Thread: What to check after crash Rotax912s

Hi All

Can anybody tell me what must be inspected after a crash on the 912S engine?

You would need to define this crash better.

Here are a few items to look at. Was it just a prop strike, a flip it upside down crash or a nose it straight into the ground crash. Each of these may carry more severity in hidden damage. For only a prop strike you need to pull the gear box and take out the shaft and check for cracks around the bearing opening. This means the bearing has to come out and you will destroy it by doing so. You will need to purchase at least a new bearing. You need to do a dye test on the bearing area on the gearbox. Before you do that you need to do a prop hub runout check with a dial indicator. You also do a runout on the engine crank shaft while the gear box is off.
If you buckled the nose gear then you most likely bent the engine mount against the firewall since that is its attachment point and possibly bent the engine mount directly in front of that. The mounting holes can be egged out. You need to at least inspect the firewall for cracks.
These are the bare minimums and may need to check much more. One way to check an engine mount is while the cowling is on is the spinner openings compared to the opening on the cowling still equal or is it hanging down more or off the one side. If it is a hard landing then you have to really check the main gear and you will possibly have cracks at the attachment points. There are numerous things to check.

Hi Roger. Seeing this thread brings up some questions I've had. Is there any way to check for fatigue cracking on carbon fiber structures? I am familiar with using dye-check and magnafluxing for metal structure but am curious about composite material. When a composite aircraft gets "tweaked" as the one in this thread may have, I'm curious if there's a method to look for structural damage in the composite structure such as firewall, landing gear bulkhead, etc.? I have seen some hairline cracks on a CTLS where the winglets intersect with the wings. I have also been told that cracks develop at the "living hinge" of the horizontal trim tab and the tape at this area is applied to cover these cracks since they will not cause problems but are unsightly. From what I read, these cracks are only cosmetic and will not cause structural failure. For what it's worth, the ***** also uses the skin as a hinge for it's trim tab. Any thoughts?

Dick

Composite structures are unfortuantly inhereantly more difficult to inspect for structural malfunction. The best way to test, but also to most costly is to X-Ray the structure, this is more of an industry standard on Cirrus and other larger composite sturctured aircraft but may not be the most cost effective on a CT. Another option is to sand the area and perform a visual inspection but then you can run into cosmetic issues. Eddy current testing is probably the best option but it requires special tooling which isnt extremely expensive and alot of set up time but very effective.

The coin tap test is also very effective in checking for disdonding in the sandwhiched structures.

Thanks Jeremy. I'll try to find info on eddy current testing. The coin tap test sounds interesting. I'll look into this too. I am curious about methods used for testing composite since there is a growing opportunity to buy used composite aircraft. Personally, I would not buy a used composite aircraft unless I knew the owner and/or knew the complete history of the aircraft and knew that there had been no events which might have compromised the structure. This is because I know nothing about inspection of composite structure for fatigue and defects and, on many composite aircraft, much of the inner structures are not accessible for inspection. In this case, the whole component must be replaced if suspect. A good example of this is the interior wing structure of the CT. If someone has a mishap and strikes a wing, I would imagine that the recommendation is to replace this wing because there isn't a way to inspect internal structure without destroying the wing. I might have to consider returning to college and take some classes on composite structure. I know very little about it and it looks interesting.

Dick

Hey Dick
You bring up a good point about composite structures. Inspection and repair can be quite a bit more extensive than with traditional metal structures. It seems like any certified mechanic can buck rivits and patch sheet metal but very few were ever trained to make a perfect scarf patch or performing a proper hot bond. The nice thing about composites is that they don't fatuige. With metal any time the material is warped it loses some of its strenght up until the point it finally brecks. With composite you can bend them as much as you want and they wil retain 100% of there original stenght up until the brecking point. For that reason it would of been nice to have a compostie landing gear on my CTSW rather then the Aluminum struts.

Dick,

After composite panel fabrication it is typical to check part integrity using an ultrasonic inspection looking for voids, delaminations or porosity. The same techniques can be used after an accident.

Here is a website which talks about techniques.

http://www.ndt.net/article/wcndt2008/papers/612.pdf

Thanks for the link Dave. This discussion gives me a good start to understanding composite construction.