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the Obsidian Files - So Much Noise!!!
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Area-51



Joined: 03 May 2021
Posts: 371

PostPosted: Mon Mar 27, 2023 4:09 am    Post subject: Re: the Obsidian Files - So Much Noise!!! Reply with quote

The past few days have been spent crunching numbers again by adding the butyl layer to 181's air box. The untreated air box was also rerun through the same analysis matrix settings as a control for comparison purposes.

Several criteria were examined on both models; the modal natural frequency, the harmonic response, and the harmonic acoustic qualities.

Two sets of solutions were applied overall based upon 1 cylinder cycle and 4 cylinder cycles from 3000rpm to 5800rpm; both provided similar attenuation plot results. The images attached are from the 4 cylinder cycle solutions.

The attached images relate to distortion of the air box at a nominated frequency of 8200hz, being 4100rpm. Blue represents zero distortion, red maximum measured distortion. The two images clearly show how well the butyl layer attenuates excitation frequencies of the air box; being the image with the most blue. Results on both standard and treated air box were consistent with the two attached images through the entire frequency test range.

The attached graphs are related to the amplitude of applied frequencies being projected from the air box to the surrounding environment, measured at a specific near field position to the air box, being 100mm above the air filter opening, rear at the firewall, inside air box under the air filter. The left scale relates to (db) acoustic amplitude, and bottom scale (x2) engine rpm (divide by 2 to get actual engine rpm.

The db attenuation qualities of applying the butyl has proven much better than expected. One point to note is the material density applied. The DCI product presents a density of 1310kg/m3 against standard 900kg/m3 of other similar products.

It was surprising to make the distinction between the lower amplitude levels on the graphs to the different power setting rpm selected in real flight situations; they are identical to where the smooth running points are being perceived to be. This identifies the air box as a signal point for pilot perception. it is a sound box after all being excited by the engine. 🤷🏼‍♂️

Again these tests are not for determining induction noise affects, they are for determining the inherent acoustic qualities of the air box and how it is affected by environmental frequencies along with its ability to adsorb vibrational frequencies; can it or can it not absorb and dissipate a specific kind of kinetic energy...

The next round of tests will have to examine the muffling ability of the box when a sound pressure source is added at the carburettor ports. Moving further forward the addition of internal baffles can then be assessed and results compared.


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Last edited by Area-51 on Mon Mar 27, 2023 2:21 pm; edited 1 time in total
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Area-51



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PostPosted: Mon Mar 27, 2023 1:22 pm    Post subject: Re: the Obsidian Files - So Much Noise!!! Reply with quote

[quote="n7188u"]Today I finally had a chance to get a longer flight in. It's hard to say how much improvement the install of the sound deadening material on the air box has on the internal noise. But there is certainly improvement!! The flight today was very pleasant and more enjoyable. But what really struck me is that, as A51 experienced, I had to lower the intercom volume quite a bit since it felt too loud. Same thing when I was playing music as I generally do. So, even though I can still hear relatively high frequency sound, but maybe less, it seems that overall there is a reduction in noise.

But, I have to admit this is all just based on perception. It is indeed hard to quantify the change. But I have to say that despite the increase in weight, it is a keeper.

On a different note: I finished rebuilding my spray booth and getting closer to starting the painting process. I will hold off taking the airplane apart this week to see if I fly it to Sun n Fun but by next weekend it will come apart so no more flying until it is done. I also have a couple of pending jobs I want to perform on the airframe.

Chris[/quote]

-------------

Chris, i noticed you mention calc on the added mass of your air box being 0.6kg. This aligns with the lower density of products out there. The affects will be reduced... Adding a second layer will bring the results closer to what the DCI product has provided, but will of course add another 0.6kg.

Reviewing the graphs demonstrates the db reduction achievable for a given rpm. The average is 10db but some points it is as much as 25db... Any high frequency vibrational load upon the carbi rubbers that was previously passing through connection points is reduced as well as a result.

