4 meter scratch build - Glass schedule / reinforcement questions

[thenated0g]

Thanks guys! One question i at the moment is how long should my joiner bar be? I have 60" of carbon tube in total, 30" up into each wing core. It seems that most of the pressure is going to be right at the middle of the joiner bar (welded steel tube). My thinking is that a shorter bar is going to apply force to a very small area of the carbon tube and a longer joiner would spread that pressure out, but i dont think it needs to be full length. My current guess is to make it 24-36" long, going shorter and copying what i have seen the manufactured ones look like.

 

[Konrad]

You are correct that the bending moment is greatest at the center line assuming a floating spar. If the joiner is attached to the fuselage the point of most stress is often at the wing to fuselage part line. Imitation is the sincerest form of flattery. Measuring my 3m to 3.7m gliders none use a joiner longer than 350mm. The key really is how you distribute the load from the wing into the joiner system. You DON'T want an abrupt change in the cross section of the load members. So how are you protecting the ends of the joiner tube so as to NOT make a stress riser (load concentrator). I like to use a lot of layers of composite to act as a leaf spring allowing the stiff wing joiner system to blend into the flexible wing structure. You can see some of this in my Mefisto build. But as I'm doing this to a built wing I did it on the outside. You might want to make these layered load spreader in the lay up proper. So where do you want the wings to start to flex? Is there a need to keep the wing root area real stiff (linkages and flaps etc.)? Looking at what you show I don't think so. So don't make the joiner too long going deep down the wing span.

All the best,
Konrad

P.S.
Note that in my wing the force concentrators are the wing hold down bolts and to a lesser extent the servo pockets. You can think of the ends of your joiner much the same and add the layers from there.

Mefisto build (BLEJZYK)

Yes, that was an error I made, no key for the back of the slip on nose cone. I had to adjust with some tape. Lesson learned. Looks super nice, glad you got the glue to cure. I remember gluing on the nose on mine, that is a big step!

forum.alofthobbies.com

 

[thenated0g]

Thank you konrad that makes a lot of sense. I have yet to vacuum bag so i can definitely figure out the end points and reinforce those areas.

 

[Wayne]

When bagging, you usually add another wing rib near the end of the joiner to carry the load.

 

[thenated0g]

 

[Doc J]

Nate - when making your "freehand" epoxy fillets, do three things:

1. Put masking tape on the parts of the fin and boom (in this case) where you don't want the epoxy.

2. Use an old teaspoon or even sand a bit of thin plastic to the male of the fillet shape you need (or even a variable curved egg profile one if your hand work is good) and use that to make 90% of the fillet shape before the filler hardens.

3. When making your goop, make it as stiff as you can - more like soft putty than a double cream consistency.

This makes a fillet that with a little practise only needs a very light sand down.

I do this EVERYWHERE, it saves a huge amount of time and gives a really sexy fillet.

Cheers,

Doc.

 

[thenated0g]

I usually do the masking tape thing, just forgot this time.
I usually used my gloved finger, but a spoon sounds like a good idea, will try that next time
Still working with the consistency but yeah if its too runny it loses shape before it sets,

Thanks for the tips!

 

[Wayne]

Nate, do you thin the plastic mylars at the leading edges and tips? This really helps to get a cleaner leading edge. A sharp razor blade dragged along the surface can be used to thin the plastic. This allows a thicker plastic for super straight wings, but a pretty clean leading and tip edge too. This is one of the So Cal tricks that seemed to work well once perfected. Next time you are in I need to show you the wings from a Long Shot DLG. I still have not figured out how they get such amazing results on those bagged wings. In terms of bagging, they are wonderful!

 

[thenated0g]

Thats a great idea @Wayne i will try that on the Right side when i bag it. I just kind of concluded that the leading edge was always going to be a lot of cleanup, but that should help. This time what i did was pull the leading mylar close together and over the top of that i put a strip of peel ply and taped it tight so the bag wouldnt push that into the inside. It helped to pull alot of the epoxy out and not give me as much build up on the leading edge.

 

[Doc J]

More tips for what they are worth:

I used to tape a strip of thick polythene along the front of the mylars about 12mm wide to go around the leading edges. It leaves a thin line where the join is and a sharp sprue at the very front to be sanded out, but it goes around pretty nicely under vacuum.

Also, I only used mylar on tailplanes or over balsa. Other wise I used Melamine laminating sheet - the same kind that used to be used on counter tops.

It can be cut to shape and joined at the TE, and used (Including the polythene sheet LE shaper) in much the same way as mylar can but it gives a REALLY non-bumpy wing. Needs to have all the sharp upper surfaces sanded a bit though so that the vacuum does not puncture the bag.

By the way I bagged my first wings for an "Algebra" 3M glider in the summer of 1976, I remember it because of a heatwave in the UK...Bugger thats a long time ago!

Cheers,

Doc J.

 

[thenated0g]

right when i was born lol

 

[thenated0g]

 

[thenated0g]

Realized i hadn't posted here in a while. This has been sitting waiting for sunset camp/n fly. So now we are less than 2 months away and i gotta start thinking about maidening this.



Made up some covers for the wings and fuse


Need to figure out some camera mounts if i have time.

 

[thenated0g]

Oh and final numbers:

3kg/105oz
1280 square inches / 82dm²
wing loading is 11.8oz
cubic loading 3.96

calculated stall is 17mph

 

[Diceman]

I have never had a plank with flaps. So when you set them up to work, I assume you HAVE to use crow and they have to be the same amount deployed at the ailerons, correct? Otherwise it will either pitch up or down?

 

[thenated0g]

Yeah in the early stages when I was planning I was looking at different options like spoilerons you know popping up out of the wing you know that kind of stuff and this was really the only thing that I could do I don't even know if I'm going to use this but I figured I might as well you know go three crashes high and just try it and see what happens. It's definitely going to need some adjustments to get it perfect.

 

[gp49]

Did you get a bungee for getting it airborne?

 

[thenated0g]

I'm just going to find some sucker to toss it off the hill atsunset like my f-100 2 years ago