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erichdtrombley(at)juno.co
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 Posted: Fri Aug 18, 2023 6:51 am Post subject: Cabin fresh air exhaust |
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Hello Area-51,
One area I would be keen to get some insight on with your computer modeling is cabin fresh air exhaust.
I have reviewed the paper Bud published on the topic which has some good information. While I am confident removing a piece of door seal at the top aft section of the canopy door will work, I am not too excited about the idea.
Currently, I am using standoffs on the removable D panel in aft cabin bulkhead. The spacing allows cabin fresh air to escape…somewhere. I am not really sure how it makes its way overboard, nor how efficiently. Unfortunately, this method isn’t completely effective as I still have considerable bulging of the doors. Perhaps I need longer standoffs to increase the gap. As such, I only have one door seal on at the moment allowing the air to escape via the port door which minimizes door bulging. I also notice in the winter months when I have the cabin fresh air vents closed, cold air blows on my neck which seems to be coming from the D panel.
Any comments or suggestions welcome.
Best regards,
Erich Trombley
N28ET
Classic Mono 914
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peterz(at)zutrasoft.com
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| Posted: Fri Aug 18, 2023 7:04 am Post subject: Cabin fresh air exhaust |
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I often wondered how effective troy manor’s reverse naca exhaust is, being positioned 1’ aft of the doors, on top of the fuse.
Cheers,
PeteZ
| Quote: | On Aug 18, 2023, at 10:59 AM, Erich Trombley <erichdtrombley(at)juno.com> wrote:
Hello Area-51,
One area I would be keen to get some insight on with your computer modeling is cabin fresh air exhaust.
I have reviewed the paper Bud published on the topic which has some good information. While I am confident removing a piece of door seal at the top aft section of the canopy door will work, I am not too excited about the idea.
Currently, I am using standoffs on the removable D panel in aft cabin bulkhead. The spacing allows cabin fresh air to escape…somewhere. I am not really sure how it makes its way overboard, nor how efficiently. Unfortunately, this method isn’t completely effective as I still have considerable bulging of the doors. Perhaps I need longer standoffs to increase the gap. As such, I only have one door seal on at the moment allowing the air to escape via the port door which minimizes door bulging. I also notice in the winter months when I have the cabin fresh air vents closed, cold air blows on my neck which seems to be coming from the D panel.
Any comments or suggestions welcome.
Best regards,
Erich Trombley
N28ET
Classic Mono 914
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Area-51
Joined: 03 May 2021
Posts: 395
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| Posted: Mon Aug 21, 2023 6:36 am Post subject: Re: Cabin fresh air exhaust |
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Its a good question and something that has had a bit of a study in various scenarios, yet not anything that in depth.
The attached image provides some indication however the free stream through the cabin is fairly slow, and its folding over and back upon itself constantly.
There is no discernible difference in actual ambient pressure to that which is external being detected.
Most of the ingress comes from the side vents and center control cutouts. In standard trim, on the Classic, the air then finds its way down through the fuel tap well, under the tank and then rearward out through the Hstab slots and rudder cable tubes. If the original Classic tail wheel port is still available the air exits a bit through there as well.
At this stage its unclear whether or not the flap bar slots are acting as ingress or egress. I am suspecting the former due to the positioning of the engine tail pipe on 181 and the noticeable headaches developing after longer back to back flights over more than two days. So my CO detector needs to be switched on now that the door seals are working affectively.
Based upon the trajectory and velocity of external free stream air I would expect absent door seals to allow air to flow out more rather than in, and I could be totally wrong also. A reverse naca vent would assist interior flow velocity somewhat as would some way for cabin air to traverse the D panel; this would probably have the most affect on uniform airflow through the cabin in flight and probably why an egress vent before the D panel works.
Its a subject that requires more time.
That's all I can offer right now, bit busy with other stuff for a bit.
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| Description: |
| Velocity map through XZ centerline of test environment with correlates. |
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Area-51
Joined: 03 May 2021
Posts: 395
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| Posted: Thu Aug 24, 2023 6:29 am Post subject: Re: Cabin fresh air exhaust |
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An update today; had an evening free to ponder.
