Hello all, this is my first post so please pardon me in advance for any etiquette errors. I discovered this site several weeks ago and have been avidly reading the forums gleaning knowledge from the hundreds of years of experience represented here. Thanks to all of you for sharing so much of your experiences with these great planes. I have recently been checked out to fly a PA-18-180 as a glider tow pilot, and being an old A&P/IA (old in years and old since my wrenching days!) as well as an old CIASMEL pilot, I naturally have been drawn to the maintenance records of this old girl to see what is what. She has over 13,000 hours, almost all of which have been towing. In going through the AC records, I have found over 35 337's filed on her. I don't what to write a book here, but would like to open this thread to anyone who has some input on what I should be looking for on this high time bird. Obviously the engine, full power tows and mid-power (hopefully) descents, but what in particular? She's been in Colorado and Wyoming her whole life, so I don't image corrosion is as big a deal and you guys in AK or on floats wherever else but maybe not. Looking down the leading edges of the wings I can see that there is a bit of mis-alignment there, and I have been told that the left gear is a recurring problem, which may or may not be from repeated landings with prevailing winds. Also the trim jackscrew seems to possibly be a weak link. There are 337's for an "Alaskan Gear" mod, the empennage has been replaced by a Uniivair one (I have read various places about a "boxed" empennage, maybe this is that, don't know). Has an X-brace overhead. Anyway, I'd just like to open this to any comments, if you would like. Casey
Diving into an old warhorse
- Thread starter manix37
- Start date
Steve Pierce
BENEFACTOR
Graham, TX
Univair makes tail repair sections in different lengths. Probably had some damage and that was the easiest way to repair. My Super Cub has over 12,000 hours as a power line patrol plane. Main things I see are sheet metal, bushings, control cables and pulleys. The screws holding the flap false spar to the rear spar had worked through the sheet metal making for some rubbing.
thanks for the replies...no I haven't flown a Pilatus. And yes this plane has had some damage, ground looped several times and has been over on it's back once or twice, so I think that the tail section repair was from one of those incidents. How can I tell if the replacement tail section is the stronger boxed version? This plane makes a lot of takeoffs and landings as well as dragging gliders around by the tail, so I am concerned about weakness in the empennage. I will look for that rubbing you are talking about. Also I'm concerned about the trim jackscrew, it has a bit of play in it, at the screw as well as at the mounts on the ends of the casting. Is this fairly normal? If so what are the limits of play? And is there a place to go to find this stuff out? Also the flap hinge bracket seems to have quite a bit of play, especially outboard on the right side. Thanks
Manix37, welcome to the site Casey. Good on you for wanting to delve into this old warhorse in more depth.
As always, +1 to Steve Pierce's comments above. That said, there are significant differences between a patrol 'Cub, which may land every three or four hours, and a glider tug, which probably has something like four to six landings PER HOUR, depending on the operation. So all the undercarriage stuff gets a real workout. I've seen this mostly on the back end, with broken tailsprings, or shimmy from those which have lost their arch, loose bolts, worn tailwheel saddle castings; also cracked/bent aft longerons, even though they are less prone to corrosion in CO than some other places, there's a lot of physical stress back there, just from the amount of landings. Likewise the main gear. Often overlooked on preflight is the condition of main gear attach hardware, and the fuselage lugs: MLG bolts should probably be replaced at least every ~2000 landing cycles. The bungees and hydrasorbs also take a beating. [As an aside, Mike Jensen developed a very good PMA HD maingear, based on high volume tow experience with 180 Supercubs at the "old" Black Forest and Air Force Academy operations. I "think" this eventually wound up with Airframes Alaska, although they may have done further development.] With the 180hp conversion, the tail also shakes a lot, so the tail brace wire clevises and hardware need extra scrutiny. Perhaps the "boxed empennage" is actually the aft fuselage section, to minimise this shake. And because 180 'Cubs tend to be near their forward CG limit flown solo, the trim jackscrew really gets a workout, from tow trim to descent trim, to landing trim, and back. One other area of note is ribstitching and wingroot fairings, owing to the beating from propblast. This is far from an exhaustive list, but is representative of many years running these things in glider tow operations. You didn't mention any powerplant issues, so I'll assume that the operation you're in has that pretty well in hand, and that's a whole 'nother topic. From the sound of it, at some point it would probably be worth putting the bare frame of this old warhorse in a first-class jig, like the one that Aircraft Repair in Glenwood Springs now has, just to see what warts and callouses have accumulated over the years.
And if appropriate, it would be cool to know the N-number of this one: I'll bet that a few folks on here will have fond memories, and be able to chime in on specific ummm "incidents".
