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Author Topic: flap chord  (Read 834 times)

Offline frank williams

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flap chord
« on: April 11, 2020, 08:38:27 PM »
Several threads recently have bumped into the question of the best flap chord size . If the chord is too large, a bigger negative pitching moment is produced and this results in poorer quality turns for the airplane. 

I have, through the years, built several planes with 4 inch flaps.  I remember Windy, at one Nats, had a Big Jim design that had what seemed to be like 40% chord flaps.  They flew well.  I think that the reason they performed as well as they did was because a conscience effort was made to limit the flap deflections.

Recently, Igor has made the case to make certain that the line of curvature flows smoothly from wing across to flap, a design element that Al Rabe also promoted in his large flapped semi scale stunters.

I propose that larger flaps are perfectly usable if the deflection is limited from what you might normally use for standard 2 inch flaps.  So, is there any data to support this?  Yes there is.

The attached plots are from the thesis of Gregory Williamson, a student of M, Selig at UI.                                             https://m-selig.ae.illinois.edu/uiuc_lsat/Williamson-2012-UIUC-MS-Thesis.pdf  The section of interest is a symmetrical 15% airfoil at a Reynolds number of 400,000.  The flaps are not sheet flaps like ours, but integral flaps of either 20 or 30 percent chord.

The data shows that a 20% chord flap with a deflection of 30 degrees produces almost exactly the same lift as a 30% chord flap being deflected 20 degrees.   One is as good as the other for supporting the plane at the bottom of and hourglass. 

OK, what about the difference in pitching moment effects between the two?

As it turns out the larger flap situation (30% vs 20%) actually has a slightly smaller negative pitching moment!  And, additionally due to the lesser defection, it blends into the wing curvature more smoothly than the smaller flap deflected a greater amount.

Granted, if you are on the field fixing  a poor turning plane that has large flaps at standard deflections and you can’t get to the linkages, the solution is to trim the flap chord down.  However, if designing from the ground up, you should match deflection to chord size.  The larger the chord the smaller the deflection.


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Offline Howard Rush

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Re: flap chord
« Reply #1 on: April 12, 2020, 02:13:31 AM »
Hinge moment is evil and proportional to the square of the chord. It’s a good excuse to try cold-chisel flaps.
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Online Brett Buck

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Re: flap chord
« Reply #2 on: April 12, 2020, 09:29:32 AM »
Howard beat me to it, although it is not obvious where the optimal point between hinge moment VS deflection rate VS lift increment lies even if you are only considering the lift aspect. Once you get above 20% chor

    Having flown a bunch of these "giant flap" models over the years, they all had one thing in common - wildly exponential controls, where it took tremendous effort to get it to do anything, but once you finally muscled up enough to get get it to turn, just leaped around the corner. I always found myself trying to give it huge pressure to start with, then having to greatly reduce the pressure or even counter-controlling it to keep it from going too far too fast. Control linearity and feedback counts for something, too.

      It's not like we are maxing out on lift even on conventional designs.

    Brett

Online Ken Culbertson

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Re: flap chord
« Reply #3 on: April 12, 2020, 09:47:49 AM »
Hinge moment is evil and proportional to the square of the chord. It’s a good excuse to try cold-chisel flaps.
There are times when we use terms that we think everyone knows what we are talking about.  Let me display my ignorance so that I can use the term cold-chisel in the future and actually know what it means.  I can guess that it is a) a flat flap with a rather long "V" shape at the back OR, b) an Australian rock band or, c) a full "V" shape with pointy back or, d) it really means the LE shaped like a "V" or lastly, e) the flaps are really solid steel chisels.

Reminds me of an old saying "you think you understand what you thought I said but what you don't realize is that what you heard is not necessarily what I meant."

Is hinge moment really evil?  Since it is Easter can we forgive it?

