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Author Topic: Stabilator  (Read 1547 times)

Online John Watson

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Stabilator
« on: November 11, 2017, 12:29:22 PM »
I know that years of method have evolved and been perfected but I was just wondering if anyone tried the stabilator over the conventional elevator. That is the whole horizontal stabilizer to move instead of just the elevator? Just wondering.


Offline Tim Wescott

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Re: Stabilator
« Reply #1 on: November 11, 2017, 12:54:37 PM »
It's been tried.  Didn't work well, AFAIK. I've got a picture of a set of plans in my head, but can't recall a name.  You might be able to get it to work with -- well, work -- but it'd take a lot of fussing, aerodynamic knowledge, and mechanical ingenuity (I'm pretty sure you'd need a working servo tab).  I doubt that when you were done you'd have something that's as good as, much less significantly better, than what we use now.
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Online John Watson

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Re: Stabilator
« Reply #2 on: November 11, 2017, 01:36:58 PM »
I worked with Navy aircraft and most modern jets use the stabilator so I was just pondering I might try just for the heck of it but I was sure someone had tried.


Online Target

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Re: Stabilator
« Reply #3 on: November 11, 2017, 02:26:21 PM »
Stabilators have a "dead zone" around neutral that the articulated elevator doesn't have.
Stabilators are better than articulated elevators at lower airspeeds (probably why they are on the jets, for good pitch authority at take off and landing speeds).
A properly setup stabilator could use less effort to throw than an articulated elevator.
You will never have to worry about decalage (wing to stab incidence).

Combat planes have an unbalanced stabilator, if you think broadly.

Building a plane with a stabilator would allow you to have tails that are removable and of different areas to try out.

This was all gained knowledge from my extensive RC competition sailplane experience, which may not apply directly to stunt flying.
« Last Edit: November 11, 2017, 04:21:36 PM by Target »
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Online Howard Rush

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Re: Stabilator
« Reply #4 on: November 11, 2017, 03:21:07 PM »
Stabilators have a "dead zone" around neutral that the articulated elevator doesn't have.

I don't think so.  How would the stabilator know where neutral is?

The reason for them on jets, as I recall, is to avoid a transonic flow problem.  Our airplanes are subsonic and don't have that problem.  I intend to try a stabilator on a stunt plane for a different, but not necessarily good, reason.
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Online Dan McEntee

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Re: Stabilator
« Reply #5 on: November 11, 2017, 03:59:43 PM »
   Howard was a top notch c/l combat pilot in his time in the hobby and combat models used stabilators and they help with the radical types of turns that combat models make. There has been at least one published design that had a "flying stab" that was published in M.A.N. magazine and that was the Pegasus by Jean Pailet, I believe. It was a twin boom design in order to help make the tail more effective,  I think. The model was NOT a resounding success and the wing was cut out to use in another design that was also published but the name escapes me, maybe it was the Playboy, as the legend goes? I think the main issue with the flying stab is the need for a c/l stunt model to "groove" and be stable in level flight when returning from changes in angle of attack. A control line stunt model needs to be basically stable.  Flying stabs work well on R/C sailplanes because they fly in a varying speed range from quite slow to quite fast sometimes and requires different angles of attack with minimal trim changes. On a full size combat jet, they are inherently unstable by design to make them more maneuverable, have the technology advantage of computers to help the pilot stay ahead of the airplane. Watching a F-18 making a landing approach to a carrier deck, or even a runway for that matter, and the stabilators are never standing still, constantly moving and making small corrections the pilot can't possibly make. They even assist in rolling maneuvers also, and makes it possible for a jet to operate at greatly different speeds and angles of attack also. It's a matter of two completely different requirements for performance for the same part of two different airplanes.
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Offline Trostle

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Re: Stabilator
« Reply #6 on: November 11, 2017, 04:16:38 PM »
As Howard mentioned, stabilators on high performance jets are used to avoid transonic flow and control problems.  That is hardly a regime our stunt ships operate in.

Stabilators are used on some light planes which allow a smaller horizontal tail which then translates into less drag and better fuel economy, hardly a requirement for our stunt ships.

Full size and model sailplanes use them.  Because, again, the tail surfaces can be smaller and create less drag.

Stabilators are used for our CL combat ships.  Gives quick control/response which is desirable for combat.

Now, I am going to sort of repeat what Dan just posted.

Every so often, someone comes up with the idea for stabilators for our CL stunt ships.  It has been tried many times by different designers/builders with a wide variety of experience and flying ability.  We have not yet seen a stunt ship with a stabilator instead of a conventional tail/elevators ever get into the top 20 at the Nats.  There is probably at least one good reason for that if not several good reasons.  From my own experience and talking with others over the years, the problem with a stunt ship with a stabilator is that they do not "groove" and it is difficult to maintain a track through consecutive maneuvers.  That is not a requirement for combat but sort of important for a stunt ship.

Another problem with a stabilator is a structural one.  Yes, there are ways to attach it to the fuselage and to make it rigid, but rigidity and structural integrity have to be considered coupled with weight problems.

