Design > Stunt design
Thinned elevators
Clint Ormosen:
This topic may have been beaten to death, but not by me so…
Most of the stunters I’ve built use 1/4” sheet stabilizers and elevators. I’ve gotten into the habit of leaving stabilizer thickness at the full 1/4” for the entire chord, but I taper the elevators down to about 1/8” at the trailing edge. My (probably erroneous) thinking is that this makes the elevators less effective while making very small control adjustments in level or inverted flight, allowing for small height corrections using the flaps without pitching the nose unnecessarily.
Does this actually work?
Ken Culbertson:
--- Quote from: Clint Ormosen on April 04, 2023, 11:36:21 PM ---This topic may have been beaten to death, but not by me so…
Most of the stunters I’ve built use 1/4” sheet stabilizers and elevators. I’ve gotten into the habit of leaving stabilizer thickness at the full 1/4” for the entire chord, but I taper the elevators down to about 1/8” at the trailing edge. My (probably erroneous) thinking is that this makes the elevators less effective while making very small control adjustments in level or inverted flight, allowing for small height corrections using the flaps without pitching the nose unnecessarily.
Does this actually work?
--- End quote ---
I am far from the aerodynamic wizard on this site but let me add some observations from my own fleet over time. Back in the 70's it was a common practice to have about 1/8" of slop in the elevator to create a dead zone like you are describing. Some of our best fliers used it. However, with the elevator not moving the flaps have the opposite effect. If you are drifting down a minute amount of up control may actually make you go down further and start porpoise like hunting as you start overcorrecting. Once you get used to it however, it is very effective, but I never did. I started using airfoiled stab and elevators with as little slop as possible. IMHO if you are going to use slop to give you a dead zone, it should be at the flap horn, not the elevator.
Now I will leave it up to the engineers - Ken
Dan McEntee:
--- Quote from: Clint Ormosen on April 04, 2023, 11:36:21 PM ---This topic may have been beaten to death, but not by me so…
Most of the stunters I’ve built use 1/4” sheet stabilizers and elevators. I’ve gotten into the habit of leaving stabilizer thickness at the full 1/4” for the entire chord, but I taper the elevators down to about 1/8” at the trailing edge. My (probably erroneous) thinking is that this makes the elevators less effective while making very small control adjustments in level or inverted flight, allowing for small height corrections using the flaps without pitching the nose unnecessarily.
Does this actually work?
--- End quote ---
The practice of having the elevators thinner than the stab goes back a long way. I think it is a better route to go than the "purposeful slop" method. At the thicknesses you mention, I think the chances of warping a surface are higher. Increasing the thickness of the stab and elevators will help in that area. Depending on the size of the model, 3/8" tp 1/2" for the stab isn't out of order these days, and the elevator thickness thinned appropriately for the dead zone.
Type at you later,
Dan McEntee
Tim Wescott:
Hopefully a Brett or a Ted will weigh in here. As far as I've seen, while the top guys use tapered elevators, they also use sealed hinge lines which should keep the elevator responsive to even the smallest control inputs.
I just try to follow the tip of the development tree rather than chasing down all of the old branches. My understanding is that the whole "slop in the elevator" thing was fixing problems that are better fixed with the "modern numbers" that came in sometime in the late 1980's along with bigger engines that could be regulated more reliably. (I.e., a bigger tail, a longer tail moment arm, coupled with an engine that didn't demand that you gyrate your way through the pattern to keep line tension). With those changes, you can trim the airplane out to the point where it just flies right.
Howard Rush:
Folks intuit that the elevator won't have much effect until it peeks out from behind the stabilizer. If so, this would only happen when the flow is parallel to the stabilizer, something I don't think you can count on in level flight.
It is currently fashionable to make extra-thick elevator trailing edges.
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