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Gee, Ernest, I don't know.
But, perhaps we can get a handle on it starting with F = m*a.
lets take one cubic foot of air and assume no losses in accelerating it from 0 to 150 Mph. Now we need a time interval and it has to be around 1 rpm (one revolution of the blades) so that is approx 60/7000 = 0.00857 sec/rev. Since we want 600 cfm of air to flow at 150 mph we need to have the blower flow 600/7000 = 0.857 CF per revolution. 0.857 * 7000 = 600 CFM - checks!
At 7000 rpm the e shaft needs 0.00857 sec per rev. So we want to accelerate 0.857 CF of air from zero to 150 mph in 0.00857 seconds.
A cubic foot of air has a mass of 0.0765 lbs at sea level. So M = 0.0765 lbs. We need to accelerate it to 150 mph or 220 ft/sec velocity in 0.0086 seconds. So dV/dt = A = 200 ft/sec/0.0086 sec = 25,666 ft/sec^2 or 25666/32 = 802 Gs acceleration. Therefore F = m*a = 0.0765 * 25666 = 1963.5 lbf/sec = 1963.5*0.001818 = 3.56 HP Since we continuously need to accelerate that amount of air it would appear that not counting for any losses that you would need approx 3.56 HP or approx 1/2 of the amount your increase air supply might contribute to power increase in the engine.
However, this is a really back of the envelope calculation which even if correct does not taken into consideration any losses.
Perhaps a more realistic approach is to consider what size electric motor does the fan blade usually have mounted to produce that 600 cfm flow?
Hey anybody jump in that disagrees or has a better handle on it. We are all trying to help Ernest - hey, if provides sufficient benefit, he may have started a revolution.
Ed
----- Original Message ----- From: "Ernest Christley" <echristley@nc.rr.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Tuesday, December 18, 2007 5:51 PM
Subject: [FlyRotary] Re: Supercharging
wrjjrs@aol.com wrote:
Ernest,
All that the leaf blower is is the compressor scroll of a turbo charger. many of the aircraft superchargers, circa WW2 used a centrifugal supercharger which is exactly what you are describing. Think you will find it more trouble than it's worth. Mainly due to breakage of the parts at high RPMs. You will have to design your own drive, and it is a drive even if simply a shaft connection. You would probably find a belt driven centrifugal supercharger and using a underdriven (reducing) system. You will find a supercharged 13B will make 200 HP very easily.
Bill Jepson
Ed, how many Hp would be required to accelerate 307CFM of air from 0 to 150MPH? That would be the extent of the power that the fan blades would have to absorb, wouldn't it? Would there be a major drag component?
The drive is already designed and built, but what parts do you think might break, Bill? It's a compressor wheel bolted up to the flywheel. Should I expect to see problems with it shedding blades? I've looked into the leaf blower components, specifically because they were designed to run at the RPM we're looking at. Literally, trying not to reinvent the wheel. I'm assuming that they can take the RPM, since it is an industrial component that workers carry on their backs.
The shroud is the bellhousing. Not optimum, but sturdy and simple. I will probably have to add some extra aluminum sheet to keep the housing tight, but I don't see having much problems with that part.
Like Ed said, it's just an experiment at this point. I'm really just guessing that it will be worthwhile, but it's just such a simple mod that I've got to try. The labor, weight and dollar investments are all about right. I just have to see how much payback there is while avoiding throwing pieces of metal around.
--
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