Molded Supra Pylon

[markStockton]

Hi All

I noticed that my molded Supra has developed a fair amount of softness in the pylon where the wing mounts. What is happening is that the fuselage can twist in relationship to the wing. However it just did a complete weekend of hard towing off some strong F3B winches. So the system holding the wing down seems to be fine.

I think the softening of the pylon is due to the loads imparted through to many F3J spot landing's. So my question, with our first leg of F3J team trials just a few weeks away should I be worried about this model shedding it's wing during tow. And if the answer is yes, is there anything that can be done to correct the situation.

TIA

Mark

[Tuomo]

Hi Mark,

Supra is a plane I would like to fly. The light glass version is specially interesting. I have stayed away from it because of the much discussed wing seating issues and wing flex.

What version you have and how do you like your Supra (forget the sof pylon :rolleyes: )? Full pedal winch launches ok?

(sorry, slightly offtopic)

[markStockton]

What version you have and how do you like your Supra (forget the sof pylon :rolleyes: )? Full pedal winch launches ok?

Mine is one of the early light glass models #78, however knowing about the center section sheer web problems (and because of an accident) I got Vladimir to bring a strong full carbon center section to the World Championships in Slovakia for me. This model with this center section now weighs around 1.9kg but is very strong. I will give it full power winch launches except when the wind is very high (this is because I still have the light tips on the model). This weekend I was usually out launching a full carbon Experience Pro off winch in F3J like competition.

I like the model so much my next one (glass) is in transit and being delivered later this week. As I understand the glass wing's have been improved so that they can take a full F3J launch. Furthermore all the other issues have also been sorted out. I would not hesitate to recommend the model as well as Cape Sailplanes (http://www.capesailplanes.com) our local agents.

If you are planning on using them for competitive F3J get both a light glass as well as a stronger carbon (or at least carbon center sectioned) model to cover all conditions.

[glderguy]

Tuomo I think I posted about the newer Supras ability to take a launch. We had three
newer glass Supras w/all upgrades flying at an F3J practice using mono on US TD winches. Strangely enough, it was very windy in the morning then calmed way down in the afternoon, which is sort of opposite of how it usually is. Anyway, even in the wind, ballasted, full pedal the Supras took the launches fine. Yes, tips flexed, but then again they are supposed to. They pulled very hard on launch and launched as high as the Icons, Perfects, Espada, Superiors, etc we also had flying that day. As far as excessive pylon flex/etc, cant comment as I didnt notice any. I really like the Supra and thought it was easily the equal of any of the other planes out at the field that day. Sorry about the off topic , sort of, post.
Walter

[Kiesling]

Mark,

Presumably this is one of the models without the aluminum wing mount reinforcements?

My guess is that the softness you are seeing is from micro cracks in the matrix generated by repeated landing impacts. I expect that you will eventually reach the fatigue limit and will have a problem.

You should probably consider re-doing the mount or ordering another fuse. To re-do the mount, you should cut a hole in the carbon saddle over the pylon. If I remember correctly there is an open area where the wiring harness comes through the pylon. This will let you see a bit better as to what is allowing the fuse to twist. From what you describe I dont expect you to see any major cracks - just the fuse sides deforming. To fix it I would make a mix of chopped fiber and epoxy and fill in all the space of the pylon. Before you put the mixture in I would wet the interior fuse walls with some reall low viscosity epoxy (MGS laminating resin or Pro-set).

The way I would do it is pull out the wiring harness and put in a large diameter driking straw as a place holder. I would put some waxed threaded rod into the wing mounting threads. I would also put some packing tape on the bottom of the wing and wax it. Once all this is set up I would put the glass epoxy mix into the pylon. Over fill it slightly. Then put a piece of carbon over the wing saddle (push the threaded rods through it. Wet out the carbon. Put the wing on and put nuts on the threaded rod to sinch the wing down to make a new saddle.

Once it is cured you should be good to go. Hopefully this makes sense.

Tom

[markStockton]

Thanks Tom. Sounds like an excellent plan I will start on it tonight and let you know how it goes.

Mark

[eye_rc_soar]

Definitely follow Tom's advice. I lost the wing pylon on Supra fuse #48 under a hard launch (wing separated from fuse taking with it the wing hold down portion of the pylon -inner portion of the pylon - leaving the pylon shell). I had also noticed a softness in the pylon mount due to too many dork landings, but could not see any structural cracks. It turns out the cracks were all interior cracks between inner wing saddle and the exterior fuselage pylon shell.

This problem was fixed in later fuselages making the wing mount more rigidly attached to the pylon. If you look into the fuselage and see the two metal rings capturing the ballast tube located under each wing bolt - you have the modified fuselage and do not need to worry loosing a wing.

Don

[glderguy]

Personally, rather than doing the repair and hoping it holds, Id just buy another fuse.
I know many will chime in saying their repaired fuses are now good, and who knows they very well may be. None the less..........a fuse is much cheaper than a wing.
Walter

[mdennis]

Please excuse my ignorance.

Are we talking about the Kennedy Composites molded version or the Phil Barnes Bagged version? Are both versions having the same problems with the pylon/wing mounts?

[Kiesling]

We are talking about the molded one distributed by Kennedy Composites.

The bagged version by Phil Barnes typically use either a Luckenbach or Lachowski fuse. These both require the builder to install the wing mounting system. I have not heard of this problem with either of these fuses.

Tom

[mdennis]

Thanks.

I started another thread with more questions so I wouldn't get this one off track.

[Phil Barnes]

http://www.rcgroups.com/forums/showthread.php?p=7181585#post7181585

[tonyestep]

Tom, if I understand your proposed fix, you would fill all the open space inside the pylon with the epoxy/fiber mix -- is that right?

[Kiesling]

yes

Since the pylon is fairly thin, this will not add much weight.
I used end grain balsa to fill the pylon in my scratch built Supras. This takes a bit of fussing to get a good fit. The method I described above should do the same job, but will be much easier with a small weight penalty.

Tom

[markStockton]

Tom, you where spot on. However the cracks wern't so micro. The a divorce between wing and fuse was on the cards sooner rather than later. I opened her up and filled the pylon last night with a mixture of epoxy, cotton flox and carbon chopped strands. This was topped off with two layers of 200 gram carbon cloth.

I received my new glass model last night and have noticed the changes to the pod. I also see the boom is a fair bit lighter.

Mark