Does anyone know if the percentage reduction in effective venturi size resulting from the use of an air filter made from one layer of nylon stocking material has been calculated (or even can be calculated)?  I'd like to compare the relative effects of layers of this material vs switching to a smaller venturi.  Thanks.

Does anyone know if the percentage reduction in effective venturi size resulting from the use of an air filter made from one layer of nylon stocking material has been calculated (or even can be calculated)?  I'd like to compare the relative effects of layers of this material vs switching to a smaller venturi.  Thanks.

    I just to it experimentally. I am primarily using it to generate turbulent flow more than for increasing the fuel draw, and only use one layer.

   Brett

Pantyhose does a great job of keeping grass out of the innards. 

Of course, when you cut off all the air, it has no choice but to draw fuel. 

Of course, when you cut off all the air, it has no choice but to draw fuel. 

   The same issue arises with a partial restriction. IF you get everything exactly right, Bernoulli effect may create a situation where you get more fuel draw for the same flow, or more flow for the same fuel draw. That will possibly get you more power - possibly, not certainly, because what happens downstream of the inlet matters, A LOT in some cases. The right conditions appear to be very difficult to achieve and probably rarely if ever occur in real life. A huge fraction of the fuel draw is do to simple flow restriction. I think Frank Williams has some interesting information on the topic.

   But even assuming you do get the conditions just right for more power, they aren't likely to stay that way as you maneuver around nor does more power = better. Power is a non-issue in stunt, we are flying airplanes with piped 75s that we used to fly with ST46s. What is far more important is consistent response in flight. That's where I have found various schemes to ensure consistent flow with different loading and different input air directions to be critical. The diffuser on the inlet had tremendous beneficial effects on the run consistency far out of proportion to any possible restriction effect. And it worked far better with a large inlet and a diffuser than a tiny inlet and no diffuser. My current #5 venturi with a spigot and diffuser (single layer of pantyhose) clearly draws less my initial #12 venturi with a spigot, but it runs much more consistently.

     Brett

If the area of the crotch is used, you get better breathing as it is less dense  (more open weave) at that point.

   You just wanted to say "crotch", didn't you?

   Brett

   

Accordig to what Richard Oliver stated some time ago.  It takes experimentation with the nylon hose you use.  When the wife wonders why there are a hundred holes cut in her panty hose you can explain what it is for.  Best to use panty hose that has been discarded.  The O rings to hold the nylon peices in place is available at your local auto parts store.  Take your engine so you can get the right size.  Remember to keep notes as some days it may require more nylon peices than other days.   

   The same issue arises with a partial restriction. IF you get everything exactly right, Bernoulli effect may create a situation where you get more fuel draw for the same flow, or more flow for the same fuel draw. That will possibly get you more power - possibly, not certainly, because what happens downstream of the inlet matters, A LOT in some cases. The right conditions appear to be very difficult to achieve and probably rarely if ever occur in real life. A huge fraction of the fuel draw is do to simple flow restriction. I think Frank Williams has some interesting information on the topic.

   But even assuming you do get the conditions just right for more power, they aren't likely to stay that way as you maneuver around nor does more power = better. Power is a non-issue in stunt, we are flying airplanes with piped 75s that we used to fly with ST46s. What is far more important is consistent response in flight. That's where I have found various schemes to ensure consistent flow with different loading and different input air directions to be critical. The diffuser on the inlet had tremendous beneficial effects on the run consistency far out of proportion to any possible restriction effect. And it worked far better with a large inlet and a diffuser than a tiny inlet and no diffuser. My current #5 venturi with a spigot and diffuser (single layer of pantyhose) clearly draws less my initial #12 venturi with a spigot, but it runs much more consistently.

     Brett

This information proved to be extremely helpful to me.  I tried a nylon filter/diffuser on a somewhat skittish Magnum 36 yesterday and the difference was like night and day--much smoother, more consistent run.  I was amazed at such a large result from a seemingly small change.

This was in cold, heavy fog conditions.  It will be interesting to see if warmer, drier conditions make a difference.

Thanks, Brett.