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View Full Version : Hinges under stress - mechanical engineering type question


Corrie
July 31st 03, 12:56 AM
Thinking about a hinge like this (end view): ____(O)____ where "___"
is the plate, "( )" is the barrel, and "O" is the hinge pin. It would
be bolted through the plates to the surface below. The barrel sits
"on top" of the plates. Hope that makes sense.

It's in tension and/or compression (some torsion also), so obviously
the hinge pin needs to have a lot of shear strength. Clevis pins are
designed for this application, so it's a matter of doing the sums and
selecting a properly-sized one from the catalog.

But the *barrels* of the hinge are a weak point. A plain rolled
piano-type hinge would obviously just pull apart if the barrels aren't
connected back to the plate. What's the best way to prevent this?

Weld the barrels back to the plate so they are closed and can't pull
open? Makes sense - but how sure can you be of the tensile strength
of that weld? Build a test article and test it to destruction?

Or perhaps you could make the hinge by folding a strap around the
clevis pin, and back over itself. Then you have a double-thick plate
- extra weight. And tension would tend to pull the barrel out of
round and make the clevis want to center between the straps:
=====<O>==== rather than "on top": ____(O)____. Also, you'd have a
sharp reflex bend - potential crack site - where the barrel comes down
around the pin and then flattens out as the top layer of the two-layer
plate: __(

Ideas? I know somebody has to have already solved this. btw - assume
that the issues of properly bolting the hinge to the material below,
and properly heat -treating the assembly, have been solved. We're
just looking at the mechanics of the hinge barrel, unless I'm missing
something.

(Rich, yes, you know why I'm asking... ;-) )

Corrie "alllllways thinkin'..." B.

James R. Freeman
July 31st 03, 01:25 AM
Most suppliers have the extruded piano hings that will not pull apart before
failure. I know Aircraft Spruce has them in 6 Ft lengths aluminum or
stainless steel.

"Corrie" > wrote in message
om...
> Thinking about a hinge like this (end view): ____(O)____ where "___"
> is the plate, "( )" is the barrel, and "O" is the hinge pin. It would
> be bolted through the plates to the surface below. The barrel sits
> "on top" of the plates. Hope that makes sense.
>
> It's in tension and/or compression (some torsion also), so obviously
> the hinge pin needs to have a lot of shear strength. Clevis pins are
> designed for this application, so it's a matter of doing the sums and
> selecting a properly-sized one from the catalog.
>
> But the *barrels* of the hinge are a weak point. A plain rolled
> piano-type hinge would obviously just pull apart if the barrels aren't
> connected back to the plate. What's the best way to prevent this?
>
> Weld the barrels back to the plate so they are closed and can't pull
> open? Makes sense - but how sure can you be of the tensile strength
> of that weld? Build a test article and test it to destruction?
>
> Or perhaps you could make the hinge by folding a strap around the
> clevis pin, and back over itself. Then you have a double-thick plate
> - extra weight. And tension would tend to pull the barrel out of
> round and make the clevis want to center between the straps:
> =====<O>==== rather than "on top": ____(O)____. Also, you'd have a
> sharp reflex bend - potential crack site - where the barrel comes down
> around the pin and then flattens out as the top layer of the two-layer
> plate: __(
>
> Ideas? I know somebody has to have already solved this. btw - assume
> that the issues of properly bolting the hinge to the material below,
> and properly heat -treating the assembly, have been solved. We're
> just looking at the mechanics of the hinge barrel, unless I'm missing
> something.
>
> (Rich, yes, you know why I'm asking... ;-) )
>
> Corrie "alllllways thinkin'..." B.

Corrie
July 31st 03, 08:46 PM
john > wrote in message >...
> On 30 Jul 2003 16:56:37 -0700, (Corrie) wrote:

> "MS20001P aluminum hinge is extruded. The closed hinge loops cannot be
> pulled apart. Furnished with hinge pin. Anodized finish."

