RickP

My Feedback: (2)

I know you've been working on this, whats the latest?
RP

RobT

My Feedback: (17)

I thought I took photo's last week...but can't seem to find them. Set the stab incidence...

With the wings set at zero...Screw down the L brackets onto the stabs. Slide the stabs onto the tube and up against the fuse. Angle Finder onto the first stab. Position the first stab to zero degrees and lock it into place by gluing some scrap blocks to the side of the fuse.

When this is locked into position trace the outline of the L bracket with an exacto. Slide the stab away and relive the 1/8 balsa fuse sides at the location of the L bracket.

After the side is relieved The stab can be replaced to the same position due to the balsa blocks. check to make sure the stab is still at 0 degrees. Drill through the L bracket and into the 1/4" ply for the 6-32 screw, again remove stab and open the fuse hole to accept a T-nut. last check to make sure the stab is still at zero. Repeat for other side.

RobT

My Feedback: (17)

Due to internet rumors, I decided to back up the L Bracket with some 1/4" dowel. So after both stab incidences were set one was removed and a hole was drilled through both fuse sides parallel to the stab tube at location of the 1/4" ply and the stab. By using the 1/4 ply which is already in the fuse I didn't have to add any extra wood.

wgeffon

My Feedback: (4)

Rob,

No rumors. I personally saw three broken L brackets last year.
2 planes wiped out. One was fixable.

Your Anti rotation pin will help.

RobT

My Feedback: (17)

Installing the retainer screw hard points...

RobT

My Feedback: (17)

Wayne,

Thanks for the heads up. I have seen many Carden's have long lives without any mods. I wonder what caused the failures...Is it possible the L Brackets in question were experiencing additional twisting / flexing forces due to something in their particular setups?

None the less that is why I took the insurance and piece of mind by adding the dowel. And by using the hard point that was already in the fuse their was minimal weight gain.

paf

My Feedback: (1)

I had one bracket start cracking on my Cap years ago. It was due to slight mis-alignment of the surfaces. The bolts were slightly stretching the plastic. It also seems that the stab tube always has a little play in it and the stabs can move up/down slightly. This movement gets transfered to the L bracket as well, so over time, it could weaken it enough to fail.

Wayne - the first hand failures you know about - did the owners inspect the brackets regularly, or did they leave their stabs on all the time and maybe overlooked a developing crack ?

P.

wgeffon

My Feedback: (4)

Paul,

Two were on planes that had the stabs removed all the time.
Both of those planes had one season on them.

The other plane I am not sure if the stabs came off or not.
I am pretty sure they did as he doesnt have a trailer.

Flyin Woodbutcher

My Feedback: (3)

Hey fellas for a little more insurance. Install a dowel in the ends of the stab tube. Drill and tap this for a longer retetion bolt. I have a 8/32 bolt in my 35 cent Cap. When the bolt is tightened down the stab can not move away from the fus. Even if the plastic bracket breaks the extra antirotation dowel will stay connected.

FWB

jmiracle

My Feedback: (9)

I think an extra dowel in the stabs is all that's really needed to solve any questions over whether the plastic L brackets will hold up. Aeroworks setup their older kits with a AR pin and a bolt through the ends of the tube only and those seemed to hold up fine...I've seen several with many many seasons on them with no problems.

We trust the wings to a simple AR pin and a couple small bolts to hold them to the fuse...no reason it won't work just as well on the stabs.

With a bolt in the tubes, a dowel in the root, and root tabs or L-bracket....there are no structural worries if built correctly.

wgeffon

My Feedback: (4)

I am not trying to dispute any theory put on here but, one of the planes I witnessed had a dowell in the stab tube and also had an anti-rotation pin in the stab root.
Once the L bracket broke the LE of the stab rotated up 90 degrees ripping out the anti rotation pin and the bolt in the stab tube.

This is what we came up with on my Carden's to do away with the L brackett alltogether.

Flyin Woodbutcher

My Feedback: (3)

hows that a lot better ? The ply is only glued to foam. Have seen ARFs come loose here.

FWB

wgeffon

My Feedback: (4)

These planes I witnessed were all built by preffered Carden Builders.
(It can happen)

wgeffon

My Feedback: (4)

The ply is glued to the foam root and is also encapsulated by the sheeting locking it in.
The anti rotation pin and the stab phenolic also lock the root rib in place.
The anti-rotation pin sticks into the foam at least an inch.

