PDA

View Full Version : Fuselage alignment- how critical???



qsmx440
08-03-2010, 01:27 PM
Excluding the why's or wherefore's of this.. I came up with a garage sale (let's call it) PA18 (stripped, I mean nothing not welded on) fuselage with zero rust in very good condition except for a slight tweak near the front door center cluster (rear bottom of windshield area right side). I will either use it in an experimental or use it as a form to build an experimental fuse. Anyway the legalities are not my question. My question concerns alignment. I was told this was "off" a little after it had been through an A&P school of some kind and was supposedly signed off as good by the schools IA (no paperwork, can't even identify it as originail Piper except it obviously is PA-18). When I got it home I leveled it up and found these things: Plumb bob level at door punch mark, wing mounts level across and 2.5" difference front to back (center wing mounts)or 4.5 degrees difference front to back (I know that is not the AOI), fuselage floor is level across, tailpost level both directions, firewall level and top firewall bolt holes measure even to rear of sides behind seating area. Strut mounts within 3 degrees of each other and sides from wing attach to strut mounts are within 1/4 inch side to side. Piper tolerances found on Christian Sturms sight are tighter than that with a max of 1/8 inch (you could say one side was 1/8" to long and the other side 1/8" to short) I think on the strut fittings BUT would the things I found fall within a "normal" used fuse?? I believe the plane should fly ok and respond correctly after proper rigging but is that a reasonable idea?

Now the real concern. With everything leveled up in my garage I stand in front of the plane and using my most critical eye I sight through the center line and then looking side to side I perceive the right (front of door cluster) side to be "straighter" up and down than the left side at the front door post cluster ( at bottom rear of windshield area) referencing the top and fuse floor. I drop a string centered between the front wing attach fitting bolts and the string sets 1/2 inch right (to door side) of the center line (tailpost to firewall) string. My eyeball "fix" is confirmed. It would seem the right side could be pushed out at the front-of-door cluster to fix all this but wait.. Before grabbing the porta-power I check the distances from center bolt to center tube, (front wing mount bolts to lower longerons) and the right side comes up 1/4" shorter (my top and bottom levels did not indicate the 1/4 inch difference and I attribute this to my inability to measure "level" as good as I can measure distance). So the right side is shorter top to bottom than the left and will only get worse if I push the center front of the right door cluster "out".. What I think: The cluster needs to go out on the right by 1/2 inch, and the tube going from the windshield bottom to the right wing mount cluster needs to be "lengthened"1/4"+. There is new paint in this area so I think some work was done there. Me, I want to leave it alone. The welds everywhere look good, If it ain't really broke don't fix it, etc.. I can use the cowl formers to make everything look very good outside (tubes will be inside cowling) on the cowling and only the most critical eye maybe would spot this. The planned use for the plane is poking holes in the sky and not show. Thoughts?? I would not expect anyone to fess up to having a fuse more than .00034" out on their own plane but you could say " I have a friend that has a cub like that and it fly's fine". I'm really looking to find out if others are flying slightly "bent " fuselages successfully or if I absolutly positivly must fix these things or during the first stall the plane will roll over on it's back in an unrecoverable inverted flat spin! :-)::: Seriously it looks like the student got a tube a little off and that's where the problem is. Like so many posts I'm looking for validation that I can use this "as is" dimension wise ( I know structural welds are not discussed here and that is MY responsibility). If it really is not a good idea or fairly common I will (grudgingly) deal with it. Thanks in advance to all thoughtful responses. Dave

P.S. For those who are churning inside about using this in an experimental I have contacted DAR's and FAA (who just won't confirm or deny) and if I build everything else it "may", heavy emphasis on "may" be ok. I lose all fuselage 20 points or so out of 140 or so (windshield is part of the fuse so I get to buy a commercially made windshield and I think torque tube and sticks if I want since they don't count). And I did find out if it fails I can strip all my other parts off, buy or build a fuse and try again with no penalty except "DAR bucks" , reusing my logs for the parts I did build, and spending the time to build it and the worst part of that : welding clusters. I started working on tail feathers a few weeks ago before this came along and it really helps to have something to attach "built" parts to even if it doesn't eventually wind up in my plane.

