Announcement

Announcement Module
Collapse
No announcement yet.

Spill Plates and general aerodynamics.

Page Title Module
Move Remove Collapse
X
  • Filter
  • Time
  • Show
Clear All
new posts

  • Dave Cofone
    started a topic Spill Plates and general aerodynamics.

    Spill Plates and general aerodynamics.

    I was wondering about the need for spill plates running down the topsides of a hydro's deck. I know the basic reason is to straighten out the airflow over the airfoil but frankly I can't believe they do all that much on such a small 'wing area'. Perhaps there is another reason and that is what I am trying to find out. I want to learn as much as I can about the hulls and the aerodynamics of the late model boats. Tunnel width, wing camber, straight bottom or S bottom etc. I have even seen vortex generators on the leading edge......this is very interesting to me, please give me your thoughts.....

  • Ram4x4
    commented on 's reply
    Look at one compared to what we drive. Much longer, lay down, different weight distribution. As for speed, they have jacks they can raise and lower the motor while driving, etc.

    To be honest, I've thought having wind fences on our boats would tend to make the front want to windmill around once moving (like tossing an arrow backwards), but some say taking them off has adverse effects on handling. I don't have an explanation, aerodynamically speaking, as to why that would be other than no fences is allowing air to spill off the sides which is causing some kind of adverse yawing. But, there are some designs that have little or hardly any fence at all, soooo...

  • KURPS
    commented on 's reply
    Different hull design. Explain please!
    Both are hydros, one is fast the other not so fast.

  • Ram4x4
    replied
    Different hull design.

    Leave a comment:


  • baries
    replied
    I've read with interest the articles posted and yes some good information has been shared, but no one has said much about the design of the euro PRO boats with speeds in excess of 100 mph and not a fence in sight, imagine that.

    Leave a comment:


  • Dave Cofone
    commented on 's reply
    This discussion has brought to light a ton of interesting theories and information I would not have found without all of your input. My take away is that although the theories are interesting and thought provoking, the one thing that stands out is real world experience. All the math in the world still doesn't explain why those who have driven boats without the spill plates and then went back to them have noticed a difference in the handling both on the straights and the cornering. I see even the record setting boat used the fences. I would love to experiment and maybe one day I will be able to but for now I have to conclude the fences are needed for boat handling. Thanks to everyone for their input, I have learned so much......

  • Dave Cofone
    commented on 's reply
    I get what your argument is.....and you are 100% correct about the Magnus effect and I stand corrected on that point. However you explanation of the sail on a sailboat falls down for two reasons. First the very reason for tell tail windows cut into the sail is be able to see if there is flow on the backside of the sail. If the tell tail is not streaming straight back then airflow has broken away from the sail (wing). This is where the jib comes in to help keep the airflow stick to the low pressure side of the sail. Second, ridgid wing sails (actual wings) that are now popular on America's Cup boats are completely symmetrical and way more efficient than fabric sails. Very little deflection lift here and a ton of speed especially on a direct beam reach........

  • Dave Cofone
    replied
    Bernoulli theory is ideal flow in a incompressible fluid without friction thus no boundary layer which is a major part lift analysis. The inclusion of friction and fluid air deflection needs to be included as discussed below:

    http://hyperphysics.phy-astr.gsu.edu...s/airfoil.html

    http://www.aviation-history.com/theory/lift.htm

    It seems we have a difference of opinion. This is a good thing and so are the articles you have posted. Lots of learning going on which can only be a good thing. I love a spirited debate because I always learn something.
    Yes we do. To really understand lift study what happens with lift generated on a symmetrical curved surface like a thin sheet of fabric on a sail boat. The sail, if trimmed right is curved smooth with no ripples, generates lift when tacking into the wind in the horizontal direction and the forward part of that lift force causes the sailboat to go tacking into the wind. This lift is the air deflection part from circulation theory. Same thing happens with a wing on a plane.

