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Old Feb 08, 2012, 09:22 PM
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Kevlar Live Hinge Question

Hi,

I was wondering how you cut the hinge so the surface slides under the trailing edge. I was looking at the Composite ARF Spark EDF which is totally gapless and slides right under the trailing edge. It looks like the surface is cut loose about 1/8 in front of the hinge line. I tried doing this on my plane and I still had to trim the elavtor back about 1/16 before it would move freely and slide under the trailing edge of the stab.

Thanks!

Brian
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Old Feb 09, 2012, 11:34 AM
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pictures? Your description has me confused for sure.
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Old Feb 09, 2012, 11:37 AM
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Its hard to take a pic of what I mean. Lets say the hinge on the top of the stap is 3" from the trailing edge. That is where you file down to the kevlar. On the bottom where you will cut all the way through would be 3 1/8 from the leading edge based on how the composite arf planes are done. On those planes the cut on the bottom is gapless but if you move the elevator down, it still slides onder the trailing edge of the stab.

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pictures? Your description has me confused for sure.
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Old Feb 09, 2012, 12:33 PM
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sorry , dont know the plane. sounds like a hollow moulded wing
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Old Feb 09, 2012, 12:39 PM
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Yes, Hollow molded wing. Sorry if that was not clear

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sorry , dont know the plane. sounds like a hollow moulded wing
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Old Feb 09, 2012, 02:04 PM
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If it won't tuck under then the cut needs to be made farther ahead of the hinge line. Also the cut should be beveled. If the cut is square then the edges will hit. Make the cut at an angle and it will slip right past. If the cut is too far ahead of the hinge line then it will stick out into the airflow when the surface is deflected up. Typically you only want to use this technique if you will be also adding a wiper.

I will typically draft the profile into a CAD software and rotate the surface a the hinge line. I can then find the best position to make the cut ahead of the hinge line.

Joe Manor did a great tutorial on making the cuts and making the wiper but I can't find it.

Another way to do it is the way that do them on wood slope wings. See pdf below:
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Old Feb 09, 2012, 02:07 PM
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Generally that is referred to as a :wiper.

I did a little search because I know there is a video on this site that shows the process but I never found anything.
try your luck here:http://www.rcgroups.com/forums/searc...leron%20wipers
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Old Feb 17, 2012, 03:46 PM
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Joe's Wipers.

http://www.rcgroups.com/forums/showt...wipers&page=76
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Old Feb 17, 2012, 07:21 PM
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Bingo!!! Thanks Jim, thats the one I had look for
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Old Feb 17, 2012, 11:46 PM
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Thanks Adam. I am trying to avoid having to making any type of additional gap seal. On the planes I have seen from BVM and Composite ARF, there is less than a 1mm gap simply because of the location of the cut. I am still trying to find the sweet spot that makes them happen for my plane.

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Originally Posted by wyowindworks View Post
If it won't tuck under then the cut needs to be made farther ahead of the hinge line. Also the cut should be beveled. If the cut is square then the edges will hit. Make the cut at an angle and it will slip right past. If the cut is too far ahead of the hinge line then it will stick out into the airflow when the surface is deflected up. Typically you only want to use this technique if you will be also adding a wiper.

I will typically draft the profile into a CAD software and rotate the surface a the hinge line. I can then find the best position to make the cut ahead of the hinge line.

Joe Manor did a great tutorial on making the cuts and making the wiper but I can't find it.

Another way to do it is the way that do them on wood slope wings. See pdf below:
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Old Feb 18, 2012, 12:56 AM
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Confusion again!

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Originally Posted by Tumbler View Post
Thanks Adam. I am trying to avoid having to making any type of additional gap seal. On the planes I have seen from BVM and Composite ARF, there is less than a 1mm gap simply because of the location of the cut. ...................
I for one am confused again. I think we must be talking about different "gaps" here.
It's simply not possible to have a gap that small between the wing and the LE of the control surface opposite the hinge. The surface would not articulate sufficiently. (ie: provide enough "throw" or deflection).

I can only echo DLG's post #2.
Pictures convey a lot.

Jim.
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Old Feb 18, 2012, 01:18 AM
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Jim, if you make the cut on the bottom ahead of hinge line it will tuck up into the wing. It's quite possible to have a small 1mm gap.

Here is a little series of renderings of an 8" chord airfoil with a gap of only .008".
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Old Feb 18, 2012, 01:35 AM
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Quote:
Originally Posted by wyowindworks View Post
Jim, if you make the cut on the bottom ahead of hinge line it will tuck up into the wing. It's quite possible to have a small 1mm gap.

Here is a little series of renderings of an 8" chord airfoil with a gap of only .008".
I see what you mean Adam. I did try that on my last wing and could not get it to happen. Maybe I did not have the cut sufficiently forward enough.

Jim.
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Old Feb 18, 2012, 12:09 PM
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Definitely possible. I see it all the time. Here is a pic of an BVM Electra. Much easier than having to add a gap seal later.

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I for one am confused again. I think we must be talking about different "gaps" here.
It's simply not possible to have a gap that small between the wing and the LE of the control surface opposite the hinge. The surface would not articulate sufficiently. (ie: provide enough "throw" or deflection).

I can only echo DLG's post #2.
Pictures convey a lot.

Jim.
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Old Feb 18, 2012, 03:47 PM
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I realise I am out of my depth in this discussion. I've not had enough experience with moulded wings.
I'll have a good look as some examples next opportunity before I comment any more.
Thanks,

Jim.
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