Crash and Lessons Learned

[Bill Rusk]

Folks

We had a mishap recently and I would like to take a moment to try to share some lessons learned for the benefit of the community. This is a picture of the aircraft post mishap. All things considered the damage is not all that bad. There was no post accident fire and both occupants got out on their own power with just bruises and a few cuts.

We have discussed on this site the benefit of "X" bracing the firewall so that it does not collapse and crush the front seat pilots feet.
The Stock Supercub has one diagonal tube in the bay aft of the firewall going from the top of the firewall down to the gear attach cluster as in this photo.....

The modification being made on most of the experimental cubs being built by Backcountry and by Javron looks like this.....

You can see that we have added an additional diagonal brace tube from the bottom of the firewall up to the cluster where the instrument panel sits. This extra brace helps keep the firewall from collapsing upwards possibly trapping the pilots feet and or breaking his ankles. The Backcountry kits do not weld these tubes together (they have about a 3/8ths inch gap where they cross). I have asked Jay at Javron to put a spacer in and weld these tubes together at the junction where they meet. This will add very little weight and will significantly strengthen this brace. He will be doing this on all future kits that have this firewall "X" installed which I highly recommend.
In the picture below you can clearly see where the firewall tubing is buckled and the collapse has started. This is from the mishap aircraft above.

Unfortunately I do not know for any STC for this mod for the certified Cubs. The Airframes Alaska fuselages and the Univair fuselages do not have this brace. It would have to be done by 337 but if I were rebuilding a Cub this is a mod I would strongly recommend.


Next topic

The mishap cub had Atlee Dodge 30.5 Gallon tanks. These tanks are significantly larger than standard and the top of the tank is used as the top of the wing. As a result the tank is attached directly to the wing spars. If there is ANY distortion of the wing in a crash it will likely cause the tank to split open as in this photo.

Both occupants from the mishap were soaked in fuel after the mishap. Thank the Lord there was no post impact fire. I was not aware of this characteristic of these tanks. I would strongly recommend that you consider changing these tanks out if you have them. Any tank is subject to rupture in a mishap but it is my opinion that these are far more likely to split along the seams and spill fuel into the cockpit area.

Hope this helps.

Bill

 

[mike mcs repair]

there's usually fuel leaks at wing root in big crash like that.... that's why you MUST move the electrical OUT OF WING ROOT... as that wing rotates down(as shown), if there are breakers there the compresion member or butt rib will be making sparks..

atlee tanks REST on top of spars on a channel, held down by a couple weak clamps, just to keep tank there... they will give in normal use.... a crash is NOT normal use

your bushing idea is good, but making the tubes intersect would be many times stronger... prolly get away with a smaller tube then too....
that said, NEVER have I installed these brace tubes or had it requested......

you could add tubes all over and yes it WILL be stronger.... but somewhere you must stop.... or you will have a TANK and not a PLANE....

 

[Iflylower]

Mike, your scaring me on the wing root electrics. I gave a lot of thought on this with my build. Any creative ideas on a barrier around the lectrics to seal them? I tried for a shrink type mat or tape, but came up empty so far.

Bill, I did the same welded tubes on my frame. Heard about some crushed legs in accidents. I sure don't want a tank, or crushed legs... I like mikes smaller tubes and crossed into the other diagonals idea. It'd make the interior panels fit slightly better too.

 

[Bugs66]

For electrics, do your best to kill the master before going in.

 

[cubpilot2]

I've been installing these tubes for a few years now, as discussed in the following.

http://www.supercub.org/forum/showthread.php?21440-Supercub-quot-crashworthiness-quot-improvements

I think that there are several out there now as I have sent several drawings litterally arround the world about it, but have not heard of any accident reports from anyone that had them; which is a good thing. I am one to sacrifice a couple of pounds for a good portion of added safety.... heavy rear struts, tie downs, heavy gear etc. Maybe that is why I convinced myself that the 180 conversion was also the "right thing" for me. (to drag arround all of the added safety features)

Incedently at the time of the first installation my PMI said that it was a toss up as to being a minor change (since it did not intersect the other diagonal tube and affect its strength). The FA committee at the time was undecided so he just field approved it anyway to settle the issue.

 

[mike mcs repair]

Mike, your scaring me on the wing root electrics. I gave a lot of thought on this with my build. Any creative ideas on a barrier around the lectrics to seal them? I tried for a shrink type mat or tape, but came up empty so far.

rubber baffle material is what i add to existing ones.. wrap the compression member with it.... and try to do some on spar if its gonna connect....

