I acquired a Cap 231 EX on the cheap. I am going to put a 26 to 30 gasser in it. I'm not building this for 3D, just for basic aerobatics and fun flying. I know that this plane will be a little heavy and the wing loading will be a little high. I'm thinking about adding winglets to improve the efficiency of the wing. I work at Airports and I see a lot of planes with winglets (biz jets, passenger planes). I'm not sure about the shape or height. I'm also not sure if the winglet should encompass the ailerons or stop just short of the aileron. Any Advice would be appreciated?

I'm putting a racing design on a Hangar 9 Mustang 150. The typical tip you see is a hoerner tip. If designed right they should be effective.

Google search for sites and images give you a lot of information on them

Thanks for the info on the hoerner tip. I'm really not thinking about a wing tip as such, but a winglet. The winglet is a vertical surface added to the wingtip. The hoerner tip would probably work but would be harder for me to fabricate (I have limited experience in built up balsa stuff).

The winglet is for economy by reducing the span-wise flow of air.

They definitely do NOT belong on an aerobatic model.
BTW they only work upright unlike the SFG's. (side force generators)

This setup may help but if your wingloading is really over the top -nothing will help The end dam and even a dam at midpoint a tall one really does work in models this size
the removable sideforce generators (dams too)on the Showtime models demonstrate this very clearly
I clipped the wings on this EDGE and having flown the unclipped version - I liked the clipped one better
subtle but slight improvement - roll faster (shorter span ) and slow speed hung in a bit better

Why must answers always be in "absolutes". Winglets do not belong on aerobatic models? That is a strong statement and not very helpful. I would be very suprised if my winglets interfere with my style of flying. Thanks for the photo Mr. Hanson. That is sort of what I had in mind, except my winglet would only extend above the wing, not below. I'm not looking for a side-force generator but just a little help in wing loading and tip stalling. I had this same plane a few years ago with a Zenoah Mag. G26 on it and it flew OK. I knew to keep the speed up in turns and landing but the plane was a pretty good flier (basic aerobatics and flying the pattern). This Cap should be 1 to 2 pounds lighter than that plane, so I don't think the wing loading will be excessive, just a little high.

Kennydee,

Be careful putting on winglets only to the top....make sure they are vertical. Hanson shows the lets symmetrical about the wing's center for a reason. If you install top only winglets at an angle, you will probably get some unwanted roll coupling.

On the other hand, if the model has any roll couple tendencies now, you can angle the winglets the right way and take the roll coupling out. Since you want to play with winglets, why not do the experiment?

Done properly, vertical surfaces on wings definitely DO belong on aerobats for aerodynamic reasons other than wing efficiency

BTW, who came up with the term SFG? It's mostly a misnomer...vertical surfaces on wings don't create side forces (unles the model flies knife edge all the time) but rather they serve as pivots for other forces to act upon

MattK

Well winglets of the type that are there to make the tip vortex work to lower drag in a straight and level flight aren't going to do much for you in an aerobatic model so it is reasonably correct to say they aren't too useful. I am speaking of the nicely curved kind that hang down under the wing tip.

What Dick shows works fine for both upright and inverted to keep the tip flow nice as well as working in the SFG mode. You don't have to be in knife edge, you can get the effect in a side slip maneuver. If you calculate the total force it isn't much though. The fuselage is producing most of the side force.

They would be appropriate to put on the wing at around the semi span point also. It would stop span wise flow at high angles of attack. Of course the down side is you would be knocking them off all the time while handling the airplane.

Here is an example of dual SFG on an airplane from a gentleman from Mexico at the last XFC contest. I forget his name right now. His were removable. He set up this configuration to work at the altitudes of Mexico City and at the altitude of Indiana it would do nice knife edge square loops. It reminded me of one of the little foamy indoor models.

The change in chord forward at the tip was an attempt to adjust the aero center at high angles of attack. The airplane flew pretty nicely as it was very light and over powered (again to cope with Mexico City).

Ben

SFG is -I believe - George Hicks idea.
George is an aeronautical engineer by training and vocation.
also a active modeller who does not "go along with the flow " when it comes to design work.
His little biplane foamie design "Tensor"sold by Horizon a few years back was an exercize in SFG uses.
If you tilted inthe roll axis- the model did NOT turn -it just drove merrily along with one panel down the other up. It was sometimes very disconcerting to fly as a turn, required rudder - always . I would say, as a model designer, he is as good as it gets if you are looking to figure out or fix an aerobatic setup.


EDITED

My winglets will be removable. I intend to try different shapes and I do intend to make them vertical. It will be interesting to see what kind of results I can with different shapes and sizes.

Excellent idea..... report back on the results.

Ben

Geez, I know of George. I should have known that I suppose.

The original appendages on a model was pioneered by Nat Penton about 25 years ago give or take. George has discussed shop with Nat many times over the years. Nat is a good friend and we bounce concepts off one another occasionally.

