While surfing through some old slides...this "G-GOBBLER" with the flying stab...keeps boggling my britches...ever since seeing Lynn Howard Dooty socked it to us by winning the first Tacoma Mall contest here in the NW 40 years ago with a flying "stab-a-lator"

Here is a shot taken at the nats...about that same time...showing a Geiske Nobler utilizing the same set up.  As I remember...I too was quite impressed with this models  sharp corners and turning radius.
However, every time this subject of FLYING STABS comes around...Most flyers discount and blow off any advantage that could possibly be an advantage to CLPA.
One advantage after seeing Lynn's model fly....was that he could VIRTUALLY SWAP ENDS...with that stunter of his...expecially when finding himself needing that extra turning punch during those heart stopping "OOOPS...TOO LOW PULL OUTTAVA' REVERSE WING OVER...ETC?
GIFTED CLPA-DESIGNER GRUNTS?

ANY IDEAS OR FURTHER THOUGHTS or JABS...ABOUT FLYIN STABS?
 

Did you try putting in a little down stab when the flaps were neutral?  Did it have a pointy LE?

Wow, Schultzie.  You've got my nostalgia genes all agog.

That Nobler was Bill Fitzgerald's.  He flew it more or less stock at a mid '70s Nats.  Engine quit while inverted and none other than Bobby Who (Hunt) played Willy Mays and caught it before it hit the deck.  Problem was, Bobby was slightly "aloft" when catching it and one leg came up as a result of the impact of three pounds traveling 25 or 30 MPH and kicked the tail off.  Oooops!

Bill took it home and more or less copied what I had done with a Banshee that had had a mishap.  He rebuilt it with the flying tail and discovered the same issues as did I with the Banshee.  Both were hinged at 25% of the chord and both were occasionally out of control in level flight.  Symmetrical airfoils have no pitching moment about the 25% point and as a result are perfectly happy to remain at any angle relative to the general airflow.  Both airplanes were at times perfectly willing to do almost anything in level flight.  In maneuvers they were pretty much OK but trying to fly level when they were displace by turbulence or wind was a real chore.

Both were tamed down eventually by taping some additional area onto the trailing edge so the hinge point was no longer right at 25%.  The Nobler still exists.  The last time I saw it it was still hanging in Bill's downstairs shop, still looking like it was painted with a dozen coats of white Aero Gloss.  In actuality, the wing and tail were covered with monokote and the fuse painted with white Hobby Poxy.  The trim is all sticky monokote.  (Son David may have the airplane at his place now.  I'm not sure.  He has threatened to bring it out again)

Another great pilot who is no longer with us (Roger Barrett) came up to Bill at the first Nats he brought the Nobler to and asked what he had painted the ship with.  Yes, it was that good!  

Another great ride for a Big Art .35.  We had a lot of them in those days.

Ted

p.s.  Just noted the "76" on the rudder.  That tells us that the ship first showed up at the Nats the same year, 1976, as did my Moby Dick in the other thread.

Howard,

It had a sharp leading edge and was "hinged" at the 50% point.

  D'OH!

As an old VooDoo and Combat Cat flyer, I had a lot of 'em.

I found that any amount of COUNTER BALANCE, that is, elevator are in front of the hinge, is too much. 

Counterbalance is needed on real planes, but a man can move the flipper on a model without help.

Hey guys, I was about 17 when I built it. Seemed like a good idea at the time.   

Wow, Schultzie.  You've got my nostalgia genes all agog.


Another great pilot who is no longer with us (Roger Barrett) came up to Bill at the first Nats he brought the Nobler to and asked what he had painted the ship with.  Yes, it was that good!  

Another great ride for a Big Art .35.  We had a lot of them in those days.

Ted

p.s.  Just noted the "76" on the rudder.  That tells us that the ship first showed up at the Nats the same year, 1976, as did my Moby Dick in the other thread.

Ted...
Speaking of great old rides...Ted! I have always loved this paint scheme of yours...here is a revamped enhanced photo of that great model.

I remember my first VooDoo.  Built it box stock and tried to fly it.  Folded the wing on the first loop.  Second VooDoo I cut the controls down to where there was only about 15 degrees each way.  Made for a better flying plane and had no problems with level flight.

It was Scarinzi's Giant Killer that would take about three or four laps to get up to speed.  It was sensitive on controls.  Once up to speed it flew great.

Someone mentioned the Humbug.  I had one at VSC this year.  Only problem with the plane was the little OS 25 FP is not enough motor.   It flew alright for me.  Level flight was great to me and it would go where I wanted it.  Of course on my first official I didn't realize it was coming in at the third turn of the hourglass.   I am in the process of building another one.  But, will use a little more power. 

