Flying Stab with Coupled Surfaces

There was a design in Pampa that showed a flying stab, or stabilator, and the notes on the drawing said that this may be instable. Meaning that it would possibly lock up or lock down from air pressure on the surface when the stabilator was deflected from neutral.
On a stabilator part of the surface is in front of the hinge point helping to push the other side behind the hinge point in the direction of the deflection. Too much surface in front of the hinge point causes the surface to stay deflected and to continue to deflect when push from the pushrod is released.
Normal stabs and elevators have all of the deflected surface behing the hinge point and the pressure on the surface causes it to move back to neutral when the push from the pusrod is released.
But in thinking about the stabilator, I forgot about the flaps, which would help to push the surface back to neutral besides the portion of the stabilator behing the hinge point. I'm probably not stating this very well, but when you couple the flaps and the stabilator together doesn't the flap area act as the back side of the stabilator?

P.S. The holy roman empire was neither holy nor roman - ok talk amongst yourselves

The flaps would probably work, but I just wouldn't trust coupling the surfaces to get them to work properly. If the stab is overbalanced, simply build it with less counterbalance, so it is self centering, to a degree. Having the stab overbalanced would just inviting flutter.

If I was experimenting with a prototype stabilator I'd make the front of the stab square and tape on counterbalances of different sizes to find the best size. you can calculate the moments from Bill Netzeband's articles. He has a graph and some equations and nomograms for calculating the torque on the hinge and the pushrod force. they seem to work reasonably well, and you can use the same procedure to calculate for a stabilator.

I believe it was Bob Emmett who used to bring in a demo fuse with a control system hooked up to a control handle labeled "Touch Me" to the Puyallup Expo for many years (when nearly everything else there warned "Don't touch"). It had a one piece flying stab.

His experience with it was - "didn't work".

Hi

The trick with fully flying tailplanes it to hinge them on the aerodynamic centre. That way, there is almost no load on the
control system. Then they will not lock, up, down or centred.
The reason this works is that for symetrical sections, the lift
centre is very stable (remains in the same place) regardless of
the angle of attack of the surface. The lift centre is about 25%
of the mean aerodynamic chord. This can be easily found on
simple tapered wing plan forms. A good rule of thumb is to
have 25% of the area ahead of the pivot or hing point.

Flying tailplanes are employed on soaring gliders a lot to avoid
the camber effect of elevators. In a stab/elevator arrangement
where a high lift camber wing is used, the tailplane load is
opposite to the direction of camber. That sound crazy but the way
it works is this. You apply up trim. That initially causes a down
load on the tail and rotates the wing to a higher angle of attack
(AOA). The lift centre moves forward, perhaps ahead of CG. Now lift
and weight form a moment couple that further lifts the nose. Nose up
pitch continues untill the tailplane achieves sufficient positive
incidence and lift to reballance this force moment.

A negative geometric trim on the tailplane has eventually lead to
a posative tailplane AOA and loading by the time equilibrium is
established again. The load would then be opposed the the direction
of camber for the tailplane leading to higher than optimum profile
drag.

As soarers spend the majority of their time in stable filght at various trims and speeds, min sink or max distance (Cl/Cd),
a symetrical flying tailplane is a lower profile drag solution
for the majority of the flying time.

A stunter is another case entirely. To iniate a turn, the
tailplane must overcome the enertia of the plane to get it
rotating. To do that quickly, the tailplane needs to generate
high loads. A cambered surface is capable of higher loads than
a symetrical surface. The usual stab elevator arrangement is an
approximation of a cambered surface and therefore can generate
the higher load at lower drag to get the plane turning. Once the
plane is turning however the tailplane is not generating much force
over all especially if the wing is unflapped. If the wing is
flapped the overall tailplane load may well become opposed to the
camber for the same reasons as the soarer but that is of less
importance to us. In this later condition, stab and elevator
loads are opposed and profile drag is higher than optimum.

