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Author Topic: CLG bunts too much!?  (Read 676 times)
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Tapio Linkosalo
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« on: February 15, 2018, 07:23:58 AM »


For the fun of it, I built a 150mm CLG. Wings with 15-20mm balsa LE and aft of that, depron sanded to sub-mm-thickness. I made some slight test flights at home, and launching from floor at 45 degrees the model bunts to glide next to ceiling, some 2 meters higher. So it seems to me that the model bunts too much even for Cat1 flying. How to fix? Glue stiffening ribs to the flaps? Or make new, thicker flaps?



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Olbill
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« Reply #1 on: February 15, 2018, 09:49:54 AM »

Could be too much flex in the fuse or too much flap deflection or not enough decalage.

But first try a straight up launch or even a launch past vertical (backwards). Nearly all of my indoor gliders require a straight up launch.

The problem I had with a F1N-150 is that I couldn't see it during the launch.
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Tapio Linkosalo
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« Reply #2 on: February 18, 2018, 02:26:53 AM »

First attempt, no success. Depending on the CG, the model either stalls or dives after gentle catapult launch. I guess my tailplane area is too small. And possibly fin area, too, as the model tends to porpoise slightly when hand launched to glide. Time to modify the model for next version!
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Olbill
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« Reply #3 on: February 18, 2018, 11:51:07 AM »

I would copy one of the European models for a first try. They've had some outstanding success with the class.
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Tapio Linkosalo
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« Reply #4 on: February 18, 2018, 01:07:43 PM »

Itried to copy the one attached, but made rectangular wing instead of elliptic. Maybe the added area was too much, and I need to increase tail area also?http://nacrti.weebly.com/uploads/1/2/8/3/12832786/f1n-150.jpg
CLG bunts too much!?
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Olbill
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« Reply #5 on: February 18, 2018, 04:57:15 PM »

Possibly. Trying increased stab area would be one of the easiest changes to make.

Is fuse stiffness adequate?
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Tapio Linkosalo
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« Reply #6 on: February 19, 2018, 12:49:58 AM »


I think it should be. I'm using 0.5mm carbon rod, which I doubt would bend under gliding loads. Thus I do not think that makes the glide unstable.
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Olbill
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« Reply #7 on: February 19, 2018, 10:08:32 AM »

That is really small.
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Tapio Linkosalo
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« Reply #8 on: February 20, 2018, 10:23:05 AM »

Ok, correction. The fuselage is 0.8mm diameter carbon rod. The first piece that I got my hands on, and looked suitable, did not measure it... :-)
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Stan
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« Reply #9 on: February 20, 2018, 04:52:42 PM »

Forget about the fuselage, it is not the problem. Yes, if the stab is too small it will cause the type of stall you noted. The bunt can be caused by: Not enough incidence; undercamber in the un-flapped portion of the wing, flaps that are too weak, or launch style. Sometimes a bunt can be reduced by launching nearly vertical and being careful to let go very smoothly, almost slowly.

Flaps can be stiffened by adding 1/4" wide strips of freezer tape by 3M (a quality masking tape, a bit soft, fairly sticky, used to label food packages going into the freezer). I imagine other tapes could work nearly as well. I have also done it with chord wise lines of CyA. 

Undercamber in the front stiff portion of a wing can simply be reduced by careful finger manipulation
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Tapio Linkosalo
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« Reply #10 on: March 04, 2018, 01:12:23 AM »


Slightly larger (maybe 20% ?) tailplane helped a lot. Now I know that my flaps are too flexible, I could not launch the model more that half the hall height, adding power just made it bunt too early, too much. So back to the building board! But now I have a reference to work with.

I had constant problems of the model sticking to the launch rubber band. I tried to attach the rubber as low as possible on the hook, and that helped some, but occasionally still the rubber got stuck. What would help? Better hook design?

Also I had problems of estimating the proper launch power. Too much, and it over-bunted. Too little, and a stall. What is the trick that the "pro"s use, how to achieve consistent launch power?

 
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Stan
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« Reply #11 on: March 04, 2018, 08:21:47 PM »

Adjust rubber cross section and length so that long stretch just makes it to the ceiling.

"Hook" should not be hook shape. Just a small stub of  balsa works.

Too much negative incidence in the wing can cause "sticking" to the launch rubber.
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