Mike Connor

My Feedback: (5)

This is a Delta aircraft that I am moving the vertical stabilizers to the wing tips. I am having trouble deciding what angle to use and would like your thoughts. Maybe a poll will get some of you guys (that view but seldom post) to participate. The bottom picture is a side view to help visualize the end product.

Any comments about aerodynamic issues or appearance are welcome.
Thanks

da Rock

Acute angles create more drag. The 2nd choice above for example.

Also, any angle on a working surface like a rudder winds up creating a couple of some sort. Why do that? They often drive you nuts with couples when they aren't angled.

The angles you see on some of the modern fighters that have their two surfaces relatively close together could actually be there in an attempt to get some of the effectiveness back that is lost when they're too close together. They may also be there as the results of wind tunnel tests that showed better results overall with some angle. The designers certainly would have wanted to avoid the extra interference drag of the non-perpendicular joints.

The primary reason tiplets on most full scale point up is that they didn't have a way to operate the aircraft with the winglets in line with the wing. Commercial aircraft have no room at gates for wider wingspan. Fighters spans are often decided by the hangars the airforce uses. But since you're looking for yaw stability and rudder function, and don't need more span, ignore that last idea. Wish I'd not taken the time to type it.

If you are looking for yawcontrol/rudder effect, and you're putting the structure out where it's mass is going to have more dumb bell effect, make it as efficient a fin/rudder as possible. Straight up. Mass with leverage has more effect than just mass. And you're not looking for more mass in the fins, just more yaw control. Heck, put 'em about 2/3 the span if the mass seems excessive to you. But they will be less drag if the joint simply is a corner, not an intersection. Puzzling isn't it.

And a delta planform is changed when you square off the tips. And having these at the tips chops the delta planform. Truth is, who cares or knows which planform would be better, so do what looks good to you. Even with squared off tips, it'll do what deltas do.

Are you going to put rudders on them?

If not, why not make them plug-ins, and try a couple of different styles. Like ones that take the area you've drawn and project half above the wing and half below. It'd be interesting to see the difference in trim from the one sided type to the end-cap type. And the inverted part could serve as landing skids.

Mike Connor

My Feedback: (5)

There will be no rudders on this one. My second prototype had rudders and would even snap and knife edge but is hardly be worth the effort on a small high speed Delta. Rudders on winglets would really be a chore.

Plug-ins are an interesting thought I may consider. The last 2" of the wing tip is solid balsa so maybe I could have the winglett slide over it and pin or zip tie.

The 30* winglets add 5" to the wingspan so the 14 oz per sq ft wing loading should be reduced even more with out adding any frontal area to the airframe. Not sure that is a fair way to look at it. My main goal is looks and drag reduction.

You said "extra interference drag of the non-perpendicular joints". I thought that perpendicular joints caused drag and that is the reason for fillets.

"But they will be less drag if the joint simply is a corner, not an intersection". What is the difference between a corner and an intersection (x vs L)? I was planing on some rounding at the wingtip and winglet joint..

The # of people participating in this poll shows that most do not have an opinion or I am very boring.

js3

My Feedback: (3)

Mike,

I am a musician not an aerodynamicist. Model airplanes are my hobby, not my profession so you may wish to take my comments with a healty tablespoonful of salt. That said, my understanding is that the smaller the angle between two surfaces, the greater the drag. Using your examples, I would think the third (bottom) example would have the least amount of drag, the second example would have the most and the first (top) would be somewhere in between. You want to avoid angles equal to and less than 90 deg.

Personally, I like the looks of the third example.

Mike Connor

My Feedback: (5)

Thanks for your thoughts John. I should have been more clear in my poll that I want to know what looks best. The aerodynamic issues are secondary in this poll but appreciated. I kind of like #3 also but the final decision will probably come at that point in the build I can see it 3D.

combatpigg

My Feedback: (3)

Mike, I think having tip fins with no central fin works great on the flying wings that I've built, but none of them are deltas and none of them are fast. It doesn't take very much surface area to do the job. From a pure looks stand point, I think the blended and radiused tips like on ARF Zagis looks the best. Make sure that they are very stiff and well stuck on there, or I'm sure they will produce an equally unstable effect on your speed ship.

da Rock

Fillets are what you thought, drag reducers. But where two surfaces meet, if they meet at 90degrees, that'll have more drag than if they meet in an obtuse angle of more than 90degrees. And a meeting with less than 90degrees is worse than 90. Fillets or not. Pulling that quote out of context actually makes it into something not true when standing by itself, btw. Your tilted winglet to wing joint would have two angles neither of them perpendicular and both less drag than a 90.

