Your master and starter relays should be as close to the battery as possible. The wire from the battery to the master is unprotected, and so is the wire from the master to starter relay. You want unprotected (especially high current unprotected) wires to be as short as possible, preferably with no bulkhead penetrations. The shorter they are, the less chance of insulation fraying and the wire shorting out.Originally Posted by Dan Gervae
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I’ll mount my relays right above and to the right of my battery. On another note...Wayne from Southern Aero finished up my strut fittings...once they arrive with the streamlined aluminum material He’s sending with it, I can build my aluminum lift struts. He does nice work.
I have been working hard at finishing the hangar Too, I got the ceiling up, lights in, and blown in insulation done too.
time to focus on finishing the Cub!
getting some wiring done...should be close by the end of the week. Planning to build new aluminum lift struts this weekend.
Last edited by Dan Gervae; 03-16-2021 at 07:28 PM.
I can't wait to see how these go together for you.I’ll mount my relays right above and to the right of my battery. On another note...Wayne from Southern Aero finished up my strut fittings...once they arrive with the streamlined aluminum material He’s sending with it, I can build my aluminum lift struts. He does nice work.
The front struts are together..I have the rear struts drilled and have only to drill the eye bolt holes at the jury strut locations...I’m doing this instead of strut clamps.
I have been made aware recently of an issue with using eye bolts for the jury struts rather than the old Piper clamps. It seems that removing the flexibility of the clamps causes the rivets which hold the upper jury strut fitting to the wing spar to loosen. Will you be looking at those rivets during every preflight? Then if you beef up the rivet attachment with bolts, the eye bolts break in the strut.
Airplanes flex in many places where most of us don't think they flex. When one makes an "improvement" which stiffens that flexibility location, it is not unusual for that "improvement" to fail. By removing that flex location you are stiffening the whole flexible wing/strut assembly so that the flexing is concentrated on your eye bolt.
I have another question. It appears the wall thickness of those struts is the same around their entire circumference. Has anyone done a calculation as to the bearing load carrying capability of the bolts in the strut wall?
Why do I ask? Long ago a friend bought a J-3. The lower end of the wing struts had been cut off with an alternate fitting bolted in as shown in your pictures. One day Mr. FAA came by, spotted it and placed a red tag on the Cub. Fortunately I had a friend who was a DAR stress analysis specialist. He looked at it and agreed with Mr. FAA. The fix was to weld on two steel straps (both sides) which doubled the wall thickness of the strut where the bolts went through.
Your struts are aluminum, the J-3 struts were steel. The bearing strength of aluminum is lower than steel.
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The profile cannot be seen well in the picture...the inner view shows thicker “flats” in the center area and the extrusions themselves are substantial. I believe the tensile strength of these extrusions exceeds that of a steel strut...the steel struts are substantially thinner wall thickness. I don’t have the numbers at the top of my head... but I sure do appreciate feedback on this. I also am going to take your comments on the jury mounting to heart and do some research before I drill the hole. Jay is doing this on his Aluminum struts...are Javron jury upper mounts the same as Pipers? Does the clamp method introduce flexibility by spreading the load along the clamp? Or doe the clamp flex enough to add this flex into the system? Is it the single point that adds stiffness causing the issue you describe? This is interesting. Thank You Pete. I always pay attention when you respond.
This pic is grainy, but you can see how I mounted my jury strut tab to the spar
The airplane which had the eye bolt issue to which I was made aware of was a Cub Crafter airplane. I do not know how Jay does this.
The flexibility is in the pivot which is allowed by the bolt which passes though the clamp thus acting like a hinge. When that "hinge" is removed, something else has to absorb the flexing. It is the bolt that allows the flex, not the clamp.
Picture that long strut vibrating. When the lower half moves down the upper half is moving up and vice versa. The jury strut attachment divides those two halves. Thus the bolt which holds the jury strut to the clamp acts as a hinge. When that hinge is rendered inoperable that flexing has to be absorbed elsewhere.
Your fitting to the spar looks like a couple of AN3s. Certainly adequate. It's the eye bolt in the strut which is my concern.
