stab mod

[steve]

i cant find the thread, but it was stated that the ailerons were cut 90 deg from the TE so they would clear the wing as they moved up and down

(and have a small low-drag gap).

last month a had asked that very same question about the rutter cut out:confused:

no reply, from the forum so i guessed

and based on that thread my cut will not work.

or will it...........

[longez360]

Yes, 90 degrees to the hinge line laterally (to get past the opposing skin). Ensure you have a plans gap there too for gap under load.

 

On another note, hinge lines are the reason I reeeeeally dislike the hotwiring process as the final cut. Lag causes binding in hinges. Hotwire oversize, sand to size per the Ronneberg method always gives perfect results. I used an aluminim rectuangular cross section about 5 foot long for the winglets.

[Wayne Hicks]

I cannot find where the rudder cut line posts were, so I'll put it here and hope someone can move it to the approriate thread.

 

If you don't cut the rudders at 90 degree angles to the rudder hinge line, the tops and bottoms of the rudders will bind as the rudders swing open. But there is a way to get around this if you want your rudders cut parallel to the ground for asthetics or function, your choice. All you need to do is cut the inboard cut lines to be higher than the outboard cut lines. See the attached conceptual figure. Of course, these cuts start from the rudder hinge line and will meet at the trailing edge. When looking trailing edge on, the angle between the inboard and outboard cut lines is equal to the angle between where the 90-degree cut line should be versus where you want the outboard cut line to be. Take that angle and make the inboard cut line to be that many degrees higher than the outboard cut line. A little hard to explain, but it works.

[steve]

very cool.....

[SAF_Zoom]

You will have a problem with the top cut in your picture as it will prevent the rudder from deploying outward (the two cuts are angle the same way and not opppsite to one another)

[Wayne Hicks]

Very sorry, I forgot to reverse the top cut line. I was in a hurry with the explanation.

[TMann]

Wayne ..... are you using that Microsft Engineering tool? (Visual Paintbrush)

 

Here's what I was planning to do on mine:

[Jack Morrison]

Gee Tom, that looks like a split rudder. Go for it.

 

Jack

[mfryer]

Wayne ..... are you using that Microsft Engineering tool? (Visual Paintbrush)

 

Here's what I was planning to do on mine:

But why??

 

 

?

[Bruce]

I can see where it adds some cool factor to the look. But, will it be just as effective as the regular rudder or will you loose some?

[Ron Springer]

I can see where it adds some cool factor to the look. But, will it be just as effective as the regular rudder or will you loose some?

It is more effective. This idea was proposed on the Cozy mailing list by Todd Parker on March 2, 2005. Look it up in the archives to see the discussion that took place ...

[Neverquit]

Look it up in the archives to see the discussion that took place ...

I did, lots of conflict. General consensus, "just another fix to a non-existent problem". Quote from Burt, "do you want to fly, or do you want to build"?

[Marc Zeitlin]

It is more effective...

In theory, and not by much. NASA reports indicate a maximum Cl for plain flaps (what the regular rudder is) of about 2.5, give or take, theoretically. They also indicate a maximum Cl for a split flap of about 2.6, give or take, theoretically.

 

BFD, IMNSHO. Unless someone's done some testing on standard vs. split flaps on Long-EZ winglets and gathered ACTUAL Cl data, I wouldn't bother modifying anything based on a theoretical increase in Cl of 0.1, which would be unmeasurable and unnoticeable anyway. My guess is that the EZ/COZY rudders don't generate anywhere near that level of Cl anyway, since the rudder is far less than 30% of the chord, and you never get to the AOA's that would generate those numbers because the slip angle would be crazy. In that case, it's hard to imagine that the lift curve slope for the split flaps would be any different at all from the plain flap.

 

Now, if building from scratch, as Mr. Mann is doing, and it's not really any extra work to do the split flap over the plain flap - what the hell - it doesn't hurt anything, and does have a couple of advantages - aesthetics, and more importantly, the rudder won't flap around (crappy pun) in the wind, since the breeze can't get at the back surface to push it off its stop.

 

I might consider it for those reasons, but not for extra effectiveness - if it increased the crosswind capability of the airplane by 0.5 kt, I'd be really surprised.

[Wayne Hicks]

I often wonder how a thinner rudder holds up to delamination over its lifetime. Rudders take a fair amount of abuse, especially when using them as air brakes as we do when coming down hard. I would imagine thinner rudders would see more abuse.

 

Also, it's going to look ugly if the now two trailing edges don't line up and remain lined up over the plane's lifetime. "Yeah, you've got split flaps. Cool. But why the ugly gapping?" The workmanship better be spot on.

[Ron Springer]

In theory, and not by much. NASA reports indicate a maximum Cl for plain flaps (what the regular rudder is) of about 2.5, give or take, theoretically. They also indicate a maximum Cl for a split flap of about 2.6, give or take, theoretically.