MattK

I put big tip plates on a pattern model in the early 1970's. The results were zero because the airplane crashed on the first flight due to radio failure. Oh well ........

Remember when using tip plates, even those I had the photo of, that the lift isn't going to be a great amount. You can calculate the lift based on the total areas - just assume it's a small wing of the same area as the two plates added together. Look at the typical 30% scale aerobat doing a low knife edge pass. It will have an angle of sideslip of around 40 degrees. That flow angle over the fuselage side is giving the lift. The fuselage isn't nearly as efficient as a winglet planform but it can give you a guess as to what to expect from the winglets.

The indoor flat foamy airplanes usually have very deep fuselages and large (very large) winglets and in the case of biplanes upper and lower wing supports. They fly almost as well on the side as upright and are a delight to watch in action.

Our large models of the CAP, etc., simply haven't gotten the big sizes of winglets to be super effective. You might try the two winglets per panel approach and vary the size of each but think about going big. The airloads will be fairly high so make the mounting setup fairly strong. It might look strange at first but if the results pay off then it would look great!

Good flying with them,

Ben

I recommended the hoerner tips, because there is a winglet design. They use them on racing planes to reduce drag and increase lift to slow the landing speed of clipped wing planes.

I'm making mine from pink high density insulating foam to make it easier to work with.

The "enhancers" George developed ,really DO add improvements to 30% and smaller models .
In playing with them I did not concern myself with any factor EXCEPT
"what direction does the air really travel at high angles of attack"
The obvious (no tunnels red'd) result wa that air really does take the path of least resistance and the "enhancers" dam the air in it';s s race to slide around the tip
As experience is the real proofin anything, I tried taking off th plates on my Showtime -replacing -over n over and found that at high angles of attack and stallining speeds, the model instantly stabilized using the enhancers (SFG's)
Some full scale aerobatic stuff uses funny tip plates like I used on my EDGE
PS say "Hi" to Nat- He was buying and flying some of my models back then -

It all depends on what you expect the tip plate - winglet - to do. If it is to stop outboard flow at higher angles of attack almost any size will be better than non at all. I think that in pattern work they aren't used because the typical FAI type of pattern ship doesn't do any high alpha work. A plain wing works fine for their maneuvers.

If you are stooging around trying to win the XFC then they will help give an edge with almost any size you put on - the bigger the better like the dual SFG of the Mexican entry ( until the judges start thinking they look funny and get prejudiced against the airplane). After all in a contest like the XFC the airplane spends a lot of time in extreme flight/airflow-conditions. Last year I saw a roll after takeoff as soon as the wing tip would clear the ground. That might have been the last level flight during the whole flight!

If you expect a decrease in sideslip angle in knife edge flight then the big ones that Dick had in the first photo are the way to go. If the full wing will pull 10g or more then the big SFG have enough area and can get enough sideslip angle to fly level flight nicely. But the airplane won't suddenly fly level in knife edge flight if they are small like the other photos.

A nicely designed SFC/tip-plate does look good.

Ben

Wow, great photos and info. My main purpose is to improve the efficiency of the wing and to help make the wing a little less tip stallee. I'm not really trying to improve the knife edge capability. Best I can remember, the first Sig 231 I had knifed edged pretty good stock. Again, I expect the plane will be a little heavy with a gasser in it. I'm want to experiment with winglets/air dams to see if I can improve the slow flight characteristics of this wing. Most of my big plane flying is around the pattern, touch and go's and basic aerobatics. I purchased the first 231 EX I owned RTF and it came with a Mag G26. That plane flew OK. This plane should be at least 6 ounces lighter than the first one, maybe more. I'll post my winglet test results as soon as I get the plane built.

That Sig 231 is a nice plane - just needs to be kept light
We helped a friend with one - the powerplant was a glow setup with tuned exhaust -

I tried rather large winglets, actually more like tip plates on a competition fun-fly model. I had to give them nearly as much area below the wing as above, to reduce their dihedral effect. Made them of epoxy laminated balsa, with hardwood hard points for mounting by small nylon screws so that they would break away without damage on ground contact.

The reason for my tip plates was to reduce induced drag. A slightly longer wingspan would reduce induced drag much more efficiently, without nearly as much increase in parasite drag, but a longer wing would also reduce the roll rate. With the tip plates in place, the model loops considerable tighter and faster, and also handles nicer, with very friendly behaviour much deeper into stall, due to its greatly increased yaw resistance. As you would expect, the bird also knife edges far better.

Also tried ugly detachable vertical airfoils at about half span on wing of a piped Webra 120 powered, frantic flying 9 pound aerobatic monoplane with coupled flaperons, trying to make it knife edge as well my bipes, with mixed success.

OK, I currently putting together the CAP. I just finished each wing half and I have added the Winglets. This is the first style, I will try both smaller and larger winglets.

Any results or findings on your CAP?