Elastic launched gliders B

[BilalHayat19]

Does anybody know which point on a glider wing should start to curve to create that air foil? i think its somewhere between the middle but i just want to see what other people are saying...

[bjt4888]

Bilateral,

Good question about airfoil shape. Most of the glider designs for this event will use very thin sheet for the wing, which won’t require a very sophisticated airfoil. And the flapper designs get the most important part of their airfoil shape from the curved flap. It still is not a bad idea to sand the forward portion of a flapper or a 1/16” thick sheet wing non flapper into a reasonable airfoil shape.

The typical airfoil high point would b about 30% of the wing chord (wing width). For a wing with a 3” chord at wing center, this would mean that the high point would 0.9” from the leading edge at the wing center.

There is quite a bit of information on the web regarding airfoil shaping for optimal efficiency, but this aspect of glider design is only a tiny factor compared to getting down to minimum weight and having proper wood density and stiffness of components, and proper trim and launch, leading to a perfect transition from climb to glide.

For high ceiling gliders (maybe over 50 ft.) airfoil shaping is a little more important. For the fun of it, look at the .pdf “Accurate Shaping of Solid Balsa Surfaces” in the Related Construction Notes of this page:

https://www.charlesriverrc.org/articles ... on%20Notes

Brian T

[bjt4888]

Sorry, bad autocorrect. Bilal, not bilateral.

[fifty_missions]

To answer the original question, the airfoil should begin at the leading edge of the wing. The high-line of the airfoil can be anywhere between 1/4 to 1/2 back from the leading edge. The local team uses plexiglas templates of the total wing shape so that -

1) They can mass produce complicated shaped wings such as elliptical formats.
2) They can simply shift the template aft on top of the new wing and using the leading edge on the form to mark the high-line for the airfoil.
3) This allows the various airfoils to be tested on different wings. I would suggest a modular system such ans gluing the wings to a standardized strip of wood to tape onto a singular fuselage assembly to minimize the variables. This should allow serious data on airfoil choices.

Generally, SOME amount of airfoil will always perform better than no airfoil. Aircraft that have "Flat Airfoil" wings will always have a difficult time recovering flight attitude changes and stalls. This is especially true with ELG where the aircraft needs to transition from a high speed climb with a high angle of attack to a flat glide. Using up half the altitude to recover from transition is not an efficient use of air space.

50 Missions

[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!

[Maxout]

Generally, SOME amount of airfoil will always perform better than no airfoil. Aircraft that have "Flat Airfoil" wings will always have a difficult time recovering flight attitude changes and stalls. This is especially true with ELG where the aircraft needs to transition from a high speed climb with a high angle of attack to a flat glide. Using up half the altitude to recover from transition is not an efficient use of air space.

I have to disagree with this. In 20+ years of flying all types of free flight gliders, I've yet to see airfoil, or lack thereof, having any measurable influence on the glide transition. Yes, a good airfoil will improve the glide, and a properly designed airfoil will improve launch height, but you should be looking elsewhere to get an effective transition.

Also, the latest flapped F1N gliders all have the high point forward of 10%. Given that they're kicking our butts in flight performance, I'd follow their methods.

[builderguy135]

Generally, SOME amount of airfoil will always perform better than no airfoil. Aircraft that have "Flat Airfoil" wings will always have a difficult time recovering flight attitude changes and stalls. This is especially true with ELG where the aircraft needs to transition from a high speed climb with a high angle of attack to a flat glide. Using up half the altitude to recover from transition is not an efficient use of air space.

I have to disagree with this. In 20+ years of flying all types of free flight gliders, I've yet to see airfoil, or lack thereof, having any measurable influence on the glide transition. Yes, a good airfoil will improve the glide, and a properly designed airfoil will improve launch height, but you should be looking elsewhere to get an effective transition.

Also, the latest flapped F1N gliders all have the high point forward of 10%. Given that they're kicking our butts in flight performance, I'd follow their methods.

10% of the chord behind the TE?

[Maxout]

10% of the chord behind the TE?

10% of chord behind the LE.

Not kidding. For an idea of what crazy stuff is winning, this is currently the dominant low ceiling indoor glider, worldwide: http://jhaerospace.com/wp-content/uploa ... 24x497.png
I predict this design will take the FAI Cat I hand launch record to 55 seconds in the next 3 years. One here in the US is already demonstrating sink rates just barely over 0.5 ft/s. 42 seconds, launching to a shade under 22'. Obviously no SO legal ELG can do that, but the Reynolds numbers are similar, especially for wide chord models, so one may assume that the optimal airfoils will be similar.

[Chvan]

I am just wondering what people have been getting for flight times in 20 foot ceilings.

[builderguy135]

I am just wondering what people have been getting for flight times in 20 foot ceilings.

I can get 22 consistently, PB is just over that?