Elastic Launched Gliders B

[NewSciolyer]

Hey guys,

I am using a Guru kit 19' glider. I have been trying to reduce the weight to the minimum weight of 3.5, but the best I can do is a 4.2. In case there is a high ceiling for state (Johns Hopkins University), is there anyway to strengthen the wings and fuselage and wings while it being light? Does reducing the fuselage length and width help? Should I add carbon fiber to the fuselage?

Many thanks,
NewSciolyer

P.S. If there is any tips on anything, especially launching, I'm all ears (and eyes) ! I've been getting 12 second flights for 25ft high ceilings (not state competitive) and would like to know how I can improve on it. Thanks again!

[bjt4888]

New,

You will progress rapidly in understanding of best solutions to the ELG event if you read the rest of this wiki.

There are many ideas and a number of glider designs presented here that will get you more duration.

Build a proven high-performing design and pay special attention to wood density, quality and stiffness for each part of the glider. We fly a glider that uses a minimal amount of carbon on the fuselage as the wood quality throughout is high.

Congratulations on your efforts so far,

Brian T

[builderguy135]

I think it's my flaps that are flexing, but that's what's supposed to happen. My wing right now has no undercamber either, it's just mounted on flat fuselage with no pylon.

When you launch does the glider make a slight buzzing sound? If it does, that is FLUTTER. That is Drag to the max and whatever height you got, that is all you will ever get with that.
glider.

It seems counter intuitive but John Hance's (GuRu Glider) suggestion to apply a good cellophane tape along the root of the flapper section will both reduce cracking and Flutter. The worse that can happen is the flap's flex is slightly reduced and the glider climbs is a "BUNT" trajectory. This is not bad just odd to see. The glider may make a curve (nose coming down) path during the vertical high-speed launch. It should slow down and settle into a level glide at the apex.

Send me a video. and email me a head-on, side and top view of the glider.
http://www.sandmanoverhaulplus@gmail.com

BTW, the top three finishers in the Indiana State Competition last Saturday all had my coaching and used my designs.

Good Luck,
50 Missions

I don't think it's fluttering. I was able to consistently shoot 26' high with the same plane in January. I think the problem is that I'm nervous to launch at such high speeds. In Cornell invy i broke one of my planes this way as well.

One thing I've also seen is that the plane doesn't launch consistently at high speeds. At Cornell i noticed this but i didn't know if it was my fault (flexing wing) or the REALLY bad draft (my winning time had less than an average of 20 seconds in a 35' hall... draft was just that bad)

I don't plan on making any modifications right now, as my plane is already well trimmed for most cat I ceilings. (Personal record is 29 seconds in 26'). I did buy the cf that mr. Finn suggested and i will try that out to minimize flex.

[builderguy135]

Builderguy,

High point of airfoil is 25% of wing chord. So, on a 4” chord at wing center, 1” back of leading edge at wing center. Congrats working on customizing the design. With a wider chord, might want to add 1” to the nose to make it easier to balance with minimal clay. Keep the distance between the wing TE and stab LE unchanged and kee the stab area at about 14% or 15% of wing area. Keep fin height (and area) the same if wing dihedral height remains 1.25” each side (recommended).

Brian T

Thanks. How would i modify the wing tip plates? I'm thinking of keeping the same height but increasing its length along the chord. Would this work?

[bjt4888]

Builder,

Sorry, I thought that we were discussing my design “2014 Flapper”. Disregard the nose extension and stab size from the above if you are working on the Bill Gowen Category II Record Holder. Everything else recommended would apply (high point, fin height, wing to stab distance). Bill’s stab area is closer to 13% and his nose length of 6” is adequate for scale up. Also, retain the wing taper angle and % of area dedicated to flaps would be my rec for ceilings up to maybe 45 ft.

In order to keep the wing tip plates from fracturing while sanding to .025”, I have both tips as one piece of wood until sanding is complete and the trim apart with a very sharp blade and steel straight edge (this is tricky). Bill uses very slight toe-in (less than 1 mm) for the tip plates too and this must be done evenly.

If using Stan’s Littl Sweep fuselage, don’t be concerned by the soft flex laterally. It’s the vertical stiffnesstjat really matters. Stan’s fuselage design shows .003” unidirectional carbon top and bottom and no carbon on the sides. .003” is not available anymore and a reasonable substitute is CST .005” (which is not unidirectional) which I sand for about five minutes on each side to reduce weight about 15% (clean with rubbing alcohol on paper towel after sanding to get dust off; use a dust mask and do this outside or with a dust collection system). I bond this carbon to the fuse with thinned duco cement (one thin bead on fuse, then wiped off quickly, one thin bead on the carbon, then wiped off quickly; then a bead on the fuselage while fuse braced with pin blocks against a steel straight edge, then apply carbon quickly and smoothe to the glue with your finger; let dry overnight ideally then do the other side).

Brian T

[builderguy135]

Builder,

In order to keep the wing tip plates from fracturing while sanding to .025”, I have both tips as one piece of wood until sanding is complete and the trim apart with a very sharp blade and steel straight edge (this is tricky). Bill uses very slight toe-in (less than 1 mm) for the tip plates too and this must be done evenly.

I've been doing this too!

