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Propeller servicing


Steve1300
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Pjvr99\'s addition about prop inconsistance in filling from dry really intrigues me.

..... and and the inconsistancy is still the only consistant thing in prop servicing. Just had

one that showed 4 inches of fluid above the mark on the atmospheric stick, and fluid

above the ledge of the pressurized - 2 minutes after start low light came on. We continued

the run to see if there would be any flux - rock solid! but had to shut down for a chiplight

warning :-( Took another gallon to get a reading on the pressurized dipstick

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  • 11 months later...

The pressurized sump, because of its dimensions, can only hold approx 6 qts. This sump is the "reservoir" for the system. The main, standby and aux pump, pull from this reservoir, pressurize the fluid and then the valve housing directs the pressurized fluid to the fwd or back side of the pitch change mechanism (dome piston). In simple terms, "what goes in must come out". The fluid comes out of the dome and into barrel. In the back of the barrel, moved by the #1 blade, is the beta feedback shaft. This shaft is hollow, which is the escape route for fluid in the barrel. When exiting the shaft, fluid is now returned to the atmospheric sump. The scavenge pumps suck it up and return it to the pressurized sump. With a basic understanding of how fluid travels through the propeller, let's address servicing. Remembering that the pressurized sump can only physically hold approx 6 qts, it is impossible to overservice this sump. Sure, you pull the cap to insert the dipstick and sometimes fluid WILL spew out, but this is NOT overserviced. As mentioned above, pressure may be slow to bleed off and fluid under pressure will rush towards the path of least resistance, ie. an opened toilet seat cap. Under operation, all supply pumps, internal passages, dome, barrel, etc are filled with fluid, not air. The only place that is not filled to capacity with fluid is the atmospheric sump. If a prop is truely overserviced, this is the only place for that extra fluid, hence the addition of the atmosphic dipstick. On a properly serviced prop, with the pumps operating, the atmosheric sump will have approx 17 oz of oil. This coincides with the mark on the atmospheric dipstick. During a service check, cycling the prop 3 full cycles is to purge any air from the internals. On the final cycle, with the aux pump never being allowing to stop, the atmospheric dip stick should be pulled, wiped, inserted and pulled to give an accurate reading. If the fluid is at the bottom 1/4" of the stick, your prop is serviced correctly. If its higher than that, your prop is overserviced. If there is nothing on the stick, your prop is low and should then be verified by checking the pressurized sump dipstick. Keep in mind that after performing major prop maint, such as prop change or dome removal air will usually will be locked in the system until a run is performed. Centrifugal force and the combined 60 QPM flow of the main and standby pumps will remove the air and often give a "low oil" light during the run. That is why, following tech data, a service check is required after the first run. This is the "nuts and bolts" version of proper servicing. There will always be potential variables, such as acft lean, aux pump condition, internal leakage, clogged orfice cups in the pitchlock regulator, and so on.

Edited by ezurk1
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I'd like to thank all of you guys for your responses. We have stopped many of our "NOSE BLEEDS" by spending more time figuring out where our fluid levels really are and by parking our #1 blades high at the end of the day. It is simply amazing what paying attention to tech data can do for you (and sometimes, how it can screw things up!), so maybe Hamilton Sundstrand might one day actually explain the relationship between the atmospheric and pressurized sump dipsticks. We know now that it takes two dipsticks to ensure proper fluid levels and not just one.

We still seem to get more pump housing front cover leaks, but it looks like those are coming from clogged valve-housing vents if not from corroded or warped covers.

I guess that is why maintainers have a job...... nothing works ALL the time.

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Around 1974 HS came out with a mod (service bulletin no. 39) to the pump housing which incorporate a dip stick for the atmospheric sump. The new dip stick was to aid in proper servicing. The dip stick had an OP LEVEL band and if the fluid level was in the OP LEVEL band while the aux feather pump running things should be good.

After many static fluid leaks from the rear lip seal in 1981 HS came out with a mod (service bulletin no. 101) to the atmospheric sump dip stick. The bulletin had you remove existing markings from the dip stick and remark one line just about where the old OP LEVEL lower mark was and this becomes the new FULL mark.

Now if there is any runback of fluid from the pressurized sump to the atmospheric sump while the prop is static the likelihood of a rear lip seal leaking due to overfilling is less.

Our HS rep told us that after initial prop servicing there is no need to open the pressurized sump cap to check levels. We safety wired the caps closed to remove the temptation of opening them. This procedure worked well.

Feb 1970 Service Information Release, Code SIR 54H-72 was issued which read:

“54H60 Propeller Servicing Procedure

Originally the various HS manuals specified that at the time of servicing 54H60 propellers, the No. 1 blade would be positioned in the 12 o'clock position. The theory that the beta feedback shaft would assist in purging entrained air has subsequently been proved invalid. There is no apparent difference in rate of air purging regardless of the location of the No. 1 blade.

In view of the foregoing, the requirement for prepositioning the propeller for servicing has been deleted from all publications as they have come up for revision. Naturally there is no objection to positioning the No. 1 blade up-right prior to servicing any more than there is an objection to positioning it downward. This point is brought to the attention of all concerned in order to simplify to the maximum the already complex servicing requirements for this propeller model.â€

Vic

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Around 1974 HS came out with a mod (service bulletin no. 39) to the pump housing which incorporate a dip stick for the atmospheric sump. The new dip stick was to aid in proper servicing. The dip stick had an OP LEVEL band and if the fluid level was in the OP LEVEL band while the aux feather pump running things should be good.

After many static fluid leaks from the rear lip seal in 1981 HS came out with a mod (service bulletin no. 101) to the atmospheric sump dip stick. The bulletin had you remove existing markings from the dip stick and remark one line just about where the old OP LEVEL lower mark was and this becomes the new FULL mark.

Now if there is any runback of fluid from the pressurized sump to the atmospheric sump while the prop is static the likelihood of a rear lip seal leaking due to overfilling is less.

Our HS rep told us that after initial prop servicing there is no need to open the pressurized sump cap to check levels. We safety wired the caps closed to remove the temptation of opening them. This procedure worked well.

Feb 1970 Service Information Release, Code SIR 54H-72 was issued which read:

“54H60 Propeller Servicing Procedure

Originally the various HS manuals specified that at the time of servicing 54H60 propellers, the No. 1 blade would be positioned in the 12 o'clock position. The theory that the beta feedback shaft would assist in purging entrained air has subsequently been proved invalid. There is no apparent difference in rate of air purging regardless of the location of the No. 1 blade.

In view of the foregoing, the requirement for prepositioning the propeller for servicing has been deleted from all publications as they have come up for revision. Naturally there is no objection to positioning the No. 1 blade up-right prior to servicing any more than there is an objection to positioning it downward. This point is brought to the attention of all concerned in order to simplify to the maximum the already complex servicing requirements for this propeller model.â€

Vic

You might want to tell the folks at Hamilton Sundstrand about that. I attended their training course a couple years ago, and they disagree with this publication. They still instruct us to park the blades at 12 o'clock. If you have even pulled a pump housing off the prop, you would see just how fast the fluid leaks past the Beta feedback shaft.

The latest revisions to our maintenance manuals still require the #1 blades up as well.

Yup, you may have to inform the manufacturers........

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