Dodged a Bullet on my Aviation Models Extra

[jongurley]

I always pin my firewall with about 4 pins per side (1/8" dowel rod, gorilla glue in),,, never had a problem,,,

[samd]

Al,

Sure is a shame the Boeing Surplus store in Kent is no longer in business... Lots of extrusions in that place...

BTW: Every time I'm over in your area, I marvel at the crane in the shipyard... One of those things you have to see to believe. I've a history book of the shipyard with some pics of the crane when it was first put into use. The picture shows the crane picking up some big-ass shaft (probably a prop shaft out of a carrier, I suppose) with a guy standing on the shaft, hanging on to the lift sling... Have a feeling they might frown on that sort of thing, these days.

[Al Lewis]

When they first built that thing they actually hooked up a huge steel plate and had like 200 employees stand on it while they lifted it about 4 feet. You won't be seeing that trick anymore either!! LOL You're right about Boeing surplus although I worked at enough machine shops supporting them that I could probably get some extruded aircraft angle if I tried. That stuff is awesome. I keep trying to explain to people about the radius thing but they seem to think I'm kidding or crazy. LOL

[50%plane]

	Quote: Originally Posted by as722
	Actually it probably had nothing to do with the torque of the engine. Vibration kills aluminium angle, specially if it is bent alum. Albert

wrong. Vibration will work harden certian types of aluminum, resulting in cracks/failure.

	Quote: Originally Posted by samd
	Being from China and being extruded has less to do with the failure than the fact that there appears to be no inside corner radius but, rather, a sharp corner. So, you have a super high Kt combined with high cycle vibration and the resulting fatigue failure shown in Al's photos. Replace it with angle that has a decent inside corner radius (as well as a radius or chamfer on the outside corner) and the problem should go away. BTW: chop those protruding bolts short, they're just adding weight!

Not exactly. Extruded angle is a unbent peice of metal.(think molded) Handformed(i.e. bent) metal needs the proper radius. The problem in this case was poor material.

	Quote: Originally Posted by Al Lewis
	.......You're right about Boeing surplus although I worked at enough machine shops supporting them that I could probably get some extruded aircraft angle if I tried. That stuff is awesome. I keep trying to explain to people about teh radius thing but they seem to think I'm kidding or crazy. LOL

Those people are stupid.

Al, I'd just get dimentions and take it to the machine shop and have them bend you new braces at the proper radius.(much stronger than extrusion when bent cross grain)

50%

[pitviper51]

wow!! that engine was telling you something when it made you decowl for tuning! glad you found it intime!. my small plane is acting up,, but dang it i cant find nothing wrong ....
mike

[samd]

Chris,

I'm familiar with extruded material; aluminum, plastic, what have you. As for the bent aluminum you describe, this will work, after a fashion. Proper material and aging is necessary for formed ("formed" not "bent" being the terminology used in the aircraft industry) material to perform in a structural application- things the typical machine shop probably won't have. Formed parts are typically used when extrusions of a specific configuration are not available- not vice-versa.

A radius is necessary to prevent a high Kt whether the material is formed, extruded or machined- it's one of those fundemental aspects of structural design that's hard to ignore no matter how the final shape is achieved.

[Al Lewis]

Before going to work for the Government as a toolmaker and designer I made Boeing, and many other, airplane parts. I can assure you that there aren't any sharp inside corners on airplane parts. Sharp internal corners cause fracture points on anything. Extrusions used in the aircraft industry are basically forms that are pulled through progressive forms and rollers which effectively forge the material to some extent making it extremely strong. Forged aluminum alloy is stronger then steel and very flexible in comparison. This is what makes it so useful in planes. Planes flex a lot. It keeps them from breaking. In order for that to take place safely they need to be made from a strong material that can flex and return to it's original form repeatedly. Even so, stress cracks will appear in aircraft from time to time which is the reason for the inspections that Southwest evidently didn't do. Extruded aircraft angle has a generous radius in the inside corner and both outside edges. This form takes away the likelihood of stress cracks from vibration, repeated twisting, or bending. The original mounts to the DL were a prime example. They were cut from an extrusion without inside radii and therefore most of them failed. Those that haven't yet will. It's a matter of design and physics. We will now return you to your normal programming.

[Jason Michael]

Geesh Al. Mine is here in front of me on the table. The SD Yak with the ZDZ 80. Wondering if I should change out the crap aluminum stock as well straight away to avoid any mishaps.
Or at least put a few metal straps from the side of the friewall box to the front of the fire wall itself...
Good catch dude
Looking at your pictures the aluminum is on the inside of your engine box. On my plane it is on the outside of the box.
Would that make any difference.
Also anyone finds a place to get there hands on some high quality aircraft grade aluminum with an inside radii shoot me a pm and I will do the same.
There is a couple "aircraft engineers" in the club. One designed airframes. So I will put an inquiry in to them and see what they come up with.

[Al Lewis]

The manual, for what it is, calls for it on the outside however, the angle they sent my was .5" and couldn't be bolted on the outside due to interference issues with the nuts for the bolts. I would certainly reinforce yours before you have a similar problem. BTW If you manage to find angle with a radius you will have to install it on the inside as the outside corner of the engine box will hit the radius. Also my firewall was so thin it was pretty useless trying to pin it which would be a great way to go. If yours is thicker you should definately consider doing that also.

[jaguar bone]

IMHEstimation-
The alum. angles in my kit were extruded. You can tell by the sharpness of the corner angle. I recall them being lightweight for the thickeness and size they are. Had the weight of plastic actually - as I recall.

I believe the aluminum is simply a very inferior ALLOY for the job (or intentional alloy mix to achieve a lightweight part?... - - - Nah! no way. ) and or possibly the result of poor, negligent or next to nonexistent quality controls.
The die lines wearing on the surface tell me the extruding die is close to catastrophic failure ie. it's life span- FWIW.

I do promise to check mine before it goes to the back of my car. Been a while since I checked the prop bolts anyhow! Now all I need is a desire to fly the EXTRA over the YAK!

[bill hatcher]

I don't see the motor box cover in any of your pictures.

[Al Lewis]

That's because it's not there.

[Wild Thang]

The engine box of my RichModel Extra 330L is thinner than that and it's being held by just epoxy . I was thinking about puting some angle brackets on the motor box but it seems to be fine.

[Bob S]

	Quote: Originally Posted by Al Lewis
	That's because it's not there.

Did you ever have it glued in?

[anders e]

	Quote: Originally Posted by Al Lewis
	So I pull the cowl off of my Aviation Models Extra 260 to do some engine tuning on it's DL-50 and just happen to notice this!! Turns out the POS aluminum angle supplied with the plane wasn't strong enough for the torque of the DL. No doubt that one more flight would have pulled the firewall out. I went to the LHS and got some thicker 3/4" angle and replaced it. Whew!!! That was a close one.

i also had that problem. 30% with da-50. the top was also on the engine box.engine pulled the firewall off. i was lucky and landed the plane perfectly.
i replaced it with thicker alu.