Elevator Trim

[GlynnSr]

I hope someone can offer advise.

My 1949 PA16 Clipper requires full down trim to maintain level flight at cruise RPM (2300) & if I have any weight in the back seat I have to hold forward stick to maintain level flight.

The trim is in fact at full adjustment (all the way at the top of the jack screw)

The weight & balance is good, with no adverse flight characteristics (not pitch sensitive - gentle stall into a mush)

Any ino on this problem will be greatly appreciated.

Thanks, Glynn.

[Gilbert Pierce]

What position is your stick in when the horizontal stabilizer is in the middle of the trim range?
It should be pretty much centered in it's throw.

When you run the trim through on the ground does the stick somewhat follow the trim?
If the stick is not centered in it's throw with the trim centered and the stick does not move as you run the trim thru it's range I think maybe one of your bungee springs or attachment cable to the elevator horn is broken.

Sitting on the ground with the trim in the middle of the range the stick should be in the middle of it throw. As you push or pull it you should feel spring tension. If you have tension in only one direction you may have a broken bungee spring or bungee cable in the tail or the cable has come of the pulley, which is hard to imagine as there should be a lot of tension on it.

[Stephen]

Wow! what great looking hardware. All new.

[Gilbert Pierce]

Actually only the bungee spring is new. The rest of it except for the turnbuckle barrel I had cad plated and baked to remove any hydrogen ions that cause embrittlement. Some of it was "white" cad and some "yellow". The only difference is they drop the white cad parts in bucket of yellow something to make yellow cad right after it comes out of the barrel plater.

[JohnW]

I'm gonna bet a dollar (make that a regular coffee, no Fat Pill) on this one,[attachment=0:2g2ixwn6]TMD002.jpg[/attachment:2g2ixwn6] sight unseen. I'm gonna say the jackscrew frame is installed upside down.

THIS is how it is SUPPOSED to look when seen looking down (aft) inside the fuselage.

[Gilbert Pierce]

John, my first thought was the same thing. I even posted a picture of mine when I took my Clipper apart and found it upside down and a picture of how it looked when I put it together right side up.
Then another thought occured to me looking at the pictures. I think you would have the opposite problem with the yoke upside down. Also, I flew my Clipper for about 1000 hours with it upside down and didn't know it and flew and trimmed just fine. I could trim it for 65 mph glide to the runway no problem and it would trim for cruise flight no problem.

After I rebuilt the airplane and put the yoke per the drawing it flew the same. I did install the double groove pulley because with the 150hp engine the trim cable wanted to slip when I trimmed at cruise. I had to unzip the headliner and push the cable tighter while trimming so it would not slip.

The first attachemnt is the Piper Drawing for Yoke installation in a Clipper. Drawing 12004.

[Steve Pierce]

I agree on the jackscrew yoke being installed upside down. First thing that came to mind when I read the problem.

[GlynnSr]

First, I'm new to the club and the Clipper (owned a Luscombe 8 E for 12 years)

Second, I'm learning to love my Clipper (trim problem aside).

Third, you guys are quick & sharp, my yoke IS upside down the pictures made it so easy and obvious to see.

Thank you all for such a quick and precise response.

Now, for the hard part. Is this a major repair? I've been unable to locate a maintenance manual, some say there never was one.

What ever it takes, at least, now I know what the problem is and can correct it.

If any of you are ever in Salinas (SNS) look me up - breakfast & coffee are on me at the airport diner.

Thanks Again,
Glynn.
(831) 809-3020

[JohnW]

Noooooooo problem. All in a day's -uhh- play.

No. correcting the upside-down casting is not a Major Repair. It IS a Major, Payne-inna-azzz though. The GOOD part is that you do not have to remove the stabs, unless the crosstube is upside down, too. You have a couple really nice pictures available now to see how they are SUPPOSED to be in there and can likely get through this with those, but the best expense you can make at this point is to get yourself a copy of the ShortWing Piper Club Drawings CD. This is SINGULARLY the best tool you can buy for working on your ShortWing, BAR NONE! Cheap at twice the price.

The difficult part of this is that it is pretty much a one man job, because you have to get down headfirst inside of there! I HIGHLY recommend you carefully and adequately begin by raising and supporting the tailwheel so that you can shinny your way down in there. After a few minutes "head-down", you'll begin to red out as the blood flows to yer noggin, so try to get the bottom longerons close to, or slightly higher in the rear than, level. Secondly, it really pays to have a second person OUTSIDE to chase wrenches, cotter pins, maybe a sandwich, cup o' Jo... and lend a "third hand" at opportune moments (through the trim panels where the stabs gozinta the fuselage, You want to remove those slotted panels for access). You won't want to get in and out of there TOO MANY TIMES, if you can help it. I have heard it said that you CAN do it all from the outside, but I just don't see it.

What you REALLY NEED is a vertically challenged, Thin Man type weighing in at about seventy pounds (ladies can fit the classification! some of 'em) without claustrophobia issues, preferrably with an A&P license. You unbolt the cross tube on each side of the yoke, remove the washers, et al on the top of the jackscrew, remove the jackscrew and cast "yoke" as a unit, and unscrew the jackscrew. Invert one or the other, rethread the two back together, and reverse order of removal. "That's it." (!) Lemme know if you think you came up with any swearword combinations that you might think I haven't blurted out yet. Just remember, others have gone before you in this.