Thanks. How much stress can it take, though? That's the question.
Probably the hinge pin or the rivets holding the plates would be the
first to fail at a few hundred pounds, but still... <musing> I
suppose one could order some and find out.... If the specific alloy
were known, it could be looked up.
http://ourworld.compuserve.com/homepages/MJVanVoorhis/T003.htm shows
yield and tensile strengths for a number of allows. They tend to be
around 30kpsi. The catalog doesn't give the thickness of the flange.
Assume it's .1", and the hinge is 6" long, that's .6 sq. in, at
30kpsi.. 18,000 lbs? But some alloys are as low as 5kpsi - that's
3,000 lbs. Impressive for a small hinge, but would it suffice for the
application? Marginal at best, I think.

The largest hinge at AS&S is just 2" wide, and they all seem to have
the same size pin - .089 stainless. That's .006 sq. in. area. I
can't find a reference for shear strength for stainless, but taking an
optimistic SWAG at 200kpsi (the highest yield strength for drawn ss
referenced at http://ourworld.compuserve.com/homepages/MJVanVoorhis/T006.htm),
that's 200,000 x .006 = 1200 lbs. Not nearly good enough. </musing>


My guess is that if it's not specifically rated and labeled, it's
unknown. Not something to put in a critical area. So, then, back to
the original question. Assuming you don't have the ability to extrude
a larger piece of aluminum (in order to use a larger pin), how *do*
you solve the problem?

Big John
July 31st 03, 09:39 PM
Corrie

Just think out of the box.

Go to hardware store and buy some farm gate hinges with the 1/2 inch
bolt in them. They may be over engineered for your proposed use but
they are hell for stout and would probably do the job ok without a lot
of paper engineering..

Big John

On 31 Jul 2003 12:46:24 -0700, (Corrie) wrote:

>john > wrote in message >...
>> On 30 Jul 2003 16:56:37 -0700, (Corrie) wrote:
>
>> "MS20001P aluminum hinge is extruded. The closed hinge loops cannot be
>> pulled apart. Furnished with hinge pin. Anodized finish."
>
>Thanks. How much stress can it take, though? That's the question.
>Probably the hinge pin or the rivets holding the plates would be the
>first to fail at a few hundred pounds, but still... <musing> I
>suppose one could order some and find out.... If the specific alloy
>were known, it could be looked up.
>http://ourworld.compuserve.com/homepages/MJVanVoorhis/T003.htm shows
>yield and tensile strengths for a number of allows. They tend to be
>around 30kpsi. The catalog doesn't give the thickness of the flange.
>Assume it's .1", and the hinge is 6" long, that's .6 sq. in, at
>30kpsi.. 18,000 lbs? But some alloys are as low as 5kpsi - that's
>3,000 lbs. Impressive for a small hinge, but would it suffice for the
>application? Marginal at best, I think.
>
>The largest hinge at AS&S is just 2" wide, and they all seem to have
>the same size pin - .089 stainless. That's .006 sq. in. area. I
>can't find a reference for shear strength for stainless, but taking an
>optimistic SWAG at 200kpsi (the highest yield strength for drawn ss
>referenced at http://ourworld.compuserve.com/homepages/MJVanVoorhis/T006.htm),
>that's 200,000 x .006 = 1200 lbs. Not nearly good enough. </musing>
>
>
>My guess is that if it's not specifically rated and labeled, it's
>unknown. Not something to put in a critical area. So, then, back to
>the original question. Assuming you don't have the ability to extrude
>a larger piece of aluminum (in order to use a larger pin), how *do*
>you solve the problem?