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Offline Howard Rush

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Re: flap chord
« Reply #4 on: April 12, 2020, 10:37:46 AM »
There are times when we use terms that we think everyone knows what we are talking about.  Let me display my ignorance so that I can use the term cold-chisel in the future and actually know what it means.  I can guess that it is a) a flat flap with a rather long "V" shape at the back OR, b) an Australian rock band or, c) a full "V" shape with pointy back or, d) it really means the LE shaped like a "V" or lastly, e) the flaps are really solid steel chisels.

Reminds me of an old saying "you think you understand what you thought I said but what you don't realize is that what you heard is not necessarily what I meant."

Is hinge moment really evil?  Since it is Easter can we forgive it?

Happy Easter - Ken

Sorry.  It’s my own definition, from the recent flap trailing edge thread.  See https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930092890.pdf .
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Offline frank williams

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Re: flap chord
« Reply #5 on: April 12, 2020, 10:39:12 AM »
If you built and flew a plane with the standard one to one flap / elevator and equipped it with a large flap, you wouldn’t like it.  When you flew these planes, had the ratios been adjusted for the larger flap.?

Hinge moment is proportional to chord squared.  OK.  But, hinge moment is also proportional to deflection angle.  Smaller deflection with a larger flap might have a similar hinge moment as a smaller flap with a larger deflection angle.

I’m pretty sure a “cold chisel” flap trailing edge is a simple flat rather than tapered edge.  Another variation of this is “T” strips, kinda like double “Gurney flaps”.  Actually the idea of thickening the trailing edge with rods attached to the top and bottom of the trailing edge goes back to the ‘40’s in Wartime Reports.

Online Ken Culbertson

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Re: flap chord
« Reply #6 on: April 12, 2020, 04:47:06 PM »
Sorry.  It’s my own definition, from the recent flap trailing edge thread.  See https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930092890.pdf .
Thanks Howard.  That clears it up.  But, the illustrations raised another issue.  Granted those illustrations were for full size aircraft but the flap hinge method is the one I use (insanity runs in my family).  Has anybody tried sealing the flaps on a stunter using cover plates?

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Online Brett Buck

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Re: flap chord
« Reply #7 on: April 12, 2020, 08:34:05 PM »
If you built and flew a plane with the standard one to one flap / elevator and equipped it with a large flap, you wouldn’t like it.  When you flew these planes, had the ratios been adjusted for the larger flap.?

     In many cases, yes, including a pretty extensive experiment with my 1988 airplane where I made 3 different sets of flaps. I always ended up liking the response better with moderate-chord flaps and more movement, in fact, usually, 1:1 with the flap area adjusted in chord to suit seemed to work the best.

     Brett

Offline jose modesto

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Re: flap chord
« Reply #8 on: April 12, 2020, 11:39:58 PM »
The large flap high aspect planes used a 2/3 to 1 control ratio.
I built many of these models in the early 80’s
Our main challenge was whip up in the wind.
 No low pitch pros or high teving motors were in use
Most powered by ST 46 and 60
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Offline Ted Fancher

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Re: flap chord
« Reply #9 on: April 13, 2020, 07:08:24 PM »
The large flap high aspect planes used a 2/3 to 1 control ratio.
I built many of these models in the early 80’s
Our main challenge was whip up in the wind.
 No low pitch pros or high teving motors were in use
Most powered by ST 46 and 60
Jose modesto

Hi Jose.  Good to hear from you!

I'm curious if you all played with CG locations and handle line spacing in an attempt to reduce the control input required for a desired rate of pitch change?   Your comment about winding up in the wind brought that question immediately to mind.

Also, how big was the stab/elevator area with respect to the wing/flap area? 

I remember seeing one of Windy's big flapped ships at a Circle Burners dinner event I attended back when I was New York on a layover.  I can almost remember my eyes growing to nearly the same surface area as those flaps!!!  Quite an adventuresome approach for sure.