Jim Miller
08-05-2010, 02:51 PM
Do you by chance live in or near Texas. Steve Pierce has a 18 jig and maybe a few cut welds could fix your problem. As it stands you aren't going to know the signifiance of the errors until it is done and flying.

Billy-250
08-05-2010, 04:02 PM
Regarding the strut attach fittings, I'd be a bit concerned about the 3 degrees difference. Each degree different from the 22.5 degrees strut angle is going to throw the fit at the wing attach out by about 2". You could end up with quite a bow in the struts...

Bill

behindpropellers
08-05-2010, 04:10 PM
Would you build a house on top of a crooked foundation?

PerryB
08-05-2010, 09:59 PM
It sounds like you're trying to convince yourself that it'll be OK. Personally, I wouldn't touch it. If its your only way of getting into the air within budget and you're willing to accept the limitations (it will be unsellable and will fly crooked,I guarantee this), then go for it. I'd consider all money spent on this project gone forever.

Steve Pierce
08-05-2010, 10:10 PM
Get the fuselage drawing and make it right. You will get paid back dividends in a nice flying Super Cub when you are done.

qsmx440
08-06-2010, 01:25 AM
First thanks to all for your responses. Before I left this morning I had had no comments for a couple of days and was wondering what I had done wrong.

Jim: I live up in Washington state so no to Steves jig.

Billy: Great info. I didn't mention the smart level actual reading;; it's 24.4 R and 27.4 L so really screwed up if 22.5 is the correct #. Nope don't want any bend in the struts!! Some how that sounds like a really bad thing!

behindpropellers: hmmm maybe but I wouldn't try to fly it :-)

PerryB: Well it is in my budget but it is possible for me to do the repair myself so money is not the problem since it will be time and ingenuity that will be invested if necessary and that is the reason for the request for comments in the first post. This is not to be a show plane but I want it to fly correctly. This project will never be sold and I never considered any money spent on something like this anything but gone ( I do things like this because I like to build and learn). Education always costs something.

Steve: I have been using the online drawings for the tail feathers I built. This fuse almost exactly matches those L-21A drawings. For some reason there is not a lot of "angles" given that I have found in the drawings so you have to figure them out from length measurements hence my ignorance on the strut attach fittings. Up until this came along a couple weeks ago I have been concentrating on the back of the plane and tail feather drawings purposely ignoring the rest of the plane so as not get overwelmed. I'm still futsing about how to swedge the 1" stabilizer leading edge .012" for 6". I don't want to weld a sleeve to it.

This fuselage thing will probably be set aside for this winter as I have thousand(s) of little parts to fabricate and actually this along with the wing kit came along a year or two to soon. It's a great place to hang things and get a true visual perspective of the build. I did talk to an IA about this and also had a PM from a gentleman who had a similiar fuse and both felt it would fly ok but here I have 5 negative responses here and I definently (and would not fly with) any bend in a strut tube so right there some great info from this discussion . Again thank you for your responses. dave

mike mcs repair
08-06-2010, 02:09 AM
Before I left this morning I had had no comments for a couple of days and was wondering what I had done wrong.

it was too long.... I still have not been able to read it all .... I hang out here for fun :drinking: :drinking: :drinking: :drinking:

Longwinglover
08-06-2010, 07:58 AM
Jim: I live up in Washington state so no to Steves jig.
dave

If Cubcrafters in Yakima doesn't have a frame jig, try contacting Dennis Houdak cubdenn@aol.com . He has a frame jig and I think he is in Idaho .

John Scott

qsmx440
08-06-2010, 10:33 AM
Before I left this morning I had had no comments for a couple of days and was wondering what I had done wrong.

it was too long.... I still have not been able to read it all .... I hang out
here for fun :drinking: :drinking: :drinking: :drinking:


.......................Yup!

qsmx440
08-07-2010, 04:28 PM
Get the fuselage drawing and make it right. You will get paid back dividends in a nice flying Super Cub when you are done.