Rick Pellicciotti
July 31st 03, 10:01 PM
"Corrie" > wrote in message
om...
> john > wrote in message
>...
> > On 30 Jul 2003 16:56:37 -0700, (Corrie) wrote:
>
> > "MS20001P aluminum hinge is extruded. The closed hinge loops cannot be
> > pulled apart. Furnished with hinge pin. Anodized finish."
>
> Thanks. How much stress can it take, though? That's the question.
> Probably the hinge pin or the rivets holding the plates would be the
> first to fail at a few hundred pounds, but still... <musing> I
> suppose one could order some and find out.... If the specific alloy
> were known, it could be looked up.
> http://ourworld.compuserve.com/homepages/MJVanVoorhis/T003.htm shows
> yield and tensile strengths for a number of allows. They tend to be
> around 30kpsi. The catalog doesn't give the thickness of the flange.
> Assume it's .1", and the hinge is 6" long, that's .6 sq. in, at
> 30kpsi.. 18,000 lbs? But some alloys are as low as 5kpsi - that's
> 3,000 lbs. Impressive for a small hinge, but would it suffice for the
> application? Marginal at best, I think.
>
> The largest hinge at AS&S is just 2" wide, and they all seem to have
> the same size pin - .089 stainless. That's .006 sq. in. area. I
> can't find a reference for shear strength for stainless, but taking an
> optimistic SWAG at 200kpsi (the highest yield strength for drawn ss
> referenced at
http://ourworld.compuserve.com/homepages/MJVanVoorhis/T006.htm),
> that's 200,000 x .006 = 1200 lbs. Not nearly good enough. </musing>
>
>
> My guess is that if it's not specifically rated and labeled, it's
> unknown. Not something to put in a critical area. So, then, back to
> the original question. Assuming you don't have the ability to extrude
> a larger piece of aluminum (in order to use a larger pin), how *do*
> you solve the problem?

Like this:

http://www.zenithair.com/kit-data/ht-aileron.html

Rick Pellicciotti

Ernest Christley
July 31st 03, 10:43 PM
Corrie wrote:

> The largest hinge at AS&S is just 2" wide, and they all seem to have
> the same size pin - .089 stainless. That's .006 sq. in. area. I
> can't find a reference for shear strength for stainless, but taking an
> optimistic SWAG at 200kpsi (the highest yield strength for drawn ss
> referenced at http://ourworld.compuserve.com/homepages/MJVanVoorhis/T006.htm),
> that's 200,000 x .006 = 1200 lbs. Not nearly good enough. </musing>
>
>

That's 1200 lbs at each hingepoint, that is every place that you could
slip a feeler guage down and touch the pin. That's about every 1/2" or
so on most of these strips.
--
----Because I can----
http://www.ernest.isa-geek.org/
------------------------

Peter Dohm
August 1st 03, 02:21 AM
Corrie wrote:
>
> john > wrote in message >...
> > On 30 Jul 2003 16:56:37 -0700, (Corrie) wrote:
>
> > "MS20001P aluminum hinge is extruded. The closed hinge loops cannot be
> > pulled apart. Furnished with hinge pin. Anodized finish."
>
> Thanks. How much stress can it take, though? That's the question.
> Probably the hinge pin or the rivets holding the plates would be the
> first to fail at a few hundred pounds, but still... <musing> I
> suppose one could order some and find out.... If the specific alloy
> were known, it could be looked up.
> http://ourworld.compuserve.com/homepages/MJVanVoorhis/T003.htm shows
> yield and tensile strengths for a number of allows. They tend to be
> around 30kpsi. The catalog doesn't give the thickness of the flange.
> Assume it's .1", and the hinge is 6" long, that's .6 sq. in, at
> 30kpsi.. 18,000 lbs? But some alloys are as low as 5kpsi - that's
> 3,000 lbs. Impressive for a small hinge, but would it suffice for the
> application? Marginal at best, I think.
>
> The largest hinge at AS&S is just 2" wide, and they all seem to have
> the same size pin - .089 stainless. That's .006 sq. in. area. I
> can't find a reference for shear strength for stainless, but taking an
> optimistic SWAG at 200kpsi (the highest yield strength for drawn ss
> referenced at http://ourworld.compuserve.com/homepages/MJVanVoorhis/T006.htm),
> that's 200,000 x .006 = 1200 lbs. Not nearly good enough. </musing>
>
> My guess is that if it's not specifically rated and labeled, it's
> unknown. Not something to put in a critical area. So, then, back to
> the original question. Assuming you don't have the ability to extrude
> a larger piece of aluminum (in order to use a larger pin), how *do*
> you solve the problem?