If using Stan’s Littl Sweep fuselage, don’t be concerned by the soft flex laterally. It’s the vertical stiffnesstjat really matters. Stan’s fuselage design shows .003” unidirectional carbon top and bottom and no carbon on the sides. .003” is not available anymore and a reasonable substitute is CST .005” (which is not unidirectional) which I sand for about five minutes on each side to reduce weight about 15% (clean with rubbing alcohol on paper towel after sanding to get dust off; use a dust mask and do this outside or with a dust collection system). I bond this carbon to the fuse with thinned duco cement (one thin bead on fuse, then wiped off quickly, one thin bead on the carbon, then wiped off quickly; then a bead on the fuselage while fuse braced with pin blocks against a steel straight edge, then apply carbon quickly and smoothe to the glue with your finger; let dry overnight ideally then do the other side). [/quote]

Would this technique still apply to applying CF on the wing or is it just the fuse?

[bjt4888]

Builder,

I don’t use .005” carbon on SO wings. I believe that it’s stronger than necessary and it’s double the weight of 1k carbon tow. As SO gliders are heavy, you should be able to use wood of 6.0 lb cu ft for 1/16” thick wings and 5.5 lb cu ft for a thicker .090” wing (only needed for very high ceilings) and this wood, if properly taper sanded over the span and sanded to thickness for airfoil and flap attach point, should only need a single span thread of 1 k tow for Bill’s glider (as shown in the pictures on my link).

1 k tow weighs .0025 g/in before glueing and .005 g/ in. after gluing with three coats of thinned duco. Apply one thin bead of duco on the wing wood and wipe smooth (wipes about half of it off), then apply another bead on the wood and quickly put the carbon on top of this bead and smooth the carbon into the glue with your finger (standard method of handling tow is about 1” over length in each direction and a piece of masking tape stuck to the last 1/2” on each end, the tape becomes your handles for the tow allowing you to position it nice and straight and tight); after the duco dries for about five minutes, apply another thin bead of glue all along the carbon and wipe “into” the carbon quickly (quickly before it dries too much); don’t wipe as much off in this step; wipe into and somewhat wipe off (trick to describe).

Again, as SO gliders are pretty heavy, I’m not sure any carbon is needed on the wing if using good quality wood of the correct density that is properly sanded. If you don’t have good wood and need to use very light wood that doesn’t have much structural strength, carbon is appropriate.

Have fun with this,

Brian T

[Maxout]

Two things I'm noticing...

The 25% chord high point thing persists... Well, it's true for non-flapper designs. I use a 25% high point for the Carbonette series. For flappers, you should be placing the high point at 5-10%. This is has become the standard in European F1N designs of all sizes. I've tried it and it works. This is a function of low Reynolds numbers. There should be no curvature on the leading edge of the wing. Just a straight taper. For an illustration of this, look at the plans for the Yashinskiy glider: http://jhaerospace.com/wp-content/uploa ... 24x497.png

I still have to disagree on carbon tow vs laminate/strip. You'll never get full strength from the carbon using Duco as the shear component of the composite structure. It's ok to use it to bond the carbon to the wing surface, but the carbon fibers really need to be bonded using a high strength epoxy with the highest carbon-resin ratio possible. If .005" seems to thick, sand it down a little, however you'll find that 1k carbon tow and .005x.039 carbon strip don't cause a significant weight difference on a completed model. Take that from the experience of someone who's used both materials in some pretty critical installations on unmanned systems.

Running carbon from leading edge to trailing edge at the wing root, top and bottom, on a Guru Glider is probably a good idea. I did a review video on one (yet to be released) and the flaps kept shredding from the wing root when I launched it. This is hopefully a wood quality issue since I flew someone else's unmodified Guru Glider several months ago and had none of these problems. I can say for certain that launching much above 25' with that design is going to require some carbon to keep the flap area from stripping away and fluttering.

[builderguy135]

Two things I'm noticing...

The 25% chord high point thing persists... Well, it's true for non-flapper designs. I use a 25% high point for the Carbonette series. For flappers, you should be placing the high point at 5-10%. This is has become the standard in European F1N designs of all sizes. I've tried it and it works. This is a function of low Reynolds numbers. There should be no curvature on the leading edge of the wing. Just a straight taper. For an illustration of this, look at the plans for the Yashinskiy glider: http://jhaerospace.com/wp-content/uploa ... 24x497.png

I still have to disagree on carbon tow vs laminate/strip. You'll never get full strength from the carbon using Duco as the shear component of the composite structure. It's ok to use it to bond the carbon to the wing surface, but the carbon fibers really need to be bonded using a high strength epoxy with the highest carbon-resin ratio possible. If .005" seems to thick, sand it down a little, however you'll find that 1k carbon tow and .005x.039 carbon strip don't cause a significant weight difference on a completed model. Take that from the experience of someone who's used both materials in some pretty critical installations on unmanned systems.

Running carbon from leading edge to trailing edge at the wing root, top and bottom, on a Guru Glider is probably a good idea. I did a review video on one (yet to be released) and the flaps kept shredding from the wing root when I launched it. This is hopefully a wood quality issue since I flew someone else's unmodified Guru Glider several months ago and had none of these problems. I can say for certain that launching much above 25' with that design is going to require some carbon to keep the flap area from stripping away and fluttering.

What do you mean by wing root?

[IvanGe]

the flaps kept shredding from the wing root when I launched it. This is hopefully a wood quality issue since I flew someone else's unmodified Guru Glider several months ago and had none of these problems.

The same thing happened with me. Ended up using carbon and it solved the issue.