Humor Random Comments Thread

[mojoey]

http://lmgtfy.com/?q=CODAG

tl;dr MOAR POWER!!!!!1!!

 

[Linguofreak]

What does CODAG mean for us not-so-cool kids?

Combined diesel and gas, IIRC.

 

[Urwumpe]

Speaking of LCSs...the shiny new LCS-5, USS Milwaukee, had an "engineering casualty" and had to be towed into port for repairs 20 days after commissioning. :facepalm:

https://www.rt.com/usa/325710-littoral-ship-milwaukee-breakdown/

Some garbled information about metal filings in the lube oil system. I believe it is a CODAG system with twin screws, so I don't know what would cause a complete loss of propulsion like this, unless they had a main gearbox failure of some sort. It was either something not caught during sea trials (bad, very bad) or a flaw (bad, very bad).

A typical source for such problems are too small or too soft gear bolts. That kind of thing happens in the world. Usually, you have a magnetic detector at the lube oil filter to detect such problems before the gear box is completely destroyed.

 

[Thunder Chicken]

What does CODAG mean for us not-so-cool kids?

Sorry, talking shop. :hesaid: A lot of these sorts of ships have multiple propulsion units (diesels or gas turbines) geared onto a common shaft, usually to efficiently operate between cruise speed and maximum operating speed, as well as to provide redundancy. My favorite is the COGOG system in the Russian Tarantul class missile corvette (which I actually got to see on the Hiddensee at Battleship Cove on a special engine room tour). It has two cruising gas turbines of 4000 hp, and two main gas turbines of 11,000 hp each, so you could idle around on one 4000 hp engine, or put the spurs to it and have 30,000 hp. The main gas turbines, while not really jet engines, produce enough exhaust that they deliver extra thrust, and so there are distinctive doors on the stern of the vessel that are opened when the main turbines are operated. If everything hits the fan, there is a diesel engine (same kind as used in the T-62 tank) for emergency power.

 

[C3PO]

FYI It 'gas' like in 'gas turbines', not 'gas' as the petrol in 'murican cars. :lol:

The complex gearing shown on the wiki page looks like an engineer's nightmare IMHO.

 

[Thunder Chicken]

FYI It 'gas' like in 'gas turbines', not 'gas' as the petrol in 'murican cars. :lol:

The complex gearing shown on the wiki page looks like an engineer's nightmare IMHO.

That gearing provides a lot of operational flexibility. Normally it should reduce the probability of a casualty completely knocking out propulsion. That is what is so strange about the USS Milwaukee. Sounds like something major was shaving metal and they had to secure the shaft to prevent damage.

 

[BruceJohnJennerLawso]

A bit more HOI3, not my game, but damn am I jealous.

Still makes more sense than going house to house in Stalingrad :lol:

 

[RisingFury]

The main gas turbines, while not really jet engines, produce enough exhaust that they deliver extra thrust, and so there are distinctive doors on the stern of the vessel that are opened when the main turbines are operated.

Every turbo-shaft produces residual thrust.

In a "jet" or "low bypass turbofan", some energy is extracted from the air stream to drive the fan and compressors, but a lot of it is left, so the exhaust comes out as high velocity. Lots of thrust is produced, because F = mdot * v, with mdot being mass flow and v exhaust velocity of the engine. In addition that that, gas pressure plays a role and the gas pressure is still somewhat high.

In a turbo-shaft, the turbine drives a shaft through a speed reductor (slower RPM, higher torque). Measures are taken to extract as much energy out of the gas stream as possible. That means slowing it down, decreasing its pressure and temperature. While a lot can be done, some energy is still left in the gas stream.


In aircraft turbo-props, about 10% of the thrust is produced by the turbine, with the rest from the propeller.

 

[Thunder Chicken]

Every turbo-shaft produces residual thrust.

Even reciprocating engines will produce some thrust with their exhaust if they are eating enough air. The Rolls Royce Merlin had rearward facing flared ejector exhausts for this reason. The Spitfire picked up about 10 knots on its top speed due to this effect.

 

[Andy44]

Even reciprocating engines will produce some thrust with their exhaust if they are eating enough air. The Rolls Royce Merlin had rearward facing flared ejector exhausts for this reason. The Spitfire picked up about 10 knots on its top speed due to this effect.

Even cooler, the radiator housing for the Merlin on the P-51 Mustang, underneath the fuselage, was used as a sort of mini jet engine and actually produced a couple pounds of thrust instead of drag. Forgot where I read that.

 

[Thunder Chicken]

Even cooler, the radiator housing for the Merlin on the P-51 Mustang, underneath the fuselage, was used as a sort of mini jet engine and actually produced a couple pounds of thrust instead of drag. Forgot where I read that.

That's the Meredith effect. :thumbup:

 

[mojoey]

Was there any inherent differences between the RR Merlin and the RR/Packard Merlin, or was it a 1:1 license job?

 

[Andy44]

Was there any inherent differences between the RR Merlin and the RR/Packard Merlin, or was it a 1:1 license job?

Looks like there were several variants:

https://en.wikipedia.org/wiki/Rolls-Royce_Merlin

https://en.wikipedia.org/wiki/Packard_V-1650

 

[Linguofreak]

On Earth, curiosity drives scientists. On Soviet Mars, scientists drive Curiosity.