You will notice that you probably have the single sheave pulley on the jackscrew, like in Gilbert's "before" picture, rather than the double sheave pulley in his "after", and in my "as Piper built it" pic (of a Colt, BTW, but the installation is oriented exactly the same in all the ShortWings). The CUBS have this yoke installed the "other way up" (and that is probably why so many ShortWings have them in WRONG!). The single sheave pully is original in the Clipper, and the TriPacer/Colt double sheave is a modification Piper made (see Piper Service Instruction No. 176 for the "Americana" of it, if desired) that stopped the slippage problems that the additional friction from the second turn around the pulley(s) corrected. This S.I. was for modding the 1950 and 1951 Pacers, and the 1951 TriPacers to an "improved" cable system that did not creep. The Clipper was noted for this, esp when the cables stretched a little over the years, but was not included in the Piper Kit to mod the early Pacers and Tripes.

Only other thing I have to say is that this is definitely a " Licensed Mechanic Required" piece of maintenance. This is a "secondary flight control" and is NOT on the Preventative Maintenance Addenda that can be found in Part 43. Other than that, note whether the correct order of assembly was there when you removed all the washers, and stuff, and I recommend before you even START, that you check the up/down play in the jackscrew-to-yoke threads for excessive loososity. The Drawings call for .015" clearance (Clarence) at this "mesh", so "much more shake" than that, and you ought to be thinking "new jackscrew and/or yoke. NOW would be the time if you need to tighten it up, while you have the old yoke off the jackscrew!!!

[edit] Oh, yeah...there is no Maintenance Manual per se for the ShortWings. It is maintained iaw AC43.13 and Piper's "techpubs" (S.B.s, S.I.s, S.L., Memos, et c). I repeat..."there IS NO maintenance Manual proper." There IS a "Parts LIst" available as a reprint, but it is NOT "illustrated", and the Drawings CD not only has the part numbers for each subassembly, it shows you the OOA (Order of Assembly) in most cases.

[Gilbert Pierce]

Due to the fact that the airplane did not have enough trim range to keep the nose down I would bet the cross tube is upside down. Like I said and you can see it the picture, mine was upside down and trimmed fine. The cross tube is on top of or above the yolk.
It looks like to me that with the yoke upside down and everything else ok you would have MORE nose down trim.

[JohnW]

Okay, I been hittin' the books (Drawings) and hoofin' it back and forth over to my Clipper, over to the hangar, and back and forth... and doin' a bunch of "cipherin'". Here's what [I think] I've come up with...

First, if the cross tube (Piper calls this the "link tube ass'y") is installed incorrectly (and I'm not throughly convinced that it CAN BE), it can indeed be the problem. This tube has two attach "horns" that mount it to the cast piece (yoke) and one [centered] "horn" to which the upper and lower elevator bungee cables are mounted. When correctly installed, if you align the two cross shaft-to-yoke mount holes with the centerline of the cross tube so that they are HORIZONTAL , the mount horn for the bungee cables must be pointed AFT and UP appx 45 degrees from the horizontal (all readers also please note: This shaft has to be positioned "swung UP" when the surfaces are installed, or the geometry is wrong and sever binding will take place!). If it points DOWNWARDS the same amount, then you have incorrectly positioned the "starting point" (or "null point" of both the upper and lower elevator bungee cables. This will SHORTEN the effective "pull" of the down elevator bungee when the yoke is screwed all the way UP the jackscrew, and the elevators will NOT be in the maximum "nose down position" that is intended with the jackscrew at the end of it's travel. To correct this shaft being installed correctly, it would be necessary to first remove the elevators, then the horizontal stabs. ALL the empennage cabling would need to be disconnected to remove the surfaces in order for the cross tube to be "swapped end-for-end" (also to include the tailbrace wires, which have to be "let down" to remove and/or re-install, and will necessitate a complete re-rig of the tail surfaces).

Secondly (and more likely!), the upper and lower elevator bungees are NOT (as some people incorrectly believe) the SAME LENGTH. If I have correctly waded through the MESS that is the part numbers on the drawing versus the part numbers in the Parts List...the UPPER cable is 22 3/16" long (NOT including the bungee spring) and the lower cable is 20 1/2" (ditto). If the upper and lower bungee elevator cables were installed "switched" from their correct locations (top for bottom), the same "travel limitation" on the elevator position relative to the stab "elevation setting" would be evident (altho' maybe not to the exact same degree). If the cross tube were upside-down as well, the errors would be cumulative! But...If BOTH "mistakes" are present, I would probably have to call the airplane "dangerously unpleasant to fly". However, I did not "get that" from the original Post. I got a "it doesn't have quite enough trim whine" :lol: out of MY reading... If ONLY the cables were switched and had to be exchanged, the elevator cables would have to be disconnected at the elev horns (and that pissant PULLEY mounted on the vert stab removed!), but the tailbrace wires would NOT have to be removed, nor would the flight surfaces.

NOW, (let me hear your thinking on THIS, Gilbert! Mainly because I admit to being -very temporarily- SLIGHTLY PO'd at your statement that your airplane -in its previous life- "flew just fine" with the yoke upside-down. That has NOT been MY personal experience, and I wanted to "puzzle out" why a man I otherwise respect could have such a diametrically opposite experience! Good place to practice a little "think before you speak", eh?) if EITHER ONE of these mistakes were present IN CONJUNCTION WITH the yoke being installed upside down on the jackscrew... it is conceivable that the two combined mistakes would (could?) negate each other to whatever degree and the aircraft would quite possibly have been "completely acceptable to fly" under normal loading conditions. I would SUSPECT that if the elevators traveled "stop to stop", but the STABS weren't making full travel, that unless the travels were actually MEASURED, a reasonable person may not ever know the difference! There is virtually NO REASON I can think of for a pilot to NORMALLY trim an airplane "full nose down" unless there are extenuating (or "exigent"?) circumstances. I would suspect that the most immediate (and most noticeable) "malfunction" with the yoke installed upside down would be the inability to make full "nose up" trim, because the yoke would BOTTOM on the jackscrew, but the cross tube would be positioned "higher" than it would be with the yoke "right-side-up". This would probably make the aircraft COMPLETELY "unstallable" (and where have you heard THAT before???) and have a negative effect on making nice touchdowns (at which point, let us not forget the age-old "not enough elevator authority" complaint!).

