LRFitch

Some pattern airplanes have anhideral stabs, and some have T-canilizers. How/why did the designers/builders decide to use these "modifications" in their airplanes? Asked another way, did they add either/both of these to some prototype to alter/improve flight or are they designed into the airframe at the beginning of the design effort?

Larry

Roberto B.

I suppose that anyone have their own method and design philosophy.

Malydilnar

My Feedback: (1)

My dad designs them with adhedral stabs from the beggining, as it actually helps roll performance. T canalizers are just nonsence

rcpattern

My Feedback: (45)

Anhedral stabs give the same effect as a lower stab on the fuse. Thus helping roll coupling while keeping the stab from being blanketed by the wing. Canalyzers are not nonsense and they do help. They increase rudder performance and yaw stability. They do not necessarily improve every design, but they can help with certain designs. You can run less wing area near the tip, increasing snap performance and the canalyzer compensates for this as well. I personally am not a fan of them, but I am anxious to try the new BJ Craft episode. They obviously work as many designers, such as CPLR use them very effectively.

Arch

Ryan Smith

My Feedback: (25)

I noted a huge difference in flight performance on my Partner (which I had flown for five years prior, so I knew a thing or two about how the airplane flew).

Anhedral stabs give the effect that Archie noted, but there are some negative side effects- chiefily positive and negative snaps are very inconsistent from one another and the airplanes that I've flown with them didn't particularly seem to lock in. Personally, I haven't seen enough benefit to outweigh the negatives of having anhedral stabs, and I have seen a huge advantage to the use of a canalizer.

Your mileage may vary.

Rendegade

I've also found a good change from a canalizer. That said, I've not been able to go from a flat tail to an anhedral tail to compare and contrast.

If you're unsure as to whether it's going to work, fit a temporary canalizer mount on, and fly.

I did that 2 years ago. I haven't bothered to fix it permanently, but if it falls off, it'll be a permanent fixture from now on.

MTK

I've used anhedral on a couple designs in the past and my latest also has the feature. I tend to agree with Ryan and Archie that not every model benefits from anhedral. My latest tends to not lock as well as I want. I have also found that CG latitude (how far one can move CG) is diminished considerably. Running CG a bit aft, is a big no-no. Cross wind flying with CG even at 33% MAC is two handfuls. I suspect that one should not use anything further aft than 28%MAC. I am currently running my CG at 30% MAC and it's barely passable. I abhor having to add nose weight............

On current 2m models I don't see much benefit and will not use the feature again in any future design that is 2 meter or larger

On the other hand, a dorsal fin at midships helps a great deal in the way Archie mentioned. Consider why a shark is an apex predator.....take his central dorsal away and he becomes bait

LRFitch

Thanks fellas for all the discussion. I'm currently sitting at the drafting board thinking through a 2M design excercise, and have been wondering if I should include either of these in my drawings. I must say I think they both "look cute"-to paraphrase my daughter. I've always liked the tails on the old F4 Phantoms, and of course the Curare. While I understand what each is designed to do to an airplane's flight performance, it's hard to guess how much of an affect either will have before being flown with some "base case" without these alterations, and I'm not sure I'm up for building three or four airplanes as a design verification effort.

MTK, I take your comments about CG latitude to mean you've experienced a reduction in the acceptable latitude due to the anhedriel stabs, ie. needing the CG farther forward? That's very interesting, and wonder if that comment is similar to the few comments about "locking on" which is often related to CG location.

Larry

MTK

Cross wind conditions will hit the affected stab half and will pitch the model. If CG is a little aft, the pitch effect is exagerated causing the model to wander and feel very uncertain: upright flight pitches the model up and inverted flight pitches the model down. That doesn't happen with flat stabs, at least nowhere near as severely.

I like the looks of the anhedral stab but not its aerodynamic effect. It is very strange to have the same model in the same flight trim condition fly so differently in wind down the runway and in cross wind.