The second layer does not require total coverage; just patches of at least 25% of target areas. From the modal analysis results these patch positions will be centroid to each broad surface area of the air box, being rear face, side faces, lower under face... probably an extra 150g added... a nominal 1" rebate in from existing edges would probably be sufficient all three additional points; rear face i would give 2" rebate on vertical edges...


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n7188u



Joined: 15 Nov 2015
Posts: 395

PostPosted: Mon Mar 27, 2023 4:26 pm    Post subject: Re: the Obsidian Files - So Much Noise!!! Reply with quote

Thanks for the advice A51. I am right now in the process of disassembling my airplane to paint. When I finish this phase I will get back to the sound issue. Will continue following your analysis and experimentation.

Best,
Chris


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Area-51



Joined: 03 May 2021
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PostPosted: Wed Mar 29, 2023 8:04 am    Post subject: Re: the Obsidian Files - So Much Noise!!! Reply with quote

Always onwards into the realm of investigation and dissection... "trust the science"!!!! 😂😂😂

Ever wondered what's inside a 912's factory Rotax muffler?

Today's episode of "shut that noise up" was spent looking at the back end of the rotax; running the numbers on the factory stock 912is exhaust muffler... how well does it actually look on paper? 🤷🏼‍♂️

Well, let's tear it apart and find out?!

Thankfully no destructive work was required; and no animals were harmed in this episode.. these days we can simply grab a CAD model and whiz it through some predefined plugins and see what gets spat out... personally when i first turned the cad viewer to xray i was astounded, i said to myself "that is a joke; that won't be doing a bloody thing... what's the replacement price on that again?!"... let's come back to that knee jerk assumption later...

So we ran our pre calc's, established our base frequency range for 5000rpm, and got to work preping the model for analysis.

Several tests were run looking at low band, medium band, and wide band results; the focus here is primarily on the low band results.

Well, the low band results showed zero attenuation of sound transmission until 320Hz with awesome attenuation capabilities of 32db at 460Hz!!! This is great!! Only problem being, in this mode of acoustic analysis, 460Hz equates to 12600rpm, and 320Hz equates to 9600rpm 😃 so my knee jerk assumption appears supported.

But let's return to the subject for conclusion... the factory 912is muffler is as affective as that of a Chonda generator, i.e, empty expansion box with pipe going in and pipe going out...

To be fair the muffler does provide affective mid range attenuation in the frequency range most noticeable for human hearing (200Hz-5000Hz), which is mostly the higher frequencies being generated by the header pipes and muffler itself as acoustic energy from the cylinders excites the resonant material. Any result of 10db or higher can be considered a useful reduction.

And all things as they are I have heard, or better put, been forced to endue, listening to a 912 take off with straight through pipes; i think an F1 screaming down the home straight is about the same volume; was expecting the thing to explode any second... so the factory stock "reactive" muffler, functioning as an expansion chamber with a mesh exit gate, clearly does do something regarding "harmonic" noise attenuation. However it is doing nothing to suppress the predominant deep Low Frequency pressure waves. Employing a secondary tuned silencer and tail pipe can be used to address these lower sound wave lengths.

It would be great to compare a CKT muffler but i won't be cutting 181's unit apart any time soon to CAD it up.


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Area-51



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PostPosted: Thu Mar 30, 2023 4:18 am    Post subject: Re: the Obsidian Files - So Much Noise!!! Reply with quote

An update on yesterday's recon into an exhaust muffler... spent the day trying a few different things mods; all that was mostly achieved was a transposition along the frequency band but not much db reduction... gave up for now and went back to testing the carbi box... and...

Well as expected 181's stock factory air box did pretty much zip to shut things up; on average about 3db across the whole range. Then the Mod box got some scrutiny.

Mod box rocks... on average around 25db to 40db reduction through the target range; WOT rpm primary frequencies are returning up around 30db and secondary harmonic ranges are returning around 15db reduction.

Will have to build this Mod box and see if the actuals match!

A 25db noise reduction from the engine will make eating cheese inflight more enjoyable again.