Ted

Offline jose modesto

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Re: flap chord
« Reply #10 on: April 14, 2020, 12:05:33 AM »
Mr. Fancher. Great to hear from you.
In the N30 section there is a thread Big Jim Designs with numerous photos of the high aspect LJ and BJ models

First the high aspect ratio model  were 7 to 1  with controls 2/3 flaps to one for elevators.
The LJ ST/46. 63” span. 25% airfoils (measured with out flaps  Rabe style) the stab we’re built in two ways  design stab Jim Called the tadpole stab ( see N30 thread for plans )

Second option was standard 1/2” thick 3”to 2” 31” span

Our challenge Speed gain in consecutive maneuvers in the wind ( hold on )
The high aspect ratio wing was very efficient,add the  large flaps with reduced travel and you had tremendous lift with minimal
Drag

You wrote a column  in 84 that was a bit controversial
Unfortunately I’m not in NYC and don’t have access to my plans, notes and models
Jose modesto



Online Brett Buck

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Re: flap chord
« Reply #11 on: April 14, 2020, 04:29:37 PM »
Our challenge Speed gain in consecutive maneuvers in the wind ( hold on )
The high aspect ratio wing was very efficient,add the  large flaps with reduced travel and you had tremendous lift with minimal
Drag

    Smaller flaps with more deflection would have had even *less* drag. It's more about the aspect ratio that it is the flaps.  That was the same issue everyone had with it, and with a 4-2 break engine, there wasn't a good solution. It might work a lot better now, electric with feedback would not permit it to wind up that way. 

Quote
You wrote a column  in 84 that was a bit controversial

   It wasn't controversial at all. The trim setup of those airplanes was the *diametric opposite* of what Ted (and the other successful pilots) were doing at the time, he merely pointed out how different it was.

    At the time, no one understood how insecure/hyper-sensitive Windy and his cohorts were, nor that you might take pretty mundane observations about trim and airplane setup and turn it into a blood feud. So people tip-toed around you for a long time, until we couldn't anymore (2004).

     Brett

Offline frank williams

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Re: flap chord
« Reply #12 on: April 14, 2020, 06:45:29 PM »
    Smaller flaps with more deflection would have had even *less* drag. It's more about the aspect ratio that it is the flaps.  That was the same issue everyone had with it, and with a 4-2 break engine, there wasn't a good solution. It might work a lot better now, electric with feedback would not permit it to wind up that way. 
I not sure I understand that.  The data shows that the drag is greater for a 20% chord flap at 30 deg deflection than for a 30% flap at a 20 deg deflection.  Looking at one of the very large flapped BJ models (~40% chord) with a small deflection .... if you were to keep the same overall wing chord and build with a smaller flap chord and deflect it a greater amount to get the same lift ... that it probably create more drag.

Offline jose modesto

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Re: flap chord
« Reply #13 on: April 14, 2020, 11:50:08 PM »
Brett in the n30 thread. Ther is a photo of ted winning the Nat’s and two high aspect ratio models that placed in the top five
Windy and Bob Baron  Baron with the LJ 63” span  Windy with the BJ 72” span
Windy placed in the top 5 five for 5 consecutive years flying the 72” models with the large flaps. Baron placed top 5 two times with the 63” models
Sounds like successful models based on their placing
In your second paragraph you used “you “  who is the you in that paragraph
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Offline Mark wood

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Re: flap chord
« Reply #14 on: April 19, 2020, 09:26:16 PM »
I not sure I understand that.  The data shows that the drag is greater for a 20% chord flap at 30 deg deflection than for a 30% flap at a 20 deg deflection.  Looking at one of the very large flapped BJ models (~40% chord) with a small deflection .... if you were to keep the same overall wing chord and build with a smaller flap chord and deflect it a greater amount to get the same lift ... that it probably create more drag.

That's one of those things about data. How does it relate to actual operation? I once consulted on a sprint car wing design and did the, "well if you set the wing at 15 degrees the drag will be lower and you'll go faster" and we went out and tested it. Turned out the raw down force was more important than the drag. The impact of increased traction far out weighed the drag impact of the wing.

