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Big Tires and Expensive Lessons

kevin said:
STMAWR14 said:
So why did he put in a longer spring? What was the overall orginal length? and what is the new length with the longer spring?

I put in a longer spring because I am planning on using an O 320, PA-18 feathers and wanted to duplicate the PA-18 tail section. The back half of the plane will be -18. The lengths are shown in the pictures with the tape measures.

kevin,
am i adding that up right the overall cable and spring compo is ~3" longer on the-18 one? hard to tell, maybe not that much???

that would definitely not be as effective, well it would come into effect later in travel, but bigger spring would offer more effect when it did...

I not sure if you can even get the small spring now? can you?

i always use the old overall combo length to make the new combo.... never have had an issue....

I wounder if seaworthys was done with what you show, that would cause his issue for sure....

does the STC for the larger tail you are doing actually call out to change the cable & spring to -18 or you just doing it?
 
Mike,

According to the pictures, I show 3" too. This is a ballpark since it is hard to measure when it is around the bungee pulley.

I'm not sure you can get the small spring.

I don't have the STC yet for the larger tail. The cable and spring is something that I did to duplicate the -18. To be honest, I never thought about the length of the cable. I thought that the heavier spring was due to the bigger engine on the -18 over the smaller engine on the -12. If I have to change the cable, no problem. I'll gladly do it. Would you/have you used the longer, heavier spring with a custom made shorter cable to compensate for the overall length of the stock spring/cable combination?

Tom, It doesn't hurt to call Clyde Smith Jr. It's worth a shot right now. I'm not sure if a manual exists like what you are looking for other than the shop manual. I know the shop manual does not give any dimensions. Please keep me informed either on sc.org or email me personally. I am interested in this so I don't have this issue too. If I can be any more help to you, I will do my best.

KG
 
kevin said:
Mike,
...... Would you/have you used the longer, heavier spring with a custom made shorter cable to compensate for the overall length of the stock spring/cable combination?
KG

yes, I always use the old setup to make the new one.... (I did not make stewarts, he had already done it, but I assume he made it off the -12 one, not the -18)

will have to dig out the old one for this one someday and see what it is

not sure if he has the full paperwork here on the previous -18 tail install... concerning that cable/spring...
 
There is no reason whatsoever to change the length or strength of the bungee! The tail rigging where it attaches to a -12 feather is the same as on a -18 feather.

The purpose of the bungee is to relieve elevator stick pressure. If the spring is too long it won't do its job, or won't do its job as well as it is supposed to.

The bungee won't change how much elevator you have -- only the rigging will. If he is flying with the stick all the way back to keep it level, no amount of bungee assistance will give him more available stick.

He must have the rigging wrong or the plane is grossly misconfigured for CG.
 
mike mcs repair said:
kevin said:
Mike,
...... Would you/have you used the longer, heavier spring with a custom made shorter cable to compensate for the overall length of the stock spring/cable combination?
KG

yes, I always use the old setup to make the new one.... (I did not make stewarts, he had already done it, but I assume he made it off the -12 one, not the -18)

Mike, just so I understand, you are using the heavier, longer PA-18 springs and making your own cables. The length of your new cable is shorter than the original -12 cable because the -18 spring is longer. So if the -18 spring is say 3" longer -12 spring, the new cable you make is 3" shorter? By doing this, your cable/spring length is the same as the original?
 
kevin said:
mike mcs repair said:
kevin said:
Mike,
...... Would you/have you used the longer, heavier spring with a custom made shorter cable to compensate for the overall length of the stock spring/cable combination?
KG

yes, I always use the old setup to make the new one.... (I did not make stewarts, he had already done it, but I assume he made it off the -12 one, not the -18)

Mike, just so I understand, you are using the heavier, longer PA-18 springs and making your own cables. The length of your new cable is shorter than the original -12 cable because the -18 spring is longer. So if the -18 spring is say 3" longer -12 spring, the new cable you make is 3" shorter? By doing this, your cable/spring length is the same as the original?