I would EXPECT you (Gilbert) would have not trusted 100% to the "That's the way I took it apart" philosophy, but when you reassembled everything, you would have researched the correct installation(s), and you would have completed them correctly, as well. So... when you corrected the upside-down yoke, you (perhaps "unbeknownst" to having HAD that "extra" problem?) also correctly installed the bungee cables (for example???) and "cancelled out the cancellation". If I HAD to go double or nuttin' on that cup of Regular (not that it was actually PLACED with anybody!) I would take a bet that you and Steve actually DID do the control surface travel checks.

And...there is something to be said for confirming "book" control surface travels. Not only for "compliance", but for "troubleshooting", as well.

[Gilbert Pierce]

Well John let me clear up one thing. I had no idea the yoke was upside down. :o I bought the Clipper as a very nice flying airplane with a pre-buy annual inspection and an agreement with the seller that any discrepancies that would cause the airplane to be unairworthy he would pay for. Some were found and he paid for them. I then flew the airplane from January 1996 until October 2003, almost 1000 hours. During that period we recovered the wings, added the right fuel tank, replaced the O-235 with O-320, new instrument panel and new interior. The airplane flew great and during this period I flew several other Clippers that didn't fly any better then mine. It was hands off rigged, ball centered and wings level. I could and did trim it for 65 mph on a stabilized final. Notice the grease on the jackscrew at the top in the picture of the screw still installed in the airplane. The trim was never run all the way up. I really cannot imagine needing to fly the airplane with the trim all the up and mybe not all the way down. I never have.

Okay, now it's time for Steve to jump in here and say my Clipper flew as well as his and all of the others we have flown with my yolk upside down. :)

In October 2003 my wife and I flew it to Steve's in Texas and took it apart to rebuild the fuselage and make some improvements. When I took the fabric off I took pictures (several posted) of everything. No major problems were discovered at that time other then the bungee springs were badly rusted.

In January of 2004 I started installing some of the control systems in the refurbished modified fuselage. I had purchased a new yoke and jack screw as well as bungee springs and cables from Univair. Being a retired manufacturing engineer in an ISO 9000 certified manufacturing plant I fully embrace process documentation and the need to follow it. During the winter of 2003/04 while Steve was replacing suspect tubing, adding seat belt attachment, building new door frames and welding in double groove pulley brackets I occupied my self by putting together an assembly manual with hardware call outs and detailed assembly pictures taken from the drawing CD. All new hardware was purchased and all of the smaller control parts were refurbished. The whole kit and caboodle was packaged with the assembly hardware in assembly kits so when I started putting it together I would have everything I needed and I would not have to go searching for it.

When I got in to the assembly it became apparent comparing the pictures I took of airplane while disassembling it to the CD drawing for the elevator and trim system, my trim yoke had been installed upside down. I do not know what else was installed wrong. I did not measure bungee cables when I took them out but I am confident that all is installed per the drawing when it went back together. In fact it flies no different now then it did before the rebuild except the trim cable no longer slips while trimming at cruise. It will trim nicely at 140 mph.

From the pictures you can tell the before and after. With the exception of the bungee cables you can see that the cross tube-yoke relationship is the same before and after. i.e. the cross tube is above the yoke not below. The only unknown would be the proper installation of the bungee cables. Short on the bottom and long on top.

And yes John I did the control surface checks per the TCDS using Steve's digital level. Sometimes digital stuff tells you more than you really need to know. I may be almost as annal as you are on those things.

Bottom line, I have found too many things assembled wrong by others. I am always suspicious unless I assemble it. If you don't have the documentation on your airplane (Drawing CD, Lycoming Overhaul and Parts manual) you ought not to be working on it.

[JohnW]

Okay, then. That must be it.

Oh...I'm not very anal AT ALL when it comes to digital levels (but I SURE AM when it comes to researching doing things RIGHT). I own a Pro 360 (and lie and say I don't when I think somebody is about to ask to borrow it!), but I outgrew the tenth of a degree very soon after I bought it. But. It is ABSOLUTELY faster to use for most things on lightplanes, and EASIER (gotta LOVE "zero set") and it saves me time and time is money. But I have to shake my head and turn away when the talk goes to settin' the washout on a SuperCub with one, or I'm gonna hurt somebody. So...IO gotta go. Right there is a CLEAR UNDERSTANDING that the guy doing all the talkin' doesn't have Clue One about what he is trying to show everyone he is an EXPERT at. Rigging? You'll find me under a wing with the dry chalkline stretched overhead and a 6" scale in my breast pocket, a plumb bob swinging gently in the door, and a 30" 2x4 with "DOF" written on it in red grease pencil, and a pine spacer taped to it (vinyl electrician's), and my Pro360. Back at the tail, you'll see me with a 2" or so long hunk of snapped off paint stir stick, and my Pro360. For the rudder swings, you'll spot the plywood rigboard hangin' on the sidewall "over there". Gee. Maybe I AM anal.

[GlynnSr]

Hello John W,

My first report that my jack screw yoke WAS installed upside down was not true. I printed out the pictures posted and took them to my hangar to compare and it IS in the correct orientation.

