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afward last won the day on September 3 2019

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  1. A round parachute is so large (and non-rigid) that the pressure fields & gradients change moment by moment and parcel by parcel across the entirety of the captured area. In other words, it's a really turbulent (downright chaotic) flow, which is great for generating drag. Our planes' inlets aren't that big. In fact, a perfect inlet would have zero turbulent flow at cruise speeds. Real world we just try to minimize the turbulence. One way we do that is by limiting the size of the inlet so the pressure field is relatively uniform across the inlet (at least at a given distance from the lip; obviously the center of the flow won't have the same pressure as the edge). All that aside, having slept on it I realize your idea could be easily tested and might have some merit: The Sam James RV-10 cowl is both faster and cooler than stock, yet it does not have cowl flaps (stock does). It would probably be pretty easy to modify to include an upper deck bypass system in the cooling plenum (I'd think it would need to re-accelerate the bypass flow and dump it as close to the cowl outlet as possible, though). Now that I've thought of it, I'd be curious to know the results of such an experiment. Might be worth a post to Van's Air Force to see if someone will try it.
  2. Yep, hence the reference to the clever people. I more thinking of the simplicity of the arrangement; Make the cone bigger than the inlet, and contour the inlet throat to fit. One moving part. In theory, having the cone stick out of the inlet can help to optimize the airflow around the lip (it would help move the pressure gradient), but I might be wrong about that. The other idea I had was NACA inlets on either side of the cowl, which would be passive but as I said earlier probably has been considered before and rejected for good reasons.
  3. ^^^ Awesome ^^^ As I recall, the pressure drop target across the cylinders is usually about 1/2 psi. That's not much, but is sufficient to ensure good cooling at speed. This is, of course, why leaks in your baffles wreck so much havoc on CHTs. I still think a cone in a round inlet is the best design (some clever people in Burbank used that one for a, uh, "high speed" application back in the late 50's). It just won't work as well on our planes due to prop clearance concerns.
  4. That might be beyond my skill to answer. Yes, but real-world is messy so it's never truly stable? Honestly I'm not sure.
  5. If anything, I'd say the open end will experience slightly higher force than the closed end, primarily because it will experience more turbulence and a region of reversed flow that the closed end won't have.
  6. Well, I got a permission error trying to load that. CAFE's Mooney cowl is a thing of beauty, though.
  7. Don't think of it from the perspective of flows. Flows are a result of pressure gradients. So it's better to think about it in terms of "where is the pressure" and "how will that pressure move" (yeah, I know, sounds like a flow... stick with me). For a cowl with a flap, you're not changing the airflow so much as changing the pressure gradient in the lower deck of the cowl (and specifically the outlet area; some cowl flaps even create a pocket of even lower pressure due to their effect on the exterior airflow). By opening the flap, the lower deck pressure is reduced, allowing a lower upper deck pressure to sustain the same flow rate (vs. cruising with the flap closed). It's really elegant in its simplicity. All that said, I'd _much_ prefer a passive system... ducted cooling plenum and a cowl with CFD-designed ramps will do everything we need without the extra drag of an oversized fixed system or an open cowl flap.
  8. Wow, I missed what you were saying there. Makes sense, but I still see issues: 1) It doesn't take a lot of bypass air to completely wreck cooling flow from upper to lower deck. I'd think you'd want to duct the bypass air down to the outlet so this isn't an issue. That has drag implications. 2) You're always going to flow the "same" amount of air at a given airspeed, which means the flowrate at cruise will be quite a bit higher than necessary (because sizing is controlled by Vx climb cooling requirements). That also has drag implications. 3) Both the above items mean substantial drag at higher speeds, with spillage being a possibility if conditions are right. In theory, cowl flaps sidestep all of that by allowing the inlet & outlet to be sized for cruise, while still allowing for enough flow to cool during a Vx climb. Now, someone with a CFD model can probably work through all this and come up with a working design. What I don't know is if it'll actually be any better than what we have today.
  9. I'm no (aerospace-) engineer, but I don't see how merely putting a flap downstream from the intake is going to address the pressure spillage problem around the intakes. To really have an effect, it would have to be at the intake itself such that the intake doesn't swallow any more air than the system intends to allow through. A movable spike in a round inlet is an obvious solution, but for our planes that would be problematic due to the closeness of the back of the prop. We could in theory build a circumferential intake with movable ends (it would look like the CAFE Mooney's intake), but that has weight and complexity concerns. I've thought on many occasions that a large NACA inlet on each cowl cheek would probably perform better than what we have now, and would be throttle-able with a reduced drag impact, but surely people far more knowledgeable and capable of testing it have already thought of it and rejected it for some really good reason I'm not aware of...
  10. The Acclaim, obviously! Because red carsplanes go faster, right?
  11. Ha, yeah. Lots of not-quite-tech-savvy companies make that mistake. "Repeat after me: Host it on the root domain, or put in a redirect". I wonder how many people have gone to "" to research the airplanes and have decided to look elsewhere due to the missing redirect? Or is that a "new" thing? I know it had me going for a moment when I clicked your link...
  12. The screw is in that picture?! Wow... I'm not seeing it, though.
  13. Most likely all of them can, but the interfaces are different (vacuum is whacky at best, analog has polarity and voltage ranges to deal with on multiple possible inputs, and digital is a whole new level of complexity beyond that). ARINC-429 theoretically addresses all that, but it came after the legacy APs in our vintage Mooneys and frankly misses the mark a bit by having multiple different ways to drive an AP (like just about every other "standard" in the digital realm, it's only a standard if everyone actually follows it...).
  14. As I understand it (and I'll defer to an actual avionics expert here), the reason for STEC being first is that the interface is just the single heading deviation input (and I assume for the -60 and above, an altitude deviation input). Other APs need more inputs (I think for the gyros?), so they are more complicated to interface with.
  15. But that's kinda the point I'm making: Make the wings and h-stab non-swept, move the engines into the leading edge, swap the engines to be piston + prop, convert to tricycle landing gear (not a big change), and what's really that different from a B-29? Let's ignore the (rather large) size difference; had it been desired, the B-50 could've been a scaled-up version of the B-29 rather than just being a re-badge. Aerodynamics aren't changing, so until we get a radical new powerplant, there's not a lot of room for a groundbreaking new design to replace Mooneys, Bonanzas, Cessna 206's, etc. Even the "lowly" PA28 is unlikely to see a radical new competitor anytime soon.