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flyinhwn

prop brake

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you always her people say "prop brake is really stiff on this one" ive been doing some digging through the books and im having trouble finding the real reason some props are harder to spin than others. from what ive red the prop brake keeps the prop from spinning in reverse while flying. can anyone shed some light on this phrase for me?

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The Prop brake is physically located inside the Reduction Gearbox and is meant to hold the propeller shaft steady. Prop brakes are composed of two cone-shaped components that come together to create friction, much like the brakes in your car shaped like bowls. The brake is held in the applied position by spring tension. When the propeller rotates backwards, the cones are forced together to create a wedge effect. To release the brake, starter torque is converted to thrust through helical splines to overcome spring tension and separate the brake assembly. After a certain engine RPM is developed, oil pressure has been built up enough to overcome spring tensiton and hydraulically separate the brake assembly.

The reason some brakes are stronger than others may depend on several factors such as: How much are the brake pads worn? Is there build-up on the pads that reduces friction? How old is the spring that holds the brake together? Has the brake been damaged? Because these conditions have an infinite number of combinations and levels, no 2 engines could be exactly the same.

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from what ive red the prop brake keeps the prop from spinning in reverse while flying

It is also there to assist the engine/prop in slowing down and stopping after being shut down on the ground and prevents any high winds from spinning the engine/prop (guess if you have a hurricane this might be an issue); but yes the primary reason for the prop brake is to lock the prop and prevent reverse rotation of the prop following an inflight shutdown

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Dan, Isn't it also the reason for the prop feather angle to be 92.5 degrees? Airload on the prop pushes it into the prop brake making for a tighter brake?

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George,

You are correct, when the prop turns backwards the inner cone of the brake rides up on a set of helical splines as well. This action pushes the inner cone farther into the outer cone and prevents any further rotation. If it makes it easier to understand I will attempt to post a picture

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You could make a rough guess whether the gearbox was a high/low time one by how much oomph it took to pull the prop thru. Low time hard, high time easy.

During accomplishment of the dash one preflight some FEs would pull the prop in reverse to ensure the brake would set. I would always follow and pull it through a bit to hopefully preclude starter shaft failure.

The sqd. I was in at the time flew hi altitude long duration missions. On occasion, the crew would shut down outboard engines so as to achieve maximum sortie duration. After a couple of hours in feather with the gearbox cold soaked the prop would slowly begin to rotate backwards. Not surprising the crew wrote this up. The powers in maintenance, with help from our Lockheed field rep., finally convinced ops. to cease writing this up.

All in all the prop brake is, for the most part, trouble free assuming the prop is rigged properly.

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Prop brakes can and do fail for the same reasons drum brakes on your car fails, sometimes its due to contamination of the linings but more often its simply due to the lining being worn beyond limits. This is why the first step for a failed prop brake is to flush the prop brake, trying to clean any contamination from the linings.

I used to push the prop backwards during my -1's, mostly to watch the poor crew chief freak out LOL but mostly to get an idea of just how worn it was. Was never dumb enough to write up one that turned backwards on preflight.

Another thing most people dont know is its only bad by the book (on the ground) if you use a steady push backwards and it rotates, if you "pop" it backwards its allowed to bust loose and rotate backwards.

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Watching the FE pulling the prop in reverse didn't freak me out but it did make me wary of the FE's intentions. My response to such action was to stick to the FE like glue for the remainder of his PR. In all fairness some FEs after pulling the prop in the opposite direction would then pull/push the prop in its intended direction. Further, all the above was a rare occurance. Most FEs pre-flighted using the dash one checklist. Those who checked items not on the checklist usually did so because of a negative experience involving that compenent. I did the same myself when cw the dash six.

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Yeah, I would always have to pull the prop thru in normal direction as after I moved the prop backwards as I would lock the prop brake to check it; after I did this I would explain to the CC why I was doing it. Never wanted to get known as someone trying to brake the airplane.

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Never wanted to get known as someone trying to brake the airplane.

We had an FE in the 37th at Rhein Main back in the late 70's that was notorious for breaking airplanes. He was on every crew chief's $hit list. I won't name any names, but his last name was an animal that builds dams. I gave him a checkride once and we went through at least 3 airplanes. Legitimate, but nit-picking discrepancies. My theory has always been that I can fly with a lot of crap (7 years with Transafrik), I just don't like surprises.

Don R.

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Don

I really agree with you. Almost all the Herk engineers I flew with had your attitude. I really only remember one FE who was always breaking Herks, but he was honestly afraid to fly and was looking for any excuse not to. After 17 years in Herks, I was shanghaied to C-5's. Always was embarrassed to say I flew C-5's. It was like having a sister in a whorehouse. But the C-5 world was the direct opposite of Herks. Any excuse to break was the norm. The plane was pretty complex and the training philosophy was let the FE's learn all the systems and give the pilots cursory knowledge. The pilots were pretty much at the mercy of the FE's. I had a C-5 Stan Eval FE tell me, "if the airplane is flying we are not doing our job." I really enjoyed the can do attitude of the herk crews and maintenance folks.

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Some of the crews now have never seen what a herk can really do, or don't have the systems knowledge and are scared of minor discrepencies. While it's our job to know when to ground the airplane it's also our job to know what we can safely fly with when there's a real mission to get done. I've seen more FEs who will explain to the crew why they should go fly than not.

