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Author Topic: Thinned elevators  (Read 1870 times)

Offline Clint Ormosen

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Thinned elevators
« 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?
-Clint-

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Offline Ken Culbertson

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Re: Thinned elevators
« Reply #1 on: April 05, 2023, 12:08:05 AM »
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?
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
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Online Dan McEntee

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Re: Thinned elevators
« Reply #2 on: April 05, 2023, 08:10:40 AM »
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?

      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,
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Offline Tim Wescott

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Re: Thinned elevators
« Reply #3 on: April 05, 2023, 09:54:36 AM »
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.
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Offline Howard Rush

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Re: Thinned elevators
« Reply #4 on: April 05, 2023, 01:49:04 PM »
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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Online Bob Hunt

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Re: Thinned elevators
« Reply #5 on: April 05, 2023, 05:08:35 PM »
It is currently fashionable to make extra-thick elevator trailing edges.

Sorta like bell bottoms for elevators...

Bob

Offline Clint Ormosen

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Re: Thinned elevators
« Reply #6 on: April 05, 2023, 05:14:24 PM »
Folks intuit that the elevator won't have much effect until it peeks out from behind the stabilizer.

Yes! This is exactly how I envision it working. Apparently it doesn’t, though.
I never liked the idea of slop in the control system for fear that it might make the maneuvers difficult to do, or at least make them ugly.
So how do you achieve the effect I’m looking for? To have the controls do near nothing around neutral. I know I can set it up for slower controls in general, but that’s not what I want either.
-Clint-

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Offline Ken Culbertson

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Re: Thinned elevators
« Reply #7 on: April 05, 2023, 11:02:40 PM »
In the "for what it is worth" department, the picture below is the stab airfoil I have been using the past 4-5 years.  The plate on the TE is new and PERMANENT.  No slop.  The stab is 1/2" and the elevator 3/8".  I use Robart hinges on the elevator only with the pocket in the stab.  With the rounding of the stab TE the elevator keeps the curvature of the upper surface and the airflow does not separate until it hits that mini wall at the end.
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Offline Howard Rush

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Re: Thinned elevators
« Reply #8 on: April 06, 2023, 03:33:18 PM »
Yes! This is exactly how I envision it working. Apparently it doesn’t, though.
I never liked the idea of slop in the control system for fear that it might make the maneuvers difficult to do, or at least make them ugly.
So how do you achieve the effect I’m looking for? To have the controls do near nothing around neutral. I know I can set it up for slower controls in general, but that’s not what I want either.

I use Igor's flap mechanism. 
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Online Brett Buck

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Re: Thinned elevators
« Reply #9 on: April 29, 2023, 09:00:41 PM »
Yes! This is exactly how I envision it working. Apparently it doesn’t, though.
I never liked the idea of slop in the control system for fear that it might make the maneuvers difficult to do, or at least make them ugly.
So how do you achieve the effect I’m looking for? To have the controls do near nothing around neutral. I know I can set it up for slower controls in general, but that’s not what I want either.

   I am not sure why you want that, but if you want to try it, use Larry Renger's exponential handle. No airplane modifications required.

     I am curious what problem you are having, because that is not normally a problem we have, in fact, it's the other way around. I submit it might be a trim or design issue.

     Brett

Offline Ken Culbertson

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Re: Thinned elevators
« Reply #10 on: April 30, 2023, 12:54:33 AM »
Elevator slop was very popular in the late 70's and into the 80's.  I used it and so did some of the big names of the day, but it simply did not work as we thought.  What it does is allow slight flap movement before the elevator moves.  This causes the plane to go in the opposite direction slightly before the elevator makes it go where you want it to go.  It may have some benefit in stopping the mildest of hunting from starting but it also makes it nearly impossible to stop it once it starts.  It can cause flats in the intersections of round maneuvers and that nasty wiggle locking out of corners - flap with no elevator and the plane goes the wrong way.  If you must have intentional slop, make it at the flap horn, not the elevator, but then only if the controls are so free that they will self-center in the airstream.   I agree with Brett that you need to reduce sensitivity through trim and study your grip as well.

Try some of the elevator TE fences we batted around a few months ago.  I have them on all of my planes now.

Ken
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Offline Clint Ormosen

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Re: Thinned elevators
« Reply #11 on: May 02, 2023, 12:47:24 AM »
   I am not sure why you want that, but if you want to try it, use Larry Renger's exponential handle. No airplane modifications required.

     I am curious what problem you are having, because that is not normally a problem we have, in fact, it's the other way around. I submit it might be a trim or design issue.

     Brett

For me it’s always the same issue regardless of what model I’m flying. I’m always wanting to make small height adjustments while in level flight, either upright or inverted, without the plane jumping around or having the nose pitch up or down. I can set the handle up to be insensitive enough to achieve this, but then it requires too much control inputs for the rest of the pattern.
-Clint-

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Offline Ken Culbertson

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Re: Thinned elevators
« Reply #12 on: May 02, 2023, 07:44:28 AM »
For me it’s always the same issue regardless of what model I’m flying. I’m always wanting to make small height adjustments while in level flight, either upright or inverted, without the plane jumping around or having the nose pitch up or down. I can set the handle up to be insensitive enough to achieve this, but then it requires too much control inputs for the rest of the pattern.
I cannot speak for others because our ways for dealing with this are all over the place.  What I can say is having any slop in the controls will not work if you are giving the plane *conscious* control inputs. For large changes like turbulence of a wind shift, etc. yes, you need conscious inputs but not for the small stuff and drifting.  For me this had always been a problem until some unnamed expert on handle position convinced me to drop the palms up grip.  Once I got my brain retrained to not do that automatically I discovered that I rarely had to make those little adjustments anymore and when the plane did start to drift, I let my subconscious do the correction by just thinking up or down.  The problem with the conscious is that by the time you know you need to make an adjustment it is too late to make one that is not noticed.  That is just my method of dealing with it.

ken
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Offline Steve Glass

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Re: Thinned elevators
« Reply #13 on: June 26, 2023, 11:11:00 AM »
In the "for what it is worth" department, the picture below is the stab airfoil I have been using the past 4-5 years.  The plate on the TE is new and PERMANENT.  No slop.  The stab is 1/2" and the elevator 3/8".  I use Robart hinges on the elevator only with the pocket in the stab.  With the rounding of the stab TE the elevator keeps the curvature of the upper surface and the airflow does not separate until it hits that mini wall at the end.

Ken, do you seal the hinge-gap on your tailplanes? If so, how?

Steve

Offline Ken Culbertson

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Re: Thinned elevators
« Reply #14 on: June 26, 2023, 04:30:41 PM »
Ken, do you seal the hinge-gap on your tailplanes? If so, how?

Steve
Yes, with a full span "scocth" tape.

Ken
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Offline Steve Glass

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Re: Thinned elevators
« Reply #15 on: June 27, 2023, 10:09:06 AM »
Ken,

Thanks for your reply.  One last question about your tailplane design.  Is the pointy stab LE important?

Steve

Offline Ken Culbertson

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Re: Thinned elevators
« Reply #16 on: June 27, 2023, 10:25:39 AM »
Ken,

Thanks for your reply.  One last question about your tailplane design.  Is the pointy stab LE important?

Steve

Yes, always.  I have used the original Nobler airfoil forever.  Recently I have added a CF insert in the front and a cap in the back.

Ken
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