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Old Sep 23, 2012, 07:20 PM
Just thumbing through...
victapilot's Avatar
United States, SC, Simpsonville
Joined Feb 2009
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Could be damaged servo gears.
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Old Sep 23, 2012, 08:21 PM
BGR
Foam Junkie
United States, CA, Oceanside
Joined Dec 2003
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Originally Posted by Zangetsu57 View Post
After a crash and repair, I've noticed my Axn is doing the following:

1. When flying with and without motor power, my Axn seems to "teeter" left and right often. This happens at both fast and slow speeds, but is more pronounced at slow speeds. I just flew in fairly light wind. What might be causing this? Too much slop in the stock aileron servo connectors (I'm using HK orange digital servos, which are much better than stock). The only other thing I can think of is I reinforced the elevator with a 3mm CF rod. The rod was placed flush, hot glued in several locations, then taped over with fiber glass reinforced tape to produce an even surface. I did not, however, cut a slit in the foam and embed the rod, as I figured this would weaken the foam too much since it is quite thin as it is.

2. It likes to pitch up quite easily, and I have to trim quite aggressively. Perhaps this is common with pusher props.
Any changes made to the sleek lines of the AXN will have negative effects on flight performance and behavior. You stated that the carbon rod is on the elevator, did you mean horizontal stabilizer? Either way nothing should be sticking out, covering it with tape to smooth it out still creates a bump and that will change everything...especially when it effects the tail surfaces because they have alot of leverage due to the long fuselage, crow bar effect. You need to embed the rod into the foam so it does not stick out.

The pitch issue... if it is not caused by that carbon rod bump on the tail it may be that your AXN is tail heavy. To check the CG get some altitude then fly straight and level, cut power and put the AXN in a 45 deg dive and let go of the sticks. If it pulls out to level flight your CG is good, if it pitches up it is tail heavy, if it continues to dive it is nose heavy.

Teetering is a strange behavior for a AXN, it is so sleek and aerodynamic. However if you have something flapping around or in any way disturbing the smooth airflow over the AXN it can cause some stability issues. It could also be caused by twisting of the fuselage, loose wings, that carbon rod and tape you put on the tail... etc.
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Last edited by BGR; Sep 23, 2012 at 08:31 PM.
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Old Sep 23, 2012, 08:37 PM
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Originally Posted by BGR View Post
Any changes made to the sleek lines of the AXN will have negative effects on flight performance and behavior. You stated that the carbon rod is on the elevator, did you mean horizontal stabilizer? Either way nothing should be sticking out, covering it with tape to smooth it out still creates a bump and that will change everything...especially when it effects the tail surfaces because they have alot of leverage due to the long fuselage, crow bar effect. You need to embed the rod into the foam so it does not stick out.

The pitch issue... if it is not caused by that carbon rod bump on the tail it may be that your AXN is tail heavy. To check the CG get some altitude then fly straight and level, cut power and put the AXN in a 45 deg dive and let go of the sticks. If it pulls out to level flight your CG is good, if it pitches up it is tail heavy, if it continues to dive it is nose heavy.

Teetering is a strange behavior for a AXN, it is so sleek and aerodynamic. However if you have something flapping around or in any way disturbing the smooth airflow over the AXN it can cause some stability issues. It could also be caused by twisting of the fuselage, loose wings, that carbon rod and tape you put on the tail... etc.
Yeah, I meant the horizontal stabilizer. I'll embed the CF rod properly and give it another go. Thanks for the heads-up.

As for CG, my understanding was that the CG should be at the wing spar. When I balance the AXN with my finger tips at the spar (+/- 0.5cm), it balances perfectly with a 2200mAh pack. Is this a bad way to test CG?
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Old Sep 23, 2012, 08:45 PM
BGR
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United States, CA, Oceanside
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Originally Posted by Zangetsu57 View Post
Yeah, I meant the horizontal stabilizer. I'll embed the CF rod properly and give it another go. Thanks for the heads-up.