I have not made this one yet....

but yes i always make it same overall length as the one removed... I just pound a nail in 2x4, hook one end of old setup, pull snug and put nail at other end and make new one same on those nails......
 
Tom,


This thread has really got my attention. I've been thinking about it and I was looking thru my pictures that you posted for me. My elevators are in the neutral position. The jackscrew is in the neutral position. I remember measuring the up/down travel in the jackscrew when I installed it. From what I remember, my travel was where it was supposed to be. I guess what I am saying is that I never thought twice about it, but now I have. I will most likely put a new cable on that compensates for the longer spring to make my cable/spring length equal the factory lenght cable spring. and re test the travel.


I got to thinking something else. I pulled out my paperwork. With it, I have the Aircraft Specification No. 780. This is from the Department of Commerce Civil Aeronautics Administration. This sheet states that the stabilizer travel is supposed to by 1 degree, 15 minutes up(1.25 degrees) and 5 degrees, 30 minutes down(5.5 degrees). I checked mine by laying a smart level on the stabilizer and trimming it to where it showed 0 degrees then I zeroed it out and trimmed up and down and recorded the results. I zeroed it out by following the instructions that came with the smart level. As I said above, my results were very very close to the factory specs, plus my elevator was trimmed neutral when the smart level showed the stabilizer at 0 degrees. I would get a smart level(I got mine at Sears) and measure your trim movement the way I described how I did mine. Start with the easy trouble shooting first.

If this is O.K., then there is one other thing I would check. Has your airplane ever been wrecked? I ask this because I remember reading in a Cub Clues Newsletter where Clyde Smith was explaining to a J-3 owner what could cause a tail heavy J-3 after rebuild. He said that it could be a problem with the longerons. He said that a J-3 longeron goes straight back then bends down at the jack screw. If the longerons don't bend straight down and go straight back, that could cause the plane to want to always be climbing. He said that on J-5's, PA-12's and -14's, the upper longerons bend up slightly at the jackscrew. If your plane has been wrecked at one point, maybe your upper longerons are bent other than what they are supposed to be. I checked mine and they were bent up after the jackscrew. How much up, I don't know.

I don't mean to not make you sleep tonight by saying this, just trying to eliminate the possibilites. Tom, I would check your stabilizer movement and if it is good, call Clyde Smith and explain the situation and ask him about the longeron theory. If you want me to email you the article in the Cub newsletter, I will and I can send you the Aircraft Specification sheet for the PA-12. Let me know.

KG
 
Perhaps someone here with a known good 12 will measure the angle between the bottom of the wing at the root and the stabilizer with it trimmed full nose up against the stop (longerons). This should give the answer of any discrepancy in any repairs to the fuselage that may have been done in the past.

Does anyone know if the 12 engine mount has the same 4 degree nose down as the 18? And is the firewall perpendicular to the longitudinal axis as is the 18?

This information should help Seaworthy get started in his investigation.
 
skywagon8a said:
Perhaps someone here with a known good 12 will measure the angle between the bottom of the wing at the root and the stabilizer with it trimmed full nose up against the stop (longerons). This should give the answer of any discrepancy in any repairs to the fuselage that may have been done in the past.

Does anyone know if the 12 engine mount has the same 4 degree nose down as the 18? And is the firewall perpendicular to the longitudinal axis as is the 18?

This information should help Seaworthy get started in his investigation.

actually in my picasa picture galley bellow I have this...
 
At Minam Creek, the Thrustline mod guy told me that PA-12's already had the zero-degree built into the design, unlike the PA-18.

windy
 
Seaworthy:

I was at Millinocket yesterday chatting with the experts. You should give Tony Cesare a call at West Branch Aviation, 207-723-4375. He has a -12 and has a lot of insight to W/B tire issues. I think he has been thru the same stuff you are dealing with, although I think his engine conversion is different than yours.