In the past when someone comes up with this idea, it is suggested to go ahead and try.  Maybe they could come up with a configuration that actually gives some decided advantage as far as increased ability to fly a rulebook pattern.  Who knows,  maybe there could be formula that would really work.  It is just that it has not yet been found.

However, before you get too involved with this, just do a search on this forum for "stabilator".  You will be surprised what you will find.

Good luck with your endeavor and let us know how it works out.

Keith

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Re: Stabilator
« Reply #7 on: November 11, 2017, 04:17:19 PM »
I don't think so.  How would the stabilator know where neutral is?


That's what the sailplane nerds all tell me. And based on my experience flying both styles, I would have to agree. This "dead zone" is actually useful for the sailplane application where minute trim changes are wanted. Plus, there is never a worry about the fixed mounted stab being at an incidence setting that you may not want. That alone is huge, because with the stab neutral and a fixed CG, you only have one perfect trim speed, and the flying speed envelope is huge.
Allegedly, an articulated elevator on a fixed stab is more efficient and also more effective, because you are changing from a zero camber profile to a cambered profile, and that is much less draggy than tilting the whole profile (at small deflections).

The thing that is hugely different is that the RN that the RC sailplanes operate in are a far wider range than the C/L stunt plane does. Fortunately, the tail booms are so long that the volume for pitch is also large, otherwise slow speed flight would be really dicey. It's bad enough with the V tailed F3B and F3F planes that I fly. Built more purpose oriented for high speed than low speed handling, they can be a handful and much less friendly than their cross tailed cousins, simply because they have less pitch volume due to inappropriately small tail panels (for low airspeed).

I won't engage in a theoretical design argument, but since I have real world experience in that topic, I feel competent to share what the perceived outcome was, even though it is in another aspect of modeling, and even though I possibly won't explain how the result is arrived at correctly aerodynamically. All that being said, the real world effect was noticeable. The stabilator equipped sailplane of the same model felt a little less pitch sensitive around neutral (trim) than the moving elevator version of the same model.

I think that Stunt planes have a much easier aerodynamic job, since their airspeed is a much smaller envelope. With sailplanes having to "stab the nose in" to a 3" dot in the grass at slowest possible speeds in a contest sailplane event to score points, the pitch authority NEEDS to be there. The Stabilator at a good deflection FEELS more responsive in this low airspeed environment than a fixed stab with moving elevator does. Just my observation.

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Offline Traian Dorin Morosanu

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Re: Stabilator
« Reply #8 on: November 11, 2017, 07:47:13 PM »
Here we go. I have built both in my glides and it is obvious that when you need the hard cornering in flight the full flying stabilizor is best.
Yes it works in combat planes and is good and can work well in stunt too. The critical thing is the pivot point. If at the CP is unstable and will upset the plane, if at the LE it requires a lot of force to move. I would test in tunel and push the pivot point forward till is stable with no flutter. After that use that point or a little in front of it for pivot point.
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Online Howard Rush

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Re: Stabilator
« Reply #9 on: November 11, 2017, 08:29:57 PM »
Stabilators are used on some light planes which allow a smaller horizontal tail which then translates into less drag and better fuel economy, hardly a requirement for our stunt ships.

A couple of us proposed a stabilator for the airplane that became the 787.  It had an elevator that remained faired until max travel, where it would help out.  We even came up with a mechanical mechanism to do it, our chief engineer being a cautious man who was skeptical about electronics.  The L-1011 had something similar.

We have not yet seen a stunt ship with a stabilator instead of a conventional tail/elevators ever get into the top 20 at the Nats.  There is probably at least one good reason for that if not several good reasons.


I may rediscover these reasons!  For that reason, I don't intend to invest much paint in the prototype.
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Online Howard Rush

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Re: Stabilator
« Reply #10 on: November 11, 2017, 08:59:08 PM »
That's what the sailplane nerds all tell me.

All?  Among them is one of the world's most renown aerodynamicists.   You are no doubt observing something real, but I'll bet the difference is caused by something other than an aerodynamic deadzone in the single-surface stabilator.

Plus, there is never a worry about the fixed mounted stab being at an incidence setting that you may not want.

Yep.

Allegedly, an articulated elevator on a fixed stab is more efficient and also more effective, because you are changing from a zero camber profile to a cambered profile, and that is much less draggy than tilting the whole profile (at small deflections).

I wouldn't allege that, unless each side of the stabilator rotates next to the fuselage and leaves a gap when it's deflected.

You are correct that sailplanes have a different set of design requirements than stunt planes.  Although "Stunt planes have a much easier aerodynamic job", it's still kinda challenging. 

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Online Brett Buck

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Re: Stabilator
« Reply #11 on: November 12, 2017, 10:19:55 AM »

You are correct that sailplanes have a different set of design requirements than stunt planes.  Although "Stunt planes have a much easier aerodynamic job", it's still kinda challenging.

     Everyone seems to want to underestimate how difficult stunt can be, and how demanding the requirements are.

