Our Cub Project Part 2

This thread will be about the modifications and improvements that we make to our Experimental Super Cub.

Our Build can be found here, http://www.supercub.org/forum/showthread.php?37340-Our-Cub-Project and as of today, we have a whopping 10.2 hours on our cub. Our first modification has been the addition of Vortex Generators. I selected the Stolspeed series of VGs and purchased them from Aircraft Spruce. The kit comes with the necessary templates and adhesive in a nice little box. I ordered a box of 120 and 80, and I will have to order another box to complete the tail. The instructions for installation can be found here, and are detailed enough to make the process go pretty smooth.

Follow the instructions and use denatured alcohol to clean them with, it is pretty cheap, and does not leave the house stinking too bad. The placment of the VGs on the adhesive takes a while, in all honesty, it took longer to clean and put them on them on the adhesive then it takes to put them on the plane. Take your time, do it over a table and keep your fingers out of the glue. I used a razor blade from the back to lift the top layer off.




We lightly painted ours with aerothane, Juneau White to match the airplane and them look fine. They were painted on the adhesive taped to a 2x6.



VG placement has been beat to death here and Jerry Burr has provided us with very good explanations of aerodynamic concepts that I have no business repeating. What I did get from the many threads is a consensus that the VGs need to be placed, on an uncuffed, unslatted wing, between 2 and 6% of CHORD. On a stock Cub, that Chord is 62 5/8" and the table below can be referenced to get your measurements.


We used 4% or 2.5" from the leading edge, using a sheet rock square on the bottom and a small square on the top to find the spot. This was repeated three more time and a string was pulled across the marks and secured with masking tape to give us our VG nose forward position.



The VGs from Stolspeed come with three templates for installation, 30mm spacing for the tail, 60mm for the first 15 on the outboard and 90mm for the remaining inboard section of the wing. Because this is an experimental aircraft and its primary reason for leaving the ground is education and recreation, we decided to experiment and place all the wing Vgs at the 60mm spacing. This results in a need for 82 pieces a wing or 164 total. I only bought 200 and the tail at 30mm over 1320mm (52") is 44 a side or another 88! This is a total of 252 needed for a full install. So I am going to get another 80 and some will become extras.



The entire install took about an hour. Make sure that you wipe the area clean where you are planning on sticking the VG's to the wing with alcohol and keep your hands clean.

The overall change in flight charastics seems to be on par with what you will read in your research, lowered stall that is more like a mush with aileron control still available in the stall. I did try to "pump" a break into the stall, but I was unsuccessful. We really can't tell a difference in slow flight down the runway, but the stall was affected dramatically.

I just can't bring myself to put them damn things on my nice smooth clean wings.

"T" Thank you for another of your very informative posts!! One thing I don't remember anyone commenting about (I know some one did but...) how do the ailerons compare when cross controlled in what I guess would be a cross controlled stall. For instance getting to slow turning to final, ruddering around to turn while keeping the wings level with aileron. Is there less tendency to start a spin?

Tail VGs....

Again, we used Stolspeed Vgs available from Aircraft Spruce to install the Tail VGs. I followed the directions that say to slightly sand off the curvature on the bottom on the VG to allow it to fit the bottom of the horizontal. The spacing suggested was 30mm apart and 4 inches (100mm) forward of the hinge line. Using the tape and string method that we used to install the wing set, it took me about 45 min to make the install. Each Horizontal takes 38 VGs.

All total, we used 210 VGs. Something to know, each pack comes with 8 extra VGs. So the 60 has 68 etc.

Numbers? What was the stall speed before the VGs and what was the stall speed after the VGs were installed? Also what was the flight tested CG when you established those numbers? If the comparison wasn't done at the same CG, the results will be invalid.

I have flown one Super Cub on EDO amphib floats both before and after VGs were installed and could not detect any difference, no numbers. I know that statement is blasphemy here, but that is what I found.

I have some numbers at the airport, I will get back to you on that. However, our testing was conducted using an extremely unscientific approach. Because the airspeed indicator is USELESS at the angle of attack where VGs start to matter, we are chasing the aircraft with an accord down the runway looking for a decrease in ground speed. Without, we were seeing between 31-29 at 1600 rpm and a constant altitude in ground effect. With we get 30-27. Pretty scientific. More importantly, I can tell you for sure that before the VGs vs. with VGs, the Stall went from a straight ahead break with no discernable aileron control to a straight ahead mush with very good control. Stall speed decrease? I cant be sure that the number decreased, but control in slow flight was definitely improved. Seat of the pants feel and overall enjoyment of operation were improved. Worth the 2 aviation units and a weekend.

Here is an interesting idea on making your own gap seals.

http://www.eaavideo.org/video.aspx?v=3801322456001

They are extruding Pool Noodles into gap seals....where can I get some white pool noodles?

http://www.ebay.com/itm/Water-Noodl...Domain_0&var=410249427528&hash=item19e5fea02b solid core, thats using your noodle.

Another unique part of our Cub is its ability to carry a scooter. From the beginning, my father and I thought about how we could get a scooter down to Sun N Fun. We welded in hardpoints on the left side of the fuselage and on the left main gear, and used the rear float fitting for the aft attachpoint. For now, the scooter is a 1989 Yamaha Razz. We have made a few modifications to the scooter to allow it to be attached to the Cub and reduced its weight to 100 lbs. The scooter's mass is centered under the seat where the engine and fuel are and that mass is centered on the CG of our empty cub. When we weighed the cub, we included two calculations for empty CG, one with the scooter installed and one without, much like you would if you added a removable pod.













The scooter was tested to normal category limits while installed using quikrete bags for positive g's and a floor jack to simulate a negative load.



Our flight test plan set our test criteria for operations with and without the scooter. The first 10 hours were flown without the scooter installed to verify that the plane flew like it should. Then we attached the scooter and made some short hops to make sure that nothing weird was going to happen.



After a short debrief, the scooter was flight tested on the aircraft.




After Dad landed we discussed what he found during the flight. First the scooter is rock solid on the airframe in all modes of flight. No shaking or strange movements were observed. Second, he said that if you could not see that there was a motorcycle on the side of the fuselage, you could not tell that it was there. There is no yaw to the left, does not make the left wing heavy and it still goes 100mph. The scooter is going to get a winter rehab and paint job so it will be ready to rock for the upcoming airshow season.

Nice work. You can tell people , "I've done 100 mph with my Razz". I found pool noodles at Dollar General.

Skywagon, the numbers that we collected before and after the VGs are a little skewed, different pilots, days, time of day, wind conditions. But like I said overall it feels like it made a difference in the stall behavior, takeoff and landing are hard to judge.

tcraft128 said:

Skywagon, the numbers that we collected before and after the VGs are a little skewed, different pilots, days, time of day, wind conditions. But like I said overall it feels like it made a difference in the stall behavior, takeoff and landing are hard to judge.

Click to expand...

Thank you for this tcraft. Behavior is an important improvement even if the numbers difference is small.