Thought I'd reopen this thread, as I've been contemplating some winter cowl mods, and the great discussion of exit work going on in
Ken's cowl flap thread, as well as the great info in
Dan's Shrinking Exit thread has me looking at many possibilities.
One mod on the to-do list is to redesign my induction air inlet, and this thread has some great discussion I hope to re-energize. Mark Frederick, Greg Nelson and I had some great talks about this at Reno this year, and so far my top choice is to go with one of Mark's curved-bottom, flat-topped low speed inlets, like the one on Ol' 84, as discussed earlier in this thread by Mark.
However, we all had the opportunity to talk with Dave Anders at the Races, and he strongly recommended going with a round inlet, and lowering it to get it away from the thick boundary layer close to the spinner. Reminds me of the Paeser inlet from
Speed with Economy...I think.
Seeing Pooner's post earlier in this thread about his success with a round inlet and a conical filter generates a few questions for the brain trust. Would love to hear your collective opinions, and/or get pointed to some references for this area of inlet design.
Here is my current Ram Air inlet. Normal induction air is pulled through a filter in the left cooling air inlet, and fed to the servo via a scat tube. Opening Ram Air bypasses that and provides unfiltered air to the servo. I think I'm losing some MP due to losses in the filter and scat, and gaining some back with Ram (I see about a 0.8" MP rise when I open it in cruise). I'll dump the scat-fed method if I go with a Rocket smily intake or a round intake.
I know I have work to do on my spinner (outer circumference too small for the cowling size, and large lips at the blade openings). My set up seemed to get less ram rise than Greg's, though I was running a faster RPM than he was with his MT prop, which may explain some of the delta...but not all. Those losses I talked about are some of the issue...perhaps.
The next few pics are of 4 Rockets with different styled inlets, for comparison and discussion. Would love to hear opinons.
Here is Greg's fast Rocket, with the high speed curved-on-top-and-bottom inlet. He says that, Like Ol' 84, he sees no loss of MP with the filter in place...surprising to me, but he's tested it a lot, and is a meticulous guy...I believe him.
Here is the best pic I can find of Ol' 84's inlet (got any more Mark or Doug?)
Both this and Greg's inlet seem to be moved out and away from the spinner and that boundary layer issue. Neither seem particularly far removed from the spinner though, so I'm wondering how far away is far enough to get good free-stream air.
Here's Mark's current inlet on El Toro. Its for a 550, but its an interesting study of placement near the spinner.
This placement is in top for the TCM motor of course, but looks like Mark took the page out of the P-51 book, and has it right off the spinner. Leads to another question, that being, if you go with a location right at the spinner to get accelerated air coming off the spinner, how close is good, and at what distance when moving away from the spinner do you run into boundary layer issues?
Finally, here's an HRII with what looks like a Bower intake
This is where I'd love to hear Bob's input on his round-inlet set-up, and if you have any pictures, that would be great to see. I'd also be interested in whether you lose MP with the filter in place (if you've tested it with and without).
I think I may use nutplates as Greg did, so I can play with the shape a bit over time. Any thoughts, or vectors to references, are most appreciated!!
Cheers,
Bob