 

BFD, IMNSHO. Unless someone's done some testing on standard vs. split flaps on Long-EZ winglets and gathered ACTUAL Cl data, I wouldn't bother modifying anything based on a theoretical increase in Cl of 0.1, which would be unmeasurable and unnoticeable anyway. My guess is that the EZ/COZY rudders don't generate anywhere near that level of Cl anyway, since the rudder is far less than 30% of the chord, and you never get to the AOA's that would generate those numbers because the slip angle would be crazy. In that case, it's hard to imagine that the lift curve slope for the split flaps would be any different at all from the plain flap.

 

Now, if building from scratch, as Mr. Mann is doing, and it's not really any extra work to do the split flap over the plain flap - what the hell - it doesn't hurt anything, and does have a couple of advantages - aesthetics, and more importantly, the rudder won't flap around (crappy pun) in the wind, since the breeze can't get at the back surface to push it off its stop.

 

I might consider it for those reasons, but not for extra effectiveness - if it increased the crosswind capability of the airplane by 0.5 kt, I'd be really surprised.

I am not promoting this mod, just answering the question about whether or not there would be a loss of effectiveness. But now that you bring it up, why are you only talking about lift, where the split flap makes a small difference, instead of drag, where the split flap makes a big difference?

 

Now I will directly refer to Todd Parker's statement on the mailing list that a split flat has 20% more lift for the same deflection and three times as much drag. I haven't verified it myself, but he is usually correct. I could certainly see the drag being really high due to the creation of a large wake.

[Ron Springer]

I will also point out that I do know the drag of the rudder will be a lot less than the lift, but the drag force should have a moment arm of about 14 ft from the CG, and the moment arm of the lift force will be much less. So, the effect of drag on yaw will be amplified by the ratio of the moment arms compared to the effect of lift on yaw.

 

There are some calculations that could be done here, but I'm not going to do them ... too busy!

[Marc Zeitlin]

I am not promoting this mod, just answering the question about whether or not there would be a loss of effectiveness.

Understood. There will be no loss of effectiveness, but the INCREASE in effectiveness is questionable, and that was the original rationale for the modification.

 

But now that you bring it up, why are you only talking about lift, where the split flap makes a small difference, instead of drag, where the split flap makes a big difference?

Because the lift predominates. If the L/D ratio of the vertical stab is 20 (wild guess with the rudder extended), then even if the moment arm (discussed below) is a factor of three different, the lift component will still dominate.

 

Now I will directly refer to Todd Parker's statement on the mailing list that a split flat has 20% more lift for the same deflection and three times as much drag. I haven't verified it myself, but he is usually correct.

I agree that Todd is usually correct. I will also state that his claim is not necessarily in conflict with the claim of a 5% higher maximum Cl, if the split flap changes the lift curve slope. It's also possible that various sets of data indicate various things, depending upon how the experiments were done - i.e., flap %age of chord, aspect ratio of wing, etc.

 

Three times as much drag is a claim I'd not heard before - I'd certainly be interested in references for that.

 

I could certainly see the drag being really high due to the creation of a large wake.

As you state, without doing some superposition calcs on lift and drag, it's hard to say what the overall effect will be. It may be a little more effective, if at all (my guess), or it may be somewhat more effective. It's very difficult for me to believe that it'll be a LOT more effective.

 

One very simple way of testing this would be for someone (if I were flying now, I'd do it, but I won't be for a few months) with a standard rudder installation to fabricate a 3 BID "plate" that backed up the standard rudder, and hold it on with some aluminum tape. Install it on one rudder without changing the installation in any other way. Extend both rudders to the maximum extent (equally), and see if or how much the plane yaws. Done.

[Ron Springer]

Regarding Todd's drag claims ...

 

I just flipped open my "Theory of Wing Sections" book and flipped to the page where they compare a split and plain flap drag polar. The split flap does have a slightly higher max CL, but at the same CL, the split flap has the same or lower CD, at least for a NACA 23012 with a 20% chord flap. That's actually a bit counter-intuitive.

 

But, the drag polar plot does not really address the flap deflection. I think his claim of three times the drag for the same deflection may be true ONLY for very small deflections. It is definitely not true across the board. At very small deflections, the air may be able to stay attached to a plain flap, but the split flap forces a large wake. At larger deflections, both styles of flaps have large wakes.

[Marc Zeitlin]

Regarding Todd's drag claims ...

So all of that tends to support my contention that the theoretical improvement in yaw capability with split rudders is small if existent at all. Interesting info, and good that it's consistent with the Cl info I saw via the NASA reports/book. Drag-wise, that's what I would have expected - not much difference at high deflection angles.

 

So, back to doing it for aesthetics and/or protection from cross-wind breezes and banging around.