However your post described more accurately my planes symptoms. Based on you detailed report I now believe the bungee cables are reversed.

With full up trim, in addition to the leading edge of the stab moving down, there is substantial up elevator.
Additionally, when in full up trim the stab (& the yoke on the jack screw) are only in the bottom third of the jack screw, not all the way to the bottom.

Yet with full down trim, the stab moves ALL THE WAY to the top of the jack screw travel and there is only a small amount of down elevator deflection. (less than 5 degrees of deflection)

As I said earlier, there is ample up elevator, I can trim to any slow speed I need and then some but when I fly at a cruise RPM of 2300 I must use full down trim for level flight (no adjustment left). If there are bags or additional weight in the back I must hold a touch of forward stick at all times for level flight.

If I cruise at 2100 or 2200 RPM there will be some trim adjustment available both up and down.

Do these explanations make sense for the bungee cables being reversed?

Thanks, Glynn.

[JohnW]

Glynn, I hafta say Yes, I think this could be the problem. What I will actually have to "insist on", however, is that you perform a real and true "travel check" on the horizontal stabs, and find out just EXACTLY what the travels ARE. This will also give you a MUCH BETTER UNDERSTANDING of "what to Hell to we are talking about, here." Your "description" is no doubt "representative" of what you are observing. That's all well and fine, but if the actual travels on the system are in fact "by the book correct", then there are LOTS of other problems that COULD BE causing us to eternally spin our wheels. A most BASIC example could be this: The "Slots" in the finish panel that the stabs mount to the "cross tube" through, are cut wider AND taller than they have to be. This was to accomodate Production tolerances, and what could be called "hole creep" when the original Piper cotton cover shrunk. The slots HAVE TO BE oversized to some degree, and the stabs may APPEAR to be "travelling short" in YOUR observation of this, while in fact they are NOT.

Also, knowing what exactly the travels ARE "focus" on where the problem is (take my meaning?)..."won't go up all the way", et c.

How much understanding and experience do you have regarding "leveling" these airplanes, and do you "have the technology" to do a "travel check"? ARE YOU an A&P, and/or "Do you have access to one"? If you aren't, and you don't... at some point very soon you will be needing one. Now would be a real good time to involve whomever will be doing your first Annual (BTW...every airplane should have control surface travels confirmed, at the very LEAST, the first time an IA inspects it, and then again any time work is performed that may alter the travels, as well as "periodically". I cannot get over how many airplanes fly on and on, year after year, MAJOR "way out of rig", or with control surfaces assembled incorrectly...when a required travel check would have highlighted the problem immediately! All that can possibly be saying is that "somebody ain't doing it." Let's start actually "fixing this" by going there. Whaddayasay???

[GlynnSr]

Hi John W.

I went to the hangar and took some measurements for you to ponder.

First: Trim in neutral setting (half way between full up & down) - stick in center of travel - elevator on same plane as stab - 9" of travel up.

Second: Trim in neutral setting (half way between full up & down) - stick in center of travel - elevator on same plane as stab - 2 1/2" of travel down.

Third: Trim in full up setting - stick moved rearward maybe half its available travel - elevator up 9 degrees from stab centerline.

Fourth: Trim in full down setting - stick moved forward maybe two thirds of its available travel - elevator down 3 degrees from stab centerline.

I have photos but I do not know how to get them on the sight - can anyone tell me how?

Thanks, Glynn.

[JohnW]

Ahhh, Glynn. No, I cannot digest that information. I'm sorry. Here is how you check the aircraft for design control travels. Parenthetically, let me explain...the travels are measured from a control setpoint of "zero degrees". For the stabs and elevators, that means "horizontal". Ya see, aircraft engineers don't work in the abstract. Every airplane has what is know as a HRL. That is "Gov'tspeak" for Horizontal Reference Line. So, "how do you set that?", you might ask. Simple! You LEVEL the aircraft! On the ShortWings, you do this by use of a quite ingenious setup that dates back to Barney Rubble, You need a plumb bob, on a string. When your airframe was built in one of the jigs at the Factory in Lock Haven, the jig was leveled, and the tubes where all "jigged"...built in repeatability! About the LAST step before the frame was "knocked down" from the jig was to hang a plumb bob from the (right side) upper door frame, and place a punchmark on the forward seat crosstube in good alignment with the bob's point. The upper hole was already in that frame when it was welded into the structure. From that point on, the definition of "leveling the aircraft" was to hang a plumb bob from the infamous plumbobhangin' hole, and jockey the airframe around until the point of the bob points directly into the center of that punch mark. Lots of things can happen over the years to tweak an airframe, so a certain amount of actual misalignment may take place. This is where a little "common sense" comes in (later")

You can't ever SEE the HRL except for there being a dotted line in the Production Drawings tagged "Horiz Ref". You don't NEED to see it! When you have "leveled" the a/c, the HRL is horizontal!!! "Zoot! Alures!!!" Now, [in theory] certain parts of the aircraft are lined up with the HRL (well, none really DO, I don't think...but the "locations" of things like wing attach fittings and all that stuff are measured from the HRL. This takes a little elementary math sometimes -you know..."add" and "subtract", but it works. None of that for US, though! Nothing that mentally taxing! We are looking for paralleling certain tail feathers in alignment with the HRL. But! We can't SEE the HRL, can we (we can't)? Ah...but we know where it is! That's all we need! Once we have the a/c levelec, we can take a garden variety spirit level (that is what Piper used....we can use a digital level nowadays, but it's almost TOO GOOD, if you can guess my meaning) and using the CENTERLINE of the fwd and aft main tubes of the stabs, we run the trim until the bubble in the level centers. THIS is parallel to the HRL. This is also known as "Zero angle of incidence" for the hor. stabs (and it would be -1 degree, for the wings, because THEY are welded on at +one degree angle of incidence. BOY! Are we learning stuff NOW, or what!?!!) Or (back to the stabs) more "vernacular-like" yet..."Neutral". We have to THINK just a wee bit here, because the forward and aft tubes of the stabs are made from different diameter tubes, and WE are searching for leveling the CENTERLINES of these members. I'm gonna put you to work a little here, on your own (but...shhh!...think KISS, like in "paint stick", or something like that, on top of the smaller of the two tubes!!!). Okay, so we now have "neutral", or "zero degrees" Boy, that was FUN, wuzzent it??? We is airplane mechanix, now!!! Yepper, boy!