Looking at the picture of the Nobler with the flying stab, I would have cut down the control throw on the stab and eliminated the flaps.  DOC Holliday

25% is the aerodynamic center, so if the stab is hinged behind that, there would be trouble unless there's a very stiff linkage to the flaps, or there's a double-hinge scheme like some Piper airplanes.

I used aerodynamic balance on combat plane stabilators.   It let me get away with wimpy pushrods.  The stabilators were hinged at about 15% chord.  I build maybe 100 airplanes that way.  

Well Shultize, when you rebuild that Chip's tail, why don't you try it and show us how it's done?   

Ty,
That was Wild Bill's very own Humbug.  It is essentially the prototype for the RSM kit.
Steve

Ty,

Actually they do work if hinged properly!  I just don't think I want to try since I build so few airplanes.......


Ted,

If you did fly the original Moby at Concord in May 74, I judged all day after boinking the original Akromaster there when the engine quit at about 60 degrees into the first part of the reverse-wing over.  I hadn't been flying it since 1971 and got the tank full of crud.  Thought I had it cleaned out but nnnnoooooo!

If you remember the day it was hot, hot, hot and kind of devoid of much wind!

Ted, t o your Post#17 -

1) Glen Allison, down here in Tucson, did a profile that had a stabilator, hinged about 50% MAC on one of his orig profiles. The model was IIR unflapped. He controlled the "aft of MAC" tendencies with, in effect, an anti-servo tab. He and Keith T had an interesting discussion at a Cholla Choppers meeting about the exact nomenclature and function of the TE counter-tab. It did work, though... Glen had an article on it in the same SN issue with Drindak's 80% hinged stabilator model... Short, ~ 1 pg articles...

2) I also dabbled with them for a while, and found pretty much what's been aired in this thread. Restated, a bit closer to my observations, stabilators can have enormous turning power. That includes a risk of "locking-over" too far, and not being easy to bring back to neutral. I 'd also been flying some RC soaring about that time, and many of those models used 25%-hinged stabilators.

Figuring I did not want to lock one over, and that LE-hinged layout might require to much muscle, I designed the hinge at 20% MAC. That, at least, worked reasonably well.

Then there's an idea that such a layout does not need the vast horizontal tail area of fixed-stab/moving-elevator designs. Also true.

As was an idea you and I may have been known to mention over lo, these many years. (Well, you maybe - who listens to me? ) The idea that a stabilator is pretty much a symmetrical airfoil control surface, while the stab+elevator forms a crude, cambered-airfoil surface. Also true.

That suggests the stabilator doesn't need as much angle to get similar control force. ...that perhaps an angle comparable to the "chord line" (LE to TE straight chord line) for a deflected stab+elev is adequate. Also true, and in spades - the symmetrical section doesn't have the awkward bend in the middle that compromises 'streamlining' and adds drag...

Now, before anyone runs out and tries it on the basis of all these positive ideas, there were some negatives, too.

STATIC balance for the stabilator was important. If the surface static balanced aft of the hingline, the model tended to gallop. (The terms "up" and "down" I'll use refer to the direction of required lift, not ground and sky, ok?) In level flight, and aft-heavy stabilator tends to trail at a slight positive AoA, meaning a "down elevator" tendency. With the 'prongs' of the joiner wire bent forward, and perhaps another touch or two of ballast to make sure the surface static balanced just ahead of the hinge, the 'free-trailing' tendency was slightly nose-up. Since level flight requires a positive AoA - however slight - it didn't cause the same divergence tendency as an aft-heavy stabi.

Grooving? Tracking? No, VERY unlikely. You fly the beast every inch of the way... That didn't affect RC soarers, since the servo pushrods are a 'dead hand' in effect. Where you move the stick to is where  the servo wheel stops, and thus also the control surface. With our immediate, direct, free, feedback in CL it don't woik that way at all. Generally, it wasn't too bad, about like solo-sailing a small sailboat in choppy and gusty waters... A challenge, but (almost) physically enjoyable...

And, finally - ultimate control/stability power. Ain't got it... That big fat stabilizer in front of that big fat elevator on modern stunter layouts do got it... Plenty of elevator to start and execute a sharp turn, and plenty of stabilizer to stop it. On my 5 or 6 experimentals I learned that oversize stabilators were more nuisance - excess control force, poor exit damping, balance, etc... So, a stabilizer proportioned for fully adequate control in soft conditions ran out of muscle in nasty weather. Particularly at places like the bottom turn of the hourglass. Guess how I found out...

