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-   -   Ultra Stick 60 rudder design question (https://www.rcuniverse.com/forum/questions-answers-154/4066657-ultra-stick-60-rudder-design-question.html)

Ernie Misner 03-22-2006 03:05 AM

Ultra Stick 60 rudder design question
 
Greetings, my Ultra Stick 40 (older, origional rudder) absolutely does not like knive edge; it wants to snap out to the canopy side badly. The rudder has a strong triangular shape, narrow at the top and wide at the bottom. I am assembling a US 60 now, and might build a new rudder since it is the same. It appears to me that the extreme triangular shape of a rudder will give a lifting force (bringing the nose up) as well as the yaw that it is supposed to be doing. (much like a v-tail works...)

Am I way off here? Thanks for any input!

Ernie

redfox435cat 03-22-2006 10:32 AM

RE: Ultra Stick 60 rudder design question
 
most high winged sport planes you have to compensate with ailerons and elevator to get it to hold, it the wing position not the shape of the rudder, also the shape and size of the fuse has allot to do with it. Take the great planes GEE BEE. you think it wouldn't have a chance with that puny rudder, it knife edges with the best of em, because the fuse creates lift. If ya want to knife edge get something in a mid wing long tail configuration morris the knife morris balsa nova any extra type aircraft 300 321 21 320 or cap type aircraft suikoy

Ernie Misner 03-22-2006 10:39 PM

RE: Ultra Stick 60 rudder design question
 
Picture a rudder with EXTREME triangular shape, much more than would be used. Go full left or right with that shape in your mind. It turns into a lifting elevator. Now picture a rudder with EXTREME triangular shape, except with the very wide part at the top, and the very narrow part at the bottom. Go full left or right with that. I believe it will act as "down elevator" as well as yawing as a rudder......

Ernie

DVI 03-26-2006 08:56 PM

RE: Ultra Stick 60 rudder design question
 
I fly a Hangar Nine Ultra Stick 60 with a OS 61FX two stroke engine, and I have no trouble flying knife edge. It does pitch towards the top but I just use the elevator to keep it stright.
By the way, I never thought that I would pick an AFT airplane as my favorite plane to fly!

Ernie Misner 03-27-2006 03:18 AM

RE: Ultra Stick 60 rudder design question
 
Good, DVI. Thanks for your input. Maybe it's just the old version of the US 40 that is so bad. The newer one has a balanced rudder. On the US 60, I did go ahead and built a slightly larger, rectangular rudder, so we will see.

Ernie

DoggyDoo 03-28-2006 06:03 PM

RE: Ultra Stick 60 rudder design question
 
I've got a newer US and had the same problem. I'm not the greatest pilot and got a friend who is an excellent pilot to fly it. He couldn't make it knife edge either. Cut the wing tips off and Voila!, it does a nice knife edge. It's also a lot better at snaps, spins, harriers, etc.

Ed_Moorman 03-28-2006 09:03 PM

RE: Ultra Stick 60 rudder design question
 
1 Attachment(s)
Ernie, I have tried many different shape of rudder and none of them made much difference. The only thing to cure roll in knife edge is anhedral or downward end plates. I did an experiment on my Little Stick with some lite ply plates. I found that 3/4 inch down below the rib line would cure the roll.

As for knife edge with a Stick, it doesn't have much side area. You can add the side force generators-very large plates at mid wing or on the tips. One thing I did years ago during my knife edge phase was to make strakes down the side. For a Stick it was easier to get a chord-long or longer piece of lite ply that was 2 inches wider than the fuselage. Put this on the bottom bolted on by the gear. Use a couple of screws at the rear. What you have made if a fence on the bottom of the fuselage just like the wing on the top. When the plane is on its side, this fence channels the air down the fuselage, rather than letting it go around the fuselage, creating lift. If you don't like it, you can always unbolt it.

In the photos, you can see the lines on the plates. I started with 1 1/2" hang down and flew. In knife edge the plane had too much effective anhedral from the long plates so it tended to roll over on its back. I would land and trim off a quarter inch and fly again. At 3/4" the roll effectively stopped. The plane originally had flat tips and would do a barrel roll with rudder, as all Sticks, flat wing or not, will do. Try it. You need anhedral or effective anhedral from the plates to kill the roll.

Ernie Misner 03-29-2006 03:21 PM

RE: Ultra Stick 60 rudder design question
 
Great info Ed and Doggy. Thanks loads, I am reading and digesting still.

It is pitch coupling on my older (rudder) model US 40 that is terrible. It pitches towards the canopy so bad it goes into a harrier with rudder application.

Ed, what are your basic coupling thoughts on plane design? For example, high wing in knife edge = ?roll....... dihedral in knife edge = ?roll......... anhedral in knive edge = ? roll, etc. I need to get this down 1st, then go back to your info.

Thanks loads once again,

Ernie

Ed_Moorman 03-29-2006 03:58 PM

RE: Ultra Stick 60 rudder design question
 
Ernie,

High wing location, sweep back and dihedral cause roll in the direction of the rudder

Low wing location, sweep forward and anhedral cause roll opposite to the rudder.

On a high wing plane, you will always need anhedral or forward sweep to counter the pro-direction roll. Conversely, if you build a low wing plane with a flat wing, it will roll opposite to the rudder. I have shown this to several people who thought they were helping by building a low wing plane with a flat wing. Pattern planes with a flat wing will use a swept leading edge to counter the roll.

As for pitch, this is harder, a high wing low tail will pitch toward the top. Sticks need a higher tail-their's is usually on the bottom.

Low wing and high tail will pitch down (toward gear). A Kaos will usually need a lower tail.

I don't know if you have flown either of the UCD's, 60 or 46, but the 60 size has a lot of roll and, with its high tail, right on top of the fuselage, the plane pitches down pretty badly with rudder. The UCD 46 has the stab at mid fuselage, which I think was an attempt to corrrect this.

It's all a compromise and since mixing was invented, there has been less experimentation with solving the problem. The experts in pattern usually mix everything out.

Ernie Misner 03-29-2006 04:48 PM

RE: Ultra Stick 60 rudder design question
 
Alright Ed, you just spoke volumes of wisdom and education. I will print that out. Once the basics are grasped, I think we can "see" or visualize what is happening much as the pros us a tiny hand held plane to prepare for their routine. In it's simplest form, a 2 channel glider rolls correctly with rudder input (yaw), because of the dihedral. Picture a plane with dihedral coming straight at you and then yaw it a bit, and you can see how the dihedral makes it want to roll.

Ernie


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