Discusion Thread: Raceair Skylite Build and sub-kit developments

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GeeZee

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Marc, a fuselage CAD model would be a tremendous help. Thanks!! I’m only 5’11” but extending the cabanes sounds like a good idea for general visibility and “roominess“. I have Fusion 360 and have poked around at it but not really learned how to use it and have downloaded freecad but haven’t even looked at it yet so maybe either of those can be used as a “viewer”.
 
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...elsewhere in the plans it shows a standard 1/4-28 threaded Ball end and McMaster has loads of them in various versions...

Loading a 3/8" rod end shank in bending as depicted gives me the heebie jeebies, but looking at my engineering tables, it is probably going to be okay unless badly abused.

Loading a 1/4" rod end shank in bending as depicted probably won't break immediately, but looks like it would be a huge fatigue liability, and I wouldn't want it flying over my house.
 

cluttonfred

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Loading a 3/8" rod end shank in bending as depicted gives me the heebie jeebies, but looking at my engineering tables, it is probably going to be okay unless badly abused.

Loading a 1/4" rod end shank in bending as depicted probably won't break immediately, but looks like it would be a huge fatigue liability, and I wouldn't want it flying over my house.

So what do you think of putting rod ends on both ends of the elevator pushrod and making the reverser with tabs and a bolt at both ends?
 
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Ok so I had a chance to take everyones suggestions and made the changes today.

1649799502468.png

Circled in Red is a ball end for an AN3 bolt with a 1/4-28 shank. Circled in blue is a weld in rod end blank that will be drilled out for an AN3 bolt. This will keep the internal pushrod from rotating. The reverser is now made from a piece of Square tubing to make fabrication a bit easier. Only thing I may change is the bent metal yoke parts likely need a larger radii around the AN3 bolt hole to have more edge clearance. I also upped the diameter of the main yoke tube a bit from that used on the Lil Bitts since the Skylite has a longer internal pushrod so Ed chose .5" in diameter and I needed more clearance for it to raise and lower as it actuates.

Now for another question. How much stroke (stick movement) should I am for in Pitch and Roll. I currently have about 25 degrees in each axis from neutral. I can back figure what I have to a linear dimension if needed, but it seems quite a bit in the CAD model so far.

Thanks again to everyone for their suggestions. I am feeling a bit better about this over the side loaded rod end.
 

TFF

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If I’m reading it right the solid part needs to be on the stick and the rod end needs to rotate inside the elevator idler.
 
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If I’m reading it right the solid part needs to be on the stick and the rod end needs to rotate inside the elevator idler.
Not sure what you mean by this TFF. If you look back in the thread I originally modeled this control column based on the original plans and layout. Boku pointed out that I should redesign to not have a ball end on top of the reverser rod being loaded off axis to the thread shank. the reason for the ball end is as the column is rotated so is the aft end reverser that is attached to the elevator pushrod and the ball end takes up the misalignment for that to happen. Fix was to relocate the ball end from the reverser to the elevator pushrod so all loads are mostly in line with the threaded shank. Downside is now the elevator pushrod has the ability to rotate but I can likely solve that with a rolled pin in one ball end, Tack weld or safety wire.
 

TFF

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The rod end does need to be off the reverser it’s self, but a joint still has to rotate at that point. Switching positions with reverser and rod, not eliminating it. With that type of setup that whole unit moves to handle the ailerons and it has to pivot at that point. Pivot at the stick not important as it’s only pitch.
 

cluttonfred

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I actually don’t see any need for spherical bearings where red and blue circles are at either end of the tube that transfers pitch input from the stick to the reverser. That could be a simple square tube with flat tabs to fit inside the tabs on the control stick end and the reverser end with a steel tube spacer and a well-greased bolt and safetied castle nut at each end. There is no rotation in those joints as the whole assembly moves together when roll input is applied. Rod end bearings on both ends of the push-pull tube to the elevator as discussed would handle the skewed angle when the stick is hard over.
 
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I actually don’t see any need for spherical bearings where red and blue circles are at either end of the tube that transfers pitch input from the stick to the reverser. That could be a simple square tube with flat tabs to fit inside the tabs on the control stick end and the reverser end with a steel tube spacer and a well-greased bolt and safetied castle nut at each end. There is no rotation in those joints as the whole assembly moves together when roll input is applied. Rod end bearings on both ends of the push-pull tube to the elevator as discussed would handle the skewed angle when the stick is hard over.
Your correct, no rod end is required on the pushrod that passes through the main Column Tube. I only left one end with the rod end so that I could have adjustment after welding to get the stick and reverser aligned parallel to each other. Suppose I could use a threaded rod end that is not spherical and do the same thing. And yes the connection from the reverser to the elevator pushrod as well as the connection to the elevator horn need the spherical joint to allow for the miss alignment as the connection between column and pushrod swings with roll application.
 
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Also remember this is an ultralight so the ball ends will not see the same loads as an airplane flying 3X UL speed. In retrospect due to this, the spherical joint likely would have been just fine on the top of the reverser, but from a why not do it the right way point of view Bobs suggestion to move it is the correct way to go.

On another note, I showed Ed my mods and he gave me the green light as well but also said something similar to the above about the low speeds but also said the whitman tailwind is done the same way and that thing fly's close to 4x UL speeds.
 

cluttonfred

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I only left one end with the rod end so that I could have adjustment after welding to get the stick and reverser aligned parallel to each other.

Cool, I am no engineer and was wondering if I had completely understood the issues. On this last point…as long as you’ve cut and measured everything reasonably accurately, what difference would it make if the stick and reverser are slightly out of parallel? It seems like an unnecessary cost and complication when the two rod-ends on the elevator pushrod give you plenty of leeway for adjustment.
 

BJC

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It seems like an unnecessary cost and complication when the two rod-ends on the elevator pushrod give you plenty of leeway for adjustment.
That will allow for one adjustment, but if anything is different on a specific aircraft, the additional adjustment allows tayloring the stick movement vs elevator position.


BJC
 
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Cool, I am no engineer and was wondering if I had completely understood the issues. On this last point…as long as you’ve cut and measured everything reasonably accurately, what difference would it make if the stick and reverser are slightly out of parallel? It seems like an unnecessary cost and complication when the two rod-ends on the elevator pushrod give you plenty of leeway for adjustment.
Since the assembly still requires welding, make one end a telescoping tube size and fix location during fit assembly by using a rosette weld then finish weld the fish mouth offline before final assembly
 
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