Twin screws

XabbaRus · 12-03-08, 04:54 PM

OK on a real submarine how would this look on DEAMON?

How do you figure it out in real life, without going into classified stuff?

suBB · 12-03-08, 05:21 PM

Quote:

Originally Posted by XabbaRus

OK on a real submarine how would this look on DEAMON?

How do you figure it out in real life, without going into classified stuff?

Taking a common sense approach here… :hmm:

I like to think of this like playing a guitar through a guitar amplifier, same frequency(fundamental) but ‘twice’ gain (sound)

That said, I would think the DEMON display on twin shafts would be the same, but the freq lines on twin shafts would display 2x amplitude(brighter) since you have two shafts(twice propeller noise) spinning at the same frequency (rpm)

I would also think that since both shafts will be spinning at same (rpm) on a direct course, if not you’ll suffer inefficiency in propulsion(drag). But while going into turns, (rpms) could vary to give up better handling, if so then the frequency lines could alter for a brief moment of time.

Just a thought…

goldorak · 12-03-08, 05:51 PM

Here's an interesting read :

http://www.fuzzytech.com/e/e_a_kumm.html

Example of a single screw 5 blade propeller :

Dr.Sid · 12-03-08, 06:38 PM

Subb: it's not that easy. When two exactly same frequencies sounds together, phase-difference comes into play. It may double the amplitude, but it may cancel the sound completely.

On guitar this never happens as the frequencies are always little different and also they always change a bit, so there is never good real match. And sound also comes not only from the string, but from the guitar body so the phases can't really exactly cancel.

On sub it too should not really cancel, but it may lower the amplitude significantly. Of course only in case the both props are EXACTLY at the same frequency. Which may be the case if they are propelled by the same engine. If they are not they will only have similar frequencies, and you would just see two lines (I guess) or one line a bit stronger, but far from twice.

Now if such props are synchronized or not, I don't know.

Btw. where does the second picture come from ?

goldorak · 12-03-08, 06:41 PM

Quote:

Originally Posted by Dr.Sid

Btw. where does the second picture come from ?

http://www.kaon.co.uk/kraken.asp

MBot · 12-06-08, 04:14 PM

Thise DEMON pictures are fascinating. Could any of the experts perhaps explain what exactly we are seeing there? I can not figure out how that works.

12-03-08, 04:54 PM	#1
XabbaRus Navy Seal Join Date: Sep 2001 Posts: 5,330 Downloads: 5 Uploads: 0	Twin screws OK on a real submarine how would this look on DEAMON? How do you figure it out in real life, without going into classified stuff? __________________

12-03-08, 06:38 PM	#4
Dr.Sid The Old Man Join Date: May 2005 Location: Czech Republic Posts: 1,458 Downloads: 6 Uploads: 0	Subb: it's not that easy. When two exactly same frequencies sounds together, phase-difference comes into play. It may double the amplitude, but it may cancel the sound completely. On guitar this never happens as the frequencies are always little different and also they always change a bit, so there is never good real match. And sound also comes not only from the string, but from the guitar body so the phases can't really exactly cancel. On sub it too should not really cancel, but it may lower the amplitude significantly. Of course only in case the both props are EXACTLY at the same frequency. Which may be the case if they are propelled by the same engine. If they are not they will only have similar frequencies, and you would just see two lines (I guess) or one line a bit stronger, but far from twice. Now if such props are synchronized or not, I don't know. Btw. where does the second picture come from ? __________________ ComSubSim forum at CADC Last edited by Dr.Sid; 12-03-08 at 06:39 PM.

12-03-08, 05:51 PM	#3
goldorak Admiral Join Date: Apr 2005 Posts: 2,320 Downloads: 0 Uploads: 0	Here's an interesting read : http://www.fuzzytech.com/e/e_a_kumm.html Example of a single screw 5 blade propeller :

12-06-08, 04:14 PM	#6
MBot Loader Join Date: Apr 2002 Location: Switzerland Posts: 90 Downloads: 3 Uploads: 0	Thise DEMON pictures are fascinating. Could any of the experts perhaps explain what exactly we are seeing there? I can not figure out how that works.