The 181 model received a reverse naca vent beginning aft of the door frames and ending just forward of the fuel vents.
A free stream solution was dialed in for 100kt with a level attitude.
The results were pleasing. The exit vent caused the forward side vents to flow a great deal more volume into the cabin. So the reverse naca vent works. It just may not be located at the ideal position as it's trade off is additional Drag and some acoustic related energy.
Porting through the D panel produced no benefits worth mentioning.
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| Description: |
| Exiting cabin air flow from the reverse naca vent causing disruption over the empennage and Hstab root |
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| Side cabin vent air flow is noticeably greater. |
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budyerly@msn.com
Joined: 05 Oct 2019
Posts: 287
Location: Florida USA
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| Posted: Thu Aug 24, 2023 10:36 am Post subject: Cabin fresh air exhaust |
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I would caution using the term reverse NACA duct.
The NACA duct with its isentropic sharp edged curvy entrance is an inlet design not an exit. The vortex coming off the curvy sharp edged sides creates a vortex guiding the boundary layer into the inlet. It is an excellent inlet. But not designed as an exit. It can work because of the discontinuity between the boundary layer and the surface will create a small vacuum. There is no observed exit vortex aiding in the vacuum draw. The more efficient draw can be done using simply straight sides and about an inch or so exit ramp. It is easier to make also. However, to close it off, one has to get cosmic on how to seal this type ramp in rain.
For an exit, a simple reverse ramp is all that is generally needed but the best solution uses is a cowl flap design to rapidly build an exit vacuum draft. Make as any cowl flap. The lip can seal if gasket material is used to make a reasonably watertight surface when closed. Ideally a duct connected to a belly vent would be my first choice for reasonable weather tightness but that just adds time, weight and a longer operating control mechanism the farther it is from the cockpit. Its only advantage is the rain wont get into the airplane.
The best air exit is always done at a low pressure area of the wing or fuselage. On the Europa, the wing is too hard to use but the top of the canopy is not bad. One could use the area beside your elbow just above the wing fairing as an exit area for a flap but Im not excited about that. The canopy (the back of the Thorp and other canopies had a flap that opened like a cowl flap and drew the air out of the low pressure area just behind the peak of the canopy glass. Of course, it leaked in the rain unless it incorporated a seal. Anything behind the wing on the fuselage is basically static air pressure so not the best draw for the cockpit. Hence the vents in the D tube are limited in their ability to draw air but do work on trigear aircraft using ram inlet air from the cockpit as a way to flow air out somewhere. My 12AY air exit around the D panel is fair but not perfect by any means. It is more of a pressure release than a true air draw area. Whereas the small opening of the door seal just behind your head is a fair draw out of the cockpit unless your doors fit nice and tight to the fuselage, then that is not so great. (My pilot side vents air out better than the tight fitting pax door. The door seal is the easiest to try. Simply pull the seal off at the back and go fly. Hold a piece of paper to the gap and see how it works. Mine is pretty fair on the pilot side only due to door fit.
One or more of our British friends added a vent to the top of the canopy center glassed area and had good air exit, but it leaked in the rain on the ground also. No surprise there. Mono fliers found on grass the draw may actually increase the amount of grass and dust drawn through the wheel well gear handle and airbrake levers on landing and takeoff. Nasty and dirty if the vent is left open for takeoff and landing on dirt/grass.
What is the best solution? It is hard to say on a fully finished aircraft. On trigears, the belly access hole can be used, and vents are put into the center tunnel which is more work. I don't care to do that but a one inch cowl flap on the bottom access door did seem to work as it sucks a piece of paper and two 3 inch round vents in the sealed tunnel was somewhat useable. On Trigear conversions at the original Classic tail wheel, we cut the wheel off and simply put in an exit duct around the hole for a draw. It looked cool but I didn't see any advantage as I believe the exit duct simply pulled air out of the flap drive holes.
USE CAUTION as installing cockpit air inlets near the leading edge of the wing tend to draw engine exhaust into the cockpit. I did a paper on that some time ago. Keep the vents high. Use some dark oil painted on the fuselage and fly and look at the flow. It goes from the exhaust up and over the wing from the exhaust pipe on the XS unless the exhaust pipe is very long.
