Marshy 30 Posted June 7, 2011 Share Posted June 7, 2011 Hey Grinna - you are our resident expert - how come sharks can go fast with rough exteriors? Power... A massive super grader launch can still go fast with a dirty bottom? Link to post Share on other sites
Guest Posted June 7, 2011 Share Posted June 7, 2011 Opting out of this debate. Far from not being able to see the wood from the trees, I lecture this stuff to commercial and airline pilots..... must be teaching them a load of baloney. Link to post Share on other sites
wheels 543 Posted June 7, 2011 Share Posted June 7, 2011 No don't go spitting the dummy C29. It is well obvious you are clued up in the field. What I am trying to say (and probably poorly) is that what takes place is different to what takes place in the "normal world" of Aerodynamics and laminar flow. So much so, that there are people in this field that realise this works and are playing right now with surfaces that will do just this very thing. The entire process is very different to air over a surface. You need to forget that point completely. That is dealing with just one fluid, that being air. The ruff surface in water idea is to create a turbulent surface. Cavitation is not quite right in one sense, but probably a perfect explanation in another. It's is like creating airbubbles over the entire surface, but of course you are not creating airbubbles, it is more like cavitaion. This causes are "layer" of turbulance that then the next stable layer of water slips over. I am sorry, I am most likely not describing this well, but I know it exists and I know they are playing with the idea. Link to post Share on other sites
Guest Posted June 7, 2011 Share Posted June 7, 2011 Opting out of this debate. Far from not being able to see the wood from the trees, I lecture this stuff to commercial and airline pilots..... must be teaching them a load of baloney. How close is my often befuddled memory? Close or would you recommend I don't take passengers who don't have an extreme death wish? It's all a bit of a head f*ck at times this drag stuff. I just know what speeds my aircraft is going to stop being an aircraft at and make sure I never get near them. Also watch for ice and all that stuff that changes those speeds. Link to post Share on other sites
Guest Posted June 7, 2011 Share Posted June 7, 2011 So Sharks have ' Golf balls"? one wonders how AA managed to get that information. I have had a rough girl freind or two but getting up close and personal with a shark! Way to go AA!!. I put antifoul on with a roller and my unscientific impression is that the boat is faster. I assume that subsiquent clean offs remove the stippling effect as performance of a clean hull monthst later does not seem to match that of the new antifoul, in my un scientific opinion. Link to post Share on other sites
Guest Posted June 7, 2011 Share Posted June 7, 2011 Mythbusters did a show about the dimple effect of golf balls. They put a layer of clay over a car then did tests like that. They then gave the entire car a golf ball dimple effect (hence the clay) and they found it used less gas with the dimples than without..... much to both the dudes surprise. So one could assume from that a dimpled effect is faster or requires less power to get to a certain speed. Link to post Share on other sites
Grinna 2 Posted June 7, 2011 Share Posted June 7, 2011 I just know what speeds my aircraft is going to stop being an aircraft at and make sure I never get near them I'm hoping that's not quite true there KM. Presumably, when you land your aircraft there's a point where you want it to stop being an aircraft and start being a landbased vehicle so you're going to have to transition through the speed where it stops flying and becomes a funny looking car steered by a system akin to a childs soapbox trolley. Admitdely, you don't want that to occur too far away from the ground though ..... otherwise it can result in quite a large bump. Link to post Share on other sites
Guest Posted June 7, 2011 Share Posted June 7, 2011 The good old firemans steel pole is not smooth, but has "scales" to reduce friction. The size and number of dimples on a Golf ball are strictly regulated to keep distance driven under control. Link to post Share on other sites
wheels 543 Posted June 8, 2011 Share Posted June 8, 2011 I hope they install the pole the right way up then. It'd be a bit ruff otherwise. Yeah I didn't know, till just recently, that you can get Golf Balls spec'd to fly differently. Link to post Share on other sites
Guest Posted June 8, 2011 Share Posted June 8, 2011 Mmm drag if I shave my beard off and wear a dress nah, forget about that Link to post Share on other sites