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PostPosted: Thu Mar 30, 2023 4:32 am    Post subject: the Obsidian Files - So Much Noise!!! Reply with quote

question:  the mod is an additional resonating structure installed within the stock box?
thx,
PeteZ

On Thu, Mar 30, 2023 at 8:25 AM Area-51 <goldsteinindustrial(at)gmail.com (goldsteinindustrial(at)gmail.com)> wrote:

Quote:
--> Europa-List message posted by: "Area-51" <goldsteinindustrial(at)gmail.com (goldsteinindustrial(at)gmail.com)>

An update on yesterday's recon into an exhaust muffler... spent the day trying a few different things mods; all that was mostly achieved was a transposition along the frequency band but not much db reduction... gave up for now and went back to testing the carbi box... and...

Well as expected 181's stock factory air box did pretty much zip to shut things up; on average about 3db across the whole range. Then the Mod box got some scrutiny.

Mod box rocks... on average around 25db to 40db reduction through the target range; WOT rpm primary frequencies are returning up around 30db and secondary harmonic ranges are returning around 15db reduction.

Will have to build this Mod box and see if the actuals match!

A 25db noise reduction from the engine will make eating cheese inflight more enjoyable again.




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Area-51



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PostPosted: Thu Mar 30, 2023 2:12 pm    Post subject: Re: the Obsidian Files - So Much Noise!!! Reply with quote

Correct.

Grafted component, either 3D print or dissolvable Styrofoam plug with fibreglass skin

Attached image of revised internal chambers of air box post mod.

Still have some porting variations to run but this first test demonstrates and exceeds target sufficient performance. Attached image related to air box pressure at 5800rpm.

Any similar pre-carbi induction system similar to early twin stromberg Rover V8 will provide descent results toward noise reduction... Many early european air filter boxes on prestige vehicles were double skinned pressed tin with a thin layer of tar, asbestos, or lead sheeting sandwiched in between... on one occasion i found 3.00mm of fine powdered sand sandwiched in between the sheets in a burnt out exhaust muffler...


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PostPosted: Fri Mar 31, 2023 12:26 am    Post subject: Re: the Obsidian Files - So Much Noise!!! Reply with quote

Loving your posts on this topic, a great mix of detail and humour. Can i ask where you get your geometry from - do you use a 3D scanner? And which CAD and CAE analysis tools please?

On the potential to improve exhaust silencer re-radiated noise, i worked with the owner of CKT a few years ago to help him develop a cabin heater based on a shroud around the silencer (loads of heat power there). It didn't progess to a for sale product for internal reasons, but i know them fairly well/they might let me have redacted CAD geometry for it that might help what you are doing?

Reducing the noise radiated from the cylindrical silencer is always going to be difficult. The flatter ends are a possible area. Think Rayleigh pistons - where noise radiation is concerned as the size and stiffness of the surface controls both frequency range and ability to re-radiate.

