Parking Brake Locked Up in Flight??

[Shadrach]

On 12/30/2018 at 9:56 AM, Yetti said:

I think I do it to circulate warm oil through the hub.   If you tell me that warm oil is already circulating then I will have learned something new.

 

The hub holds about a pint of oil at most. Inside the prop hub there is a hydraulic piston. There is no oil return by which to circulate oil through. It’s not a loop.  The governor is fed by engine oil, which it pressurized to a much greater degree (3 to 4 times engine oil pressure). That pressurized oil is then sent to the hub to actuate a counter sprung piston.  Oil going to the prop hub travels back-and-forth through the same passage, it doesn’t really circulate. 

I think it’s a good idea to verify that your prop works. I do that on every flight. I just do it at a tame 1,000 RPM during taxi.

I honestly think the multiple pull run up came from old warbirds with huge props that held a considerable amount of what was then likely straight weight oil. Under those circumstances, it makes more sense. 

Leave it to Yeti to make a post that tempted me to break my no more hijack post promise...

Edited January 1, 2019 by Shadrach

[Yetti]

I do see the Oil PSI drop, so something is happening...

[0TreeLemur]

30 minutes ago, Yetti said:

I do see the Oil PSI drop, so something is happening...

I'm confused.   Doesn't the drop in rpm indicate that something is happening?   Isn't the drop in oil pressure just a symptom of decreased rpm?

[gsxrpilot]

35 minutes ago, Yetti said:

I do see the Oil PSI drop, so something is happening...

 

4 minutes ago, Fred_2O said:

I'm confused.   Doesn't the drop in rpm indicate that something is happening?   Isn't the drop in oil pressure just a symptom of decreased rpm?

Of course something is happening... the point is, why make it happen three times? It will either happen or it won't. One pull is sufficient.

[Shadrach]

4 hours ago, Fred_2O said:

I'm confused.   Doesn't the drop in rpm indicate that something is happening?   Isn't the drop in oil pressure just a symptom of decreased rpm?

Its a symptom of lower engine RPM but also the governor scavenging oil from the system to feed the prop. They are separate but connected systems. The pressurized oil going to the hub is pressurized by the governor.  The engine oil pump merely delivers oil to the governor in sufficient quantities to for the governor to do it's job

Verifying the drop in oil pressure is good for those that need to verify that they're standing in the rain by looking to make sure their clothes are wet.

Edited December 30, 2018 by Shadrach

[Skates97]

1 hour ago, Shadrach said:

The hub holds about a pint of oil at most. The prop hub Is a hydraulic piston. There is no oil return by which to circulate oil through. It’s not a loop.  The governor is fed by engine oil, which it pressurized to a much greater degree (3 to 4 times engine oil pressure). That pressurized oil is then sent to the hub to actuate a counter sprung piston.  Oil going to the prop hub travels back-and-forth through the same passage, it doesn’t really circulate. 

I think it’s a good idea to verify that your prof works. I do that on every flight. I just do it at a tame 1,000 RPM during taxi.

I honestly think the multiple pull run up came from old warbirds with huge props that held a considerable amount of what was then likely straight weight oil. Under those circumstances, it makes more sense. 

Leave it to Yeti to make a post that tempted me to break my no more hijack post promise...

No worries about hijacking the thread, it's been a good read. 

Here's a great article about props, and what is happening and why.

https://www.avweb.com/news/pelican/Pelicans-Perch-16-Those-Marvelous-Props-182082-1.html

[Yetti]

38 minutes ago, gsxrpilot said:

 

Of course something is happening... the point is, why make it happen three times? It will either happen or it won't. One pull is sufficient.

Dang it now you are going to send me on a search for how all this works.  I know there is an oil line that run up the front of the engine and there is a governor.....  and a piston that move the blades.

[0TreeLemur]

38 minutes ago, gsxrpilot said:

 

Of course something is happening... the point is, why make it happen three times? It will either happen or it won't. One pull is sufficient.