Guest Posted June 8, 2011 Share Posted June 8, 2011 I just know what speeds my aircraft is going to stop being an aircraft at and make sure I never get near them I'm hoping that's not quite true there KM. Presumably, when you land your aircraft there's a point where you want it to stop being an aircraft and start being a landbased vehicle so you're going to have to transition through the speed where it stops flying and becomes a funny looking car steered by a system akin to a childs soapbox trolley. Admitdely, you don't want that to occur too far away from the ground though ..... otherwise it can result in quite a large bump. Ah yes there is that point, one at which you don't want to hear stall warnings until over the end of the runway. In the aircraft I fly that buzzing noise starts around 5-10kts before you plummet. I know those numbers well. We do have to periodically demonstrate we can turn a IFO into a aircraft but we do that above 3000ft. I got stopped coming home from the Aero club one evening for speeding, 125kph he said. The cops said I could easily lose control and crash. He wasn't amused when I said I'd been doing nearly 200kph on a wobbly tricycle steering only with my feet for most of the afternoon so 1/2 that speed using my hands was a doddle. Probably about as easy as it was for him to fill out and hand me the ticket. A nice fine and he even was nice enuff to chuck in some bonus demerit points, bugger! Link to post Share on other sites
Steve Pope 251 Posted June 8, 2011 Share Posted June 8, 2011 wouldn't be a good look Max Link to post Share on other sites
Guest Posted June 8, 2011 Share Posted June 8, 2011 Water is a Newtonian fluid ie has a constant viscosity. When it moves along a solid boundary it will incur a shear stress on that boundary. The no-slip condition dictates that the speed of the fluid at the boundary (relative to the boundary) is zero, but at some height from the boundary it must equal that of the fluid column. The region between these two points is named the boundary layer. In fluid dynamics attention is paid to controlling the behavior of the boundary layer to minimize drag. Two effects have to be considered. First, the boundary layer adds to the effective thickness of the body, through the displacement thickness, hence increasing the pressure drag. Secondly, the shear forces at the surface of the surface create skin friction drag. Form and shape are also important. Skin friction arises from the interaction between the fluid and the skin of the body, and is directly related to the wetted surface and the area of the surface of the body that is in contact with the fluid. This is seen in the drag equation which shows the relationship between drag and the density, velocity, affected area and the drag coefficient. This drag coefficient varies with the speed of flow, direction of flow,and other factors. Also on a smooth surface it has a value much lower for laminar flow than for the turbulent flow created by a rough surface. Link to post Share on other sites
Atom Ant 0 Posted June 8, 2011 Share Posted June 8, 2011 There you go! The golf ball thing is merely to help you all understand that smooth isn't always faster. The golf ball flies faster and further by spinning while it's dimpled surface - ah sh*t I can't be bothered going over it again. It's all been said. A really good book to read is called The Symmetry Of Sailing by Prof Garrett (?) It is in two parts. The first part is for brain boxes who want to understand the physics of sailing and how it all works and the second part is for super nerds who understand physics at a higher level than I can even begin to comprehend - or can be bothered trying to - to be fair. It's a great read and for the most part will help yachties understand why it is that they do what they do to make their boats sail. I think he has a whole section on drag too, so knock yourself out! Link to post Share on other sites
Guest Posted June 9, 2011 Share Posted June 9, 2011 this is what i came up with for KMs dimpled car thing. when youredriving in a ute the flowing air forms a pressure vortex in the tray, so the air coming off the cab flows nice and smoothly over it (as in drawing1.) so maybe that also goes for a dimpled car? all the dimples create small vortexs wich the air rides over, and as we all know air on air drag is alot less than air on car panels drag, so the air you are driving through rides over the car on the air pressure waves, almost like rollers ( as in 3 and 4) yes i know its most likely all wrong but atleast i made myself think that im smart Link to post Share on other sites
Marshy 30 Posted June 9, 2011 Share Posted June 9, 2011 Oi you... less doodling more grinding Link to post Share on other sites
wheels 543 Posted June 9, 2011 Share Posted June 9, 2011 So based on that JH, we can go smash the crap outa KM's Samyong with a sledge hammer and tell him he will get better milage from it Link to post Share on other sites
Guest Posted June 9, 2011 Share Posted June 9, 2011 Ball Pein Hammer all over it. Put the tailgate down as well for less drag. Link to post Share on other sites
Guest Posted June 9, 2011 Share Posted June 9, 2011 putting the tail gate down stops that vortex forming thus creating more drag. what would i do without mythbusters Link to post Share on other sites
Guest Posted June 9, 2011 Share Posted June 9, 2011 Actually a mate proved otherwise on the dragstrip. The V8 HQ did the 1/4 mile 1/2 a second quicker with it down. Link to post Share on other sites
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