https://pdf.sciencedirectassets.com/271589/1-s2.0-S0307904X00X01564/1-s2.0-0307904X94902275/main.pdf?X-Amz-Security-Token=IQoJb3JpZ2luX2VjEK%2F%2F%2F%2F%2F%2F%2F%2F%2F%2F%2FwEaCXVzLWVhc3QtMSJGMEQCIFCPjos5H%2FxtbWXTp0wy4ttVGOOXES6hmuoA3NU%2FelO3AiBSvyBAtdtBgFV0%2FZeEEveCMCdsEnkhYVcq8DmHIghHFSq8BQiI%2F%2F%2F%2F%2F%2F%2F%2F%2F%2F8BEAUaDDA1OTAwMzU0Njg2NSIMT87Jt%2B5AWqa5DONdKpAFFgQ0ZRCs%2BitnanKhrL9SRt6alPFvk%2BiZkTt7tJo2%2FG9CanwenQDevtY7EQ%2BHBl3YN%2FlajVeD6YMlJY5Kmi2AdNAYiEpFML20kNU0ZGnfzVl0HRPGpfIFfK1LtqDQx%2Fkhg2sKGG3ULSJnWiGADe7VNGZ5PGuT8S27rgKuqdYgpjmvOPbPA4Q7kfy0B56JQNLLi1XrBJSZVQdmEKcOvZxGZiKvlSGYkTvyx0nzynw7Je%2Fb%2Bl54FWPgTiGnQD6JTDkxJOOcBs2ESO%2FwFbwuTi01nTLz8xGidWom6Ti7BA4kbgPS6IIPcX12uwBGv1l%2BxaTnVVt5Sn733EqFMAyty2EHnuLTJPSNcHPkkVwAEDDa4ZlAsMEjWiIBZSE6Y6A30ls%2FMtge0oS9Go3wKM5EAh73widuMW%2BQVxly64tmb%2BmhH08SfdVKosb6kUh%2F6MYP7OXcQAv%2B0CFZcwbX0LPhBkIYKO6QhvhuhDwheTUvWSuigOjlgnFrnj571yyxuSbjcfiRAKqf%2BghFPXVDCSEPdDSrhAtvS%2Fg%2FzyhbX3C6WWdQXTctXp9mqcYVStRHQfcQyvNDxpc4hdLjlekWrbeUFwC4tItne2hiFzc%2FZKYFwpklF%2Bmtjc2NoPYauVHs2CvwWh6b62YZXb%2BvCmb3tHeLWKm4jKFCYCADmAG%2BWgiLspajl3LR3Emsc6Y3YQGMpCKGwGhgb8vnlIuu8W36C7DFVVmgCAF%2FZtmxcMZy0EkVOgIBk1ZiUsSTkBQb9jeCMlc2ui4K4HlXmXkk9sSE4%2Bb8tYOREhQqo9e1GGwnlsnw0tZcBAUqHm3NUaUz7Ws5W7V3qBvxrhlII2QAUE3cihyeAkv7GNWxMR%2FHDW0YVCTq%2By99gPEwrIWaoQY6sgGidEQi4U%2FVUKVRIurC1fytQzTPz%2FF57FzXZezoRYdSbAAi%2B1RqeVpNiv5M5jyYQ5LdJlHo78KQBSjYkG6VDLYdJSBnDErV17oswO%2FTuclaFYYjAvc0DdMbs1dcgUioy61xSgU%2BZT%2BOaAD5EzGjvKckqnIp5LAFU4oPO%2B3ZkoSHPcUEoBvgmRjJyhFZSGXiwUP33vUUDPWw0khKdb%2BqSCLJyDWL7CooxhHiJ0N%2BbvioMb0I&X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Date=20230331T082620Z&X-Amz-SignedHeaders=host&X-Amz-Expires=300&X-Amz-Credential=ASIAQ3PHCVTYZ2H7EOU6%2F20230331%2Fus-east-1%2Fs3%2Faws4_request&X-Amz-Signature=0b39266fb3035ffa19801e2e95d6f48fd7439ded42e3d98af17ed78b5cf3afc8&hash=c94750c0094bd2380a79e3269efbeb9952004ef59c085c9357d5c3952ac56d5c&host=68042c943591013ac2b2430a89b270f6af2c76d8dfd086a07176afe7c76c2c61&pii=0307904X94902275&tid=spdf-d9a29853-e7ac-4f32-be27-28a83645038c&sid=ef7407d46aa3e3448c68b7f301780e85663egxrqb&type=client&tsoh=d3d3LnNjaWVuY2VkaXJlY3QuY29t&ua=01015901545057560352&rr=7b0734f35bafdd77&cc=gb


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Area-51



Joined: 03 May 2021
Posts: 371

PostPosted: Fri Mar 31, 2023 1:31 am    Post subject: Re: the Obsidian Files - So Much Noise!!! Reply with quote

Thanks Clive,

Most of the CAD is reverse engineered; the europa is an OCD paradise.

Open Foam is open source and great for people that want access to physics analysis, but if you can learn the other industrial commercial level packages thats great too; same same results... Blender has just upgraded to a full CAD capability; another free open source package... after a while they all taste like chicken to me though.