It is a very difficult thing to take engineering data and apply it to every day operations. The reality is that he pilot in the loop aspect changes the dynamic. That 30% flags have less drag for a given Cl is a good point to ponder and that the data says it should work better. However, do you know what the design point Cl is? The assumption in the analysis is that the input is full deflection controls. While that may be the case, often times that full deflection is only a very brief transient. Wind tunnel data is very rarely transient but rather steady state.

Lift and drag are quite different transiently. In order to understand how that works, you have to look at data from helicopter testing where they test airfoils moving cyclically in time. Transiently, lift is always higher than static and drag is lower. In square maneuvers more than likely pitching moment is is the dominant characteristic in the response of the aircraft. The smaller flaps have a lower pitching moment and the result is the pitch rate will be greater. Given that lift leads drag transiently, pitch rate is most desirable over Cl/alpha rate. This, in turn, favors lower Cm / Cl which then explains why airplanes with smaller chord flaps seem to perform better.
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Offline frank williams

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Re: flap chord
« Reply #15 on: April 22, 2020, 12:13:04 PM »
Hi Mark

I agree that the man-in-the-loop aspect of the problem introduces a different dynamic into the analysis.  In the end it’s got to feel right even if the analysis says otherwise.  I also understand that airfoils in transient motion don’t “look like” their stationary counterparts and have different mean chamber lines and forces than ones fixed on a sting in a wind tunnel.

Your case with the sprint car is interesting.  You were indeed correct in speculating that the aerodynamic drag from the spoiler would be less at a lower angle of attack.  The resulting reduced downforce turned to be a bigger player than the aero drag.

Actually I doubt that the proper experiment has ever been done regarding flap percentage of total chord.  One really needs to build two separate wings of the same overall chord length and vary not only the size of the flap chord but also the ratio of control throw to the surfaces.  I have built planes with 4 inch flaps that flew fine and qualified at the Nats.  However, these planes did not have a 1 to 1 flap/elevator hookup.  More like what Jose said, a 2 to 3 ratio. 

There are many ways to “skin the cat” in trying to design the perfect stunt ship.  That’s the fun part of the sport.  I just don’t feel that bigger than norm flaps are a death sentence for a design.

The attached plots have been colored to more easily demonstrate the equality of the two designs.

Online Ken Culbertson

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Re: flap chord
« Reply #16 on: April 22, 2020, 02:30:24 PM »

There are many ways to “skin the cat” in trying to design the perfect stunt ship.  That’s the fun part of the sport.  I just don’t feel that bigger than norm flaps are a death sentence for a design.
Amen to that.  Over the years I have cut back on flap and recently added some back.  I don't like a ship that pops it's nose up in a turn.  Large flaps on my ships have produced too much lift early on and made turns look like the plane was turning around the tail and pulling the nose around instead of flying tangent to the turn.  Particularly aggravating in the rounds.  A "Green Box" Nobler does that.  Less movement helps but so does less area. My last ship hit the balance perfectly.  It flew tangent to the curve, didn't yank the nose or kick the tail in corners  It had 1 3/4 mean chord flaps and 1:1.

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Online Brett Buck

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Re: flap chord
« Reply #17 on: April 22, 2020, 08:24:39 PM »

Actually I doubt that the proper experiment has ever been done regarding flap percentage of total chord.  One really needs to build two separate wings of the same overall chord length and vary not only the size of the flap chord but also the ratio of control throw to the surfaces.  I have built planes with 4 inch flaps that flew fine and qualified at the Nats.  However, these planes did not have a 1 to 1 flap/elevator hookup.  More like what Jose said, a 2 to 3 ratio.

   One thing everyone should be aware of is that the flap/elevator movement ratio is a *very sensitive* adjustment. Very small adjustments can make a *huge* difference in the response. As a result, it's very easy to go overboard on the change and jump from too little elevator to too much. Extreme ratios are only required in extreme circumstances (like Windy's "40% flap") models or those made abnormally heavy or light compared to the design weight.

