Date
1 - 12 of 12
COZY: Vent Buzzing
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Marc J. Zeitlin
Andrew Anunson wrote: But they leak at speeds of 165 ktas and higher. Hmmm. Very strange. The vents create a Very LOUD high pitched buzzing sound, like a stall horn on 36 volts. The eyeball piece vibrates at a high frequency that makes a loud and alarming sound. I have the larger version of those vents: and have never heard/seen that, and I've flown in other planes with both the large and small version of those and haven't seen it in them, either. Somewhat anomalous... I have disassembled the vents, cleaned, and properly reassembled. I have tried sealing them to the panel with silicone. Neither made a difference. Yep - very strange. Happens with both of them? Or only one? And they make this buzzing noise without any air passing through them? I can't even discern what a mechanism for causality that might be. IAS is what creates the pressure on the upstream side - TAS would be the speed of the air molecules passing through the vent, if there was any flow. As with Joel Ventura's discussion of flutter, it's the speed of the air particles that excites the vibration of the mechanical bits. But if there's no flow through the unit, then I'd expect IAS/pressure to be the gating factor here, due to the stagnation pressure on the upstream side. So maybe where you have your inlets (NACA'ish?) is somehow causing an oscillation in pressure at some relatively high frequency? Hard to imagine, but... Maybe I'm missing something... Has anyone seen this before? Anyone know how to fix it? Nope, and nope... Sorry... |
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Andrew Anunson
On Mar 1, 2023, at 9:50 PM, Marc J. Zeitlin <marc_zeitlin@...> wrote:Both of them. Or only one? And they make this buzzing noise without any air passing through them?Only when closed all the way, no air passing through them that I can detect. There could be air leaking around the eyeball, but it has a fiber seal thats in good condition. I can eliminate the vibration by opening the vents an slmost undetectable amount (this is my current solution). maybe where you have your inlets (NACA'ish?) is somehow causing an oscillation in pressure at some relatively high frequency? Hard to imagine, but...Located as shown in the attached photo. You’ve got the evidence that I have. I may try partially changing/blocking the naca vents with tape to see if that changes the mystery. Thsnks Andrew Anunson |
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Bulent Aliev
I had the same vents, but I also installed screens on the NACA scoops to prevent bugs and wasps crawling inside. Maybe that’s why I had no such a problem? On Wed, Mar 1, 2023 at 10:13 PM 'Andrew Anunson' via COZY Builders Mailing List <cozy_builders@...> wrote:
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Hennie Engelbrecht
It may be the sharp vertical edge of the naca duct that acts as a whistle. A bit of duct tape over that edge might just stop the airflow from whistling
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On 2 Mar 2023, at 11:13 am, 'Andrew Anunson' via COZY Builders Mailing List <cozy_builders@...> wrote: |
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Marc J. Zeitlin
Andrew Anunson wrote: Only when closed all the way, no air passing through them that I can detect. There could be air leaking around the eyeball, but it has a fiber seal thats in good condition. Hennie Engelbrecht wrote: It may be the sharp vertical edge of the naca duct that acts as a whistle. A bit of duct tape over that edge might just stop the airflow from whistling So Hennie brings up an interesting point. If the vents only make noise when they're NOT flowing air, and any airflow eliminates the noise, he could be right that it's not the vent that's making the noise, but the NACA. How sharp is the vertical edge? How thick is the unsupported skin just aft of that edge? I've seen all sorts of "NACA" ish things - yours is hardly the least NACA shaped vent entrance, but maybe you just serendipitously (or whatever the opposite of "serendipitously" is) hit upon a shape that vibrates at 165 KTAS or above, and no one else ever has. Good thought to try changing the shape of the vertical edge, and/or stiffening the skin aft of that vertical edge. I also have (as Bulent Aliev indicated) a screen in the vent to prevent bug ingestion. Having had a bee hit me in the chest and bounce up into my full-face motorcycle helmet while traveling at 75 mph on my motorcycle (and immediately pulling over, slamming on the brakes, and ripping my helmet off, none of which can be done in a plane) I have no interest in having some insect flying around inside the cockpit. And maybe that screen affects the vibration characteristics as well. |
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Dale Martin
Andy, 2 things come to mind. One is; the canopy seal. I have witnessed this several times and although it sounds like this is not it I know a way to test it. Borrow a corded microphone and plug it into either the pilot or co-pilot mic jack. Fly at the speed you hear the noise, change the radio freq to one not used and move the microphone around to your vents and also your canopy seal to trace the source(s) of the sound. If you try to use "hot-mic," it may not break the squelch setting currently used. The second method if you suspect it is the exterior skin vibrating is the skin thickness as mentioned and I have a cure that works. Use a 3-ply piece of cured BID glass and sand the fore and aft edges down to a soft small curve. Size it to fit inside the vent and bond it in place with a small amount of flox and use a spring clamp to hold it in place until it cures. This will stiffen the exterior skin enough to stop it from vibrating (if it really is vibrating). (Use all the standard techniques for adhesion and bonding). I use the microphone technique to ensure my canopy seal is sufficient and working properly. Let us know what you find out! “The only thing necessary for the triumph of evil is for good men to do nothing.” – Edmund Burke.
