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Vortex generators for Naca vents for RV-4

rvator51

rvator51

Well Known Member
In my never ending quest to get the cockpit cooler (not to mention CHTs but thats another story), I made and temporary stuck a set in front of each naca vent on the rv-4 canopy. The vents are in the location called out for in the plans. However, air flows out of the front vent instead of in and the rear vent doesnt have a large volume of air flow. Hopefully these will help reverse that. If they dont work, I will make different ones that have a lot more acute angle on them. Has anyone did this with success?
 
rvator51 said:
In my never ending quest to get the cockpit cooler (not to mention CHTs but thats another story), I made and temporary stuck a set in front of each naca vent on the rv-4 canopy. The vents are in the location called out for in the plans. However, air flows out of the front vent instead of in and the rear vent doesnt have a large volume of air flow. Hopefully these will help reverse that. If they dont work, I will make different ones that have a lot more acute angle on them. Has anyone did this with success?
Click to expand...

Interesting idea, let us know it works out.

:cool:
 
Heres a picture of the first trial set:

vortex1.png
 
NACA Vent

The NACA submerged duct works by generating a vortex off the ogival shaped sidewall intersections with the body surface, in this case the airplane fuselage. By doing this the two opposing vorticies draw air down from the freestream and into the duct entrance.

Therefore, adding an additional vortex generator in front of the duct is counterproductive.

One way to increase duct performance with thick boundary layers is by adding deflectors to the sidewalls.

Have a look here for the document NACA RM No. A7I30 figure 6
http://naca.central.cranfield.ac.uk/reports/1948/naca-rm-a7i30.pdf

I agree with the previous poster: if the pressure inside the cockpit is higher than the pressure at the NACA duct inlet, air will flow forward out of the duct.
 
I flew first test flight this morning. The vortex generator is letting air flow into the cockpit now. Still feels like air is also going out at the same time. So is an improvement as only air flowed out before. Going to test a different vortex generator with more acute angles next. Thanks Terry and Lotuswheelnut. Seems like a good point about positive pressure causing reverse airflow and also using deflectors that follow the naca shape instead of vortex generators. Will keep trying different shapes/things to see if the unusable vent can be made to work. I do not want to cut any more holes in fuselage for more vents.
 
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Gave up on canopy scoop

I gave up on those worthless side scoops. I cut a vent hole on the lower right below the cheek cowl. Used a naca scoop, hose and eye ball vent. Works great only needed one, idle prop blast will send air into cockpit. Plus very quiet.
Wish I would have done it 25 years ago!
 
RV-4 Vents

On the way back from the KC Formation Clinic we were down low VFR and I realized in the summer in Missouri I like to be up a little higher. It was quite warm so I turned on the autopilot and started playing around with the NACA vents I have. Not to worry, I had a wingman keeping an eye on me. What I found was all I needed was some deflectors on the inside attached to the back of the NACA vents to direct air towards me. The vents as they are right now seem to just dump the air to the back behind me which is of no use to me.

I think I have a solution in some cheap easy to make sheet metal deflectors that I will RTV to the inside of the canopy at the back of the vent. I will post some pics after I test them out to see if they work.

Oly
 
Thanks Oly,

At least you are getting air in through yours! I wonder why you are getting flow in while my flow is out? I am investigating on how to lower the pressure in the cockpit so air flows in more easily. I wonder if anyone has ever put louvers on the bell-crank access panels in the wing?
I dont think I am getting high pressure air from the tail as the fuselage is sealed off completely at the back of the baggage compartment. That leaves the wing, flap holes, naca vents and canopy as the only areas for air to come in/go out of.
 
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It might be worth having a cockpit air outlet, a designed-for-the-task air exit from the cockpit. It's got to go somewhere and if it's not going where it should it's making drag.

Dave
 
Thanks Dave,
I agree with you. In reading previous threads, it seems some locations work for some and dont work for others. Must be a lot of variables and I dont want to cut another hole in RV until I know for sure it is a good location for air outlet.
 
RV-4 Vents

Don't know if it's pertinent to the issue or not but I have a Sam James Cowl so perhaps there is a different airflow pattern around my cockpit. I am getting lots of air through both NACA vents but it just goes right down the side of the canopy to the back. The back seaters say there's good flow back there. I am going to steal the air and just deflect it towards me.

A couple RV-4 guys around here have the CA LV-3 Vent that Vans Acft sells. I have been in the back seat of both and they work great and you can aim the flow. I have two NACA vents in the front & one on the right side in the back. I am going to install one of these CA LV-3 vents in the back on the left side. They are made of aluminum and can be painted to match the airplane. Picture below:

9h3rkx.jpg


Oly
 
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Venting...

rvator51 said:
In my never ending quest to get the cockpit cooler (not to mention CHTs but thats another story), I made and temporary stuck a set in front of each naca vent on the rv-4 canopy. The vents are in the location called out for in the plans. However, air flows out of the front vent instead of in and the rear vent doesnt have a large volume of air flow. Hopefully these will help reverse that. If they dont work, I will make different ones that have a lot more acute angle on them. Has anyone did this with success?
Click to expand...
Tom,
My 89' RV4 plans had several poor ideas that (like leisure suits) seemed good at the time, tank sloshing and canopy rail Naca vents. I quickly found on my test flight in my home states 90/90 conditions that they fell well short of claims. I tried the VG"s and they slightly improved the forward vent air. I also tried wing root fairing holes similar to Cessnas, which worked OK.
The fix came when I purchased a beta test version of Larry Vetterman"s vents pictured by Oly above long before he sold them to vendors including Van"s. I installed them on the left side of the fuselage 6" below the canopy rail front and rear cockpit per an Aero Engineers suggestion and a third on right fwd. Problem solved partly.

The bigger fix was to drill holes around my rear seat bulkhead and turn my aft fuselage into a Venturi, drawing a noticeably large amount of air through. I added many to friends RV4"s over the years. For vents now I suggest the underside right wing NACA duct ala RV8 for rear cockpit and RV10 flip out vents on the fwd fuselage below the aft cowl bumps. Both are invisible on the ground (if closed) but work amazingly well when open.

Redneck A/C at it"s finest...:)

V/R
Smokey
 
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Hi Smoky,

Thanks for all of your accumulated wisdom! I have been hearing that the tail is a high pressure area and opening a vent in the baggage area to it would let in high pressure air. Are you saying its a low pressure area and cockpit air will vent to the tail if you open holes in the aft baggage bulkhead?
 
vortex generators for Naca vents

Has anyone used something like vents on rv10, I am considering in side of fuselage on -4 under construction ? Tom
 
RV-4 VENTS

All

I have one of these (CA LV-3 vents ) on the right rear skirt of my RV-4 and it does really work and looks good.I also have 2 Naca ducts about 6 '' under each cheeks and there is so much air going thru them that they set the squelch off my radio...

I also have a small flap on the left fwd side skirt which I rarely use these days even with temps in the 90s like last week..

So there are ways to cool an RV-4

I'll try to take pictures tomorrow.

Bruno
 
Location, location, location

It's not just for real estate. The place on the skirt you have is a low pressure area. I was helping a friend with this very problem and we eventually gave up on using the existing NACA vents in that location. Placing the NACA vent below the cheek works great as is mentioned. On my RV4 we did something else. The duct was glassed onto the cheek cowl a bit lower than midline (so rain on the ramp is no problem). They work extremely well. You can feel them puffing with the engine idling at 650 RPM. In the air they produce a huge volume. I also have one one the lower right wing similar to the 8 which goes to a separate large eyeball vent in the aft cockpit. I can send some pictures if you like.
 
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