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Old Sep 19, 2012, 02:22 PM
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BMatthews's Avatar
The 'Wack, BC, Canada
Joined Oct 2002
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Since this design isn't intended for high performance in terms of running FAI speed runs or scratching back from low and downwind such as on a sailplane there would be no downside to increasing the size of the tail up to around 15'ish%. And very likely a lot of positives to counter adding a little drag.

Since we now know that this is for a photo model you will also want to look at the size of the forward equipment pod and consider what effect the side area distribution of the fuselage areas will have on the Vertical Tail Volume. Normal fuselages tend to be self cancelling. But a big and long forward pod with boom style tail shifts things around a LOT and the designer has to counteract this by making the vertical tail area larger. Yes, I know that the VTV equations do not have a spot for filling in fuselage areas but that's because the procedure ASSUMEs that you're using a more or less normal shape that has no oddball football sized bubbles connected to a stick like tail boom to foul up the Feng Shui....
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Old Sep 19, 2012, 11:48 PM
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Estonia, Harju, Tallinn
Joined May 2012
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Quote:
Originally Posted by BMatthews View Post
Since this design isn't intended for high performance in terms of running FAI speed runs or scratching back from low and downwind such as on a sailplane there would be no downside to increasing the size of the tail up to around 15'ish%. And very likely a lot of positives to counter adding a little drag.

Since we now know that this is for a photo model you will also want to look at the size of the forward equipment pod and consider what effect the side area distribution of the fuselage areas will have on the Vertical Tail Volume. Normal fuselages tend to be self cancelling. But a big and long forward pod with boom style tail shifts things around a LOT and the designer has to counteract this by making the vertical tail area larger. Yes, I know that the VTV equations do not have a spot for filling in fuselage areas but that's because the procedure ASSUMEs that you're using a more or less normal shape that has no oddball football sized bubbles connected to a stick like tail boom to foul up the Feng Shui....
Yep, any surface forward of the CG has a destabilizing effect. At the moment the vertical area is a bit larger than the horizontal area because the v-tail dihedral is 48 deg. I'll try increasing the tail area.
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Old Sep 20, 2012, 10:17 AM
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Estonia, Harju, Tallinn
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Ok, the results AVL gives me are very similar to XFLR5. There is some difference in flight speed.

The following results are from AVL:
Name: design_trim.jpg
Views: 30
Size: 92.5 KB
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The plane wants to fly at alpha=~2,4 deg

Name: elev-2deg.jpg
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Size: 65.2 KB
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So, I deflect the elevator 2 degrees up --> now the plane wants to fly at alpha= ~10 deg.
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Last edited by martig; Sep 21, 2012 at 06:03 AM.
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