I really feel like a big dummy, because I may have missed the obvious,
and I know that I may have nothing usefull to add after all ... but ...

What are these hinges supposed to hold???
pressurized canopy?
undercarriage trunion?
control surface?
some kind of single hinge application?

Peter

Bill Daniels
August 1st 03, 03:11 AM
"Peter Dohm" > wrote in message
...
> Corrie wrote:

> I really feel like a big dummy, because I may have missed the obvious,
> and I know that I may have nothing usefull to add after all ... but ...
>
> What are these hinges supposed to hold???
> pressurized canopy?
> undercarriage trunion?
> control surface?
> some kind of single hinge application?
>
> Peter

Well, the Sisu 1A sailplane used aircraft grade piano hinges in instead of
spar root fittings. The right and left wings were joined to each other with
1/16" piano wire inserted through hinges riveted to the upper and lower wing
skins. The fuselage was hung from the joined wings.

See: http://www.nasm.si.edu/nasm/aero/aircraft/arlington.htm

Bill Daniels

Jay
August 1st 03, 08:51 PM
For the people that didn't visit the Zenith link, thats a sheet metal
hinge, no moving parts, just flexing sheet. I've seen this up close
and its pretty slick. One of those "Why didn't I think of that!" kind
of moments.

Regards

"Rick Pellicciotti" > wrote in message news:<3f298016$1@ham>...
>
> Like this:
>
> http://www.zenithair.com/kit-data/ht-aileron.html
>
> Rick Pellicciotti

Corrie
August 1st 03, 10:13 PM
Peter Dohm > asked, quite reasonably
> What are these hinges supposed to hold???

The spar. I'm thinking about the possibility of considering the
feasibility of investigating a folding wing. The spar would have a
hinge installed top and bottom. To fold the wing you remove the
bottom pin. GW of the aircraft in mind is ~1500lb. It would need to
be able to take 6 g's, hence my concern about strength.

The sailplane may have used standard piano hinges, but it was about
500 lbs, and probably not stressed for more than 3 g's.

Ernest Christley
August 1st 03, 10:36 PM
Corrie wrote:
> Peter Dohm > asked, quite reasonably
>
>>What are these hinges supposed to hold???
>
>
> The spar. I'm thinking about the possibility of considering the
> feasibility of investigating a folding wing. The spar would have a
> hinge installed top and bottom. To fold the wing you remove the
> bottom pin. GW of the aircraft in mind is ~1500lb. It would need to
> be able to take 6 g's, hence my concern about strength.
>
> The sailplane may have used standard piano hinges, but it was about
> 500 lbs, and probably not stressed for more than 3 g's.

The Dyke Delta does this with a 1/2" pin that passes through fittings in
the top and bottom spar. Max gross is 1950lbs.

--
----Because I can----
http://www.ernest.isa-geek.org/
------------------------

BD5ER
August 2nd 03, 03:41 AM
>The Sisu 1A Maximum Airframe Load Factors: + 6 G, - 4.6 G
>The Gross weight: 730 lb

And the wings are probably a lot higher aspect ratio than the ones your
considering. Long skiny/thin wings need stronger spars than short fat 'uns.

Just a WAG your probably looking at around 30,000 ft/lbs at the spar root for a
cantilevered wing? For a 6 inch deep spar that's around 33 of those little
hinge points - IIRC the numbers from the earlier thread correctly.

Of course getting 33 of them coplanar so they fold might take a bit of
length......

Then again with the ever reducing cost of CNC machine work you just might
consider one-of-a-kind units in a larger size.

I also remember seeing a post here a year or 2 ago about some extruded
graphite/carbon fiber hinges. I have no idea if they are even as strong as
aluminum (kind of doubt it) ones but it might be worth a quick internet search.

Peter Gottlieb
August 3rd 03, 05:23 PM
"Jay" > wrote in message
om...
> For the people that didn't visit the Zenith link, thats a sheet metal
> hinge, no moving parts, just flexing sheet. I've seen this up close
> and its pretty slick. One of those "Why didn't I think of that!" kind
> of moments.
>

I'm concerned about corrosion on such a flexing member and how the
imperfections introduced could concentrate stresses during flexing and cause
premature failure.