A fully flying tailplane on a RC thermal soarer requires about
5 degrees up deflection and around 15 to 20 degrees down to be
capable of loops and inverted flight. I suspect the control deflection for CL would be significently less than that for
elevators. I expect a flying tail would not achieve as snappy
a turn as the conventional stab elevator of the same dimensions.

>But in thinking about the stabilator, I forgot about the
>flaps, which would help to push the surface back to neutral
>besides the portion of the stabilator behing the hinge
>point. I'm probably not stating this very well, but when you
>couple the flaps and the stabilator together doesn't the
>flap area act as the back side of the stabilator?

So you get a form of power steering. Sort of. But the short answer, for everyone who has had this idea (and it comes up avery 6 months or so), is that it doesn't work. The issue, in a nutshell, seems to be: the torque from the stab goes up a lot faster than the opposing torque from the flap, and you can never get enough slop out of the system to prevent flutter/hunting. There have been a lot of them built that way as experiements, and they always ended up junked, shelved, or rebuilt.

Flying stabs, in and of themselves, work OK (as long as you pivot them ahead of the Cl), but not noticably better than a regular tail, and they have very significant structural implications.

I don't want to discourage you from thinking about it, but I just don't think the underlying premise is workable.

Who was it here that had the F-104 stunter? There were pictures posted about a year and a half ago, more or less. That one had an all-flying tail.

>Who was it here that had the F-104 stunter? There were
>pictures posted about a year and a half ago, more or less.
>That one had an all-flying tail.
That was me with my N-104 Starfighter with all flying tail and anhedral wing. I built it in 2001 as a take-a-part with removable wing, landing gear and horizontal tail. I made two horizontal tails for it. One is a stabilator and the other is a standard elevator. Both work well, but I prefer the elevator tail more. It is somewhat crisper and more predictable in hard maneuvering. The pivot point of the stabilator is 30% MAC. It is slightly ahead of the aerodynamic center of pressure or as Brett calls center of lift. The flaps do give some natural restoring force, but the tail should be set up to be stable both dynamically and statically. I still have it and fly it quite a bit. It turns well both inside and outside even with the high T-Tail.

Lovely airplane, Tom!

[photo not recovered: 3e69bb3870f12ad5.jpg]

"When you choose the lesser of two evils, always remember that it is still an evil." -Max Lerner

Thanks Larry. Now if I could only retrieve the original thread that we all did about this experiment from several years ago. I have tried the search function using N-104 and stabilator to no avail. There was a lot of good gouge in what was written.

>Thanks Larry. Now if I could only retrieve the original
>thread that we all did about this experiment from several
>years ago. I have tried the search function using N-104 and
>stabilator to no avail. There was a lot of good gouge in
>what was written.

Tom,
I have these three links bookmarked for reference. There is a lot of good information in them on the flying tail and your RB-104. There may be more but my searches didn't turn up much that was useful. There may have been some posts that have been lost due to previous system problems. Even in these posts there are some pictures that are disassociated with the post. With your permission I will post some images of the plans I am doing for you on the RB-104.

http://www.clstunt.com/cgi-bin/dcforum/dcboard.cgi?az=read_count&om=3246&forum=DCForumID1

http://clstunt.com/cgi-bin/dcforum/dcboard.cgi?az=read_count&om=3376&forum=DCForumID1

http://www.clstunt.com/cgi-bin/dcforum/dcboard.cgi?az=read_count&om=5329&forum=DCForumID1

Are plans available by any chance?

Dave Fincher is transforming my tracings into CADCAM. How about it Finch? When we will see the finished plans?

>Dave Fincher is transforming my tracings into CADCAM. How
>about it Finch? When we will see the finished plans?

I'm using Corel Draw instead of CADCAM but the plans are coming out nice. I'm attaching a picture of the RB104 plans as they currently exist. Up to this point the wing is just about complete, minus the hardware and I am working on the horizontal stabilizer and the fuselage. I have also attach included a jpg of the plans that I did for the NVCL Nova-Clone. The Nova Clone plans were done with the with Corel Draw and I can print either the nice color version or I can reduce it to a line drawing and print a parts template plan.

