Great Planes Pitts--cabane brackets--again
 

http://www.rcuniverse.com/showthread...7&pagenumber=4

I have heard of these breaking---in the above post the thread was closed before I could get an answer--(seems sombody with broken brackets did not express themselves very well, and I never heard back from AnnMarie--see last page of the thread)--Well it finally happened to ME today after the 3 flight. I transport my plane in a trailer-I keep it together all of the time-but I had just taken it apart last week to inspect everything--all was fine. No indication anything was going to break. Then on the 3rd flight I noticed constantly having to add down trim. After the 3rd time I decided to land-(it was very windy, so I thought that had something top do with it.) I only noticed it when I went to pick up the plane and felt the wing shift--no damage to the plane
I can get more brackets from GP--but I REALLY WANT A PERMANT FIX --WHAT IS EVERYBODY ELSE DOING? I attached a picture if you are having trouble understanding..

It's the ally
 

is it too soft ? Or is it cracking due to it being brittle ?

Maybe the bend has some fracture existing from its forming process.

Would some T6 work better ?

Great Planes Pitts--cabane brackets--again
 

They looked fine--these have probably 20 flights or so--more than a few people inspected them before installation--all agreed there were strong and able and it must have been a bad batch the others got. I guess we were wrong.

Re: Great Planes Pitts--cabane brackets--again
 

Dam the picture is very explicit. GP must do something about that.
That problem can kill the plane and a human...My pitts is almost finished and I am worry about that glitche.

Sergee

Great Planes Pitts--cabane brackets--again
 

I have 60+ flights on my Pitts with no sign of any brackets broken. What engine are you using, and what engine are the others with problem using?

Great Planes Pitts--cabane brackets--again
 

That REALLY sucks. Good thing you saved the plane. Question...before you installed them, did you check if the holes were the same distance from the bend? For some reason, I *think* I recall mine being slightly different, so I put the "long" dimension in the cabane direction.

There is NO doubt in my feeble-not-metallurgical-mind that this is a fatigue stress fracture caused by vibration and tension cycles on the radius of the bend. In my past experience this is usually due to too tight a radius. Of course, the material and how it was formed has a lot to do with it, too.

Like you - I yearn for a "permanent" solution...before MINE fail.

Great Planes Pitts--cabane brackets--again
 

I am using a Taurus 52-and many will say it is 11cc over the recommended engine range and voids the warranty and I remember reading that gas engines in itself were to blame, (something to do with hamonic vibrations)--but then a number of people using glow had the same problem. One of the club members (and RCU members-thomasw-is a machinist-he looked at them and said they were fine and could see no problem. I am seriously thinking of mounting an I-hook through the spar with a nut and washer on both sides of the spar-then a bolt through the cabane and the hole in the I-hook--anybody got a better idea?

"T" Extrusion
 

You could find a piece of "T" extrusion material that could be made to work for this application

Great Planes Pitts--cabane brackets--again
 

The T extrusion sounds fine...but if not available, how about some of the 90* alum extrusions? Could just slice a couple of those, and put em back to back...would the fact that the alum is extruded and not bent be what makes this a better approach?

Great Planes Pitts--cabane brackets--again
 

How about a large (Dubro) fiber-filled nylon control horn ground down to proper dimensions and bolted through the spar with blind-nuts on the inside. I think you need to stay away from metal and use a strong but flexible nylon casting.

Yak

I would think
 

That if you use two pieces you will have to use rather thin material. Then wouldn't you be reducing its properties by half that of the one piece extrusion ?

Great Planes Pitts--cabane brackets--again
 

TheEdge - good point...hadn't considered that....what do you think about the nylon "T" suggestion made??

I think that,
 

This idea is also a good alternative. I am unsure how the blind nut thing would work out.

I would still stay with the piece of mind that metal offers versus, the not knowing shear load or strength of the plastic

Great Planes Pitts--cabane brackets--again
 

I received my GP Pitts ARF just this last week. It is unopened. Shall I send it back?

I bought an ARF because I don't have much time or energy available to put toward building, modifying or troubleshooting. If this model is going to take extensive coddling to make it fly safely, I don't want it.

If Great Planes shipped the model KNOWING in advance that it had a problem that could lead to an in-flight failure, I don't think that it is fair to expect me to pay for the return shipping. What say ye, fellow modelers?

Great Planes Pitts--cabane brackets--again
 

I wouldn't send it back..this modification (below) should take 30 minutes. Think about how strong that wing is to survive the bracket failure!!! Amazing...it should have folded but didn't.

I'm looking at the Dubro part number 366 "Large Scale T-Style Control horn" in my hand and this will work. It has four bolt holes for the spar. It appears to be made from the same material as fiber-filled motor mounts. Dubro could answer that question.