BD5ER
August 4th 03, 07:23 AM
> A 1500-lb aircraft pulling six g's puts a 9,000 lb
>load on the spar whether the wingspan is 25 feet or 50 ft. Unless
>I've forgotten something fundamental, you'd have 2250 lbs of tension

Either I'm mis-reading or you have forgotten something fundanental. The length
of the wing does have a very real effect on the spar attachment points.

A quick example. Pick up an 8 lb sledge hammer by the head at arms length. 8
lbs in your hand. An easy thing to do. Grab the handle half way and hold the
head out away from you again. Bit of a strain on the forarm muscles isn't it.
If you go to the gym on a regular basis try again at 3/4 of the handle.

Another visual aid is a gymnast on the rings trying to do an "iron cross".
Almost anybody can hold themselves up on the rings with your arms locked at
your side but as your "wing span" increases so does the strain on the upper
body muscles.

The same thing happens to spar attach fittings. My little 600 lb 16 ft span
canard has over 100,000 lbs on its little spar caps at the fuselage at 6 G's.
3 is about all it will ever see unless I bounce it real bad.


>I hadn't considered laid-up carbon fittings.

Forget hand laid carbon. The end result is generaly no better than E glass.
Graphite takes considerable process control to take advantage of it's full
potential.

Corrie
August 4th 03, 07:17 PM
(BD5ER) wrote in message >...
> > A 1500-lb aircraft pulling six g's puts a 9,000 lb
> >load on the spar whether the wingspan is 25 feet or 50 ft. Unless
> >I've forgotten something fundamental, you'd have 2250 lbs of tension
>
> Either I'm mis-reading or you have forgotten something fundanental. The length
> of the wing does have a very real effect on the spar attachment points.
>
> A quick example. Pick up an 8 lb sledge hammer by the head at arms length. <snip>
> The same thing happens to spar attach fittings. My little 600 lb 16 ft span
> canard has over 100,000 lbs on its little spar caps at the fuselage at 6 G's.
> 3 is about all it will ever see unless I bounce it real bad.
>


I haven't forgotten the bending moment. It's just that I don't think
it comes into play. For a given weight of airplane, the tensile force
on the bottom spar cap is the same for any length wing, because the
downward force creating the tension is acting through the airplane's
center of gravity. The moment arm from the cg to the hinge doesn't
change with span - only with the spanwise location of the hinge.

Yes, the balancing upward force acts through the wing's center of
lift, but remember - the lift force is actually a distributed load,
not a point load. If the span is longer, then the lift-per-unit-span
is smaller for a given weight. It cancels out. I'm willing to admit
that I'm in error - my aero structures and statics classes were a long
time ago. But I think I'm figuring things correctly.

> >I hadn't considered laid-up carbon fittings.
>
> Forget hand laid carbon. The end result is generaly no better than E glass.
> Graphite takes considerable process control to take advantage of it's full
> potential.

Makes sense to me. Thanks for the advice. I'm strongly leaning
towards aluminum or steel - assuming I do this crazy thing at all,
mind you!

Rick Pellicciotti
August 4th 03, 07:40 PM
"Peter Gottlieb" > wrote in message
. net...
>
> "Jay" > wrote in message
> om...
> > For the people that didn't visit the Zenith link, thats a sheet metal
> > hinge, no moving parts, just flexing sheet. I've seen this up close
> > and its pretty slick. One of those "Why didn't I think of that!" kind
> > of moments.
> >
>
> I'm concerned about corrosion on such a flexing member and how the
> imperfections introduced could concentrate stresses during flexing and
cause
> premature failure.
>
Corrosion protection is critical on any metal airplane part. If you read
the dissertation on the web page, Chris Heintz goes into a lot of detail on
how they tested it for fatigue and they even damaged it intentionally and
tested it.

Rick

Peter Gottlieb
August 5th 03, 01:46 AM
That sounds like a very good record. I guess there's no need to worry.