      Brett

Online Gerald Arana

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Re: Stabilator
« Reply #12 on: November 12, 2017, 02:56:35 PM »


 With sailplanes having to "stab the nose in" to a 3" dot in the grass at slowest possible speeds in a contest sailplane event to score points,

[/quote]

And therein lays the reason I (well, one of them anyway) quit flying glider competitions. The dreaded "Dork" landing.  What the 'L is the point of that? Have you ever seen a full scale glider "dork" land? Neither have I.

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Offline Steve Helmick

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Re: Stabilator
« Reply #13 on: November 12, 2017, 04:55:03 PM »
Will the "Dork Landing" be the next big rule change for F2B? Mmmmmaybe.  VD~ Steve
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Online Dan McEntee

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Re: Stabilator
« Reply #14 on: November 12, 2017, 06:15:50 PM »

 With sailplanes having to "stab the nose in" to a 3" dot in the grass at slowest possible speeds in a contest sailplane event to score points,



And therein lays the reason I (well, one of them anyway) quit flying glider competitions. The dreaded "Dork" landing.  What the 'L is the point of that? Have you ever seen a full scale glider "dork" land? Neither have I.

Jerry
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   I thought lawn dart landings got eliminated for safety reasons, and that is why everyone went to some sort of aggressive nose skid? I can't remember. I had already eased into C/L stunt by that time. Still have some of my sailplanes and hope to get back to it in at least a small way some day. Itwas fun!
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Re: Stabilator
« Reply #15 on: November 12, 2017, 06:27:49 PM »
Skegs are only allowed in USA thermal duration.
Fai doesn't allow them.
So, no skegs in f3j (thermal duration soaring, two man towed mono line launch), f3b (multi-task- duration, dustance, speed, winch launched on mono line), f3f (slope racing for timed runs).

The problem is if you fly American Thermal Duration and do use the allowed skeg, and also fly F3J, where the skegs are not allowed,  it messes you up on precision landing.
F3f is where planes are normally very heavy, and no skeg is wanted. Same for distance and speed in f3b, the planes are heavily ballasted, you don't want a skeg anyway. So only f3j and the duration task of f3b use the "dork" landings. And dorking isn't required, but it happens to be the most effective way to land on a spot at an exact moment.

As far as safety goes, a proper dork landing is likely safer than sliding it in, since the plane is less likely to hit someone standing near by. Wet grass in early morning events is notoriously slippery and that's when unwary pilots hit their own shins sliding through. Little to no headwind helps to cause this also.

Back to full flying surfaces on stunt planes.
« Last Edit: November 12, 2017, 06:54:56 PM by Target »
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Online Paul Smith

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Re: Stabilator
« Reply #16 on: November 12, 2017, 07:43:50 PM »
If you build a model airplane that goes over 600 MPH you better have a hydraulically powered stabilator.  Up until then a hinged, cable controlled flipper will do the job.
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Re: Stabilator
« Reply #17 on: November 12, 2017, 08:00:06 PM »
Target,
You might want to get the article on ships call Nuts & Bolts. As I recall theses ships had full flying 50/50 stabilators. In the article as I recall it states that the ships are touchy to get use to. It seems that changing the split to something between 15 - 20% front 85 - 80% rear makes it better. This is close to the arrangement on the combat ships. The trick is to balance the stabilator deflection with the flap movement.

Best,      DennisT

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Re: Stabilator
« Reply #18 on: November 12, 2017, 08:00:39 PM »
Actually the RC sailplane Dynamic Soaring speed record is 513 mph currently, and they use standard linkages, Paul.
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Re: Stabilator
« Reply #19 on: November 12, 2017, 08:02:24 PM »
Very interesting Dennis, I will do a search. thanks!
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Online Brett Buck

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Re: Stabilator
« Reply #20 on: November 12, 2017, 11:52:20 PM »

You might want to get the article on ships call Nuts & Bolts. As I recall theses ships had full flying 50/50 stabilators. In the article as I recall it states that the ships are touchy to get use to. It seems that changing the split to something between 15 - 20% front 85 - 80% rear makes it better. This is close to the arrangement on the combat ships. The trick is to balance the stabilator deflection with the flap movement.

      Guys, I would strongly suggest reading the many previous threads on this topic. In particular, for stunt (after everyone and their dog has tried it) you have to pivot the stab at less than 25% of the MGC so it is stable by itself - you cannot count on the flap stabilizing it and you cannot turn it into "power steering" by pivoting it aft of the CP. It will require about half the movement of conventional elevator.