 

[skywagon8a]

My Backcountry fuselage was done differently than that which is shown above. Instead of the "V", which is in the center of the first station at the firewall, there is an "X" which connects the 4 engine mount attach bushings. The extra side tube is also installed. I have often wondered why the base of the "V" is centered on the cross tube as there is nothing else joined there to stabilize that cluster. The extra weight to form the "X" would only be that of about a foot of tubing. The "X" does not interfere with the rudder pedal travel as the tube passes just below the "T" on the pedal. The only objection that I have to the "X" is that it precludes the installation of a prop governor if one was desired.

 

[sj]

Bill, very good thread and observations. I agree with Mike on the electrics for sure. I had a small fuel leak in the wing root of my first cub that had the electrics up there, and when I pulled the panel out to get at the leak and saw the mouse chewed wires, etc, YIKES! I have heard that electricity is almost always the start of a post impact fire and in the case of this accident, there was really no time to consider flipping the master - especially if it was not right in front of you.

I have always said that hotrod lightweight cubs are great fun to fly, but I would never want to crash in one. I'll take my fat daddy-o cub any day instead. A 20% TO/LD performance hit (or whatever it is) is worth the peace of mind to me.

sj

 

[tempdoug]

guys:
Just got word from the Anchorage FSDO today on my application for a field approving the two added "compression members" to the front bulkhead.
In a nutshell they (more then one inspector) reviewed the paperwork and came to the consensus that this could be done as a "minor change".
Basically since the tubes do not intersect the existing tubing; it does not "appreciably" effect the structural characteristics.
They are to send me a written response of their evaluation which will be included as part of the aircraft records. (and mine, for future reference).
Can't get any easier then that!!!
I am all smiles on this; as many can maybe be "a bit safer" without all of the paperwork worries.

Please be advised that this modification has not been functionally tested nor do I ever intend to! Therefore the exact benefits may be unknown. I advise it only because it looks like the "right thing" to do. We can only hope for the best. Kind of like insurance and ELTs. You have it but never plan to use

 

[tempdoug]

theres 2 threads in the library on this website and this was a quote there. I dont know how to bring up the 2 so they could just be clicked. I tried it and did it wrong again. very good reads. the threads are 21440 and 19905. Sure not trying to infringe here it just adds to this, hope nobody minds. great reminders.

 

[foxflyer]

I would like to add that the reason anyone walked away from this was because of superb piloting after the initial lack of. Had the pilot tried to lift the stalled wing with the stick this would have gotten really ugly. Instead he used the rudder allowing the oily side to stay down. The starboard wing took most of the energy of the crash and it wasn't until the last second was he able to pick it up. All the tubing in the world wouldn't have helped if they would have impacted in a nose down or upside down attitude.

I think any wing tank would have ruptured in this type of impact.

I hope I haven't overstepped any bounds with this post. The biggest lesson I learned from this is that the skills that the pilot used to save himself have to be reflexive. There wasn't enough time to think or enough altitude to screwup. More than likely the reason they walked from this one was the pilot reacted correctly to the situation with little time to think. I think I'm going to go out and do some falling leaf stalls.

 

[tempdoug]

Bill, if you didnt want to weld to the piper designed structural tube could you wrap a piece of 1/4 inch cable around the center of the x and nicopress it?

 

[Bill Rusk]

Well ...it might help a little. You really don't want to make a std joint there because in order to do that you would have to bow one of the tubes outward to intersect the other tube and that would pretty much eliminate most of the straight line brace you are trying to achieve. The two tubes do not normally touch due to the geometry of the front end. You must put a spacer between the tubes in order to lock them together and keep them straight. If you put in a spacer then wrapped the X in cable it would help some to prevent the diagonal tubes from buckling. The idea is to reduce the length of the beam. It is easier to break a 12" popsicle stick than it is a 4" piece. Same concept.

Bill

 

[OLDCROWE]

A crash has energy that has to be dissipated. I think we would all support the moving a known crumple zone away from the pilots feet however remember you can't eliminate all crumple so it becomes relocated or distributed elsewhere. The questions becomes will that energy find release in some other significant frame member and what harm will that cause or will there be many little failures for a best case in crash energy dissipation. Unfortunately, without significant analysis there is really only one way to really determine where it ultimately moves to in this type of crash.

From the pictures and a little study I like the extra tube.

 

[Fortysix12]

I"ve always had this idea of a fuel tank bag. Would add weight but contain an aluminum fuel tank compromise. Kind of like the Indy Car fuel tank mentality although as seen this weekend has it's limits. But rubber cells would be more forgiving. If it was possible to zip up a tank inside a tough synthetic bag and hose clamps around the cross tube. Move the sight gauges somewhere else, something like the Decathalon. everything outside the cockpit. Don't most severe
Super Crashes end in fire?