Finally, what has worked was just ram pressure. The ultimate vents and NACA vents are excellent inlets, but only two inlets arent really enough in a hot SE or SW US summer unless properly directed. I have two NACAs and two Ultimate Vents. The NACA ducts have no flow direction which would be nice but the air impacts the pax and pilot legs only. So, the NACA air enters and circulates around the legs and groin. Later I added Ultimate vents in the windscreen side glass which directs air at the upper body and more importantly the face. These are tolerable but I would like more air on my face AND central body when doing pattern work. I have no issues with air velocity coming in using the D tube as it is effective as a ram air pressure release of cockpit pressure. Putting in new fuselage ducting with vents in the rear fuselage is out of my patience level anymore. Ill carry some cool water and just wear shorts and a T shirt and close the vents when I get up to altitude in summer. The oil tank and sun are sufficient warmth for cruise at 10,500 in summer. I put on more clothes for winter. If I have to go farther north in the winter or higher in altitude (which I have no intension to do) Ill buy a heated motorcycle suit and wear wool socks. I have the available amps or will use the pocket batteries to warm me. We were always taught, dress for the worse conditions anticipated. Today, I simply dress for cockpit comfort, and carry a jacket handy behind the seat and pack some jeans as I go north.
Nice discussion, and it would be great to get more feedback from our hot weather fliers and get some fresh ideas. My last good idea was asking my wife to marry me. At least that mod to my life didnt take tweaking to get it to work right. Nothing works it seems in aircraft design and construction without tweaking to get exactly what you want, or need.
Best Regards,
Bud Yerly
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DuaneFamly
Joined: 16 Jan 2022
Posts: 22
Location: Chandler, AZ
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| Posted: Thu Aug 24, 2023 11:37 am Post subject: Cabin fresh air exhaust |
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“Acoustic related energy”? Do you mean “noise”? LOL
Sent from the all new AOL app for iOS
On Thursday, August 24, 2023, 7:30 AM, Area-51 <goldsteinindustrial(at)gmail.com> wrote:
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Area-51
Joined: 03 May 2021
Posts: 395
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| Posted: Thu Aug 24, 2023 5:01 pm Post subject: Re: Cabin fresh air exhaust |
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Yes, fancy way of describing noise and padding out the content with exciting and conversational inspiring fodder :)
Fully agree with all Bud's points. Somebody at the beginning mentioned a reversed naca vent arrangement so that's what got reviewed but other exhaust arrangements can be played with at some later stage. At this point it has been established that providing a cabin exhaust vent to the outside improves flow through capacity of cabin ventilation. Belly mounted exhaust vents downstream of the rear cabin wall along with a vent at the wall is probably a suitable position as the air flow is already a bit dirty from the cowling shape and mono undercarriage and would assist sucking out any undesirable vapor or smoke should that arise.
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budyerly@msn.com
Joined: 05 Oct 2019
Posts: 287
Location: Florida USA
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| Posted: Fri Aug 25, 2023 6:10 am Post subject: Cabin fresh air exhaust |
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I was staring at work that needs to be done and my N12AY was setting in the corner of the shop and I noticed something I missed on ventilation exhaust.
The two curvy slots for the flap exit could easily have a small ramp added to it to draw air out of these slots. I'm wondering if that would be a reasonable experiment to do in the future. The flaps are about 1/8 inch from the upper surface to the fuselage on 12AY but the bottom is slightly wider and of course as the flaps extend the gap between fuselage and flap increases further.
Just another tweak in my life. Maybe I'll do that this fall.
Best Regards,
Bud Yerly
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Area-51
Joined: 03 May 2021
Posts: 395
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| Posted: Fri Aug 25, 2023 7:03 am Post subject: Re: Cabin fresh air exhaust |
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Do a quick explanation sketch Bud.
Played with this a bit more today by adding an additional belly vent aft of the curtis valves; then another pair of vents just below the leading edge of the Hstab; then added a passage through the D panel.
