Forward curved flap horn

[Steve Dwyer]

I'm curious what was the thinking was behind the forward curving flap horn. I realize it reduces the radius difference between both linkages to approach a 1:1 throw ratio. When did this come about? There is a ton if info here dating back to the very early years 60s on control ratio but no where can I locate an explanation on the curved horn. Here's a shot of the Pat Delaney Pathfinder Twin plan using it.

Steve

[Lauri Malila]

It’s just that you need to cut a smaller notch in the t.e. for clearance. L

[doug coursey]

Its done to make the pushrod 90 degrees to the control horn from the bellcrank

[Dennis Nunes]

I'm curious what was the thinking was behind the forward curving flap horn. I realize it reduces the radius difference between both linkages to approach a 1:1 throw ratio. When did this come about? There is a ton if info here dating back to the very early years 60s on control ratio but no where can I locate an explanation on the curved horn. Here's a shot of the Pat Delaney Pathfinder Twin plan using it.

Steve

Hi Steve,
  When did this come about? I have no idea. May be some of the "historians" on this forum can shed some light on this.

  The purpose of the "curved" (or slanted) horn is as Doug mentioned and that is to maintain the 90 degree angle between the bellcrank and the flap horn. But it doesn't stop with just the flap horn. It should continue on to the elevator horn too. It was explained to me that this insures the equal travel of the flaps and elevators around neutral. See attached picture. Trying to maintain the geometry is one of several reasons why I make my own flap and elevator control horns. The horn layouts in the picture is what I use on my "inline" configuration (wing and stabilizer on the same elevation).

Dennis

[Doug Moisuk]

I was told the 90 degrees will give you equal up and down of the flap with the same up and down movement of the handle/bellcrank.

[Brett Buck]

Hi Steve,
  When did this come about? I have no idea. May be some of the "historians" on this forum can shed some light on this.

  The purpose of the "curved" (or slanted) horn is as Doug mentioned and that is to maintain the 90 degree angle between the bellcrank and the flap horn. But it doesn't stop with just the flap horn. It should continue on to the elevator horn too. It was explained to me that this insures the equal travel of the flaps and elevators around neutral. See attached picture. Trying to maintain the geometry is one of several reasons why I make my own flap and elevator control horns. The horn layouts in the picture is what I use on my "inline" configuration (wing and stabilizer on the same elevation).

Dennis

  I note that the "crook" in the upright is to clear the wing or stabilizer trailing edge, so you don't have to cut a very deep slot to get full travel.

       Brett

[doug coursey]

I'm curious what was the thinking was behind the forward curving flap horn. I realize it reduces the radius difference between both linkages to approach a 1:1 throw ratio. When did this come about? There is a ton if info here dating back to the very early years 60s on control ratio but no where can I locate an explanation on the curved horn. Here's a shot of the Pat Delaney Pathfinder Twin plan using it.

Steve

He explains it in the diagram...to get equal throw in both direction

[Steve Dwyer]

To get my head around this I have to make a movable rigid paper system so I can measure the throws in both directions. I agree the curvature will reduce the the cutout in the trailing edge.  I'll post my mechanical proof shortly.

Thanks,

Steve

[Howard Rush]

I realize it reduces the radius difference between both linkages to approach a 1:1 throw ratio.

I don't realize that.

I was told the 90 degrees will give you equal up and down of the flap with the same up and down movement of the handle/bellcrank.

Don't believe everything you're told.

[M Spencer]

To get my head around this I have to make a movable rigid paper system so I can measure the throws in both directions. I agree the curvature will reduce the the cutout in the trailing edge.  I'll post my mechanical proof shortly.

Thanks,

Steve

I normally x#!*&+ anyone who suggests I need to draw something up twice full size  TO CHECK IT . ( Its always the fabricators who make the mistakes ! ) But Id suggest you do it FOUR or TEN times actual size .

This way any variations are way more evident , and fine tooning positions of things is vastly more refined .
Bacxk to reality , all the ANGLES are the SAME as your big one , so its easy to littleafy it after youve gottit sussed .

[doug coursey]

Tom Morris flap horns are called 90 degree horns on the package.....The bent flap horn was designed to keep the pushrod at 90 degrees to the pushrod....the smaller notch was just a side benefit

[Doug Moon]

Remember that everything that is "stock" is really just an approximate. Each of our airplanes requires exact calculations to ensure equal movement of the flaps and elevators in each direction. Howard has a nifty program that enables us to do a much more precise setup for each plane.

