Prop Strike Damage Assessment

[Scott Todd]

Try to be objective and look at things from an engineering perspective. First of all, aluminum airplanes are VERY fragile when loaded in directions they are not intended for. It doesn't take much to really wrinkle one with a simple ground touch. For example, the wing rib dent could almost happen from someone bumping into it on a walkaround. I've seen it happen. This airplane is not showing signs of significant damage. Contrary to urban legend, it wont just fly apart in the air because something is slightly bent. Of course it should be fixed but 'hidden' damage is really hard to miss on aluminum airplanes.

I must not be looking at the same pictures as everyone else. I don't see why the entire front end has to be re-built because a motor mount is bent. That those parts off and further inspect. I suspect the material around there is in good shape and a new angle bracket can be installed.

The gear leg may have been straightened. So what? Our airplanes are designed to fly, not crash. They are not tolerant of hard landings. Pound it and bend it. Get some proper training and learn how to land. My students don't pound airplanes. But many do...The quality of current flight instruction could be a new topic for another day.

The tip wing rib is nearly a non-issue. Look at the loads out there. Theoretically they go to zero at the tip. The tip is NOT supporting the entire weight of the airplane. removing the rib and bending it all back to original shape is probably fine. Again, NO loads out there.....

The upper machine screws were not pulled into the angle. The countersinks were deep. The loads required to deform the aluminum by 'pulling' a screw head into it are unimaginable. Unless the countersink was WAY too deep, stuff would bend and break before that deformation could be seen. Looking at the backside will tell but I suspect it wasn't 'pulled' in. Put one in a press and try it.

I've also worked on and flown Sonex's that were far more damaged than this one from hard landings and off-field landings. But I've also seen pilots that see a small dent in an airplane and deem it complete scrap and would NEVER get in it. Dale mentions to check the squareness. I think it would be pretty hard to knock one out of square without a lot more visible damage but its a good starting point.

[Scott Todd]

I don't see how a 'tweaked' firewall can cause prop tracking issues. Prop tracking issues come from bent engine parts and damaged propellers. Wood props are REALLY hard to get out of track without bent turning engine parts.

I don't see where a whole lot of rivets need to be removed to replace the angle brackets. And if so, fine. Its pretty easy to drill out rivets once and put back the same size. More than once becomes an issue but this one isn't there yet.

The FAA will probably never issue a Repairman certificate for a re-build. Who cares. There are plenty of A&P's in your local EAA chapter that will be glad to help.

I think repairing and bringing something back to life can be just as rewarding, if not more, than putting new parts together. Lots of people restore airplanes instead of building new ones :)

FWIW, I'm an EAA Tech Counselor, Flight Adviser, current CFI, and retired Mechanical/Aerospace Engineer. My Onex was my third completed airplane (Kitfox and scratch built Biplane). I also restored/flew a crashed Sonex and helped re-build another one with serious landing damage. I watched an A&P friend rebuild one that was flipped over in a storm. All three of those were WAY worse than the one in question.

[Area 51%]

The upper machine screws were not pulled into the angle. The countersinks were deep.

I partially disagree. There is evidence the screws have been pulled into the holes rather than simply deep countersinks. As you stated, it would require a monumental amount of force to push/pull those fasteners through the angles. That would be the case if trying to drive the screw straight through the hole. However, the screw head is no longer parallel to the angle's surface, but has been pulled on an angle causing the head to depress at the rear, leaving witness marks in it's wake, and become "proud" in front.

[Scott Todd]

That's a good catch. I can now see how the screw has been moved or angled to one side. I didn't study the photo as well on the first pass. I jumped the gun trying to dispel a myth. The deformation casing the two parts to move against each other and dragging the screw is totally plausible. The screw being 'pulled' into the countersink and deforming the aluminum is not as much.

I did a Tech Counselor visit on an RV project recently. It was acquired from a deceased friend. The new Owners inspection revealed a rivet with an deformed shop head in the middle of the vertical fin. He was told by various sources it was un-airworthy and the skin would have to be removed. He was also told he couldn't drill out all those rivets and re-use the skin. He was asking for advice on buying a laser cut skin, making one from scratch, or possibly using a pulled rivet to replace it. He was also told a pulled rivet wouldn't be strong enough to replace the solid one. All for one deformed rivet in the middle of the fin. I think we convinced him to leave it alone. He is worried it will catastrophically fail in flight causing his airplane to disintegrate. His words. These myths and well intended, but misguided, opinions are killing GA.

[Twosblind]

Loren, thank you for that insight. Looking into the B model front end conversion a little further gave me a little bit of sticker shock. It seems like with the price of the aircraft as-is and the B model conversion I would be in the neighborhood of just buying a flying Sonex with a Jabiru already installed. I like a project but I definitely have to weigh this one.

Scott, I tend to agree that from what I see on this aircraft the damage is not extensive and likely doesn't go beyond the L brackets that the engine mount attaches to. In a previous life I was a mechanical engineer (now just a braindead stick jockey) and thinking about the load transfer that was likely absorbed through first the gear, then the prop, then the crank, then the engine mount and finally (hopefully) the L brackets and machine screws; it's difficult to imagine there was enough left over to deform the airframe itself. I could be proven completely wrong on this upon further inspection but I think it's worth the look.

I also agree that a well intentioned but overabundance of caution is hurting the hobby of GA overall. Some of the repairs made to supersonic jets with 15k hours on the airframe would draw the ire of many GA pilots at your local grass strip and yet those jets keep on just fine. Definitely good to be careful but we aren't talking about the space shuttle here either.

Thanks again for everyone's responses on both side of this debate. Still waiting to hear back from Sonex on this. I'm not sure what they'll be able to tell me from a liability standpoint but I'm definitely interested and will keep this thread updated.

[lgsievila]

Scott Todd, you are correct. What I meant to say was thrust centerline could be affected by a tweaked firewall which may or may not be a big deal. I still wonder how the wing shows damage from a prop strike and how much heat was applied to the landing gear. Really hard to be sure about anything by only seeing pictures.

[Twosblind]

So the wing was damaged when the left gear struck it as the left strut collapsed. The tire impacted the bottom of the wing. The strut was removed from the airplane and a torch was used to straighten the strut tube before it was reinstalled to allow for moving the airplane around post crash. Obviously the strut tubes are writeoffs but the heat was at least applied while the strut was removed.

[Bryan Cotton]

I am not sure I like the Sonex gear alignment procedure. If I was replacing gear legs I would probably figure out a way to set the alignment of the axle mounts with weight on the gear. You have a golden opportunity here.
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