NACA VG Installation

Here is the factory template for installing vortex generators ahead of your NACA scoops to improve engine cooling.

Also, here is the Nasa/OSU paper on how to install the VGs ahead of a NACA. Finally, here's a link to CCI, where I purchased my vortex generators.

Media:NACA VG - Template.pdf
Media:N4415_7x10.pdf

This is from the Velocity Views volume 29.

We, along with a couple of our customers, have been testing VG’s to see if we could provide better cylinder cooling on the NACA type cooling ducts. Even though all three of the airplanes we have here have the NACA ducts and have had normal cylinder temperatures, (410 degrees F max.) some of our customers have seen 450 degrees or more. What we done was to place a couple VG’s about 1” in front of each of the NACA inlets at the proper angle and the results have been amazing (see photo below). One can expect about a 40 to 50 degree reduction in cylinder temperatures with the VG’s. Our first Service Center customer, Dick Affenit, had to run his mixture at 150 degrees rich of peak to keep his cylinder temperatures at 400 degrees or below. He said if he leaned to peak EGT, the CHT temperatures would go to 450 degrees and this was just not acceptable to him. We put on the VG’s (with a dab of silicone) and he now reports that at peak EGT, his cylinder temperatures max out at 395 degrees F. For Dick, this results in a fuel saving of over three gallons per hour.

The next test was to install two VG’s down the throat of the NACA inlet about 2” from the front (see photo above). Max CHT’s prior to the VG’s was 408 degrees when leaned to peak EGT. After installation the max CHT’s was 387 degrees, this gave us a reduction of 20 degrees.

I have a theory about the success of the NACA cooling scoops when comparing a fixed gear with a retract. On every fixed gear XL we have flown, the max CHT’s tend to be a good 30 to 40 degrees less than with the RG. I think the faster we go the air is separating away from the NACA scoops allowing less air to cool the engine. On one of the RG’s here, we flew at 150 knots and found the CHT’s running about 400 degrees. Speeding up to 180 knots the temperatures went up to 440 degrees. At first I just figured this was due to the additional power needed, however, now I am not so sure. Installation of the VG’s reduced this back to less than 400 degrees.

With this success in mind, it was decided to try the VG’s on the armpit scoops of our XLRG demo airplane (see photo below). In this installation, we plumb the air from the armpit scoops up to the plenum chamber and then down through the cylinders. Placing two VG’s about 4” in front of the armpit scoop entrance has resulted in a 40 degree reduction in cylinder temperature. I would have never guessed we could achieve this much reduction but the numbers don’t lie. If you’re having a difficult time getting your cylinder temperatures down, this might be your answer. Keep in mind that if your using the updraft type cooling through the arm pit scoops you need to add about 40 degrees to what your indicating. This is due to the fact your CHT probes are installed on the bottom of the cylinders and the fresh air coming from the scoops are cooling the probes. If you want to try it on your airplane, let us know and we will send you 4 VG’s and you pay only a shipping and handling charge. In our installation the leading edge of the VG fins are 1.5 inches apart and the trailing edges of the fins are 2.25 inches apart. This results in a total difference of .75 inches and will provide the proper “kick out.” If you are trying this on a standard fuselage NACA installation, you will need to move them closer together. The important measurement is the .75 inch that provides the proper angle. (see picture # 3)

Also, keep in mind that the attach surface of the VG should be sanded prior to the silicone installation. The VG’s are made of a plastic material and if used where the sun will get to them, they should be sanded and painted to reflect the UV’s.

Picture3