I’ve been “on the road” for a few days, and put this together, thinking something similar might have been already posted when I got back. There is some overlap with other posts, but I decided to leave it as is for now. This is supposed to be a “thought starter”, not a solution, ya know!

Edit: Ooops! Now there is some overlap! Apparently Lou posted while I was trying to JPEG.

“On the Road” Post
Control sensitivity and lack of stability should be “curable” stabilator issues, given some experimentation and thought.
Control Sensitivity
 Start with the simplest case – an unflapped airplane with a zero-zero-zero incidence setup. The top sketch below shows the start of an outside loop with a conventional stab-elevator. (I chose to sketch an outside loop to show the empennage lifting “up”). The wing is a few degrees negative, which of course means the stab is also a few degrees negative. (In other words, the stabilizer is attempting “stabilize” the airplane by bringing the nose back up, and out of the loop.)
   The “chord line” of the stab-elevator combo (with down control on the elevator) is slightly positive to the relative airflow, creating enough lift to maintain the loop. The stabilator chord line in the lower sketch is also drawn slightly positive to maintain the loop. Two big differences between the stab-elevator sketch and the stabilator sketch are:

1. Regardless of the base airfoil for the stab-elevator, a “bent plate” airfoil is not a powerful final airfoil. The chord line of the stab-elevator will have more incidence than the equivalent airfoil (even if both are flat plates) in the stabilator to produce an equal turning force.

2. The number of degrees of actual stabilator rotation needed to achieve the “same” stabilator incidence as the stab-elevator chord line incidence is much less than the degrees of elevator rotation needed for the same chord line angle. Depends on the ratios of elevator to stab chords, and the number of total degrees, but some trig and “Kentucky Windage” will give degrees of rotation for the stabilator of half or less than those of the elevator – just to match the chord lines, or “equal effect” chord lines, anyway. The sketch shows a red stabilator at the same angle as the elevator, and, that has to be wrong, doesn’t it?

A guess: A starting point for control sensitivity for an unflapped plane is in the neighborhood of 40% to 50% of the same airplane with a stab-elevator. A longer control horn, shorter bellcrank pushrod arm, or some combo of the two that gives the lesser ratio should do.

An extension of these observations also suggest a reasonable starting point for control ratios of a flapped model converted from stab-elevator to stabilator. Keep handle to flap ratios (flap control sensitivity) the same as with the conventional stab. Decrease the flap to stabilator ratio to half or less of the former elevator ratio. If elevator / flaps were 1:1, use a longer stabilator control horn (or connect lower on the flap horn) so the stabilator moves 40% to 50% of the flap rotation.

Stability
A sort of half-truth is that us Intermediates know one thing better than experts – how difficult it is to nail all the straight-leg portions of maneuvers! For a design to be a viable PA contender, for most us straight and steady, at any time and in any direction, has to be, literally, “right around the corner.”
   The TVC calculations for a stabilator and stab-elevator are identical. Potential stability is the same for both. Expressing the TVC formula in terms that “speak to us”, we can write:

 TVC = (Wing Area / Empennage Area) * (Tail Moment: wing 25% MAC to empennage 25% MAC) / Wing MAC

Or in English, Tail Volume Coefficient (TVC) is the ratio of empennage area to wing area multiplied by the tail moment, expressed as a number of wing chords.
A tacit assumption is that the first ratio (empennage area to wing area) is an expression of the relative lifting power of the two areas. We seldom build stab-elevators that are the aerodynamic equals of our wings, but a stabilator is potentially as good as or better than a wing, particularly a flapped wing vs. a clean mini-wing stabilator. In short, strictly from a TVC perspective, the stabilator model should be as stable as, or more stable than, a conventional stab-elevator combo.
{Side note: Although in the actual flight of an airplane, the TVC tail moment operates from the CG, not the 25% MAC, for most purposes it is easier to keep track of what we are about by using the MAC to MAC number. Just keep in mind that a trimmed airplane that has the CG forward of the 25% MAC will be more stable than our “raw” TVC would indicate; i. e., a larger trimmed TVC}
   But that is not true in practice, because the calculations assume non-movable surfaces for the wing and empennage. The calculations are more representative of actual stability for a conventional empennage, as the stabilizer is, indeed, a non-movable surface. A stabilator is more of a stabiLATOR than a STABILator in actual practice.
   Of course, using less movement (as mentioned under Sensitivity) should help some. But a stabilator begs for a non-linear bellcrank / horn setup, perhaps half again as sensitive near neutral as at maneuvering angles. The more “fixed” at neutral the stabilator is, the more true the TVC prediction of stability. Conceptually, we’d like a “bellcrank” more like rack and pinion steering, but with an elliptical “pinion” – with the flatter side of the ellipse engaged at neutral. A good engineer might be able to come up with something practical that behaves more like a rack and pinion than a normal bellcrank does. Or, maybe the reduced sensitivity would do the job by itself, we’d have to see.
   Slop, or play in the controls, some folks like anyway – personally I can’t see designing some “dream” control system that depends on something as crude as “slop” to function “correctly”.

