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Dec 11, 2019, 11:42 AM
Everything's A Composite
Knoll53's Avatar
This is a fantastic build log. With my humble FRP skills, I am barely able to follow along.
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Dec 11, 2019, 11:50 AM
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Kenneth Paine's Avatar
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Quote:
Originally Posted by Knoll53
This is a fantastic build log. With my humble FRP skills, I am barely able to follow along.
Thank you Kent. I just wish I could spend more time in my workshop and be quicker.

K
Jan 12, 2020, 06:42 AM
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Kenneth Paine's Avatar
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Wing Shear Web Part 1


I worry that this stressed skin wing will be prone to delamination, so despite the monumental ball-ache and risk of fowl up that this presents, I feel compelled to install a shear web to bind the top and bottom skins together as well as adding to the core’s shear resistance.

Naturally I can’t make anything simple so I am going for glass cloth tape on the bias as per the scale sketch below. The trailing edge hinge line facings have already been completed successfully as detailed in post #51 for the stab.

I chose to make the shear web follow the highpoint of all three panels, so it has three sections and is not a straight line from root to tip. It would have been simpler to make the shear web a straight line between the root and tip but then it would have passed through where I want the aileron servo to be. Pushing the servo backwards would force it to protrude from the wing, something I want to avoid.

Originally I intended to hot-wire cut the core using a little plunge blade tool I made, but when trialling the tool I found that the kerf was not consistent along the depth of the cut – it was wider at the tip of the blade than at the root. Also, pushing the tool through the core span-wise would have been a painfully slow process. Increasing the cutting speed by raising the temperature of the blade would lead an unacceptably wide kerf. I had to think of a better method.

I thought about using a blade to cut through the core but how to keep it perpendicular so that each of the three segments would be aligned when the blade cut through to the opposite side of the core? You can see below what I dreamed up using materials I had lying around.

The cutting guide is built around a 1" (25mm) square aluminium tube that guides the blade along the cutting line as well as keeping it perpendicular. The guide is held together by double sided adhesive tape so it can be pulled apart easily after use. The core and guide are kept from sliding around using weights so that both my hands are free to guide the blade.

Three cuts were made per wing, one cut per panel. Patience and light initial cuts are the path to success. If you start too fast you risk the blade wandering off the line. Once the cut is 6mm (1/4") deep or so you can apply more downward pressure on the blade. The results are magnificent for such a rudimentary tool.
Jan 12, 2020, 11:37 AM
Everything's A Composite
Knoll53's Avatar
Big thumbs up on the addition of shear at the thick point.

Here's my thinking. It you look at the wing segmentally, that is sliced up lengthwise into strips, each strip can be considered a beam. The deepest strip is the most rigid, meaning that it will take the most load, due to it's rigidity. A strip near the TE will be so thin that it will have to flex a lot before it even begins to contribute to bending resistance. To my thinking, this is the weakness in stressed skin over foam. Even though the hope is that the bending load is distributed over the entire skin, it is not. It is more localized in the area of a spar, if there were one.

Delamination in stressed skin at the thick point is certainly the main weakness, especially if you have a hard landing. Having a continuous shear web as you have done solves this.

You might consider a glass layout per the sketch. It has a double thickness of shear vertically and more surface area to the skin for distribution, that is it engages more of the UNI glass skin. Shear loads decrease more or less in a linear fashion from root to tip, so some sort of stepping down of shear reinforcement could be justified.

Jan 12, 2020, 12:01 PM
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Kenneth Paine's Avatar
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Hi Kent,

I suspected you might be the first / only one to comment , and as usual your comments are very welcome.

I agree with your sketch. The reasons why I was originally going to make the shear web as per my sketch are with hindsight too poor to warrant explaining so I won't bother. I will probably do a double web to half span as per your sketch and single from the half span to the tip.

Kenneth
Jan 12, 2020, 12:54 PM
Everything's A Composite
Knoll53's Avatar
With 4000 views of this thread so far, there are a lot of eyes following along, none of whom choose to post a comment. Go figure. My theory is that your build log is of such high quality that the typical viewer doesn't want to clutter it up with a comment. If it were up to me, lurkers would be banned.

Looking forward to how you plan to attach the foam parts when you lay up the shear web. Those foam parts DO like to slide around.
Jan 12, 2020, 02:26 PM
Everything is broken
JimZinVT's Avatar
Some of us just like to watch
And learn.
I am subscribed to the thread though. I hope that spares me when the lurkers are banished

Another great build thread Ken. Been watching from the start. I recently acquired two 1/6 scale sailplane fuses that will require 2.25m & 3m wings. I'll be doing vac. bagged composite construction too, so threads like this are a great resource.
Jan 12, 2020, 04:39 PM
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Kenneth Paine's Avatar
Thread OP
Quote:
Originally Posted by Knoll53
With 4000 views of this thread so far, there are a lot of eyes following along, none of whom choose to post a comment. Go figure. My theory is that your build log is of such high quality that the typical viewer doesn't want to clutter it up with a comment..
Easy now! Flattery will get you everywhere.

Quote:
Originally Posted by Knoll53
If it were up to me, lurkers would be banned.
Not at all! I am a lurker on many threads and have learned a lot this way. I only comment if I have a question or in the very rare occasion that I think I have something of value to add.

