DHC-6 wing bolts

longjon · Post by **longjon** » Thu Oct 12, 2006 5:18 pm

This is a technical question for DHC-6 guys .

One I,ve not gotten a decent answer to

Why are the wing attach bolts hollow in design?

Lifting/hoisting HMMMM????? Must be more.

dhc-t2 · Post by **dhc-t2** » Thu Oct 12, 2006 9:35 pm

Ok, you may think this is crazy but I am 99% sure that that pin you speak of is hollow because it is actually designed to be the weakest link. That does sound crazy being the main attach bolt. The bolt is over 1" dia. and if it was solid it would be way overkill for the application. It is designed to shear on impact of the aircraft. A solid pin would cause a lot of really bad things to happen to the fuselage structure if there were to be a serious impact. There is a "wing restraint mod" for the rear spar attach fitting that keeps the spinny things from coming through stn. 111 of the twin otter on impact.
Anyway, thats my theory. If anyone has a better idea then let me know. Don't tell me it is to save weight.

longjon · Post by **longjon** » Fri Oct 13, 2006 2:00 pm

No I dont think the weight saving has much merrit even though it was tossed around in the discussion.

I recall hearing someone say it was hollow for crack retardant or something to that effect but just can;t get my feeble brain to comprehend this concept.

The wing is under a shear load and the hollow bolt may have more tensile strength. Im afraid I dont completly buy the weakest point theory but has some good argueable points, thanks for the input.

twotter · Post by **twotter** » Fri Oct 13, 2006 10:59 pm

Hoisting..

dhc-t2 · Post by **dhc-t2** » Sat Oct 14, 2006 5:04 pm

I have access to some very reliable resources & will look further into this one as I am quite interested to know myself. I know the hoisting sling is also indeed related as previously mentioned.

dhc-t2 · Post by **dhc-t2** » Sun Oct 22, 2006 7:59 am

After looking into this one further & looking at the bolt details I would like to retract my last statement from the record. This bolt in not the weakest link, even with a hole drilled through it. This bolt would keep Quebec attached to Canada.
The hole is indeed for hoisting as previously mentioned.

twotter · Post by **twotter** » Sun Oct 22, 2006 10:09 am

Nice of you too have faith in what I say

splitpin · Post by **splitpin** » Sun Oct 22, 2006 3:40 pm

Most wing bolts (heavier aircraft) and helicopter blade bolts are hollow.
It's nothing to do with shear, etc.
The plain simple truth is that a hollow bolt is much, much stronger than a solid bolt. The stress is spread equally on the inside and outside surfaces, instead of just the outside surface as in a solid bolt. The result is you now have a hollow bolt, say 2" diameter, that is at least twice as strong as a solid one. An added bonus for Rotary wing is that is where the lead shot is kept to balance the rotor system.

longjon · Post by **longjon** » Sun Oct 22, 2006 3:46 pm

I agree with the last post.

The hoisting is a bonus but not the main reason for the hollow construction.

splitpin · Post by **splitpin** » Sun Oct 22, 2006 4:10 pm

In addition to wing bolts, the same principle applys to axles, turbine shafts, push-pull rods, drive shafts, propellers, bones, and on and on and on.

. ._ · Post by **. ._** » Sun Oct 22, 2006 4:29 pm

splitpin wrote:Most wing bolts (heavier aircraft) and helicopter blade bolts are hollow.
It's nothing to do with shear, etc.
The plain simple truth is that a hollow bolt is much, much stronger than a solid bolt. The stress is spread equally on the inside and outside surfaces, instead of just the outside surface as in a solid bolt. The result is you now have a hollow bolt, say 2" diameter, that is at least twice as strong as a solid one. An added bonus for Rotary wing is that is where the lead shot is kept to balance the rotor system.

That's pretty interesting.

Cool!

