Clevis pin failure

[PatMc]

Posted by Tom Wright 2 on 17/12/2012 20:26:03:

Posted by PatMc on 17/12/2012 20:04:42:

So it seems like the impact was the cause & not the result of the broken clevis.

Pat.

Lets say the clevis failure is a possibility ,although unlikely , and at the end of the day it is impossible for anyone to reach a final conclusion .......unless a video of the incident is available, or further conclusive information became available.

Tom.

 

Edited By Tom Wright 2 on 17/12/2012 20:27:00

My typo Tom, I meant to say "it seems likely" not "it seems like".

Edited By PatMc on 17/12/2012 20:38:13

[Mark a]

Hi all.

Thanks for all of your comments interesting reading all. The clevis had failed in flight i had no rudder control on the approach.The plane was only lightly damaged with no damage to the tail at all but as a picked it up off the ground the rudder flopped over and pin was missing from the clevis as the clevis was no longer attached to the rudder horn.

You live and learn thats what i say no real harm done.

Mark.

[Flanker .]

Posted by PatMc on 17/12/2012 17:08:55:

I only use rudder on the approach if I'm need to steepen it to avoid an overshoot. There should be no reason to use it otherwise & plenty of reason not to use it.

You steepen your approach with rudder ? Funny I tend to keep lined up and control drift with mine. I seem to use the elevator to control pitch on my aircraft. I try to avoid rocking the wings about near the ground and at low speed. Any pitching with rudder suggests an oddly set up air frame or too much rudder. The poor thing, the most underused control in modelflying ! We would all fly so much better if we got to grips with it.

A good game is trying to do figure eights with a low winger on rudder and just using aileron to keep level .

Ho hum , F

[PatMc]

Flanker,
Using rudder to steepen the approach has been a common full size practice for light aircraft not equiped with flaps since the early days of flying.
If you're using rudder to keep a model lined up (to land?) then you're mis-using it. Not sure what you mean by "control drift".
You seem to be confusing pitch with controled landing descent.
Not sure what the wing rocking comment is about.
Pitching down with rudder application is a known phenomena caused by the airflow over one half of the taiplane being blanked due to a yaw. It's a design flaw apparent in a number of model & full size aircraft. The Druine Akrobat is semi scale, based on the Turbulent so probably also a characteristic of the full size aircraft.
The rudder is generaly underused because we don't have the benifit of a turn & slip indicator. But rudder is often incorrectly used in landing approach when it's effect isn't understood. So yes, model flying would improve if people got to grips with it.

The wing position isn't relevent if you want to do unbanked figures of eight. But because of the previously mentioned characteristic it's easier to do them inverted with the Akrobat.

[Chris Reid]

Is it a coincidence that the clevis failures seem mainly with the rudder? Or is it because tail wheels are usually connected to the rudder in some way? Are ground running loads being passed to the clevis which the rudder servo will resist causing fatigue of the pin joint?

Chris

[Turbycat]

Well, I used to fly a full size Turbulent and I can't recall the rudder causing undue pitching. I would, however, use rudder combined with opposite aileron to create a controlled sideslip, on approach, if i was a tad high. Just like I was taught to do in gliders.

Andy

[PatMc]

Andy, the pitching is quite pronounced on the model, I know other people have found the same with their Akrobats so it isn't peculiar to mine. I have no experience of the full size Turbulent just assumed it might be due to the fin shape/position relative to the tailplane. I'm not sure how close the model's accuracy is to the full size, the relative areas may be different & the model's tailplane is certainly thinner than scale. When the model is inverted the rudder is very effective in it's designed capacity with no pitching.
The Priory Silhouette has the same pitching characteristic but has an entirely different fin/tailplane layout. I didn't explore whether or not mine behaved the same when inverted.

[Turbycat]

I had one of the Akrobats and didn't find a lot of pitching with the rudder. Some definately but not a huge amount. However it was some time ago. I did convert mine to ic from electric so maybe that made a difference?

As far as similarities between the full size and the Akrobat go I think it is just a case of a passing resemblence. More sport than scale. Both are very nice to fly. I used the model until it fell apart!

Andy

[Flanker .]

Posted by PatMc on 19/12/2012 17:18:06:

Flanker,
Using rudder to steepen the approach has been a common full size practice for light aircraft not equipped with flaps since the early days of flying.
If you're using rudder to keep a model lined up (to land?) then you're mis-using it. Not sure what you mean by "control drift".
You seem to be confusing pitch with controlled landing descent.

I need to stress that I am not criticising or being "humphy" Different flying styles are something we can learn from. It comes down to terms. By steepen the approach you mean "side slip" - losing height quickly with little gain in unwanted speed by banking, holding down to prevent a turn and holding nose up with rudder ? I took "steepen approach" to mean a nose down pitch. On my strip there are only two safe ways in due to trees and things depending on wind. The said wind does not always blow directly down (up?) the approach path so I use rudder to control the drift off track , or just to correct alignment errors (lots of rocks to hit) By wagging wings about I mean correcting track with aileron/elevator .( as opposed to keeping wings level.) I agree that coarse rudder movements near stalling speed are asking for trouble.

When on my PPL we were taught to use rudder on approach as our trimmed pitch was controlling speed, and bank and yank could cause unwanted speed changes.I was always getting told off for steering with ailerons alone ! Obviously we use aileron to keep the aircraft level. I got into models after that so I guess it has become a habit. Anyway it works for me in that the only spins that happen are done on purpose from high up !

Anyway all good stuff - I'm off flying.

F