The top mounted exit vent provides the most volume flow through the entry vents into the cabin. However eliminating both top and belly exit vents and retaining the D panel port and rear exit vents provides a more uniform flow and less disturbance to exterior free stream air upon exit.
Utilising all the options together shows air being sucked in through the belly exit vent.
The model being tested has the flap bar slots blocked off; there would normally be air exiting or entering from this area; which is possibly where CO is getting in from prop swirl turbulence.
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| Description: |
| Entry vent flow velocity, top exit vent without D panel port |
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| Entry vent flow velocity, rear exit vents and D panel port |
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| Dual rear exit vent position |
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Last edited by Area-51 on Fri Aug 25, 2023 7:15 am; edited 1 time in total |
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budyerly@msn.com
Joined: 05 Oct 2019
Posts: 287
Location: Florida USA
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| Posted: Fri Aug 25, 2023 7:09 am Post subject: Cabin fresh air exhaust |
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I'll take some time tonight.
Bud
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budyerly@msn.com
Joined: 05 Oct 2019
Posts: 287
Location: Florida USA
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| Posted: Fri Aug 25, 2023 8:19 am Post subject: Cabin fresh air exhaust |
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A quickie sketch at lunch time.
Just a small ramp fabbed and then tapered to clear the flap may draw a bit of air out of these rather ugly gaps in the aircraft side. However ugly these slots may appear to be, and we do pretty them up slightly, but it makes for expedient construction and my thought was it may be a useable exit for cockpit air ventilation.
The ramp will have to clear the lower edge of the flap as it extends initially so on my plane 5mm may be maximum height. I'm thinking I may just do a quick photo, and 3D print a rough ramp so it can be tapped in place (3M sticky two sided tape most likely to preserve my patience.) I would think just stick it on and go fly. Put a small pressure sensor / Arduino and check outside pressure vs inside pressure to determine the effectiveness.
Personally, my pressure vents are fine except for the pilot side NACA which is too low and allows exhaust fumes to enter when climbing from 75-90 Knots climb speeds. At cruise my pilot side NACA duct is free of exhaust fumes. I'm thinking longer exhaust pipe. Time and energy permitting of course.
That thinkin stuff will get you in trouble.
Bud Yerly
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erichdtrombley(at)juno.co
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| Posted: Fri Aug 25, 2023 8:59 am Post subject: Cabin fresh air exhaust |
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Hello all,
I appreciate the discussion this thread had yielded. So, in my case I have a ram air NACA duct in the lower cowl which provides more than sufficient airflow to the two eyeball vents located in the lower portion of the center instrument panel. The challenge I have, as previously mentioned, is getting the air to exit the cockpit in order to relieve the pressure which causes excessive bowing of the door frames. Unfortunately, the standoffs on the D panel aren’t sufficient on their own, and I currently have just the pax door seal on at the moment.
If I understand the latest analysis by Area-51 an exit near the horizontal stabilator may do the trick. This may also require longer standoffs on my D panel if that becomes the flow constraint.
I am also interested in hearing from Pete who has a reverse NACA installed just aft of the doors on the top of the canopy. Noise and weather concerns notwithstanding, does this solution get the job done?
Thanks everyone for providing their time and energy to this question.
Erich Trombley
N28ET
Classic Mono 914
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peterz(at)zutrasoft.com
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| Posted: Fri Aug 25, 2023 9:13 am Post subject: Cabin fresh air exhaust |
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wrt to Troy's reverse Naca behind the doors on top, I am not convinced it makes much of a difference.
Hopefully I will get up soon again and check it out at various airspeeds (I've been grounded the last two weeks due to recovery from surgery ....)
Cheers,
PeteZ
On Fri, Aug 25, 2023 at 1:07 PM Erich Trombley <erichdtrombley(at)juno.com (erichdtrombley(at)juno.com)> wrote:
| Quote: | --> Europa-List message posted by: Erich Trombley <erichdtrombley(at)juno.com (erichdtrombley(at)juno.com)>
Hello all,
I appreciate the discussion this thread had yielded. So, in my case I have a ram air NACA duct in the lower cowl which provides more than sufficient airflow to the two eyeball vents located in the lower portion of the center instrument panel. The challenge I have, as previously mentioned, is getting the air to exit the cockpit in order to relieve the pressure which causes excessive bowing of the door frames. Unfortunately, the standoffs on the D panel aren’t sufficient on their own, and I currently have just the pax door seal on at the moment.