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Andrew Anunson
Dale, I will definitely use your technique to look for canopy seal leaks, thanks for the idea! As for the buzzing Wemac vent, its such a strong vibration that the eyeball portion of the vent looses its built in friction and the vent moves. The "eyeball" starts moving, usually going from level to pointing down (gravity). Its nice with the perfect amount of friction you expect from a good vent and could never move on its own without the vibration. Also I can feel it vibrating, and I can't dampen the vibration by pushing on it, only by slowing down or opening the vent. Its a strong vibration, like a buzzer. I will film it next time I go flying. And both vents do this (pilot and passenger side). Thanks, Andrew Anunson
On Thursday, March 2, 2023 at 03:48:57 PM EST, Dale Martin <niceez@...> wrote:
Andy, 2 things come to mind. One is; the canopy seal. I have witnessed this several times and although it sounds like this is not it I know a way to test it. Borrow a corded microphone and plug it into either the pilot or co-pilot mic jack. Fly at the speed you hear the noise, change the radio freq to one not used and move the microphone around to your vents and also your canopy seal to trace the source(s) of the sound. If you try to use "hot-mic," it may not break the squelch setting currently used. The second method if you suspect it is the exterior skin vibrating is the skin thickness as mentioned and I have a cure that works. Use a 3-ply piece of cured BID glass and sand the fore and aft edges down to a soft small curve. Size it to fit inside the vent and bond it in place with a small amount of flox and use a spring clamp to hold it in place until it cures. This will stiffen the exterior skin enough to stop it from vibrating (if it really is vibrating). (Use all the standard techniques for adhesion and bonding). I use the microphone technique to ensure my canopy seal is sufficient and working properly. Let us know what you find out! “The only thing necessary for the triumph of evil is for good men to do nothing.” – Edmund Burke. _._,_._,_
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Andrew Anunson
I doubt I could have created the "perfect" shape vent on both sides of my Cozy to cause this. They are both "made from scratch" and don't match each other at all. I'll get some up close photos of the submerged inlets. Thanks for putting thought into this. I plan to try different things to change the inlet... tape, sponge, screen, perhaps even a tiny hole drilled in the ductwork to let off some pressure (venting outside air up, towards the IP cover and not cold hands). Andrew Anunson
On Thursday, March 2, 2023 at 01:34:19 PM EST, Marc J. Zeitlin <marc_zeitlin@...> wrote:
Andrew Anunson wrote: Only when closed all the way, no air passing through them that I can detect. There could be air leaking around the eyeball, but it has a fiber seal thats in good condition. Hennie Engelbrecht wrote: It may be the sharp vertical edge of the naca duct that acts as a whistle. A bit of duct tape over that edge might just stop the airflow from whistling So Hennie brings up an interesting point. If the vents only make noise when they're NOT flowing air, and any airflow eliminates the noise, he could be right that it's not the vent that's making the noise, but the NACA. How sharp is the vertical edge? How thick is the unsupported skin just aft of that edge? I've seen all sorts of "NACA" ish things - yours is hardly the least NACA shaped vent entrance, but maybe you just serendipitously (or whatever the opposite of "serendipitously" is) hit upon a shape that vibrates at 165 KTAS or above, and no one else ever has. Good thought to try changing the shape of the vertical edge, and/or stiffening the skin aft of that vertical edge. I also have (as Bulent Aliev indicated) a screen in the vent to prevent bug ingestion. Having had a bee hit me in the chest and bounce up into my full-face motorcycle helmet while traveling at 75 mph on my motorcycle (and immediately pulling over, slamming on the brakes, and ripping my helmet off, none of which can be done in a plane) I have no interest in having some insect flying around inside the cockpit. And maybe that screen affects the vibration characteristics as well. You received this message because you are subscribed to the Google Groups "COZY Builders Mailing List" group. To unsubscribe from this group and stop receiving emails from it, send an email to cozy_builders+unsubscribe@.... To view this discussion on the web visit https://groups.google.com/d/msgid/cozy_builders/CAMCASg4q34bs8LfKjqvJ7wSKSkuhH%3DNaRZDx8saqtfQ1baBUxQ%40mail.gmail.com. |
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Andrew Anunson
Hennie Engelbrecht wrote: It may be the sharp vertical edge of the naca duct that acts as a whistle. A bit of duct tape over that edge might just stop the airflow from whistling There isn't a whistle or any type of air noise, it sounds like an electric buzzer. Marc Zeitlin wrote: If the vents only make noise when they're NOT flowing air, and any airflow eliminates the noise, he could be right that it's not the vent that's making the noise, but the NACA. How sharp is the vertical edge? How thick is the unsupported skin just aft of that edge? I've seen all sorts of "NACA" ish things - yours is hardly the least NACA shaped vent entrance, but maybe you just serendipitously (or whatever the opposite of "serendipitously" is) hit upon a shape that vibrates at 165 KTAS or above, and no one else ever has.Good thought to try changing the shape of the vertical edge, and/or stiffening the skin aft of that vertical edge. I have attached phots of my submerged inlets. 2 plies of bid for the inlets, like the plans show. Andrew Anunson Cozy MKIV #1273 Pound, VA |
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Andrew Anunson
While at the hangar today, I took a close look at the Wemac vents and discovered there is spring loaded movement (part of the design). I wonder if this movement is the buzzing? Perhaps with no airflow, the submerged inlet has a buffeting effect, and the built in movement of the vent gets going real fast... Hmmmm. Andrew Anunson Cozy MKIV #1273 Pound, VA See this video of the vents: |
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Certainly that blunt edge is not going to vibrate. Maybe that OAT probe vibrates when air swirls when vent is closed. Keith
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Dale Martin
Gang, We need to pitch in and buy Andy a wrench organizer!! :)) “The only thing necessary for the triumph of evil is for good men to do nothing.” – Edmund Burke.
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