Emergency Landing in a COZY MKIV

Folks:

For those interested, we had an experience this weekend in our COZY
MKIV when the propeller decided to proceed along a different path than
the rest of the airplane. You can read the details at:

http://www.cozybuilders.org/Desert_Center/

comments welcome.

--
Marc J. Zeitlin
http://www.cozybuilders.org/
Copyright (c) 2006

Marc J. Zeitlin wrote:
For those interested, we had an experience this weekend in our COZY
MKIV when the propeller decided to proceed along a different path than
the rest of the airplane. You can read the details at:

http://www.cozybuilders.org/Desert_Center/

comments welcome.

Congratulations for making a safe landing, and on airport ! One
question, if I could:

Even though you couldn't see behind you (?), you almost immediately
figured it was the propeller. I'm not sure many people would think of
that right away. Had you previously thought of that situation, or was
just the smoothness... and could you hear the engine still? (I'm not
sure I'd trust the gauges if they said my engine was running but I had
no thrust ;-)

Regards, Kev

Kev wrote:

Even though you couldn't see behind you (?), you almost immediately
figured it was the propeller. I'm not sure many people would think of
that right away. Had you previously thought of that situation, or was
just the smoothness... and could you hear the engine still? (I'm not
sure I'd trust the gauges if they said my engine was running but I had
no thrust ;-)

I could hear the engine, and could hear the difference as I changed
throttle settings and watched the RPM change on the tachometer. The
only thing that I could imagine that would make the engine SMOOTHER
while still running was if the prop disappeared. I don't believe that
I had ever contemplated this particular situation - the whole prop
departing. I've heard stories of prop BLADES departing (wood props,
mostly), and know that the vibration is horrendous and that shutting
down the engine as quickly as possible before it tears itself off the
firewall is paramount. So I have always thought that if vibration was
severe, shutting off the engine was task #1. But this vibration was
nowhere near this level - this was more along the lines of one spark
plug not firing, or a bit worse than that, but the whole plane was NOT
shaking.

--
Marc J. Zeitlin
http://www.cozybuilders.org/
Copyright (c) 2006

Wow, nice writeup. Glad everything worked out so that you landed safely.


--
Jack Allison
PP-ASEL-Instrument Airplane

"To become a Jedi knight, you must master a single force. To become
a private pilot you must strive to master four of them"
- Rod Machado

(Remove the obvious from address to reply via e-mail)

Great write up. Everything sure lined up nicely for an on-airport landing
and you took full advantage of it. Nicely done.

A question I have is, were the prop bolts safety wired? Even properly
torqued bolts can come loose if they're not properly safety wired. Sounds to
me like they were under torqued or not wired and worked loose just enough to
subject them to some slight bending moment, but also to the impacts of each
cylinder firing. This was happening over a fairly long period of time. The
bolts eventually fatigued and gave up the ghost. They should be, and remain,
torqued beyond any forces they will encounter.

Just my $.02 and worth every bit of it.

mike

"Marc J. Zeitlin" wrote in message
...
Folks:

For those interested, we had an experience this weekend in our COZY MKIV
when the propeller decided to proceed along a different path than the rest
of the airplane. You can read the details at:

http://www.cozybuilders.org/Desert_Center/

comments welcome.

--
Marc J. Zeitlin
http://www.cozybuilders.org/
Copyright (c) 2006

mike regish wrote
A question I have is, were the prop bolts safety wired?

Doesn't matter...I had this happen to me once...same outcome,
un-eventful landing on the runway.

With a wood prop, when cold, dry, winter sets in, the wood
shrinks away from the previous torque settings allowing the
bolts to fail in just a few minutes. All of the safety wire
in the world doesn't help.

Bob Moore
1/2 VW Powered MiniMax

I was wondering about the prop composition, too. So it was wood. Safety wire
might not help, but wood props do require regular retorqueing for just the
reason you state. And the probable reason for the bolt failures was due to
the bolts becoming undertorqued due to wood shrinkage.

mike

"Bob Moore" wrote in message
46.128...
mike regish wrote
A question I have is, were the prop bolts safety wired?

Doesn't matter...I had this happen to me once...same outcome,
un-eventful landing on the runway.

With a wood prop, when cold, dry, winter sets in, the wood
shrinks away from the previous torque settings allowing the
bolts to fail in just a few minutes. All of the safety wire
in the world doesn't help.

Bob Moore
1/2 VW Powered MiniMax

Congrats on a safe landing. Do keep us informed on actual cause. I
also have a Catto three blade prop on an RV-6A. The "undertorqued"
option seems unlikely since you no doubt can properly torque bolts.

Is there a chance that a change in humidity from your normal location
caused a change in torque?

Finding the prop could answer a lot of questions.

Ron Lee

(Ron Lee) wrote:

Congrats on a safe landing. Do keep us informed on actual cause. I
also have a Catto three blade prop on an RV-6A. The "undertorqued"
option seems unlikely since you no doubt can properly torque bolts.

Is there a chance that a change in humidity from your normal location
caused a change in torque?

Finding the prop could answer a lot of questions.

Ron Lee



Seems like others had the same idea. How long were you in a dry
climate before this event?

Ron Lee

Ron Lee wrote:

Congrats on a safe landing. Do keep us informed on actual cause.

I don't think that it will ever be possible to say absolutely, but
after a day of discussions on the COZY and canard-aviators mailing
list, and a ton of email from many experts (Burt Rutan and Mike
Melvill, both of whom I work for, included), the consensus (with which
I agree) is that the prop bolt torque was low, causing bolt failure.

For Mike Regish, yes, the bolts were safety wired, but as Bob Moore
points out, with a wood core prop that doesn't necessarily mean diddly
:-).

.... I also have a Catto three blade prop on an RV-6A. The
"undertorqued" option seems unlikely since you no doubt can
properly torque bolts.

You know, however smart, qualified, and wonderful a person may or may
not be, mistakes can be made. I know that I make them at least my
fair share. I might have screwed up in my torqueing technique; I
might have had one or two bolts that were bottomed out; I might have
had them loosen due to temperature/humidity changes; or who knows what.

Is there a chance that a change in humidity from your normal
location caused a change in torque?

Well, I've been out here in the desert for over a year now, but it's
possible that even when I THOUGHT I was testing the REAL torque, I
wasn't, since I didn't loosen them and retighten them - I just pushed
on the torque wrench.

I will heretofore be checking torque at every oil change, rather than
only at the condition inspection.

Finding the prop could answer a lot of questions.

It could, but this is the classic needle in the haystack. No roads
nearby at all. To me, it's not even remotely worth the effort to find.

--
Marc J. Zeitlin
http://www.cozybuilders.org/
Copyright (c) 2006