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What caused the low pitch stops to retract?


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I know that they are retracted by prop oil pressure, and that it takes 240-260 psi to retract them, but what causes the pressure to build to that level? (or keeps it from building to that level when you don't want it to?)

My previous ride, the DC-6 had Hamilton Standards which had a very similar low pitch stop, but on that plane, the standard unaided governor pressure wasn't enough to retract the stops, you had to have higher Px oil from the electric feather pump, which was switched on when you pulled the throttles into reverse range. . No feather pump, no reverse.

On the Herc, it seems (and maybe I'm missing something ) that the standard prop oil px is enough to retract the stops, so what keeps that from happening in flight?

I'd appreciate any input that would help me get a better handle on this.

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I'm a little rusty on my Valve Housing internals, but I'll take a crack at it. The pressure doesn't ramp up that high in the low pitch stop until the Beta Set Cam and the Beta Followup Cam inside the Valve Housing differ. The Beta Set Cam is basically your throttle movement, your "desired blade angle", and your Beta Followup Cam represents your "current actual blade angle." When you retard the throttle to flight idle, the Beta Set Cam sets the blade angle to 17.5 degrees. The beta followup cam will read 25 degrees because of the low pitch stop. There is a difference, but not enough to build up enough pressure to retract the LPS levers. As soon as you move the throttle in the ground range, the blade angle difference between desired and actual makes the system pressure increase enough for the LPS to retract. I'm sure it's more complicated than that, but that's the basics of it.

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Thanks Lkuest,

That makes sense. A follow up question, if you don't mind; Is the required pressure generated only by positioning the pilot valve, or does the little walking beam arrangement that rides on the blade angle cam and the Beta follow up cam also actuate some other valve that increases the pressure to the prop?

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The cams (mentioned above) are used to position the "Back Up" valve in the valve housing which ports pressure to allow the low pitch stops to retract.

Here is an extract from my Lockheed Engine manual, too bad the engine manual is the only one I kept when I retired. I thought I had given them all away and found this one hanging out in the attic a couple of years ago :rolleyes:

When the throttle is moved below flight idle, the back-up valve will open.,

Decrease pitch pressure (which is high pressure) is ported to the selector valve. The pressure on the spring side of the low pressure relief valve will be increased when decrease pitch or reverse is selected. Higher pressure will then be available to the pilot valve for release of the low pitch stop (below 28 degrees on the coordinator) and reverse pitch operations.

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The cams (mentioned above) are used to position the "Back Up" valve in the valve housing which ports pressure to allow the low pitch stops to retract.

Here is an extract from my Lockheed Engine manual, too bad the engine manual is the only one I kept when I retired. I thought I had given them all away and found this one hanging out in the attic a couple of years ago :rolleyes:

That sounds like a better explanation. I've rebuilt a coupe of valvehousings, but it was quite a few years ago, so it's all fuzzy. Thanks Dan.

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seeing as how a FE can't do much about a valve housing in flight and they are mostly changed on the ground by maint specialist,when a SEFE asked me to explain one I usually said they work good,last a long time,don't screw with them.

I logged 6,000 hrs and never failed a check ride.

Wayne D.

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seeing as how a FE can't do much about a valve housing in flight and they are mostly changed on the ground by maint specialist,when a SEFE asked me to explain one I usually said they work good,last a long time,don't screw with them.

I logged 6,000 hrs and never failed a check ride.

Wayne D.

Interesting. Once had a FE who started out as a scanner at LRF. He accumulated a lot of hours that way on many, many overwater trainers doing eye light-leak checks. When he became a FE he would "brag" about his 5,000 hours in the Herk. Only around 1,500 was as a FE. So I asked him when he got his annual did he want to be evaluated as a 1,500 hour FE or as a 5,000 hour FE? He thought about for a minute and decided that a 1,500 hour FE was what he was. Never heard a peep about 5,000 hours again.

The SEFEs i've known wouldn't Q-3 you for comments like that, but they sure would make the appropriate comments on the Form 8. Some even to the point of a Q-2. A FE's job all boils down to system knowledge, professionalism, and credibility. My 2 cents.

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The cams (mentioned above) are used to position the "Back Up" valve in the valve housing which ports pressure to allow the low pitch stops to retract.

Here is an extract from my Lockheed Engine manual, too bad the engine manual is the only one I kept when I retired. I thought I had given them all away and found this one hanging out in the attic a couple of years ago :rolleyes:

Dan, thanks for that. That seems to agree with a description I just found in a Lockheed manual

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seeing as how a FE can't do much about a valve housing in flight and they are mostly changed on the ground by maint specialist,when a SEFE asked me to explain one I usually said they work good,last a long time,don't screw with them.

I logged 6,000 hrs and never failed a check ride.

Wayne D.

