Do you have issues folding up a FB wing?

[Hai-Lee]

Over the years I have struggled at times with getting a wing folded and warp free. It took me a fair while but I managed to develop techniques, (all FT inspired), to get my wings to look identical to the FT videos.

It could take quite a bit of time and effort. One problem I often had was the tearing of the LE where the fold started leaving the tip piece starting to straighten. This tear does often cause a premature wing failure and is a weak spot in the event of a crash.

Again I developed methods to make the wing LE more sound but then they were not always effective.

Well today I traced the problem down to the grade of the foam and the fact that often the foam density is not as uniform as it would appear. The way I found out was because I was forced to select a different supplier due to stocking issues and the new foam is much firmer and the paper much lighter and weaker. Well I bought the material to fill an order and the first effort to make a wing had been a disaster even though I used the same plans as I had used almost 100 times before.

The order cannot wait so I investigated and managed to find a way of using the stiffer foam and get the wing folded in a way that leaves NO wing weakness and does not leave the wing with the serious internal stresses that some of my builds had suffered from in the past. The results of those stresses included delamination and even warping with age.

What did I do different? It is so simple that I am somewhat amazed the FT doesn't already use it because it is so CNC friendly and gives almost perfect results without trying. It has reduced my labour input to the wing assembly by over 50%. The only real change required to the wing FB piece is to increase the depth/cord of the wing underside panel by the thickness of the FB material.

At the wing fold line I just cut a channel which is the same width as the thickness of the FB, into the wing bottom panel and removed all of the foam in the channel. Then I marked a line or cut the paper only on a line which was 10mm from the edge of the newly cut channel, (on the wind underside panel). From the 100 line back to the edge of the newly cut channel I bevelled the foam.

To fold the wing I just apply glue and wrap the paper, of the channel, around the LE. Then I apply glue to the bevelled foam, the spar/s, and the wing TE and then fold the bottom panel to its final position. PLEASE NOTE: The wing profile cuts and curve are already formed and the spars fitted in the required position before the wing is folded into its final form.

A large amount of the previous internal pressures are gone and I actually was able to manually mark, cut, and fold a wing in less than an hour and I use a liquid glue for my assembly.

Just what is now to become my wing fold of preference!

have fun!

 

[Duck]

Hai-Lee,

Can you share pictures of what you mean?

 

[Hai-Lee]

Sorry it took so long but I was cutting out wings and then needed to find a camera that could show enough detail.

Anyway here goes!

This pic is of a failed wing which had packing tape applied to provide extra strength prior to the fold. You can see the at the end of the fold there is a tear developing.

Here is the same tear as viewed from under the wing!

Here is the change in the wing fold preparation I now am using.

Here is the top view of a fold in a new wing using the new prep standard. Please note there is NO reinforcing packing tape used, or needed, on the fold trying to keep it together.

And here is the view of the underside of the same "New" fold.

I hope you can see the difference. Without the serious amount of pressure on the wing Leading Edge it is far quicker to get the wing into shape and glue.

Have fun!

 

[Hai-Lee]

Hai-Lee,

Can you share pictures of what you mean?

Sorry I started to compose the reply before I realised that I had not quoted your post.

Please refer to and read the above post. If further info is required please let me know.

have fun!

 

[mayan]

I have the same problems sometimes and have also come to find out the the foam that I am buying from different suppliers was a bit different. Though they are all 5mm think and looked the same some foam boards had small “balls” in the foam. When I tried score cutting the foam board for the wing fold over these balls would break apart and cause unexpected holes which make it hard to keep things folding easily. I do use packing tape on all models to inforce the LE but only cause I fear that it will tear but also to ensure it holds if I end up crashing hard. In the last FT SC I built I even ended up using this tape to make sure I had a solid LE.

 

[n0ukf]

I have the same problems sometimes and have also come to find out the the foam that I am buying from different suppliers was a bit different. Though they are all 5mm think and looked the same some foam boards had small “balls” in the foam. When I tried score cutting the foam board for the wing fold over these balls would break apart and cause unexpected holes which make it hard to keep things folding easily.

Using the sharpest blade possible should reduce this balling up. It also reduces the amount of force needed to make the cut.

 

[BorisTheSpider]

Sorry I started to compose the reply before I realised that I had not quoted your post.

Please refer to and read the above post. If further info is required please let me know.

have fun!

I may be dense, but I'm not getting it. Is it possible to draw a diagram like the FT plans? That, and/or a short video would go really far I think.

 

[Hai-Lee]

I may be dense, but I'm not getting it. Is it possible to draw a diagram like the FT plans? That, and/or a short video would go really far I think.

Sorry it took so long as drawings are not quick and easy on the drawing software I use!

See attached drawing!

I hope that helps!

Have fun!

 

[BorisTheSpider]

Sorry it took so long as drawings are not quick and easy on the drawing software I use!

See attached drawing!

View attachment 128605
I hope that helps!

Have fun!

Oh yeah, that really clears it up! "Took so long"? I didn't expect you to get to that request for a day or so, if at all. Heck, the best I was hoping for was a napkin drawing. This makes it very clear. Thanks! May try it on the next build.

