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Old Sep 23, 2012, 07:30 AM
Aussie Aeromodeller
Nitro2Burn's Avatar
Australia, NSW, Chittaway Bay
Joined Feb 2005
129 Posts
Discussion
Seagull MXS-R 91-120 wing tube bending.

Hey guys,
I have recently bought the Seagull MXS-R 91-120. Although I have fitted it with a 30cc petrol with an APC 15x14, this is about the equivalent power wise for an OS120AX. There are a few other mods that I have made like 4-40 pushrods on the elevator and dual elevator servos, carbon UC, plus extended the wingtips by 65mm each side.
Having taken it for a test flight (nothing too serious) in the third flight I noticed it had some new found dihedral so landed to check it out. Turns out the wingtube had a pretty decent bend in it. I am just trying to find out if anyone else has had any issues like this? I have since replaced mine with a carbon wing tube and it is great now.
Keep in mind I know it is a high pitch prop but the plane is for RedBull class air racing here in Australia, and the first few flights the plane was put no where near its racing conditions so far as tight turns and top speeds.
I allerted one of my friends who bought the same plane and fitted an OS120AX into his and he strengthend his tube and it still did the same thing. I also notified seagull who assured me mine was the only one and they had extensively tested theirs (obviously not to the planes full abilities).
I can honestly say though now with the carbon wing tube the plane is awesome.
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Old Sep 23, 2012, 09:00 AM
Fueled by Arabica Beans
ChillPhatCat's Avatar
United States, NY, Syracuse
Joined Oct 2008
4,038 Posts
I imagine that more people buy it to do 3D than as a race plane... sounds like you found a real weakness for use as the latter. Seagull won't take action until a certain percentage of buyers experience this problem.
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Old Sep 23, 2012, 09:32 AM
Aussie Aeromodeller
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Australia, NSW, Chittaway Bay
Joined Feb 2005
129 Posts
I agree that not a whole lot of people will purchase it for speed, though the control surfaces aren't suited to 3D, the elevator is reasonably small (another reason for choosing it) as is the rudder and the ailerons are what I would class as aerobatic ailerons but definately not 3D.
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Old Sep 23, 2012, 10:10 AM
Fueled by Arabica Beans
ChillPhatCat's Avatar
United States, NY, Syracuse
Joined Oct 2008
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Quote:
Originally Posted by Nitro2Burn View Post
I agree that not a whole lot of people will purchase it for speed, though the control surfaces aren't suited to 3D, the elevator is reasonably small (another reason for choosing it) as is the rudder and the ailerons are what I would class as aerobatic ailerons but definately not 3D.
I wouldn't either, but I've seen plenty of people hovering them and trying to tout their 3D capabilities. In my eyes, as an aerobat, it's more of a "casual 3D" ship that can do a few things outside of an unlimited routine.