I'd agree that this level of detail is a bit beyond what's needed for a flight crew checkride. Mostly it's curiosity on my part. I just like understanding how things work. I'm one of those guys who is always taking things apart to see how they work. However, if somone from our Mx Department looks out on the ramp and sees me straddling a nacelle and dismantling a valve housing, chances are good that I'll get fired, so asking here is probably a better approach.

BTW, what is SEFE? Stand.-Eval. Flight Engineer?

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seeing as how a FE can't do much about a valve housing in flight and they are mostly changed on the ground by maint specialist,when a SEFE asked me to explain one I usually said they work good,last a long time,don't screw with them.

I logged 6,000 hrs and never failed a check ride.

Wayne D.

Well the answer I would always give my students when they said what your saying it this: As an FE the more you know about your systems the better your qualified to determine what you can safely fly with and what you need to have fixed before you fly.

(The word "safe" is relative though, sometimes safety just has to take back seat to the mission.)

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BTW, what is SEFE? Stand.-Eval. Flight Engineer?

Yep, that's it. Years ago, it used to be FEFE (Flight Examiner Flight Engineer), but I guess that sounded a little too -- um, you know.

Are you with Lynden?

Don R.

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My (over) 6,000 hrs was all loged as a C-130 FE. I have 2,200 hrs Combat time in SEA,A DFC and 11 Air Medals,10 stars on My VM campaign Ribbon.

I was an instructor,FCF,Awads,Halo, Lapes, Plads,Grads Etc.

before going to "Flight Mechanic"yes that was the name of the course at

Sewart AFB in July 1964 I was a crew chief on C-130A 55-0013 at Tachi.

Pope 779th 64-66 (3 deployments to SEA)

Mactan 66

Sewart(61st)67-68

CCK 345th 68 -73

LRAFB(61st)73-ret-77

Utapao, Easter Bunny(air drops in Cambodia) 6 months(179 days)

2 rotes to Howard AB canal Zone

so many rotes to Mildenhall,and Rhein Main I can't even count them.

Most SEFE that asked crap questions were just tryin to show how smart they were. Some of them would fly"in country" toward the end of the month.give a few "no notice" check rides,get credit for 2 months combat pay then fly back to home base,set around the office thinking up chicken shit questions trying to impress people with there useless knowledge.

I declined becoming a SEFE as I prefered Flying Missions instead of setting around bragging about how much systen knowledge they had.Learn your Emergengy Procedures,and study the "G"file but that is why we carried the TOs.If you know where to find the info you need,a lot of that "Minutae" is just useless crap. Learn about things you can do something about in flight and how to get your ass back on the ground.When you go to debriefing then you can explain the problem to the proper Maint Troop.

My 3 cents worth

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My (over) 6,000 hrs was all loged as a C-130 FE. I have 2,200 hrs Combat time in SEA,A DFC and 11 Air Medals,10 stars on My VM campaign Ribbon.

I was an instructor,FCF,Awads,Halo, Lapes, Plads,Grads Etc.

before going to "Flight Mechanic"yes that was the name of the course at

Sewart AFB in July 1964 I was a crew chief on C-130A 55-0013 at Tachi.

Pope 779th 64-66 (3 deployments to SEA)

Mactan 66

Sewart(61st)67-68

CCK 345th 68 -73

LRAFB(61st)73-ret-77

Utapao, Easter Bunny(air drops in Cambodia) 6 months(179 days)

2 rotes to Howard AB canal Zone

so many rotes to Mildenhall,and Rhein Main I can't even count them.

Most SEFE that asked crap questions were just tryin to show how smart they were. Some of them would fly"in country" toward the end of the month.give a few "no notice" check rides,get credit for 2 months combat pay then fly back to home base,set around the office thinking up chicken shit questions trying to impress people with there useless knowledge.

I declined becoming a SEFE as I prefered Flying Missions instead of setting around bragging about how much systen knowledge they had.Learn your Emergengy Procedures,and study the "G"file but that is why we carried the TOs.If you know where to find the info you need,a lot of that "Minutae" is just useless crap. Learn about things you can do something about in flight and how to get your ass back on the ground.When you go to debriefing then you can explain the problem to the proper Maint Troop.

My 3 cents worth

Pretty impressive Herc resume. But of all that experience, how much of it was passed on to other less experienced FE's. I'm not slamming your career at all, just asking. About 1/2 of my time was spent flying the line with the 32nd and the 17th. Spent some time with the 6594th. But a fair amount of my time was with the 16th, trying to pass on experience, knowledge, and the way to do the job safely and with professionalism.

When I was a SEFE I flew the line as much as the other FEs in the 17th, and didn't sit on my a** thinking up chicken-shi* questions. The big difference was that when the FEs weren't flying they were off fishing, hunting, etc. While I was in the office doing the 8-5.

There was a FE at LRF getting checkride was dark, early morning. Got to the bird, jumped out of the crew bus, plugged the ext power in and started it. Was Q-3'd on the spot. You might have a problem with this, hope not.

There was a time I laid in the snow on a cold day at Ft. Wainwright, repairing a boken anti-skid wire so we'd have anti-skid for take-off and landing at EDF. System knowledge.

