springs

[mwilli7119]

on page 37 of the VE O-235 engine installation plans in paragraph 3 springs are mentioned to return the mixture and throttle controls. What size springs do I use. the only numbers I can find are C161 and Century Springs says that those are compression springs. these should be extension springs.

thanks in advance.

Mike

[Anonymous]

On a related note, worth bringing up again...

I don't know if this is a new installation, or if you are replacing previous springs.  Assuming you are using the Ken Brock "carb control bracket" (CCB) I believe there has been at least one incident/accident which occured after one of the springs pulled free.

As originally installed, the hard steel springs pulling against the aluminum CCB have a tendancy to "cut" there way through the aluminum holes through which the springs insert in the CCB.  There are a few fixes for this, one of which at least is to install a small machine screw through the hole in the CCB with a locknut holding the screw in place.  Before torquing the screw down, lock the spring hook around/under the screw.  With this method, the hard spring pulls against the steel machine screw, which itself is torqued tight against the CCB.

This may not apply to you, but this is one of the things that needs regular inspection on our birds.

[Drew]

You might want to also check out the thread "throttle_mixture controls" on this site.

[Anonymous]

On a related note, worth bringing up again...


This may not apply to you, but this is one of the things that needs regular inspection on our birds.

Key words, regular inspection.  I had a throttle failure in a Quickie and got lucky when I kept some power.  After that event word went out to add a spring to default to the full power side on those pissant Onan engines.

You just want a very light spring to default to full rich and full throttle.  Spring failure rates are pretty damn low compared to other hardware.  Name the last time a garage door spring failed?  If it did, how many ops did it have.

Burt likes springs for a very good reason.

Jack

[Dan Patch]

I believe there has been at least one incident/accident which occured after one of the springs pulled free...

Correct, and your summary of the problem is quite accurate.  I remember it very well.... since it happened to me!     :shock:

By pure good luck, nothing got bent, and I didn't even know I had a spring failure until applying power to taxi clear of the runway after landing.  (Power?  What power?)  A full description of the "whys and what happened and the fix" can be found in the Canard Pusher, CP65, Oct. 1990 - it's too long to reproduce here.  One good approach to preventing this type of problem (spring resonance sawing through an Al bracket) is nicely outlined above.  

There is another point that should be mentioned, however.  If you rely on a single spring and it breaks, for whatever reason, you could be out of business, depending on the specifics of your installation.  (BTW, every one of the four springs on my garage door has broken at least once, some twice, and no vibration involved! - I agree, a lotta ops though.)  So anyhow, I originally used two springs in parallel thinking that I had redundancy.  But it turned out that neither spring alone was quite strong enough to pull the throttle open on its own (because of the force needed to drive the accelerator pump on my Cont. O-200), so that my 'redundant system' actually turned out to be TWICE as likely to fail!  So whatever you decide to do, (I'm currently using a three-spring, damped system), try to be sure that your throttle and mixture controls aren't subject to either single-point or to 'double, single-point failures'.  'Zero, single-point failures' is a lot better plan!    

Oh, and you are right about the required springs being extension, not compression springs.

[mwilli7119]

does this mean that I should use just any 'ol extension spring that fits and works or does anyone have a suggestion. It is obvious that the CS part number won't work.

thanks again

and, by the way,  I AM using the Brock bracket. I appreciate the advice on how to attach the spring. I had read about it but had forgotton. This might have saved me some serious embarrassment.

[Dan Patch]

does this mean that I should use just any 'ol extension spring that fits and works or does anyone have a suggestion. It is obvious that the CS part number won't work....

Maybe we have a 'spring expert' in the group?  My answer, FWIW, is that matching the spring fit and force to do the job is the goal, and that there isn't any magic 'super spring' that must be used in this application.  The springs that I happened to use are about the diameter of door springs, but cad plated and use finer (thinner) wire, with a modest pre-load (takes some force to begin to stretch).  I custom cut the springs to the right length to get the fit and force I needed.  My advice is to be particularly careful not to nick or 'over-bend' the spring wire if you choose to form new ends on an existing spring, because this is an obvious place to introduce a fatal 'weak spot' in an otherwise sound spring.  

Unless your throttle/mixture systems work perfectly without ANY springs installed, I personally would never rely on a single spring in this application unless I was prepared to replace it every annual as a 'life limited item' - and I probably still wouldn't do it even then.  With springs it is purely a question of 'when' not 'if' they are going to break (of course, a million hours to failure would be nice if you could count on it!).  While I absolutely, completely agree with the importance of careful, regular inspections, (better eyes probably would have spotted my bracket problem!), springs generally fail without any obvious signs of distress.  


...This might have saved me some serious embarrassment....

We all make our share of mistakes, and us 'early-timers' (old-timers?) certainly have explored lots of ways to get into trouble - some pretty obvious (with hindsight), some pretty darn subtle.  Making mistakes is life, but repeating mistakes that somebody has already 'paid the toll on in full' is painful to all concerned.

Keep the blue side up!    
SDEZ Squadron Safety Officer (retired?)