I have considered purchasing this plane for my OS 120 AX and am glad to find out about this weakness... will definitely get a carbon tube if I make the purchase. What prop is your buddy running?
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Old Sep 23, 2012, 07:01 PM
Aussie Aeromodeller
Nitro2Burn's Avatar
Australia, NSW, Chittaway Bay
Joined Feb 2005
129 Posts
Casual 3D sums it up pretty well, I will ask to find out exactly but am pretty sure it's an APC 15x10. Although I don't expect it, it would be great to see Seagull provide a carbon tube with it as this would cure any issues so far. I have used a PBG 3/4"carbon tube though it is slightly undersized so I had to build it up a little which I did with 2 wraps of cello tape. I also have specs for a graph tech wing tube but need to measure the current one to see what it measures exactly to see if the graph tech one is any beter suited.
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Old Sep 24, 2012, 12:32 AM
ProBro, 3D
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United States, FL, The Villages
Joined Jul 2008
946 Posts
Perhaps the extra wing length you added caused it to bend??? I agree, aluminum tubes are just cost savings/old school and Mfgs. should bite the bullet and upgrade them along with landing gears to CF.
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Old Sep 24, 2012, 10:08 AM
Aussie Aeromodeller
Nitro2Burn's Avatar
Australia, NSW, Chittaway Bay
Joined Feb 2005
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Hey Gregory, I did consider the extra bit on the tips, however with the first few flights I was not putting the airframe through any major manuevers or turns. For the extra price of carbon legs and joiner tube I don't think this would price the models out of the purchase range, infact I think it would attract more purchasers if it were noted on the box that it had carbon gear inside.
My friend that had it happen also who added strengtheners to his tube shouldn't have had to worry wbout the same thing I would have thought.
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Old Sep 24, 2012, 10:23 AM
ProBro, 3D
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United States, FL, The Villages
Joined Jul 2008
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I hear ya! I have a Seagull Edge 60-90 size that I'm going to try to mount a DLE20 on. I'll probably bend the tube on that one as well. I'll probably start looking for a CF tube now. Any suggestions on who supplies CF tubes?
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Old Sep 24, 2012, 10:43 AM
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San Diego, California
Joined Dec 2004
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Looks to me that the tubing is just the WRONG alloy of aluminum. My son's hang glider was made exclusively of aluminum tubing, and never had a problem. A number of our planes had aluminum tubing for wing attach, and had no problems. If they are using "O" (oh) condition, that is the problem.

Les
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Old Sep 24, 2012, 11:38 AM
Aussie Aeromodeller
Nitro2Burn's Avatar
Australia, NSW, Chittaway Bay
Joined Feb 2005
129 Posts
The 60-90 edge (assuming it's the 68" one) is a good little plane and has the same wing tube, my friend has the same with a 120AX in that also, stiffened the tube and never had a problem. The CF tube I'm using at the moment is a PBG brand one but is a fraction small so I wrapped cello tape around it to take up the free play it had. I will hopefully find time in the morning to do some more precise measurements on its diameter as Graph Tech also makes a decent carbon tube that may fit a little more snug.
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Old Sep 24, 2012, 11:39 AM
Aussie Aeromodeller
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Australia, NSW, Chittaway Bay
Joined Feb 2005
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Hey Les,
You could well be correct as i does feel like a softer alloy than a few other tubes I have.
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Old Sep 24, 2012, 04:51 PM
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United States, MI, Macomb
Joined Apr 2009
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Could it be because you lengthened the wing by 5 inces?
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Old Sep 24, 2012, 06:50 PM
Aussie Aeromodeller
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Australia, NSW, Chittaway Bay
Joined Feb 2005
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Hey Tacx, in the first few flights the plane was not tested to anywhere near it's limits (obviously except for the wing tube) so I doubt the extended tips had anything much to do with it, plus like I said earlier, it doesn't explain why my mates one with a stiffened tube then bent also?
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Old Sep 24, 2012, 07:53 PM
ProBro, 3D
gregory.da's Avatar
United States, FL, The Villages
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Quote:
Originally Posted by Nitro2Burn View Post
The 60-90 edge (assuming it's the 68" one) is a good little plane and has the same wing tube, my friend has the same with a 120AX in that also, stiffened the tube and never had a problem. The CF tube I'm using at the moment is a PBG brand one but is a fraction small so I wrapped cello tape around it to take up the free play it had. I will hopefully find time in the morning to do some more precise measurements on its diameter as Graph Tech also makes a decent carbon tube that may fit a little more snug.
Yes, it's the 68" size. How did your friend stiffen up the alum wing tube?
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Old Sep 24, 2012, 10:47 PM
Aussie Aeromodeller
Nitro2Burn's Avatar
Australia, NSW, Chittaway Bay
Joined Feb 2005
129 Posts
All you need to do is use a couple 3mm (1/8) ply strips interlocked to form an X shape, then use blasa tri stock to fill the emptyness and round it off till it fits in snuggly. Push it down to the required pos and secure with a little epoxy, keep in mind this doesn't need to go full distance as they only seem to bend across the fuselage edges so as long as you go about 100mm (4 inches) past the fuse edge on both sides you will be right.
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