multicasting

I have a .40 size Ultra stick, (Newer design) that I can't seem to shake the roll coupling on. Setting up for a knife edge requires a decent amount of aeleron. In fact, I can barrel roll with just the rudder at an impressive rate. I thought the lack of dihedral would allow this aircraft to knife edge better without so much opposite aeleron. This is a really great aircraft otherwise.

Bob

w8ye

My Feedback: (16)

Is it the new style with the counter balance rudder?

Might try a little anhedral?

Also a dorsal fin to give the plane a little more side area?

Enjoy,

Jim

Ed_Moorman

My Feedback: (1)

A flat wing will rudder roll in knife edge. It just rolls less than one with dihedral.

You have 3 choices to fix the roll, mix, end plates or anhedral. I have flown a zillion Sticks and shoulder wing planes and have put anhedral in numerous. I think the manufacturers are afraid to put anhedral in a plane, thinking no one will buy it. Turn a 4*40 over and what do you have, a high wing plane with anhedral.

1. A lot of guys mix. You'll probably need 2, rudder to aileron for roll coupling and rudder to elevator for pitch coupling (most high wing planes move toward the top or need down elevator in knife edge).

2. You can saw the wing apart, put in 3 degrees each side, about 1 1/2 inches on each side, and glass it back together. I've done this a lot, too. It only hurts the first time you do it. After your plane flies better, you'll think it was all worth it. A radial arm saw works great. Set the blade at 3 degrees and zip. Set the other side and cut. I don't cut all the way through, just enough so I can bend the wing. I 5-minute the ends together, then use 30-minute epoxy and use 6 oz glass cloth 6 inches wide. Don't worry about a dihedral brace. I have glassed 80 inch wings like this and have yet in 35 years of RC to have a failure.

3. Add downward end plates. They should be flush on top, but extend down from the tip. You'll probably find that 3/4 inch down works fine, but make some from 1/8 lite ply so you can trim them. In one of my columns not long ago, I showed this technique. You fly and do knife edge or put in rudder from level flight. I started with the plates going 1 1/2 inches down on a Stick. With this much, the plane rolled opposite to the rudder. I landed and trimmed 1/4" off. I had lined off 1/4" lines on the plate. You fly and try, trimming until the plane holds pretty good knife edge. Once you find the correct depth, you can remove the lite ply plates and make some nice ones, covered to match the plane.

da Rock

What Ed said.........

I've just slapped together a $40 chinese ARF that looked like they actually meant to have dihedral in the sucker but the plant workers did it upside down. The first version of the sucker I saw had about 1degree anhedral. When I got my kit, it's wing joiner was so undersize, I could have put almost any "hedral" into the wing I wanted. The inside ribs were thick, spongy "liteply" and set up for about 1degree anhedral, so I ran them through the sander and came out with about 2.5degrees in the wing.

It's the 1st anhedral I've flown. It has a lot less roll couple in knife edge, but part of that is because the rudder has about the area you'd expect in a 1/2A trainer. And the sucker won't actually do a knife edge and maintain altitude. Actually, maybe it will, but so far the workload to fly the sucker sorta masks what it might be able to do after it's trimmed out better.

Anhedral will surely turn some heads at your flying field. I flew the other day in conditions that, around here, keep most people at home. It was windy and cold. When I pulled up at the parking area, I noticed three guys I've never seen before. They obviously were good flyers. Two of them were dinking around the sky with that .40 size Hobbico twin, swapping the TX back and forth. The other guy looked at my anhedral wing when I laid it on the ground and went back for the fuselage. When I walked up, he asked if I'd flown "that wing" yet. Then he asked why I had the servo mounted on top of the wing. chuckle..... All three of them could fly really good, but this guy hadn't ever seen anhedral and none of them knew the term.

da Rock

BTW, that upside down wing trainer has a really bad yaw in roll. It's got a wing that's nowhere close to symmetrical airfoil. And the anhedral seems to want to work in roll opposite what a dihedral wants to do. So I've changed the single aileron servo to give differential aileron. Been wanting to ask an experienced anhedral flyer about that........ so...........

Ed??? any observations about what anhedral acts like in roll? and in yaw?

I've noticed that on takeoff (low airspeed) when I aileron roll and pull some elevator the nose yaws out like crazy. I've yet to fly the differential setup, btw. And when I yaw the model on purpose, like for crosswind landings, it just yaws; I don't see much roll (either direction, clockwise or counter). Is that what they do? Or is the cambered airfoil mixing up things?

RVator

My Feedback: (1)

Here is a picture of an enlarged rudder on a US60. I got the idea from Dave Robelen. He did the same thing to a US120. It is held on with packing tape for a trail. It did provide more rudder authority but I still ended up using 2 mixes rudder to down elevator and rudder to aileron. Trying to fly the Ultra Stick in knife edge made me want to hold too much elevator when I started flying my Extra and profile Katana which has almost no coupling.

Ernie Misner

If you look at a plane with dihedral from the FRONT, and yaw it, you can see how the wing drags to roll the plane in the same direction as the yaw. This obviously is how 2 channel airplanes manage to roll and turn properly. With anhedral, wouldn't you get opposite roll coupling?

