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Old Jun 08, 2008, 09:59 PM
Hot Dawg Glider Pilot
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United States, TX, Weatherford
Joined Nov 2002
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The REAL secrets of the Legionair

I built many of these models. I lived pretty close to the designer and kit manufacturer, Cecil Haga. These models were large area, thin airfoiled models that flew well if built light. However, I saw more that one of them that just didn't fly worth squat! Without exception, these models all had decalage problems. Setting the stab absolutely parallel to the flat surface of the wing behind the spar was the most critical part of building these models. On my later personal models, I set the stab with 1/2 degree less positive decalage than the designer called for. They were almost 0/0, but not quite. After all was said and done, I then trimmed the flight mode of these models by removing nose weight until they were pretty squirrilley, and then I added back 1/4 to 1/2 oz. I never tripped this airfoil. I could climb with just about anyone and out climb most.

Another secret that I learned quite by accident... Blunt the leading edges, slightly... ie... make the leading edge radius slightly larger and use 1/4 sq. instead of the 1/8 X 1/4 of the original. If this is done, the tail saddle will have to be modified to give no more than 1 degree positive decalage, and the trimming by CG will have to take place all over again.

Trimming by CG... what? Here's how... Measure from the CENTER of the leading edge radius and the trailing edge of the wing to the table. Continue to move stuff around until the centers are equal distance from the table. With the wing at 0 degrees with the table, set the tail decalage to 1 degree. In other words, the trailing edge should be enough higher than the leading edge to be at a perfect 1-degree angle. This needs to include the elevator in absolute neutral trim if the surface is articulated, (stab with hinged elevator.) With that set, and the CG set at the center of the recommended range, get ready to apply some up elevator on first flights. Start moving the CG back to where it doesn't dive at neutral elevator. Continue to move the CG back until you reach the limits of your comfort level... but do all of this without changing the elevator trim or neutral point. When you're no longer comfortable flying the model, add 1/4 to 1/2 oz to settle her down. It may take some getting used to - flying the model in this setup. It will show lift very well, penetrate better with less ballast, and range further. This goes for all models, not just Legionairs.

There'll be a Legionair 132 build log coming soon... I hope...

JW
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Old Aug 16, 2009, 09:49 PM
Detail Freak
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Harbor City, CA
Joined Oct 2003
21,680 Posts
Jack-

Do you still hold the 1 degree positive incidence to be the best setup with a plane such as the Xplorer??

Target
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Old Aug 16, 2009, 10:16 PM
Hot Dawg Glider Pilot
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United States, TX, Weatherford
Joined Nov 2002
7,793 Posts
Target,

The 1-degree setup is the best (IMHO) because it forces one to fly with an aft CG, which makes my Xplorer show lift very well, and it seems to run across the sky better, losing less altitude... ie. it makes her legs look better...

Jack
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Old Aug 16, 2009, 10:21 PM
Detail Freak
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Harbor City, CA
Joined Oct 2003
21,680 Posts
So, that's with the stab TE lower than the LE, right??
Cause in your first post it sort of reads to me like the tail has up pitch in it instead.

Thanks,
Target
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Old Aug 16, 2009, 10:32 PM
Hot Dawg Glider Pilot
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United States, TX, Weatherford
Joined Nov 2002
7,793 Posts
Target,

The tail DOES have up pitch... just very little up pitch. A lot of guys are flying with 3 to 5 degrees of up pitch and a lot of nose weight to counter it. It's all about setting the exact amount of up pitch and then adjusting the CG to it, rather than setting the pitch to the CG.

Jack

Quote:
Originally Posted by target
So, that's with the stab TE lower than the LE, right??
Cause in your first post it sort of reads to me like the tail has up pitch in it instead.

Thanks,
Target
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