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RC Gliders, Sailplanes and Slope Soaring Discuss rc gliders,rc sailplanes and slope soaring in this forum. Thermaling techniques, airfoils, tips, etc

Plank design info requested.

Old 08-13-2007, 03:33 AM
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atwoved1
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Default Plank design info requested.

I've just finished building my new plank 1,5 mt win span pw profile.
I built a quick fusolage and a tail. Didn't know how long and how much area, so I made something that looks good.
The plank flyes very well, but I'd like to know if there is some rule to size correctly the boom lenght and the tail area.
Does anyone have some info about ?
Thanks
Bye
Old 08-13-2007, 09:37 AM
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slopemeno
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Default RE: Plank design info requested.

On the planks I've flown, you can easily tell ones with undersized vertical stapbs- they hava a real tendency to "nose-walk" or yaw as you pull up suddenly. The nice thing about most plank designs is that things like this are easy to change.

What profile are you using- PW-51?
Old 08-13-2007, 02:35 PM
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daveosoar
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Default RE: Plank design info requested.

How do you have a fuselage with a plank? Surely the definition of a 'plank' is that it has NO fuz.
Daveosoar.
Old 08-13-2007, 05:15 PM
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Default RE: Plank design info requested.

Like a Birdworks "Zipper".

Overall an OK flying sloper, but the EH210 airfoil has some real pitch changes with speed. It can tear around at breakneck speed and slow down nicely with elevator trim mixed into the throttle stick. PW-51 seems to suffer less from the pitch changes, and some guys I know were discussing cutting cores to update their Zippers. I got a 60" er, but I'd probably pick the 48"er next time since it fits in the trunk without folding the seats down.

*Tiny* elevator throws seem to be the way to go.
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Old 08-14-2007, 06:23 PM
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Default RE: Plank design info requested.

I also read an article that suggested the nose weight be set up on a track that is controlled by the throttle servo to allow a variable CG movement for a trim or "throttle" control. The advantage being that you can maintain the airfoil shape during slow flight rather than increase the reflex and even further reduce the useful lift coefficient range over what most reflexed airfoils already have.

Ideally if you don't take this TOO far you can pull the CG back and add DOWN trim to prevent a stall and actually increase the airfoil's camber and gain a little extra useable lift coefficient for slow flight. Obviously if this goes a little too far you'll end up with an unstable model. But it's the sort of trick that would be fun to try on a quicky build hack ship..... and about 4 mistakes high....
Old 08-14-2007, 11:49 PM
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Default RE: Plank design info requested.

I flew mine with the CG so far back that one time I was flying at Mendocino CA (Heeser St) and flew through a shear layer due to the sharp lip of the slope. My Zipper bunted violently, and began flipping foreward uncontrollably. It rotated all the way to the ground, landing in some brush. I was never able to get it to do that again, so I suppose I was right on the edge.

I've never seen anyone with the moveable CG, but I suppose its do able.
Old 08-15-2007, 02:35 PM
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Default RE: Plank design info requested.

I read about it on one of the European sites. It was also done on at least one model with good reports. As I sort of said the idea is to achieve a pitch and flying speed trim function without the need to alter the camber of the airfoil. Especially since plank wing airfoils don't have a lot of camber to begin with thanks to the need for a forward high point and reflex. Combine that with a further reduction due to the up trim required for slow speed flight where the lift coefficient needs to be running in the higher range and you have a good recipe for high drag and doggy performance. The variable CG apparently gets around that.

Obviously the range of travel for the CG needs to be small. Something like 3 to 5% of the wing chord at the most. The last thing you want to do is run it back behind the 25% MAC point or even get too close to that point. Perhaps if it can move from about 18% to 24% at the extremes that would be a good point of experimenting and then limit it to a range that doesn't produce any flight issues? So a fairly small weight on a movable setup over a fairly small range of travel is all that is needed.

I should also note that this was all being done for a thermal flying plank design. Slopers just don't need to worry about that last couple of % efficiency unless they are racing.
Old 08-16-2007, 06:03 PM
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soaredg
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Default RE: Plank design info requested.

Thought I would show you my plank wing for thermal flying. It is an my enlarged and updated version of David Jones's Raven 2M. My Raven 2K is 100" span ( 48" center section with 24" tips). uses a BW050209 airfoil and is wood with 1/2" carbon tube spars. It was a good flyer till it rekitted itself on launch last fall. A new 120" version ( 48" center section with 36" tips) is on the board and will fly next spring.
Edg :-{
Pittsburgh
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Old 08-17-2007, 08:58 AM
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atwoved1
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Default RE: Plank design info requested.

For slopememo
My plank has a pw75 profile. 1,2 mt wing span, 16 cm tip and 20 cm root.
It flies great even if it's so small. I did it with some spare foam sheets I had, just to try. I think to build next one about 3 mt wing span.
I have to check if will it be better use pw51 rather than pw75.... Don't know now.
Old 08-17-2007, 12:30 PM
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Default RE: Plank design info requested.

You should google images of Scott Hewitts "Mudda", which is a 100" slope plank, similar in appearance to the Zipper. VERY fast. In the Dave Reese video "Lift-Ticket" theres some video of it ripping up and down the coast in Santa Cruz very fast. A 3-meter one would RIP. Do you have any spots for DS'ing where you fly? Planks excell at it.
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Old 08-23-2007, 01:46 PM
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atwoved1
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Default RE: Plank design info requested.

Unfortunately no ds site here aorund....
Only slope with mixed thermal and dynamics conditions.
The dinamics owever is not so strong .

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