So, when we have found "zero" for the stabs, guess what we do NEXT? Well, that's RIGHT! We run the stab trim crank until the stabs are all the way UP in the front and can't move any further. This (as we can see at the plate at the crank handle) happens to be " Full Nose DOWN" trim. We take a handy dandy bubble protractor (or digital level, or failng having that, we will have to MEASURE the distance and resort to Trigonometry (never though you would use that in the Real World, didja?)! If we HAVE a bubble protractor (about six bux at Ace hardware, last I knew, the real aviation version -if you can find one- now goes for just under a GRAND), we already now know what the Down travel is 'cause we read it directly off the protractor. So now we run the trim until the stabs are all the way DOWN (and can't go any more) and we measure the Up travel the same way. Now...we know exactly how far the stabs travel in each direction. Since this info is written not only on the Factory Drawing, it is also in the TCDS (Type Certiicate Data Sheet) that we can ALL get to 24/7 on the internet at http://www.faa.gov. The limits are there, and the tolerances are there (2 degrees). So NOW we have something that I can deal with!!! We also know if the problem is AT THE TRIM MECHANISM, or somewhere else (pretty much!).

I'm sorry you went to all the trouble of getting your measurements. Gilbert wanted to do a "first, rough guess" when he asked these basic questions early in this Thread. Again, I'm sorry...I want the real numbers that are ACTUALLY THERE, measured in a scientific (and repeatable) manner. "stab in such, and stick is "here"...man...I could change all that in twenty seconds and it wouldn't tell us thing (at THIS point!).

So, I kinda hope this "put you off a little". I mean that in the kindest way...this is A&P Mechanic Territory. NOT that you or a couple hundred thousand OTHER PEOPLE couldn't "get through this". But the fact remains, you can't legally DO THIS without an A&P License (unless you are doing it under the supervision of one. No...me typing here, and you reading there...that is NOT MY IDEA of "Supervision". We are not doing this "over the Internet". Not MY idea of [adequate] supervision. [here comes a tough one: "I'm doing the best I CAN, Fred!". Who said that?]

This is one of those things where Airplane Owners sometimes get a little RESPECT for Licensed Mechanics (well. MOST of them) (Okay, SOME of them. It isn't a Perfect World). Not that this is all that "cerebral". Not really. But MOST PEOPLE think A&Ps are just glorified wrench monkeys. Well, some ARE. But we aren't SUPPOSED to be stupid, OR lazy. We are SUPPOSED TO BE Professional Mechanics, and anybody that thinks a guy at the Ford dealer that reads "what is wrong with your motor" from the LCD screen on a $75,000 box is a "Trained Mechanic" ought to consider two things 1) how hard IS IT to plug in a cord and read a Cheat Sheet on what buttons to push, and maybe have to undo four small bolts and change out a black box? and 2) maybe there's a REASON why Transport Canada calls "Airplane Mechanics"... "Aircraft Engineers". I don't want to overstate it, but there is a little more to this that "taking out screws and washing out gascolator screens".


I left a lot of nickel-dime details OUT OF this explanation (but a decent mechanic could get through it from what I HAVE said). So can you accomplish this [legally; physically]? You are GOING to need a maintenance signoff when this is fixed. That means involving somebody, someone that has seen this or something very much like it, done before, NOW. Once you do that, you PROBABLY don't need ME anymore (but I am willing and able to answer your questions, even if I WON'T turn you loose on your own airplane from over the Internet). But I WILL answer any intelligent questions, and even discuss "theory" in depth, if you are so inclined.

Game on?

[GlynnSr]

John,

Don't panic, I have no intention of making any kind of repair or adjustments on my own, I'm already keeping my A & P in the loop of what we are trying to do here.

My goal is to gather this basic information in an effort to pinpoint where the problem most likely is so I don't have to pay for hours of trouble shooting that may or may not be in the right direction.

Tomorrow I'll go back to the hangar and make the measurements you discussed and let you know what they are. However, I'm not clear as to how these throw measurements will confirm or reject the thought that the bungee cables are reversed since (if I understand your instructions) they do not take into account the bungee controlled movement of the elevator with trim adjustments.

Thanks, Glynn.

[JohnW]

Glynn; HAHA! I promise not to panic! In order to "fess up" to you about this, I have to ramble just a little bit (I really don't NEED anybody's "permission"...just warnin' ya)...about WHY your measurements are "unusable" at this stage. If my Clipper was fully assembled (and I had gone this road on it myself, so that I KNEW it was completely "correct" as far as bungee cable length, et al) I could very quickly repeat your measurements and get a pretty good idea of whether they were "representative". But, I HAVEN'T done all this yet on my airplane, and there isn't a Clipper within 150 miles that IS "beyond reproach" that I could just walk up and repeat your measurements. And... the plot thickens.

