Elevator "slop"?

I've never liked the enlarged hole at the elevator approach. Just seems like you're building in a wear point. But that's probably just me.

Wasn't there a thread on this forum about using a turbulator on the stab leading edge to address this? I did a search but didn't find the thread I thought I remembered... Have any of y'all tried this? Did it work?

I enlarged a SkyRay stab/elevator (+13%) and rubber cemented a turbulating thread to the leading edge, fearing that it might have been stalling. The plane seemed to turn better, but there were too many changes at once (area, resultant c.g. shift, turbulator, revised elevator deflection amount and symmetry) to know what caused what. That the flat stab was also thin probably means that the turbulator wasn't needed. It was just an "insurance" thing, and ultimately didn't seem to hurt anything; so I left it on.

Note: I don't recommend more than one change at a time. In this instance, I just wanted an immediate fix so that I could practice. Now it "works right". It might only have needed the horn re-set for correct deflections!

SK

Ron;

One of the things some of us didn't know about was the benefit of slight (one or two degrees) of positive stab incidence. My theory is that some slop in the system allowed the elevator to hang down a degree or two in level flight, thereby giving the same effect.

With the advent of ball links and adjustable controls, we can pretty well dial in the incidence that works best for each ship and still have the crispness of "slopless" controls.

Just my theory...

###CORRECTION AND ADDITIONAL DETAIL ADDED LATER###

I should have checked my math. I typically shim using between 1/64" and 1/32". That gives a built in positive incidence of 1/2 to 1 degree. So, above it should say: "One of the things some of us didn't know about was the benefit of slight (1/2 to 1 degree) of positive stab incidence. My theory is that some slop in the system allowed the elevator to hang down a degree or so in level flight, thereby giving the same effect."

My mistake.

However, when one builds in "slop" from oversized holes, it can be difficult to be accurate with the amount of slop. I have seen ships with intentional slop that the elevator easilly moved 1.5 to 2 degrees with the flaps fixed. Of course, this gets worse with wear.

I have been usin' elev slop in all my models includin' the ones with a slight amount of positive incedence, with a thicker stab than elev, and regular stab and elev bein' the same thickness..
I have not had a problem with any, and can't see that one is better than another.. Please don't think that there are not other ways that work because there are, this works for me..Also these models aren't "piped engine models" some are low pitch high rev's and others are 4-2 breakin'engines..
Hope that this helps...

...And if it works for you, great. I merely posted my observation based on personal experience. Since going to ball links and adjustable controls, any ship that "hunted" in level flight could be taken care of with sometimes just a half turn of the elevator pushrod to give a little downward incidence to the elevator, creating the same effect as upward incidence to the stab.

The difference I did notice when I eliminated all slop was the crispness of the response and the ability to point the ship exactly where the controls told it to go. Note - this does not necessarily mean it went where I wanted it to go, but that is an eye/hand coordination problem, not a problem with the ship... .

Ay Carumba - two degrees is FAR more than I ever suggested anyone use. David got up to about .6 degrees, and I was hesitant to recommend even that much be built in. If it works for you, fine, but I think this is quite likely to have noticable effects on inside/outside turn response, and probably tracking as well, in a general case.

>With the advent of ball links and adjustable controls, we
>can pretty well dial in the incidence that works best for
>each ship and still have the crispness of "slopless"
>controls.

That's pretty much what I think, too.

BTW, I really don't think the "aerodynamic slop" (elevator smaller than stab) really works very much like intended.

Caramba is right. See the message posted below on correction. I should have done the math before posting. Getting just the precise amount of "slop" necessary to eliminate hunting is difficult. Much easier to build and adjust with a semblence of precision

>> BTW, I really don't think the "aerodynamic slop" (elevator smaller than stab) really works very much like intended<<

Maybe it's just my imagination. But I do know that I've do a direct swap, tailplane for tailplane and cured a hunting problem by going to a thinner elevator. It worked for me, but it could just be the simulated sag of the elevator.

While slightly off the subject, I also recommend the Ted Fancher article(s) on designing the Imitation.

