4 An - 4 bolts holding a jabiru on? Say it aint so....

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Comment by Neil Corella on November 5, 2010 at 4:54pm
That good stuff to know. Makes me feel better about it. Thanks for all the input.
Comment by Phill Barnes on November 5, 2010 at 4:46pm
Never ever ever ever have I heard of a Jabiru engine breaking it's AN4 bolts, has any body else??

Comment by Bob Pustell on November 5, 2010 at 3:33pm
The designers know what they are doing. AN hardware is expensive, high quality and STRONG. The bolts that hold wings on, landing gear assemblies, all kinds of things, seem smaller than intuition would make you want to be there. Intuition is not accurate. Also, weight is the enemy in aircraft, every time you everengineer something or upsize fasteners, you add weight. If you do decide to substitute a bolt other than AN in order to fit in a bigger one, be damn sure it has the same or better specs than the bolt you are replacing. As someone else pointed out, strength alone is not the only consideration, there is ductility, yield points, all sorts of stuff.

My short answer would be stick with what the designers selected.
Comment by Chris Aysen on November 5, 2010 at 1:49pm
Strength values are according to the alloy of the material. For instance 4130 sounds close to 4140 but actually 4140 is considerably more brittle because of higher carbon content. AN bolts are closer to the 4130 alloy in terms of brittleness. In other words they are more likely to bend and give versus shearing. As far as your allen head question its not the head geometry it is the alloy of the bolt. Most of the applications on bolts on these aircraft are not tension significate. They are mostly carrying yield pressures where yield resistance is key.
Comment by Chris Aysen on November 5, 2010 at 1:25pm
Stay within wall thickness limits (area where the hole actually is) it may limit a larger size bolt. I'm not familiar with Jab mounts. But I still maintain it will be OK. Just monitor the situation.
Comment by Juan Vega on November 5, 2010 at 10:17am
A t-28 trojan has a radial engine, the Cylcon 9, 86 B, a 1500 SHP beast! That engine is held in place by three bolts, AN 6!!. the same bolts holding your wings. Remember what your mom taught you" Son, it ain't the size of the shaft, its all about the quality of the substance."
Comment by Neil Corella on November 5, 2010 at 7:29am
Does an Allen head have the same strenght ?
Comment by Neil Corella on November 5, 2010 at 7:27am
I was thinking about upgrading the bolt to an AN 5. Not enough room to get a socket head because of engine mount. I think they make AN bolts with Allen heads???
Comment by Chris Aysen on November 5, 2010 at 7:06am
Each bolt has roughly 100,000 psi in tensile strenght. You'll be OK. But I know what you mean; when you think about the size of engine and vibration concerns they seem SMALL. I believe my Rotax has AN5 where the mount is screwed into engine case and AN6 where the Barry mounts are; WAY over engineered.
Comment by Max Johansson on November 5, 2010 at 2:32am
Well, if it makes you happier, a 912S on the old 701 engine mount is also held in place by just four AN4 bolts...

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