Strut ad

[Dano"T"]

Re: Strut ad

just buy someone else's struts that they have left over from a replacement and save yourself the trouble....just get them tested first.

[Hank Jarrett]

Re: Strut ad

A sleeve and a scab patch are totally different. Sleeve patches go all the way around the strut and are edge and rosette welded to the tubing. My longerons have been repaired that way and I have several old struts with sleeve patches. They look like H**L but are strong, safe and approved for use by the Feds.
A scab patch is only over the damage area and I haven't looked it up so I don't know for sure, but I don't remember them being approved for longerons or struts. You DO see them on cluster welds fairly often and the book says that is OK. Of course at a cluster all of the steel has also been heat affected already, not true if you weld in the middle of a strut. Remember the critical load in a strut at the middle is BENDING. That can be impacted by changing the temper of the steel.
Final word is with whoever signs it off. It doesn't matter at that point if it is really safe or not, just whether the guy doing the signing SAYS it is safe. I always add my own evaluation to what the inspector says after he is done. I can go MORE conservative than him, just not less. If an IA says it's good to go and I don't like it, I CAN replace the part anyway (I have replaced someone, but that also involved replacing him. He was a flight instructor and didn't like my disagreeing with him, so I fired him.)
Hank

[T-Rex]

Re: Strut ad

Blake, I am in the Twin Cities area and when I replaced my struts with new Airframes Inc. struts I had one patched orignal strut on one side and a Univair Sealed strut on the other side. If you wanted to buy the univair strut to replace your bad one you could drive up and get it. You could also look at buying another from univair and then at least your front struts would be sealed. Get the rear ones inspected and then in four years replace those or have them sealed. this way the cost will be spread out. I also have a full set of original struts that have not been inspected but they look questionable. They would at least be good for holding your wings up while yours are off. IMHO I would fly with a properly patched wing strut but to fill a dent with bondo, JBweld or any cosmetic repair is crazy. All you are doing is sweeping a problem under the rug, out of sight out of mind right. Keep in mind they are probably approaching 70 years old and in my opinion ready for replacement. With an old engine if it quits you glide to a hopefully safe landing, if that strut fails, well we all know what happens there. Just PM or email if I can help.
Brad A&P

[N96337]

Re: Strut ad

As an IA, I'd much much rather see the dent, than notice "bondo" or some other filler trying to cover a dent (been there, done that, and found a real mess underneath!!). I've seen the results of prolonged exposure of filler to moisture, and if it were on my plane, I'd remove the filler and run it, unless the dent is really deep. Like has been said before, the strut is in tension 99% of the time, so I doubt the dent will affect it much.
John

[Guest]

Re: Strut ad

A sleeve and a scab patch are totally different. Sleeve patches go all the way around the strut and are edge and rosette welded to the tubing. My longerons have been repaired that way and I have several old struts with sleeve patches. They look like H**L but are strong, safe and approved for use by the Feds.
A scab patch is only over the damage area and I haven't looked it up so I don't know for sure, but I don't remember them being approved for longerons or struts. You DO see them on cluster welds fairly often and the book says that is OK. Of course at a cluster all of the steel has also been heat affected already, not true if you weld in the middle of a strut. Remember the critical load in a strut at the middle is BENDING. That can be impacted by changing the temper of the steel.
Final word is with whoever signs it off. It doesn't matter at that point if it is really safe or not, just whether the guy doing the signing SAYS it is safe. I always add my own evaluation to what the inspector says after he is done. I can go MORE conservative than him, just not less. If an IA says it's good to go and I don't like it, I CAN replace the part anyway (I have replaced someone, but that also involved replacing him. He was a flight instructor and didn't like my disagreeing with him, so I fired him.)
Hank

Hi Hank,

Thanks, I think I got it.

Sounds like what you call a scab patch is the repair desribed in AC43.13-1B figure 4.34 and 4.36

Here are some details;

4-94. WELDED-PATCH REPAIR. Dents
or holes in tubing may be repaired by using a
patch of the same material, one gauge thicker.
(See figure 4-36.)
a. Dented Tubing.
(1) Dents are not deeper than 1/10 of

tube diameter, do not involve more than 1/4 of
the tube circumference, and are not longer than
tube diameter.
(2) Dents are free from cracks, abrasions,
and sharp corners.
(3) The dented tubing can be substantially reformed,
without cracking, before application
of the patch.
b. Punctured Tubing. Holes are not longer
than tube diameter and involve not more than
1/4 of tube circumference.