Like I said, I am not trying to dispute any theory or solution posted here. I am just stating what I have personally seen and what we did to eliminate the risk.

Watching three beautiful Cardens go in last year was enough to make me want something different.

Flyin Woodbutcher

My Feedback: (3)

just a ? , no dispute. Stabs staying on is the main objective.

FWB

jmiracle

My Feedback: (9)

no dispute here either....no doubt about what you witnessed...

the only piece that doesn't make sense in my mind is what difference a ply tabs makes vs. a plastic L bracket. The ply tabs will without doubt fail before the stock brackets if any side loads are present....but there be no side-loads on the tabs/l-brackets when everything is fully assembled......6 of one half-dozen of another as far as I can figure.

All flight loads trying to rotate the stab around the tube should be carried by the AR pin and the tube....which is what you show in your pic. The bolts in the ends of the tubes and in the ply tabs are just redundant methods of keeping the stabs from sliding off the tube. It's exactly the same way on the wings only the bolts run inside-out instead of outside-in. Walt even mentions this in the 300 build thread...enlarged the holes for the DA stubs so alignment is handled entirely by the AR pin....the studs just keep the wing from sliding off.

No big deal...I think everybody agrees the stock method needs minor improvement...


Great build-thread Rob....your 300 is looking great....can't wait to see more!

wgeffon

My Feedback: (4)

The difference is that the tabs are integral to the root rib.
They set the incidence. The pin just adds to take away load from the tabs.

The L brackett is a stand alone peice that has to hold two seperate parts together.

wgeffon

My Feedback: (4)

I have also.

3 different Preferred Carden builders on these planes.
Relatively low number of flights on each etc..
You just need to see a plane go in one time with half of the L brackett on a broken fuse and the other on a broken stab to not use them IMO.

paf

My Feedback: (1)

I presume there was a screw in the stab tube as well, so it couldn't simply slide out. If so, it sounds like flutter brought that one down. There's no way any regular force would break off a properly installed anti-rotation pin. However, it is quite possible for flutter to tear apart pretty much anything - L brackets, dowels, plywood plates etc. On my C-arf SX, the stab tube ripped a nice 4" hole in the fuselage side before the stabs departed due to flutter.....

In my opinion, any mod that could/would have saved at least one airplane is a worthwhile investment.

wgeffon

My Feedback: (4)

We also thought flutter initially on these crashes..
I guess it could be but none of them had stripped servos....

paf

My Feedback: (1)

So what evidence were you able to gather to support/disprove different reasons for the failure ? It would be nice to figure it out with some certainty.

A broken L bracket on it's own does not a crash make.....

RobT

My Feedback: (17)

Sorry Wayne, I think You proved there was something else going on. ...Once the L Bracket broke the LE off the stab?? Sounds like the 1/4 ply block came out not a failure in the L bracket.

I also feel some people are throwing out the baby with the bath water. Using Dennis's method for mounting the stab you gain two things:

1) setting the incidence is very easy.

2) If after you are done you find you are off by a little bit you can sand the L bracket to lower the L.E. of the stab, or add a shim / glue to raise the L.E. of the stab.

I am not sorry I added the dowel, but I think I added weight more than anything. It is hard to improve upon anything Dennis has done with his kits.

That said however later I will be adding a dowel in the wing as I did with my 330. Why? This way I can slide the wing on and it is automatically aligned... plus it won't flop while I go to my field box to get my screws.


Your are right Paul...any mod that could save even one airplane is worth doing.

jmiracle

My Feedback: (9)

determining the "why" would definitely be nice...but I suspect that will never be known....sometimes things just go bad...it happens.

....but, I do feel the same as you paf....something "else" lead up to the L-bracket failing and the AR pin ripping out. Under normal conditions, each on it's own is capable of supporting the stab. Even IF the bracket managed to break on its own in flight...the AR pin should have held the stab in place as long as there was a bolt in the stab tube to prevent the stabs from sliding off.

regardless...on with the build!! I'm anxious to see one of these 300's finished!!

as722

My Feedback: (1)

A broken L bracket on its own can and will cause a crash. The minute the L bracket brakes flutter takes over and the rest is history.

Albert

paf

My Feedback: (1)

I was referring to the setup with a screw through the stab tube, dowel pin and the L bracket.....

The best thing would be a detailed carnage pics. Things usually don't "just happen". There's always some cause, but it might be very unusual and impossible to find. Otherwise it's called a miracle

Good luck with the build Rob. I hope you'll put it to a good use in next year IMAC season !