Most crash worthy Sonex build?

[ryoder]

Thanks for the info.
Yeah if I build one it would be a quick build. I am more interested in flying and fitting it with the look and avionics I want than fabricating parts.

[fastj22]

The cause of engine out? I had wired something too close to a hot point in the engine that was critical. Once the wire melted and created a short, the engine quit. I encourage everyone to get a second set of eyes on your project to see things you might overlook.

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Michael Crowder
ex Sonex N293SX

Michael, thanks for the info. I've been waiting for the NTSB to publish the findings. From your signature line, was your Jab3300 electronic fuel injected? Was that the wire that shorted?

[sonex293]

Yes, the engine is injected. The crank position sensor shorted. The engine will have a backup before putting it in a new project.

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Michael


Sent from my Nexus 7 using Tapatalk

[radfordc]

Here is an example of how the titanium gear absorbs crash energy. I got off the runway into rough terrain and ended up on the nose. The gear leg took most of the damage with just a little dented aluminum on the wing tips. It took a 50 ton press to straighten the leg. The plane was flying again in two weeks.

gear leg.JPG (420.98 KiB) Viewed 5233 times

Here is another example. Engine out on final and couldn't reach the runway. Ploughed into soft muddy ground and took both axles off the ends of the gear legs. The pilot walked away without a scratch. Can't say the same about the plane.

[tonyr]

I don't know that the seat, as designed, would collapse to the floor. There are a lot of rivets to shear or edges to tear out. I also think you would see the bottom floor collapse up toward the pan if you had gotten far enough to flatten the gear.

The thing that everyone seems to miss is that the space under the seat is not clear to the floor. There are the pieces of channel that run directly under your coccyx. The lowered seat mod can bottom out on that channel if its down too far, as I found out. That is a greater risk to the spine in a vertical deacceleration. So much so, I raised the seat sling up about 20mm and I have placed some styrofoam blocks under the seat area either side of the channel to create a crush zone, and combine this with some decent foam cushioning on the seat to provide some spinal protection. Might be a fire hazard, but we seem to have more heavy landings and controlled crashes than cockpit fires in these aircraft. I'd rather protect my spine in the first instance.
Cheers

Tony #813
paint 'n' polish to go, then inspection

[vigilant104]

There are the pieces of channel that run directly under your coccyx. The lowered seat mod can bottom out on that channel if its down too far, as I found out. That is a greater risk to the spine in a vertical deacceleration. So much so, I raised the seat sling up about 20mm and I have placed some styrofoam blocks under the seat area either side of the channel to create a crush zone, and combine this with some decent foam cushioning on the seat to provide some spinal protection.

Tony,
Have you taken a look at the force needed to break the seat pan free so that it can collapse onto/take advantage of the styrofoam blocks underneath? For example, if it turns out that it takes 50Gs to cause the rivets to rip through/shear off, then the spinal damage will already have occurred before the styrofoam could come into play. You might need to increase the rivet spacing, etc. Building the seat pan low to begin with and putting a thicker dense viscoelastic foam pad on top would seem to be a more reliable approach for handling vertical deceleration loads (and also offers the opportunity to gain more headroom later if a subsequent buyer/owner/pilot needs it). For what it is worth . . .

[tonyr]

Tony,
Have you taken a look at the force needed to break the seat pan free so that it can collapse onto/take advantage of the styrofoam blocks underneath? For example, if it turns out that it takes 50Gs to cause the rivets to rip through/shear off, then the spinal damage will already have occurred before the styrofoam could come into play.

As the the seat pan is only .025" sheet, it has a tendancy to will bow towards the floor under your bum. With the lowered seat mod this deflection can be significant as the lower rear bend is around 40mm below the hinge line. If you concentrate weight at the bum line, i.e. by standing on the seat along the rear pan, it will pull the lower back edge forward and pull down on the spar end flattening out the bends in the seat until the seat contacts the channels. I was intending to arrange the blocks so that they were touching the underside of the seat when occupied.
The standard seat would be more resistant to this effect as the lower bend is on the hinge line.
I would also expect the hinge loops along the lower edge, and maybe the spar to deform before rivets let go.
Cheers T