There is many a reference or statement to the canalizer or dorsal fin being used to correct, or in effect become a bandaid for some airplane's deficiency. Other people would say, "my plane don't need a T-canalizer." If CPLR is using it, there is something valuable going on. If Akiba saw fit mount one to a Proline which already has lower strakes on the belly pan, there must be some value. If a Brio flies well without one, and better with, there must be some value. It if helped Dave's Prestige or my Agressor, etc....

Many people with various platforms have gone from without, to with and felt the plane flew better. Do all these plane have the same design deficiency? What is the design deficiency?

For my own experiments on my Abbra and Aggressor I installed a dorsal fin of approxiamtely the same area as a playing-card, behind the canopy of each plane - did so after a discussion with Dave L. The planes are totally different: Mid-wing mid-fuse thin stab versus mid-low-wing, wide-body thick stab, etc - totally different designs in every possible way. The addition of this small fin had the EXACT SAME EFFECT on each plane. The longitudinal position of the fin doesn't seem to matter much as the one on the Aggressor is mounted to the removable canopy, and the one on the Abbra is mounted a little further back.

The predominate flying quality change to each plane was that it counteracts negative pitch with rudder application - dramatically. After setting the pitch mix to zero and still recognizing a pull to the canopy for knife-edge, I trimmed the height of the fin until it was zero on say left rudder and maybe 1-2% on right. There was left a very tiny difference between left and right rudder.

Did it only fix knife edge? No. Some planes may have a low knife-edge mix but still react with a lot of negative pitch in level flight rudder turns. The dorsal fin seemed to not only fix knife edge, but also really help flat rudder turns. You can hammer the rudder pretty hard now and get mostly yaw without funny business. At some point the plane gets upset, but that is way beyond the normal inputs for rolling circles, rolling loops and such.

The other mild improvement was that overal tracking: inverted, upright, power-on, power-off, all seemed to just lock on better - both planes. I could not detect a change to the roll mix of the planes either. So at this point, I see no negative flight quality change, and a bunch of positivie changes going on. It flew so well that I abandoned the next step in the experiment of adding the top piece (.... maybe I should try though??)

So back to the main question or critism - what is the single thread of plane deficiency between all these designs? Could it be rotational prop thrust? If its rotational prop thrust is the design flaw that the platform is not straightening out the flow before it hits the tail?

For me, I'm going with a simple explanation that given such a small addition of fuselage side area and the aspect ratio of the fin, that it is basically straightening out some of the prop flow before it hits the tail and that is helping the plane. It would be great to wind tunnel test it to know for sure, but I'm just as happy to be ignorant of the exact cause and be happy with the measureable, noticeable effect.
Thanks,
Jim W.
- yes I have an aerospace engineering degree, ERAU 1996 Prescott, AZ