Ernie

AeroDave

even the one with counter balanced rudder exhibits quite a bit of coupling. In fact, I don't the the counter balance has anything to do with it. Anyway, just mix it out. On my 9C, its just a matter of one mix for each aileron (providing they're on seperate channels) and one for rudder to elevator. I setup all my planes with these four mixes activated, even before test flight. Then I roll right to KE, observe coupling, land, add mixing witht eplane idling at my feet, take off, do it again until left rudder is pure. Then repeat with a roll to the left into KE, for right rudder, etc. THen do this again for pitch coupling. One or 2 tankfulls will yeald a well behaved plane. BTW, this really helps with rolling harriers, which a well mixed ultra stick will do quite nicely.

Ernie Misner

Hey Dave, thanks for the input! For the rolling harriers, are you using a full "up, right, down, left" stick movement for each revolution plus blips of the throttle while inverted and rightside up? I am trying to get the hang of that........

Thanks,

Ernie

da Rock

Ernie, I was hoping a real expert would jump in on your question, but they haven't so I'll throw out a few words.

When a dihedral airplane yaws, the wing that yawed back winds up seeing less angle of attack that it saw before the yaw. Obviously, the wing that yawed forward sees more angle of attack. That outboard wing gets increased lift from the increased AOA so it "climbs". The inboard wing has just experienced a reduced AOA and that give is less lift so it "dives". And both working together cause the model to roll in the direction of the yaw. All this comes about when the airframe is forced into the yaw by the rudder or some other "force". If the wing has ailerons and they were deflected, all simplicity ceases to exist because a bunch of other things happen.

But taking the simple situation where an anhedral wing is forced into yaw like a dihedral wing, then it's still fairly simple, but not as simple. The outboard wing will see a different AOA for either. It will be more for the dihedral wing, and it will be less for the anhedral wing. It's somewhat less simple for the anhedral wing because the situation we all visualize starts with our model tooling along straight and balanced. When our models are doing that, they're usually holding some positive AOA, at least when they're holding a steady altitude. So the outboard wing on the dihedral airplane already is feeling some positive AOA and with the yaw, simply sees more positive AOA. It's increase in lift will just be more (whatever is up the L/D slope drawn on the chart for that airfoil). A lot of airfoils have a L/D "bucket" that shows up on the airfoil chart around zero AOA. What that amounts to for this situation is that when our anhedral wing that's flying along with some positive AOA gets yawed, one wing will go from a positive AOA through a zero AOA to get to a negative AOA, and might dance through that bucket. Or not.... What happens with an anhedral wing just isn't as simple to predict is all.

I'm flying an anhedral that's about 2.5degrees. It's also a cambered airfoil and thanks to Chinese craftsmanship, actually has a somewhat different airfoil in the right wing than in the left. And I've had to heat warps out of the sucker twice so far. And just last night, cut off a really screwed aileron and put it back straight. So my experiences flying an anhedral are muddled at best. But I think that I have most everything sorted and TODAY SOON will give the sucker another flight or two.

But I have goten one strong impression from flying that potatoe chip so far. I've switched the ailerons to differential throws. The airplane seemed to show strong yaw away from the turns when the turns were aileron/elevator turns. And the model would do fairly flat rudder turns. (Which is what your question leaned toward.) BTW, the rudder has somewhat minimal authority. And it's a highwing airplane, so will naturally resist roll induced by rudder induced yaw. So what do I know..... chuckle....

AeroDave

Ernie,
for me the rolling harrier is like an a slow roll, in that you feed in and out top rudder, and appropriate elevator input. It just takes a bit more 'cause you're keeping the nose higher. Its also (obviously) dependent on the plane, but I've found its way less than full deflection. Another consideration is that, just like in a slow roll, when you're going from, say knife edge to inverted, the elevator needed to keep the nose up effects heading between KE and inverted. So if you're doing a rolling harrier to the right (I practice them both ways) as you approach KE you feed in left rudder. Then as you leave KE heading to inverted you start feeding in down elevator the nose will want to veer to the left. So you hold the left rudder(which is in effect reversed when inverted) a little longer to keep the nose straight. In a really, long, slow roll you might even need a bit more than you did in KE.

Bla bla bla, the point I'm trying to make is practice slow rolls until the feeding in and out of controls and the corrections needed become second nature. Then, when you try rolling harriers you'll have a skill you can build on. Just use a bit more input.

AS far as throttle goes, I just sorta do that by feel, working it as needed.

I hope this helps. Best of luck!

Dave

Ernie Misner

Thanks Dave, it does help. I am on the right track. For my slow rolls I find it helps a lot to go to low rates on the ailerons so I can peg that stick. So you are not blipping the throttle at any exact time in the harrier rolls? I keep trying that as the plane approaches right side up and upside down. Maybe I am thinking too much?

Ernie

AeroDave

I think everyone finds their own way through these things. I keep the throttle pretty much constant. I'm going for a smooth, consistant roll, maintaining angle of attack, roll rate and altitude. I know lost of folks set up a flight mode for rolling harriers so they can get a consistant roll rate by using full throw on the ailerons. I guess we've strayed into the domain of another forum. 'still fun though....