Had an engine that would turn but not start at Ketchikan. Cool, rainy day in Feb. Stood on a ladder jumping the speed switch. Still didn't work. On the ladder again and found that the geneva lock wouldn't open. When I called ALCC I knew what to tell them and to make sure that they sent the special wrench that was used to change it. System knowledge.

Neither one could be "fixed" in flight but with no maintenance people on the ground I became the maintenance guy.

As for the "Minutae, chicken-shi* questions. They do serve a purpose. mostly to lighten the "mood" on the student/examinee.

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The majority of the places I flew to we did not carry a C/C.I have jumped SSswitches,Removed and padded starters,generators,Swaped Tach generators from an eng with a Gen to one with out a Gen to get RPM,while using freq meter on the other,Made numerous no flap TO,Flew with all 4 TD valves in Null and all 4 props in Mech Gov Lots of missions flown wit inop fuel booster pumps. Flew non pressurized with MLG chained to the floor,1 bralke capped on each side,antiskid inop, on planes so bad we had to wear our chutes and could not carry any one(including C/C.26 pages of serious maint problem that could not be fixed in Viet nam. When I retired The SQd Commander of the 61st Lt.Col Stewart said I was a "pain in the ass but if He had to fly a Combat Mission He would want Me as his FE. In all the years I flew in SEA I only left 2 or three planes,Because of G/B or Turbine failure.My 7 years as a C/C served Me well when it came to doing repairs in the field. I will put My system knowledge up against anyone's.Every day I went out to flyI wanted to know if the acft could fly the mission,instead of trying to find some reason NOT to fly.Ask some who know Me such as Muff Millen.

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Yep, that's it. Years ago, it used to be FEFE (Flight Examiner Flight Engineer), but I guess that sounded a little too -- um, you know.

Hahaha

Are you with Lynden?

Don R.

Yes. I think we may have had an exchange about an extreme gradient STC on another forum.
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Damn Wayne, you really must have issues!

In no way did my post criticize your systems knowledge, hell I dont even know who you are so how could I judge your experience or knowledge?

As for Stan Eval, hell I got fired from that job three times even before I was even certified, seems the commanders didn't care for some of my answers, so you see some others of us were a pain in the zero's butt as well:rolleyes:

Seems I am chronically "Politically Challanged"

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Yes. I think we may have had an exchange about an extreme gradient STC on another forum.

Yeah, I remember that STC. It was on the Africa Aviation forum -- right?

Say hi to "CL" for me. He was supposed to tip a few beers with me last week -- he was teaching a recurrent class at CAE, but he had to get right back to ANC as he was moving his family to someplace in Delaware. I guess Darwin's Theory is gonna take a hit in their beer sales!

Don R.

Edited by DC10FE
spelling; what else!
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I remember getting a check ride from a E -9 (CMSGT) from MAC HDQRS .He only had 200 hrs C-130 time but had 15,000 hrs in sub sonic bug suckers( C-141 -C-5) I could not understand why he was qualified to be evaluating my performance. I retired after getting bored flying 10 hour over water nav/night missions,and flying 5 hour training missions,

I wanted to do interesting flights and flew missions doing experimental air drops

at Yuma and El Centro. I think I may have become an "adrenaline junkie" as I prefer to fly interesting , challenging missions.

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Yeah, I remember that STC. It was on the Africa Aviation forum -- right?

Say hi to "CL" for me. He was supposed to tip a few beers with me last week -- he was teaching a recurrent class at CAE, but he had to get right back to ANC as he was moving his family to someplace in Delaware. I guess Darwin's Theory is gonna take a hit in their beer sales!

Don R.

I'm sure there are plenty of other pilots and engineers to keep Darwin's in business. ;)

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Yep, SEFE=Stand. Eval Flight Engineer

Good news is, I believe, the Electronic Valve Housing is gaining momentum in replacing these relics. Much higher reliability and accuracy, with or without the 8 blades.

I'll believe we are getting them when I see them. They've been talking for years. The latest rumors I heard was H1's get the electronic valve housing, and H2's and above get the 8-blade and AMP. The NP2000 is supposed to pay for itself within 5 years, which would make me think they are planning on retiring the H-1's in 5 years. If that is the case, why modify the H1's with anything in the first place. I don't think anybody knows what's going on right now. It would be great, but we'll see.

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I guess I am an antique as I crewed a C-130 A with 3 bladed props. I also spent 3 years at Dreux AB in France(57-60) on C-119-Gs and C-123-Bs

I also was TDY to

TSN in 1962 for 60 days to the 309 th (Provisonal) Squadron(Ranch Hand).

I have just been diagnosed with Non-

Hodgkins lymphoma. I guess it took almost 50 years for (Agent Orange) to try to kill me,but I AM STILL AN ONERY OLD BASTARD, AND WILL GO DOWN GASPING (for my last breath)!

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