    The feel and feedback is just as important as the technical details of the lift VS drag, maybe more so, because running out of either lift or power has been a non-issue for at least 30 years.

      Brett

Offline Matt Piatkowski

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Re: flap chord
« Reply #18 on: April 23, 2020, 09:38:06 AM »
Please see https://stunthanger.com/smf/open-forum/flaps-geometry/ started my me.
The end of this thread deviated from the subject because of my discussion with Igor Burger that, though quite interesting, concentrated on trimming his Max Bee II and my Big Red that is based on Max Bee II.
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Offline frank williams

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Re: flap chord
« Reply #19 on: April 24, 2020, 05:57:35 PM »
   ....... or those made abnormally heavy or light compared to the design weight.

      Brett

I've occasionally toyed with the idea of using heavy/light flaps to allow the rotational forces of the maneuver to provide some level of pitch stability augmentation.

Offline Howard Rush

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Re: flap chord
« Reply #20 on: April 24, 2020, 07:13:27 PM »
We don't mass balance our control surfaces.  Maybe we should, but my planes are heavy enough already.
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Offline Mark wood

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Re: flap chord
« Reply #21 on: April 24, 2020, 10:27:43 PM »
We don't mass balance our control surfaces.  Maybe we should, but my planes are heavy enough already.

That's another can of worms in itself. The primary reason why the 4/4 scale aircraft balance their surfaces is to prevent flutter which is generally not an issue with models. Models have stiff relatively tight controls and as such, don't require balance. Many of the treatments that the 4/4 size aircraft do such as spades and 25% hinge line surfaces are done in order to reduce stick forces which would be of interest. The latter would be interesting as, when combined with control surface profile changes could lead to better performance. The latest trend is to make the aileron fatter than the parent airfoil at the front which reduces the pressure and when it is combined with the hinge offset to the 25% chord of the surface acts as a kind of "power steering". This same effect could help with the non-linearity of the flapped airfoil lift curve although, it's hard to say if that is really an issue as a result of the dynamic nature of the particular maneuver transient. Interesting thought channel though.

On the 4/4 aircraft we can tune the stick forces by variation in the size and shape of the spades forward of the hinge line. This is something which could be used in the same manor of the CL model. I'm not very experienced in the nuances of the flight trim on these CL aircrafts but I am learning. The mass balance of the control surface has to be in front of the hinge line to prevent inertial coupling driving the flutter oscillation. The spade puts weight out front and some area which offsets the hinge moment of the surface. A model with "too large" of flaps which cause high control forces but work well in terms of the Cl/Cd could quite reasonably be tuned using spades. For that matter any size flap / elevator combo could be tuned by variations of spades.

Here's a couple of photos of a plane flap aileron as used on the Stephen Akro / Laser. One is a couple of spades sitting on each other and the other is doing static balance. The last one is of Leo's airplane where you can see how they are mounted on the lower part of the wing. Even though static balance is good the stick forces without spades are quite high. With the larger spade the stick forces are light on that particular aircraft even out to 230 MPH.

This aileron is very similar to what is used as a flap in the CL models and the same methodology could be employed as a trimming practice. In reality they probably wouldn't be all that heavy. There are drawbacks however, sometimes there is poor centering and can be some non-linearity. The approach is to gradually make the spades larger until the desired control feel is achieved. There are a number of NACA test reports available on this and can be a very interesting read if that's your thing. Otherwise, making a mount for a spade on a flap really isn't any harder than installing a control horn and making a provision to hold onto a small flat plate. Thin 1/32 ply would work because it would only require a couple square inches.

This is one of those times when a couple good tests would be worth doing and fun to mes around with.