If I understand the latest analysis by Area-51 an exit near the horizontal stabilator may do the trick. This may also require longer standoffs on my D panel if that becomes the flow constraint.
I am also interested in hearing from Pete who has a reverse NACA installed just aft of the doors on the top of the canopy. Noise and weather concerns notwithstanding, does this solution get the job done?
Thanks everyone for providing their time and energy to this question.
Erich Trombley
N28ET
Classic Mono 914
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peterz(at)zutrasoft.com
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| Posted: Fri Aug 25, 2023 9:15 am Post subject: Cabin fresh air exhaust |
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Looks like the trim slots are candidates for exhaust?
On Fri, Aug 25, 2023 at 11:11 AM Area-51 <goldsteinindustrial(at)gmail.com (goldsteinindustrial(at)gmail.com)> wrote:
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Area-51
Joined: 03 May 2021
Posts: 395
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| Posted: Fri Aug 25, 2023 2:30 pm Post subject: Re: Cabin fresh air exhaust |
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Peter the trim slots are shielded by a forward bulkhead feature on 181, so air flow to these slots is very limited.
Implementing rear side exhaust ports near the Hstab has its own set of challenges and issues regarding structural integrity and fatigue of the Hstab root area.
Some tricky "multi-phase" solutions are required on this subject to factor in prop swirl and exhaust gas paths from the engine's tail pipe; which means a "press Solve button and go to bed" situation.
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peterz(at)zutrasoft.com
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| Posted: Fri Aug 25, 2023 2:51 pm Post subject: Cabin fresh air exhaust |
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Area of the bulkhead slot isnt any smaller than my existing reverse naca behind the doors fwiw.
| Quote: | On Aug 25, 2023, at 6:40 PM, Area-51 <goldsteinindustrial(at)gmail.com> wrote:
Peter the trim slots are shielded by a forward bulkhead feature on 181, so air flow to these slots is very limited.
Implementing rear side exhaust ports near the Hstab has its own set of challenges and issues regarding structural integrity and fatigue of the Hstab root area.
Some tricky "multi-phase" solutions are required on this subject to factor in prop swirl and exhaust gas paths from the engine's tail pipe; which means a "press Solve button and go to bed" situation.
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=511352#511352
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Area-51
Joined: 03 May 2021
Posts: 395
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| Posted: Fri Aug 25, 2023 3:28 pm Post subject: Re: Cabin fresh air exhaust |
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If you have cutouts in the bulkhead through to the trim slots then air will probably flow out of there, and it could also just as easily get sucked in. Without the D panel port the rear situated exhaust vents showed a tendency to suck air in at 100kt.
I recently designed and fitted a header tank in a Pipistrel Sinus and each time we purged the system we would get fumes filling the cabin. We discovered the air was being sucked up the vent at the end of the tail up into the cabin and out the side window vents. Air does weird things some times and goes where ever there is a lower point of pressure.
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DuaneFamly
Joined: 16 Jan 2022
Posts: 22
Location: Chandler, AZ
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| Posted: Fri Aug 25, 2023 4:49 pm Post subject: Cabin fresh air exhaust |
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I would imagine that if someone finds a way to remove air from the rear of the fuselage, whether through reverse NACA vents under the stabilatorsor if Bud can figure out a way of removing air through the flap vents, then standoffs under the “D” panel could help draw air out of the cabin.Now a drawback would be if the pressure drop inside the cabin might start bringing in more exhaust fumes on the mono?
Doesanybody have any concern of any structural issues with a flap-style vent on top behind the doors?
