Hinges under stress - mechanical engineering type question

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/
------------------------

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.

"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.

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.

cal (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!

"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

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

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/
------------------------

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/
------------------------

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/
------------------------