PS, the attachment police wouldn't let me post all the photos.
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Offline Mark wood

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Re: flap chord
« Reply #22 on: April 24, 2020, 10:53:45 PM »
A follow up my previous post. The Photo of Leo's airplane hanging in the Smithsonian and one of my airplane so you can see how the spades are relative to the wing. The spade acts as a kind of canard for the aileron and move the aerodynamic center forward reducing the hinge moment. When you consider the control surface needs weight anyway this is a great way to install it. Obviously the model doesn't need the weight but the ability to trim could pay it's way onto the aircraft.
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Offline Howard Rush

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Re: flap chord
« Reply #23 on: April 25, 2020, 04:37:16 PM »
Hinging the flaps aft of their leading edge would be good.  What's a low-friction way of sealing the gaps, assuming they need sealing?  Spades sound interesting.  They wouldn't have friction, but I would fear that they'd be really nonlinear and take a lot of fiddling.  I can't experiment much right now, but I want to try some of that stuff.   You "4/4 scale" aerobatics people are doing mighty cool controls trickery.    I've used balance tabs (picture).  They work, although I want to come up with (although I am not smart enough to do so) a mechanism that reduces their gain near neutral and increases it near max flap deflection.  Meanwhile, I'm using Igor's nonlinear flap mechanism, which, in addition to its other virtues, reduces hinge moment at high flap deflections. 
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Offline frank williams

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Re: flap chord
« Reply #24 on: April 25, 2020, 08:24:18 PM »
Mark.... that is a beautiful plane ..... aerobatics flying has to be tremendous .....  The spades are bigger than I thought they would be ... they might be useful on a stunt ship ...

Howard ... I was thinking that if one were to implement stability augmentation in a stunt plane, one of the first sensor feedbacks you would need would be pitch rate and normal acceleration.  I was looking for inertial moments and forces present in plane dynamics, like the centrifugal effects on flaps and elevator.  Maybe a weighted "servo tab".   

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Re: flap chord
« Reply #25 on: April 25, 2020, 08:57:23 PM »
 “ They work, although I want to come up with (although I am not smart enough to do so) a mechanism that reduces their gain near neutral and increases it near max flap deflection. “

Howard,
Leo’s spades accomplished what you may be looking for.  He called them flying spades.  The spades in the picture of Leo’s airplane have a symmetrical airfoil that is hinged similarly to a all flying stabilizer with bob weights forward of the leading edge just visible in the picture. In operation they floated around center providing no reduction in stick force with adjustable stops in both directions.  As the aileron was deflected the spade would stay in the relative wind until the stop was reached.  From that point to full aileron deflection they worked like a normal spade providing essentially power steering. 

The benefit was good centering and lighter stick forces as the ailerons are deflected.  Leo’s solution was a very clever design. I am not aware of any one else ever using it. 

Tim

Offline Howard Rush

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Re: flap chord
« Reply #26 on: April 25, 2020, 09:55:24 PM »
That’s too cool.

I was also thinking of trying your aileron strips on the flaps together with a high- gain tab.
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Offline Mark wood

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Re: flap chord
« Reply #27 on: April 28, 2020, 12:55:22 AM »
Mark.... that is a beautiful plane ..... aerobatics flying has to be tremendous .....  The spades are bigger than I thought they would be ... they might be useful on a stunt ship ...

Frank, I honestly think so which is why I mentioned it after reading the discussion on the control force impacts of the flaps. Yes, the spades on my Laser are fairly large. Larger than most and are quite effective. Like many aspects of this airplane stuff, they can be as much science as they are art. There are some elements to them though such as they can be non-linear or cause centering issues. The delta plan-form, such as what I used, seems to work reasonably well in both those regards.

Having said that, spades are a bit of a band-aid. Control surface balance is often done by other means such as offsetting the hinges back in the surface. One of the more obvious examples is the rudder on the DC3. The trouble with doing it that way is the difficulty in making changes which spades can be done in very short order. Modern aerobatic airplanes are using a combination of both techniques. The Laser is an older design and it uses a plane hinge flap for the aileron, today we wouldn't use that style.