-istp

chubbee · Post by **chubbee** » Tue Oct 24, 2006 11:24 pm

Whats the difference between a "hollow bolt" and a pipe?
Any pipe I have experience with is weaker than an equivalent diameter solid round bar of the same material (Perhaps this is not so for a given installed fastener weight).
If this theory were true drilling a hole thru an installed solid rivet would not weaken the rivet, which seems contrary to logic.
A clearer explanation is needed to substantiate the claim that removing material increases absolute strenght rather than strength relative to weight.

splitpin · Post by **splitpin** » Wed Oct 25, 2006 7:31 am

chubbee wrote:Whats the difference between a "hollow bolt" and a pipe?
Any pipe I have experience with is weaker than an equivalent diameter solid round bar of the same material (Perhaps this is not so for a given installed fastener weight).
If this theory were true drilling a hole thru an installed solid rivet would not weaken the rivet, which seems contrary to logic.
A clearer explanation is needed to substantiate the claim that removing material increases absolute strenght rather than strength relative to weight.

Maybe you should consider going to school and learn all about mechanical thingys.

chubbee · Post by **chubbee** » Wed Oct 25, 2006 1:31 pm

An arrogant uninformed response splitpin.
What school taught you that air was stronger than steel or some other metal?

Troubleshot · Post by **Troubleshot** » Wed Oct 25, 2006 2:11 pm

All tow bar lugs on Boeing aircraft have hollow bolts to attach them to the nose gear...this would lead me to believe they are designed to shear as it is a very likely it will need the protection due to stress it may incur .

On the the flip side the Landing gear is also designed to shear-off on Boeing products in the event the leg gets caught up in something it doesn't tear a huge hole in the fuel tank (wing) and cause a huge fire...this bolt is solid...

dhc-t2 · Post by **dhc-t2** » Wed Oct 25, 2006 6:01 pm

[quote="chubbee"]Whats the difference between a "hollow bolt" and a pipe?
Any pipe I have experience with is weaker than an equivalent diameter solid round bar of the same material (Perhaps this is not so for a given installed fastener weight).
If this theory were true drilling a hole thru an installed solid rivet would not weaken the rivet, which seems contrary to logic.
A clearer explanation is needed to substantiate the claim that removing material increases absolute strenght rather than strength relative to weight.[/quote]

I hear your point with tube vs. bar stock but in this case the bolt in question has some serious wall thickness going on. The bolt is also heat treated to a temper that would scare most people. Probably wouldn't cut it with a hack saw.

About the strength comparism between hollow/tube Drilled or not vs. bar or rod stock, it really depends what the application is & also what the temper & alloy in question is.

chubbee · Post by **chubbee** » Thu Oct 26, 2006 10:05 am

Yeah dhct2 it is a complicated issue, there was an old radio program that used to have a catch phrase "and that's the rest of the story". Similarrly I think there are a lot of detailed technical resons behind the use and fabrication of hollow bolts in aircraft applications which vary from application to application. I do not believe it is an identical design problem in all cases.
In some cases the diameter of the fastener may relate to the material it is installed in. The original twin otter wing fittings were aluminum and a larger diameter pin would distribute stresses into the fitting over a larger bearing area. A half inch high strength steel pin could maybe carry the load but would put too concentrated a point load into the fitting it passes thru?? I was doing a myth busters type trial the other day at Tim Hortons trying to determine if the donut or the hole/Tim bit, had more strength qualities but I ran out of test material and can not produce results just yet.

nighthawk · Post by **nighthawk** » Fri Oct 27, 2006 10:52 am

I know that the fact that the bolts are hollow makes them a hell of alot easier to change as you just insert a bullet in the hollow end and drive the old ones out and the new ones in .Makes for a fast wing bolt change when they are done one at a time.

twotter · Post by **twotter** » Sat Oct 28, 2006 3:20 am

Yup, gotta agree with you Nighthawk.. I't much easier..

I think the rest of the posters are just over complicating things here..

longjon · Post by **longjon** » Sat Oct 28, 2006 7:50 am

So its agreed on? The hollow design is for strength and not hoisting.

Did you really thing the Engineers would put the hoisting factor into the orignal design?

Riverman · Post by **Riverman** » Mon Oct 30, 2006 9:05 am

Yes agreed

I'm going to work now to drill holes through all of the fasteners on my aircraft. To think, all this time we were carrying all this unnecessary weight in the form on solid fasteners.

I'm going to contact the manufacturer of our wing attatch bolts and suggest they remove all excess material. Might as well go paper-thin. It will be stronger.

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