Hi..

Some airplanes have full flying elevators (Piper cherokee and Seneca series, Cessna Cardinal, F-16 among other fighters)

Some people build into these airplanes the tradicional elevator/stabilzator to keep things simple but for a scale airplane, it looks goofy..What are the considerations to keep in mind when using full flying stabilizers?? How to measure incidences in this set up?

The biggest concern is aerodynamic balance and flutter. Hinge line should be close to 25% chord, or a little forward. Incidence is set the same as a fixed stab, only it is adjustable.

Lots of model sailplanes use full flying stabilators just fine. It avoids the need for a drag producing hinge line and takes advantage of the requirement to remove the stabilizer for transport.

Total throw needs to be reduced. To start with the change in angle of a full flying stabilator should mimic the change in overall stabilizer airfoil angle of attack produced by the elevator movement.

The pivot used needs to be sufficient to take all the flight bending loads while still not flexing so much that it causes a binding in the hinge bearing. Or the bearing should be designed to float a little in angle much like power shaft pillow block bearings are self aligning.

Otherwise yeah, there's no reason at all why these designs should not be duplicated correctly. However in the case of ARF designs the added cost to properley produce a well engineered solution will likely keep them "cheating" and making fixed stabilizers with separate elevators.

An all-moving stabilizer/elevator (stabivator) combination looks attractive on paper, since it can be built lighter than a conventional stab/elevator combination. Elimination of the hinge line also reduces drag.

I tried one on a 125 MPH model many years ago.I hinged it at about 20 percent of the mean chord behind the leading edge. Getting a strong and stiff enough hinge seemed to wipe out much of the potential weight benefit. The airplane handled well, but I could ascertain no advantage. It also got into a scary low-speed flutter once, probably because it was not counterbalanced. Counterbalancing would have added far more weight than that of the counterbalancers on conventional elevators . I didn't repeat the exercise.

Piper used an all-moving tail on the Aztec and Comanche. I recall hearing of alleged fatal accidents that may have been caused by a nearly fully deflected trim tab causing the center of pressure to move ahead of the pivot axis. The tail might suddenly take the bit in its mouth, slam to full deflection and tear loose from the airplane, but I don't have much factual information on this. Maybe someone out there has the dope on late 1950s accidents with early flying tails on light aircraft.

An all-moving stab develops a much lower maximum lift coefficient than a conventional stab/elevator combination, which acts like a heavily cambered section when the elevators are considerably deflected. Cessna was forced to use an inverted slot to get sufficient downforce from the stab to force the wing into maximum lift angle of attack. The slot probably adds more drag than that of a well-faired hingeline.

I think the strongest condemnation of the all flying stab is that in certain areas of operation they can stall, thus causing the loss of the aircraft.

Designing a light, stiff and slop free axle can take some ingenuity. I've used wood filled aluminum tubing riding in maple bearing blocks. The control horn needs to be anchored to the axle with a goodly amount of glue surface area. The axle gets cross drill for lengths of aluminum welding rod to lock the sheet balsa stabilator half to the axle. Use as tall a control horn as will fit in the model, typical 1.25" tall for a .40 and under model will give the linkage lots of mechanical advantage and give the model surgical control resolution.

Here is one I Scratch built with the use of a stabilator. Works Great!!! Very easy to do also, all I used to accomplish the task were two pieces of brass tubing one inside the other.I can take a few more pictures of my setup if you are interested?
jerrysu29 Call Sign Wild Man

Hi Folks..

I would like to thank you all for your replies, appreciate your inputs..

I love that Nomad! We have one of those derelict parked at the local airport!!
If you have more pictures, that would be great..

By the way, what kind of engines does it have?

All Piper Cherokees, the Seminole, Comanche, Twin Comanche, Aztec, and other models had the all-flying tail...called a "Stabilator". It worked excellently. They did not have a trim tab, but had an anti-servo tab, which increased the camber of the stabilator as it was deflected and increased control forces with that deflection. Without the anti-servo tab, the elevator 'feel' would be too light, and the stabilator would not trim well. Adjustment of the centering of the anti-servo tab changed in-flight trim, just as the trim tab on a standard stabilizer/elevator setup.

There were no difficulties known to happen because Piper used stabiliators...unless the aircraft was flown well outside of its speed envelope, but there never was any "snatch" in the control system.

So can an stabilizer/elevator combination. It all depends upon the design and the amount of control deflection.

First Flown with OS 91's (2 cyclye engines ) Plane was featured in the Rally of the Giants Video 2001 in 2003 We re powered the Nomad with OS 108 2cycle engines. Some of the runways we fly from were rather short and on a HOT day we could not haul all four Skydivers up to drop them due to the density altitude being so high. Then in 2007, we re powered the Nomad again with 2 YS 140 4 cycle engines, There is no problem know with getting the Nomad airborne off a short runway on a hot day with all four Skydivers loaded. We also Use the Nomad for the Candy Drop (can take up 12 lb. of candy in the belly of the Nomad) We take each piece of candy and hot glue a 6" length of colored ribbon on it. Looks like a multicolored slurry drop when released, very Impressive to the Crowds and the Kid's just love it. The ribbons glued to each piece of candy make the candy easy to find.
jerrysu29 Call Sign Wild Man

Here are some more pictures I moved over from my lap top. This plane is a joy to fly!
jerrysu29 Call Sign Wild Man

jerrysu29,
That is an awesome model. Those are brilliant engineering designs and applications on that airplane. WOW!!!! Congratulations!!!......job well done.
larrysogla

Flying tails are better where smooth flight is needed.
Many gliders use them, as the drag from a surface with no spanwise hinge line is a bit less, and when trimmed, the drag from the trim angle comes from the surface alone, not the flapped surface of the conventional plane.
For manuvering, the flapped surface generates more lift.
And there's less load on the fixed surface relative to the concentration of the load at the hinge line on a flying tail.