Winglets that continue a wingspan really are just a corner. Like where a driveway happens to turn sharply, people call that a corner. And in the context, I was talking about moving the tiplets inboard from the wingtip. However they were affixed to the wing inboard of the tip, the place they were attached would be an intersection. And the main reason intersections are more drag than kinks is because there are even more corners than just an inside and outside.

One argument for a T tail is that it only has two places where different surfaces come together. Move the horizontal tail down and you wind up with four.

Hey, you ain't boring me. But I bet I'm boring more people than you are. Wanna start a poll on that? grin.........

da Rock

Hey, I'm retired, so take that into account. It's my excuse when I say anything wrong. grin

Actually that is sorta right, but not completely. Any time there is a "kink", joint, change of direction, whatever........ As the angle goes from 179degrees to 1degree, the drag increases. However, when the angle goes less than 90degrees there is additional drag generated, and it's at a faster rate than it increased from 179 to 90.

The 2nd from the top would have more drag than the 3rd. The acute angle is the reason.
And I like the third too.

BMatthews

The first one will have the most pure fin effect. The second looks badboy and a little otherworldly. The third will definetly have some dihedral like effect in a side slip that tries to level the model out and may end up with some rolling effect when doing inverted turns that mess you up. How much rolling effect will depend on how much yaw there is when your delta is turning.

Some of the extra drag of the slightly canted on option could be avoided if you use a shaped connector that has about a 1 inch inside radius. Sort of alike an upturned Hoerner tip but with fins attached to the ends.

Mike Connor

My Feedback: (5)

If I understand you correctly the bold test above is a typo. Is it correct to say that an obtuse angle is little drag, a right angle is more drag and an acute angle is even more. If so, would two obtuse angles have the same drag of a single angle equal in degrees to the two angles?

The airlines winglets, costing .75 million USD a set on a 737, are usually blended with a gentle curve to an angled winglet adding up to 5' to the wing span. They probably have it figured out as well as anyone.

Glad you aren't bored but lets skip the poll. There may be a bigger turnout then either of us want. [X(]

combatpigg,
You call the Zagi winglets blended but they look anything but blended to me with their 90* corners. Am I looking at the wrong Zagi pictures or do I not understand blended?

BMatthews,
I think you just put my favorite look to rest.[] A dihedral effect in a turn or inverted would not be acceptable. Now I am wondering if 10* may have a negative effect. Maybe well rounded with large fillets on a 90* winglet.

combatpigg

My Feedback: (3)

Mike, the Zagi I have is a downsized version. The wing/winglets is just some kind of molded foam, one continuos piece. It looks pretty "swoopy", too bad it is such a dog with the supplied motor and battery..

da Rock

Thanks for spotting that Mike, I used just exactly the wrong word. I went back and corrected it.

Mike Connor

My Feedback: (5)

The second picture has the 2" wing tips angled up at 10* so the winglet is actually perpendicular to the tip. Therefore there are no acute angles. It is starting to grow on me.

da Rock

Jeez, starting to grow on you?

You need to stop sleeping in your shop.

(Do they grow on your arms first or where?)

Mike Connor

My Feedback: (5)

No wife, no kids and no pets. My whole home is my shop.

Mike Connor

My Feedback: (5)

I finally got started building this project and went with "None of the above" as far as angles. Bruce brought up a good point about "dihedral effect" so the 2" wing tips are 10* and the vertical fins are 0*. I think it will look good when finished.

Mike Connor

My Feedback: (5)

The winglets actually tilt in about 2*. It was a sawing error that I decided to leave alone because I liked it.

BMatthews

Looks good. Got a link to the flight report in, I assume, the Extreme Speed Prop forum?

Mike Connor

My Feedback: (5)

This one has not flown yet. Here is a video of the one with with regular vertical fins. It should and I hope it flies as good as my first and second prototype.
http://www.youtube.com/watch?v=qxrRfL5wz4g

pkrautter

The 30 degrees out is the most stable. As the plane turns the difference in lift on the two tips will cause an automatic banking proportionate to the rate of turn. Vertical would cause no benefit in stability. An inverted tip would induce instability. Try taking a minute to test a paper glider model to verify this.