Another crude solution to reduce sensitivity near neutral, is to choose a stabilator airfoil that creates very little lift at very low angles of attack – such as a blunt rounded, but not really “airfoiled”, stabilator. Anyone have a good airfoil candidate? Maybe a diamond airfoil? Point is, even our worst choice will likely be better at maneuvering angles than the bent plate stab-elevator combo.
   Or maybe the opposite approach would work? Make the stabilator as efficient as possible, as thick as the wing(%), and reduce the total stabilator sensitivity even further?

Feel
I added this after I got back. Part of stability is certainly control feel and feedback – a “feel” for neutral. Intuitively, a pivot point somewhere in front of the leading edge of the stabilator should be better. I can’t think of a good way to do that that wouldn’t be either butt ugly, structurally unsound, or both. A swept leading edge stabilator, hinged at the “point” might work to some degree. Pivoting anywhere aft of the leading edge has to be wrong.

Larry Fulwider

. . .
Then there's an idea that such a layout does not need the vast horizontal tail area of fixed-stab/moving-elevator designs. Also true. . . .
. . .

Lou –

I briefly thought about stabilator area reduction. Hearing you say it convinces me it is part of the solution. Check out my “confirming” reasoning.

Consider the parts of the pattern where you transition from a sharp corner to straight, grooved flight in some direction. As good an example as any is the first upward vertical of an inside square.
   Go back to the TVC factor of (Empennage Area / Wing Area), which should be the ratio of lifts between the two surfaces, but typically is not because of the C_L differences, which we ignore. That is, we slightly overstate TVC with a normal stabilizer setup.
   During the correction millisecond when we slightly over-control down to smooth the transition from the square corner to a vertical flight path, the normal stab-elevator combo is mildly crippled by its lower C_L, the feel of which is “normal”.
   Reducing the stabilator area from that of the combined stab-elevator would bring the stabilator (Empennage Area / Wing Area) ratio more in line with a “corrected” stab-elevator TVC. I don’t know what the correction factor would be, maybe .6, maybe .8, maybe only .99? Whatever, the math says whatever number we assume becomes the trial stabilator area reduction. That is, guessing it is .9, we have:

Stab Elevator TVC Area Ratio (corrected for CL) = ( (.9 * Empennage Area _stab-elev) / Wing Area)

Reduced Stabilator Area TVC Ratio = (Empennage Area _stabilator) / Wing Area),

Where (Empennage Area _stabilator / Empennage Area _stab-elev) = .9

Of course, that ratio is true not just during the transition, but at maneuvering angles also. That’s OK too, my guess.

The trick is finding the correct stabilator area reduction and the correct reduction in control linkage sensitivity combo to bring us “back home” to a more stabilizer-elevator feel in both maneuvers and in grooviness.

A skeptic might well ask, “So, if all that works, which I doubt, all you did was duplicate the performance of a conventional stab-elevator configuration with a lot more hassle, right? You gained nothing!”

I don’t think so, but that is a whole ‘nother thread.

Larry Fulwider

My plane, the Tapeworm, a stabilator design with an OS 40, flies quite well with a tail volume coefficient of .21 to point .23.  This is using a TVo chart that takes in wing area, stab area AND the LTo or length of tail coefficient.   One other result of this chart is to give safe location to the CG.    Points are taken at 1/4 chord of stab, stab area, and area & MAC of wing.  The LTo = LE of wing measured to 1/4 chord of stab.  I have extended the Bogart & Rhodes chart that I used for many years in Free Flight.  This chart has never lied to me even as I use it in control line. For control line I use a line .24% to the left of the Free Flight line.  I believe proper stab sizing and LE hinging to be very important. 
NOTE:  the original chart refers to TVo while common usage refers to TVC.  SLEEPY

I haven't sulked off into a corner on this one.  Some very interesting input from Lou and Larry and others.  The reduced deflection is a no brainer for sure.  I also liked the comments regarding static balance (not to sure I'd expect too much from that but the logic seems sound) and the anti-balance tabs for aft hinged surfaces to provide some centering forces.

