Cabin Air vents in boot cowl

[Nev]

I’ve started a new thread on this topic - there is a similar thread regarding wing root vents with a lot of good info.

My plan is to install NACA intakes on the upper boot cowl, with a short scat tube feeding 2 inch panel mounted air vents on each side of the instrument panel.

Some of you have already done this, and I see there were some reported issues where engine compartment cooling vents allowed warm air into the cold air intakes. I don’t plan to have engine compartment venting on the sides, just the standard lower outlet with a cowl flap.

Has anyone experienced rain water running down the cowl and entering the NACA ducts while parked on the ground?

If so, does it enter the pax compartment when speed increases, or does it trickle back out the way it entered as the tail comes up ?

Has anyone managed to combine both warm and cold air into the same outlet vents - similar to a car ?

Are there any other considerations I should be thinking of ?

[Mark Goldberg]

My experience is that not enough airflow happens from NACA ducts on the boot cowl. For the Texas summer heat. I prefer the Cessna style leading edge fresh air inlets. Mark

[Bcone1381]

A Kitplanes article in 2017 shows +/- pressure that a fuselage skin experiences in flight. Magenta is low pressure. A vent located in a magenta area may experience negative pressure and suck air out of the fuselage.

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I see Cub Crafters puts vents on the lower cowl in the same area that the above aircraft has magenta. I suppose.....its function is to suck air out of the lower cowling. Maybe air can accelerate around a fuselage like it does our wing creating low pressure.
Screen Shot 2020-10-10 at 1.12.47 PM.png

[TimTall]

Every airplane is a little different but they work amazingly well on my Murphy. At idle they blow hard enough to help, by 120mph they blow harder than the strongest setting on my car. The eyeball vent is located perfectly to blow right up your shorts too!

I'm hoping to set up the same system on my Bearhawk. I've never had a problem with water getting in and my plane lives outside.

I guess placement is critical though. I'm not sure how to figure out exactly where to put them. I May wait until it's flying and tape some string to the boot cowl and see what the air flow looks like.

[Nev]

The eyeball vent is located perfectly to blow right up your shorts too!

Great data point thanks Tim !!

My understanding is that the NACA by design will draw air in as it creates its own low pressure area in the divergent duct. Presumably for the sum of the pressures to remain equal the airflow should increase in dynamic pressure.......my memory of Bernoulli and his ideas being somewhat distant......

[svyolo]

I they don't work, at least they will still look cool. Make up something if somebody asks.

[PaulSA]

In the RV10, the NACA vents are just forward of and below the windscreen - work great.....

[whee]

I wanted NACA intakes in my boot cowl and vents in my panel but I did not have the panel space and putting them below the panel would interfere with my legs. So far the only time I need vents is in the summer while taxiing so I just open the door.

Good chance I'm remembering wrong but I think NACA vents rely on smooth airflow over the surface. Being in a low-pressure zone should not be a significant factor as long as the airflow is smooth. Tuft testing is a good idea.

[Pbruce]

The ones in my RV9 worked hardly at all. It seems comments about placement and different types are accurate. My vents were of the most basic cheapest type available, and they leaked badly when dialed closed in winter, so consider investing in quality. I’d love to know if they work out on BH Patrol.

[Battson]

The new wing root vents sold by ACS definitely don't leak.

[spinningwrench]

I am planning to add NACA vents to my boot cowl. Mike Silvernagle used them on his Patrol and says they work extremely well. On my Citabria there are little vent "windows" on the boot cowl that work very well. I find air coming up from around my legs is more effective for cooling in summer than just Cessna style vents blasting me in the face.

[Nev]

I wonder if the performance of all air vents is just as dependent on the outlet for the airflow as it is the inlet ? I’m planning to have an outlet at the rear underside of the fuselage near the tailwheel, basically a hole in the fabric.

[Rollie]

The vent in the boot cowl goes to scat tubing routed under the floor to vents for the back seat. I haven't had any issues with water. That vent is mounted in an access panel that provides easier access to the back of the instrument panel and I also have a panel without the vent for cold weather. The vent in the engine cowl routes air to the muffler heat muff.

[Ryan Koeneke]

Hey Nev, any chance you can give us an update on how the NACA vent placement worked out for you? Any issues with water, heat, or airflow in that area?

[Nev]

Hey Nev, any chance you can give us an update on how the NACA vent placement worked out for you? Any issues with water, heat, or airflow in that area?

Hey Ryan,

Actually it works very well and I'm happy with it. The placement of the vents is simple and the airflow easy to aim at the face/body. There's plenty of airflow too. It does take panel space which is a consideration, but in my case it all fits well. Passengers understand the operation of them intuitively.

One minor downside is when I wash the plane water tends to pool in bottom of the duct. When you first open the vents in flight you're then treated by a blast of well aimed water to the face ! The solution is to blow it out after washing, and could probably be mitigated by tilting the intake slightly. Probably an issue with any vent though. I haven't flown in much rain yet but I don't expect any issues there due to the NACA duct design, the water should pass along the fuselage. All in all, very happy.

CA645762-CF5A-4145-8BB1-ECEB3F7ED2D8.jpg

[Ryan Koeneke]

Thank you sir. I appreciate the report. I've already budgeted space in the panel for eye ball vents. I'll prolly take the advice from your 4 month checkin and move the naca vent slightly forward to avoid conflicts with my thick legs lol. I'll also plan on angling it upwards towards the panel as you suggest as well. I appreciate all the info! I was thinking about doing the cessna wing vents as well but was worried that would just be overkill. However, it looks like Rollie has both of them which makes me feel better lol.

[TimTall]

Mine work great. No issues with water getting in in flight or on the ground. They're angled just enough that any water that gets in them on the ground will spill out before flowing into the scat tube. The eyeball vent used makes a difference in how well they seal. I used aluminum units that were kinda pricey but they look good, seal well, and are quite adjustable for airflow and direction. I really like having vents in the panel. I can point them right up my shorts on a hot day.

[triumphantduke]

I think ill be doing it similar to Mr. Tim, although it would be really cool for someone to volunteer hours of their time and smart on the subject to run a cfd sim for the bearhawk cough cough lutinplunder