4-91. REPAIR OF TUBULAR MEMBERS.
a. Inspection. Prior to repairing tubular
members, carefully examine the structure surrounding
any visible damage to insure that no
secondary damage remains undetected. Secondary
damage may be produced in some
structure, remote from the location of the primary
damage, by the transmission of the damaging
load along the tube. Damage of this nature
usually occurs where the most abrupt
change in direction of load travel is experienced.
If this damage remains undetected,
subsequent normal loads may cause failure of
the part.
b. Location and Alignment of Welds.
Unless otherwise noted, welded steel tubing
may be spliced or repaired at any location
along the length of the tube. To avoid distortion,
pay particular attention to the proper fit
and alignment.
c. Members Dented at a Cluster. Repair
dents at a steel-tube cluster joint by welding a
specially formed steel patch plate over the
dented area and surrounding tubes. (See figure
4-34.) To prepare the patch plate, cut a
section of steel sheet of the same material and
thickness as the heaviest tube damaged. Trim
the reinforcement plate so that the fingers extend
over the tubes a minimum of 1.5 times the
respective tube diameter. (See figure 4-34.)
Remove all the existing finish on the damaged
cluster-joint area to be covered by the reinforcement
plate. The reinforcement plate may
be formed before any welding is attempted, or
it may be cut and tack-welded to one or more
of the tubes in the cluster joint, then heated
and formed around the joint to produce a
smooth contour. Apply sufficient heat to the
plate while forming so that there is generally a
gap of no more than 1/16 inch from the con
tour of the joint to the plate. In this operation
avoid unnecessary heating, and exercise care to
prevent damage at the point of the angle
formed by any two adjacent fingers of the
plate. After the plate is formed and tack
welded to the cluster joint, weld all the plate
edges to the cluster joint.




Dave

[shawn coleman]

Re: Strut ad

replacing my struts in nov have xrays from 2 years ago they will be for sale dont want to bother on taking them off every 2 years

[VictorBravo]

Re: Strut ad

Hank, per your recent post...how are the struts loaded in bending under normal positive G loads???

This is one of them fancy engineering puzzles, ain't it?

[Hank Jarrett]

Re: Strut ad

In a positive "G" condition the only way would be if the jury struts were WAY out of rig or something hit the strut.
Bending loads come in whenever the plane is in negative "G", like in turbulence or on the ground with load (snow?), or, the most common way, when some knuckle head lifts up or pulls down on the strut. There is also a bending load anytime you push or pull the plane on the ground by the struts, but that is taken up on the major axis of the strut and isn't as much of a problem as a kid swinging from the struts or your mother-in-law deciding the strut is a good foot rest to get in or out.
Hank

[VictorBravo]

Re: Strut ad

Under negative G loading wouldn't the struts be loaded in compression, as long as the jury strut keeps it aligned properly?

With a point loaded bolt at both ends, and the strut's ability to "rotate" around those bolts, it would seem to me that it is very difficult to actually have a bending load without first going through a lot of compression load? If the jury strut is way off, as mentioned, then a bending load at one small location (next to the jury strut attach) could occur.

But how could a bending load be applied in between two "pivoting" ends between the supports?

As a wild guess, I'd have to guess that if a wing strut were seeing any genuine bending loads (like a spar) there would be a shear web in the strut somewhere to get those loads carried by the upper and lower skins.

[Hank Jarrett]

Re: Strut ad

The bending load happens as soon as the neutral axis of the strut moves away from a line between the centers of the two pins (bolts). If you keep the deflection small, the loads don't build enough to fail the strut. The failure usually isn't a true bending failure. It is called a crippling failure where the compression in the inside of the curve is much higher than the tension on the outside. In a pure bending failure the compression and tension are equal in magnitude with the neutral axis in the center of the tube.
By putting the jury strut in you effectively make the strut two tubes half the length which significantly increases the resistance to bending and crippling.
Hank