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Yak 55 parts and... Final Prop Strike comments

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jill(at)m-14p.com
Guest

Posted: Thu Jul 18, 2013 8:45 am Post subject: Yak 55 parts and... Final Prop Strike comments

Group,



I have been offered a set of NEW Yak 55 ailerons and a rudder: available for

sale.  If you want to see a picture, go to our M-14P, Inc. Facebook page or

contact me offlist.



We wanted to share our final thoughts on the commentary about prop strikes

and engine teardowns.  There is conjecture about all manner of hidden

damage. Most people do not want to take the time to understand the forces,

loads and physics on the engine and the different outcomes. There are a

number of things we can say with some certainty, drawing from over 50 years

of collective experience on M-14Ps (80 years of collective radial engine

experience): two of us being  graduates of the M-14P factory overhaul

school, visits to the Shakhty overhaul factory, experience in performing

teardowns for prop strikes, hydraulic lock repairs or overhauls of 40 -50

AI-14, Housai and M-14 engines.  This is what we do, day in and day out. 

The only nosecase damage we have seen, was on an AI-14 and an M-14P that had

link rods fail in flight; which sheared off the propeller shafts.  The AI-14

has 3 planet gears, the M-14P has 6.  The first thing that is affected, if

anything, is always a rotation of the rear cheekplate on the crankshaft.

This produces a wobble in the front of the crankshaft which jams the cam

drive gear into the idler gear and breaks teeth. (We have had one Housai

engine that popped the camplate up when the nosecase was removed.)  Because

the crankshaft is held by 3 bearings, all of which have some side clearance,

it is simply not possible to accurately measure the runout with the

crankshaft held in those bearings. The runout limit at the end of the

crankshaft is .03mm. The runout would be absorbed by the bearing clearances,

if the crankshaft is measured in the engine. The crankshaft has to be

removed from the engine and checked with a dial gauge in v-blocks.

We are aware of at least 3 of the aforementioned jammed/broken teeth

failures; which occur many hours after the event.  The engine then ceases to

make power.  While twisted accessory shafts occur, along with broken blower

drive gears, they have all been the result of hydraulic lock and not prop

strikes.  A hydraulic lock is a far more serious problem than a prop strike

with WOOD or COMPOSITE blades. The full load torque on the prop shaft is

almost 1000 ft.lbs.  Engineering practices would require double that for

failure.  With any forward motion, on a flat surface (runway), breaking the

blades to the rear, the blades used on these engines will simply not

transfer that much torque to the prop shaft.



Anything beyond what is in the Maintenance Manual requires more data.   We

have spent a lot of time and money to acquire the data, tools, procedures,

fixtures and expensive lessons in learning (some the hard way).  What you

can save in doing it yourself, is less than damage you may incur without

having the above. If you are not sure of what you are doing, give us a call.

BTW, we are all still learning.  : )

Jill, Carl, Roger & Kevin

M-14P, Inc.

928-681-4400

- The Matronics Yak-List Email Forum -

Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:

http://www.matronics.com/Navigator?Yak-List

mark.bitterlich(at)navy.m
Guest

Posted: Thu Jul 18, 2013 11:46 am Post subject: Yak 55 parts and... Final Prop Strike comments

I for one would like to thank you for writing this.  This email is a keeper ..... forever. 



Mark





From: Jill Gernetzke

Sent: Thu 7/18/2013 12:43 PM

To: yak-list(at)matronics.com

Subject: Yak 55 parts and... Final Prop Strike comments




Group,



I have been offered a set of NEW Yak 55 ailerons and a rudder: available for

sale.  If you want to see a picture, go to our M-14P, Inc. Facebook page or

contact me offlist.



We wanted to share our final thoughts on the commentary about prop strikes

and engine teardowns.  There is conjecture about all manner of hidden

damage. Most people do not want to take the time to understand the forces,

loads and physics on the engine and the different outcomes. There are a

number of things we can say with some certainty, drawing from over 50 years

of collective experience on M-14Ps (80 years of collective radial engine

experience): two of us being  graduates of the M-14P factory overhaul

school, visits to the Shakhty overhaul factory, experience in performing

teardowns for prop strikes, hydraulic lock repairs or overhauls of 40 -50

AI-14, Housai and M-14 engines.  This is what we do, day in and day out. 

The only nosecase damage we have seen, was on an AI-14 and an M-14P that had

link rods fail in flight; which sheared off the propeller shafts.  The AI-14

has 3 planet gears, the M-14P has 6.  The first thing that is affected, if

anything, is always a rotation of the rear cheekplate on the crankshaft.

This produces a wobble in the front of the crankshaft which jams the cam

drive gear into the idler gear and breaks teeth. (We have had one Housai

engine that popped the camplate up when the nosecase was removed.)  Because

the crankshaft is held by 3 bearings, all of which have some side clearance,

it is simply not possible to accurately measure the runout with the

crankshaft held in those bearings. The runout limit at the end of the

crankshaft is .03mm. The runout would be absorbed by the bearing clearances,

if the crankshaft is measured in the engine. The crankshaft has to be

removed from the engine and checked with a dial gauge in v-blocks.

We are aware of at least 3 of the aforementioned jammed/broken teeth

failures; which occur many hours after the event.  The engine then ceases to

make power.  While twisted accessory shafts occur, along with broken blower

drive gears, they have all been the result of hydraulic lock and not prop

strikes.  A hydraulic lock is a far more serious problem than a prop strike

with WOOD or COMPOSITE blades. The full load torque on the prop shaft is

almost 1000 ft.lbs.  Engineering practices would require double that for

failure.  With any forward motion, on a flat surface (runway), breaking the

blades to the rear, the blades used on these engines will simply not

transfer that much torque to the prop shaft.



Anything beyond what is in the Maintenance Manual requires more data.   We

have spent a lot of time and money to acquire the data, tools, procedures,

fixtures and expensive lessons in learning (some the hard way).  What you

can save in doing it yourself, is less than damage you may incur without

having the above. If you are not sure of what you are doing, give us a call

- The Matronics Yak-List Email Forum -

Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:

http://www.matronics.com/Navigator?Yak-List

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