As for CG, my understanding was that the CG should be at the wing spar. When I balance the AXN with my finger tips at the spar (+/- 0.5cm), it balances perfectly with a 2200mAh pack. Is this a bad way to test CG?
No it is not bad but IMHO is just to get the CG close before the initial flight. Each aircraft is a little different even if it is exactly the same model. So doing the dive test is the best way I know to get the CG right.
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Old Sep 24, 2012, 05:24 AM
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Is this a bad way to test CG?
I put glass headed pins into the underside of the wings of all my models at the correct CoG point, cut off to suit the wing thickness. I don't think that fingertips without a proper balance point is accurate enough. Of course, once you find the correct battery weight and position, you don't need to check the CoG every time, but I use the AXN as my video platform and often add things like cameras and/or an OrangeRX stabiliser, so then I need to recheck the CoG and the pin heads really help.
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Old Sep 24, 2012, 05:33 AM
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Australia, VIC, Rosebud
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Originally Posted by richard9999 View Post
I put glass headed pins into the underside of the wings of all my models at the correct CoG point, cut off to suit the wing thickness. I don't think that fingertips without a proper balance point is accurate enough. Of course, once you find the correct battery weight and position, you don't need to check the CoG every time, but I use the AXN as my video platform and often add things like cameras and/or an OrangeRX stabiliser, so then I need to recheck the CoG and the pin heads really help.
I use small rubber grommets that are big enough to put your fingertips in.

Works well

Kev
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Old Sep 24, 2012, 01:56 PM
Argue for your limitations
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Lincoln, CA
Joined Oct 2006
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Quote:
Originally Posted by Zangetsu57 View Post
After a crash and repair, I've noticed my Axn is doing the following:

1. When flying with and without motor power, my Axn seems to "teeter" left and right often. This happens at both fast and slow speeds, but is more pronounced at slow speeds. I just flew in fairly light wind. What might be causing this? Too much slop in the stock aileron servo connectors (I'm using HK orange digital servos, which are much better than stock). The only other thing I can think of is I reinforced the elevator with a 3mm CF rod. The rod was placed flush, hot glued in several locations, then taped over with fiber glass reinforced tape to produce an even surface. I did not, however, cut a slit in the foam and embed the rod, as I figured this would weaken the foam too much since it is quite thin as it is.

2. It likes to pitch up quite easily, and I have to trim quite aggressively. Perhaps this is common with pusher props.
You have the classic "tail heavy" problem. Make sure that your CG at 50mm from LE of wing to start with. Then, do the test attached below.
AJ
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Old Sep 24, 2012, 08:52 PM
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Thanks for the feedback everyone, it is very helpful.

I'm actually glad it is tail heavy. It should give me a bit more lee-way once I start loading FPV equipment. Speaking of which, is there a good method for doing this? I was going to build a rudimentary FPV pod out of lite ply, but the last thing I want to do is end up with something that is not flyable due to horrible balancing.
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Old Sep 24, 2012, 11:58 PM
Argue for your limitations
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Lincoln, CA
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Originally Posted by Zangetsu57 View Post
Thanks for the feedback everyone, it is very helpful.

