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Jun 01, 2017, 02:13 AM
Registered User
I lost a lot of work, so I hope people understand my frustration. Lets look at spar systems, one of Pat's other designs for example. His 60" Stinson Voyager. It's a solid wing, one piece and I trust it. The wing spars are glued and connected together by a hard wood sub spar. That is normal. The hardwood sub spar carries the weight across the wing joint from spar to spar. In this Super Cub design, the sub spar is removed, but instead of replacing it, that is connecting the spars with the mounting rods, there's a gap between the spars and the mounting rods are floating in the ribs. The spar and the tubes are designed to carry the weight, they should be. The ribs are not.
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Jun 02, 2017, 12:03 AM
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Gerry Markgraf's Avatar
Bleu

I understand your frustration - believe me, I've been there.

However, I've built several of Pat's designs with this same wing design and I'm finishing up the Stinson SR-10. I don't plan to change anything on this kit or any in the future as I understand Pat's design philosophy that these models are designed very similar to the real thing and are designed to fly as such. I've built a number of other models with cantilevered wings and they usually feature "D" tube leading edges with top and bottom spar caps and shear webs all the way out, plus the generally heavier structure and power to carry the extra weight and sustain the required higher speeds. I like to watch my creations sweep by low and slow so they look like the real thing.

An important feature of Pat's design (and the real planes as well) is that they are designed with functional struts. If the strut fails, its very likely that the wing will fail - whether its on a real Piper Cub or on one of Pat's model Cubs. I don't believe the modifications you suggest would change that. The spars on Pat's wings are simple balsa sheet, not very thick, scalloped in some case and notched halfway through every few inches to accommodate the rib notches. I believe with your modification, the breakage point might move a bit outboard from the inner ribs to the point of the spars where the end of the tubes is. This would be a stress riser on both spars. The plane would fly fine until the struts failed and then the wing would fail - just a bit further outboard on the wing. Those spars are not designed to be cantilevered.

Looking at the excellent photos you supplied of the wreckage, I can't imagine how the initial failure was the wing fuselage joint. You said the right wing failed, I assume in the classic barn door failure. I would suggest that the strut had to fail first, followed almost instantly by the wing. I took a look at my Piper Cub plans and the breakage point on your strut looks to be about where the hole was drilled for the wing strut/fuselage attach wire. Could it be that this is where the initial failure point was? I think for lessons learned (at least for me), I will take a closer look at all of my struts cause its obvious that they are a more important part of the structure that we might realize. Perhaps a ply doubler over the spot where that strut broke might be a more meaningful fix.

I realize that you are closer to the wreckage than I am and you saw the accident as it happened, but I do not believe there is any design weakness in these kits. They are what they are and are no weaker than the original Cubs or Stinsons. They are designed to fly in the same manner as the original and will fail in a manner similar to the originals if there is a fault or if their design parameters are exceeded.

Gerry
Jun 02, 2017, 08:50 AM
Neophyte hacker
portablevcb's Avatar
I have built, flown and beefed up several of Pat's designs. I have also crashed them, some in a spectacular fashion. I have flown with Pat for almost 10 years so I have seen almost all of his designs flown and even the maiden flights of most.

I always recommend to build and fly Pat's designs the way he does. Light. Flown slow. With the recommended power setup. Yes, you can beef them up a bit, or change a part of the design for more strength, and I have done that as well, frequently in the landing gear mounting area (I am not hear as good a pilot as Pat ).

Modifying the design as described. Yes, you can do that. But, it won't change much in the strength of the wing. The spars are not that strong to begin with. All you would do is change the failure point to the end of the joiner tubes. As mentioned before, the wing strength is in the struts, not the root section.

