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Matt Throckmorton's wrecked F1 Rocket

vlittle

Well Known Member
I noticed the bad news on Matt's site today http://www.docthrock.com/.

Looks like no injuries, but the aircraft was written off. Oil line let loose, followed by a quick landing and nose over/prop strike.

What I really took away from this is his engine tear-down. In particular, how his low time, 2-3 year old engine had unrepairable camshaft corrosion.

The corrosion did not cause his engine failure, but it's pretty clear that at some point it would have become a problem.

I hope the engine folks can chime in here. When I buy my IO540, I can't tolerate this kind of latent problem!

Vern
 
A real shame!

Another plugs for an engine dehydrator me thinks.

I didn't fully get how they worked...But when I realised that burning the fuel is what makes the water vapour..then water vapour at very high temp ends up in the crankcase (blowby). as it cools it will make a LOT of condensation..which then drips on the camshaft.

pushing minus 40F dewpoint air will mop it up in no time however.

Either that or fly it every other day will keep everything oiled up


Frank
 
What puzzles me....

...is the fact that the crankshaft bolt was loose and backed out by 5 threads, according to his web site. That couldn't have happened on the noseover....seems like it was a problem that just hadn't manifested itself yet.

The loss of oil and the resultant feathering of the blades is what brought the airplane down, according to him.

Regards,
 
Internal engine corrosion prevention

Another plugs for an engine dehydrator me thinks.

I didn't fully get how they worked...But when I realized that burning the fuel is what makes the water vapor..then water vapor at very high temp ends up in the crankcase (blow-by). as it cools it will make a LOT of condensation..which then drips on the camshaft.

pushing minus 40F dew point air will mop it up in no time however.

Either that or fly it every other day will keep everything oiled up


Frank

Lots of info on engine pickling on this recent thread. See

http://www.vansairforce.com/community/showthread.php?t=48554

Charlie Kuss
 
Agreed Pierre, from the information he provided I don't see how that would be related to the oil line. Fortunately the airplane suffered the worst and everyone was able to walk away, but it looks like the issue with the bolt wasn't too much further in the future.

From this picture he posted, it appears the head was rubbing on something, also he commented about the pin shearing off in the gear the bolt was holding on.
IMGP0362.JPG


Sorry to hear Matt....Glad you are alright!
 
I'm thinking that the dowel pin sheared and allowed the gear to turn, loosening the bolt. Not that the bolt was already loose.

For instance if the dowel could have been magically removed and the gear turned in the direction that would cause loosening of the bolt; then the bolt would back out as the gear continued to turn.

So, I'm thinking something stopped the crank and the gear kept rotating briefly.
 
Consider the direction of rotation. Viewed from the pilot's perspective, the crank turns clockwise. If the crank stops suddenly, the inertia of the other rotating components tries to continue turning the crank gear clockwise....which shears the pin and tightens the bolt.

Two possibilities, given the evidence.

One, the bolt was already backing out before the accident. (Doc said the lock tab was "loose", whatever that means.) The sudden stoppage popped the gear out of its recess, and side load from the cam gear bent the bolt.

More likely, the internal crank threads were pulled when the pin sheared at stoppage and the gear tightened the bolt. When the threads gave way, the gear got cocked by the side load from the cam gear, which further pulled and bent the bolt. Might seem a little far-fetched, but consider how the bolt was thread-locked enough to break when he tried to remove it.

Crank gear mystery aside, I hope the lesson everyone takes away is that a dial indicator on the crank flange tells you zip about the accessory end after a sudden stoppage.
 
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OK, I might be missing something here...

The picture of the gear with the retainer next to it suggests that the retainer was improperly used. The tabs are both bent in the same direction. Shouldn't one be down and one be up (thus keeping the bolt from turning)?

Even if you make the assumption that the tabs were bent to remove the bolt, I would expect that one tab would be bent "down" and the other straight out to the side.

Just a thought.
 
It looks fine to me.. one tab is bent down (the one "facing" you) and two ears are the tabs that are bent up (they seem to have been bent up at some point, before the bolt head turned)...
 
The issue of the crank gear, bolt and drive dowel is a situation that can occur with a prop strike. It is the subject of an FAA AD note and a supporting Lycoming Service Bulletin that requires inspection and or replacement of these items after a prop strike, because damage to these components can happen in varying degrees, up to what occurred in this engine, after a sudden stoppage.
The AD originally came out as 91-14-22 and was revised to this AD in 2004:
http://www.airweb.faa.gov/Regulatory_and_Guidance_Library/rgAD.nsf/0/9fa5e5f8683a0a4686256e9b004bc295/$FILE/041014.pdf
Good Luck,
Mahlon
"The opinions and information provided in this and all of my posts are hopefully helpful to you. Please use the information provided responsibly and at your own risk."
 