There is likely something worth investigating in these refinements but I'm still pretty much willing to let others do so based on my past experiences and the fact that I can pretty much get all the corner I can handle from a plain vanilla stab/elevator so don't see much to be gained from the time spent experimenting (other than the search for more wisdom).

Good stuff.

Ted

A stabilator, if you get it right, has the potential of somewhat easing the powertrain chore of coping with those different drags. The potential advantage, for us bottom-feeders anyway, would be an unpiped powertrain that flies more like a piped ship. The huge change in lift requirements from level to a square means there will always also be a huge difference in drag between the two configurations. However, diminishing the difference should give some advantage, somewhere.

     I have no doubt that you might gain a minor aerodynamic advantage from a flying stab (minor, because the wing is lifting maybe 60 lbs, and the tail maybe 5, and even if the L/D of the stab is relatively bad, its still a small part of the overall induced drag). But I think that is greatly outweighed by the structural and/or weight disadvantages for a stunt plane.

     Brett

I feel like that with the reduction in stab area allowed by the stabilator, any weight difference would be negligable. 
Structural issues can be easily overcome with a little non traditional thinking. 

     I am not sure how you can reduce the stab area. The stabilator is somewhat more effective at producing control torques than a conventional stab/elevator for a given area but you wlll certainly reduce the static stability and damping. When it's not deflected it's just like any other stab,

   I would be interested in how you get the pivot and pivot bearing through the fuse with the same rigidity as a conventional stab. I don't see how, myself, traditional or otherwise

    Brett

Brett, re: your post 41,

For the flat plank stabilators on a profile, a plywood center-plate mounted across the fuselage, within the plan view of the tail and extending about an inch outboard each side, provided a solid bearing mount. A 1/8 (ID or OD, depending on model size) brass tube was glas'ed and epoxied to the bearing tube platform. The appropriate diameter MW passed through it forming the 'spreader,' which reached 1.5" to 2" into each stabilator half. That's a long enough bearing length to prevent wobble, and provided the required strength. 

For thicker, airfoiled tails, the bearing plate was faired into the stab planforms and airfoils.

Only two models needed a TE "tie" of light music wire, to prevent binding due to air drag fore/aft distortion. One was (still is, btw) a 200 sq in Sarpolus-like sheet wing 1/2A built VERY light - flying weight under 6 oz, dry. The other was an 09 powered lightweight. 3/32 spreader in 1/8 ID tube was adequate for the large area profile I mentioned, and 1/8 in 5/32 OD tube served for a couple of .35 size built-ups.

Clearance between the moving and fixed parts was very close, maintained and kept from sliding spanwise by a washer as a standoff, soldered to the spreader on the inboard side, and epoxied to it on the outboard side. I used a control horn at the fuse centerline on the built-ups, and trapped the spreader spanwise by the horn and the two pieces of bearing tube.

Simple enough stuff for exeprimenting, and a heck of a lot more solid than those wobbling-wonder 2 meter sailplane installations.

 One Full size thing has about 7 Deg. Total movement ( flying tailplane )  a jet .

Picture of another great artist with his plane.  Thanks Ole Dad.  DOC Holliday

Lou and Larry have the correct answer!

Balance it or it will hunt and other weird stuff.

You know how a tail heavy wing acts--the flying stab/elevator is a wing.

LONG control horns, lots of bell crank movement and ridged, no slop linkage.
This worked well for me on last combat design at border line tail heavy.
Estimate it to be about 15-20% aero counter balanced and mounted to a stub stabilizer for ease and strenght--dead soft balsa.
Just fly it to where you wanted it with out looking at the airplane. very stable.
Control horn lenght in the 1 1/2 to 2 inch range.
Outer hole for push rod on bell crank.
Outer holes for lead outs.
Small E Zjust hotrock handle.

I wouldn't put the pivot back more than 25% and 33% would be absolute max.
Static balance it!!!!!! it is a wing now.

Would probably help to use an airfoil that the CP does not move around much with angle of attack changes.

Just my 4cents worth.

David

Pics posted during Chemo nightmare are here.
http://stunthanger.com/smf/index.php?topic=2510.0

I wouldn't put the pivot back more than 25% and 33% would be absolute max.

     For almost any airfoil, it would have to be ahead of 25% in almost all cases. I can't over-emphasize - the stab will have to be stable on its own. You can't count on the flap stabilizing it.

      Brett