You will have to cut open the top of the wing again to install the blind nuts. There is no way I would just use screws. If you are really scared, you could could install one horn on either side of the cabane strut and then you will have 8 bolts and two strong brackets holding the wing on. You'll rip the tail off first!

Yak

Great Planes Pitts--cabane brackets--again
 

If I remeber correctly, when you attatch the bracket to the wing, in one position, there isa gap between the brackets, but if you turn them and use the other holes at the wing they fit together tight. I can see where it would put excess stress on them if there is a gap between them, and you tighten the mount screws. Just thinking this may be where the problem starts.

Great Planes Pitts--cabane brackets--again
 

TLH101 - That's what I was describing with my question about the hole spacing on the bracket. Makes sense, but I'm not gonna take mine apart to check!! :rolleyes:

Great Planes Pitts--cabane brackets--again
 

How many people have actually had this problem? I have done some searchs and this only the second plane I can find. One thread talks about it happening twice to the same plane I believe.

Great Planes Pitts--cabane brackets--again
 

I guess it only matters if it is your plane--- This has bothered me for a while---I was gettein post together for the other thread before it was closed, and I found 4 different people. Again, not a lot unless it is yours-I really like the idea about the control horn--Andy T (of RCU) suggested cutting a braket from bar stock--PS--DO NOT SEND THE PITTS BACK. It is one of the best flying and looking planes you will find. Trust me!

Great Planes Pitts--cabane brackets--again
 

I've had my Pitts flying for about a dozen or so flights, then during a flight, it suddenly needed a lot of down trim to stay level. Made one more pass, and realized something wasn't right. Then when I started to turn it around, the ENTIRE top wing, INCLUDING the wing struts ripped off the plane! This happened about 200 feet.

I knew I was in serious trouble, and was about to loose a $2200 investment of my Biplane! I throttled back, and the motor died, Knew the only chance I had was to keep my speed up. So, I pushed the nose over, and dove straight down, waited till the last minute (about 30 feet) and pulled all the elevator I could. It pulled up, just past level and I managed to set it down (land?) at about 30+ MPH on the wheels. It did flip over just before it came to a stop. But it didn't even break the prop!


The top wing finally floated down ground. When we examined the plane afterwards. A 1/3 of the covering was ripped off the bottm wing where the wing struts where, The 2 front screws that hold the top wing on had pulled out of the wing, the wood blocking in the back of the top wing (center) was still bolted to the fuse, the blocking in the bottom wing where ripped out of it as well (when the top wing separated), and the landing gear spread eagle badly.

The amazing part is that with the top wing gone, the ballace point was more than an inch in Front of the bottom wing! And I managed to semi land it!

Great Planes Pitts--cabane brackets--again
 

I have managed to repair the Pitts, Installing 1/4" ply plates behind every where it had separated and installed blind nuts, It was not until after the wing separated, that I learned about the holes being drilled to close to the front edge of the blocking, go figure. :mad:

I have reinstalled the flying wires (which I believe are now functional). Flew it several more weekends, got it ready to take to Bomber field for the big bird. Got down there and was pluging it in to charge up over night, but when I went to move it, the top wing shifted. Looked a little closer and the 90 degree brackets in the center (top wing) were brokeat the bends! :stupid:

I drove 200 miles down there and was unable to fly! I was frustrated and looking for something to fix it. I found a vendor that had some mechanical retracts (40 size) that were made out of 90 degree bent anodized aluminum. bought them, cut the ends down to 1/8" x 1" x 1" angles and mounted them to the Pitts and it worked! :)

Great Planes Pitts--cabane brackets--again
 

Here are some pics:

Great Planes Pitts--cabane brackets--again
 

another one:

Great Planes Pitts--cabane brackets--again
 

AJF
After looking at your pics again it looks just like the failures I have had over the years on machinery caused by side loading/flexing.
Bending those brackets caused a stress crack before you even flew it. You cannot bend metal without giving up some strength unless you put in gussets afterwards and then the weak spot is the weld area.You probably would be better off with an extruded "T"
Just my 2cs
At

Great Planes Pitts--cabane brackets--again
 

hey, AJF--2

it may have been my post a few weeks ago that you read about
my brackets breaking a couple of times......... i took some of the relpacement brackets that GREAT PLANES had sent me to a local
metal shop and had some new ones made out of stainless steel.
the thickness is not much more than the factory ones, but a whole heck of alot stronger. i received a call from GREAT PLANES
earlier this week with news of them sending out some replacement brackets to me. the new brackets (as explained to me) are the new updated ones that are stronger than the originals. i hope to receive mine by monday or tuesday just so i can test them myself. i have another one of these planes NIB to assemble for a friend. hopefully they will be strong !!!!!!!!!!!!!!

PITTSMAN