Elastic Launched Glider B

bjt4888
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Re: Elastic Launched Glider B

Postby bjt4888 » Tue Feb 10, 2015 12:49 am

drcubbin wrote:
I saw on one of the Launched Glider videos that an "accelerant" is used to dry the CA glue much more quickly. Does anyone know where I can buy that (without having to order and wait since we are in a bit of a rush?) I thought they said it is sold at Walmart, but I couldn't find it there. And are there any types that are preferred?


In my experience having coached quite a few students through construction for the glider event (and about 50 years of model airplane building), accelerant is unnecessary. If you are referring to the Kurt Krempertz video on the AMAGlider website, he uses accelerant for instant setting of super glue (CA) for all joints.

My students for the last couple of years also constructed the Stan Buddenbohm Littl Sweep kit as their first glider and all construction was done with fresh, good quality, super glue (ZAP Medium is my favorite) and joints set in about 60 seconds with this glue. All joints were simply held together for this short amount of time till set. The only joint we allowed a little more setting time for was the wingtip dihedral. We held these joints together temporarily with masking tape just as Kurt demonstrates and applied glue and propped the wingtips up to the correct dihedral angle and put a small weight (a 1"x2"x4" piece of wood) on the wing center section until the joint set for about five minutes. One tip dihedral is set and glued at a time. Then we carefully added four or five more drops of super glue along the joint.

All glue is applied with an applicator, not the bottle, the bottle usually allows the glue to flow too quickly and gets way too much on the joint. The "applicator" is simply a short stick of 1/4"x1/4"x4" balsa with two pins inserted through one end at very shallow angles (opposite each other) so that the points form a sort of a "pincer" that will pick up a drop of glue by capillary action from a bigger drop of glue sitting on a piece of wax paper.

Good luck and good flying,

Bjt4888
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Re: Elastic Launched Glider B

Postby slytherin » Tue Feb 10, 2015 3:21 pm

Do you guys have any good plans for ELGs that will fly for around 10 or more seconds? Or websites that I can use to find some plans?
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Re: Elastic Launched Glider B

Postby jander14indoor » Tue Feb 10, 2015 5:41 pm

Check back up the chain for a number of suggestions and links. One page back should do it, two at most.

Jeff Anderson
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Re: Elastic Launched Glider B

Postby bernard » Tue Feb 10, 2015 6:29 pm

"One of the ways that I believe people express their appreciation to the rest of humanity is to make something wonderful and put it out there."

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Re: Elastic Launched Glider B

Postby slytherin » Tue Feb 10, 2015 9:31 pm

bernard wrote:This is the reply he is referring to.
jander14indoor wrote:
dragonmaster57 wrote:Does anybody have any good links for Elastic Launched Glider?


There are a lot of VERY good links on the web, not to hard to find with a google search and some already in this string if you go back up.

To get started, here are some for the presentation I give at clinics, some may be repeats from up string.
http://soinc.org/elastic_launched_glider_b
http://www.amaglider.com
http://www.sciencetoystore.com/contents/en-us/p307.html
http://www.rcgroups.com/forums/showthread.php?t=793903
http://www.americanjuniorclassics.com/i ... patent.htm
http://makeprojects.com/Project/Folding ... wn!/1934/1
http://www.amaglider.com/?p=view&a=basi ... techniques
http://legacy.amaglider.com/assets/outd ... iders.html
http://www.amaflightschool.org/diy/how- ... e-olympiad
http://legacy.amaglider.com/assets/intr ... ndles.html
http://legacy.amaglider.com/assets/gene ... aunch.html
http://www.soarmd.org/science-olympiad/11-wright-stuff
http://amaflightschool.org/video/how-fl ... nch-glider

Jeff Anderson
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Re: Elastic Launched Glider B

Postby bernard » Sat Feb 14, 2015 9:19 pm

The glider I'm working on isn't transitioning well. I'm using a flapper design. I originally had problems with it nosediving when launched at a positive angle but I added ballast to the front and it doesn't happen anymore. I think it isn't dealing well with the fast launch speeds. Has anyone else had issues with this?
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Re: Elastic Launched Glider B