Gentleman,
Thank you all for a good discussion. I will not be building a flying stab anytime soon. I had thought of it for non planar (is that the correct term?) surfaces such as the tail on the f4f Phantom. or the small Canards on the B1b bomber.
I believe that Mr. Chuck Yeager said the flying Tail is what allowed Supersonic flight - It might have been the discovery channel or PBS I can't remeber which. The plane was the Bell x1 I believe.

What if I (or someone) built a plane with a flying canard surface - similiar to the elevator in front of the wing as well as a stabilizer/stabilator.

How about a full moving wing?

One of big ARTS son did this. canard in front with standard tail in back. Im working on a secret project, all flying tail front an back 1/2 size of normal. fox 35 power should be interesting, big jim does not think it will be controlable. hinge point at 25% flying surfaces.A dream of a 15 year old must build to end the nightmares. Mid oct.launch date.

Jose,

That airplane also won senior stunt at the 1972 Nats much to the dismay of my friend Mike Thompson who apparently forgot to do his trianges and ended up 4th instead of 1st if he had! At least that's something I have been told. I have no independent verification of that story though. Anyone who was there and knows please chime in? I lost contanct with Mike during the spring of 1972 so I don't really know if it is fact or not.

>Jose,
>
>That airplane also won senior stunt at the 1972 Nats much to
>the dismay of my friend Mike Thompson who apparently forgot
>to do his trianges and ended up 4th instead of 1st if he
>had! At least that's something I have been told. I have no
>independent verification of that story though. Anyone who
>was there and knows please chime in? I lost contanct with
>Mike during the spring of 1972 so I don't really know if it
>is fact or not.
>
>Jim Pollock
Jim

I don't think that was the triplane. It was Denny Adamisin who won senior (and, I believe, the Walker Cup) that year flying a semi-scale that was published in AAM.

If I remember correctly it was Denny's older brother Archie who flew the triplane probably in the early '80s. It not only had the strange three-surface planform but also used a single bladed prop.

The Adamisins are nothing if not innovative!

Ted,

OK must have been the Hurricane then?
I still would like to know about Mike's alleged misfortune though!
Anyone on here that flew Senior at the 1972 Nats, please feel free to chime in!

> One of big ARTS son did this. canard in front with standard
>tail in back. Im working on a secret project, all flying
>tail front an back 1/2 size of normal. fox 35 power should
>be interesting, big jim does not think it will be
>controlable. hinge point at 25% flying surfaces.A dream of a
>15 year old must build to end the nightmares. Mid oct.launch
>date.

Sounds cool, Jose. You've probably already considered the following but, just in case...

Airplanes have a theoretical (and real) aerodynamic parameter sometimes referred to as the "neutral point". This point is more or less the aerodynamic center of the entire vehicle including everything...wings, tails, fuse, landing gear, wheels, etc.

In theory, as long as the center of gravity is located forward of that neutral point the vehicle will be "stable". The aerodynamic surfaces are the largest contributors to the equation and basic stabililty calculations can be derived from a study of the area and location of those surfaces relative to one another. This is the reason that modern stunters with larger tails can be stable with CG locations much further aft than many of the classic designs with tails in the area of 15 or 16 percent of the wing area.

On a design with multiple lifting surfaces such as yours, it is important to give consideration to the neutral point. When you make the tail smaller and/or the forward (canard) surface larger, you move the neutral point forward. To get the equivilant degree of stability you must move the expected CG forward to accomadate the forward neutral point.

The distance between the CG and the neutral point defines the degree of stability and is often called the "static margin". As long as your ultimate craft has the requisite "static margin" it will be stable and can be trimmed to fly.

Martin Simon's book "Model Aircraft Aerodynamics" has a great discussion of the subject in the Trim and Stability chapter. He also has a practical method of forecasting a reasonable location of the neutral point which should be a must for you to determine the proper CG location and leadout exit point.

If you haven't access to Martin's book drop me an email and I can fax or mail copies to you.