Thanks. cubscout
As always, +1 to Steve Pierce's comments above. That said, there are significant differences between a patrol 'Cub, which may land every three or four hours, and a glider tug, which probably has something like four to six landings PER HOUR, depending on the operation. So all the undercarriage stuff gets a real workout. I've seen this mostly on the back end, with broken tailsprings, or shimmy from those which have lost their arch, loose bolts, worn tailwheel saddle castings; also cracked/bent aft longerons, even though they are less prone to corrosion in CO than some other places, there's a lot of physical stress back there, just from the amount of landings. Likewise the main gear. Often overlooked on preflight is the condition of main gear attach hardware, and the fuselage lugs: MLG bolts should probably be replaced at least every ~2000 landing cycles. The bungees and hydrasorbs also take a beating. [As an aside, Mike Jensen developed a very good PMA HD maingear, based on high volume tow experience with 180 Supercubs at the "old" Black Forest and Air Force Academy operations. I "think" this eventually wound up with Airframes Alaska, although they may have done further development.] With the 180hp conversion, the tail also shakes a lot, so the tail brace wire clevises and hardware need extra scrutiny. Perhaps the "boxed empennage" is actually the aft fuselage section, to minimise this shake. And because 180 'Cubs tend to be near their forward CG limit flown solo, the trim jackscrew really gets a workout, from tow trim to descent trim, to landing trim, and back. One other area of note is ribstitching and wingroot fairings, owing to the beating from propblast. This is far from an exhaustive list, but is representative of many years running these things in glider tow operations. You didn't mention any powerplant issues, so I'll assume that the operation you're in has that pretty well in hand, and that's a whole 'nother topic. From the sound of it, at some point it would probably be worth putting the bare frame of this old warhorse in a first-class jig, like the one that Aircraft Repair in Glenwood Springs now has, just to see what warts and callouses have accumulated over the years.
And if appropriate, it would be cool to know the N-number of this one: I'll bet that a few folks on here will have fond memories, and be able to chime in on specific ummm "incidents".
Thanks. cubscout
Thanks a lot for your reply cubscout, seems a lot of useful information. I don't think there is any reason I shouldn't post the N-number, it's right on the avatar as well, which is N4785F, based in Boulder since 1971. I've been spending a lot of time pre-flighting this girl, with particular attention to the things I have been told are recurrent issues: landing gear mounts and bolts, jackscrew and mounts, tailwheel assy, wingroot fairings, but I am curious about the hightime stuff that could be lurking unknown to all, such as the longerons you mention. Is there an easy way to inspect that area? I will track down the landing gear mod that you reference. As far as the engine is concerned, I have also spent a lot of time with flashlights and fingers checking out things under the cowl, and I am hoping I can work with the local FBO to bring her in for basically a 100 hour inspection, compression check, mag-timing, etc, but I would love to hear your thoughts on that topic as well. She badly needs recovering, and I'm hoping I can get up to speed on cubs so I can give input to what we should do in the process of recovering with pulleys and cables and the like. The club also has a Tost release that I want to install ASAP as I understand it is a big safety improvement over the Schweitzer release currently installed. I would really like to get the fuselage on a jig and get things straightened out. Casey
It might be better off with a new fuselage in the long run. The labor cost of repairing the fuselage may be more than the cost of a new one. Have the fuselage bead blasted before you bother with the jig, this will uncover a lot of the bad tubes to start with, take a punch to all of the tubes after that and you will have a better feel for the work ahead. With the damage history you stated I aggree a jig is in order. The boxed tail is just 4 small tubes in the tail section. Before you start on this project you really need to find a IA that has experience with rebuilding Cubs from what you are describing it can easily snowball into a 100 grand project. That might not be what you want to hear but it happens often.
DENNY
DENNY
Steve Pierce
BENEFACTOR
Graham, TX
If you have a worn jackscrew I would look at the Dakota Cub jackscrew assembly. Proven to last longer especially in extreme operations. The boxed or "X" tail is more an off airport mod in my opinion though I guess it might help stiffen the frame on the 180 hp SC.
ColoZKS6
Registered User
Lakewood, Colorado
I seem to remember 85F having an O-320 back in the late '80s. Watching tow performance compared with the two O-360 Cubs Bruce Miller had at the Cloudbase made a real impression. I also seem to remember 85F being stolen somewhere along the way - might be wrong about that. When will she morph out of the white paint and become yellow like her rudder? She certainly is a working girl.
LOL! I'd love to see her morph out of the white Ceconite into Yellow, if for no other reason than to be more visable here in a crowded airspace! Unfortunately the white rudder was a bit damaged in an accident a month or so back and is getting repaired, so she'll be more white than yellow for a while. Great insights guys, thanks for any and everything, it's as if I'm sitting with a bunch of long-time cub guys drinking a few beers and talking about this girl. Don't know about any theft but I will inquire. I'm going to have to do some digging in the records to see when the main and tail bolts were replaced. One of the great things about this plane is the A/C records seem to be all here. Does anyone have any suggestions about checking on the engine? Since this club is a non-commercial operation there is no requirement for a 100 hour nor if I understand my FAR's a TBO on the engine. I may be wrong here but if not...Yikes! Casey