A fore CG is necessary for reasonable flight trim with any model but for the anhedral stabbed model one has no latitude to explore other locations to fit his style and preferences.....Good luck!

rcpattern

My Feedback: (45)

I think the amount of anhedral comes in to play as well. Small amounts, such as Mike Hester used on the Black Magic, 5 degrees total, 2.5 on each stab, which is rougly what the Nuance has minimized this compared to stabs such as the Tipo, or Curare.

Arch

Malydilnar

My Feedback: (1)

Adhedral stabs make a noticable difference, while the small canalizer has no big effect. It might help a tiny bit, but not as to a point where I need it on my airplane. The big T canalizers (I guess thats what you call them) such as on the oxai model flown by the french guy make a difference, as it is a 1.5 wing kind of plane.

Ryan Smith

My Feedback: (25)

You win.

rcpattern

My Feedback: (45)

OK, I'm gonna ask. How do you explain that it has no effect? Putting a simple 2" X 2" strake in that location makes a HUGE difference, even without the wing. It definitely cleans up the airflow back to the tail. There are other ways to get the same effects, but I don't think you can say it has no effect, as I've flown planes that it had a HUGE effect on. The Black Magic VF3 series from Mike Hester is a perfect example. The plane is over 5 years old and had limitations with some of the much more rudder heavy maneuvers in FAI. Don Szczur added the T-Can and I have flown the plane. It made a HUGE difference. They do have an effect. Some planes do not need them, but to say they have no effect is a little much.

Arch

David Bathe

That is my take on them, exactly the same way that adding dihedral has the effect of raising the wing.. and vise-verse.
Could be wrong but it's always been my quick fix. A lot simpler than re positioning the wing or stab.
This shark fin and T-Can thing really is something though... specially for a monoplane.
Expect to see derivatives on full sized aerobats in the comming years.

Here's a sketch of a design concept done at least 8 years ago intending to use counter rotating props.... that wasn't available.
Shark fins/T-Cans top and bottom. Smaller wings etc.
Not so much a plane... more a machine designed to carve lines.

MTK

Looks a little like Nat's VooDoo Xpress, the grand-daddy of all of these extended surface models. Nat came up with the concepts some 30 years ago and applied them to his VooDoo, before any complexity in the schedules was developed to take advantage of these design features. Way ahead of his time

rcpattern

My Feedback: (45)

Nat's VooDoo's are a blast to fly. They fly amazing and really don't care what attitude you are in. I was fortunate enough to fly his Voo Doo 3D several times. That plane would do things that airplanes simply shouldn't do.

Arch

Magne

I think that adding dihedral has some added effects other than just that of equalling raising the wing.
If you yaw a plane with no dihedral, there will be no or little rolling effect.
If you yaw a plane with a lot of dihedral, the "forward" wing (right hand side wing in a left yaw) will hit the oncoming air with a much larger angle of attack then the other wing, causing a roll.

I would expect that there are similar effects on a tailplane with anhedral. Yaw the plane left and the plane should pitch up. The two sides will not cancel each other out, because one side is facing the sideways wind and is more effective, while the other side is blanketed behind the fin/rudder. I therefore think that tailplane anhedral should reduce pitching to the belly in knife edge. I could also be totally wrong.

Magne

jnhiller

You guys got my interest again.

Anhedral stabs go back to bottom mounted non-adjustable (incidence) one-piece wing designs and AMA style pattern. Those small fuselages had little side area to carry knife-edge and the faster the airplane the better. Everything is different in modern turnaround and nearly all designs have two piece centrally mounted wings, which I don't believe are as sensitive to dihedral or vertical placement.

I often thought anhedral stabs were incorporated to effectively reposition the stab (vertically) after the fiberglass fuselage mold was made. To fly right several other design criteria needed to be in line with the designer's setup and flight trim such as weight and CG location, not to mention straight building practices. One man's nice flying design may be another man's headache.

Roll couple is mostly a wing dihedral issue but the flying height of the stab relative to the wing noticeably influences pitch couple. Altering wing incidence, CG location and down thrust also contribute to pitch trim and coupling with rudder application. High yaw requirements of FAI offer additional design challenges I've not yet had to deal with but I expect the fuselage side profile also contributes greatly.

For what its worth
Jim