Chris,

The wider thickness at stab TE, than elev LE, style has been used since at least the time Baron came up with the Avanti, possibly earlier. Thee are claims that the wake off the thicker TE 'masks' the first few degrees of elev motion, or something like that. I.e., less sensitivity off the neutral mark, so less jumpiness around neutral, with no loss of effect at larger angles.

I always shudder when any of us say that a DESIGN won the Nats or any major meet. The model had to be flown by somebody... Some relatively unpromising "designs" have done very well, because of who flew them. The loose nut at the slow end of the lines is as important, probably more so, than the properly tightened nuts and bolts at the fast end of the lines. Bob B was an exceptionally GOOD flier...

Like the NYC joke about how you get to Carnegie Hall: " Practice! Practice! Practice!..."

Actually, when Bob won the '96 NATS he was flying a slightly modified Patternmaster with a ST 60.  I launched him a few times in practice.  It wasn't an Avanti.........

ahhhh.. makin more and more sense now.. I understand the need for crankcase cooling.. I was curious as to the diameter of the tubing.. is 1/4" enough and that appears to be OD... as for Bob winning with the Avanti...I garnered that from a post on here somewhere.... Its cool to see the improvements in technology since ive been out of the hobby,,, I Bought a Tom Morris Bellcrank for it ... lots of difference there too. Its always been fun to build.. but its even more exciting now... thanks for the input...

By the way... i read a post somewhere about a plane that had a 1/4" Longer Outboard wing  a Teoswaki i believe... and it was supposed to be better than the longer inboard wing.. has anyone tried this on one of their planes??

Chris,

The wider thickness at stab TE, than elev LE, style has been used since at least the time Baron came up with the Avanti, possibly earlier. Thee are claims that the wake off the thicker TE 'masks' the first few degrees of elev motion, or something like that. I.e., less sensitivity off the neutral mark, so less jumpiness around neutral, with no loss of effect at larger angles.]

I don't know who used this empannage configuration first, but it happens to be the configuration used on my 1972 and 1973 Nats winning Sea Furys.  They were designed in 1970.  The stabs were built with a 3/8" core. The elevators used 1/4" cores.  they were all sheeted with 1/16".  A photo of these cores was in the "Go for Broke" Sea Fury article in March 1973 American Aircraft Modeler.

In the Mustang article "Evolution of a Thoroughbred" there is a photo of what became my standard stab and elevator construction.  My stabs are typically built using a built up spar consisting of a 1/4" x 1/8" balsa web with 1/16" x 3/16" spruce top and bottom spar caps.  The ribs are aerodynamically contoured, about 1/4" thicker than the trailing edge and about 5/8" at the root .  This gave the sheeted stab about 3/4" thickness at the root with 3/8" elevators..  This was a 1973 design, and the configuration I still use today.

This stab/elevator configuration wasn't detailed in the articles as I didn't see anything that unusual in them.  It was a full scale aircraft practice and only seemed worth incorporating on stunt ships.

The intent, of course was to soften elevator response around neutral using this configuration instead of the then more common practice of using "slop" in the elevator horn bushing. 

Al

Al
Thanks for the information...  very enlightening ...It makes sense now.. and I am building the plane as per the plans.. Its interesting that this is a product of the 70's  as I seem to be finding out.. many things are but highly refined in todays modeling..


Thanks again to everyone who posted to help me with my questions

Chris

I've never quite been convinced about the working of this "thick tailplane/thin elevator" theory. Using my own ignorant layman's understanding of aerodynamics, when all is said and done about t/p's, what makes the plane go up and down is a pressure differential between the topside and underside of the elevator. Up elevator leads to increased pressure on the topside which pushes the t/p down which points the nose up. I suspect a thinner elevator is not working in some sort of shielded environment which renders it less effective due to being shielded by a thicker t/p. Certainly the airflow will "rareify" a bit as it spills past the hinge line, but the degree of rareification must depend on the angle of the elevator. If there is any +/- angle to the elevator it will affect the degrees of rareification (i.e. pressure) above and below the elevator and therefor give a definite up or down control input.
Well, I know what I am talking about anyway.

There is a nice little single seat light plane designed by a man named Molt Taylor, called the Taylor Monoplane. It has a very thick stab, and a much thinner elevator.

Small single seat racer types typically have super sensitive reactions to stick inputs. I have flown a few different designs and know it to be true by personal experience.

This Taylor Monoplane is very tiny, yet the action of dampening by this aerodynamic technique keeps the pitch sensitivity to the level of an airplane with much longer moments.

Because there are many designs that have flat plate control surfaces, one cannot dismiss control surface deflection as a part of the total aerodynamic action taking place.

This, along with Al's, Bob Whitely's and many more designer's using the fat stab/thin elevator technique, has convinced me that it works.

Chris...

For the last 10 or 15 years, I always showed a thinner elevator section, vs's the stab, for the very reasons mentioned in this thread. It does indeed work to soften the controls around nuetral.

I do believe there's a drawback to the practise though.

As I gained more experience, I found it difficult to do extact transitions from insides to outsides in the Eights. I had to anticipate the intersection or I would tend to get a flat spot, and the outside tended to be larger in radii than the inside.

Lately, at the suggestion of my mentor and flying buddy, Gordan, I started going to 3/8" stabs and elevators. We found that by utilizing proper incidences, as suggested by Bob Whitely, and, building as straight as we could, that the plane will groove very well without the slop, either mechanical, or areodynamic.

It became much easier to hit the intersections in the Eights. The transition from inside to outside were smoother, and resulted in even sizes between insides and outsides.

At least, that's what we found for us on our airplanes.

The latest plans I've drawn all show equal thickness for the stab and elevator.

actually... on this plane.. they are 3/8" at the LE.. and 1/2' at the TE.. the LE is sanded down and rounded and the TE is not sanded.. just 1/2"
Chris

I am not sure whether Thinner elevators and sloppy pushrod holes help anything. I think the most important part of any plane is how strait it is. The other thinks work ok but You have to trim the setup to work the way you intended. A lot of these things I have tried over the years and the only one that I think is worth while Is making the elevator thinner than the stabilizer. Onther thing that really orks good is positive incidence in the stabilizer. This was done4 by David fitzgerald so I tried it on my Odyssey. This plane really sits in the grove both directions.

Leo,

Like you, I no longer like the idea of sloppy controls to mask or "fix", a flying problem.

Since I've been using down and a little right thrust, coupled with slightly possitive incidence at the stab, I've not felt the need for loose, sloppy controls, or the need to use a thinner elevator.

Straight airplanes, with proper incidences built in, usually fly great.