---------- Post added at 00:42 ---------- Previous post was at 00:19 ----------

Even cooler, the radiator housing for the Merlin on the P-51 Mustang, underneath the fuselage, was used as a sort of mini jet engine and actually produced a couple pounds of thrust instead of drag. Forgot where I read that.

It is pretty much exactly a ramjet, just with an alternate heat source.

If you pull up a video of a P-51 flyby on YouTube, the whistling from the P-51's little ramjet is distinctly audible.

Example: http://www.youtube.com/MCAA8BuimcE

 

[MaverickSawyer]

On Earth, curiosity drives scientists. On Soviet Mars, scientists drive Curiosity.

---------- Post added at 00:42 ---------- Previous post was at 00:19 ----------



It is pretty much exactly a ramjet, just with an alternate heat source.

If you pull up a video of a P-51 flyby on YouTube, the whistling from the P-51's little ramjet is distinctly audible.

Example: http://www.youtube.com/MCAA8BuimcE

That whistle is actually the gun ports in the wing acting as, well, whistles. You'll notice it's missing from "clean wing" birds like Voodoo and Strega.

---------- Post added at 23:09 ---------- Previous post was at 23:08 ----------

Was there any inherent differences between the RR Merlin and the RR/Packard Merlin, or was it a 1:1 license job?

Not as I recall. The Packard version was slightly reengineered to enable easier mass production.

 

[Linguofreak]

That whistle is actually the gun ports in the wing acting as, well, whistles. You'll notice it's missing from "clean wing" birds like Voodoo and Strega.

It's also missing from the P-40, which also has 6 wing-mounted 50-cals. Of course, in either case, it could be missing from the videos we're looking at because of other factors, such as AOA if its the gun port or radiator settings if it's the radiator, and airspeed in either case.

The F4U had a well-known whistle that was supposed to be from the oil coolers.

I wonder if anyone has ever instrumented a P-51 with microphones placed by suspected whistle sources to try to get rock-hard data on the true whistle source. I still think radiator is most plausible, but I hear people arguing with equal vehemence for radiator, supercharger, guns, and guns + laminar flow wing.

 

[Urwumpe]

You don't need to instrument the aircraft, a matrix of microphones can also be used for that. I remember that the German Aerospace Agency used such 2D arrays for measuing sound of landing aircraft and during wind tunnel tests to find the biggest noise sources during landing, making the sources of sound visible in videos.

But I would rather bet on the supercharger there, the two-stage supercharger of a P-51D is much louder at low altitudes than the single-stage supercharger of earlier Merlin engines.

 

[Evil_Onyx]

Was there any inherent differences between the RR Merlin and the RR/Packard Merlin, or was it a 1:1 license job?

Short Answer, No.

Long Answer, most of the modifications where to do with ease of manufacturing and some different ancillary equipment used, Different Superchargers, alternators ect.

If you ever see a RR Merlin next to a Packard Merlin out of aircraft,(I got to see this at IWM Duxford) other than the markings they are hard to distinguish.

 

[Thunder Chicken]

It is pretty much exactly a ramjet, just with an alternate heat source.

And subsonic, so the diffuser and nozzles vary in area in the opposite way as a supersonic ramjet (the subsonic diffuser diverges, the subsonic nozzle converges). The Meredith effect really only offset drag when flying in the subsonic but compressible regime (0.4 < Mach < 1.0).

---------- Post added at 06:05 AM ---------- Previous post was at 05:58 AM ----------

Short Answer, No.

Long Answer, most of the modifications where to do with ease of manufacturing and some different ancillary equipment used, Different Superchargers, alternators ect.

If you ever see a RR Merlin next to a Packard Merlin out of aircraft,(I got to see this at IWM Duxford) other than the markings they are hard to distinguish.

I think the Packard Merlin was also retooled to use customary unit hardware (1/4-20 bolts vs M6x1, that sort of thing). Not so much a manufacturing issue as making sure that it could be serviced by American units in the field.

---------- Post added at 08:21 AM ---------- Previous post was at 06:05 AM ----------

Ahh...finals day. 4 hrs of watching students desperately trying (but failing) to find examples in the book that look like my exam problems.

 

[Urwumpe]

Ahh...finals day. 4 hrs of watching students desperately trying (but failing) to find examples in the book that look like my exam problems.

You are evil. :lol:

4 h for an exam is quite a lot how many tasks did you expect for full score?

My worst case exam is still the pre-diploma exam for spaceflight technology. 2 hours, no helpers allowed except a pocket calculator, 25 exam problems. leaving you with about 4 minutes per problem. Including knowing (coarsely) the characteristic velocities of certain solid propellants.

On the next day, I noticed I stuffed so much information into my brain that I had forgotten some less important things. Like the PIN for my bank account. :facepalm:


I noticed this weekend that the German phrase "Bei jemanden ist Schmalhans Küchenmeister" (lit.: "Poor John is chef in someones house", it means your food budget is really extremely meager, either by poverty or avarice) does not have equivalents in other languages... despite it being a very old phrase (from about 1663).

If you are a student here, you often know what this phrase means too well.