Tee Dee 049/051 venturi hole size question

the early ones did run good on suction.
the later ones with the screen i'm not so sure about because by the time they appeared, we started running bladders and naturally bored them to the max size.

i realize that most here probably only run the sport cox's, so i'll have to experiment.........

I prefer the screened ones because mine do eat dirt now and then. I just pop the screens out to bore them and press it back in. I form it into a slight dome over the tip of my pinkie and lay it upside down over the groove and press until it pops inverted and locks in.

I know that's not relevant to your question, I'm just blabbing.

no, it's relavant.....i'm interested in all info that any of you have to give.
i won't gore you with the details, but cutting balsa a week ago ended with my thumb into the blade of my table saw (and i've been a wood man for over 40 years) that postponed my testing til at least another week or so............so what does one do when one becomes bored and wondering the outcome.......ha, bug other ones on said site

MikeM wrote:no, it's relavant.....i'm interested in all info that any of you have to give.
i won't gore you with the details, but cutting balsa a week ago ended with my thumb into the blade of my table saw (and i've been a wood man for over 40 years) that postponed my testing til at least another week or so............so what does one do when one becomes bored and wondering the outcome.......ha, bug other ones on said site

I guess it's either that or take pain killers and daydream about flying. Forum surfing is probably healthier.
*deleted the story of my recent shop injury*

RknRusty wrote:I prefer the screened ones because mine do eat dirt now and then. I just pop the screens out to bore them and press it back in. I form it into a slight dome over the tip of my pinkie and lay it upside down over the groove and press until it pops inverted and locks in.

I know that's not relevant to your question, I'm just blabbing.

What size do you bore your td venturis to? How many rpms do you gain?
Thank you,
Jim

Good information there, I have been looking for those diameters.

Phil

I bore them to get less air restriction when I run bladder pressure. I can give you my most successful bores if you can wait until I go out to the shop and measure the ones on my Li'l Satan and the Baby Streak. I've tried a couple of sizes and the most conservative bore didn't wake it up as much as the larger. There was a big difference. I'll get back to you on that. You can go too wide and lose performance.

Okay, here's what I've got. First off, understand that a venturi isn't just a fancy name for a hole. It's an engineering term that involves a taper with a specific point of maximum constriction. So proceed at your own risk, integral calculus be damned.

That being said, I've never been too hesitant to use a sledge where a tack hammer will do. When I bored my Tee Dee venturis I started with a conservative bore. A stock venturi with a screen on it would let the back side of a 7/64" drill bit pass through it with some slight wiggle room. Maybe .110". When I first bored it I drilled a 1/8" bit through, and then rolled some fine sandpaper around a dowel and polished it out to about .130". I was using a 5.5x3 prop at the time and it ran okay and I stayed with it for a while. Later after reading a post by Paul Gibeault on boring venturis, he said the widely accepted max size was about .140". That happens to be about the size of a 9/64" bit. He also says it should be reamed with a taper rather than boring straight through(what I said about engineering). In my brute force way of ignoring the experts, I bored one out with that bit and polished it, and the engine ran much more happily. I dropped my prop down to a 5-1/4x3 and was happy to find the plane really woke up. No bogging in the turns, just all out bust-ass power for my sport flying. I had to put it on longer lines. I'm happy with that and see no reason to try bigger.

Paul also said the late Joe Klause's K/K pressurized venturis went as high as .150". And they work well in the 22-24,000 rpm band. Paul says he tried finding the limit and went as wide as .165 and it lost RPM unless you cut down a prop to a very small diameter(less than 5") and run it at 26K RPM, then there is a small gain. But Tee Dees are precious these days and I'm not about to try that just to see.

I hope that helps answer the questions.
Rusty

Yes, it answers quite a few. Thank you

Phil

Thanks!

To my understanding venturi screens were eliminated to cut production cost.

I leave them in place on my earlier engines because........................ (they look kwel)


SD