      Brett

Offline Traian Dorin Morosanu

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Re: Stabilator
« Reply #21 on: November 13, 2017, 07:40:56 AM »
When we designed the Evolution3.1 DLG we tried both types pf stabilizer one hinged and the other full flying Stabilizer. What we found out is that both performed great except for the push over at the top of the launch where at top of climb you needed to "park" the glider on glide slope (hard push over from near vertical) the full flying had the edge by quite a bit. The rest of the flight was breaking even maybe a little less drag overall.
How does this translate for stunt? Lops rounds will do just fine as any other hinged system. When we corner there is a lot of drag created in conjunction with lift to get the model to turn, and subsequently you have to recover the lost speed to get to next way point and to be able to do it again, because the full flying will create less drag with more authority than the hinged counterpart it will hold an edge in corners.
I saw the argument of how come there are no full lying stabs in the top fliers and the answer is simple, first full flying stab is harder to make than the hinged stab it requires some research on best location for pivot point and it requires good bearing support for smooth operation etc and second reason is because the guy next to you is not using it that must mean is not good.
Yes make horizontals big as a shovel to keep up with the demand, most copy what the the top guys are doing who are copying what the predecessor and of course you can track it down to the classic first flaps designed stunters like Paternmaster or Nobler. From that time to today there was not much research or thinking out of the box to at least try alternatives.
Gliders use it because they are better. Most glider manufacturers who do not do full flying stabilizer because it is more complex in some cases and because they want a more robust system. In DLG there was the danger of having the stab slip out during launch and also was complicated to produce due to extra hardware but overall it is better. When you throw a glider to over 230ft (some launch "throw" in the neighborhood of 300ft) and the model departs at 80+mi per hour you want robust system.
I am glad that this discussion came about because I might retrofit a REvolution to try full flying stab on it.  But that will come later. Now I want to get it done and try it as is. Will work on refinements and experiments later.
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Re: Stabilator
« Reply #22 on: November 13, 2017, 07:48:56 AM »
Oh come on, if no one has done it yet successfully, it can't be any good, right?
This is the motto of innovation.

Sarcastic rant off.

R,
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Online Brett Buck

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Re: Stabilator
« Reply #23 on: November 13, 2017, 09:39:26 AM »
Oh come on, if no one has done it yet successfully, it can't be any good, right?
This is the motto of innovation.

Sarcastic rant off.

   No, but when various highly competent people try it time after time, and either can't make it work or don't find any advantage, you might want to at least take note of it. Just about everyone has looked at or tried it at one point or another. So far, I have had no one counter or address the two issues that cropped up every time - you can't use it as "power steering" like they almost all start, and, the mechanics of it are both weak and heavy.

     The "power steering" is a classic stability issue that is solved by pivoting it ahead of the CP/25% mark, and then it will at least be acceptable. The "weak but heavy" part was completely unworkable in the first wave in the early-mid 70's. When carbon fiber became available, it became at least conceivable, but so far, no one has managed to come up with a sufficiently stiff and light axle at the same time.

    If someone it dead-set on it, I would suggest starting with a carbon-fiber tube axle sized to slip-fit into a 3/4" thin-wall aluminum tube, and use that glued over the carbon as the bearing for the shaft. In the airplane, maybe short brass tubes (maybe 3/16" long) on either side as the bearing, embedded in aircraft plywood that is then glued to the fuse sides as a doubler. Leave oil holes in the brass to lube it. Put the pivot at 22% of the MGC, make the size the same as you would otherwise (24-28% of the wing). I would strongly recommend making the aspect ratio as low as you can stand, 4:1 or thereabouts, just to reduce the loads. The short bearings and the aspect ratio are intended to reduce the bending loads on the axle and to reduce the binding in the bearings when it does bend.

     So far I can't see how this doesn't end up ~3 ounces heavier than a conventional system, meaning it will cost you a total of about 6-9 ounces total once you balance it, but maybe someone can come up with something better.

      Brett

   

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Re: Stabilator
« Reply #24 on: November 13, 2017, 10:04:52 AM »
Yes make horizontals big as a shovel to keep up with the demand, most copy what the the top guys are doing who are copying what the predecessor and of course you can track it down to the classic first flaps designed stunters like Paternmaster or Nobler. From that time to today there was not much research or thinking out of the box to at least try alternatives.

   Oh, good Lord! The Patternmaster came along in the early-mid 70s. And, they were only marginally successful and not very influential despite the delusional claims and cult worship of the East coast mob.  There are still a bunch of idiots running around claiming this and that  airplanes (Impact, Trivial Pursuit/Star Gazer, and Infinity in particular) are "modified Patternmasters" despite none of us (Paul/Ted/Brett) having ever seen the plans for one until we had been flying the things for a decade.

      There were literally *thousands* of original designs exploring the extremes between 1951 and 1975, solving every design flaw of the Nobler (most of which were understood in the 50's). This includes multiple attempts at flying stabilizers. Like this one:

https://stunthanger.com/smf/stunt-design/flying-stabs-and-stabalators-revisited-)/msg112740/#msg112740

   flown at the 76 NATs.

    Brett

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Re: Stabilator
« Reply #25 on: November 13, 2017, 12:32:26 PM »
Target,
Seems the structural issue could be addressed using a twin boom design. This would allow the bearings to split the load and also keep the surface from twisting relative to the wing. I like the idea of the carbon spar although with the twin boom I think you could get away with a 1/4" diameter rod with some ball bearings on the ends (likely can find some helicopter or car bearings that would work or call Boca Bearings). I have done the twin booms and for a full size stunter (40 and above) I would use the twin bellcrank approach and drive the stabilator (and flaps) from both sides (search on Jack Sheeks twin boom models). I would use the slider adjustable horns making sure you had access to make the adjustments.

