Elastic Launched Glider C

theging
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Re: Elastic Launched Glider C

Postby theging » January 27th, 2013, 4:49 pm

Looking for an opinion...We've been playing around with different ideas, longer nose, larger wing (span), different wing position. Even mixing componants from different gliders. We have a glider now that has an absolute beatiful glide, slow, stable, reasonable sink rate, 3.5 grams. Great glide but when you launch it at more than 45 deg it will nose down and pile drive. It appears that when it is launched up and the climb speed terminates the wings have no lift yet, the nose rotates over at just about the CG ( slightly behind mid wing span). If high enough and there is time for the wing to develop lift and you get a great glide with whatever height you have left over. If launched at 45 deg or less (more less flat), again you get a beautiful glide but not much height. This model has the longer nose design. What does it take for a glider to nose over and begin gliding? Starting to see the dynamics but still missing something.
I've had this problem too. When planes do this, I have found that the flat part of the wing (between the two dihedrals) is at a slight anhedral (not sure if correct term; what I mean is angled down not up). It's very slight but if you bend that up I found it helps.

If that's not the case, sorry. Maybe making it more front heavy will help? I've also learned that sometimes a nice hand glide does not mean that it will launch/transition/glide down nicely.

arooj1a2b3c
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Re: Elastic Launched Glider C

Postby arooj1a2b3c » January 28th, 2013, 12:52 pm

I've been having this problem with a Simple Simon glider I built where the plane keeps looping backward when launched with a rubber band at a 70-80 degree angle. It glides normally with some added clay to the tip; the looping motion only happens when it is launched with a rubber band. I looked at the 2012 thread and it was mentioned that the best fix for this was to add weight to reduce the excess lift. I added extra weight to the tip to the point where the plane glides and the gliding time is greatly reduced, but still had the same problem when launching with a rubber band. I was wondering whether adding even more weight would help. I also heard of moving the wings a bit back on the fuselage, but I was unsure over whether this would be a good idea to reduce the looping motion for this design. I bent the horizontal stabilizer a bit on the plane to generate the turn if that is affecting the looping problem somehow.

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Re: Elastic Launched Glider C

Postby jander14indoor » January 28th, 2013, 1:33 pm

No, DON'T add weight to solve a looping problem. Assuming the center of gravity is right, which you indicate it is with your glide tests. Solve the looping problem by getting the launch right. See discussion back up the thread, loops are inherent in the flight profile of an ELG. Instead tilt the glider right as well as angling it up and turn the loop into a climbing spiral.

Jeff Anderson
Livonia, MI

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Re: Elastic Launched Glider C

Postby baker » January 28th, 2013, 2:23 pm

Thanks for the come back. Will give the tilt a try. If glider is setup for left hand turn, will a right hand twist confict with flight? It will be a couple of days before we get a gym free. Will post how we make out.
No, DON'T add weight to solve a looping problem. Assuming the center of gravity is right, which you indicate it is with your glide tests. Solve the looping problem by getting the launch right. See discussion back up the thread, loops are inherent in the flight profile of an ELG. Instead tilt the glider right as well as angling it up and turn the loop into a climbing spiral.

Jeff Anderson
Livonia, MI

jander14indoor
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Re: Elastic Launched Glider C

Postby jander14indoor » January 28th, 2013, 2:57 pm

Left turn glide with right tilt launch is common practice. Its supposed to help the glider roll out of the launch spiral and transition to level flight.

Jeff Anderson
Livonia, MI

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Re: Elastic Launched Glider C

Postby gsjbjt » January 28th, 2013, 3:16 pm

Left turn glide with right tilt launch is common practice. Its supposed to help the glider roll out of the launch spiral and transition to level flight.

Jeff Anderson
Livonia, MI
?? So it seems that we've been doing it wrong, because our glider turns right (i.e. it does a clockwise turn) with a right tilt launch... How would you make it go left by rolling it right when launching?

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Re: Elastic Launched Glider C

Postby jander14indoor » January 29th, 2013, 4:51 am

I said "common" practice. If R-R works for you, go with it. Data on your own gliders beats opinion.

Of course if it doesn't work well, try R-L.

Jeff Anderson
Livonia, MI

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Re: Elastic Launched Glider C

Postby erikb » January 31st, 2013, 6:01 pm

Here is an example of a Left-Left and using his left hand to pull.

This is also an example of too much left roll and too much pull on the rubber band. This is seen by the glider coming out too fast at the top. Causing him to loose several seconds of air time. The glider should just run out of energy and "flop" or "slide" over into the glide.

However, Notice how he triple checks angle of ascent, roll and length of pull, before releasing. It is very important to be consistent if you want to find the sweet spot over and over.

http://www.flickr.com/photos/joorgawt/8 ... hotostream
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schen
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Re: Elastic Launched Glider C

Postby schen » February 1st, 2013, 3:47 pm

Here is an example of a Left-Left and using his left hand to pull.

This is also an example of too much left roll and too much pull on the rubber band. This is seen by the glider coming out too fast at the top. Causing him to loose several seconds of air time. The glider should just run out of energy and "flop" or "slide" over into the glide.

However, Notice how he triple checks angle of ascent, roll and length of pull, before releasing. It is very important to be consistent if you want to find the sweet spot over and over.

http://www.flickr.com/photos/joorgawt/8 ... hotostream
It's not a matter of the amount of pull on the rubber band or the amount of left roll. It "falls" into the glide because of the flaps.

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Re: Elastic Launched Glider C

Postby erikb » February 1st, 2013, 11:33 pm

It's not a matter of the amount of pull on the rubber band or the amount of left roll. It "falls" into the glide because of the flaps.
Then how do solid winged gliders "fall" into their glide?

What the flaps do is change the wings shape to reduce lift in acceleration. If the wings did not flatten out, the gliders would loop back onto themselves.

Only after the glider has decelerated the flap changes the wing shape to provide more lift. The flap does not act as a brake. If the flap changes the wing shape before fully decelerated then you get those gliders that loop over at the very top and are upside down for a few feet before rolling over into the glide.

No matter what, the plane must decelerate first before transition into the glide. You have to get the glider in the right path with the enough deceleration that the inertia will be stopped, so the glider can transition into the glide at the slowest possible speed. Solid wing or flapped it makes no difference. You still have to have just enough energy to get it to the glide but, no more.

If not, you carry that inertia into the glide and if you have a "flapper" the flap will still be pushed up, the lift will be less and will not slow down and drop faster.

It's all in the launch, angles and energy placed into the glider.
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