Spent yesterday and today rechecking everything to the drawings. Found one glaring problem. Tube between upper right firewall hole and front center door cluster (cluster where door latch hole is) is 1/2" to short. It sticks into and is welded to a short larger tube with the door latch on the other end. This is a critical tube support to upper right engine mount so just grind out the welds around clusters to replace or leave ends alone and double 30 degree scarf an extension/sleeves piece in the middle? I will be cutting/grinding, to allow movement, the one leg of the "X" brace also. The short tube explains the right side problem and revisiting my previous measurements corrected the rest of the anomolies. Thanks in advance for the grinding/replacing advice.

floats
08-07-2010, 07:38 PM
Dennis Houdek is in Roseburg, Oregon, I think.

HOUDEK DENNIS E
185 ACORN DR
ROSEBURG , OR, 97470-9401

He has several Cubs registered to him at this address.
He straightened two J3 fuselages for me when he lived in Jacksonville, FL.
Has a great Jig and a lot of knowledge! Very good welder! And a good guy.

qsmx440
08-07-2010, 08:39 PM
Thank you. Thats the closest one so far and very do-able. I'll try to contact him. I'm pretty sure I have it figured out as to whats wrong but not positive what is the best way to "de-weld" the joints. Proboably just grind them out but thought I'd get some expert advice here. Taking to Oregon is not that big of a deal and I was never going to finish weld anyway. Dave


Dennis Houdek is in Roseburg, Oregon, I think.

HOUDEK DENNIS E
185 ACORN DR
ROSEBURG , OR, 97470-9401

He has several Cubs registered to him at this address.
He straightened two J3 fuselages for me when he lived in Jacksonville, FL.
Has a great Jig and a lot of knowledge! Very good welder! And a good guy.

Darrel Starr
08-07-2010, 08:51 PM
Dave, to "de-weld" get a Dremel with a carbide disk (several) and a set of 5/8 dia. sanding drums. Then get a stool and a nice bright light so you came "operate" on the welded joint. Carefully cut the tube and prep the joint. Start with the carbide cut-off disk then finish with the sanding drums. When done carefully, this method will result in a clean and untraumatized area for a new tube to be attached to. Bob Eckstein and I did 23 tubes this way without nicking into the tubes we wanted to preserve.
Darrel

mike mcs repair
08-07-2010, 10:12 PM
i just use a die grinder like thing

http://www.aircraft-tool.com/shop/detail.aspx?PRODUCT_ID=ATS8502

http://www.aircraft-tool.com/shop/dbpics/large/ats8502.jpg

with a 3M Green corps 3"x1/16" cutoff wheel.... you can zip right along....

AkPA/18
08-07-2010, 11:13 PM
qsmx440

Another option is Wayne Mackey in Miles City Montana. Maybe some of the folks that have had their fuselages in his jig can chime in here. The performance coming out of Wayne's jig is quite good. Anyone out there want to chime in?

If you want more info give a call.

Mark

qsmx440
08-08-2010, 01:55 AM
Montana is to far (probably). I have a call in to Dennis in Oregon and will see if he gets back to me. I'll be attempting the one tube myself to tacked and then see from there. I do most everything myself but do appreciate advice on DIY. Gonna think on it a few more days and double/tripple check everything before the "cut" but that tube is wrong no matter how I check it. I have one of those die grinders and that's what I'll use. I think it would be easier to work on something that was wrecked than chasing down a good looking but incorrect repair. It will be a while but I'll get back after I have finished and tell how it came out.


qsmx440

Another option is Wayne Mackey in Miles City Montana. Maybe some of the folks that have had their fuselages in his jig can chime in here. The performance coming out of Wayne's jig is quite good. Anyone out there want to chime in?

If you want more info give a call.

Mark

jgerard
08-08-2010, 08:44 AM
What part of WA do you live in? I could possibly help

Jason

qsmx440
08-08-2010, 10:26 AM
What part of WA do you live in? I could possibly help

Jason

I live over in the woods in Quilcene, across the pond from Seattle on the Olympic Penninsula. Is there a SC jig in the Seattle area Jason? So far as levels, plumb bobs and tape stuff, I'm pretty competent at that but I wouldn't recommend flying in anything I've finish welded. :crazyeyes: Eventually I'll need help with the finish welding on all the parts.. I guess there are some good welders here in Port Townsend at the boat building places. dave