Never thought of trying to spin the prop backwards myself though, maybe I'll do it just to see what my crew chief says next time...

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I'd forgotten all about that guy, Don. Hated flying speghetti runs with him . . . when I started to read your reply, my first thought wasn't him, tho . . . it was No-Go Nolan.

kim

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Never really understood why maintenance thought the FEs would try and break the planes. If they were broke we had to sit on our asses until they were fixed or they were finally cancelled. But that could take many hours for that to happen, so we just sat on the ramp waiting. So instead of a 5 hour PP, we sat for 5 hours and then flew a 5 hour PP.

Don't know how many of us here ever experienced that, but I know that I did on a number of occasions. Sometimes we'd move to a spare sometimes not.

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I'd forgotten all about that guy, Don. Hated flying speghetti runs with him . . . when I started to read your reply, my first thought wasn't him, tho . . . it was No-Go Nolan.

kim

Hi Kim,

Aah yes, Leslie Nolon. He certainly earned that nickname. I can't think of any other FE's there that would rather sit around waiting than fly -- well, maybe Amort, too.

Don R.

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We had an FE in the 37th at Rhein Main back in the late 70's that was notorious for breaking airplanes. He was on every crew chief's $hit list. I won't name any names, but his last name was an animal that builds dams. I gave him a checkride once and we went through at least 3 airplanes. Legitimate, but nit-picking discrepancies. My theory has always been that I can fly with a lot of crap (7 years with Transafrik), I just don't like surprises.

Don R.

Ahhh you must mean Charlie Beaver, he was still there when I pcs'ed in and still there four years later when I psc'ed out.

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I was reading your post about the prop brake and i thought about another queston. When you do a windmill taxie start you line up prop with cuf. that the puts the prop in the pitch range so the prop is is pitch locked when you start down the runway. how does it get un locked.

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Its in the range and locked due to no hyd pressure. As the prop rotates hyd pressure developes seperates the PL and blade angle can reduce allowing the engine to start.

We feather the prop start the run go to AS at 40kias to unfeather and rotate the prop then the same process takes place.

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I recall one time during my Phase II training. During pre-flight the RW isolation valve did not close all the way. We sat there for a couple hours waiting on a fix or a spare. If you have an Examiner or an Instructor, breaking a plane is the worst. Plenty of time for them to ask any and all questions that pop into their mind. Playing stump the dummy!!! :confused:

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We had an FE getting a check ride from a 22nd AF examiner. The examiner kept getting deeper and deeper in systems and finally our guy said "you know, were only going to fly this thing for a couple of hours not build one".

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Once got a check ride from Bill Knox at Hickam. I went there from the 16th, so I was the use to asking all the questions. Anyway, it was question after question when ever the chance arose - from the ice impact panels on the side of the plane, 1st aid kits, windows, pressures, limits, warning lights, and other obscure info. Finally about half way through the ride I asked Bill that if I could ask him a question that he couldn't answer then the check ride would be over and his questioning stop. He agreed. hahahaha. I asked him how many times a minute the tail lights on a B model flash. He said 85. Nope. That's on E's. On B's it alternates 40 for the white and 40 for the amber. Tada! Qual 1. ;)

All the morning flights at Hickam were scheduled for the same launch time, 8 am I think it was. Anway, one day Bill Knox and Jim Sweeny were doing a preflight. Think it was Jim admining the checkride. I had finished my -1 and was catching a smoke and I swear they were still on the exterior. Each asking questions.

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If you have an Examiner or an Instructor, breaking a plane is the worst. Plenty of time for them to ask any and all questions that pop into their mind. Playing stump the dummy!!! :confused:
Well I was supposed to fly an 8 hour overwater when Mark Vogelgesang showed up for a no notice check - great just the way I wanted to start the day.

Well we went to Zahrbruken and picked up pax that were eventually going to Sembach, well lucky us when we broke ground we lost GB oil press and then the prop locked up on us at about 30% on the shutdown. I spent the next 12 hours getting grilled and figured "finally" its over - NOT, he jumped a train the next but not before telling me to come by his office when I got back for more debreifing. Crap another 8 hour day and he finally gave up, I would never have made a good evaluator, got fired from the job twice before I could even get started:)

Back to the prop brake, I loved it when I got one off the gunship wreck, its so much easier to explain what helical splines/gears are if you can just show them.

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Prop brake. I was taught a little different . I was taught that when you made a windmill taxi start you were in the pitch lock range there fore the prop is pitch locked and the only way it can become un locked is to increase blade angel. and the nts system does that. when decend you have to move the throttles up to stop the native torque some times.

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Damn, having to wind my way through a lot of cobwebs.

Windmill taxi start, prop on cuff, best angle to get the prop turning to wind engine up to light-off. Once GB oil pressure gets up it positions the prop accordingly.

NTS during decent, etc., prop trying to drive the engine and NTS is increasing blade angle to get a bigger bite and to stop trying to drive the engine instead of the other way around, which could lead to a decoupling. NTS could also drive the prop to a too high of a blade angle and inadvertently send the prop to feather or cause the RPM to stagnate, accel bleed valves to open, etc.

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