Here is the picture to the last post.

Quote from: Dave Hull on March 09, 2026, 02:46:23 AMIf the goal was to "unload" the high flap control forces from large flaps, then incorporate either spades or better yet, anti-servo tabs.

Like this?  They work, but effectiveness seems to be higher at low flap deflections than at high flap deflections.  One might come up with a cam mechanism to fix this.  Igor's nonlinear flap system seems to be better at relieving hinge moment at high flap deflections.

Good stuff, guys. Thanks for the pictures!

There's an old Scarinzi plane that explores the huge flap, low throw concept. Flaps look to be about 50% of wing area, move just past making the airfoil flat bottom (or top). Super Flipper (oz13296)

Reducing hinge moments is what all of my dialog regarding off setting hinges is about. It should be possible to have flaps as large you wish with very little hinge moment. A hinge placed around the 25% chord line results in near zero hinge moment which we really don't want to go too far as then the surface can snatch as in go to full deflection. I'm currently a flying stab model that has a tendency to that when the lines get slack during maneuvers. I managed to invent a new maneuver which I am calling the vortex. After I observed occasion un-commanded rate increases as in sever tightening of the corner in the square 8 on the up wind side and similar event during the overhead 8 I decided  to do what I do and see if I could intentionally induce it. Sure enough I figured out first what was happening which was the flying stab was going fully to the stop when slack. I am using a centering style bellcrank because the flying stab has no inherent centering of it's own. During the overhead 8 test case the airplane wound upin a very type uncontrolled loop directly over head. It was simultaneously entertaining and frightening because it coming down on top of me. Balanced surface hinges are used in pretty much all of the modern 4/4 scale aerobatic aircraft. There's more treatment than simply balancing we can do and gain significant Clmax while reducing the drag. But that requires a new airplane design paradigm for Cl PA.

The full flying stab is a case in point. It has a very low hinge moment. I don't know how little it really has and I was planning a sequence of tests from an significant offset bellcrank to low and then finally neutral geometry. But with the experience I just had, I may not. First thing I'm doing is balancing the surface properly. The CG of the surface is behind the hinge pivot line which is statically balanced but force wise divergent stick stick. I have statically balanced the stab now and will go back out and test again.

There are other ways of balancing the flaps than servo tabs, spades and hinge offset that are used. You will often see horn in play although they typically small. My 4/4 laser had a small one but I don't think it contributed much. The spades on the hand were significant. Spades are teh stuff when it comes to flexibility in trimming away control forces and are perfectly usable on models. In my experience and build plans, the combination of offset hinge and spades are very usable.

Flaps on the order of 30% - 40% are in the zone of reasonable wit h very little hinge moment necessary. Once your mind departs the concept of a flap being part of the and is considered a wing itself then how to make it work is much less of an intellectual challenge. The flap can be considered a wing and when properly balanced will fly just fine.

Control feedback wise my intended design direction is to get the flap flying with minimal hinge moment and use the elevator as the feedback element to the pilot. The full flying stab is on the extreme side of that balance equation and I'm not sure if it will be the right solution. Not because it isn't workable but more because it is very responsive around neutral, ie smooth level flight is a touch more difficult than the standard elevator.

Spades absolutely work - too well in fact. Mark designed a set for me, and I installed them on my Trifecta.  The difference in handle backpressure in maneuvering was dramatic.
I suppose if you didn't rely on that backpressure in your corners, it would be fantastic. To my surprise I unexpectedly found out I did.  Learning how to change a subconscious trigger is like stopping palms up inverted after 65 years of doing it that way.

Ken

Quote from: Ken Culbertson on July 16, 2026, 03:35:07 PMSpades absolutely work - too well in fact. Mark designed a set for me, and I installed them on my Trifecta.  The difference in handle backpressure in maneuvering was dramatic.
I suppose if you didn't rely on that backpressure in your corners, it would be fantastic. To my surprise I unexpectedly found out I did.  Learning how to change a subconscious trigger is like stopping palms up inverted after 65 years of doing it that way.

Ken

The answer to that is you can adjust size of the spades larger or smaller to suit your taste. The spades you flew initially were arguably too large. I was surprised when you flew them as my advice was  to make some smaller ones first. Sizing spades should begin small and get bigger, not go large and back down. The problem occurs when they are too large and the deflection force becomes divergent which causes the surface to want to increase it's angle and go full stop. The term used for this is called "snatching". We don't want that. In this arena such concepts are foreign. In the 4/4 scale aerobatic arena this is method of trimming stick forces. When we're discussing larger flaps the limit of effectiveness is the available hinge moment. The maximum deflection of a large surface will be 1) the physical stop or 2) when hinge moment equals available hinge moment. Making flap and elevators larger does not equal more maneuverability if the latter is already limiting the deflection. Then other issues happen when the airplanes slows down and the balance allows increased surface deflection. The term snap loop or flip come to mind in that case. Or if the airfoil has a nasty stall characteristic then the proverbial snap loop on a string can happen. I have an airplane that does that too. 

Quote from: Mark wood on July 17, 2026, 08:22:30 AMThe answer to that is you can adjust size of the spades larger or smaller to suit your taste. The spades you flew initially were arguably too large.   

You are right.  They were too big at first, but they were downsized considerably more than the even the picture in the prior post which is the smaller set you sent. After I changed to the smaller set you sent, I downsized them even further. It was after many flights that I realized that they really worked but this plane didn't need them.  Remember the Trifecta has logarithmic flaps.  I imagine it is something like going from a stick to fly by wire.

Ken   

Quote from: Ken Culbertson on July 17, 2026, 11:16:45 AMI imagine it is something like going from a stick to fly by wire.

Ken   

Not really. FBW systems have feedback but it is linearly proportional. I think Howard can speak to that better than I can. I have participated in a couple aircraft that had FBW but I'm the FADEC guy. On the 4/4 they take you from shoulder hurting stick forces to manageable stick forces. On my Laser for instance it was more than just the stick forces. At high velocities I huge stick force to push the stick to full extent at 220 knots wound the drive toque tube up such that the 27 degree static deflection of the ailerons was only about 10 degrees. The resulting roll rate was meager. After installing spades the repeat test with much reduced stick force resulted in near full deflection and a good 200 degree/s roll rate. The full size spades improved even further. Small flaps and elevators are fine. But playing in the extreme in entertaining. Another way of reducing the hinge moment and on the very good approach is to increase the aspect ratio. Two otherwise similar stabilizers with different aspect ratios and elevator stab chord distribution say 60/40 the higher aspect ration combination will have lower hinge moments as the result of smaller chord of the elevator. Bonus is the surface has a steeper lift per degree slope.

Quote from: Michael LeGate on March 24, 2026, 08:07:47 PMThere's an old Scarinzi plane that explores the huge flap, low throw concept. Flaps look to be about 50% of wing area, move just past making the airfoil flat bottom (or top). Super Flipper (oz13296)
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