"Bryan Martin" > wrote in message
...
> in article , Peter
Gottlieb
> at wrote on 8/3/03 12:23 PM:
>
> >
> > "Jay" > wrote in message
> > om...
> >> For the people that didn't visit the Zenith link, thats a sheet metal
> >> hinge, no moving parts, just flexing sheet. I've seen this up close
> >> and its pretty slick. One of those "Why didn't I think of that!" kind
> >> of moments.
> >>
> >
> > I'm concerned about corrosion on such a flexing member and how the
> > imperfections introduced could concentrate stresses during flexing and
cause
> > premature failure.
> >
> >
>
> The system has been in use for over 20 years on hundreds of planes and
tens
> of thousands of flight hours and, to my knowledge, none have ever failed.
> The deflection angle of the ailerons is relatively small.
> --
> Bryan Martin
>

Ernest Christley
August 5th 03, 02:54 AM
Corrie wrote:

> Ernie, what's the Delta stressed for? I perused your site, but didn't
> see an illustration of the spar attach fittings. A half-inch pin
> sounds right. But what kind of fitting does it go through, and how is
> that fitting tied into the spar? That's the real question.
>

Normal category. 1950lbs gross.

I just put a couple pictures and and explanation at the bottom of the
'Frame' section of my website. Follow the link below.
--
----Because I can----
http://www.ernest.isa-geek.org/
------------------------

Richard Lamb
August 5th 03, 04:13 AM
Hey Earnest, have you ever seen the plans for the rubber band powered
model Dyke Delta? I think they were published in Model Aviator mag
December of 197something.

I've always wanted to build a Peanut Scale (13 inch wingspan) balsa
Dyke and see how it flies.

Richard


Ernest Christley wrote:
>
> Corrie wrote:
>
> > Ernie, what's the Delta stressed for? I perused your site, but didn't
> > see an illustration of the spar attach fittings. A half-inch pin
> > sounds right. But what kind of fitting does it go through, and how is
> > that fitting tied into the spar? That's the real question.
> >
>
> Normal category. 1950lbs gross.
>
> I just put a couple pictures and and explanation at the bottom of the
> 'Frame' section of my website. Follow the link below.
> --
> ----Because I can----
> http://www.ernest.isa-geek.org/
> ------------------------

Ernest Christley
August 5th 03, 04:48 PM
Richard Lamb wrote:
> Hey Earnest, have you ever seen the plans for the rubber band powered
> model Dyke Delta? I think they were published in Model Aviator mag
> December of 197something.
>
> I've always wanted to build a Peanut Scale (13 inch wingspan) balsa
> Dyke and see how it flies.
>

Never seen that. I just jumped that the fullsize model. Though, I've
got a couple boys here that need a good intro to R/C models.


--
----Because I can----
http://www.ernest.isa-geek.org/
------------------------

Corrie
August 5th 03, 07:41 PM
Ernest Christley > wrote in message >...
> Corrie wrote:
>
> > Ernie, what's the Delta stressed for? I perused your site, but didn't
> > see an illustration of the spar attach fittings. A half-inch pin
> > sounds right. But what kind of fitting does it go through, and how is
> > that fitting tied into the spar? That's the real question.
> >
>
> Normal category. 1950lbs gross.
>
> I just put a couple pictures and and explanation at the bottom of the
> 'Frame' section of my website. Follow the link below.

Tell your lovely wife 'thank' for helping out. I'm afraid it's still
not entirely clear, but it looks like the whole structure hangs on
those two 1/4" fittings welded to the spar truss, inserted into the
vertical hinge tube, and held in place by the 1/2" pin? Make certain
those are solid welds, my friend!

Corrie
August 6th 03, 08:49 AM
Ernest Christley > wrote in message >...

> Are you kidding me? The only reason that it hasn't been done yet is
> that I'm scared of it.
>
> Truth is that there'll be about 12 linear inches of weld on top and
> bottom when all is said and done, but I'm wanting to make sure those are
> the nicest 12" that I've ever welded!!

Lay that bead down as though your kids' lives depended on it. I'd be
a tetch skeered, too.

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