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Thread: Super charger

  1. #1

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    Super charger

    Looking at the pics of the Bally Bomber, which is an amazing accomplishment, it looks like the unit between the prop and the engine might be a supercharger of some type.
    Which got me thinking, Lycoming has that big flywheel on the front, turns 2700 rpm, replace it with a squirrel cage type fan, would it produce enough usable air to give a few inches of boost?
    Relatively easy to build.
    I remember reading way back when EAA was doing the mogas certification they had used an electric fan into the intake during ground runs and had seen "significant" increase in power.
    I played with a Kcar with turbo many years ago and was impressed with the small amount of air pressure produced by the turbo which made a large difference in hp.
    There was a discussion, I don't remember if it was here or on the Rvaitor about the ram air effect and it turned out to be not that big a deal.
    I have an RV style carb heat and notice very little difference when I close off the ram air and draw air from under the cowling.
    Turbo's are a small fast turning fan and we all know a big slow turning fan moves more air so maybe a 12 inch squirrel cage turning 2700 rpm might move enough air to make a difference?

  2. #2

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    Not quite the same thing, but....I read a story (with accompanying YouTube video) on a car forum about some guys who used four gas powered yard blowers to "supercharge" a little econobox car, and actually measured the resulting rear wheel power on a dyno. It really did measurably increase the power.

  3. #3

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    just a quick reminder that horsepower costs,so driving a fan with the engine WILL incur a cost to the output.It is all about is the power in and out.This is why a turbo charger is more efficient than a supercharger as the supercharger uses engine power to drive it. Cheers Ross

  4. #4

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    But nothing gives you that Hot Rod look better then a Supercharger...

    https://www.youtube.com/watch?v=HRhDrt87ojY

  5. #5

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    Back in the 60's a dude named Smokey Yunick who also just happened to be a former B-17 Bomber pilot found himself to be a successful race car builder in the new burgeoning sport of NASCAR stock car racing. Having a dyno in his shop and an inquisitive mind he was known for his many...shall we say innovations that gave his cars an advantage on the track. He fashioned a supercharger that worked off of vanes he had welded to the spinning clutch assembly inside of the cars bell housing and recorded huge horsepower gains on the dyno but was unable to conceive a way to get the air to the air intake in such a manner that would elude detection of the tech inspectors. He did lots of stuff like that such as placing air pressure sensors in the wheel wells of test cars so he could collect actual data when he made changes to the wheel opening shapes on his race cars to reduce drag without visiting a wind tunnel.

  6. #6

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    From basic physics, the name of the game with a fan type supercharger is how fast can you make the blades move. If you can get them to move 100 ft/sec say, then the maximum pressure gain per stage will be about 0.6 ft of water - or only about 0.25 psi (about 1/2 inch of mercury). At 2700 rpm your fan would have to be at least 8 inches in diameter (per stage) and you would be hard pressed to see the difference. But since the max pressure gain goes as the square of the velocity, the easiest thing to do is raise the RPM - a lot.

    (I hope I did my estimates right........)
    Last edited by nrpetersen; 11-25-2013 at 11:21 PM.

  7. #7

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    Ol' Smokey's model would have been an 11 inch clutch spinning in a bell housing say13 inches in diameter and he was looking for a gain around 7,000 RPM. That sounds like a pump that might move some air. He proved it on a dyno. the numbers went to the grave with him.

  8. #8

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    Quote Originally Posted by 58boner View Post
    Ol' Smokey's model would have been an 11 inch clutch spinning in a bell housing say13 inches in diameter and he was looking for a gain around 7,000 RPM. That sounds like a pump that might move some air. He proved it on a dyno. the numbers went to the grave with him.
    That could only be about 2 inches of Hg pressure gain - per stage.

  9. #9
    Cary's Avatar
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    The old Mooneys have a ram air valve, which when activated adds maybe 1 to 1 1/2" of manifold pressure--not a significant gain, but adds a little bit of power--and it's free.

    Years ago, my pards and I were about to have our Skylane overhauled, and there was a manually operated turbo charger available at the time, from Rajay. It would have about doubled our overhaul costs, which was manageable, but our overhauler had a lot of misgivings, especially about the real possibility of pilot error causing massive over-boost and catastrophically destroying the engine. Ultimately we opted just to go with the overhaul, which was a wise move.

    On the "there's no free lunch" side of the ledger, pretty typically maintenance costs increase with any kind of supercharging, largely because the extra stress that the engine incurs. TBOs are typically shorter, and few people have the fortune of going to TBO. For example, for a couple of years, I regularly flew a friend's Mooney 231, and one of the constant issues was red-lining the CHT, even at moderate power settings--it was necessary to run with the cowl flaps partially open at any higher altitude cruise. All that plumbing runs pretty hot.

    Cary
    "I have slipped the surly bonds of earth...,
    put out my hand and touched the face of God." J.G. Magee

  10. #10
    Quote Originally Posted by eiclan View Post
    ( edit. . . ) This is why a turbo charger is more efficient than a supercharger as the supercharger uses engine power to drive it. Cheers Ross
    A common misconception. It takes plenty of engine power to drive a turbo. Exhaust back pressure from the turbine restriction can easily be one atmosphere. 15psi back pressure on a 5" diameter piston is 294 lbs. of force pushing back on the piston. That is 145 HP at 2,600rpm. Yes, a centrifugal device is far more efficient than other designs but they all take gobs of HP to drive them. (numbers have rounding errors)
    Last edited by Skydriver; 12-05-2013 at 11:10 PM.

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