Not a fan of and never have been one for exhaust affected cabin heating; always ends in sudden death. Recipe for disaster and up there on the top shelf for a Darwin Award. It needs a separation medium layer to be even remotely considered as an option. And with a rotax why even bother, just run it off the coolant system. 🤷🏼‍♂️

The CKT kit i can probably work out internals by tapping around with a spanner; but if someone want to through a CAD model at me i'll give it a whirl.. exhaust is a bit more tricky due to hot gasses cooling rapidly, so speed of sound is transitioning from x to y to z; so not that straight forward designing on paper or computer...

I tried to read that link to the pdf; it must be encrypted, lots of strange symbols and Greek hieroglyphs... but i will look for the equation option in the dropdown list of solution options and see what alternates emerge.


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PostPosted: Fri Mar 31, 2023 4:15 am    Post subject: the Obsidian Files - So Much Noise!!! Reply with quote

Stepping a bit over the line me thinks with the “Darwin Award” and “always” bit. Other flying risks outrank the subject by factors.

Exhaust cabin heating can be done safely, with careful inspection and inflight monitoring- especially with the stainless construction. In fact, my classic’s cabin CO levels are determined not by the heat channels but instead by the outlet position of the stock exhaust (I extended it), in combination with flap position, speed, cabin vent/heat pressurization and the europa’s open fuse flap slots in a high pressure zone.

PeteZ

Quote:
On Mar 31, 2023, at 5:37 AM, Area-51 <goldsteinindustrial(at)gmail.com> wrote:



Thanks Clive,

Most of the CAD is reverse engineered; the europa is an OCD paradise.

Open Foam is open source and great for people that want access to physics analysis, but if you can learn the other industrial commercial level packages thats great too; same same results... Blender has just upgraded to a full CAD capability; another free open source package... after a while they all taste like chicken to me though.

Not a fan of and never have been one for exhaust affected cabin heating; always ends in sudden death. Recipe for disaster and up there on the top shelf for a Darwin Award. It needs a separation medium layer to be even remotely considered as an option. And with a rotax why even bother, just run it off the coolant system. 🤷🏼‍♂️

The CKT kit i can probably work out internals by tapping around with a spanner; but if someone want to through a CAD model at me i'll give it a whirl.. exhaust is a bit more tricky due to hot gasses cooling rapidly, so speed of sound is transitioning from x to y to z; so not that straight forward designing on paper or computer...




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Posts: 371

PostPosted: Fri Mar 31, 2023 1:02 pm    Post subject: Re: the Obsidian Files - So Much Noise!!! Reply with quote

🤔🤔, 🤔🤔🤔🤔, still not convinced; happy with the abstractionated abstention....

Carrying on with noise and climate control OCD'ness.

Reverse cycle 12v portapack behind luggage bulkhead should balance out CG nicely... alternator and voltage regulator upgrade required... Unable to discuss details further here; different classified security op file...


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Area-51



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PostPosted: Thu Apr 06, 2023 3:53 pm    Post subject: Re: the Obsidian Files - So Much Noise!!! Reply with quote

Episode 82 of "shut that noise up"

Upon the eve of Easter, while out looking out over the distant full moon lit pastures for a pink and white rabbit an idea emerged instead...

With feverish reckless abandon i quickly searched through some 12,000 images of my electronic memory and found photos of 181's CKT exhaust.

Rushing back to the table with assumptions in mind the computer was turned on and the images again reviewed,.. using the burn markings of the CKT muffler a model of what could possibly be a similar internal structure, three absorber sections with a central expansion chamber, was modelled and then sent through the acoustic analyser with results being spat out shortly after.

What was found??? The CKT absorber/reflector style muffler provided better overall attenuation than the factory Rotax reflector style unit; broader low range, medium, and high range attenuation.

On a broadband level the CKT styled unit provided on average 4db greater attenuation than the Rotax. Low range was shown to be affective from 50Hz upwards where as the Rotax offers none until 320Hz. Peak attenuation levels on the CKT styled unit happened between 2000Hz and 3200Hz where the Rotax is 450Hz to 4000Hz with most attenuation taking place within this band.