For models, it would not be a hard effort to employ a spade as a trimming tool. For instance, models having large flaps that turn well but have control forces which are undesirable could have those forces trimmed using a spade to a more desirable level. It's not a new or novel idea, just hasn't yet been brought into the CL stunt arena. There's zero reason not to try it.

It would be very easy to make a mount for the spade. There area couple of things to watch out for. The spade needs to be in front of the hinge line. The spade should collide with the wing surface or create a thin gap which can cause some control irregularities. Ground clearance can be a factor as well.
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Online Lauri Malila

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Re: flap chord
« Reply #28 on: April 28, 2020, 04:05:16 AM »
Mark,

In a real plane the spades seem to be only on the underside of wings. I understand that in a real plane that gives a symmetrical effect, when the flaps (or ailerons?) are used to spin the airplane to either right or left.
But but, how would you create a symmetrical effect, to both up and down direction, like what’s needed in our stunt planes? Would you have to stick them spades on both sides of wings? With my logic they would counteract each others, leaving just additional drag.
Sorry for perhaps silly question, it’s well possible that I have missed something.. L

Online Tim Just

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Re: flap chord
« Reply #29 on: April 28, 2020, 07:24:04 AM »
Here is an example of spades on both sides of a control surface. This is standard on Panzel’s    I have seen this done on elevators too.

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Offline Howard Rush

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Re: flap chord
« Reply #30 on: April 29, 2020, 02:33:46 PM »
With my logic they would counteract each others, leaving just additional drag.

They would counter the flap hinge moment.  They would provide a moment helping to deflect the flaps, opposing the flaps' dislike of being deflected.  The hard part would be balancing the two effects over the airplane's ranges of flap deflection and angle of attack. 
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Offline Howard Rush

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Re: flap chord
« Reply #31 on: April 29, 2020, 02:40:25 PM »
Frank has a good point, I think, about bobweights.  One might start by calculating the effect of the mass of claptrap (control surfaces, pushrods, Igor linkage, etc..) in our airplanes now. 
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Offline Igor Burger

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Re: flap chord
« Reply #32 on: April 29, 2020, 02:57:59 PM »
Frank has a good point, I think, about bobweights.  One might start by calculating the effect of the mass of claptrap (control surfaces, pushrods, Igor linkage, etc..) in our airplanes now.

If you mean weight of that slot and ball bearing, then it is clear, it makes something like power stearing allowing to be CG few mm forward (goes easily to corners, but it has better static margin of stability). Try simple test, add small weight, for example 5g to trailing edge of elevator. When I do that on mine model, it flies corners aproximately with the same handle impulse. Means I not need to do corners with different effort (lighter). But if I add those 5g to fixed part of fuselage, models goes to corners much easier than before. And since that weight on elevator acts opposite way as the weight on TE of flap (like that ball bearing) then you can see effect of that ball bearing. If you do not like that positive feedback, you can cancel it by counter weight on the second bellcrank or on TE of elevator.

Offline Mark wood

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Re: flap chord
« Reply #33 on: April 30, 2020, 09:07:04 AM »
Mark,

In a real plane the spades seem to be only on the underside of wings. I understand that in a real plane that gives a symmetrical effect, when the flaps (or ailerons?) are used to spin the airplane to either right or left.
But but, how would you create a symmetrical effect, to both up and down direction, like what’s needed in our stunt planes? Would you have to stick them spades on both sides of wings? With my logic they would counteract each others, leaving just additional drag.
Sorry for perhaps silly question, it’s well possible that I have missed something.. L

Yes, the spade works in both directions. You can think of how it works in term of balancing the area in front of the hinge with the area behind the hinge in the same vein as how a stabilizer works on a wing. The only trouble is the spade is a separate surface and behaves like a free airfoil, while the flap (aileron) has bound flow conditions. Stalling is not very good when it comes to a spade which is why you see them delta shaped.
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