See Ya

You are correct. I typically shim between 1/64" and 1/32" Doing the math where sin(a)= o/h and given a stab nominally 3.5" wide and a shim 1/32" thick, sin(a) would be .032/3.5 = .009. Considering the sin(1 degree) is .0174, this is about 1/2 of one degree. If the stab was 3 inches wide, that would be .032/3 = .011. That is still less than 1 degree

Mea maxima culpa - I should have rechecked my figures before I posted and been more precise in defining what I build versus what I have seen with control that have slop in them. Fortunatley, I have you folks to keep me on my toes....

On that subject, OS. Did you ever read the series I did in the Model Aviation Stunt column on the design and trim of stunt planes?

Ted;

What year/months were these? If and when the AMA archives comes back up, it would make interesting reading.

Good point. Question - is anyone getting through to the AMA archives, or have they in the past week?

Hasn't it been repeatedly mentioned to you that self-promotion like this is so just so unseemly and tawdry?

Have you yet read my first BBS column of 2004? It is fabulous, just ask Ty, and you, lucky guy that you are, are mentioned.

I did read those articles, but did not save them as I did the Imitation articles, as well as both iterations of the "Go for Broke article." The upshot is that I haven't read those columnar articles in years.

You are right. Here is an extract of post by Warren from 28 February 2002:

------------------------------------------------------------
Back in February of 2001, on RCO, there was an excellant, and length thread entitled "Fixing the Hunt". (I don't know if those archives are still available or not.)

The subject of intentional elevator slop was discussed, and this is a portion of a post by Ted Fancher:

In reference to correcting the "hunt"...

"....If none of this has done the deed, consider slightly enlarging the hole in the elevator horn to allow about 1/8" up and down movement at the trailing edge of the elevator with no motion of the flaps. Frankly, between you, me and the fence posts, I've done this with every ship I've built for the last thirty or so years..."

**When TF speaks, I listen.**

---------------------------------------------------------------

No one can argue with Ted's success.

I do think it interesting that Ted recommends starting out with tight controls, and then using slop later only after exhausting other options.

Dunno. Personal choice, I guess.

NO stab incidence. BUILD IT STRIGHT

Scott(do it right the first time)Riese

Personally, I believe it works. I had a ship which seemed like its corners were easy to fly with no wiggle on the botton, the more I flew it, the better I liked it. Then I discovered that my brass tubing joiner on the elevator control rod link had lost its solder joint and the elevator was "slopping" as a result. When I resoldered it and "fixed" it, the ship was not as easy to fly (again).

(Perhaps I imagined it all..)

The Expocrank achieves a similar effect perhaps, by desensitizing the controls around neutral. Some very good fliers do not like this, and even favor an opposite arrangement. So, if you don't like an Expocrank, you probably won't care for slop in the elevator.

[photo not recovered: 3e69bb3870f12ad5.jpg]

"Start off every day with a smile and get it over with." -W.C. Fields

After all that, I suspect that the most likely root causes of my problems as I remember them from 37 years ago are: control system friction, unintentional wing and/or stabilizer incidence (...didn't have a laser wing incidence meter or even know I needed one ...) , and incorrect thrust line. I have attempted to address each of these issues on my new project (a Sig Chipmunk) and I'm about ready to firmly install the stabilizer. It would be easy to modify the stab and or build in 1/2 deg. (or whatever) incidence at this time. Those of you who have built or flown or observed a Sig Chipmunk: would you build your next one with any of the changes discussed in this thread (i.e. a different stabilizer/elevator airfoil, stabilizer incedence, elevator control horn "slop", etc.)?

It would be nice to get a comment here from Dave Fitzgerald. He was a several time National Champion in Junior and Senior with a Chipmunk!
And - In his D-Tails column in Stunt News one of the systems he liked a lot was the aerodnamic balance that the Chimpmunk elevators used.

Mea culpa but this enquiring mind suddenly feels seriously stupid after reading all the discussions over the years about thinner elevators behind thick stabs to eliminate hunting.