Setting your elevators in trail with the stabs, WHEN THE SYSTEM IS ACCORDING TO HOYLE, should give you a neutral trim setting AND a neutral elevator setting. In other words. if the system IS correct...you can take that to the Bank. But when the bungee cables are NOT correct, the spring tension will give you something OTHER THAN neutral on both these surfaces, when they are in trail.

I would LOVE to say "I know absolutely everything", but I'm more realistic than that! Seems that while we don't use our brains to 100% capacity, there are only so many "bumps" on it. Supposedly, each "bump" is a sort of "knot of information" (yeah, I doubt this is 100% correct, too. But gimme some license, here). It acts kinda like a telephone answering machine, ya see. When you reach the max storage capacity (whatever the max number IS) for bits of information, then when you learn something "new", a tidbit that WAS in storage gets "dropped off". I realize this is a total bunch of "Hooey", but that's my story and I'm sticking to it! At least there must be a usable metaphor in there somewhere. I believe that no matter HOW HARD I try, I can NEVER "know everything". There truly is "too much to know".

What I DON'T know is where exactly "trail" is under every possible configuration of "wrong" piece/part installations on a Clipper. I DO believe it will be in the WRONG place as compared to the "right" installation, every time. I believe you should agree that this moves the info "all over the place", and unless ONE OF US actually knew the "baseline"... well, we're peein' in the wind. Truthfully...I don't even know "offhand" exactly what these numbers as related to stick position, location in the fuselage trim panel cover slots, or so on, ARE on a 100% perfect, "as designed" system! What I DO know is that if you start with a true "zero angle of incidence" for the stabs, you can THEN measure their travels. This is in the design, and in the definition. I ALSO know that when the stabs and elevs are in trail AND the stabs are at zero, then the elevs are at zero (neutral) too. But the converse is NOT necessarily true! With THIS information "in hand", I dare say that not only would someone like Gilbert (with his fully functional, "correct acting" Clipper (and I believe him to NOT be a Dummy, and I mean that is only the most respectful way) be able to give us a relative reading of what HIS does, but I truly believe that even a Colt will have very nearly the exact same "throws" as set by the bungee trim system, AND I could actually "mock up" my Clipper in pretty short order, if the need arises (the trim mechanism IS installed, the bungees ARE there, I have the stabs and elevators, and EVERYTHING is "naked" and easy to work on). With THAT info, we could be close enough to tell us if this is absolutely where the major problem is, from your numbers. However, getting the REAL "neutral" takes ALL the GUESSWORK out of it. I THINK we are indeed on the right track, here. I wouldn't bet the Farmjust yet...but I think we are on the right track to find out what we need to.

One thing that will surprise you (or...maybe not) is that when the stabs are in the "middle of the slots", that they are NOT "neutral". There is somewhere around FOUR TIMES the travel away from neutral of the stabs in the "nose up" position than there is in the "nose down" direction (I'll be lookin' these numbers up today sometime). If you are "in trail" at the center of the stab travel. sounds like that is somewhat "wrong". This is NOT a purely "linear" observation that you can make off the cuff...there are built-in airload "windage" -and other factors- built in. What you "offered up for my consumption" LOOKS like we are on the right track...but the proof is going to be in the actual travels.

Yeah, WHEN you are "set up" and can measure stab travels...yes! DO get a reading of what the elevs do at full trim settings. "Raw", ref'd to the HRL is fine. I suppose "relative to stab" is useful, as an alternative. Piper didn't give us that info, but we can sure work with what we get! Sounds, so far, to me, that you have WAY insufficient "nose down input" to the elevators the way you are set up (and Boy, THAT would do what you describe!!!). So, let's get on the same ACTUAL DEGREE PAGE, and...tally-ho! :D

[Frank Green]

I was looking for info on cable tension and stumbled on this thread. Thought about it and wondered, could I have done it too? Sure enough SOAB!!!!Upside down. Oh well, good thing I still have a 34" waist and can fit thru that anal hole. Lets see, turn sideways, right arm thru, now tangled in the elevtor cables, turn, bend over OK now get to work. No real biggie, hour later done. (That blessed woodruff key wouldn't come out). Changed the one in the 20 before lying on a board blood stuck in my head. Not sure which one is worse but thanks to the info you can find on these sites problem avoided before the plane even left the shop. The punch list is killing me to get this thing to the airport.

[Steve Pierce]

95% done and 95% to go? Will we see you at OSH Frank?

[Frank Green]

God and wife willing.

[clipquito]

OK. At the risk of knowing just enough to get myself into real trouble ... I'd like to weigh-in here with a few concerns and questions regarding my Clipper rebuild. I have read all of the discussion here quite closely and understand most of it having watched my IA work on the rigging on my Clipper rebuild and read and studied some other stuff as well as taking apart my Clipper. Here's my concern. First, my IA didn't see the take-apart on this airplane -- I did it in Utah he was in Montana where the rebuild is actually occurring. Second, my pictures of the take-apart which I thought were OK turn out to be not so helpful (however, all the pictures you guys have posted are very helpful). I did a good job bagging and tagging however. Third, my IA doesn't seem to want to look at drawings much or the SWPC Rigging CD -- which I studied -- I would certainly recommend it in addition to the CD of the complete set of drawings. Fourth, I don't see my IA plumbing and measuring much -- hell, he hasn't at all. I do see him checking the numbers - which I gave him from the Rigging CD -- and eye-balling alot. I have been quite concerned about this all along -- especially since I already know he put the trim in backwards on a previous Maule rebuild and forgot to tighten a couple of turnbuckles when the thing was finished. I have printed all this out and will be going over it all with him, but can't understand his reluctance to do all the stuff you are talking about here -- especially since he has full access to the frame which is not covered yet.