Best,    DennisT

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Re: Stabilator
« Reply #26 on: November 13, 2017, 01:05:14 PM »
Actually the RC sailplane Dynamic Soaring speed record is 513 mph currently, and they use standard linkages, Paul.

Obviously they haven't hit the transonic point yet.  Planes like the P-38 and Learjet hit it with a bang.  Of course blowing the tail off a model isn't likely to hurt anybody.
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Re: Stabilator
« Reply #27 on: November 13, 2017, 02:25:18 PM »
AS some have said. many problems with getting a fully moving Stabilator, and  very good designers have tried,  It seems to me  , after  many many tests  , that instead of increasing the elevator area, what is working better for  C/L stunt is  increasing the STAB area, but if I were to try this again a twin boom would need to be looked at closer .

Randy

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Re: Stabilator
« Reply #28 on: November 13, 2017, 03:09:23 PM »
Rnady who tested that? I would love to hear from those who actually tested something. I would like to hear what problems they encountered how they solved it. I personalty have not seen one test model with full flying stab in the precision aerobatics community.  I have not seen it at the NATS and I have not seen it at the local clubs or local contest as well. If we say many have tried those "many" should come forward and join the conversation, post some pictures, share ideas etc.
Else lets talk of RC glider spot landings or stuff like who mad the first flapped model that helps absolutely no one and it was not the point of this thread.

I am not worried in flex in the horizontal. I have seen some models with open bay stabs that where flexing 1/4-3/8 and flew fine. on the other side if the wing flexes that much you have a big problem on your hands.

I made a paper drawing for a full flying stab.
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Re: Stabilator
« Reply #29 on: November 13, 2017, 03:18:44 PM »
The issue I see with a "Flying Stab" is it isn't an airfoil and won't respond as one. Looks like drag is it's biggest downside.

Stab with the elevator, when the elevator is deflected, lift happens because an airfoil is created.

How correct or incorrect am I?

CB

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Online Lauri Malila

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Re: Stabilator
« Reply #30 on: November 13, 2017, 03:28:42 PM »
Why just a 5 mm carbon joiner? Stabs are routinely 1/2" or more thick, so the joiner should be as thick as possible. If it is, say 1/2" thin walled tube, you can integrate some sort of an I-beam inside it. Stiffness über alles!
Bigger diameter also means more bearing surface thus less play.
As bearing, I think all you need is some thin walled, polished dural rings rubbing against slippery plastic bushes, from Kel-f, Tufnol or such.
If you can observe flex in a flying model, it has a big problem. Especially if stab flexes. L

Offline Traian Dorin Morosanu

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Re: Stabilator
« Reply #31 on: November 13, 2017, 03:48:11 PM »
Lauri look here for some reference http://www.bphobbies.com/view.asp?id=V641945 you can see here how fast weight goes up with diameter. The reason for 5mm is because is strong enough for what we do IMHO and as you can see larger parts come with a big weight penalty. The smallest strong enough wil be the lighter you can do.  The bushing is Acetal AKA Delrin which is a specialized plastic material for bushings. The ss tube is just to make a nice bearing surface to go against the Plastic bushing and it will last about forever.
I do like the idea of an I-beam ish stab with a tube instead of an I beam. Check this out http://www.thekiteshoppe.com/products/Sky-Shark-Zero-Air-32.5%22-Tapered-Tubes.html
this would make a nice center spar and you do I beam like construction on the outside. That will be light and stiff.
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Happiness is the harmony between what you think and what you do. Mahatma Gandhi

Offline Traian Dorin Morosanu

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Re: Stabilator
« Reply #32 on: November 13, 2017, 03:56:41 PM »
The issue I see with a "Flying Stab" is it isn't an airfoil and won't respond as one. Looks like drag is it's biggest downside.

Stab with the elevator, when the elevator is deflected, lift happens because an airfoil is created.

How correct or incorrect am I?

CB

Well the full flying stab uses less deflection and it has less drag. It was proven in CFD simulation for glider designs. If you look at any wing airfoil polars there is a point where more angle of attack produces less lift. That is something that should be built in the design so it is not exceeded during flight or else yes it becomes a draggy air brake.
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Online Dan McEntee

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Re: Stabilator
« Reply #33 on: November 13, 2017, 05:44:56 PM »
     One thing you have to do is quit comparing sailplane control movement  with C/L stunt model control movement, it's apples and oranges. They couldn't be more different. Between the difference in aspect rations, moment arms, there is the fact that a stunt model has to deal with all the forces a prop generates and presents to the issue. It's about a whole lot more than just "turn".  You have to start the turn and stop the turn and then the airplane needs to track straight afterwards. A sailplane NEVER flies like that.  Even in a turn for an FAI type speed run, you don't want to turn that tight because you can bleed off too much speed. You would have to have a control system that is completely with out ANY kind of slop or excess play anywhere for flying stunt. You could start out with one that was, but would it stay that way past a dozen flights??  With the advancement of technology, materials, and computer modeling that we have now. if it was desirable and workable, it would have been done and you would see it at the NATS and world champs levels by now. I'll just sit back and watch for the results while some one else tries to prove the point.
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Online Howard Rush

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Re: Stabilator
« Reply #34 on: November 13, 2017, 09:45:18 PM »
How correct or incorrect am I?