So the CKT style Absorber/Reflector muffler is more quiet on a broadband basis and works best at attenuating more mid-field frequencies than the factory Rotax unit.

Out of interest have posted db scan capture of a 100hp 912 WOT (93db) at 100' distance and P&W PT6 intake (105db) during taxi at 100'; the exhaust is fairly quiet on the PT6... its a nifty app as it displays the frequency band as well as amplitude.

Happy Easter to all...


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PostPosted: Sun May 28, 2023 11:06 pm    Post subject: Re: the Obsidian Files - So Much Noise!!! Reply with quote

Today was spent at the creative assessment console a bit more doing some revision and assessment for the "shut that noise up" project.

With a few hours in action with the DCI treated airbox there's been a bit of time to ponder the new cabin experience using the Clarity Aloft headset.

Things have been very comfortable, however a resonant band has been showing up from 4100rpm to about 4800rpm where the carbi noise is howling. This is just not acceptable and has not passed the Area-51 EQA (experience quality assessment)... These are two rpm settings most often selected for cruising.

Coming back to the console the Modal Frequency analysis file was reopened and forensic data more closely looked for evidence of Mass Vibration... The forensic's team were not required to fabricate false evidence or narrative on this occasion.

Running the Modal solution again it was found that very little resonance was being generated by the airbox; some resonance was displaying at various bands within our interrogation but we are convinced the information gained points toward another source presenting the howling; most probably the carburettor throats themselves.

While the file was open it was a good opportunity to assess the Modal qualities of the pending baffle addition Mod. These results were even better than the non baffled airbox; data gathered shows very little Modal vibration from idle through to max rpm; and this is a great unanticipated result straight off the bat... Coupled with the earlier gathered Harmonic Acoustic results we can assume that there will be very little carburettor noise in action; so its expected the howling will be successfully vanquished from the sacred realm.

Winter is almost here, and the baffle Mod must be installed.


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PostPosted: Mon May 29, 2023 2:08 am    Post subject: Re: the Obsidian Files - So Much Noise!!! Reply with quote

Moving straight into the next phase... Setting up and optimising the Baffle mod for 3D printing; computer says 45hrs...

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peterz(at)zutrasoft.com
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PostPosted: Mon May 29, 2023 2:19 am    Post subject: the Obsidian Files - So Much Noise!!! Reply with quote

i'd be worried about bits in that harsh vib/chem environ breaking off and causing bad things.  Composite sounds like a safer bet?
Cheers
PeteZ

On Mon, May 29, 2023 at 6:14 AM Area-51 <goldsteinindustrial(at)gmail.com (goldsteinindustrial(at)gmail.com)> wrote:

Quote:
--> Europa-List message posted by: "Area-51" <goldsteinindustrial(at)gmail.com (goldsteinindustrial(at)gmail.com)>

Moving straight into the next phase... Setting up and optimising the Baffle mod for 3D printing; computer says 45hrs...




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PostPosted: Mon May 29, 2023 2:49 am    Post subject: Re: the Obsidian Files - So Much Noise!!! Reply with quote

Me too! Thats why no bits are small enough to get into the carbi throat, and the baffle extension has a cutaway slot to allow air to pass through should it somehow slide out of its position.

The trial fit pieces will be PLA and working ones PETG; which is a fuel proof and very tough material... final units will be West resin fibreglass coated. Also have carbon reinforced nylon to chuck at the situation. Final airbox product will be unitised composite single piece and trial bits thrown in the recycle bin.

The Modal and CFD tests indicate a low stress neutral pressure working environment.


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PostPosted: Wed May 31, 2023 4:50 am    Post subject: Re: the Obsidian Files - So Much Noise!!! Reply with quote

Yesterday was spent recording db levels in the cockpit, and also in the car on the way home... 95-100 db on WOT, 93db on Cruise Climb, 90db on Cruise, 77-80 db at Idle... the daily driver was 70 db down the highway. Sitting in a cafe at lunch watching the db frequencies on the app allowed identification of various tones; definitely carbi throat noise and low freq' panel drumming. Going back to the console to check our earlier acoustic results which indicate the baffle attenuating the frequency range required by 30db... this is going to be interesting to observe on the actuals.