Quote:
Originally Posted by Knoll53
Looking forward to how you plan to attach the foam parts when you lay up the shear web. Those foam parts DO like to slide around.
I have just the solution for this and it works a treat! See photo 1 of post #53 as well as the photos in post #55.
Jan 12, 2020, 04:41 PM
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Kenneth Paine's Avatar
Thread OP
Quote:
Originally Posted by JimZinVT
Another great build thread Ken. Been watching from the start. I recently acquired two 1/6 scale sailplane fuses that will require 2.25m & 3m wings. I'll be doing vac. bagged composite construction too, so threads like this are a great resource.
Thanks Jim. Wait until I provide video evidence of flight before you copy my harebrained ideas.
Jan 12, 2020, 05:03 PM
Everything's A Composite
Knoll53's Avatar
Social media is more fun when there is an actual social aspect to it.

A true lurker has been a member since 2014 and has never post once. This reminds me of a welfare bum..... a social media welfare bum. Sure they don't do any harm, they just bother me. There used to be private forum called IG Horten that required all members post at least once. I see no problem in setting standards for membership to a forum or any other private club. Doug Casey has real estate development in Argentina that has fantastically detailed architectural regulations in order to join. More power to him................It's a private club. You can set any standards you want.

Not sure how that would work in social media..............View 3 times without a comment and you're out! ha, ha, ha.
Jan 12, 2020, 05:22 PM
Deniable plausibility
Shedofdread's Avatar
For what it's worth, I tried something similar to this some years back but as Kent alluded to, it's hard to stop the core sections wandering about when the pressure comes on (life reflected in building aeroplanes, eh? ).
These days, I prefer to bag the top skin on and then add the web (pre-cured carbon sheet or ply) in. This helps me to keep it all lined up but I like to keep things low stress and easy. Stress is for the day job, not for fun.....
Jan 12, 2020, 10:19 PM
TEAM GORGEOUS
SZD16's Avatar
Quote:
Originally Posted by Shedofdread
For what it's worth, I tried something similar to this some years back but as Kent alluded to, it's hard to stop the core sections wandering about when the pressure comes on (life reflected in building aeroplanes, eh? ).
These days, I prefer to bag the top skin on and then add the web (pre-cured carbon sheet or ply) in. This helps me to keep it all lined up but I like to keep things low stress and easy. Stress is for the day job, not for fun.....
Bingo! Been there done that......what I do is add spar caps made from carbon tow to the topside.....then bag the top skin to the core......flip it over and cut a channel for the shear web/joiner assembly......then add bottom spar cap and finally the bottom skin. Current project has peelply laid in for hinges on the ailerons and flaps......
Jan 13, 2020, 01:59 PM
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Kenneth Paine's Avatar
Thread OP
I know about skinning the top and then installing the structure method. Soar2Scale uses this method for his 10 metre jobs and YYZ gave a masterclass on this method in his Binder EB 29 thread. I didn't go that way on this project because I thought it too small for a proper spar affair.

This time I have found that my cores have been very prone to hanger rash; I also would rather include my compound curve wing tips in the bagging rather than adding them after the bagging. The solution came to me only yesterday for future large scale gliders:
  1. Cut all cores upside down as I have for this project - much better in my opinion.
  2. Join cores, shape wing tip and trim & feather trailing edges.
  3. Apply light glass cloth to whole panel and bag using release film between the layup and the Mylars (Can't have any wax contamination at this stage).

Why glass both sides with light cloth? The top to hold everything together while keeping the top surface contour during the installation of the internal structure, the bottom to keep core rash under control, both together to reinforce the TE and allow the inclusion of the shaped wing tip in the process.

Then:
  1. Cut spar and hinge structure channels into the bottom surface.
  2. Install spars, servo boxes, hingeing, etc.
  3. Fill and fair any recesses flush with the bottom surface
  4. Add LE ribbon
  5. Wax Mylars and bag the outer skins as normal including the compound curve wing tip (irrelevant in the case of winglets).

You see? I just can't keep it simple

K
Jan 13, 2020, 10:11 PM
TEAM GORGEOUS
SZD16's Avatar
Quote:
Originally Posted by Kenneth Paine
I know about skinning the top and then installing the structure method. Soar2Scale uses this method for his 10 metre jobs and YYZ gave a masterclass on this method in his Binder EB 29 thread. I didn't go that way on this project because I thought it too small for a proper spar affair.

This time I have found that my cores have been very prone to hanger rash; I also would rather include my compound curve wing tips in the bagging rather than adding them after the bagging. The solution came to me only yesterday for future large scale gliders:
  1. Cut all cores upside down as I have for this project - much better in my opinion.
  2. Join cores, shape wing tip and trim & feather trailing edges.
  3. Apply light glass cloth to whole panel and bag using release film between the layup and the Mylars (Can't have any wax contamination at this stage).

Why glass both sides with light cloth? The top to hold everything together while keeping the top surface contour during the installation of the internal structure, the bottom to keep core rash under control, both together to reinforce the TE and allow the inclusion of the shaped wing tip in the process.

Then:
  1. Cut spar and hinge structure channels into the bottom surface.
  2. Install spars, servo boxes, hingeing, etc.
  3. Fill and fair any recesses flush with the bottom surface
  4. Add LE ribbon
  5. Wax Mylars and bag the outer skins as normal including the compound curve wing tip (irrelevant in the case of winglets).

You see? I just can't keep it simple

K
I understand!
Jan 19, 2020, 12:25 PM
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Kenneth Paine's Avatar
Thread OP

Shear Webs


I decided to go full " ][ "section for the shear web as per Kent’s sketch in post #64. Documenting the process with the actual cores is too cumbersome so I will use a bit of scrap foam to represent my core in the process illustration.

I considered using 3M77 to fix the cloth strips to the cores but for reasons specific to my circumstances opted to use transfer tape instead. I am rather pleased with the results. Follow the annotated slide show:


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