Posts: 393
Joined: 9/15/2003 From: Etna,
CA, USA Status: offline
Well, I maidened the NitroModels Yak 54 3D 50 today. The first flight was uneventful and the plane handled nicely. The second flight, however, was not so uneventful. I did a four-point roll and then a nice, large loop with about 2/3 throttle on the O.S. .55AX. Then was going straight and level at near full throttle when all of a sudden, I watched in horror as I could see a control surface come loose and fall to earth.
I throttled back, brought the Yak around and unbelievably, was able to land. Upon inspection, I saw that the horizontal stabilizer had fractured on both sides of the fuse and that one of the elevator halves was missing!!
I read about problems with a weak horizontal stabilizer in other forums. So, before purchasing the Yak 54 3D 50 ARF, I called and talked to a guy at NitroModels and he assured me that the new ARF's had a reinforced horizontal stabilizer. I was a bit suspicious and even had a flying wire kit on order before I flew today. I thought that if I only flew some easy pattern stuff today that there would be no problem. Was I wrong! It is clear that the problem with the weak stab is not fixed! Can you please send me a replacement stab free of charge? My Order Number was: 177450.
Posts: 393
Joined: 9/15/2003 From: Etna,
CA, USA Status: offline
I just uncovered it and there it was. Yep, in fact it is just soft balsa. I agree- it's definitely an oversight / design flaw to use soft wood at a high-stress point. Thanks for your suggestion. I will PM them to see if I can get them to replace the stab / elevator. I will beef up the replacement appropriately.
Posts: 393
Joined: 9/15/2003 From: Etna,
CA, USA Status: offline
Not sure. I do have the updated color scheme which I thought indicated the new model. The tail is definitely not reinforced in any way. I PM'd them. Still waiting to hear something.
Posts: 393
Joined: 9/15/2003 From: Etna,
CA, USA Status: offline
John from NitroStaff support said he told the factory about the weak stab problem and that it would be 4 weeks before he could send me a reinforced one. I want to get back into the air sooner than that so I opted for an identical replacement stab that I will reinforce. Since they were out of the red color, he was only able to send me the older color scheme (mostly blue).
I received it last Friday. I will uncover and reinforce with hardwood and ply. Think I'll use either robart point hinges or Dubro heavy duty hinges. I also have a flying wire kit that I plan on using.
I noticed the threads on the small-diameter machine screws that hold the control arms on don't really have enough bite and that they loosened a bit on the rudder (stripped out of the backing plate). Maybe the primary failure mode here is flutter causes by loose control horns. I plan on replacing the stock control horn hardware that includes nylon lock nuts.
Posts: 357
Joined: 12/7/2001 From: Houma,
LA, USA Status: offline
My elevator halves are thicker than the stab, this will cause flutter probs at higher speeds and structual failure. I plan to build a stab to match the halves.
Posts: 5832
Joined: 11/26/2005 From: Poolesville,
MD, USA Status: offline
quote:
ORIGINAL: Jerry Sigur
Sealing the hinge gap will help but not fix the prob. The elevator halves should not be thicker than the stab, this causes problems.
I agree, but at the same time it is also ok ( of course not in this case ) if the elevator follows the stab airfoil shape too... for those planes equipped with airfoils instead of flat balsa.
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