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Author Topic: New Model  (Read 1072 times)
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greggles47
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« on: September 02, 2013, 07:27:56 AM »

On the board now is a new model for a Brodak 15.

42" span, 6.5" chord, 1.25" section

I'm looking to see the effect of a higher aspect ratio on turn rate. I've gone for a deeper section to try to keep the speed down.

Target weight is around 16 oz.

No pics yet as at present, it's just in kit form.

Looking for a name for it.

Greg
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greggles47
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« Reply #1 on: September 08, 2013, 07:21:59 AM »

It's starting to take shape, with luck it'll be flying next weekend.
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greggles47
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« Reply #2 on: September 09, 2013, 05:41:32 AM »

Today's pic shows the tailplane attached & controls installed.

Still doesn't look like a plane. It's amazing how much more quickly you go once they look like they can fly.

Still need a name for it.

Possibly WOFTAM

Greg
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greggles47
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« Reply #3 on: September 11, 2013, 05:16:46 AM »

Today's progress - & it's really looking like a plane.

Can't wait to trial it.

Greg
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« Reply #4 on: September 16, 2013, 09:13:34 AM »

Now only a couple of days work left in it.

With the expected rain tomorrow, I may stay off the golf course & in the shed.

So far I'm happy with how it's going except, I have to find a quick way of doing the tips that I find acceptable. I don't like the usual little triangles, so I'm left with bigger bits that have to be shaped.

Does anyone have any quick tip methods??

Greg
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greggles47
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« Reply #5 on: September 19, 2013, 07:22:28 AM »

Well just about ready for paint, should be ready for Saturday AM.

Covering is laminating film.
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« Reply #6 on: September 21, 2013, 05:03:08 AM »

OK, so all the balsa is on and mostly doped - so paint is next.

Weight still around 9oz, So I'm expecting good flying characteristics.

Greg
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« Reply #7 on: September 23, 2013, 12:14:08 AM »

Paint now gassing off - to fly next w/e.

Even found a name - Vortex
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Terry Fitzpatrick
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« Reply #8 on: April 13, 2014, 08:17:12 PM »

I have built several models with the raked back style wing tip, although not usually as big as on your new model. For a 10" chord I would have about 1.5" wing tip extension. I use a triangular gusset top and bottom to  to brace the wing tip, but the gusset is sized so that the covering material doesn't touch it. The covering material only touches the wing rib and the outline of the wing tip. When the covering material is taut it gives a very smooth streamlined appearance.

I don't like the look of a multitude of triangular gussets in contact with the covering material at the wing tips, and I would expect its not best practice aerodynamically, but thats what most people do.

I would expect that your thick wing section will be a benefit in regards to strength and rigidity for the  higher than usual span to chord ratio, but the main benefit will less speed loss in the turns due to lower induced drag when the wing is producing high lift. The thick wing will have slightly higher profile drag compared to a thinner section but I dont think you will notice the difference. I have a spread sheet set up to analyze three model designs at a time, so the effect of the thicker wing can be seen before you start the engine! I will set one up with your model and post it on this forum. I would expect that the wing area could have been larger particularly if the Brodak 15 is a bit of a powerhouse.

regards Terry Fitzpatrick
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greggles47
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« Reply #9 on: April 14, 2014, 12:47:22 AM »

Yes the Brodak is quite powerful, especially given the light weight.

I've retired the model, I just couldn't get it trimmed to my satisfaction. There was a basic misalignment somewhere that I couldn't track down. It would fly level upright but inverted the O/B wing would be high. Maybe the extra high aspect ratio was hiding a warp of some kind. It also didn't have the snap in the turns that I thought it should have given the weight (around 16oz.)

I was tempted to walk over it so that I couldn't waste more time on it, but for the time being it sits on the wall engineless, and will stay that way indefinitely.

Greg
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« Reply #10 on: April 27, 2014, 11:05:12 AM »

I haven't flown CL for over 40 years (tho I almost made a try about 6 years ago), so my input may be all wet, but...

the small tiplets - both oriented upwards - could it be that the outer one is acting as a tip FENCE which would reduce the spill-off at the tip?  Inverted, this could cause a small increase in effective lift, raising the outboard panel.  The inboard tiplet probably has very little effect, as it "sees" the oncoming air differently.

Just a thought...
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greggles47
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« Reply #11 on: April 27, 2014, 11:28:13 PM »

Pit,

There may be something in what you say.

At present though i'm pretty much over the model, it can sit on the wall until I get a burst of inspiration or whatever.

I had also thought with the high aspect ratio, the wing may have been flexing more than a lar model and giving the strange flight characteristics. Maybe a fixed flap would help in two ways - first change the aspect ratio and second stiffent up the structure.

Time will tell - when I get around to it.

Thanks for your input.
Greg
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