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Old Jan 24, 2013, 06:05 PM
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Knoll53's Avatar
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Cg

Based on the last day of flying, the best CG is 3 7/16" from the LE at the root.

The CG can be pushed back another 5/32" but is hard to control the pitch at that setting. Performance does improve with this setting.

Kent
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Old Jan 31, 2013, 10:46 PM
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I've got a Hump

While on the bungee, I keep seeing a "hump" in the trajectory. Tried shooting 60 frames/sec to get a better look. Some times it's more apparent than others. It takes off steep, then flattens out until release. I'm not touching the stick while on tow.

No wind today so got in some launch and land practice. Great way to unwind after work. This plane has no problem with speed, so to lose altitude, I normally just put the nose straight down. Today, just for fun, tried a few different approaches to a slow spiral dive to lose altitude. Without spoilers, it's good to have some tricks up your sleeve. With the plank, if you really pull back on the stick, it will certainly stall. But do the same thing while in a high banked turn and it slips nicely down and keeps flying.....some times. Some of the later flights had the most up elevator on the turns.

Plank 101 - Launch and land (0 min 0 sec)


Kent
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Old Feb 01, 2013, 02:08 AM
the answer 42 is
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Hey Kent Nice video, I think the hump is a ground effect, you are going through a dead air\rotor point at your slope, and then to the lift. This transition between no lift and lift, even in no wind conditions, can produce that effect.

my two cents

EZ
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Old Feb 01, 2013, 09:13 AM
Herk
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Kent, I think it's the effect of hook position. Further forward hook - less hump. Further aft hook - more hump. Question is, where is the hook????
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Old Feb 01, 2013, 10:27 AM
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If the CG is 0 degrees, the hook is swept forward about 60 degrees from the CG. If the hook were on the nose it would be about 85 degrees forward.

BTW, I'm happy about the hump. The initial climb out gets the plane clear of the ground, then its a flat trajectory until release.

The hump appears to be specific to the plank. A swept flying wing launches with an even trajectory.

Launching Horti Mini Elli (1 min 8 sec)


Kent
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Old Feb 01, 2013, 10:47 AM
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Quote:
Originally Posted by Edwinzea View Post
Hey Kent Nice video, I think the hump is a ground effect, you are going through a dead air\rotor point at your slope, and then to the lift. This transition between no lift and lift, even in no wind conditions, can produce that effect.
Maybe......I've noticed the hump while flying at in land sites too. It might be more pronounced at higher launch forces or when a heavy rubber bungee is used without a lead line. I happens mighty quick, so it's hard to say. My hunch is that it is tied to the angle of the tow line pull.

Initially, the pull is forward, which allows the plane to climb based on the tow hook location to the CG.

Then as the pull becomes more downward, that same forward tow hook location pulls the plane down.

At the beach, due to limited launch area, the bungee is just a short piece of heavy rubber.

Kent
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Old Feb 02, 2013, 01:11 PM
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Here's the altitude flight graph from a couple of bungee launches from the last day of flying.

Kent
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Old Feb 02, 2013, 02:03 PM
Herk
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Quote:
Originally Posted by Knoll53 View Post
Maybe......I've noticed the hump while flying at in land sites too. It might be more pronounced at higher launch forces or when a heavy rubber bungee is used without a lead line. I happens mighty quick, so it's hard to say. My hunch is that it is tied to the angle of the tow line pull.

Initially, the pull is forward, which allows the plane to climb based on the tow hook location to the CG.

Then as the pull becomes more downward, that same forward tow hook location pulls the plane down.

At the beach, due to limited launch area, the bungee is just a short piece of heavy rubber.

Kent
At the start of the launch inertial forces are dominant. Then as speed builds up, aerodynamic forces become more prominent.

When you release it, the CG is above the line of force from the bungee, so the model begins to nose up. Then as the speed increases rapidly the trim setting begins to take over. Aerodynamic forces are proportional to speed squared. Meanwhile the bungee force is decreasing so its effect diminishes.

As long as the plane doesn't tip stall and start to rotate during the pitch-up you are ok. Your setup seems to work very well.
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Old Feb 02, 2013, 02:19 PM
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Yes, you can't forget inertia. Both initial inertia forces and tow hook location promote a rather steep climb. With the fantastic speed during launch, trim settings would also cause a steep climb.

So the only force that would cause a dip in that steep climb would be the weight of the bungee rubber pulling down on the tow hook. As the bungee relaxes, the ratio of dead weight vs. forward pull changes to pull the plane down.

Unless, of course, I'm missing something.

At 2:10 there is a decent launch with a long light lead line....and no hump. Glider was trimmed for slow flight.

Plank 101 - Soberanes - CG way back.wmv (10 min 28 sec)


Kent
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Old Feb 07, 2013, 10:48 PM
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Looks like slope season has arrived on the West Coast.

At high rates, there is an obvious hyper stall when inverted, but some how missed it in the video....maybe next time.

Kent

Plank 101 - a few landings (0 min 0 sec)
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Old Feb 08, 2013, 09:35 AM
Herk
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I like the supersonic touch and go maneuvers.

With that wind you should be able to back it in and make a zero speed landing.
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Old Feb 08, 2013, 10:16 AM
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Funny you should mention that. As I was leaving, after about 1 1/2 hrs. of non-stop flying and chasing the plane up and down the slopes, I thought I'd try to do some landing catches, but was too tired to even try.

Was flying light yesterday. .. With added weight, the high speed touch and goes would go on forever. But this little plane has external ballast, so that would mess up the T&Gs. The Plank 2.5 has internal ballast (4 lbs.) and should be able to put on quite a show.

Kent
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Old Mar 09, 2013, 08:45 PM
KlonWarz
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ok, I read, and watched... Thank you!
...Today, where is the best source for smaller than 1/2" bungee rubber,
and,
Carbon fiber stock? tube, and tow?

has it been determined the dip in launch is the weight of the bungee?
and I DID notice the First catch since 1982 ! lol

(where is the manatee or mini elli planform? reallly difficult finding the actual plans here in nurflugel) need a beginner index to... :-)
rc
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Old Mar 09, 2013, 09:27 PM
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I got my bungee from BambuReef.com

CF tow is everywhere. You should shop for it. I've got 4 lbs. of tow, so I could sell you some if you like.

I like Goodwinds.com for CG sticks and tubes.

I nominate YOU to start a new thread for newbies as a catch all spot for general info. Go to Nurflugel and click "New Thread".

Take a look at my blog for more plan references. Not every thing is available.

Kent
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Old Mar 09, 2013, 11:05 PM
KlonWarz
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OK Kent.
I shall review your blog before i pester you folks any longer...

OK, I will begin a newbie thread when I learn the right questions.
Your initial responses were very helpful and have led me to find a number of informative posts. Still, far too many questions. :-)

Tnx
rustycase
(rc is far ez r to type!)
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