Jim
 
length matters.......

scenario 1: PA-18 tailfeathers & trim spring (5"long) with PA-12 jackscrew & bungee cable (connects between the spring & the jackscrew) = all is well. the elevator & horizontal stabilizer were neutral (level with each other) when the jackscrew was half way between nose up & nose down trim travel.

scenario 2: same as above, except replace the jackscrew with a more modern one with twice as many revolutions between full nose up & full nose down trim (30 turns instead of 15 turns). jackscrew fits into the same spot as old worn out PA-12 jackscrew. length of cable/spring was unchanged. but..... this made it so the trim had to be set at almost full nose-down trim to fly level with hands off. mods moved cg rearward so no one thought much of this peculiar development.

scenario 3: same PA-18 tailfeathers & trim spring, newer style jackscrew, but remove the PA-12 bungee cable and install a PA-18 bungee cable. now, the elevator and horizontal stabilizer are back to neutral when the jackscrew is at the half-way position. the PA-12 bungee cable is 20 1/4" and the PA-18 bungee cable is 21 3/8" - a mere 1 1/8 inches longer (plus the PA-18 spring is longer, too).

it turns out that in scenario 2 the elevator never was level with the horizontal stabilizer. the elevator was always up, in a right-side-up "V", giving it a continual nose-up (tail down) force. the elevator would be less at an angle when at full nose down trim, but never quite neutral with the horizontal stabilizer and never at an upside-down "V" angle. When the tailfeathers were installed, the mechanics kept the same spring/cable length on the trim system, but that's not really enough, it turns out. the location/configuration of where the cable attaches to the jackscrew was different, so a longer cable/spring length was needed to keep everything the same.

knowing now what I didn't know then.... make the spring/cable length whatever it needs to be so that the elevator is neutral with the horizontal stabilizer when the jackscrew is about at the half way point and the elevator angle should bend up in a right-side up "V" when the jackscrew is at the bottom of its travel (full nose up trim) and should bend in an upside-down "V" when the jackscrew is at the top of its travel (full nose down trim).

kevin - from your description, it sounds like your elevator spring/cable is the right length. thanks for bringing up the differences in the PA-18 & PA-12 springs, it's what got me to wondering about Flip's tail.

i never would have dreamed that a little 1 1/8 inch difference in cable length could make that much difference, like flying around with a wedgie all that time..... not good.

windy
 
Hi Wendy,

I think I am going to make a new bungee cable up. Since I have the longer, heavier -18 spring installed, I am going to shorten the new cable the difference between the -12 and -18 cable. This should keep the same dimensions of the -12 cable.

I have the -18 yoke, -18 carry thru tube and liner tube and -18 jackscrew. I purchased these from Univair. I think these parts with the exception of maybe the jackscrew are universal between the Cub and even the Pacer/Tri Pacer. A call to Univair could confirm. The Heavy Duty screw that you are talking about I think is from Dakota Cub.

Hopefully Tom's problem is an easy one to fix. I'm keeping my eye open on this thread for his results.
 
Mike

As things are wont to be you kind of had it doped out your first post ie the yoke. It appears it is inverted---I believe intentionally as it gave the previous owner more nose down trim as he often loaded up his 12's.
Flies great with the 8.5 X6's. Have the 26 " Goodyears in the hangar. I don't see the sense in fighting the elevator every landing and I practice quite a bit at various fields in the local area that have different approaches. You were the first to pick up on the yoke. I saw the gent from Minnesota at this years gathering at NH that had the same issue going with his 12. . He reversed his yoke and corrected his heavy nose issue.
 
Now I'm really confused. On page 2 of this thread you said your yoke was exactly like in Kevin's pictures, which is the same as in my pictures. Now you're saying that's upside down? I'd argue that. Upside down according to whom?

One of you mechanics correct me if I'm wrong, but when setting my screw up the nose up trim was limited by the cross tube hitting the airframe tubes. That limit was the same whether the yoke was flat side up or down. The nose down travel has a greater range with the yoke in as seen in Kevin's or my pictures. For normal ops I don't know that it would matter which way the yoke is installed. It was determined that flat side up was correct and there was more travel available so we went with it.

Stewart
 
StewartB said:
Now I'm really confused. On page 2 of this thread you said your yoke was exactly like in Kevin's pictures, which is the same as in my pictures. Now you're saying that's upside down? I'd argue that. Upside down according to whom?

