28 more gallons of fuel on an RV-9A
 

This is our first attempt at building wingtip tanks for the RV-9A. First flight results seem promising! We added winglets to see if it makes any difference. We show the wing and winglet aerodynamics in different stall configurations... The tanks work beautifully and we are super happy with the results :D

Correction: 14 gallons on each tank = 28 gallons total

Check out video here

Ananda
RV9A - 464CP
Engineer at Levil Technology
"Fly straight and Levil"

Tanks
 

Nice looking tanks , not so good looking winglets . What purpose do the serve ?

The main reason for the winglets is to create a high point for the tank vents, reducing piping work. The second reason is that from the analysis, the forward swept winglet is more efficient than other shapes or no winglet, giving 15% drag reduction, keeping the performance the same, even with the additional tanks. In other words... we have now twice the fuel, and no loss in performance... or at least that is the goal.

I like the idea of added fuel. When you hold the tank in your hand, it looks great and I can see the shape. Nice glass work for sure. Giving another 90 minutes + safe flight time with no performance is probably more than most of us need, but it is nice knowing it is possible. Thanks for the stall videos. That was really interesting to me. Have fun!

I like it Ananda. Do you plan a production run? How difficult/easy to install/plumb/remove on a flying aircraft? Need a beta tester? :)

Very interesting. The video suggests a few questions.

What are the forces that the winglet imposes upon the wing structure?

Do those forces account for the winglet stalling, as shown in the video, which would decrease their lift and increase their drag at wing angles of attack below the wing's stall?

Did you make any structural modifications to handle those loads?

How does the winglet stalling affect the angle of climb?

Thanks,
Dave

Wait, I recall winglets have been discussed in this forum. One camp was concerned about them because the wing isn't engineered to handle the twisting moment created by wind forces on the winglet's outer forward edge. How have you addressed this?

Very interesting and valid questions.. Although we haven't done all the tests to be able to answer all the questions, here are some interesting things we made:

- The tanks actually give 4 more hours of flight at 145 Kts.
- When building the airplane, the main and rear spar were reinforced, to handle the weight of the tank and the twisting moment of the winglet.

How does the winglet stalling affect the angle of climb?
From the tests, the winglet started stalling at 60 kts, which is not ideal, but we normally climb at 80 its, and during our standard climb, the winglet did not stall.

What are the forces that the winglet imposes upon the wing structure?
Don't know.. we made it very strong. More tests to come...

Do you plan a production run?
Negative. This is just for fun and to be able to go the distance.

PS: The RV9 is an amazing airplane as is. It does not need winglets.

Do the tanks act as Lavatory Storage too? Or you'll need a case of Little Johnnys. :D Doing the basic math, 4 hours @ 3.5 GPH= 14 Gallons. Pretty good fuel burn.

Thank you.

From the video, I'd expect that the winglet would not be stalled at the best rate of climb speed, but that it might be at the best angle of climb speed. It might be worth investigating that.

Do you have any plans to tweak the winglet airfoil or incidence so as to increase its stall margin?

It also might be interesting to see how the plane reacts in a slip as the angle of attack increases. Perhaps the drag of the stalled winglet would increase the effective yaw stability at that point. For example, full right rudder, left yaw (wind in the left ear), the left winglet should have a higher angle of attack than the right one, and might stall before the right one. Its drag should increase as the winglet stalls, thus tending to unyaw the aircraft.

Dave