 

[mayan]

Sorry it took so long as drawings are not quick and easy on the drawing software I use!

See attached drawing!

View attachment 128605
I hope that helps!

Have fun!

Great explanation, thanks.

 

[Merv]

Interesting idea; Does this give you more of a squareish, perhaps blunter LE? Have you noticed any changes in flying, more or less pitch sensitive?

 

[Hai-Lee]

Interesting idea; Does this give you more of a squareish, perhaps blunter LE? Have you noticed any changes in flying, more or less pitch sensitive?

Definitely no apparent change just as there is no obvious drag penalty on the Simple scout and many many similar FB designs. There is a extremely slight, minuscule, drag increase but the airflow actually parts ahead of the blunt LE due to the air trapped and circulated in front of the blunt edge. The flight performance is identical to the standard LE. On most fold up wings FT designs the LE is actually already blunt for around 30% or the total wing LE area already, and on the master series MORE SO!

No apparent change in pitch sensitivity just as there is no noticeable loss of control sensitivity when comparing the standard tail members LEs Vs rounded LEs.

Actually there is a little bonus to be had. The compressed FB of the normal method can and does cause some splitting, and even uneven pressure trying to expand the LE, (for the inexperienced and not so accurate builder - Newbie), which can and does cause wings to have uneven folds and non-uniform wing profiles. This method allows the wing to be built more accurately and to get uniform wing profiles without any struggle to hold the wing in shape whilst the glue sets/dries.

It is up to the individual to evaluate it for themselves. Some will actually evaluate it and others will see it through the eyes of their own experiences, prejudices, and ignorance. It works and has been put forward as a method for those who are having trouble folding up the FB wing in the original manner!

It works for me and those who have purchased any of my FB offerings locally!

Have fun!

 

[CapnBry]

That's interesting! I was actually experimenting with different leading edge folds myself today with a bunch of scrap material. I too have the issue of sometimes splitting the leading edge when forming it and always put a piece of packing tape over it before I fold it to try to mitigate it splitting right in half. The issue is that even with a double bevel, you're only getting a 90 degree bend before it stresses, and we're going almost double that. I've tried smooshing down the foam on both sides first by rubbing them hard with a tool which sort of works. I've tried sanding in more bevel too, but that usually ends with me sanding through the paper in some areas.

What I tried today was to not do a the leading edge cut at all, but instead mark a line one foam-width on either side, cut through just the paper, and remove the interior paper. Then clamp down a straight edge on one of the paper-cut lines and fold the leading edge. I was able to fold sections as long as 20" without splitting the paper but the force on the leading edge joint is still pretty high. I experimented with heating the foam with a heat gun to soften it first, as well as crushing it down with various tools to try to reduce this force with moderate success. I also tested with smashing the leading edge into things to gauge its strength and it seems good so I am going to keep experimenting with this concept. It would definitely be better if some of the foam was removed before folding.

I'm definitely going to try your method as well, because I feel like this is an area in my builds that could use some improvement. I often end up with slightly different airfoil shapes that don't quite match up, or double-taping the leading edge because it is splitting.

 

[Tench745]

Hai-Lee, great tip.
It feels like one extra step, but one extra step to get consistent results sounds worth it to me!
If my memory serves, most of the build videos for had you apply a heavy bead of hot glue in the LE fold. I wonder now if this was to help melt the foam and allow an easier fold.

 

[CapnBry]

I wonder now if this was to help melt the foam and allow an easier fold.

What a great observation! I had been trying to think of some way of removing some of the foam on the leading edge seam without resorting to using a dremel as a router to route out some sort of groove. Using the nozzle as a melter seemed like a great idea to achieve a similar goal.

I used my method of cutting one foam width on either side of the line and removing the paper between. Then I dragged the hot glue nozzle (no glue) through the center and did the fold. It seemed to be a little easier so I added a thin line of hot glue on the center, folded, and waited for the glue to dry. I dunno, this looks pretty freaking good.


Note that the short bit was against the table and the longer bit was folded over on top of it. Overall length of the scrap piece was just over 17". I also tried various forms of trauma by hitting the edge against the ruler edge at various angles, as well as slitting the edge with a razor in both directions. I was pleased to see that any splits didn't explode across the whole edge and maintained integrity.

Too bad I am already finishing up a new plane today because I want to try these new ideas on a real wing!

 

[Keno]

I don't know but a lot of interesting ideas presented here. How I do it is make the double bevel cut, flip it over and place some paper medical tape centered on the backside of the cut. Iron it down with low heat sealing iron. Turn it back over and sand the cut to clean or true. Place bead of hot glue in the "V" cut, scape out excess, if you like a rounder LE leave some of the glue in bottom of the cut. Let dry completely and fold over to form your LE. If you see that your LE in not as smoothly rounded as you would like, you can add hot glue in those areas or maybe reduce the amount of hot glue in area with a sealing iron. The best medical tape I have found is DT's, its is cheap and if you paint of seal coat it you can remove fuzz by sanding. You don't need to add any more hot glue to the "V" cut as it will anneal to itself in time. Thanks for the ideas as they may work for me on a future project. Happy flying all.