A great day again to fly, but no flying was done... instead the morning was spent trial fitting the airbox baffle insert.

The new Prusa was pulled out of the box last night after three months waiting for something to do; and it is a beast of a machine... perfect prints after carrying out Z height calibration.

Half the baffle insert and an extension was printed up.. after measuring the tolerances things were left as set by the supplier at 0.05mm under size; and that quality is pretty amazing.

Straight after pulling the baffle print off the print bed i thought; hmm looks fantastic, should of just printed a profile stencil...

So off we went to the field to see what happens... the lid came off the engine bay and out came the air filter element and in went the baffle; except it didn't fit... .... .... out came the Sharpee and the ruler and away went the hacksaw over the marker lines, choppy chop chop, sand sand sand, chop some more, and some more until the baffle fit.

Then it was time for a cup of tea and a walk down to the back hangar to sort out Norman's ignition issues. Then it was time for a cup of tea.

After another cup of tea it was time to throw the airbox into the ute and go home and ponder the day's failures and successes.... so some templates were printed up and then the baffle insert got totally remodelled... now it will slide straight into the airbox with the airfilter element nesting in the baffle as the retainer.

Tomorrow another printing session, and another step toward success! Hopefully next airfield session will involve an engine start...


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PostPosted: Tue Jun 06, 2023 8:13 pm    Post subject: Re: the Obsidian Files - So Much Noise!!! Reply with quote

Its been raining here again and the conditions are IMC... so its been a
great opportunity to sit for days on end at the terminal and create more
fluff... lots of fluff...

Among all the fluff being created the airbox got some attention. More bits
got printed up; tuned and honed to sufficient and efficient levels; took a
few goes but it got there in the end with great results.

The profile of the baffle box was amended along with a revised version of
the extension tube; all optimised for printing on the Prusa which is an
absolute beast with its custom Bontech Mosquito print head that was
specially ordered and installed by the vendor.

After discovering the wrong side of the air filter element had been used as
the dimensional a 6.0mm insert was required; I screwed up; it happens; a lot.

Carbon rods were used for doweling, and with the whole lot ready it all
fitted together perfectly as designed. With a smear of flex sealant it was
a pressing moment... ...

Then the Durabloc kit was grabbed for some precision shaping of the
factory airbox... After a productive session shaping the baffle insert was a
great fit and ready for sealing with some West System epoxy.

Next task required will be printing up a "Special Tool" to retract the baffle
extension tubes to allow baffle box removal... We like Special Tools...

Some more acoustic assessments were also run which showed that the
revised baffle assembly attenuates specific transitional frequencies to
27db, which is not as good as the original scoping design which achieved
47db, however the broadband response of the revised baffle box is wider
than the scoping version... Alternate concepts were quickly modeled up
and also tried; which is another story for another episode.

And that's the end of this episode...

The next one we will see what kind of real world results are observed
from the commander's seat... Will it work? or will it all be an extravagant
failure????


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Last edited by Area-51 on Wed Jun 07, 2023 3:16 pm; edited 1 time in total
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Posts: 371

PostPosted: Wed Jun 07, 2023 2:51 am    Post subject: Re: the Obsidian Files - So Much Noise!!! Reply with quote

SPECIAL TOOL #86-A & #86-B

Sold as a paired kit only; must purchase order both pieces.

SKU order number - SP-86-00000000000001


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PostPosted: Wed Jun 07, 2023 8:45 pm    Post subject: Re: the Obsidian Files - So Much Noise!!! Reply with quote

Ground testing today...

20-24db amplitude reduction in target 600-1500hz frequency ranges
measured on the Iphone.

Special Tool #86 worked well but needs some operational shape
modification... The top cowling cover now holds the airfilter and baffle in place,
i.e a perfect fit scenario... Leaving the baffle in over night to assess fuel
vapor impact upon PLA.

flight test tomorrow morning... then final re-print in PETG.


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