Why does my prop keep spinning? - Page 6 - SailNet Community
Seamanship & Navigation Forum devoted to seamanship and navigation topics, including paper and electronic charting tools.

Reply
 
LinkBack Thread Tools
post #51 of 56 Old 10-08-2006
Banned
 
Join Date: Apr 2006
Location: MS Gulf Coast
Posts: 711
Thanks: 0
Thanked 3 Times in 3 Posts
Rep Power: 0
 
I would really hate to have you as a navigator. You go around the world to avoid the simplest thing. Air density decreases with altitude. Period. Going fast. Going slow. Doesn't matter. There is still less air up there. Drag decreases with altitude. Going 1 knot. Going 1,000 knots. Makes no difference. Mach number does vary due to the true vs indicated airspeed. Bird strike? Do you know how high migrating geese have been seen at? Way the hell higher than 10,000ft, even 15,000ft! Are the planes restricted up there due to the possibility of a mid-air with a goose? No, they're not? Why? It's not because of a bird strike. Get real. Now, once again, get back to the subject at hand.....WATER, which, while being a fluid, has constant density, does not compress, and deals with a different type of propeller, at very different speeds. Like I said, you cannot simply draw comparisons, conclude they're both fluids, and decide they must produce the same results.
seabreeze_97 is offline  
Quote Quick Reply Share with Facebook
Sponsored Links
Advertisement
 
post #52 of 56 Old 10-09-2006
Senior Member
 
jerryrlitton's Avatar
 
Join Date: Oct 2002
Location: Phuket, Thailand
Posts: 1,666
Thanks: 7
Thanked 18 Times in 18 Posts
Rep Power: 13
 
Quote:
Originally Posted by seabreeze_97
I would really hate to have you as a navigator..
Good thing we are not talking navigation here huh?



Quote:
Originally Posted by seabreeze_97
You go around the world to avoid the simplest thing. Air density decreases with altitude. Period. Going fast. Going slow. Doesn't matter. There is still less air up there. Drag decreases with altitude. Going 1 knot. Going 1,000 knots.
All true but I was clarifying the difference between true and indicated since that was neglected the 1st time and very misleading. Water density does change with salinity I believe and not constant at all. But that is irrelevant in this discussion
Quote:
Originally Posted by seabreeze_97
Makes no difference. Mach number does vary due to the true vs indicated airspeed.
Not true, the mach number is another measurement of true airspeed and indicated is only reading the dynamic pressure exerted on a diaphragm when air is shoved in a tube (pitot). The airplane still responds and performs with indicated. For example we both know that stall is a function of angle of attack right and not airspeed. But for arguments sake we will say that in un accelerated flight and at a constant weight an airplane will stall at 100 kts indicated. At 40,000 ft or sea level it will stall at 100kts indicated but obviously as far as true airspeed is concerned it will be traveling faster at altitude. Actually temperature has more of an effect on mach then altitude.
Quote:
Originally Posted by seabreeze_97
Bird strike? Do you know how high migrating geese have been seen at? Way the hell higher than 10,000ft, even 15,000ft! Are the planes restricted up there due to the possibility of a mid-air with a goose? ..
Actually larger birds go even higher then that. The birdstrike situation is just one of many considerations when designing aircraft for commercial passenger use. I have been flying proffesionally since 1982 and I am currently a pilot for a major carrier and I am passing on what is passed on to us so I do know what I am talking about. I am not much of a sailor but I am a commercial pilot. I don't just play one TV nor do I stay in a Holiday Inn Express.

We can talk navigation also if you would like.

Jerry

"Let there be light!" said God, and there was light! "Let there be blood!" says man, and there's a sea!
Lord Byron, Don Juan


S/V Temptation
Islander 44
Very non-production
(Well, 10 were made so sort of non production)






To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

Last edited by jerryrlitton; 10-09-2006 at 10:47 AM.
jerryrlitton is offline  
Quote Quick Reply Share with Facebook
post #53 of 56 Old 10-09-2006
Senior Member
 
Join Date: Sep 2006
Location: Scotland
Posts: 2,364
Thanks: 0
Thanked 11 Times in 11 Posts
Rep Power: 9
 
Water is compressible.... much less than air, but it is compressible.

The compressibility of water does vary a very little with temperature and pressure, but it does vary.

We have to work with the figures in oil wells.... big volumes, big pressures..... and the compressibility will talk loud then.
Rockter is offline  
Quote Quick Reply Share with Facebook
post #54 of 56 Old 10-09-2006
Senior Member
 
Zanshin's Avatar
 
Join Date: Aug 2006
Location: Germany
Posts: 2,297
Thanks: 0
Thanked 29 Times in 27 Posts
Rep Power: 10
 
Quote:
Originally Posted by jerryrlitton
..Actually larger birds go even higher then that...
I've flown gliders in lee wave at FL250 and above with birds on more than one occasion, and have been less worried about a strike {even when flying multi's} than I am of large hail popping out of some CuNim 10 miles away! The hail can do a lot more damage.

Since this is not an aviation forum let us not confuse the non-flyers with indicated vs. true airspeed and mach number {thankfully we haven't gone so far down that road as to discuss Re numbes}.

The initial trigger for this was that there is a difference between propellors in water and propellors in air - and I think that all of us agree that there are differences stemming from water's non-compressability.

I still haven't really gotten an answer to the question of a freewheeling propellor at 7 knots water speed vs. having it locked in place; all other factors being equal. I think it is time to hit the library an check out a fluid dynamics book and figuring it out for myself.

-Zanshin (no ATPL, but CFI)
Zanshin is offline  
Quote Quick Reply Share with Facebook
post #55 of 56 Old 10-09-2006
Senior Member
 
jerryrlitton's Avatar
 
Join Date: Oct 2002
Location: Phuket, Thailand
Posts: 1,666
Thanks: 7
Thanked 18 Times in 18 Posts
Rep Power: 13
 
You are correct about doing more research on how water behaves and I need to quit assuming. Or we can rig up a device we tow behind a boat and measure the tension on the line with a spinning and fixed prop. I apologize for getting this conversation way off track.

Jerry.

"Let there be light!" said God, and there was light! "Let there be blood!" says man, and there's a sea!
Lord Byron, Don Juan


S/V Temptation
Islander 44
Very non-production
(Well, 10 were made so sort of non production)






To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
jerryrlitton is offline  
Quote Quick Reply Share with Facebook
post #56 of 56 Old 10-09-2006
gc
Member
 
Join Date: Feb 2003
Posts: 63
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 13
 
Over the years (more years than I care to admit to) I have seen this argument reprised many times. In person, in the letters to the editor of sailing publications in the old days, and in on-line forums. The discussions all have something in common. There is a total lack of documented hard evidence and an awful lot of (amateur) theory and "common sense (sic)".
gc is offline  
Quote Quick Reply Share with Facebook
Reply

Quick Reply
Message:
Options

By choosing to post the reply above you agree to the rules you agreed to when joining Sailnet.
Click Here to view those rules.

Register Now



In order to be able to post messages on the SailNet Community forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
Please note: After entering 3 characters a list of Usernames already in use will appear and the list will disappear once a valid Username is entered.


User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in









Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.




Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page



Similar Threads
Thread Thread Starter Forum Replies Last Post
Prop walk with a Max Prop ikent Gear & Maintenance 19 06-05-2011 08:32 PM
proposing to paint prop tappers Gear & Maintenance 16 04-06-2008 11:40 AM
Zincs for Sail Prop feathering prop jrbarn Gear & Maintenance 4 09-20-2006 10:40 AM
Max prop on a saildrive levenezia Gear & Maintenance 16 09-20-2006 12:07 AM
Prop for Pearson 35 gbeardmore Gear & Maintenance 0 04-24-2001 12:49 PM

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome