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Old 09-09-2017, 09:24 PM   #1
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Default S1 Elevator - not to plans

My S1 was built without the HS bearings/bracket and with a control attachment different than the plans.

Is this an older style or an 'improvement'?

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Unfortunately the Elevators do not have the inner tube offset so the bearing wont fit as-is....

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Old 09-09-2017, 10:00 PM   #2
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Not anything I have seen before. If you are stripped like that I would put it to the plans.


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Old 09-09-2017, 10:21 PM   #3
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I have seen that many times before. I think it was an older version of the plans
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Old 09-09-2017, 10:37 PM   #4
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I still want to know about the. H you guys talk about on the horizontal Stab.
Any photos to help explain this H
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Old 09-09-2017, 10:44 PM   #5
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Structurally the inboard strap hinges shown in the photo are replacing the centre bearing.

If it were mine I'd leave it as is.

When you add a third support, getting all three aligned becomes problematical.

Andrew.
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Old 09-09-2017, 11:11 PM   #6
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Quote:
Originally Posted by Flyboyeaa View Post
I have seen that many times before. I think it was an older version of the plans
Never seen it with the "curve out" in the arms, although it's similar to the early Pitts plans. This is a Curtis built airplane in 1970. I'd research a bit more if it was mine.
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Old 09-09-2017, 11:20 PM   #7
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I've never seen how the fork is completely on inside of the elevator pitch horns outside maybe but not on the inside with that big a gap between.
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Old 09-10-2017, 12:33 AM   #8
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Default S1 Elevator - not to plans

I'm wondering if the curve was because once he built the pushrod and elevators the horn went strait up it wouldn't fit inside his pushrod or outside so he decided to bend them so they would fit the outside? Ideal setup id think would be to remake the pushrod end with a rod end that would fit between the two existing elevator horns. That way you can tight that bolt up and you would have a bearing there not have to leave the bolt loose so it is the bearing surface as it is now. Make since? Even if the gap between the horns is not exactly what a standard rod end is you could use spacers to make it so. But by doing it that way you would have a bearing in play there not the horn and pushrod ears taking all the movement.

Don't know...just ideas.
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Old 09-10-2017, 01:23 AM   #9
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Ok - so it is not an 'improvement'. Does anyone have a plan photo that they could post so I can see what was intended?

Thanks
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Old 09-10-2017, 02:18 AM   #10
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Default Elevator

The photo in post 6 is the design immediately prior to the center bearing configuration. Note that the depth of the pushrod fork appears to be substantially greater than in the OP. This design experienced some problems with the original AN3 bolt wearing out very quickly.
All Pitts aircraft use 1.5 x bolt diameter for edge distance, measured from the hole centerline. (steel fittings) An AN4 bolt in the elevator horn probably does not have adequate edge distance.
Regarding the OP, I would be replacing the elevator horns and the fork end on the push tube.
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Old 09-10-2017, 02:20 AM   #11
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I don't have the four hinges plans, below is the push rod from pin hinge design. Sorry for the poor quality, the plans were old and faded when I got them.
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Old 09-10-2017, 03:37 AM   #12
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Quote:
Originally Posted by cwilliamrose View Post
I don't have the four hinges plans, below is the push rod from pin hinge design. Sorry for the poor quality, the plans were old and faded when I got them.
That is a drawing from the 1960's. From the factory plans for the S-1D that were released in the early 70's, copies of the production drawings, they showed the current welded male threaded rod that the bearing screws on to. I remember reading an article in Sport Aviation many years ago about the annual inspection on Tom Poberezny's Pitts S-1S (which he built from components manufactured by Curtis) and it had this old style push-rod. The 3/16" bolt had worn about half-way through. I believe Curtis came up with the new rod end bearing push-rod right after that.

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Old 09-10-2017, 06:39 AM   #13
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Bill's excellent diagram here: http://www.biplaneforum.com/showpost...47&postcount=5

And more discussion here http://www.biplaneforum.com/showthre...evator+bearing

Mine looks like Post 6 as well, and I added that lower bolt myself (AN3 for me) after thinking about the physics. Trying to recall if I replaced the original top AN3 with an AN4, after hearing all sides of the discussion.
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Old 09-10-2017, 04:01 PM   #14
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I'm just curious how that center bearing hinge works?

My guess...
1)
A short piece of tube is slid into the end of the elevator spar tube...it's then rosette welded to the spar. This inner tube is what set the spacing and is the "seat" for the KP4 to rest one side on.

2) on one of the sides a 1/4" bolt is welded to the short piece of tubing that is slid into the elevator tube. Maybe a washer like piece is welded to the short tube before it's slid in?

3) now when you install the elevators you pull the horns tight together so the two bearings are pressed to the tab off the fuselage. This tightness is held by the spacer block and the two bolts.

4) the rod end now fits between the top two ears of the horn. (Or it should if you did it right)

Just trying to understand that center hinge thing and how a bolt passes through it etc.
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Old 09-10-2017, 04:14 PM   #15
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Boy - a lot of variations.

My elevator horns are outside the fork - #6 inside.

To make to plans I'd have to make new horns/actuator tube and deal with the bearings not fitting in the elevator tubes and fab a bearing bracket.

I'f mine looked like post #6 I'd fell better, but at this point it is not current plans nor original plans it seems.

I've got to give this some thought - this plane has a lot of hours and the fork/horn holes are not worn. There is always the 'if it aint broke' line of thinking :-)

Thanks
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Old 09-10-2017, 06:03 PM   #16
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Old 09-10-2017, 09:59 PM   #17
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If it were mine I'd strongly consider putting a rod end bearing on the aft end of that pushrod (or build a new one) and using the elevators virtually as-is. It would be a 'customized' system but better than the one you have now. What that would do is to eliminate any bolt wear and slop from that joint. You would need a spacer similar in function to the one found on the later factory airframes but without the KP4 bearing pair at the spars. The spacer would set the distance between the two elevators such that the hinges are free and not side-loaded. Where the rod end is attached the spacer (or a stack of washers on each side) would allow you to tighten the bolt and clamp on the rod end's inner race solidly.

What I describe would not change any geometry or add any loads. None of the changes would not require any welding to the existing structure. You would need some 3/16" holes in the elevator arms to attach the spacer, just like the later designs have. It's a simple solution and an improvement in every way even though it's not quite as good as the later design.
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Old 09-11-2017, 02:27 AM   #18
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Bill;

Thanks for the suggestions - I think I will go this way - I have extra rod end bearings.
The spacer could be made to accommodate the curved horn and no bolt wear.

Thanks
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Old 09-11-2017, 04:18 AM   #19
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Acro 2 tail copied from Pitts;
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Old 09-11-2017, 11:00 AM   #20
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Ahhhh. So the two bearings are bolted to the horizontal and then the elevators are slid over them. Seems like it would be fairly easy for the elevator tube to bearing surface to not be tight enough?

Anyhow. I think I see how the middle bearing system works. Although I have no idea how that bearing is suppose to be tight enough to allow it not to rotate inside the elevator spar.
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Old 09-11-2017, 11:16 AM   #21
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Default Center Bearings

If everything is dimensionally within tolerance it works fine. The bearing is a snug but not press fit inside the 1" x .049 elevator sleeve. Retainer rings on the outboard strap hinges also contribute to limited lateral movement.
There have been failures of center bracket to tube, maybe on an Eagle?? I believe Steve Wolf has a mod for the center hinge that strengthens it substantially.
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Old 09-11-2017, 12:21 PM   #22
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Mine was exactly like that and I changed it to the newer design with a rod end bearing. You will also want to look at your forward torque tube bearing/ attach. That is likely the older style and a source for some slop. I had to make new pushrods as the entire stack up was a bit off. If you change one thing there will be 10 others that need it too.
FWIW- Aviat has the forward torque tube attach pretty cheap. It is a bit of a pain to machine so I just bought mine and could not have done it for what it cost.
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Old 09-13-2017, 03:10 PM   #23
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The KP bearing is designed to fit inside that tube. It fits nice and snug, especially after all the welding is done.


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