At least 30 years ago I knew a machinist (a friend of my fathers) who used something I had never seen before. When using his milling machine he used a vacuum plate (a vacuum plate is a big rectangular piece of steel that has a lot of little holes drilled into the top surface of it. Those holes all are connected to a hollow area inside the block that is attached to a air fitting that goes to the vacuum source) to hold thin items down that were things that could not be clamped or that were not magnetic, such as carbon blocks. This way they can fly cut the whole top surface of their part. His vacuum source was created by his air compressor. I am sure any of you who have done machining have seen these. He had a small piece of metal plate (about 3 or 4 inches in diameter round and maybe 1/2 to 3/4" thick) a hole was drilled all the way through one edge and out the other side of it or at least had a airline fitting one on the in and and one on the out side. On one of the sides perpendicular to the drill through line, a hole was drilled half way through only to the already drilled hole. The air compressor was attached to the in and out that went all the way through the round plate, the vacuum line to his vacuum plate was attached to the fitting on the perpendicular hole that was drilled half way through the block which intersected the all the way through hole. The air going into the block from the air compressor was regulated, as the air passed through the block it created a vacuum on the perpendicular hole. I have no idea how big the holes were, I just thought that was pretty neat at the time. It may be more complicated inside that little block than I imagined at the time. I imagined the same scenario when the exhaust idea was proposed by Darren who must have burned his lips with that hot coffee to think about the exhaust ! : ) I just assumed the idea consisted of a small hole drilled into the side of the exhaust pipe with a fitting welded around the hole and a vacuum line attached to it then going to the gyros by way of a vacuum regulator. As in my above explanation of the air compressor supplying the air flow, in this case the engines exhaust would be the air flow source down the exhaust pipe at high speed. It might work like this and it might not, it will only require someone to try it I guess. This is why I was kidding about using plastic fittings and plastic line attached to the side of the exhaust in my previous post. Here is a link below that begins to describe what I am talking about. I know my story at the top about the machinist I knew was a simplified version but that is what I imagined when I looked at that tiny round block he had the airlines attached to.
http://www.hyvac.com/Products/O_pumps/Air%20Venturi/Air_Venturi_vacuum.htm Here is one more website that may be more like what I described at the top, but the man I knew had a round plate type instead of a round rod type like this one. This site has a video that you should watch and it will clear up any fuzzy thoughts. This system uses aircompressor pressure and air flow to create the vacuum. http://www.exair.com/en-US/Primary%20Navigation/Products/Vacuum%20Generators/Pages/E-Vac%20Vacuum%20Generators.aspx?source=msn Larry Howell ________________________________ The problem is that nothing is free. One could certainly use a venturi on or in the exhaust stream, but doing so is a restriction in the exhaust, which would inhibit exhaust flow and impact engine performance. I can't estimate how much or whether it would even be noticeable. I suspect someone with more expertise than me in exhaust tuning or an engineer with fluid dynamics software might be able to give a rough estimate. I suspect the answer is that back in the 30s and 40s when gyros and venturis were first used, it was likely discovered that the impact to the engine performance was more than the impact of drag of the venturi on the plane. However, the planes of that day were much slower and draggier than our KRs, so that explanation may not hold water for our application. One thing I try to keep in mind when these ideas come up is that there are over 100 years of aviators and aviation engineers that have proceeded us, many of whom were quite ingenious. If they didn't do it, you need to look for the reasons why. This isn't the first time I've heard this idea floated, but I've never seen it in use. Doesn't mean it can't work, but makes me question why we haven't seen it before. Jeff Scott Los Alamos, NM -- Darren Crompton <kr.2s.dar...@gmail.com> wrote: Maybe I have drunk too much coffee today, but is there anything to stop one from running a vacuum line off the exhaust? -- Darren Crompton AUSTRALIA