Mike Duane
N377EA
Europa XS Conventional Gear
Chandler, AZ
Sent from the all new AOL app for iOS
On Friday, August 25, 2023, 10:00 AM, Erich Trombley <erichdtrombley(at)juno.com> wrote: | Quote: | --> Europa-List message posted by: Erich Trombley <erichdtrombley(at)juno.com (erichdtrombley(at)juno.com)>
Hello all,
I appreciate the discussion this thread had yielded. So, in my case I have a ram air NACA duct in the lower cowl which provides more than sufficient airflow to the two eyeball vents located in the lower portion of the center instrument panel. The challenge I have, as previously mentioned, is getting the air to exit the cockpit in order to relieve the pressure which causes excessive bowing of the door frames. Unfortunately, the standoffs on the D panel aren’t sufficient on their own, and I currently have just the pax door seal on at the moment.
If I understand the latest analysis by Area-51 an exit near the horizontal stabilator may do the trick. This may also require longer standoffs on my D panel if that becomes the flow constraint.
I am also interested in hearing from Pete who has a reverse NACA installed just aft of the doors on the top of the canopy. Noise and weather concerns notwithstanding, does this solution get the job done?
Thanks everyone for providing their time and energy to this question.
Erich Trombley
N28ET
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wdaniell.longport(at)gmai
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| Posted: Sat Aug 26, 2023 3:16 pm Post subject: Cabin fresh air exhaust |
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N460HJ cabin exhaust...the fuel tank outlet covers
\[img]cid:ii_llsn1q0w0[/img]
[img]cid:ii_llsn3iv41[/img]
William Daniell
LONGPORT
+1 786 878 0246
On Fri, Aug 25, 2023 at 6:52 PM Pete <peterz(at)zutrasoft.com (peterz(at)zutrasoft.com)> wrote:
| Quote: | --> Europa-List message posted by: Pete <peterz(at)zutrasoft.com (peterz(at)zutrasoft.com)>
Area of the bulkhead slot isnt any smaller than my existing reverse naca behind the doors fwiw.
> On Aug 25, 2023, at 6:40 PM, Area-51 <goldsteinindustrial(at)gmail.com (goldsteinindustrial(at)gmail.com)> wrote:
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> --> Europa-List message posted by: "Area-51" <goldsteinindustrial(at)gmail.com (goldsteinindustrial(at)gmail.com)>
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> Peter the trim slots are shielded by a forward bulkhead feature on 181, so air flow to these slots is very limited.
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> Implementing rear side exhaust ports near the Hstab has its own set of challenges and issues regarding structural integrity and fatigue of the Hstab root area.
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> Some tricky "multi-phase" solutions are required on this subject to factor in prop swirl and exhaust gas paths from the engine's tail pipe; which means a "press Solve button and go to bed" situation.
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> Read this topic online here:
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> http://forums.matronics.com/viewtopic.php?p=511352#511352
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Area-51
Joined: 03 May 2021
Posts: 395
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| Posted: Sat Aug 26, 2023 5:29 pm Post subject: Re: Cabin fresh air exhaust |
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This is proving a hot topic!!
So, Pete you are correct, I checked the model again, there is a slot in the bulkhead that allows air to flow through to the Hstab trim slots. The trim servo arm operates through it. With or without a port in the cabin D panel doesn't appear to make any difference, the air gets trapped in an internal vortex. So some additional work required here to help it flow out. My initial thoughts way back was to fit bristle brush wall to eliminate acoustic noise from this feature. Bud's idea for the flap bar slots might also help resolve this vortex situation.
William just posted pics of curtis valve covers. Minimal air does flow from here, and the volume is not high enough to adversely affect cabin flow.
I ran the model again in standard trim with the flap bar slots exposed. Air does flow through here much better when the D panel port is implemented. 181 has a flat panel piece fitted at the bottom throw position of the slot that helps to draw air out into the free stream. Elimination the flap bar slot has a marked affect on cabin air ingress volume however the greatest affect so far has been the top position aft of the doors followed by the rear side near Hstab. Structurally side vent implementation would require at least horizontal battening stretching either side to maintain integrity of the high load area
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| Section view through Vstab showing vortex at trim slot position |
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| View from rear of lower flap bar slot plate on 181; flap deployed. Not sure if this is a standard feature, or Baker built mod'. |
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Last edited by Area-51 on Mon Aug 28, 2023 8:18 pm; edited 1 time in total |
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