Entirely
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Online Howard Rush

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Re: Stabilator
« Reply #35 on: November 13, 2017, 10:32:04 PM »
My current stunt plane works OK with a stabilizer and elevator.  In maneuvers, though, it operates at a weird angle of attack.  In an inside loop, for example, the relative wind direction blowing on the stab is shown by the red line on the picture below.  It's gotta have a bunch of separated flow, yet it still has enough lift to rotate the airplane.  Now suppose I make an airplane for which this angle of attack is even greater.  Would a stabilator be an advantage?  It could operate at an angle of attack in its linear range.
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Online Howard Rush

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Re: Stabilator
« Reply #36 on: November 13, 2017, 10:36:32 PM »
Lauri look here for some reference http://www.bphobbies.com/view.asp?id=V641945 you can see here how fast weight goes up with diameter.

For constant bending strength or constant stiffness, weight goes down with diameter.
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Online Howard Rush

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Re: Stabilator
« Reply #37 on: November 13, 2017, 10:53:41 PM »
Seems the structural issue could be addressed using a twin boom design. This would allow the bearings to split the load and also keep the surface from twisting relative to the wing.

Sure.  Also, that way you could make the bearings lighter because you wouldn't have bending on the pivot.

Although Brett has superstitions about this issue, one bellcrank in one boom would suffice (assume a carbon O-beam stabilator spar.)  Would you want to put the bellcrank at the inside boom and minimize the swath the leadouts sweep through the spar or put in at the outside boom and minimize the leadout angle at the wing tip?


(edited to clarify that I think Dennis has a good idea)
« Last Edit: November 14, 2017, 12:07:39 AM by Howard Rush »
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Online Brett Buck

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Re: Stabilator
« Reply #38 on: November 13, 2017, 11:34:15 PM »
Sure.  That way you could make the bearings lighter because you wouldn't have bending on the pivot.

Although Brett has superstitions about this issue, one bellcrank in one boom would suffice (assume a carbon O-beam stabilator spar.) \

   Doing it that way invokes evil spirits.

     Brett

Offline Traian Dorin Morosanu

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Re: Stabilator
« Reply #39 on: November 14, 2017, 08:53:20 AM »
Without the evil spirits being invoked Howard there is a easy way to demonstrate that. A little camera and a yarn thread taped on the wing somewhere.
Here is an idea with a longer thread or in another position you could possibly investigate this.
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Online Brett Buck

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Re: Stabilator
« Reply #40 on: November 14, 2017, 10:50:31 AM »
Rnady who tested that? I would love to hear from those who actually tested something. I would like to hear what problems they encountered how they solved it. I personalty have not seen one test model with full flying stab in the precision aerobatics community.  I have not seen it at the NATS and I have not seen it at the local clubs or local contest as well. If we say many have tried those "many" should come forward and join the conversation, post some pictures, share ideas etc.

     Go here and to SSW and type in "stabilator". No one is going to do your research for you or provide you custom-made answers to questions you can easily answer elsewhere and have been answered many times before. Like the thread I posted earlier.

    You have never seen one at a NATs because only a few ever made it that far, and were not pursued.

        Brett

Online Brett Buck

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Re: Stabilator
« Reply #41 on: November 14, 2017, 10:51:38 AM »
Entirely
   
   Magnificent.

      Brett

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Re: Stabilator
« Reply #42 on: November 14, 2017, 11:04:18 AM »

Seems the structural issue could be addressed using a twin boom design. This would allow the bearings to split the load and also keep the surface from twisting relative to the wing.

   Better make the booms pretty beefy, because for all intents and purposes, you are cantilevering them from the wing (since they aren't connected by a stabilizer as in a conventional tail) and now, any consequential distortion in any direction binds up the stabilator bearings at each end. It also has to tolerate the misalignment of the bearings due to the wing flexing in dihedral without binding. You almost want a spherical bearing, but you might get away with just making it a bit sloppy (since unlike the conventional fuselage, you can tolerate it).

      Brett

Offline Igor Burger

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Re: Stabilator
« Reply #43 on: November 14, 2017, 11:24:16 AM »
My current stunt plane works OK with a stabilizer and elevator.  In maneuvers, though, it operates at a weird angle of attack.  In an inside loop, for example, the relative wind direction blowing on the stab is shown by the red line on the picture below.  It's gotta have a bunch of separated flow, yet it still has enough lift to rotate the airplane.  Now suppose I make an airplane for which this angle of attack is even greater.  Would a stabilator be an advantage?  It could operate at an angle of attack in its linear range.