Postby bjt4888 » Sat Feb 14, 2015 10:30 pm

bernard,
Nosediving on launch is usually caused by inadequate decalage angle. It is odd that adding ballast to the nose corrected this. Please supply much more information so that I can help you better. Example: what design are you building? What is the amount of flap droop? What are the flaps made of and how thick are they? What is your wing incidence angle or amount and what is your stabilizer incidence angle or amount? If you are not building a design that I can review the plan for on the internet, please include a full description of all measurements (and a couple of pictures would be good too). What is your center of gravity (distance along the wing chord from the leading edge)? What does you glider weigh? What is the quality of the wood you are using (ex. is the fuselage good stiff wood and are the wings reasonably light and the stabilizer and rudder light and stiff?

Thanks,
Brian T.

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Re: Elastic Launched Glider B

Postby bernard » Sat Feb 14, 2015 10:45 pm

bjt4888 wrote:bernard,
Nosediving on launch is usually caused by inadequate decalage angle. It is odd that adding ballast to the nose corrected this. Please supply much more information so that I can help you better. Example: what design are you building? What is the amount of flap droop? What are the flaps made of and how thick are they? What is your wing incidence angle or amount and what is your stabilizer incidence angle or amount? If you are not building a design that I can review the plan for on the internet, please include a full description of all measurements (and a couple of pictures would be good too). What is your center of gravity (distance along the wing chord from the leading edge)? What does you glider weigh? What is the quality of the wood you are using (ex. is the fuselage good stiff wood and are the wings reasonably light and the stabilizer and rudder light and stiff?

Thanks,
Brian T.

Here are some links to images of my glider.

Entire glider
Nose
Wing
Empennage
Broken glider
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Re: Elastic Launched Glider B

Postby bernard » Sat Feb 14, 2015 11:01 pm

bernard wrote:
bjt4888 wrote:bernard,
Nosediving on launch is usually caused by inadequate decalage angle. It is odd that adding ballast to the nose corrected this. Please supply much more information so that I can help you better. Example: what design are you building? What is the amount of flap droop? What are the flaps made of and how thick are they? What is your wing incidence angle or amount and what is your stabilizer incidence angle or amount? If you are not building a design that I can review the plan for on the internet, please include a full description of all measurements (and a couple of pictures would be good too). What is your center of gravity (distance along the wing chord from the leading edge)? What does you glider weigh? What is the quality of the wood you are using (ex. is the fuselage good stiff wood and are the wings reasonably light and the stabilizer and rudder light and stiff?

Thanks,
Brian T.

Here are some links to images of my glider.

Entire glider
Nose
Wing
Empennage
Broken glider

Here are more photos. The thickest part of the wing is about 1mm. The lowest point of the leading edge is about 5mm above the fuselage and the trailing edge is about 2mm above the fuselage. The whole glider is about 3grams.

Fuselage - about 31cm
Wing chord - about 6cm
Wingspan - about 25cm
Wing - leading edge 5mm, trailing edge 2mm
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Re: Elastic Launched Glider B

Postby bjt4888 » Sun Feb 15, 2015 2:33 am

bernard,
Good job of documenting your current glider. It appears that the pylon that attaches the wing to the fuselage is not very substantial. This is an area that you want to be quite rigid so that the wing does not flex or change incidence angle too much during launch. Also, I'm not sure why you are building a shorter span wing than the allowed 32 cm? If I were you, I would build the a 32 cm wing and build to the required minimum weight of 4 grams. I am also noticing that your fuselage is quite thin. A thin fuselage can be stiff enough if it is reinforced with carbon, but I'm thinking that your fuselage may be too flexible. It would be a very good idea to build a glider from a proven design to minimize the potential issues (or, at least to construct a new, stiffer fuselage and more substantial pylon for your current glider). I have notes earlier in this thread describing how to modify the design we used last year for the current year rules. Much more detailed notes regarding construction and trim of this glider are written on the Hip Pocket Aeronautics website.