I'm getting ready to make a fully adjustable bench top fixture that will allow me to set the exact control system measurements (placement of all components in every plane; vertical placements, distance between the TE of the wing and the TE of the stab, etc. ) of my next intended airplane and allow me to adjust all the "angles" until I get as close to equal movement in both directions of both the elevators and the flaps as possible before I start building.

In the past we have mostly relied on "after build" adjustments to achieve our flight trim goals. Taking a lot more time thinking about and planning out the complete control system geometry is time and energy well spent.

Later - Bob     

I would like to see that nifty program. Howard?

Bob, I am curious how you will you will transfer the perfectly setup system on the bench to the model without any changes happening along the way? I am sure you will come up with a very cool way to do this. Please post pics when you do this.

For me, I use the curved horn that clears the TE as well. My BC push rod to the horn is adjustable.  One the fuse I have level lines marked. The wing is installed per these lines. Once it is installed I attach a protractor to the side of the plane 0 on the level line making sure the side of the protractor is butted up against the TE of the wing. Then move the horn per the controls and adjust the rod until the throw is the same up and down. Then install the stab. Set the elevator push rod to level and go fly. Adjust elevator push rod as needed for groove and feel. I know it is super basic and I think I got this out of SN back in the 90s but it seems to work. But I am very curious about the program.   

[Gordan Delaney]

Steve, I believe you met Gordan Delaney not Pat.

Gordy

[Steve Dwyer]

Gordan,

You are very correct....my slip.

I just bench ran the two OS LA 15s together.  Also fabricated a pair of mounting brackets to enable my swapping between the OS FP 25 and the 15s depending on the power needed for my upcoming Pathfinder Twin build

Steve

[Ken Culbertson]

I do something similar to Doug but I do it outside the plane where it is easy to monkey around with things.  This jig is exactly to scale and where everything is going to be, and now is, on the plane.  It was for my Sandpiper Tirfecta with a logarithmic horn.

Ken

[Howard Rush]

But I am very curious about the program.   

Sent you the curious program.  I just tried opening it in Windows 11 and got the message, "Microsoft has blocked macros from running because the source of this file is untrusted."  Looks like Microsoft is onto me. 

[Doug Moon]

Sent you the curious program.  I just tried opening it in Windows 11 and got the message, "Microsoft has blocked macros from running because the source of this file is untrusted."  Looks like Microsoft is onto me.

Thank you!

[Matt Brown]

I’ve been thinking on this subject the last week or two. While I was still working for a living I had access to a 3D modeling program and I realized that it would have been perfect for simulating the controls of the plane I’m currently working on. I thought I had it setup pretty close but I did a recheck a couple weeks back and found that the flaps are moving equally but I’m getting 5-6 degrees more down elevator than up at max throws. I figure I’ll fly it and see how much it hurts it. At my level, I’ll probably never feel it but I’ll know it’s wrong! I wonder if there are any freebie 3D modeling apps.

Matt

[Steve Dwyer]

Matt,

If the elevator horn points down below the elevator hinge line and you have a threaded swivel fitting I'd suggest unscrewing the fitting to increase the length of the pushrod to the elevator by 1 to 2 turns to even the throws.

Steve

[Matt Brown]

Matt,

If the elevator horn points down below the elevator hinge line and you have a threaded swivel fitting I'd suggest unscrewing the fitting to increase the length of the pushrod to the elevator by 1 to 2 turns to even the throws.

Steve

If I do that then flap neutral won’t be the same as elevator neutral.

[Steve Dwyer]

Matt,

A good way to verify the throws is by using an adjustable protractor. An adjustable threaded connector on your pushrod should enable you to achieve neutral on both control surfaces. Make sure the bell crank has equal movement in both directions when connecting the flap pushrod. The hole position on the horns dictates the amount of travel and degree of throw. The closer the connected holes are on the flap horn the closer the throws on both pushrods will be. The curvature in a flap horn is primarily to reduce the cut out of the trailing edge as pointed out here earlier. Adjusting the ball link on the elevator pushrod you should achieve close enough neutral adjustment that the model will track well in level flight.

Steve