Looks like thread of provocateurs  :## . Ok, so I will repeat what was already written several times in past on old threads. May be it looks like we copy Nobler from its first day, we never use brain and we hate inovations, but when I use little bit calculator I come to this:

That Howard's angle is approximately 15 degrees (I think I have it somewhere in SN article some years ago if I remember well). Lift coefficient to create tail moment for contiguous turn is approximately 0.4 or 0.5. That is close to max lift of thin airfoil with 0 camber. So for first look it is enough but there are 2 buts:

1/ you must accelerate mases before corner, means you must overcome moment of inertia which is relatively high (battery, motor - all balanced by tail of the same moment but longer) so 0.5 is probably not enough - classic tail with stab and elevator can make lift coefficient up to 1.5 if elevator is 1/2 to 1/3 of tail, deflected to 30 degrees (standard tail). And that is 3 x more.

2/ since that AoA angle is 16 degrees, plus we need 0,5 lift coefficient, flat tail will need 6 or 7 degrees AoA on top of that. Means approximately 22 or 23 degrees. That is angle over critical AoA so it will have lot of problems accelerate it to the corner -> see point 1/ ...

3/ Yes that 15 deg AoA can cause separation on LE but it can happen when model already entered radius (we need only 0.5 lift coefficient) and it is on high pressure side so it can be only small buble, not complete separtion - however IF it happens, it can onlly help - to prevent overshooting - the drag will make little stabilizing negative feedback


Offline Fredvon4

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Re: Stabilator
« Reply #44 on: November 14, 2017, 12:13:45 PM »
I find it amazing, with my very meager education, that I can actually read through all the crud and understand these dynamic concepts

Is not the compromise between the two Tail methods all the designs with an Elevator with forward projections outside the stab that give the power steering effect?....old brain forgets what that type of elevator was called

I do remember reading years ago, as the replacement AF and Navy jets started having the flying stabilator, about the massive computer augmentation necessary to control AC stability in all the various AoA and speeds---- including limiting Gs to the pilot as the craft could easily out perform a humans ability to withstand the forces

based on that reading, I think I see the limitation of a two wire and BC system as too restrictive to exploit any benefit form a stabilization
RC systems (computer controlled) now have set points, slew rates, and a host of other exponential  adjustments
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Online Howard Rush

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Re: Stabilator
« Reply #45 on: November 14, 2017, 01:53:18 PM »
That Howard's angle is approximately 15 degrees (I think I have it somewhere in SN article some years ago if I remember well). Lift coefficient to create tail moment for contiguous turn is approximately 0.4 or 0.5. That is close to max lift of thin airfoil with 0 camber. So for first look it is enough but there are 2 buts:

Your SN article is one of the best technical articles ever written about stunt and the only stunt article I remember reading that mentioned pitching moment due to pitch rate. 

Why would one use a thin airfoil?  Thicker would be lighter and have more Clmax.  Besides, I have an attic full of 16.5%-thick combat wings that are about the right size.

1/ you must accelerate mases before corner, means you must overcome moment of inertia which is relatively high

Yes, I think that is a difficulty.  You could make the tail bigger just for that acceleration, or you could use an antibalance tab as Tim suggests, but that might make other problems.

2/ since that AoA angle is 16 degrees, plus we need 0,5 lift coefficient, flat tail will need 6 or 7 degrees AoA on top of that. Means approximately 22 or 23 degrees. That is angle over critical AoA so it will have lot of problems accelerate it to the corner...

I'm not sure of your point, but the nice thing about a stabilator is that you can rotate it as much as you need to rotate it relative to the airflow.  The fixed stabilizer is constrained.

3/ Yes that 15 deg AoA can cause separation on LE but it can happen when model already entered radius (we need only 0.5 lift coefficient) and it is on high pressure side so it can be only small buble, not complete separtion...

I'm thinking of making an airplane that would have more tail angle of attack in a maneuver than usual.  A stabilator could easily have more lift coefficient in a maneuver than a conventional stabilizer and elevator.  Also, a stabilator would be operating on the linear part of its lift curve.  The stabilizer and elevator at that adverse angle of attack with separated flow would surely be operating in a range with reduced lift curve slope, hence providing less stability.   An easier solution, though, might be to make a bigger tail.

So maybe a longer tail would need to be bigger.  Take that, "tail volume" people!

I would like to see lift data on a stabilizer and elevator at all angles of attack.  Can one trust Xfoil or Javafoil to give good data at perverse angles of attack?
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Offline RandySmith

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Re: Stabilator
« Reply #46 on: November 14, 2017, 10:04:22 PM »
Rnady who tested that? I would love to hear from those who actually tested something. I would like to hear what problems they encountered how they solved it. I personalty have not seen one test model with full flying stab in the precision aerobatics community.  I have not seen it at the NATS and I have not seen it at the local clubs or local contest as well. If we say many have tried those "many" should come forward and join the conversation, post some pictures, share ideas etc.
Else lets talk of RC glider spot landings or stuff like who mad the first flapped model that helps absolutely no one and it was not the point of this thread.

