Hello Guys,

I was out flying some easy flights on my new Skymaster Large Hawk this afternoon. 4 flights today, The airframe after today only has 18 flights total. After my flights today and during the tear down, I had a hard time pulling out the wing tube. I knew right away that this was not a positive sign. After getting the tube out of the fuse, this thought proved to be right. I had a bent wing tube and from the way I flew it today, this was hard to believe how bent it was. It even has a start of a compression at the joint of the fuse and wing root. I am not hard on my airframes with my style of flying. No hard pulls or high "G" manuvers. The largest gap from the table surface is 3/8" in attached pics.

So my big questions is, are there any substitutes for the Skymaster wing tubes ? I have tried checking my aluminum wing tubes from my planes and even a Carbon Fiber tube that I have and they are just a tad oversized compared to the SkyMaster tube on my plane.
What do you guys do in this case? Are there any sources for replacements other than Skymaster ?
If i have to use a Skymaster replacement tube, can I add a ply insert in the vertical position to help with this bending problem, and is it even a good idea ?

Thanks for any advice and help.

It is probably metric try mc master car

dragonplate has tubes. Last carbon fiber tube I bought I found on ebay. Came from china

If you can find an insert(tube) of either aluminum or carbon tube that fits inside, that will increase the AMOI of the existing tube(unless there is a seem then forget it). But you got to get this one straightened or buy a new one. Aluminum will yield and fails pretty quickly outright after you reach the ultimate yield strength. I dont think you got there yet, but it yielded in the extreme fiber for sure.

Joe,
Email Anton for a replacement. I think there were two different sizes on the Hawk. possibly you got the wrong one somehow.
Scott

When I had the Viperjet there was an issue with tubes bending and Skymaster was replacing them. Sounds like I have the same issue and I would approach Skymaster for a replacement.

PaulD

Hello Scott,

Thanks. Do you know how to get in touch with Anton?

Also thanks for the help with my lights question.

Joe

The best supplier of accurate carbon rods/tubes I can find is in Germany

http://www.shop-en.carbon-composite....st=KAT11-10113

They do high precision Carbon fibre tubes of various wall thicknesses some are centerless ground. I have bought from them in the past. The site is in english and you can use Paypal.

The best ali tubes are again from Germany and are gold anodised in colour. I had some tubes on one of my models bend and when I fitted better quality gold ones I also fitted a tube inside it glued in with PU glue. These have been perfect. If the tubes are small section they can be filled with wooden dowel rod but on a large plane will probably be too heavy.

I cannot find the German supplier of the tubes just now but if I find it I will post later.

John

Ho Joe

This tube is 38mm OD.

There's an old thread regarding this issue, regarding wall thickness of the tube. What's your tube wall thickness? There are 1 and 1,6mm thickness tubes. It is very important to let us know tube profile and thickness

I asked SM for a larger tube like this one and been trying to find it for ages...... this was the one sent with my kit

Best regards

Nuno

John, that would be nice...

thanks

Nuno, isn't that 36mm?!

Hi Mark - Nuno is correct - you read the calipers at the 0 on the bottom scale, not the metal edge. The top scale gives the decimals so the calipers are reading 38.0mm in the photo.

Regards - Pat

doh!!

Time to go grab a coffee!! [X(]

If it is a 38.0mm O.D.tube you can purchase a carbon tube from TNT landing gear. http://www.tntlandinggear.com/composite_tubes.htm
They are 1000mm long so the length might be short depending on how long the Skymaster tubes are.

Is changing over to a carbon tube a good idea with using in jets ?

I can't think of any drawback. Its lighter, and of course amazingly strong and proven in terms of a spar material choice for jets.
Aluminum spars/tubes.. the quality and type of the aluminum alloy(grade) is critical as not all are equal. And sometimes its hard to know what you've got.
In the glider world, aluminum and steel get bent all the time... hence the move to carbon tubes and solid rods!

once you get your carbon tube find a 12-20 lb balsa round stock to fill the inside of the carbon tube or use a spruce dowl and that will greatly inhanse the strength of the carbon tube. this will alow it to bend much farther than the tube with out a filler in it.

Find a friend with a lathe, buy a wooden dowel larger than the inside diameter of the aluminum tube, then ask him to turn it down so that is a tight fit in the tube. Slide or pound the wooden dowel into the tube, this will help staighten and fix the problem

Thanks guys for the tips and leads. I will see what I can find.

My Large Hawk had a carbon fiber tube, when did you buy your hawk?

I received my Hawk this past November.

What size wall does your Carbon tube have ?

that's sad, but just more crap coming from china, what do you expect? a good product.. the tube they using is probably low grade at best to bend that easy.. It should be T-6 6061 aircraft grade.. but I bet they are using recycled soda cans which has no alloy and is very soft.

Hi, Joe

please email to John. we will send the new wing tube to you as soon,

[email protected] or [email protected]

Best regards

Anton

Anton - I have the old style MB339 tube as shown in a picture further up the page (post 9). Since there were reports of failures is there a Skymaster replacement for it?

yes, please email to john and advise your address detail.