I will have to go to my hangar to look for this info, but Vintage Airplane magazine had a rather good write-up on mocking up rigging including a checklist. I gave this to my IA, but it just sits on his desk.

What do you all think although I probably already know?

[Steve Pierce]

Talk to him. The data you have gathered is the hard part, looking at it and using it is easy.

[JohnW]

Well, you can PROBABLY guess my reaction...
There are indeed hardheaded people "out there" that dismiss anything that they THINK they know as "outside the limits of necessity"; in favor of "how we always did it." (which unfortunately has been proven time and time again as translating to: "Well, you been doin' it WRONG!"). This seems to be a sad but true view of typical human behavior (which doesn't change MY thinking at all! The day I stop learning is the day after the one on which I died). If you can't make any progress from the Gentleman in the direction of what YOU can see is "sensible and "right", then you are better off finding someone with a little more "humility", and a modicum of interest in reading "what is right". Whether it might make him realize that he ain't God's gift to eyeballing an airplane, or not. Steve is very right (where, in another thread) he says "the better you rig the airplane (by the book), the nicer it will fly that first flight".

Remember...it is the Owner/Operator's responsibility to ensure that YOUR AIRPLANE gets the best maintenance you can provide. For MOST PEOPLE, that means the strictest belief that your IA is doing things RIGHT in accordance with the manufactere's Tech Pubs for the aircraft that they built. What you see in long discussions about "these things" almost ALWAYS is a result of those doing the discussion having "hands on experience", along with the fact that the people that are "right" are backed up by what Piper wrote down (some place, or another) and eventually this info finds its way into open-view reference. In other words, "someone has RESEARCHED these subjects in depth". This is not always the easiest thing to do. Especially with aircraft built during the days that providing a "maintenance manual for their product" was NOT required as a condition of sale. Some of this "Stuff" is difficult to dig out. Those that don't "feel the need" to make that kind of investment almost ALWAYS fall back on the "that's the way we always done it, and it flew just fine" argument. Don't forget that "...it flew just fine..." means one thing to the person that FLIES IT day after day, and may mean something entirely different to the person that just "works on them". Would you let somebody do Lasik surgery on your eyes, if you knew he never read the Manual for the laser machine? How about if you "brought him the Manual", and you knew he never opened it? Would you lie back and let him clamp your eyelids open?

[Go Fly]

Gang, I am putting my PA22 back together and having some issues and perhaps have an upside down jackscrew assembly or cross tube. I can't seem to get the pictures on this post. Any advice? Thanks, Mark

[Gilbert Pierce]

Here you go. Right side up.

[Go Fly]

Thanks Gilbert, My casting is correct but believe the problem is the tube is upside down. Will check tomorrow. Thanks a ton...........Mark

[Gilbert Pierce]

Having the tube upside down will definitely give you problem. I've done that.
Maybe this will help.

[pinkgas]

So, whatever happened with GlynnSr's problem/solution? I am dying to know! Is he still on the forum?

[57scooby]

So, whatever happened with GlynnSr's problem/solution? I am dying to know! Is he still on the forum?
Can some one tell a good iA in Boise that can fix my trim. Marc

[Clayton Harper]

Marc, Have you determined it needs fixing?

[pa20]

Marc,
What is the problem? The trim system is actually pretty simple. There are just a few parts that can be a pain to access!

[57scooby]

Need more down trim. Open the head liner and cable look good so clayton was saying the jack needs to be turned upside down. Well I can tell you I need to find a person that is real small and light weight. I don't think I can get there and it would be real embarrassing if my wife need to fire department to get me out LOL. Marc

[57scooby]

68446845I found out about the right side toe brakes it was set up with dual with the conversion they just hook them up. But I did ordered a AK bushwheel spring too stop the shimmy in tailwheel. Just need to find a good IA to help fix the toe in a out. I don't want to look to dunk going down the runway LOL. Marc

[Clayton Harper]

Marc,
I said the jack screw MIGHT be turn up side down. It could have been Aft CG because of the Tow Bar in the baggage bin and back seat. My suitcase behind the pilot seat probably didn't help. I would first check the "Toe" on the landing gear and the Tailwheel Alignment, then fly it. See where the trim is. After that, weigh it and calculate the weight and balance on it. You have a legal W/B, but.....

[57scooby]

Righty-o going to take every out and Roy said they can do a weight and balance Monday after I get off work. Marc

[Clayton Harper]

You might as well take out the VAL Radio if it doesn't work. That way the Equipment List will be easier to make. I'd take out the Strobe power supply too.

[Steve Pierce]

Is the jackscrew yoke pointing up?

[Clayton Harper]

Steve,
I didn't look, after 925 NM in two days I was tired. Look at the stabilizer position. This was the trim on landing. Can you get anything from that?

[Gilbert Pierce]

It looks to me the horizontal is in the full nose down attitude and is against the stop. Not likely if the yoke was upside down. The picture is my Clipper trimmed for landing. Probably about 65 to 70 mph. About because I never look at the ASI.
Landing wt. 1365lbs C.G 14.4" when the picture was taken.

[Clayton Harper]

It might have been loaded tail heavy. When Marc weighs her tomorrow and recalculates the W&B we will see. The ASI might need some attention too. I have no fear Marc will get these little issues sorted out on this nice Pacer.