    Leave a comment:


  • Ram4x4
    replied
    Speaking of Magnus effect:

    https://www.youtube.com/watch?v=K6geOms33Dk

    https://www.youtube.com/watch?v=xMoVzV-XmU0

    Leave a comment:


  • Ram4x4
    commented on 's reply
    Not true, Dave. For example, your curveball, the curve is AWAY from the higher speed side. By your example, the ball should curve into the higher speed spinning side because of the lower pressure, but it doesn't. A ball curves because of the Magnus effect.

    AoA absolutely plays a part in the symmetrical airfoil (and in all airfoils), by having an AoA, even slight, it does exactly as I explained, the downwash, or redirection of the air flow. If you think about it, that makes sense, by tilting the wing (AoA), you are changing the direction of the airflow. If AoA and airfoils don't redirect air, how then is there prop wash behind a spinning propeller? Even NASA agrees with this theory too (https://www.grc.nasa.gov/www/k-12/airplane/wrong1.html).

    It's also important to note that the classical theory is wrong in another area: the air does not speed up over the upper surface in order to meet with the underside air at the same time, this is known as the "equal transit" theory and is used to support the idea that a lower pressure is generated on the upper surface because the air has to speed up in order to meet with the underside air at the trailing edge at the same time. In reality, the upper air can actually reach the trailing edge before the underside air depending on the airfoil shape (https://www.youtube.com/watch?v=UqBmdZ-BNig).

    Bernoulli's principle does apply to a wing, just not in the way it is classically explained.

    In the case of a race car, we are creating a much lower pressure zone underneath because the air is sped up, due to the cambered airfoil surface which gradually lessens the vertical space from the leading edge through the central area in relation to the track surface. The air speeds up to try to squeeze the same volume of air through a smaller area...bernoulli. It squeezes it because the track surface is not compressible, or able to expand downward to accommodate the squeezing of the air.

    In the case of the plywood, it is exactly the air getting underneath and pushing up on the plywood that lifts it...dynamic lift. Once it starts to lift, it is exposing more surface to the continued pressure and it wants to keep lifting. Once it achieves a certain AoA it too will create the lower pressure bubble due to the speed difference of the air over the top and the boundary layer. This just helps it to lift even more.

    Ground effect is due to the wingtip vortices unable to completely form, the air that would normally roil back and down into a vortex is compressed under the wing (and so is the air), it creates a cushion of sorts. Ground effect also reduces induced drag (incomplete votices), which is why ground effect craft can float along just above the surface with less power.

    As for a hydro, the effect is less classic ground effect and more dynamic related since we don't get full flow across the underside surface.

    The largest ground effect aircraft ever made was the Russian Ekranoplan (known as the Caspian Sea Monster).

  • ZUL8TR
    commented on 's reply
    Yes we do. To really understand lift study what happens with lift generated on a symmetrical curved surface like a thin sheet of fabric on a sail boat. The sail, if trimmed right is curved smooth with no ripples, generates lift when tacking into the wind in the horizontal direction and the forward part of that lift force causes the sailboat to go tacking into the wind. This lift is the air deflection part from circulation theory. Same thing happens with a wing on a plane.

    Details here:

    http://ljjensen.net/Maritimt/A%20Rev...l%20Theory.pdf

  • ZUL8TR
    commented on 's reply
    What happens in a turn with all the side force?

  • rumleyfips
    replied
    Gee Guedo, I thought you liked wind tunnels. Re: Montana RaceCraft latest project

    [COLOR=#6A6A6A !important]07-09-2012, 03:29 PM[/COLOR]


    final results .....

    after several versions .... the wind tunnel says

    finally getting close ........ Attached Files


    Leave a comment:


  • Dave Cofone
    replied
    Bernoulli theory is ideal flow in a incompressible fluid without friction thus no boundary layer which is a major part lift analysis. The inclusion of friction and fluid air deflection needs to be included as discussed below:

    http://hyperphysics.phy-astr.gsu.edu...s/airfoil.html

    http://www.aviation-history.com/theory/lift.htm

    It seems we have a difference of opinion. This is a good thing and so are the articles you have posted. Lots of learning going on which can only be a good thing. I love a spirited debate because I always learn something.

    Leave a comment:


  • GRMead
    replied
    Thanks for the replies!
    G

    Leave a comment:

Working...
X