If you wish to use an eye bolt in this location, use some other attachment to connect the jury strut to the eye bolt which will allow the flexing (hinging).
N1PA
Another thought to consider is that this destructive vibration failure could be caused by the engine/propeller transmitting a resonance through the airframe with the result making an appearance at this eye bolt. The airplane of which I was made aware of had had two failures of the same eyebolt. The opposite side had not failed.
Perhaps a different engine/propeller combination would not create this issue?
I've seen some strange vibration things happen with different power settings, smooth air or not, different air speeds etc. Too many to recall here.
N1PA
I see the increased wall thickness in the "flats" now. It is not the tensile strength of the struts which I addressed. It is the bearing strength of the bolt holes. The ability of the strut to withstand the crushing load of each bolt on the edges of it's hole. Now that I see the thicker flats, that may not be an issue.
N1PA
Pete,
The way Dan has drilled his holes, is quite different than how Jay engineering is. Here is a picture of Jay's.
On the eye bolt issue, Tom F had let me know about the CC eyebolts failing so that is true however CC's eyebolts are made just opposite of Jay's. The CC eyebolts have the threaded connection starting right behind the eye shoulder, they are breaking there. Jay's are made with the eye and 75%of the shaft all milled interagal, the foot part
Has the threads on it ahead of a shoulder that meets the top part so you CAN not over tighten the bolt and crush the strut. We always had problems with the Piper bands moving when hauling lots of moosehorns, lots of guys wrapped black tape on struts then reinstalled the bands trying to get them to stay put! This eyebolt thing is same as the Champ set up basically? Your comments on here are always informative!
E
Below is picture of the CC eyebolts design that have failed.
Last edited by TurboBeaver; 03-19-2021 at 07:49 AM.
E, Your Jay picture also has two more bolts, reducing the load per bolt. You are correct on the thread location of the eye bolt. Not only on the crush of the strut but the crack inducing location of the top thread. Right where the loads are concentrated. Perhaps the "Jay" eye bolts will outlive the Cub Crafters bolts. It was Tom's customer who consulted with me on the issue.
N1PA
Well when the smoke all clears, it seams like Jay's stuff most of the time falls into the ' build a better mouse trap' stuff. I think he looks at how everyone else has done it and simply says " this is how I would build that".
I will keep you posted how mine hold up. They sure seam
Solid and Stout........ And are most certainly way ahead of
60 year old ones with 7/16 forks!!!��
Last edited by TurboBeaver; 03-19-2021 at 08:19 AM.
Below is picture of the CC eyebolts design that have failed.
No compression sleeve to take up space inside strut when torqued down?......................................
Last edited by Southern Aero; 03-19-2021 at 09:19 AM.
......... It doesn't cost any more to go first class! You just can't stay as long.
Here is Jay's.....
I can't seem to post the picture of the failed fitting. It was at the end next to the eye. The threads go all the way to the eye end.
N1PA
Glenn
"Optimism is going after Moby Dick in a rowboat and taking the tartar sauce with you!"
The certified aluminum struts use a traditional strut clamp for what it's worth.
Cub Crafters was having an issue of breaking strut attach fittings at the wing spar and then they started shearing the rivets of the beefed up fittings. Some think it is from people pushing and pulling on the struts.
Steve, Based upon the information which was given me, It was not from people pushing and pulling on the struts.
N1PA
I don’t know about all of this... I’m taking notes. I do know that I talked to Jay first and he said his struts were big time over kill for my 11...his are rated at 2400 lbs gross...I’m 1320, so it would make sense that mine would be less beefy. Until I held these parts in my hand, and built the struts...I had little tiny questions in my mind....now that I’ve handled them.... they are very structurally sound...the material is substantial and if pull out those AN 4 bolts somehow in flight...it would mean something significant happened. I believe these are much stronger than the struts on my J3...I’m not sure what I’m going to do with the jury struts yet....I still need faileads as well. This is a great discussion and I’m following with great interest.
I am at 1310lbs GW too and run the Univair J3 struts on my little bird. Any idea of the weight savings between the stock J3 and your new aluminum units?
Are these the guys that did those struts? southernaero DOT net/ (I can't seem to post the actual URL for some reason)
I’ll weigh them....yes, southern aero out of GA. My guess is equal or a pound or two more than J3 struts....they are the same profile (size) as stock Supercub struts.
I too would (and do) run the Univair J3 struts. I haven't yet but I need to pull mine and weigh them against the Airframes Aluminum struts. There's probably weight to be saved with AF aluminum struts over J3 struts but I doubt any saved with the Javron struts as they are very heavy duty and therefore heavier to work with a 2300lb gross weight. Just from my calibrated arm scale it feels like the AF aluminum struts are going to be lighter for the rear strut (vs J3 steel struts) and probably about a wash weight wise for the front strut.
You've already bought the struts though and they look like pretty good units. I'd say just run them and don't fret too hard over ounces or hearsay jury strut issues. Those big old struts aren't working very hard to keep the wings on a 1320lb plane.
These were a little less than half the cost of airframes struts and several hundred less than Univair....I had to build them up from the parts.. yes, but I enjoy that part. He sent them with AN eye bolts and sleeves to go inside...is anyone thinking the stresses will actually break the AN eye bolt ? Or are you thinking the sleeve will attempt to pull out? I’m thinking with my set up I’m good...I’ll keep an eye on it. This is the best forum on the internet by far. I’ll keep the updates coming, and you guys keep seeing me in the right direction.
Dan I think Crash is right you still have plenty of strut for an 11! Just get some eyebolts from Jay, and his fairleads
(Also nicely done) and I think your " golden".....
Good luck on a nice looking Project, your doing a dam good job.
E
Dan
Your stock J3 rear strut has less than .150 square inch in cross section (rolled from a 1 1/2" x .035 mild steel tube) and the 6061 aluminum cross section of the rear is .440 sq. in. The stock front J3 strut was rolled from a 2 1/8" x .035 steel tube with less than .150 sq. in. in cross section. Your fronts are 6061 with .772 in cross section. There are plenty of engineer types on here that can put numbers to that.
Crash, you're pretty much right on the weights. Actually could have run the same size smaller strut in the front and rear but would not have gained much in strength.
Last edited by Southern Aero; 03-19-2021 at 04:58 PM.
......... It doesn't cost any more to go first class! You just can't stay as long.
I noticed most Cubs have 2 big cable fairleads, and 1 small one on each front lift strut...is this necessary to eliminate cable vibration? Or, can a fella get away with 2 big ones spaced (one between the jury and fuselage, the other between jury and outboard end?
piper put 3, so I put 3
You're going to end up with one fairlead in roughly the middle of the strut on the jury strut clamp so it would be wise just to do the normal 3 per side. Do your current strut clamps have the fairlead welded in?
*edit* Duh, I should have read your last post. Good job going with the correct and original locations. The cable already moves around quite a bit with 3 fairleads so I'd hate to see what it does with only 2.
As an aside, does anyone have the drawings for the original J-3 struts? I'm looking for a cross section drawing of front and rear to calculate some stuff related to aluminum struts.
Crash
I have them as .tif files so couldn't upload here but tried to convert them. They were rolled from round tubes to these dimensions and prints don't show original sizes. Cross sectional values aren't shown but shows weights so you can convert from there, I made a mistake at #230 and duplicated the rear strut value of .150 sq. in. for the front strut .............. shudda been .234 sq. in.
Will send you original .tif files if you would like. Can make out a LITTLE better in originals
Last edited by Southern Aero; 04-08-2021 at 11:18 PM.
......... It doesn't cost any more to go first class! You just can't stay as long.
Aren't those the same as on Christian Sturm's website? They come out pretty well:
http://www.supercubproject.com/drawi...s/A3290445.pdf
http://www.supercubproject.com/drawi...s/A3310004.pdf
Hi RV
Well those sure are cleaned up nice! I didn't think to look there since these are 1945 drawings
......... It doesn't cost any more to go first class! You just can't stay as long.
Perfect! Thanks for finding those for me. I've been idly curious if the rear PA-18 aluminum struts are equal in strength to the J3 front struts so that rear struts could be used both front and rear on a J3 and save quite a bit of weight. Now to do some maths and figure this thing out. Thanks again!
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