charlie

PS any of Pat's designs I have modified did not fly like the originals. For my type of flying some did better. Others did not. Some did very poorly because I missed a key structural issue.
Jun 02, 2017, 10:49 AM
Registered User
Gerry Markgraf's Avatar
Blue's experience reminds me of a book that I recently read (America Military Gliders of WW II by Bill Norton). The book tells about an incident in August 1943 when a WACO CG-4A glider crashed in front of thousands of spectators. The American glider program was in trouble and to demonstrate the safety of the WACO, the President of the Robertson Aircraft Company (sub-contractor building them in St. Louis), the Mayor of St. Louis and a number of other dignitaries went up in a CG-4A. Unfortunately, the wing failed and all aboard (10) were killed. There is a very graphic picture on page 73 that captures the moment the wing failed. The entire wing from the root out to the ailerons has disintigrated and the airplane is sailing along for an instant as if nothing had happened. The WACO was designed in a very similar manner to a Piper Cub and I suspect the wreckage was very similar to Bleu's Cub. The failure was traced to failure of a wing strut fitting that had been machined too thin and wasn't caught. The aircraft had logged 233 hours and 800 landings, but eventually the defective strut fitting caught up with it, unfortunately in a very tragic manner. Most CG-4As logged only 1 flight and 1 landing.

Gerry
Jun 02, 2017, 11:09 AM
confused poet
HanksGB's Avatar
Blue,

You have my sympathy. I think you are right tieing the tubes to the spars will make for a better and stronger design.

FYI you're not the only one to have issues with Pat's design.

https://www.rcgroups.com/forums/show...ctric-R-C-kits

Hank
Jun 02, 2017, 04:57 PM
Registered User
roversgonemad's Avatar
Notice the guy making the noise has a suspended account.... So maybe a grain of salt is in order here.... Pretty sure he's run himself out of most of the RC forums out there.

Bottom line, if you feel that moving the tube to the spar, and lacing it to the spar is better, do so. That's really easy. In many cases, instructions are just suggestions anyway.....
Jun 02, 2017, 10:23 PM
confused poet
HanksGB's Avatar
Rovers

Which guy has a suspended account? Konrad? yes his was suspended years ago. You can find his arguments with the moderators if you search his name.

What bothers me is people can't take critism. Blue obviously had massive structural failure and most of the people who have responded to him haven't asked any questions just pointed that he probably wasn't flying the plane the way Pat intended.

I know I've seen other models from Pat that have had similar failures on one was way over gross, the other was pretty stock, but that said there have been enough of these problems to warrant a discussion.
I would like to hear from Pat why the tubes aren't tied to the spar and why he doesn't use bigger tubes. Bigger tubes are much stronger for negligible weight gain.

I have bought two of Pats designs over the years. I didn't build either one because I felt there were to many design choices that I didn't agree with and I would have to rework them to much to get what I want.

Hank
Jun 02, 2017, 11:48 PM
Registered User
roversgonemad's Avatar
I think if Pat felt the need, he'd move the tubes. He's had pretty good success with his designs. I personally like Pat's designs. They are extremely light weight. You definitely can't fly them hard. I am sure he's mulling over what bleu is saying. At the same time, he's probably never experienced that failure. There are so many variables when someone else builds your design. I really do feel for Bleu. You can't be in this hobby for very long before something goes in the dirt.... I had a seagull extra 300 that augered in on the third flight.... Totally my fault, used a weak rx battery. I lost everything but the receiver and three servos. Even my brand new Saito 90 was destroyed, but that's a part of the game. I know when I build my next Tritle plane, I'll make sure those tubes are secure, and that my wing struts are anchored well. We can all learn a lesson from Bleu's loss.
Jun 03, 2017, 01:26 PM
Registered User
P. Tritle's Avatar
Thread OP
Gentlemen, I think it's time to jump in and offer up an article that I wrote several years ago when the question of "How do you build so light?" cropped up. The explanation for my current design philosophy is found here: http://patscustom-models.com/buildinglight.html, and for those who haven't read it already, I would strongly urge you to do so before you proceed here.

Now that you understand the why's and wherefore's of why I do what I do, let me say simply that my design style of building and flying is certainly not for everyone, and that "the perfect model airplane" simply does not exist. That being said, I truly understand why builders want to modify things along the way to better suit their building and flying styles, but to call a design philosophy with a clean 21 year track record wrong is simply a total misunderstanding of what the designs and their intended purpose is really all about.

