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Phil Barnes
100 Posts |
 Posted - 12/03/2003 : 10:00:47 AM
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I have not yet flown an Aegea Mantis so I was hoping that someone could post suggested locations based either on theory or on experience with a completed and flown model.
Phil |
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Anker
83 Posts |
Posted - 12/03/2003 : 11:03:37 AM
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I balanced my Aegea/Luckenbach Mantis with the wing off the fuse. I put the CG just behind the wing holddown bolt. John Nilsson and Fritz Bien both have it slightly more forward. John more than Fritz.
My suggestion is to start with it right on the bolt hole and make sure you can easily add and remove lead from the nose. Then use your favorite method to fine tune the CG. If you don't have one go to the RCSE archives and pick up the recurring discussions on optimizing CG placement. Dive tests, inverted flying and all kinds of methods are discussed there. I change the CG until I like the way it flies.
Anker |
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Phil Barnes
100 Posts |
Posted - 01/25/2004 : 10:41:39 AM
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I wanted to renew my question about CG location for the Aegea Mantis. Anker's response is useful to some extent but I would still like to know where the CG is on the wing.
I understand that if you balance the fuselage (without the wing) on the wing bolt then when the wing is bolted on the CG will move back to some particular point. I know that the MH32 Mantis CG would move back about an inch when the wing was bolted on. I don't know how far the CG will move when an Aegea wing is bolted to a Luchenbach fuselage. So I kinda had to guess where to put my adjustable tow hook when I built my fuselage. I supose I could have built out the wing first and installed the tow hook last but in my case, I may not use a stock Aegea wing and in that case I would have no way of determining where Anker's recomended CG location is in relation to the wing.
So can anyone tell me where they have the CG located on an existing flying Aegea Mantis (in terms of distance back from the LE of the wing)? It would be nice to get a number of different answers from different people.
Can anybody do the theory to give us a theoretical answer? Each V tail has an area of 85 sq. in. The angle between the Vees is 100 degrees. The tail moment is 39".
Phil |
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Fritz
19 Posts |
Posted - 01/25/2004 : 12:43:45 PM
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Hi Phil,
Mine measures 4 1/4" from the center of the leading edge. The Aegea has less of a sweep compared to the Mantis wing due to the fact that the 75% point is straight, rather than the trailing edge.
I calculated the stability margin using ENVISIONit by Blaine Rowden. It worked out to a static margin of 0.16 Cmac.
-Fritz |
Edited by - Fritz on 01/26/2004 7:13:28 PM |
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drela@mit.edu
12 Posts |
Posted - 01/25/2004 : 3:52:39 PM
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quote:
Originally posted by Phil Barnes
Can anybody do the theory to give us a theoretical answer? Each V tail has an area of 85 sq. in. The angle between the Vees is 100 degrees. The tail moment is 39".
I have AVL all set up to do this, but my tail is a different size.
What are the root and tip chords and the half-span of the tail?
Knowing just the area isn't quite enough. Also, how do you define
"tail moment"? The distance between the center LE points is sufficient.
If you send me the info on your new tail I can check how its stability characteristics differ from the Vtail.
Mark Drela |
Edited by - drela@mit.edu on 01/25/2004 3:54:48 PM |
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jon stone
12 Posts |
Posted - 01/26/2004 : 3:55:14 PM
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Mark,
What tail moments do you recommend? Same as the Aegea 2m?
Jon |
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Phil Barnes
100 Posts |
Posted - 01/27/2004 : 11:03:27 PM
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Here is the data that Mark requested:
The standard Aegea Mantis wing mounted on a Luchenbach fuse with the standard V tails:
Distance of wing LE to tail LE: 37.5"
V tail root; 5.5" HT14
V tail tip: 4" HT12
The span of each V tail from root to tip is 17.5".
Angle between the Vees is 100 degrees.
My new conventional tail (Bubble Dancer style) Aegea Mantis on a Luchenbach fuselage:
Distance of wing LE to horizontal stab LE; 33.75"
Horizontal stab root; 5.85" HT12
Horizontal stab tip; 3.2" HT12
Horizontal stab semi span; 12.75"
Distance from wing LE to vertical tail LE (at boom); 39.75"
Vertical fin root; 6.75" HT12
vertical fin tip; 2.75" HT12
vertical fin span; 10.5"
Sub fin root; 6.75" HT12
sub fin tip; 4.75" HT12
sub fin span; 3"
All tails have spanwise centerlines that are perpendicular to the boom. In other words, the semi chord hingelines are perpendicular to the boom.
Phil
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drela@mit.edu
12 Posts |
Posted - 01/28/2004 : 8:35:49 PM
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I put Phil's V-tail and new cross-tail into AVL. For CG at 4.25" behind center LE (Fritz's location), I get the following parameters, roughly in decreasing order of importance. The relative values are mainly what's of interest.
V-tail +-tail
------- -------
S.M. 0.138 0.103 ( static margin, for MAC = 8.5")
Cnr -0.0311 -0.0334 ( yaw damping )
Cmde -0.0332 -0.0245 ( elevator effectiveness )
Cndr 0.00120 0.00078 ( rudder effectiveness )
Cnb 0.0488 0.0492 ( yaw stability )
delta(CG) = MAC * delta(S.M.) = 8.5" * (0.138 - 0.103) = 0.30"
The conventional stab is smaller than the Vtail's effective stab. So for the same pitch stability, the conventional stab will require the CG to be at about 0.3" farther forward. No big deal otherwise.
The conventional tail has a bit more yaw damping than the Vtail.
The "effectiveness" parameters indicate the pitch or yaw moment change resulting from a given control surface deflection angle. This suggests what throws to use for the new cross-tail. Say your current V-tail setup has +/-20 degrees of max rudder throw. To get the same rudder response at the TX stick, the cross-tail max rudder throw has to be
+/-20 deg * (0.00120/0.00078) = +/-31 deg
Say the V-tail has +/-15 degrees of max elevator throw. The cross-tail max elevator throw should then be
+/-15 deg * (0.0332/0.0245) = +/-20 deg
Using these conversions should make the cross-tail have about the same control feel as the V-tail.
Mark Drela |
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F3jeb
103 Posts |
Posted - 01/28/2004 : 8:53:13 PM
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I just added the "code" tags found in the entry form represented by an icon with the "#" sing on it. it will keep all your formating.
V-tail +-tail
------- -------
S.M. 0.138 0.103 ( static margin, for MAC = 8.5")
Cnr -0.0311 -0.0334 ( yaw damping )
Cmde -0.0332 -0.0245 ( elevator effectiveness )
Cndr 0.00120 0.00078 ( rudder effectiveness )
Cnb 0.0488 0.0492 ( yaw stability )
delta(CG) = MAC * delta(S.M.) = 8.5" * (0.138 - 0.103) = 0.30"
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Edited by - F3jeb on 01/28/2004 8:54:35 PM |
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tgist
5 Posts |
Posted - 02/08/2004 : 3:54:12 PM
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I'm also building a "Bubble-Dancer-tail" Aegea 3m. However, at the moment I'm planning to go with a full flying stab, just like the Bubble Dancer, instead of separate horizontal stabilizer-elevator.
Obviously, I should be able to get plenty of control authority. My question is, should I bump the total area up by 30% to get the same static margin? Or is that just overkill?
Thank,
Tom |
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Topic |
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CG Location for the Aegea Mantis?
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