Today's Message Index:
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1. 07:13 AM - Re: Re: Hydraulic lock (Jill Gernetzke)
2. 07:25 AM - Yk 52 for sale (George Coy)
Message 1
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| Subject: | RE: Hydraulic lock |
Mark & Group,
What is critical in assessing the potential for damage to the accessory
shaft on a prop strike is the rate of deceleration. If you have a 3-bladed
metal Hartzell prop on your plane and hit a fire hydrant at idle, the
potential for damage is much greater than a high speed pass down the runway,
shave the tips of the blades on a wood or composite prop.
>From the AI-14RA Engine Maintenance Manual:
"In case of propeller blade damage/broken or cracked/ at distance exceeding
1m/3.3 ft./ from the engine axis without sharp braking due to striking
against ground irregularities - the engine may be used after replacement of
propeller. In other cases send the engine to manufacturing plant or
specialized workshop for inspection."
Bear in mind, this is referring to the wood, composite Wilga blades. The
AI-14 also has a weaker planetary system than the M-14P.
And then you have the Service Bulletin issued by OKBM:
http://www.termikas.com/engines/M-14P/direktyva_angl.jpg (One must ask
what motivated the factory to issue this bulletin. The repair factory in
Shakhty did most of the overhauls on the M-14P, not OKBM.)
Have a great weekend, group!
Jill
________________________________ Message 7
_____________________________________
Time: 12:02:54 PM PST US
Subject: RE: Yak-List: RE: Hydraulic lock
From: "Bitterlich, Mark G CIV NAVAIR, WD" <mark.bitterlich@navy.mil>
Good answer again Jill. Thank you.
I wrote a separate message about an engine that had a prop strike when the
left gear collapsed after touch-down. It took off after about a foot on
either end of the stock prop was ground off, then flew around the pattern
and landed. The engine was at idle, and the pilot stated that he never even
knew it happened until after he finally landed. I.E.
No sudden stop.
The engine has since had about 300 hours put on it with no problem
what-so-ever. Which is not to say it was not inspected, it was.
However, it was not totally torn down, only partially. Some of the
decisions were based on what your company published some time ago concerning
prop strikes based on the training they had received in Russia. It seems it
turned out to be the proper decision based on good information.
The problem with replacing the engine is that you really don't know what
you're going to end up with there either. Hope for the best, but train for
the worst as they say.
In the end, my opinion is that there is a term called "PROP STRIKE!"
that we try to quantify into something that requires an exact action, no
matter what. This is what the FAA leans towards and if specific information
on the engine is unknown, they will also tend to apply information made for
other engines that they consider similar. This is of course in many cases
totally incorrect. Is the engine geared? What about specific weak points
(Accessory Shaft for instance)? These are not the same from engine type to
engine type even if they do both happen
to be "Radials". So EVERY case is unique and the actions taken can
vary within a fairly large margin, insurance companies and liabilities
excepted.
The other take-away from discussions like this is to realize that the FAA
reads the YAK LIST. This is not a guess. I know it for a fact. I was
confronted by an FAA Inspector for what I said on this list one time and
while some may say "so what, FREE SPEECH!", the fact is that when confronted
by these guys, it is not a fun experience no matter how much "in the right"
you might happen to be. Giving credit where credit is due, I've eventually
seen them make some good decisions, but the time span in the interim is not
something anyone wants to experience.
So while sharing good information is what this list is all about, I
would offer this one tiny suggestion: "WALLS HAVE EARS" Be careful
not to make arguments in public that could turn around and bite you in the
tail later on. Of course this is the "Pot calling the Kettle Black", but
hey, I'm learning.
Mark
-----Original Message-----
From: owner-yak-list-server@matronics.com
[mailto:owner-yak-list-server@matronics.com] On Behalf Of Jill Gernetzke
Sent: Friday, April 26, 2013 13:29
Subject: Yak-List: RE: Hydraulic lock
Additionally, the calculations for torque at full power are 641 ft/lbs on
the crankshaft and 936 ft/lbs on the prop shaft. (Double-check of the
calculations are welcome.) The numbers in the previous post were for a
typical prop strike which is at near idle on an "Oh, %*&$!" gear up landing.
We have had some sudden stoppage prop strikes where we fully expected damage
to the accessory shaft and there was no damage. This comes back to design
limit loads on the individual components and how much over those limits the
parts are engineered to. I do not have that engineering data.
Mark, the prop strike teardown boils down to the insurance companies and
also, the ultimate peace of mind of the owner and subsequent buyers of the
aircraft. This is a judgment call; which we handle on a case by case basis.
For practical discussion, much of what dictates the prop strike teardown
-
in the U.S. - is liability.
Jill
-----Original Message-----
From: owner-yak-list-server@matronics.com
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Sent: Thursday, April 25, 2013 12:02 AM
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Today's Message Index:
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1. 08:24 AM - Re: Re: Re: Hydraulic Lock (Bitterlich, Mark G CIV
NAVAIR, WD)
________________________________ Message 1
_____________________________________
Time: 08:24:17 AM PST US
Subject: RE: Yak-List: Re: Re: Hydraulic Lock
From: "Bitterlich, Mark G CIV NAVAIR, WD" <mark.bitterlich@navy.mil>
Actually this is very good information to keep in mind, and I am going to
chew on the physics of that answer for a day or two. It poses a very
interesting study in the stresses involved and should make for a rather
intense dinner table debate! :-) (Not you, my engineering friends!)
Thanks for writing back Jill.
So given this information, what is the advice of M14P.com regarding prop
strikes and what should be done to the engine afterwards?
Mark
-----Original Message-----
From: owner-yak-list-server@matronics.com
[mailto:owner-yak-list-server@matronics.com] On Behalf Of Jill Gernetzke
Sent: Tuesday, April 23, 2013 16:56
Subject: Yak-List: Re: Re: Hydraulic Lock
Good feedback, Mark.
Most prop strikes occur with wood composite or carbon fiber blades. (We
haven't had a prop strike teardown with a metal prop, yet.) The inertia of
energy is absorbed by the blades disintegrating or being shaved off.
I agree with your assessment of a hydraulic lock on startup, but not when
the engine fires and it pulls fuel or oil in from the intake tubes. If it
fires, there is a good likelihood that the accessory shaft will twist.
At landing speed, the aircraft travels 3.5 feet for each blade in contact
with the ground at initial point of contact. As the engine slows, this
increases. Consequently, the rearward deflection of a very thin blade
exceeds the rotational shearing. Additionally, the reduction of blade
length per rotation with a normal flare landing is less than a tenth of an
inch. In other words, the wood fails well before any engine parts are
stressed to the +400 foot/lbs of torque design load.
Jill
Message 2
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We have a very low time 1993 Yak-52 available that has lived its whole life
in the USA. Contact me off list.
George.coy@gmail.com
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