Back to the original question.... I don't think that cam was anywhere near failure given what I saw. It had a couple of pits, but not widespread pitting. Why it had those pits is not explainable to me, but I doubt they happened after he started flying... Improper storage prior to first engine start perhaps, or perhaps defective part.
 
Glide Ratio

Hard to say what happened at this point, bottom line is be ready. Matt did a nice job of flying his Rocket in an emergency and walked away. Having had three engine failures in single engine aircraft in my lifetime (one in the F-16) and three successful landings, I can't stress the importance enough of practicing flameout landing procedures. I have been practicing "FO's" in my HR2 routinely for three years and have gathered some pretty good data on gliding in both my RV4 and the HR2. A couple of years ago I wrote a blurb for Van's RV8R newsletter that shared my thoughts. Not to bore you incessantly, but here it is FYI.

Smokey
HR2

“FLY THE @#$%^&* AIRPLANE!”
Rob “Smokey” Ray

As anyone who has read an NTSB accident report or seen any TV news footage of an aircraft crash knows, pilot error is a recurring theme.
In the military, we are privy to the exploits of our less than fortunate comrades who have “screwed the pooch, packed it in, bought the farm” or suffer other, less printable, fates. We spend hours during pilot meetings listening to post-accident investigative hoopla on how our poor buddy had committed an act of buffoonery of royal proportions. The MP or mishap pilot, as he or she is always referred to, gets hammered mercilessly by the examining board almost every time. Having been the brunt of a USAF post Class A mishap investigation (Class A denotes sover 1 million dollars damage) myself, I can assure you no stone is left unturned. In my case the board concluded: “The failure of a magnesium alloy restraining band surrounding the afterburner section of the GE F110 engine in Capt Ray’s F-16C contributed to the failure and subsequent in-flight fire and ensuing forced flameout landing”. Most MPs get tagged
with the pilot error label, and why not? In most cases the board is right: the cause of most aircraft crashes is the nut behind the
stick. First, realize that it doesn’t matter what type aircraft you are in, when an emergency raises its ugly head, your posterior is on the line, period. For us RV types we have emergencies just like everybody else, it’s the nature of operating mechanical flying devices. Highly effi- cient, cool looking, fun machines, but flying devices nonetheless. So how do we in the RV world apply the techniques, lessons and hand to stick applications of in-flight emergencies (IFE) to our little world? The same way the big boys handle emergencies in multi-million dollar fighter aircraft with such aplomb. Practice, my brothers, practice. The General who quoted that “The more you sweat in peacetime, the less you bleed in war” was correct, practice makes perfect. In the military and professional civilian world, simulators are used to “dial a disaster” for hapless pilots in a con- trolled environment. The simulator instructors can simu- late emergencies with such accuracy that in cases of real emergencies the successful pilots claimed that what they did was exactly like what they trained in the simulator. (The exception is combat. When that first large caliber round or missile flies by your canopy, all that training goes right out the window. Been there, done that.)
When the proverbial feces hits the fan an old instructor of mine once told me “wind the clock” until you can’t stand it anymore, then think about doing some- thing. In simulated IFEs the first step is FTFA or Fly the @#$%^ Airplane! Following these you can either pull out a checklist, have your wingman or somebody on the ground pull one out, follow steps therein and get home safely.
The actual steps are:

Maintain Aircraft Control
Analyze the situation
Take the appropriate action
Maintain situational awareness


The one item above left out is “don’t panic”. There is nothing short of an engine failure on takeoff or in-flight fire that requires you to go into “auto flail” to handle the problem. Even then, more people than not stall/spin trying to turn around or land too fast. Bob Hoover once said “fly the airplane as far into the crash as possible”. In a fighter, you do all the important stuff without looking and later your wingman backs you up to make sure appro- priate items were acted upon In RVs you can practice all kinds of IFE in your own cockpit. You may not have a wing- man, but you probably have friends who fly RVs. Use them. In the safety of your own living room, hangar or RV cockpit (or in my case, Rocket…traitor!) you can go through the steps of any given emergency situation. Know your aircraft systems well, do a blindfold cockpit check once in awhile and know where all the switches are without looking. When you are totally familiar, have your friends be the IFE instructor and yell out simulated emergencies. While they make sound effects, wry comments and swipe beverages from your fridge, you can flail away at solving the problem. It’s all good, every second spent thinking about disaster helps when a real one emerges. This “game” makes everyone present a better pilot, improves safety and gives the NTSB one less opportunity for to conclude RV pilot error after a mishap.

Practice, my brothers, practice!


 
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