Thanks and good luck,

Bjt4888

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Re: Elastic Launched Glider B

Postby bernard » Sun Feb 15, 2015 4:35 am

bjt4888 wrote:bernard,
Good job of documenting your current glider. It appears that the pylon that attaches the wing to the fuselage is not very substantial. This is an area that you want to be quite rigid so that the wing does not flex or change incidence angle too much during launch. Also, I'm not sure why you are building a shorter span wing than the allowed 32 cm? If I were you, I would build the a 32 cm wing and build to the required minimum weight of 4 grams. I am also noticing that your fuselage is quite thin. A thin fuselage can be stiff enough if it is reinforced with carbon, but I'm thinking that your fuselage may be too flexible. It would be a very good idea to build a glider from a proven design to minimize the potential issues (or, at least to construct a new, stiffer fuselage and more substantial pylon for your current glider). I have notes earlier in this thread describing how to modify the design we used last year for the current year rules. Much more detailed notes regarding construction and trim of this glider are written on the Hip Pocket Aeronautics website.

Thanks and good luck,

Bjt4888

Thanks for your feedback! I kind of followed the plans for the Time Machine, but didn't do everything exactly the same. What might happen with a fuselage that is too flexible? What might cause it to flex mid-flight? Would you happen to know why it doesn't transition well from high speed launch to slow glide? Thanks again!
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Re: Elastic Launched Glider B

Postby jander14indoor » Sun Feb 15, 2015 2:33 pm

The Time Machine glider is actually a VERY sophisticated design with a lot of features that may not be evident to a new builder.
Example, your wing is sanded from single sheets of wood, the Time Machine is assembled from 5 pieces of carefully selected balsa with specific properties for that part of the wing.
Not stated in the design, but critical is the flexibility of the wing. If you don't match the original design (unlikely with your single piece of wood) your launch and transition behavior will be very different. Ideal settings may be nowhere near the same.
As already stated, your wing attachment is much less secure than the Time Machine design. Time Machine wing has a pylon supporting the front half of the wing chord and holding it rigid with respect to the fuselage stick. Your pylon is MUCH lest robust and as mentioned probably allows unintended changes to wing angle of attack during launch.
I don't see the carbon fiber on your fuselage that is called out on the Time Machine plan. Again, already mentioned, but this makes a big difference in fuselage stiffness. This is important during launch, a stiffer fuselage will better maintain the wing-stab relationship, allowing for more controlled/consistent launch and transition.
Weight difference, the Time Machine is a 2.0 gm glider. At 3 or rule minimum of 4 gm it has to fly much faster and again, ideal trim will be different.
And don't underestimate the importance of scaling this design to SO maximum. Giving up wing area is seldom a good thing for this kind of endurance event.

Hope that helps some.

Jeff Anderson
Livonia, MI

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Re: Elastic Launched Glider B

Postby SOCoach » Sun Feb 15, 2015 5:01 pm

Is there a good ratio of weight wing vs. fuselage? We are trying to get the weight down on our planes . . . we are consistently in the 7 gram range currently and getting 7 to 11 seconds. I realize lowering weight to the 4 gram minimum should greatly improve times but not sure where to concentrate our efforts. Is the ratio 40% fuselage - 60% wing . . . . any suggestions?

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Re: Elastic Launched Glider B

Postby bjt4888 » Sun Feb 15, 2015 11:36 pm

bernard,
Fuselage flexing will result in erratic fast direction change. Transition issues, if not related to parts flexing, are often an issue of decalage. If nosing over, add 0.5 degree of wing incidence (if you have an incidence adjustable wing mount).

SO Coach,
See the posts at this link. Read all posts by Bill Gowen (OlBill). He is the current AMA national record holder in this event. Also, read my posts in this thread and in the previous year's thread. There is extensive detial on glider design, construction and trimming.

http://www.hippocketaeronautics.com/hpa ... ic=17413.0

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Re: Elastic Launched Glider B

Postby bernard » Mon Feb 16, 2015 7:25 am

bjt4888 wrote:bernard,
Fuselage flexing will result in erratic fast direction change. Transition issues, if not related to parts flexing, are often an issue of decalage. If nosing over, add 0.5 degree of wing incidence (if you have an incidence adjustable wing mount).

Bjt4888

I adjusted my ballast so that the center of gravity is about 1/3 down from the front of the wing. It glides well when thrown slightly at a downward angle, and glides well when launched (with a rubber band) really fast at an upward angle. It doesn't seem to launch well when launched at "medium" speeds (when my rubber band isn't fully stretched.
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