RV 4 Canopy NACA vent enhancement

[GWBaker]

As most of us know, the canopy mounted NACA vents on the RV 4 are in a bad location. Most new builders are not putting them there. Those of us who have purchased an RV 4 with these already installed will not be building a new canopy just to relocate or eliminate these vents. If you are like me, you do not like having a somewhat non-functional thing attached to your plane, so my thought was "let's do something with it". I have read the posts about installing the vortex generators that Vans recommends, but it seems like most people agree that it is not that effective as it creates a low pressure in an area that already suffers from low pressure.

Please forgive me if this has been done before and mentioned, but I have not seen it on the forum yet. This is not the most elegant solution, and some will say that it will create drag. My plane did not lose 1 mph with this mod. It's basically a clear plastic scoop that is designed to interface with the NACA design. It works perfectly and makes the vents completely usable. I actually find myself modulating the vents now to adjust airflow as I cool down as apposed to just flying with them wide open all the time and getting no flow or reverse flow. I have attempted to post a picture. See below:



Pic: https://onedrive.live.com/?authkey=%...%21668&o=OneUp

Cheers,
Greg

RV4
O-320E2D

[Whitman]

Where?d you buy that?

[GWBaker]

Originally Posted by Whitman

Where?d you buy that?

Plastics 4 Performance is the company. They are in GB. Find them on EBay. Search for "clear NACA Scoops"

I bought the smaller 2" version as there are 2 versions.

[gmcjetpilot]

Had similar problem on my RV-4 and I took a different less draggy approach. I put to VG's in front of the NACA scoop.
The two NACA inlets where in my canopy skirt on RHS. A combo of the Prop corkscrew, slip stream, laminar airflow, the
air coming into cockpit was weak. After the VG Mod I had good to very good flow. Also consider cockpit exit air flow scoop.

NACA Scoop ............VG's (angle not as shown, less acute)
_______
I ..........( _____............\
I......................(___.......\
I..................... ___I
I............_____(............./
I______(....................../

I had all the dimensions and angles written down long ago. I recall I posted something. It worked great. My text sketch above
is not accurate; the angle of the VG's was more aligned with airflow. I recall VW's were 1 to 1.5" long and standard height about 3/8".
They were about 1/4" to .5" fwd of fwd edge if scoop, with a VG angle of about 20-30 degrees to airflow, with the outer edge aligned
with the outer edge of the aft end of the NACA scoop. They were temporary taped on and played with many angles and position. It
was night and day difference, when I hit on the right combo. Once the VG's were dialed in, I don't recall if bonded them on with tank
sealant or used two way sticky tape the VG's had. I do recall they were there 6 years later when I sold the airplane.

What you did is make this more of a standard scoop into free air stream. This works well but does add drag. I'm surprised you even
see 1 MPH. That is well inside the margin of error. Flight testing in standard smooth conditions from one day to the next is hard to do.
Nice work... I like it. If it works cool (pun intended). If you want to experiment I think it would be cool if you try the VG idea as well.
See if you can further the air flow (or not and just enjoy flying ).

[GWBaker]

Well, I ran WOT at 3k ft for 2 minutes before and after installation. I have a digital airspeed readout on my GRT EFIS. It bumped between about 196 and 197 before and after the scoops went on, so from my perspective and perception, airpeed at max power, where parasite drag is the most, did not decrease. And yes, I do have exit scoops in the tail to make sure the incoming air has a place to go. Of course this is not pure and accurate flight testing and there are certainly plenty of inaccuracies. Next summer, I will maybe try the vg idea to achieve a more airplane look. Thx for the pointers. ;-)

The only thing better than flying my RV 4 is being nice and cool while doing so.

Cheers,
Greg