Actually, the stabilator did give Piper some problems. The balance of a stabilator can be very critical. Check out the footage of a Twin Comanche which fluttered during a flight test. No, the airplane was not being flown faster than the red line airspeed. No, it wasn't out of rigging or balance tolerances. This event didn't occur during the actual test point. It occurred on the way home at a lower airspeed while the chase photographer was running out his film. Fortunately the pilot had quick reflexes and pulled up quickly to kill off airspeed. The pilot, by the way, was Fred Haise, later Lunar Module Pilot on Apollo 13. Some guys have all the luck.


http://www.dfrc.nasa.gov/gallery/mov...M-0098-01.html



Twin Comanches were temporarily restricted to a much lower redline speed until revisions were made to the stabilator design.

My experience with full scale stabilator design has been that it is much more critical to design properly. It's easy to stumble into a flutter problem (model or full scale) and often has control power issues. And, yes, it can have disagreeable traits even in some current full scale airplanes.

Like the swept vertical tail on many light airplanes, the stabilator is more of a sales gimmick than an engineering advantage. The parts count is higher in a hinged elevator, thus more expensive. But I look at the hinged elevator as betting more of a sure thing.

Supersonic planes with stabilators? Yep, whole different animal. You need an all-movable surface if you intend to go supersonic.

Dick Fischer



edited to fix the quote so it shows as a quote

It sounds like that problem was discovered during flight testing, although not during an actual test. It appears the test obviously didn't include enough parameters, if it was in fact a test for "stabilator rigging or balance."

No real surprise there. The reason they fly prototypes before approval is to see what the designers didn't get right.

It's also no surprise they had to change something on a prototype. Also, no indictment for having to do so. Aerodynamic design includes a huge amount of adjusting, a lot of which happens after the prototype is flying, because it's really not a simple science.

Quite an interesting anecdote. Thanks for sharing.

Yes, the Twin Comanche stabilizer flutter in the NASA footage occurred during a flight test. But .... The Comanche design had already been flight tested by Piper and was fully certified by the FAA. The airplane in the movie was a standard production model which had been rented by NASA from a fixed base operator. NASA at that time was flight testing a host of general aviation airplanes to examine stability and control issues. The Comanche was simply one of the airplanes rented and evaluated.

The specific flight in which the recorded flutter occurred came about because pilots had noted a slight nibble at higher (within redline) speeds. After verifying that everything (rigging, balance, etc.) was in order, strain gages were installed to record the behavior of the stabilator. The airplane was flown up to redline speed with photo chase to record vibration data. On the way back to base, at a somewhat slower speed, the stabilator "took off". As I mentioned before, the chase photographer just happened to be running out his film when it all happened.

The point here is that full flying tails can give nasty surprises even when folks think they've done everything right. It's difficult to build in robust safety margins and sometimes when you think all is well they can jump up and bite you just the same. I prefer the more robust safety margins inherent in a stabilizer / elevator design.

Dick

Yup

Bottom line is that aerodynamics is way more complex than most wish.

The reason for wind tunnels is because the formulas simply cannot provide 100% of the answers.
The reason for flight testing is because the wind tunnels do not dependably prove anything.
And a fairly significant percentage of production aircraft have problems.

It just ain't sound byte simple.

Some luck to modell aircraft designers at least, all RC aircraft have powered controls. (Same league as jet fighters.) As long as there is no sloppy linkages, reasonable mass balanceand the pivot is slightly in front of the aerodynamic centre, stick forces and control harmony is no problem.

There was another, I hesitate to call it a problem, but a bad tendency. I don't want to call it a problem because it was caused by poor technique by the pilot. If I remember correctly this affected mostly the Lance lineup of planes. The problem was in the landing flair. Even with normally sufficient airspeed, abrupt elevator input the stabilator or tailplane would stall. Obviously the tailplane is producing negative lift holding the nose up. A sudden loss of this negative lift cause the nose to drop and usually cause nose gear damage along with prop stikes. All this while not being slower than a normal landing speed. It has been many years, but that's how I remember it.

Flying tails... How to find the 25% mean aerodynamic chord.. and the pivot points on some models..

A friend has some jets (F16 F18 F22) and they only have stabilator, no ailerons.
So he is using a delta mix.

Does it have any advantage (except simplicity) and can we do it on a regular rc plane (40 60 size ) ?

Low aspect ratio wings with large horizontals are best for that manner of control.
It's mostly done because the jet wings are quite thin, and the typical aileron servo adds an unsightly lump out on the wing.

So, if I modify a low wing trainer, for "scientific research purpose" , will it be a big negative ?
If it's good I might mod one of my Club20, if I can