If we taper our elevators straight from, say, 1/4 to 1/16 and hang it behind a 1/4 thick stab, depending upon the elevator width, we have a turbulent airflow as thick as the stab that the elevator moves in before it has any effect.

My calcs suggest that we get about 1.8º movement each way before the elevator has any effect no matter what. That seems a fairly large movement to me but maybe I'm wrong.

What do others think?

Cheers from sunny, hot and humid Sydney where the bushfires look spectacular but do not pose any threat to property at present.

That's not really the way air works. It's not like the stabilizer "punches a hole" in the air and leaves a vacuum behind it. Having to turn a little bit of a corner might create some turbulence, but the idea that the moving the elevator in this turbulence has no effect until it "sticks out" into the airstream or "pokes out" from behind the stabilizer is just not right. Maybe at Mach 20, but not at RNs of 5000 where viscosity is a large effect. I wouldn't be surprised if you get slightly softer response with the "smaller elevator" , but the hinge line creates a lot of turbulence even if the elevator is the same thickness.

I think mechanical slop can cover some misalignment, and the "smaller elevator" may be slightly softer than "same size elevator". But I have flown a lot of airplanes with negligible slop (<1/32" at the TE) and the elevator intentionally blended in to the stab to the maximum extent possible, that tracked just fine and never had even a hint of hunting. To me this definitively proves that the slop is not necessary, and that some other factor is the cause.

In the vast majoprity of cases, virtually all in fact, hunting is caused by mechanical drag or slop somewhere in the system. Most of the few others appear to be due to alignment issues, because fixing the alignment (either with elevator/flap neutral adjustments or stabilizer shims) fixes the problem without resorting to slop.

In a very few cases - actually, one particular structural configuration in 3-4 examples of one specific design- I found that none of the usual fixes worked. I beleive that this particular case was an aeroelastic effect where the very thin and flexible stabilizer with very little taper seemed to have an unstable structure where the stab tips "washed in" under load. I have flown 4 of these airplanes and they all hunted the same way with roughly the same frequency and amplitude. One guy wrecked his, and rebuilt the stab with a different structure, and afterwards it flew as well as any other model. I will reserve the details as the model is no longer on the market, and I don't want to get into another argument.

My last airplane was all ball links and titantium threaded ends with almost no slop what so ever. The best and smoothest controls I ever installed. I played with a small amount of positve incidence in the stab but still added a very minute amount of down trim to the elevators with level flaps to get the tracking I wanted. Perhaps that miniscule amount of posi in the stab was not there at all and is harder to measure and fit than a few turns of the old ball links.

I also used the thicker stab trick in miniscule amounts like only 1/8" thicker and that seemed to work. What I have seen other modelers do is simply going to far with a really thick stab say 3/4" and 1/4" elevators with near disasterous results where the dead feeling around level flight was accompanied by a sudden burst of effect when deflected and not really controllable through the maneuvers as it seemed the coupled flaps fought with the desensitized elevators.
Talk to Larry Robertson on that subject. The old Shark with smallish stab and elevators with huge wing and flaps just would not fly accurately under this configuration.

John Sunderland

John, did lalrry build a Shark .45 configured with a thinner elevators than stab?? Why??

Mine flies great built as per plans (RSM's plans)!

Yep, Larry had a 3/4 thick stab and 1/4 elevators. I dunno why cause the stock Shark wants for nothing but after much fuss and advice from nearly every top 20 pilot...he fixed the thing and also built another stock shark that flies quite well.

John

Larry and I used to fly all the time. One thing for sure, he's not afraid to try different things. Sometimes they work, and sometimes they don't. One of his better-flying airplanes had a stab that was a full 1" thick from root to tip. Great craftsmanship always.

Goodness yes...the guy can build and flys quite well. Larry is a character and flies with us often. I usually gets several calls each winter where he runs stuff past me (and Joe R.) as well that he wants to try. He was working hard this past summer to improve his pattern and drove up from Louisville several times to fly with us.

Larry and I flew together in Lexington. I'd drive up from Richmond, and he would drive down from Louisville every Wednesday afternoon.