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Old Oct 17, 2015, 08:42 AM
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Foam is my friend!!!
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Question
Wing position, on scratch builds?

Hi All,
..
I've built several scratch built foamies, The good news is they all flew!!...
(Some better than others).

My latest build (The "All Star") is using a balsa built up wing from an "old timer" design I made last winter on a 1/2" foam fuselage that is modeled after the Crash Test Hobbies "Albatross"....

the wing cord is 11" (Slow Flyer), and the plane balances nicely with the wing LE positioned 8.5 " from the motor mount, The plane flies great as long as I fly slow (the nature of this high lift wing), but wants to climb if I increase power.

My question is would moving the wing forward or back change the flight characteristics, and in what regard?

looking forward to your insights!

Here's a vid of the "All Star"
Introducing the "All Star" (2 min 52 sec)
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Old Oct 17, 2015, 10:17 AM
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Quote:
Originally Posted by NewZee View Post
Hi All,
..
I've built several scratch built foamies, The good news is they all flew!!...
(Some better than others).

My latest build (The "All Star") is using a balsa built up wing from an "old timer" design I made last winter on a 1/2" foam fuselage that is modeled after the Crash Test Hobbies "Albatross"....

the wing cord is 11" (Slow Flyer), and the plane balances nicely with the wing LE positioned 8.5 " from the motor mount, The plane flies great as long as I fly slow (the nature of this high lift wing), but wants to climb if I increase power.

My question is would moving the wing forward or back change the flight characteristics, and in what regard?

looking forward to your insights!

Here's a vid of the "All Star"
https://www.youtube.com/watch?v=SQecfnIPs8U
Moving the wing forward or rearward will change the CG , but not the tendency to climb with increased throttle . To remove the tendency to climb with increased throttle , either put in more down thrust on the motor/prop , or put in positive incidence on the horizontal stabilizer ( raise the leading edge ) , or put in negative incidence on the wing ( raise the trailing edge ) .

Here is my slow flyer with a lot of down thrust on the motor/prop .

Lightweight 40" wingspan FT Old Fogey-ish (2 min 58 sec)
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Old Oct 17, 2015, 01:49 PM
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Great video!, I built the standard Old Fogey , flew great until the wing eventually got too "wonky" (mostly from ground loops).

I have a lot of down & right thrust on the "All Star" already, and really like it's slow fly characteristics as is, so might just leave it as is!

I will experiment a little and already considered just a degree or two of negative incidence on the wing.

thanks for the input!
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Old Oct 17, 2015, 01:56 PM
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Here is the ugliest plane I have ever built, the wing is a bit way back but the flight characteristics are very similar to my other planes which has rudder and elevator only.

Tuunattu E rist3 (5 min 13 sec)
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Old Oct 17, 2015, 02:07 PM
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Originally Posted by SpaceDrydock-22 View Post
Here is the ugliest plane I have ever built, the wing is a bit way back but the flight characteristics are very similar to my other planes which has rudder and elevator only.
She is so "Ugly" She's "Beautiful"!! and looks like she flies great!!!

I'll grant the wing position looks a little far back, so did you consider moving it forward, and sliding the battery rearward for a more conventional look?

Your plane also seems to fly good at both slow speeds, and a bit faster,
Mine wants to climb at higher throttle, and I have to make trim adjustments to fly her faster!? That's why I'm going to experiment with wing location and incidence. Thanks for sharing your design, and experience.
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Old Oct 17, 2015, 02:18 PM
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Another Idea!

