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Old Sep 22, 2012, 08:03 AM
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ShoeDLG's Avatar
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I think you're moving in the right direction. I tried to duplicate your geometry with my Vortex Lattice code. The first attachment shows the circulation distribution. The second attachment shows the Neutral Point on the right wing and the CG location for 10% static margin on the left wing. I suspect from your drawing that your actual CG might still be slightly aft of 10% static margin. The third attachment is the span loading. The fourth attachment is the tail art for the VFA-137 Kestrels (a Navy F-18 squadron I'm partial to). I think your project is cool, even cooler that it's a Kestrel!
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Old Sep 22, 2012, 09:10 AM
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Joel K. Scholz's Avatar
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ShoeDLG Can you provide more expanation as to the meaning of the first and 3rd attachment.What do the bars tell you.
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Old Sep 22, 2012, 09:33 AM
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Sure. The first is just an iPad screen shot (the bars allow you to pitch and yaw the view perspective). The 3rd attachment shows how the wing's lift is distributed along the span.
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Old Sep 22, 2012, 02:25 PM
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The old adage still applies, "nose heavy flies poorly, tail heavy flies once". You're getting away with murder thanks to the tall grass and EPP but you'd be wise to start with your CG at around 20% of the wing's MAC for a first few flight attempts and then work it back slowly and in small increments from there.

My WAG from looking at the second picture in Shoe's post above is that the forward location shown is maybe OK or you might start with it even slightly ahead of that.

I've attached a copy of the picture of your modified wing with the balance point location as a red diamond that I'd suggest to start out with for this next set of flight tests.

It's a shame that this didn't work out better right from the get go since you did such a great looking job on the paint work. But you're learning a lot and it will mean that the next one with the wings more nicely in the "soaring" position as you originally did should be possible if you can work out some VERY LIGHT structure for the rear of the wing and the tail feathers. Because certainly at the original weight plus the hunk o' lead you have added the present model simply won't have that nice Kestral like glide.
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Old Sep 22, 2012, 04:55 PM
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Thanks Bmatthews
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Old Sep 22, 2012, 11:55 PM
Fremont, CA
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Another possibility is warping. EPP is quite flexible so the airframe might distort in mid air thus creating more lift on one side than the other.
Your video reminds me of a similar situation of mine here:
http://www.rcgroups.com/forums/showthread.php?t=1688173
After stiffening all the surfaces with newspaper it flies like a charm.
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Old Sep 23, 2012, 01:21 AM
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Well , I am almost ready to test again. Even with the wings swept back I am still going to have to add about 3 oz to the nose.If I ever make another of this model it is going to have much lighter tail feathers
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Old Sep 23, 2012, 01:46 AM
Fremont, CA
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Here's another misbehaved bird of mine that needs stiffening...
Hawk Maidens (1 min 28 sec)
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Old Sep 23, 2012, 03:54 PM
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I finally got the Kestrel complete enough to do some glide test. The plane is being flown with aileron and elevator alone. I apologize for the poor quality of the video. It was taken with my little canon point and shoot.
Modified Kestrel glide test 0001 (1 min 53 sec)
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Old Sep 23, 2012, 05:18 PM
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Congrrats Joel! Very nice!

Kevin
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Old Sep 23, 2012, 07:12 PM
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Thanks Kevin, I hope to video a powered flight tonight.
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Old Sep 23, 2012, 08:57 PM
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Nice looking lake, and nice mod to get the CG right. Looks like it will work great now.
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Old Sep 23, 2012, 09:53 PM
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Test flight did not go well. Thrust line problem? wing warping? Notice the elevator setting just as it hits the ground.
Modified Kestrel powered test flight crash (2 min 42 sec)
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Old Sep 23, 2012, 11:39 PM
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The 'Wack, BC, Canada
Joined Oct 2002
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Have you added the lower belly vertical fin of clear plastic yet? If the ailerons were not able to roll the model it suggests that adverse yaw was at work when they were deflected.

In terms of pitching we're doing better than before. I did not see any sign of pitch divergence from level flight is this last video.

From the look of the throw it needs to even fly away in a level attitude I think it's safe to say that the wing loading is up to where simple test glides are not going to be able to tell you much. The model would simply be in the air for far too short a length of time.

....Unless.... you can find a long and gently slopped hill to do the test glides from the top. A slope of roughly 1:10 would be shallow enough to catch the model if trouble befalls but if you are able to glide it in a stabe or semi stable manner to learn more about the model's behaviour it would be steep enough that the model would fly out and be able to land down below. And since the model appears to have some issue with the motor running this would be a good way to isolate the model from ANY motor running issues and evaluate just the power off gliding behaviour. Simply take the prop off and have your hearty helper throw it the same way out over the gentle slope of the hill.
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Old Sep 24, 2012, 12:09 AM
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Bmatthews. I did not add a vertical fin, because I did not want to add any more weight to the tail. Glide seemed to indicate to me it was not needed. Not the first time I have been wrong. I plan on taking photos tomorrow of the two wing halves and compare to see if I can find a warp or other anomaly. The plane in the test flight seemed to be leveling until I reapplied power. I cant believe a 5 inch prop could create a lot of torgue. Could thrustline be that much of an issue? I wonder if lowering the aileron is causing some differential drag that is effecting level flight. The plane consistantly turns to the left. I wish I had a gentle slope I could glide down, but I don't know of one in my area.
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