Seaplane down off Miami Beach....

I'm wondering if fitting turbine engines on the old airframes
didn't pull something loose in the wing/mount.

Turbines run a whole lot smoother than the round Pratts that were on
originally. They don't have the power pulses that radial engines have.
I'd agree with the other posters that it sounds more like a
leaking/broken fuel fitting that went bad, ignited and led to
structural failure.

wrote in message
ups.com...
I'm wondering if fitting turbine engines on the old airframes
didn't pull something loose in the wing/mount.

Turbines run a whole lot smoother than the round Pratts that were on
originally. They don't have the power pulses that radial engines have.

I assume he was referring to the increased thrust that was probably obtained
with the turbine installation, which would create higher forces on the
structure transmitting that thrust to the airframe.

Of course, one would think that in a turbine retro-fit, that structure would
be upgraded to compensate. Hopefully, that's not actually the problem.

But I don't think Otis was suggesting that turbines would cause more fatigue
due to vibration than the original engines.

Pete

I assume he was referring to the increased thrust that was probably obtained
with the turbine installation, which would create higher forces on the
structure transmitting that thrust to the airframe.

I assumed the same. The round Pratts were 550hp engines, and the STC'd
PT6A-27 engines are flat-rated to 650hp. While the increased thrust
might add stress, my assumption was the weight reduction of the
turbines and their much smoother operation might nullify the power
increase as it relates to airframe stresses. It seemed a safe
assumption that that's what he was suggesting.

wrote in message
oups.com...
I assume he was referring to the increased thrust that was probably
obtained
with the turbine installation, which would create higher forces on the
structure transmitting that thrust to the airframe.

I assumed the same.

Curious you would introduce "run a whole lot smoother" and "power pulses"
then, if you thought those issues weren't relevant. Very odd. Even
stranger that those issues were the sum total of your rebuttal to his post.

The round Pratts were 550hp engines, and the STC'd
PT6A-27 engines are flat-rated to 650hp. While the increased thrust
might add stress, my assumption was the weight reduction of the
turbines and their much smoother operation might nullify the power
increase as it relates to airframe stresses. It seemed a safe
assumption that that's what he was suggesting.

I don't see how the smoothness of the operation of the engine relates.

As far as the weight reduction goes, if anything that would exacerbate the
problem, especially if that weight reduction is permitted to be moved over
to useful load. A heavier engine will dampen the initial acceleration (a
certain amount of the thrust is applied to accelerating the engine, rather
than the airframe to which it's attached), while a heavier airframe (ie
higher useful load) will allow higher forces to occur during that initial
acceleration.

Of course, once acceleration is relatively constant, the only real
difference is the difference in thrust, but again 100 more hp certainly
translates to more acceleration, and thus more force on the airframe.

All that said, as I mentioned before, I would expect certification of the
engine to take all of that into account.

Pete

wrote:
I'm wondering if fitting turbine engines on the old airframes
didn't pull something loose in the wing/mount.

Turbines run a whole lot smoother than the round Pratts that were on
originally. They don't have the power pulses that radial engines have.

Not that they aren't subject to resonance issues. Remember the Electra?

Reports I saws this morning said that the NTSB said they
found a fatigue crack in the main spar, maybe the conversion
was not done well or the maintenance was not though enough.
I'll bet the fleet is grounded and they require immediate,
"before further flight" NDT inspections of the wings, etc.


--
James H. Macklin
ATP,CFI,A&P

--
Merry Christmas
Have a Safe and Happy New Year
Live Long and Prosper
Jim Macklin


"Ron Natalie" wrote in message
m...
| wrote:
| I'm wondering if fitting turbine engines on the old
airframes
| didn't pull something loose in the wing/mount.
|
| Turbines run a whole lot smoother than the round Pratts
that were on
| originally. They don't have the power pulses that radial
engines have.
|
| Not that they aren't subject to resonance issues.
Remember the Electra?

Jim Macklin wrote:
Reports I saws this morning said that the NTSB said they
found a fatigue crack in the main spar, maybe the conversion
was not done well or the maintenance was not though enough.
I'll bet the fleet is grounded and they require immediate,
"before further flight" NDT inspections of the wings, etc.

Chalk's has voluntarily grounded thier Mallards and is performing an exhaustive
test of the spars on one of them now. The NTSB rep voiced the opinion that age
alone would not be sufficient to cause this failure; some additional stress
would be required.

George Patterson
Coffee is only a way of stealing time that should by rights belong to
your slightly older self.

Jim Macklin wrote:
My guess is that they had a loose or broken fuel line,
caught fire and the fuel vapor exploded and the fire melted
the spar enough for it to fail.. The airplane seems to have
been very sturdy, since the fuselage is intact after the
impact.

Any information as to what altitude they were cruising at? It seems
like it would take a minute or more to soften a spar enough to fail, but
maybe the pilot wasn't aware he had a problem in time. Then again, it
may have been something else entirely. I wonder if they could have hit
a gull or something like that also and cause a problem.


Matt

Bird strikes are common, but Grumman was called the Iron
Works for a reason, they built tough airplanes. Aluminum
melts at 1100 degrees F and has lost most of its strength at
500 degrees. Kerosene fire is high heat and energy, failure
could happen in 10-15 seconds [guess].


--
James H. Macklin
ATP,CFI,A&P

--
Merry Christmas
Have a Safe and Happy New Year
Live Long and Prosper
Jim Macklin
"Matt Whiting" wrote in message
...
| Jim Macklin wrote:
| My guess is that they had a loose or broken fuel line,
| caught fire and the fuel vapor exploded and the fire
melted
| the spar enough for it to fail.. The airplane seems to
have
| been very sturdy, since the fuselage is intact after the
| impact.
|
| Any information as to what altitude they were cruising at?
It seems
| like it would take a minute or more to soften a spar
enough to fail, but
| maybe the pilot wasn't aware he had a problem in time.
Then again, it
| may have been something else entirely. I wonder if they
could have hit
| a gull or something like that also and cause a problem.
|
|
| Matt

Merry Christmas
Have a Safe and Happy New Year
Live Long and Prosper
Jim Macklin


Go **** yourself