Mr Fancher thanks for the info. Fax any an all information to 1-718-266-4305
Who is the publisher or were can I purchase
Many thanks JOSE

>Mr Fancher thanks for the info. Fax any an all information
>to 1-718-266-4305
>Who is the publisher or were can I purchase
>Many thanks JOSE

Hi, Jose,

Just saw your message today and have faxed seven pages to the number you gave. If it doesn't come through let me know. The book is called Model Aircraft Aerodynamics, written by Martin Simons and published by Nexis Special Interests, Ltd. Nexus House, Azalea Dr. Swanely, Kent BR8 8HU; England I suspect.

It might be currently out of print, my latest edition is the fourth and was published in 1999. You might try Amazon, they often have used copies of out of print books.

Good luck.

Hi,

Jumping in a bit late on this one... Except for the Nuts and Bolts feature, two recent Stunt News items on pretty aft-hinged all-flying horiz tails were both in the same issue a year or two back.

One, by Glen Allison, pivoted the stab well aft of the ac, and had an anti-servo tab for return force -- no wing flaps... The other, possibly by Fred Bachl, was far further aft-hinged, and may have used flap airloads to power back toward neutral.

Glen put a lot of theoretical effort into laying out his system, and it does appear to work as intended. Fred, of course, must have done a similar intensive prep before cutting wood. In short, with Glen's -- which I have seen fly -- there is need for ACCURATE building and near zero slop in the linkages. I imagine the other example had similar needs.

15-20 years back I played with all-flying tail stunters. These pivoted at 20% MAC, slightly in front of the symetrical airfoil's 25%MAC ac location. In short, these CAN generate great turning ability, but are likely not to groove, level or in turns. They have to be flown at all times. Fixed stab and hinged elevator layouts have much "nicer" stability 'feel,' w/without flaps ahead of 'em.

I learned early that usual practice tail area was far too large for an all-flying surface, and quite small deflection range was absolutely ample. The best of these were flap-less. Given all this, and for most of us who are not out to prove a point by great effort, today's dominant 'formula'certainly works. The quirks have been dealt with in great detail, excellent models and engines are readily available, and -- perhaps most important -- judges are more comfortable seeing an example of them. The excellence and difference is more in the realms of finish and flier performance than novelty and innovation. (Please don't read this as a gripe, whine or complaint -- that's not how I mean it.)

I think Archie Adamisin's odd one was called a 3-surface layout, not a triplane. Tripes generally stack the surfaces vertically, right? Archie's model had a canard-like forward surface, a main wing in typical position, and a conventional-looking tail aft. I think that was the year his eyes were in very bad shape -- narrow field of vision. In one flight I saw, he lost sight of the model and flew it level and high until another Adamisin (Denny?) went out to the rescue.

Don't recall in great detail how the 3-surface model flew, but it looked very good while he "had" it.

I may not be pertinent to the Stunt field but the combat flyers have been using all-flying tails since the days of Riley Wooten's Voodoo. That one hinged the stab right at the leading edge, sort of a conventional elevator with the fixed stabilizer left off. True, the combat people are more interested in Turning than Grooving but the Voodoo was certainly stable and controlable. Would a 500 square inch slow flying Voodoo work as well???
Mild Bill

> I may not be pertinent to the Stunt field but the
>combat flyers have been using all-flying tails since the
>days of Riley Wooten's Voodoo. That one hinged the stab
>right at the leading edge, sort of a conventional elevator
>with the fixed stabilizer left off. True, the combat people
>are more interested in Turning than Grooving but the Voodoo
>was certainly stable and controlable.

I don't think there's any doubt that a flying stab, per se, can be made to work. Whether it's any better than a fixed stab/elevator is arguable, but it will work to first approximation. I think the original post was asking whether hinging the flying stab behind the quarter-chord point, and letting the flaps stabilize it and allowing the tail to act as an aerodynamic counterbalance/"power steering". I think that's pretty definitively a bad idea, based on experiment.

Aerodynamically balanced stabilators work a treat on combat planes, but they are structurally different from stunters. Stunt planes with flaps may also benefit from a reduction in elevator effectiveness around neutral elevator that makes it easier to fly level accurately.