or 2nd gear.  3rd or 4rth gear most likely won't turn the engine over fast enough to start it. 

[YNM]

5 hours ago, XB-70A said:

I'm currently driving an Optima LX, and its 2500 cm3 can stand around 700/750 rpm in idle

Huh... cars here usually idles at 1000-1500 rpm. Though mostly only 1300-1500cc.

5 hours ago, KG3 said:

wheels to turn the engine

Whoa whoa, we're not talking of jump-starting here...

Edited December 12, 2018 by YNM

[Superfluous J]

9 hours ago, p1t1o said:

Why do cars, at certain low throttle settings, usually in first or low gear, do that "lurching" thing?

The only car I've ever had that did this had an engine problem. I still have the car - and the engine problem - and am just driving it until it dies.

[ARS]

How exactly "flying low to avoid the radar" works? Does it means flying below the height of radar tower itself? To avoid the sweeping beam? If that so, on relatively clear and flat patches of land, such as desert, with no mountains around a very large area, could a radar tower erected lower than usual height to mitigate this tactic?

[magnemoe]

5 hours ago, ARS said:

How exactly "flying low to avoid the radar" works? Does it means flying below the height of radar tower itself? To avoid the sweeping beam? If that so, on relatively clear and flat patches of land, such as desert, with no mountains around a very large area, could a radar tower erected lower than usual height to mitigate this tactic?

You fly below line of sight from the radar, at sea this is below the horizon overland hills help, radar sweep is so wide you can not fly under or above it. 
At sea you will be picked up before reaching the ship but its still an huge advance as enemy get less warning and less time to hit you. 

An stealth plane flying high might be able to not getting picked up until its above the search beam, 

[DDE]

Did XLR-129 have a regeneratively cooled version of the extendable nozzle extension we see used on RL-10 with radiative cooling?

It looks like the usual propellant manifold right there.

6 hours ago, ARS said:

How exactly "flying low to avoid the radar" works? Does it means flying below the height of radar tower itself? To avoid the sweeping beam? If that so, on relatively clear and flat patches of land, such as desert, with no mountains around a very large area, could a radar tower erected lower than usual height to mitigate this tactic?

It works like this:

Source: http://www.ausairpower.net/APA-40V6M-Mast-System.html

The beam can sweep downwards, but it can’t sweep through mountains or the curvature of the Earth.

[kerbiloid]

(Without refraction-schmefraction and so on, roughly:)

https://en.wikipedia.org/wiki/Horizon

HorizonDistance = sqrt(Altitude * (2 PlanetRadius + Altitude)) ~= sqrt(2 * Altitude * PlanetRadius)

A standing human = sqrt(2 * 1.5 * 6.37*10⁶) ~= 4.4 km.

Observer and target:

Distance = sqrt(2 * TargetAltitude * PlanetRadius) + sqrt(2 * ObserverAltitude * PlanetRadius) = sqrt(2 * PlanetRadius)  *  (sqrt(ObserverAltitude) + sqrt(TargetAltitude))

[p1t1o]

10 hours ago, ARS said:

How exactly "flying low to avoid the radar" works? Does it means flying below the height of radar tower itself? To avoid the sweeping beam? If that so, on relatively clear and flat patches of land, such as desert, with no mountains around a very large area, could a radar tower erected lower than usual height to mitigate this tactic?

Apart from the horizon factors that other people ahve explained very well, there is another reason for this.

 

If a radar is looking at a contact with sky as the background, there is no reflection from empty sky, so the contact is very easy to discriminate.

However, if you are, say, patrolling at 20k feet, looking down at an aircraft on the deck, the background is not sky, but ground. The ground, and objects on it, reflect and scatter radar, so the background is much less clear than with sky, making it harder to pick out the target.

During the first half-ish of the 20th century (up to about 1970ish), this made the aircraft on the deck very hard to spot even if it is within your horizon.

 

However, they soon developed "look-down-shoot-down" technology - basically exploiting the pulse-doppler effect to make targets with relative velocities different to their background stand out, meaning a fast mover with a stationary background lights up. This essentially removes the issue of "ground clutter".

However, there is still some utility in flying on the deck, even today.

 

But not as much.

In fact, modern air combat is moving quickly towards an information-limited warfare (rather than, for example, speed or manouverability limited). Where stealth and electronic countermeasures can become so sophisticated as to make the higher altitudes available again - and large advantages are granted by altitude (fuel efficiency, weapon range etc.)

So the optimum "attack" altitude basically goes up and down like a yo-yo as technology and tactics are developed.

Relative technology and economic levels count a great deal as well - as today, "assymetric" warfare is the flavour of the week, so we can basically fly with impunity above about 10kfeet (to protect against smallarms and MANPADS) and drop whatever we like.

Edited December 13, 2018 by p1t1o

[tater]

 

[0111narwhalz]

On 12/12/2018 at 8:21 AM, Aquaticfantastic said:

All in one revolution

I thought it took two.

[Green Baron]

13 minutes ago, 0111narwhalz said:

I thought it took two.

It does. 4 piston strokes = 2 revolutions of the crank shaft.

Edited December 13, 2018 by Green Baron

[kerbiloid]

What is the proper common name in English for a room inside a ship for the diner/club/pub?
I can find "mess" as a common name and "wardroom" as a "mess" for officers.

I.e. how an orbital station module for this purpose could be called?
Not for sleeping (so, not a dormitory or habitat) but for eating/watching TV/playing.

The "mess" sounds a little weird for me like something messed (and wiki says these words indeed are derived from "porridge"), I'm not sure if "Mess Module" doesn't sound stupid.

Edited December 17, 2018 by kerbiloid

[TheDestroyer111]

27 minutes ago, kerbiloid said:

What is the proper common name in English for a room inside a ship for the diner/club/pub?
I can find "mess" as a common name and "wardroom" as a "mess" for officers.

I.e. how an orbital station module for this purpose could be called?

The "mess" sounds a little weird for me like something messed (and wiki says these words indeed are derived from "porridge"), I'm not sure if "Mess Module" doesn't sound stupid.

The proper name is indeed "mess", either "crew's mess" or "officers' mess"/"wardroom".

For space stations, we cannot know yet for sure (most likely will be "mess" just like in ships), although for any foreseeable modular space station design there is no distinct mess module as the typical maniacal mass-saving leads astronauts to eating anywhere they can do that, and the ISS normally has only six crew. Additionally, in zero-g it is not always required to use a table. On the other hand, having at least a partially enclosed space for a mess might help prevent food from getting everywhere, although space food is chosen so that you don't have to clean any breadcrumbs after eating...

[kerbiloid]

Thank you for the detailed response.

_{(That's for my interplanetary ship/orbital station, so a diner daily, but a backup hospital and an evacuation hall if something happens,)}

Edited December 17, 2018 by kerbiloid

[Green Baron]

3 hours ago, kerbiloid said:

What is the proper common name in English for a room inside a ship for the diner/club/pub?

 

Civil boats: saloon (depending on boat size).

(At least say mess-room pls. ...)

Edited December 17, 2018 by Green Baron

[Gargamel]

2 hours ago, Green Baron said:

Civil boats: saloon (depending on boat size). 

I would say this is more correct than mess, as we are talking a bar type area for recreation and socialization, not strictly for meals and such. 

I am imagining this:

more than this: