Fluid Dynamics of Drag

[SeanKewley]

I found this video about Fluid Dynamics of Drag and thought I would share. Very interesting stuff. It makes me consider putting an air foil around my rigger's boom tubes. :blink:

http://www.youtube.com/watch?v=ftq8jTQ8ANE&feature=player_embedded

 

[Joe Warren]

I found this video about Fluid Dynamics of Drag and thought I would share. Very interesting stuff. It makes me consider putting an air foil around my rigger's boom tubes. :blink:

http://www.youtube.com/watch?v=ftq8jTQ8ANE&feature=player_embedded

Looks like the boom tubes are slowing us down. Interesting due the shape of the nose of the boat hull too.

 

[Michael Costanzo]

hi, why do you think one of the reason's the Prather Spitfire ran so well, & fast too. 20+ years ago. mike.

 

[dr gary turner]

hi, why do you think one of the reason's the Prather Spitfire ran so well, & fast too. 20+ years ago. mike.

How about 30-35 yrs ago and the Wing Ding. Doc

 

[Kevin Krogness]

Holly schmolly thats a old film!!! Thats a lot of drag.....

 

[SeanKewley]

I couldn't believe how much more drag the round rod had over the larger airfoil... (9.3x) How about the wire's drag compared to the airfoil?!? Crazy. If I was making a SAW rigger I would definitely be using an airfoil over the boom tubes.

 

[Blackout]

Neat video!

 

[Rokieboater]

Doesn't the airfoil create a lift issue????

Robert

 

[SeanKewley]

Doesn't the airfoil create a lift issue????

Robert

Hey Robert!

It shouldn't create lift if its in a neutral position and there is no aileron or elevator directing the airflow. It may get lighter in the front though as it doesn't have as much drag pushing against it.

 

[Joe Warren]

Now we need titanium boom tubes shaped like a air foil?

 

[SeanKewley]

Now we need titanium boom tubes shaped like a air foil?

I was thinking more along these lines... A streamlined aluminum tube that you slide/ glue over your existing boom tubes.

K&S makes Streamline Tubes for airplane struts: http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXR857&P=7

They make it in 1/4, 5/16, 3/8, 1/2, 5/8, and 3/4" by 35" long

 

[Rokieboater]

Now we need titanium boom tubes shaped like a air foil?

I was thinking more along these lines... A streamlined aluminum tube that you slide/ glue over your existing boom tubes.

K&S makes Streamline Tubes for airplane struts: http://www3.towerhob...p?&I=LXR857&P=7

They make it in 1/4, 5/16, 3/8, 1/2, 5/8, and 3/4" by 35" long

Interesting..............

Robert

 

[TomMoorehouse]

i think i saw glann use model airplane alerion balsa stock and attach it with heat shrink tube.

 

[dwilfong]

Now we need titanium boom tubes shaped like a air foil?

I was thinking more along these lines... A streamlined aluminum tube that you slide/ glue over your existing boom tubes.

K&S makes Streamline Tubes for airplane struts: http://www3.towerhob...p?&I=LXR857&P=7

They make it in 1/4, 5/16, 3/8, 1/2, 5/8, and 3/4" by 35" long

I use this tube on my 21 rigger. A 1/4" carbon tube fits in side real snug.

and yes it lightens up the front of the boat. this with a air trap shingle sponson made the front of my boat very light on the water.

David

 

[lohring]

We've done this test on boom tubes. The AIR drag of the tubes is greatly reduced. Mike Bontoft tested that with an ingenious leaf blower wind tunnel. However, WATER drag is 800 times as much as air drag because water is 800 times as dense as air. The total drag reduction on the boom tubes does not noticeably increase the speed of a gas rigger at around 100 mph. That's because most of the boat's drag comes from what's in the water like the rudder and the prop. Rudder changes on the same rigger increased the speed 6 mph in the 100 mph area. Prop changes are even more significant, ultimately increasing the speed around 10 mph. If you want to play with air flow, use lift to reduce water drag or improve stability. The air drag penalty will be small.

By the way, I won the bet on the speed increase from boom streamlining. Thanks for the lunch, Mike

Lohring Miller

 

[SeanKewley]

Interesting. So... It does help reduce air drag significantly, but it is not as important as drag reduction in the water. Have you tested an airfoil shaped rudder? The same principles would seem to apply no matter whether it is air or water as they are both fluid. Perhaps doing both will garner a noticeable performance increase.

Edit: I found this article... It appears that an airfoil rudder isn't the best choice for high speed application. http://www.glen-l.com/weblettr/webletters-4/wl38-rudders.html

 

[Charles Perdue]

Mr. Miller, that does not mean that the air drag is insignificant, it just means that was not what was reducing the speed of your boat at that time. Reduce the drag in other areas and the air drag becomes significant.

Charles

 

[Charles Perdue]

Now we need titanium boom tubes shaped like a air foil?

I was thinking more along these lines... A streamlined aluminum tube that you slide/ glue over your existing boom tubes.

K&S makes Streamline Tubes for airplane struts: http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXR857&P=7

They make it in 1/4, 5/16, 3/8, 1/2, 5/8, and 3/4" by 35" long

 

[Jeff Schindler]

Interesting video! Looks like MIT was on top of it back in the day. Cylinders in cross flow generate quite a bit of wake turbulence at larger conditions(Re), thats the whistling you hear. Here is a good diagram of whats going on:

http://www.aerospaceweb.org/question/aerodynamics/sports/sphere-airfoil-comparison.jpg

The rectangular spar is worse, but smaller so less overall drag.

But......who's boom tubes are going 210 mph? I'll stick to round rods for reasons other than drag.

 

[TomMoorehouse]

Ummm so just thinking.... looks like the fan was roughly 10 inches diameter.... single tube had 9 lbs drag. My new design will have 34.5 inches of exposed tube.10 inches is 9 lbs then 34.5 would be 31.05 lbs drag at 210 mph. So I would have 10.35 lbs drag at 70..... sound right?