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Spar attach holes. How bad is this?

OKAK

Registered User
I am salvaging parts from an experimental to use in my project and discovered that there are additional holes in the spar under the attach bracket. The are at least 300 hours on this plane since it was registered, and I don't see cracks between the holes. My question is this... 1. is this unacceptable? 2. should I remove this part of the spar and relocate all the attachments. That would shorten the wing 8" and leave holes in the spar where all the original attachments are. or 3. get a replacement spar. May be there is another solution I have not thought of. Any advise is appreciated.DSCN0149.jpg
 

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thats fine....

the piper spar attach only had all those bolts because its a leftover design from WOOD spar days.... the piper attach bracket is just allot of dead/extra weight in itself and all those extra bolts holding it on...
 
I am salvaging parts from an experimental to use in my project and discovered that there are additional holes in the spar under the attach bracket. The are at least 300 hours on this plane since it was registered, and I don't see cracks between the holes. My question is this... 1. is this unacceptable? 2. should I remove this part of the spar and relocate all the attachments. That would shorten the wing 8" and leave holes in the spar where all the original attachments are. or 3. get a replacement spar. May be there is another solution I have not thought of. Any advise is appreciated.View attachment 17598

1 = no
2 = bad idea, then you fusk up strut length, fuel bay... and other
3 = you are experimental...

4 if it really bothers you http://www.crosswindsstol.com sells a real approved spar attach repair kit.....
 
Spar bending moment loads is pretty low at fuselage end. It will grow max at strut attach point, and it will grow parabolic. Strut attach point is that where is max bending moment at spar both ends, and wing tip and fuselage attach point have lowest moments.
 
I've used a couple hose clamps at fuselage end of cracked spar to keep crack from spreading for 300? miles of ferry flight after it was on it's back...

Wow! That is real field repair! It will work in low shear/ bending moment area like root of a wing or tip, but it need brave pilot too!
 
Thank you all for your replies, I appreciate them all. I have an email in to Crosswindsstol.com to find out what their spar attach repair entails. Good to know about the shear dynamics, and have some assurance it is not the highest stressed region of the spar.
 
Thank you all for your replies, I appreciate them all. I have an email in to Crosswindsstol.com to find out what their spar attach repair entails. Good to know about the shear dynamics, and have some assurance it is not the highest stressed region of the spar.

Piper & many aircraft manufactures did some dumb things, because they still had 1500 of some other part laying in stock and hodge podge the new part to be able to make some other ones still fit, instead of just designing 2 new parts right.... (the flap hangers on a metal spar Scout come to mind, they just welded a new pivot onto old designed hanger..)
 
Look at the holes some of the light guys are drilling in there spars. I would use that with no problem.
DENNY
 
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Thank you all for your replies, I appreciate them all. I have an email in to Crosswindsstol.com to find out what their spar attach repair entails. Good to know about the shear dynamics, and have some assurance it is not the highest stressed region of the spar.

One rough example: If your one wing is 200" long and 2000 lbs plane, that wing must carry half weight + design G load and designer safety factor. If braking point is 6 G, then it will be 4 G operational limit. Half weight of a plane 1000lbs X 4 G is your maximum operational wing loading. 4000 lbs divided 200" gives 20 lbs load on every inch of your wing panel/ spars at 4 G flight load.

If strut is middle of a wing, strut wing bending load rise max at strut attach point, 100". First inch at root and tip spar load is 20 lbs... 10 " spar load 200 lbs and 99" point 1980 lbs at both direction, tip and root. That strut attach point is place where those growing forces meet, and where is max bending moment of a wing.

That was just rough example. Designers don´t use wing weight at calculation, so 2000 lbs plane is without wing weight in these calc´s (1700 lbs?) and there is other forces like air loads that twist wing and drag loads. That wing root loads are pretty low anyhow.
 
If Piper put all those holes in the spar because it was a carry over from the wood spar wing then why wouldn't Cub Crafters, Dakota Cub and Legend Aircraft have re-engineered their designs since they are so worried about weight. Dakota Cub has stressed tested the wing in a wiffle tree with strain gauges all over the wing. Both their wing attach blocks and the Top Cub are solid and where Piper's have a radius cut along the edge. Mark told me the original design failed in the high gross weight tests.
 
That wing root loads are pretty low anyhow.

That wing root must carry fuel weight too, so it must have more strength than tip of wing. That rough calculation was just rough bending loads for G forces, nothing else.
 
...Piper's have a radius cut along the edge. Mark told me the original design failed in the high gross weight tests.

Exactly! it must only be as strong as the WEAKEST part, and thats the attach fitting block where bushing goes through to bolt onto fuselage.

they rip off in some wrecks seen many cracked/ elongated hole in spar, and you just bring a piece of angle iron or such and pickup the fuselage bolt and the first 2 bolts on spar to ferry it home..

with wing on plane/inspection time, put your finger on top of fitting at spar/fuselage attach and have someone flex wing at tip, if fuselage attach hole in spar IS Elongated the spar will move in-between the brackets ALLOT... scary amount... and yet bracket will look fine...
 
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Other than while static or when in an unusual negative G moment that area of the spar is in compression. Not tension. A few extra holes shouldn't be a problem. At least not in my feeble comprehension of the question.
 
Aren't there some engineering studies of how holes weaken a web? My impression is that a few holes in a spar will not appreciably weaken it, and if those holes are under a reinforcement maybe it is even less of an impact? A good mechanical engineer ought to be able to do a table look-up on this one. The spar cap is an extremely important structural component, and the front spar has about fifty holes in each flange.

Remember - folks are putting spar extensions on, and some of the rivet patterns make the two spars joined together look like a cheese grater before all the rivets are driven.

Speaking of modern designs, are we sure CC is not using lightening holes in their spars?
 
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