I'm actually glad it is tail heavy. It should give me a bit more lee-way once I start loading FPV equipment. Speaking of which, is there a good method for doing this? I was going to build a rudimentary FPV pod out of lite ply, but the last thing I want to do is end up with something that is not flyable due to horrible balancing.
Are you perhaps open to getting a different plane? The CF is not very well suited for FPV. It can be done. But, there are other inexpensive planes that are MUCH more suited for FPV.
AJ
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Old Sep 25, 2012, 01:26 AM
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Are you perhaps open to getting a different plane? The CF is not very well suited for FPV. It can be done. But, there are other inexpensive planes that are MUCH more suited for FPV.
AJ
I just placed an order for a Bixler (v1) as I've heard it is better, and it only costs $50 shipped from the HK USA warehouse. I know the Skywalker and flying wings are great, but I didn't want to spend a ton just yet, especially since I'm still not the best plane pilot (used to helicopters ). Maybe I'll go with a larger platform in the future if I really enjoy FPV .
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Old Sep 25, 2012, 01:32 AM
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I'm actually glad it is tail heavy. It should give me a bit more lee-way once I start loading FPV equipment. Speaking of which, is there a good method for doing this?
This is my planned FPV set-up for the Clouds Fly, waiting for a cloverleaf antenna. The FPV camera and 5.8 GHz VTx are powered from the main LiPo via a 9V regulator IC (seen on the side of the VTx), so there is no additional video battery. They sit on a coroplast FPV backpack, which in turn sits on a polystyrene "saddle" cut to fit the Clouds Fly and will be secured with rubber bands. The flat FPV backpack can easily fit on other models. Note that I haven't yet maidened this set-up in the air (though the video works in my workshop), but since the weight is low (about 60gm) and near the CoG of the plane I don't anticipate any problems carrying it in flight. I normally fly with an 1800 mAh LiPo, but can move to a 2200 mAh if I need more weight forward.
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Old Sep 25, 2012, 01:43 AM
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Originally Posted by richard9999 View Post
This is my planned FPV set-up for the Clouds Fly, waiting for a cloverleaf antenna. The FPV camera and 5.8 GHz VTx are powered from the main LiPo via a 9V regulator IC (seen on the side of the VTx), so there is no additional video battery. They sit on a coroplast FPV backpack, which in turn sits on a polystyrene "saddle" cut to fit the Clouds Fly and will be secured with rubber bands. The flat FPV backpack can easily fit on other models. Note that I haven't yet maidened this set-up in the air (though the video works in my workshop), but since the weight is low (about 60gm) and near the CoG of the plane I don't anticipate any problems carrying it in flight. I normally fly with an 1800 mAh LiPo, but can move to a 2200 mAh if I need more weight forward.
Not a bad setup! I was thinking of doing something similar, but with a pan/tilt setup with the pan servo embedded in the Axn behind the canopy magnet. I wonder if it would be just as easy to make a "backpack" to enable transfer to other models.
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Old Sep 25, 2012, 01:50 AM
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I may well add a Pan/Tilt mechanism later, but one step at a time. Many thanks to Bruce Simpson of RCModelReviews for the backpack and 9V regulator idea. The Sony 600 TVL camera is amazing.

The whole idea of the backpack is that it is easily moved between models, since everything is on one piece of coroplast. I have flown the AXN with the OrangeRX stabliser (fits in the cockpit) and this definitely improves stability for video. I must say that the Bixler cockpit looks rather small and I'm not convinced it would be much better for FPV. Plus the AXN is much more beautiful!
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Old Sep 25, 2012, 05:25 AM
RC Airplane (Recently Crashed)
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Australia, VIC, Melbourne
Joined Jan 2011
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Originally Posted by richard9999 View Post
I may well add a Pan/Tilt mechanism later, but one step at a time. Many thanks to Bruce Simpson of RCModelReviews for the backpack and 9V regulator idea. The Sony 600 TVL camera is amazing.

The whole idea of the backpack is that it is easily moved between models, since everything is on one piece of coroplast. I have flown the AXN with the OrangeRX stabliser (fits in the cockpit) and this definitely improves stability for video. I must say that the Bixler cockpit looks rather small and I'm not convinced it would be much better for FPV. Plus the AXN is much more beautiful!
The AXN is nicer looking but I am beginning to think the Bix is a better platform ... I dn't have a Bix but friends who do have pretty much convinced me.
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Old Sep 25, 2012, 06:47 AM
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Originally Posted by ajbaker View Post
Are you perhaps open to getting a different plane? The CF is not very well suited for FPV. It can be done. But, there are other inexpensive planes that are MUCH more suited for FPV.
AJ
-------------------
Could you elaborate on your opinion here ?
I'm trying a little fpv with my CF these days, and my feeling is that when loaded up with a little extra weight, it gets a high wing loading, and is a bit fast for FPV. But it is ok, as long as we talk about a very light fpv, like a 100grams extra, plus you can use a smaller flightbattery to compensate. Ok but not perfect hehe..

But what are your opinions on alternatives ? Would you say Bixler is a big improvement over CF ? I'm considering the FPV-raptor also for when I find the CF needs to retire...
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