[57scooby]

I'm going to take value out. Dayna just want me to replace soon like in next week. I was thinking putting the strobe and putting some ware else. The strobe come in handy in the backcountry most cub that I saw johnson creek that had store you really spot them .Marc

[Steve Pierce]

Strobes are not going to change your weight and balance enough to make a difference. I would pull the inspection plate covering the jackscrew and see if it points up or down.

[Lownslow]

Looking at the pic, my guess is that you are loaded tail-heavy or doing "wheel landings", which do not normally require as much nose-up trim. I also observe that you are likely not getting more "nose-down" trim because you are bound by the fairings at the front of the stabilizer. The fairing is either not installed properly or has been "home-made" of improper dimension. From the pic, it definitely looks like the stabilizer should be allowed to travel further up, which is nose-down trim. Find another PA-20 or 22 and compare dimensions of the fairings on both sides.

Lou

[Clayton Harper]

Lou, No wheel lands. Good eye on the fairing. Marc is going to weigh it today and that should let us know if I had it loaded tail heavy. Steve the comment on the strobe power supply being removed from the plane has to do with where it is mounted. It is mounted in the exact center of the Baggage Compartment, so taking it out before the W&B would good.

[Brian]

I often end up with full nose down trim on my 22/20 when landing with full flaps, so I'm not sure that alone is reason for concern. Is there another reason to suspect a problem other than the trim position on landing ? I never really saw the start of this thread before it was merged with an old thread, so may have missed something already said.

[Clayton Harper]

Brian, I used just two notches of flaps, and I needed full nose down in cruise.

[Brian]

Brian, I used just two notches of flaps, and I needed full nose down in cruise.

Okay, that is a problem for sure. If I dialed in full nose down in cruise I would be quickly doing outside loops.
Clayton did you make it up to OSH ? I was looking forward to seeing you. Sorry I missed you if you stopped by.

[pa20]

Comparing the angles of the horizontal stab in the photos of Marc and Gilbert's planes, it is apparent that there is a marked difference. I was not sure how having the yoke inverted would affect the trim for a given phase of flight as the stab needs to be in the same location for neutral trim. However, it occurs to me that the real issue would become the setting of the balance system between the stab trim and elevators.
Doing a new W&B is a good move, but if it is nominal with all other Pacers, you need to look further. As far as access to the trim system goes, if this is a -22/20 then you should have the access panel in the belly which will allow you easy access. Open it up, get a good light, and have a look. Oh...Please post some photos of what you see.
I have loaded my PA-20 to the gunnels with camping gear (rear seat removed) and never had a problem with running out of trim, or for that matter needing that much nose down trim on landing.

[Gilbert Pierce]

The Clipper trim photo was a no flap landing. I never use flaps.:o

[Clayton Harper]

Copy That. LOL

[pa20]

Marc....Did you do a W&B on your plane? Curious to know what you found. Also, as Steve has suggested, did you get a chance to look at the stab trim yoke installation?

[57scooby]

They can't to the weight Balance tell Friday or Monday going to look to nights had to work 13 hrs yesterday . Marc

[57scooby]

6853 This the b6853Estate I can do on a pitcher

[Lownslow]

It appears your trim yoke is installed correctly. I see from the pic two noteworthy concerns: 1) You need to get your trim screw lubed up, and 2) As I previously mentioned, your trim travel appears to be limited by your fairing, either improperly fabricated or improperly installed.

I have seen different lubricants recommended on this site, but I have always used Lubriplate and have had good results. I would find another PA-22 to compare the fairing(s) to.

Lou

[57scooby]

What is the way to correct it. Is something I need to dare down the fabric? Marc

[Lownslow]

I would start by comparing fairings to another PA-22. You can buy new fairings from Univair or trim the ones you have to fit. If the grommets that are attached to the fabric, that the attachment screws screw into are out of position, you will need someone with experience to get it right. But No, I would not cut any fabric until you are sure what needs to be done.

[57scooby]

Well do thank s for information.

[Jim Hann]

What is the way to correct it. Is something I need to dare down the fabric? Marc
Here is a picture of the left side of mine. your might be mounted a little low. I have also seen a couple (PeterL's maybe) that were mounted with the larger part of the plate behind the LE of the stab.

Jim

[Lownslow]

Mine after full-flap landing. See how the opening in the fairing allows much more travel upward (nose-down). I use nearly all of my nose-down in cruise.

Lou

[Pacer 24C]

Hard to believe that it could be that tail heavy - I can put 400lbs in the back seat and 100 lbs in the baggage compartment before reaching the aft limit and my empty C.G. is quite aft at 12.88 my trim for climb and glide is almost the same solo, normal cruise is 4 turns down from climb 6 turns down at full throttle @ 145 mph - but still not full down trim. Might be the bungee adjustment.

[Harold Kroeker]

I too am a member of the "Upside-down Yoke Club". On my Clipper it means that I have to land with full up trim and I cruise at about 5 turns down from there. On the ground the elevator trim moves it the full range of the slot in the fuselage so I suspect the slot was made to match the throw.

68566857

[pa20]

Here is a shot of the trim on 44K after a 1/2 flap landing. My wide, & portly butt, and full fuel was the load.

[Pacer 24C]

Looks like it would be stopped by the opening - the opening should go up nearly to the longeron as shown in pa20's pic.

[Lownslow]

I failed to mention that I have the PA-18 tail feathers. I also have the Stewart tips.... The more lift, the more you have to raise the tail, and the faster you go (I think). The opening in the fairing should allow travel up to near the top longeron, as stated.

Lou

[Clayton Harper]

I measured from the lower longeron to the top of the opening on a Pacer at my airport. 18"

[Steve Pierce]

I would check the rigging of the tail if you think there is an issue. Digital level makes it pretty easy.