I am not worried in flex in the horizontal. I have seen some models with open bay stabs that where flexing 1/4-3/8 and flew fine. on the other side if the wing flexes that much you have a big problem on your hands.

I made a paper drawing for a full flying stab.

Quite a number of people have tested them,  do a search. I tested them back in the early 80s, they work, but have problems, I tested them on a stunt ship and on slow combat type planes, I use to fly Combat with stabilators, and thought they might work better than conventional setups on stunt ships, mine were more touchy, and  did not  groove well, I never did get the hunting out of it.  I suggest  you build one and tell us  what you think .   I also think they wear faster than a conventional Stab Elev. setup, and need to have some serious stabilizing bushings in order to not run into more problems other than hunting, like  flutter as the  wear

Regads
Randy

Offline Igor Burger

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Re: Stabilator
« Reply #47 on: November 15, 2017, 01:16:39 AM »
Your SN article is one of the best technical articles ever written about stunt and the only stunt article I remember reading that mentioned pitching moment due to pitch rate. 

Why would one use a thin airfoil?  Thicker would be lighter and have more Clmax.

Thanks, I mentioned it especially to show that we DID some reserch and analyses after first flight of Nobler :-))

And yet, I will mention another great analyze in SN article - about tails by David F. - there he wrote he had good results with thin tail. So that is why. However also thicker tail will not give much better numbers. Deflected elevator has simply more muscles on begin on corner.
 
Yes, I think that is a difficulty.  You could make the tail bigger just for that acceleration, or you could use an antibalance tab as Tim suggests, but that might make other problems.

Right it will need larger tail area, but it will make even more mechanical problems with pivot.


I'm not sure of your point, but the nice thing about a stabilator is that you can rotate it as much as you need to rotate it relative to the airflow.

OK, so numbers:

Classic model like my Max has tail AoA angle in corner 16 deg and must make lift which can be reached at 6 deg AoA, that makes 22 degrees. We want make corner from straight flight by instant deflection of tail. So the tail is deflected to 22 deg from straight flight. But instead of making large lift, it is stalled and gives only 0.1 instead of necessary 0.5

If you compare to classic tail with stab and elevator, you can see that it has lot of lift close 0 AoA after instant deflection and aproximately that necessary 0.5 at 15 degrees.

The maximum of lift apears little later than 0 AoA, but we cannot do instant deflection anyway, so it is probably all the time without separation on low pressure side anyway.

Funny is moment polar, you can see that high moment is during entering radius, but when it already enters steady radius (means 15 deg AoA), moment goes down, it is clear proof of that buble on LE and thus also extra drag hich will make drag force in direction of air stream - means it will stop angular acceleration, so it makes imagination of very abrupt entry to the corner and prevents overstearing.

And yes, we are not in its linear segment, we are on opposite slope, but just that negative slope makes nice negative feedback, it is what we need for good controll of stunt model.

So maybe a longer tail would need to be bigger.  Take that, "tail volume" people!

Or opposite - short tail (like mentioned combat) has much smaller AoA in turn, so those 22 degrees from my example will go down and it can work much better, even with micro tail volume :- ))

This whole is for larger analyze, because there looks to be some optimal tail length, but I think I also mentioned it in that article, I must find it somewhere and repost ... or write new if it is not clear there.

Offline EddyR

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Re: Stabilator
« Reply #48 on: November 15, 2017, 08:17:18 AM »
  I did not read all these post so if this has been covered,sorry.
 In a back issue of SN there is a construction article about the Father of I/Beam planes and there is a a history also. He used a Fox 59 in his plane with a full flying stab.
He won many contest back in the 1950's with his design . I will look it up and post a picture here. Was it called " Nuts & Bolts"
Ed
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Online Brett Buck

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Re: Stabilator
« Reply #49 on: November 15, 2017, 10:30:43 AM »
My current stunt plane works OK with a stabilizer and elevator.  In maneuvers, though, it operates at a weird angle of attack.  In an inside loop, for example, the relative wind direction blowing on the stab is shown by the red line on the picture below.  It's gotta have a bunch of separated flow, yet it still has enough lift to rotate the airplane.  Now suppose I make an airplane for which this angle of attack is even greater.  Would a stabilator be an advantage?  It could operate at an angle of attack in its linear range.

      Yes, that is the supposed advantage - not so much the Cl, but the fact that the curve doesn't have any wild discontinuities in it due to separation.  People talk about the drag but I don't care about that very much. So I might buy that if you are slow enough on entry to avoid Igor's problem probably does help the control response linearity .On the other hand, non-linear damping is the same in either case. But the problem is made worse by the fact that the extra weight that you can't avoid is all in the worse place possible. Normally I don't care about this, but we are talking a fair increase in the moment of inertia. Many people spend a lot of time looking at aerodynamic issues but don't pay attention to plain old dynamics.

    Take Dorin's 3/16" axle, and it just doesn't matter because it's so flexible it becomes a random number generator - both torsion and dihedral. Even my 3/4" tube is probably not enough. You heard my stabilizer when it cracked - you can tell how important I think that stab rigidity is.

     Brett


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