Now, for those whose building and flying styles don't quite fit the profile for what I do offer, the right to change, modify, or re-design is certainly their option. After all, that's how I got started nearly 30 years ago, and though the years, evolution of design has produced the foundation for what I offer today. That being the case, when modification of an existing design won't quite get you where you want to go, the option of working up your own designs is most certainly a viable alternative, and one that I have highly recommended on many occations over the years. But, as when I started modifying existing designs, those changes are at one's own perril, because in my personal experience they don't always produce the results we're looking for. However, over the course of my 21 year carrear as a professional model boat and airplane designer and a veteran of well over 250 designs, I can say without reservation that not everything I tried worked, and among those less than terrific designs, some were nothing short of dismal failures. But that's how we learn our trade.

With all that considered, could I, or anyone else for that matter, call my designs perfect? Absolutely not! But for the purpose for which they're intended to serve it's the best I have to offer based on my own personal experience, and as new designs progress, I do change things that are not -- in my opinion -- well suited for the job at hand. So my challenge to those who can see a better alternative is to work up a design of your own, that based on what you know from your own personal experience would be better suited to your building and/or flying style, then put it on paper and build it. Then in subsequent designs make improvements based on what might or might not have worked as you thought it should and grow your design style from there. There is one thing I can promise though, and that is that though there is no such thing as "a perfect design", there's nothing in this world more rewarding then seeing a blank sheet of paper evolve into a successful maiden flight.

Nuff said, PAT
Jun 03, 2017, 02:10 PM
Registered User
If we look at the design of the Super Cub and the design of the DH Beaver. It can be seen that the mounting tubes are shorter on the SC. The Beaver has three ribs of support, the SC only two. That's an error. Then the tubes are larger in the Super Cub, cutting more meat off the ribs. That's an error. The weight was never supposed to be on the ribs, that's another error. Sorry, I wouldn't recommend this kit.
Jun 03, 2017, 03:19 PM
I eat glue
While you are definitely right to your opinion, I would have to disagree in not recommending this kit, unless of course the builder is not use to building light and flying them in the manner of full scale aircraft. As Pat said, these are not for everyone, but to say they are bad designs is not fair. I have never, ever, had a failure in any of Pat's designs, and I fly them a little more aggressively than Pat does, but I grew up on very light freeflight models, and building light is not an issue for me. I would suggest that the 1/6 scale Sig Cub kit is more your style of building and flying, as opposed to light weight models.
The Highlander has the same wing style as the Super Cub, here's a video of one flying quite aggressively.
Pat Tritle highlander kit (2 min 32 sec)
Last edited by baldguy; Jun 03, 2017 at 03:25 PM.
Jun 03, 2017, 04:46 PM
Registered User
Not all Pat's kits are designed like this. I have had success with Pat's kits, I'm a fan. Just not this kit. God forbid these guys quit cutting these ribs. What I offer is more of a patch. This kit needs it. Two ribs only work like one rib, when the sheer force hits the first rib, it hits the second rib as torque, like a crowbar. If the first rib gives, the tube twists out of the second rib. Three ribs spread the load as sheer across all three ribs, the rib at the end resists in the opposite direction, like a teeter totter. That right there makes this design weaker.
Jun 03, 2017, 07:19 PM
I eat glue
The Highlander has the same wing set up, that's the point I was making, and it appears to hold up quite well. I'm very surprised that my L-4 didn't destroy it's wings when it cartwheeled, it has the same 2 piece wing set up. I could see the extra sense of security by extending out to a third rib though.
Jun 03, 2017, 08:01 PM
Registered User
These things are too beautiful not to take every precaution. Every failure, to me, has to have a fix. I have to learn from my losses and apply a remedy. I did cuss a little, but as usual, that just got more laughs. We must make every effort to avoid the walk of shame! My poor bird looked like a dead chicken. I might build it again, but not like this.
Jun 03, 2017, 10:52 PM
Neophyte hacker
portablevcb's Avatar
Did you ever find out why it failed? Did the strut let go for some reason? Just want to make sure you beef up the right part. If the strut fails again your relocated tubes won't help, the wing will still fold up.

charlie


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