One of you mechanics correct me if I'm wrong, but when setting my screw up the nose up trim was limited by the cross tube hitting the airframe tubes. That limit was the same whether the yoke was flat side up or down. The nose down travel has a greater range with the yoke in as seen in Kevin's or my pictures. For normal ops I don't know that it would matter which way the yoke is installed. It was determined that flat side up was correct and there was more travel available so we went with it.

Stewart


Hi Stewart,

When I read Tom's post, I understood it that he flipped his yoke upside down so it is now opposite of what yours and mine is...

I pulled out the specs for control movement for the PA-12 Type No. A-780. It says that stapilizer is 1 degree 15 minutes(1.25*) Up and 5 degree 30 minutes(5.5*) down. This coincides with what you experienced on your bird. My carry thru tube hit my airframe too as yours did when I cranked one direction. When I stabbed my feathers on, I checked my travel. I have the same travel that the type cert. says I need to have. I checked it by placing a smart level on the horizontal, neutralizing it then cranking each way.
 
Kevin,

It appears to me that nose up trim (leading edge of stabilizer down) would still easily reach the point of interference between the carry through and the airframe structure. I don't see how the yoke being upside down could impact nose up trim. I can imagine it would limit nose down. As I said, I may be confused but looking at those pictures reinforces what I remember seeing when assembling my jackscrew.

Stewart
 
StewartB said:
Kevin,

It appears to me that nose up trim (leading edge of stabilizer down) would still easily reach the point of interference between the carry through and the airframe structure. I don't see how the yoke being upside down could impact nose up trim. I can imagine it would limit nose down. As I said, I may be confused but looking at those pictures reinforces what I remember seeing when assembling my jackscrew.

Stewart

I think they flip the stab mount tube also..... still makes no sense....
 
12 Geezer said:
cafi19 said:
I was kind of wondering about the Kenmore STC too.....Why would you move the engine forward 2 inches.....

Was the STC a gross weight increase??

I'm not following.

Thanks

cafi

I had the Kenmore STC. It uses the stock PA-12 mount with a doubler on the lower legs, but it isn't lengthened. The plane was quite nose-heavy, and I'm using the Crosswinds short mount STC in this rebuild.

That's what the Kenmore PA-12 STC says; You take the original mount and double the two bottom stays by wrapping a split tube and welding it on. Does not move the engine one bit.
I have a short mount from Day and Night, and I had that done to mine and it does NOTHING like what this describes. I no longer have room for a PA-12 muffler and the PA-18 muffler just barely fits.
Life is good, but cramped.
 
I hear what you are saying Stewart but I guess if Tom's method is working, that is what matters for him.
 
According to Clyde Smith the trim handle is on the sidewall the yoke should point down. If the trim handle is on the ceiling the yoke should point up. I would make sure you have plenty of trim per the type certificate data sheets. I have seen way too many repaired fuselages that have changed critical angles and control movements for the worst.
 
Steve Pierce said:
.... the trim handle is on the sidewall the yoke should point down. If the trim handle is on the ceiling the yoke should point up

might wan't an asterik on that?

didn't some -14's have side and then later top handle.......
 
Tom, your twin brotther pa 12 from side lk. mn. "As we talked at New Holstine our yoke's are in upside down and the stab is in the wrong position on the yoke. I removed the yoke and and jack screw ass. and corrected the problem and now I have all the nose up trim I need. I also placed 31" bush wheels on and flew the same as 8-50 's. Ray
 
Steve Pierce said:
According to Clyde Smith the trim handle is on the sidewall the yoke should point down. If the trim handle is on the ceiling the yoke should point up. I would make sure you have plenty of trim per the type certificate data sheets. I have seen way too many repaired fuselages that have changed critical angles and control movements for the worst.

Why would the location of the trim handle matter? Isn't it the tail structure around the yoke the same regardless of whether the trim is on the side or ceiling?

Would someone post a new thread with only photos of the correct yoke installation for the 12, 14, and 18s, with no "discussion," just "this is the correct way to install the yoke on a * airplane."
 
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