 

[fly_cubs]

As Bill said both the occupants of this crash were soaked in fuel- Snert and I attended to one of the pilots until help arrived and every inch of his clothing was soaked. Fuel poured from the wings and the smell of Avgas at the crash site was still very strong after the aircraft was moved.

One thing we discussed in our de-brief at the scene was the turning off of the master switch. In my mind doing so was logical- not having the electrics on with fuel and fumes everywhere would be much safer. I can even clearly remember someone pulling the broken windshield apart to get access to the switch to turn it off. Someone later noted that this was probably NOT the best practice given that the switch could arc and given the massive amount of fuel around- this less than ideal situation could have resulted in a major tragedy.

Thoughts on how to handle the electrical element of a crash when fuel spillage involved? Is this a d*mned if you do and d*mned if you don't sort of situation?

 

[skywagon8a]

Was the electrical control panel in this airplane mounted on the wing root with the original battery/fuse switch arrangement? If so, turning that switch off would still have electricity at the battery side of the switch. The electrical threat would have still existed.

 

[jgerard]

What about under seat battery installations. The seat was bent up a bit and I could see where in some installations it wouldn't take much distortion for the contacts of the battery or the solenoids under the seat to arc out and make a spark. Is it mandatory with the under-seat batt installations to remove the springs and use the alum seat bottom?

Jason

 

[mongo]

I"ve always had this idea of a fuel tank bag. Would add weight but contain an aluminum fuel tank compromise. Kind of like the Indy Car fuel tank mentality although as seen this weekend has it's limits. But rubber cells would be more forgiving. If it was possible to zip up a tank inside a tough synthetic bag and hose clamps around the cross tube. Move the sight gauges somewhere else, something like the Decathalon. everything outside the cockpit. Don't most severe
Super Crashes end in fire?

No indycar had a fuel cell burst this weekend and the have never had one since I have been involved, the fires where due to oil system swirl pots getting ripped off.

Sent from my HTC Evo using Tapatalk

 

[DW]

I want to start by thanking everyone at the incident for there quick responce and help, as mentioned above we were very luck not to have a fire. The electrical controls were in the wing root. The left wing looked to be undamaged but the flexing of it caused the tank to split at the seem, in my opinion the stock tank in its straps would not have ruptured. As for the extra support in the firewall area Oldcrowe has a good point but for me I like the extra firewall brace this aircraft did not have it and the bottom of the firewall did crush inward some and my left foot is still a little sore. That all being said Mr. Piper designed a great airplane as is. Again I want to thank everyone at the incident and on this site for there support, and my apologies for putting anyone at the incident in harms way.

DW

 

[kevin]

DW, I did not know this was you. Glad you are OK.

 

[BritishCubBloke]

Ditto. Glad you're OK, DW.

 

[On Patrol]

DW,
I thought you said it was our secret?
FMD

 

[mike mcs repair]

... Is it mandatory with the under-seat batt installations to remove the springs and use the alum seat bottom?

Jason

putting a lid in place of springs is NOT mandatory or even mentioned that i know of(maybe now??)... BUT it should be mandatory... personally I know of one inflight fire caused by seat spring being able to get down there and make contact.... you would be crazy NOT to have a lid instead of springs....

 

[Steve Pierce]

Simply putting rubber boots over the terminals is a good idea in my opinion.

 

[180Marty]

the fires where due to oil system swirl pots getting ripped off.

I wondered about the visible fire. I didn't think ethanol would look like what I saw on TV.

 

[Bill Ingerson]

Glad your okay D.W and your passenger. I would have gotten away from the plane if I could have and just left the electrical switches alone. What about a float plane with a door on the left side ? Would it even be weaker than stock ?



Bill

 

[Gordon Misch]

Ouch! Sorry Dennis - - and glad you're alright!

 

[mike mcs repair]

...The left wing looked to be undamaged but...

DW

glad you are ok...

make sure you pull the left wing front and rear wing attach blocks of wing spar and check for cracks in blocks and elongated hole in spar where metal bushing goes through for wing attach bolt, very important once wing has rotated all the way down like that or hit ground.... croswinds stol sells a kit to fix it if hole is screwed up in spar without having to replace spars....

 

[Steve Pierce]

These are pretty tough airplanes and sometimes the good Lord is not ready for us. When I from 100 feet in my Clipper the airplane was lawn darted into the ground. I saw the fuel running out of the wing and onto the ground towards the engine. I switched everything off not thinking about the 12 gallons in the nose tank. Years later when I got the salvage back I found an engine mount tube through the tank which dumped all that fuel onto the engine. Having been in a few more mishaps than I care to remember I can attest to the fact that wings and fuselages absorb a whole lot of energy.