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Page last modified 09:05, 15 Jan 2012 by internetscooter
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User:Internetscooter > Shelved till later > Highwayman Air Scoop

Highwayman Air Scoop

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    Preliminary testing of adding a scoop to the side of the engine showed a drop in temperature. Which makes sense, the faster you go the more air gets pushed over the cylinder head.

    ./300px-Highwayman Mark I.jpg ./HPIM0062.jpg
     

     

    At some time in the 80's someone had the same idea but it may have just been for looks

    ./300px-80s Air Scoop Technology.jpg

    To test it properly a test jig with air speed measuring device was made up in the cowl... it is yet to be put into practice...

    ./200px-Cooling airspeed measurement inside.jpg ./300px-Cooling airspeed measurement side.jpg

    Update (13/02/2010) - gave the test jig a quick whirl on the Lab Rat. A single rev on the engine records a speed of 34.9 km/hr.

    Another issue that has reared it's head is that because the Vespa has no scoop, the actual efficiency of the air cooling will drop the faster you go because the fan is trying to suck air in as it flys by. The faster the air going by the harder it is to suck. So there will be less cooling at ~105 km/hr than at 36 km/hr with the fan spinning at ~6,000 rpm.

    I would not be surprised if an air scoop could increase cooling efficiency by as much as 100%. This is because it would both fix the problem above and then ram additional air in as well. I am going to measure a few things with the simple device above and if it proves my theory, then I will hire a professional airspeed logger.

    Update (15/01/2012)

    An issue has been raised on what temperature is optimal for a Vespa engine, if the engine is keep too cool then it will not run optimally. The cylinder and head are obviously built to run at a specific temperature where the heat expands the metal to just the right proportions. The highwayman scoop may need to be designed to automatically control temperature, maybe blocking the flywheel fan intake when the engine is cold (to aid in getting to optimal temp quickly) and then openning up and then scooping depending on temperature.

    The above will require some mechatronics.

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    Viewing 4 of 4 comments: view all
    #1
    Steve says:
    Have you ever thought about putting a NACA duct into the engine cowling that would exit right into the shrould opening?
    Posted 15:25, 25 Apr 2009
    #2
    LabAssistant says:
    An NACA duct would look pretty cool. I haven't got around to doing the air speed measurement yet. I want to test that out first and I can then determine what sort of scoop works best (i.e. I can judge by airflow).
    Posted 20:38, 25 Apr 2009
    #3
    Steve says:
    After looking at some pics on the net, if forgot the the fan is not fully covered by the cowling - maybe only half covered. I fully understand the Highwayman concept now.

    Thinking outloud only -
    1. Install a NACA duct on the cowling to feed fresh air to all the area under the cowling. This would reduce the overall temp under the cowling.
    2. A new shrould could be fabricated to have all the fresh air feed thru the NACA duct on the cowling. The same duct could aslo feed cooler air to the carb if an aftermarket carb is installed. But the size of the duct to feed both might be too large.

    Do you have any informtion on the air flow to the cylinder by the fly wheel? I have a book on building centrifical fans for use with a home foundry. I will check out what it has as far as formulas and such, and do some measurements on the enging shroud, flywheel and cylinder cover.

    I also remember an article I read years ago about installing air scoops on a car hood - or do you down there call it a bonnet? A long piece of clear tubing was filled with colored water and the end was taped on the hood to find the position that had the greatest high pressure. The tube came into the passenger compartment and the readings were noted.

    My son and I are will be painting sometime later this summer and now is a good time for thinking about the duct installation.
    Posted 12:26, 26 Apr 2009
    #4
    internetscooter says:
    I worked at a place that used fans to drive aspirated smoke detectors. It is not a simple calculation, in that application the fan manufacturers provide a pressure/flow curve against RPM.

    The pressure with tube reading is a good idea. Thinking about it I am not sure how well a NACA duct would work as the speed is low and turbulence at the back of the scooter high (i.e. not like a plane or car). Getting some measurements of pressure would help understand the best solution.
    Posted 03:06, 27 Apr 2009
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