Just had another idea!....I might make a "mix" where I add some down elevator with increasing throttle above 50% . This might help me avoid climbing at higher speeds while "protecting" the very docile level flight at slow speeds I originally wanted from this plane!
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Old Oct 17, 2015, 03:47 PM
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The position of the CG controls how the plane handles in pitch.
A nose heavy situation makes the plane very stable but hurts its slow-flying ability because the elevator is unable to hold the nose up at low speed. Also, because of the 'up-elevator' required, the plane will want go nose-up at high throttle settings.
As the CG is moved rearward the plane becomes more responsive, less sensitive to pitch changes due to power settings and nicer to fly.
Of course if the CG is moved too far rearwards a situation develops where, with greater angle of attack, the center of lift can move forward of the CG and the plane becomes radically unstable.
The throttle mix idea is a good one. Sneak up on it though. It'll only need a small ammount.
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Old Oct 17, 2015, 05:05 PM
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Quote:
Originally Posted by Whiskers View Post
The position of the CG controls how the plane handles in pitch.
A nose heavy situation makes the plane very stable but hurts its slow-flying ability because the elevator is unable to hold the nose up at low speed. Also, because of the 'up-elevator' required, the plane will want go nose-up at high throttle settings.
As the CG is moved rearward the plane becomes more responsive, less sensitive to pitch changes due to power settings and nicer to fly.
Of course if the CG is moved too far rearwards a situation develops where, with greater angle of attack, the center of lift can move forward of the CG and the plane becomes radically unstable.
The throttle mix idea is a good one. Sneak up on it though. It'll only need a small ammount.
Great explanation!!!....Something tells me to move the wing forward just a bit (1/2"), and slide the battery back a bit so the plane still balances around the wing CG (center of lift) , or slightly nose heavy,

The wing also has a good amount of "Under camber" as an old timer design, and right now has 0 degrees of incidence, I've seen old timer designs with 1 or 2 degrees of negative incidence, so I'll play with that as well.

The plane flies pretty good as is, tweaking it, changing things, and trying to improve the flight characteristics is a big part of the fun!!
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Old Oct 18, 2015, 08:35 AM
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Flying a Falcon or a 3D plane.
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First , use a calculator like this one to help you find the CG

http://adamone.rchomepage.com/cg_calc.htm

Static margin: 0% for 3D to 15% for a trainer behavior.

You can shorten the nose of your plane or displace the battery or the wing.

In light wind if the nose goes up when throttle is added , put some washers to drop the motor ,like balsa and carbon said, few degrees (start with 2) at the time till you get no changes in trajectory.

It is the basic way to trim a plane.
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Old Oct 18, 2015, 12:06 PM
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Already had down and right thrust on the motor! the "ballooning is a function of the high lift "under-cambered" wing. The plane flies perfectly at slow speeds (Which is what I built her for), I'm just trying to find a "happy place" for it if I do want to speed up a bit.

I think I'm real close now, here is a video from this morning , this was at a faster speed than I can fly this plane as this was the flight envelope I was trying to improve.

Negative incidence didn't really help, slid the wing 1/2" forward, and moved the battery back 1/4" I'm real close now, and may still try a little elevator/throttle mix.

Oh yeah!!!...On the third flight this morning got her up high enough to catch some thermals!!!. see did lazy climbing circles hands off! would stayed up as long as I wanted

"Almost" Maiden of the "All Star" Slow Flyer (2 min 47 sec)
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Old Oct 19, 2015, 12:05 AM
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Quote:
Originally Posted by NewZee View Post
She is so "Ugly" She's "Beautiful"!! and looks like she flies great!!!

I'll grant the wing position looks a little far back, so did you consider moving it forward, and sliding the battery rearward for a more conventional look?

Your plane also seems to fly good at both slow speeds, and a bit faster,
Mine wants to climb at higher throttle, and I have to make trim adjustments to fly her faster!? That's why I'm going to experiment with wing location and incidence. Thanks for sharing your design, and experience.
Thank you!
I think I don't want to move the wing because the "block" under it is glued quite firm in the fuselage. The fuselage is made of pipe insulation foam tube, so I had to reinforced it with carbon tube and some wooden skewers. I think it is easier to build a new fuselage than operate the current one. The whole plane is an experiment to use different foams and it's so ugly that I really leave it as it is now.

There is 1.5 mm thick plywood plate under the trailing edge of the wing, without that plate the plane had a tendency to climb at higher throttle.

I really like your All Star Slow Flyer, superb colours!
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