Experimental Cub Kit with Slotted Wing 180 Hp and Big wheels any suggestions on kits

sky

I agree with you about the fixed and not stabilizer. I may not run a jack screw in mine TBD. But trim is drag no matter how you get it, the wing has to carry that down load depending on your speed and weight, the farther your CG is from the center of lift the more you trim. I am just going to see how much difference it will make. Reflexing the ailerons only is about the same as washing out the wing more............ more drag as AOA would need to be slightly higher, wouldn't it? Do you agree a "flat" wing will be a little faster than a "washed" wing? The version I'm working with will reflex the entire rear of the wing, not just the flaps or ailerons but both. But the gain it may have might not be worth the effort. If not, I'll adjust the "mixer" to be a manual motion for 0 to 15-20 and electric for the rest.

Southern Aero said:

... But trim is drag no matter how you get it, the wing has to carry that down load depending on your speed and weight, the farther your CG is from the center of lift the more you trim.

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Not quite. If you have a fixed stab and a trim tab on the elevator there will be just one CG location and speed when all three surfaces are aligned in the minimum drag position. At any other CG there will be some deflection between the three creating an increase in drag. With a trimming stabilizer there are infinite CG locations where the two surfaces will be aligned in the minimum drag position.
Your idea of adjusting the trailing edge of the wing for trimming purposes is not something that I have given much thought. It will be an interesting experiment. I can see how it will allow an expansion of the CG location while retaining a minimum drag on the fixed stabilizer and trim tab tail.

I have not found that changing the washout of a wing by small amounts makes any noticeable amount of change in drag.

sky

I'm sure there are some other guys in here that have rigged a Cub wing flat, makes a little difference. ......... especially clip wings, I always rig them flat.

SA,
Are you going to have any adjustment in the horizontal for tuning or development? Flat surfaces or airfoil?
In the planes I have designed and built in the past I have failed to get the tail right a few times, and that was when I was better with math than I am now.

With allot of pitching moment an airfoil in the tail surface has value. This pitching moment might only be present at high loads when the flaps are deployed, granted trim drag is not important here.

I am expecting enough unknowns in my build that a portion of my flight testing will be to see if my horizontal and elevator are "in plane"during cruise, not to mention not running out of reserved authority throughout the flight envelope .
Variations of this will be many factors with CG relationship to Center of pressure with relation to pitching moment. Something that obviously is ever changing.

Wing twist, a simple rectangular wing should essentially be flat. If you are going to have any LE devices there is no need for twist. The LE device will hide any harsh caricaturists. Or should at least.

MIT, the university did an intercollegiate contest to actually determine the twist withing a rectangular wing for maximum performance. The result was the wing was not actually "flat" but twisted down slightly mid span and back up a the tip. The final outcome turned out that the type of tip used offered more variables than the twist distribution spanwise. I wish I could find the link to that study.
Other variables involved were variations in spanwise flow, something that also varies with each change of loading on a wing as well as wing tip design.

My wing will be flat. I am not good enough to calculate the up twist of the tip on my rectangular wing.

Anther note, this may bust some theories.
People have used different airfoils on fabric wings with the belief they could have laminar flow.
Unfortunately laminar flow is not just front to back flow but it has a spanwise contingent as well. With the rise and fall of spanwise flow over the crest of a rib pretty much ensures the flexible surface of a fabric over ribs will not achieve the low drag of a laminar wing.

Heck very few aluminum skin wings truly have laminar flow anywhere near as close to what theory says they might.

Southern Aero said:

sky

I'm sure there are some other guys in here that have rigged a Cub wing flat, makes a little difference. ......... especially clip wings, I always rig them flat.

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SA, We are beginning to get deep into the weeds away from the topic of the thread. Charlie has given a good explanation. Here is a deep weed read if you have the time: http://www.wainfan.com/wingdes.pdf Barnaby Wainfain is a well known engineer who has a regular article in Kitplanes magazine.

We all know (or should know) that a rectangular shaped wing (Cub) has the most benign stall characteristics of any other shape due to the fact that a stall begins at the inboard trailing edge progressing forward and outboard. This ensures that the ailerons continue to provide control as deep into the stall as possible. The main purpose of washout is to ensure that the ailerons maintain this control in order to meet certification requirements.
You rigging the wings flat on the clip wings makes sense in that a clip wing's primary purpose is for those who like to perform aerobatics. Shorter wings will promote a faster roll rate. Rigging them "flat" will help the tips stall sooner thus improving certain aerobatic characteristics. Yes there are some who rig their wings flat, some who rig them with as much wash-in as possible in order to give the outboard portion of the wing more angle of attack on takeoff and landing. These folks need to be aware that there is a possibility that they could run out of aileron control when they are in a tight low speed position. They had better be good rudder users.

I take from your discussion that you feel that there is less drag when the wing is rigged with no washout. Do I understand correctly? If so, I doubt that the small amount of drag difference would be noticed without sensitive measuring equipment on a aerodynamically dirty Cub. You are a savvy guy, does the airspeed move any more than the needle moving from one side of the mark on the airspeed indicator to the other?

One very experienced local Cub pilot preferred flatter than factory wings. Not sure how much but they looked flat. His belief was that it reduced the "mush" when lifting off or landing. He spent lots of time loaded on skis where AOA was limited and at altitude in mountainous terrain doing game surveys. He was also a competent aerobatic pilot that (in my words) was willing to deal with any resulting changes in slow flight and stall behavior. One man's opinion.

Re: Barnaby's article. He claims that adding leading edge camber doesn't increase lift at a given AOA. I'd like to see some confirmation.

Gary