My confusion stemmed from the fact that the governor is an oil pump and while it does take oil from the pressurized engine oil pump, it is a tiny volume and I'm surprised that it affects engine oil pressure in a noticeable way, compared to the change in rpm.   Although it was better said by   @Shadrach

[jaylw314]

6 hours ago, Steve_B said:

I miss George.  

I was taught the same as others, 3 pulls for rpm,  MP, OP but after doing some research, I only do one except when the outside temp is really cold so then it's 2-3 to get some warm oil through the prop. Not sure if that's needed but that's what I do.

As for the runup, I will do one only if the engine was shut down. Abbreviated preflight/walkaround for fuel stops, etc., full preflight of the plane leaves my sight.

-Steve

I've never heard of checking MP during the runup?  In fact, my POH just says to increase throttle, check mags, cycle prop, then retard throttle.

If I understand correctly, the hubs we use don't cycle a significant amount of warm oil to the prop.  If prop hubs are filled with red-dyed oil, you'd expect that to go away pretty quickly if warm motor oil was being cycled into the hub piston.  That suggests the same oil is being pumped into and out of the hub, and the only mixing/warming is happening within the governor itself.

Edit: oops, I noticed @Shadrach already posted an explanation in a way that makes way more sense

[salty]

8 hours ago, Shadrach said:

Its a symptom of lower engine RPM but also the governor scavenging oil from the system to feed the prop. They are separate but connected systems. The pressurized oil going to the hub is pressurized by the governor.  The engine oil pump merely delivers oil to the governor in sufficient quantities to for the governor to do it's job

Verifying the drop in oil pressure is good for those that need to verify that they're standing in the rain by looking to make sure their clothes are wet.

I’m verifying that the pressure comes back up (and oil isn’t shooting out the prop governor line), not that it’s going down. 

Edited December 31, 2018 by salty

[Shadrach]

1 hour ago, salty said:

I’m verifying that the pressure comes back up (and oil isn’t shooting out the prop governor line), not that it’s going down. 

Whatever blows your hair back!

keep them coming folks, I’m sure there are explanations that haven’t yet been listed. 

Edited December 31, 2018 by Shadrach

[Guest]

1 hour ago, salty said:

I’m verifying that the pressure comes back up (and oil isn’t shooting out the prop governor line), not that it’s going down. 

The same thing I do, cycle the prop, watch for oil pressure drop and recovers when the prop control is put to full fine.

Clarence

Edit, there is also a Hartzell instruction concerning multiple prop cycling to reduce grease being thrown from blade seals.  I guess that multiple cycles limbers the seals.

 

Edited December 31, 2018 by M20Doc

[Shadrach]

4 hours ago, M20Doc said:

The same thing I do, cycle the prop, watch for oil pressure drop and recovers when the prop control is put to full fine.

Clarence

Edit, there is also a Hartzell instruction concerning multiple prop cycling to reduce grease being thrown from blade seals.  I guess that multiple cycles limbers the seals.

 

Thanks Clarence, would you kindly link the instruction if possible? This is the first I’ve heard of a Hartzell instruction regarding run-up operations.

[Yetti]

12 hours ago, M20Doc said:

The same thing I do, cycle the prop, watch for oil pressure drop and recovers when the prop control is put to full fine.

Clarence

Edit, there is also a Hartzell instruction concerning multiple prop cycling to reduce grease being thrown from blade seals.  I guess that multiple cycles limbers the seals.

 

While the prop it's self may only hold a pint, the govenor and lines would also hold oil.   Mine was weeping a bit of grease, I read where if you do a couple of deep cycles it would reset the blades.  I did a couple of deep cycles and it fixed the grease weep.

[bob865]

22 hours ago, Fred_2O said:

My confusion stemmed from the fact that the governor is an oil pump and while it does take oil from the pressurized engine oil pump, it is a tiny volume and I'm surprised that it affects engine oil pressure in a noticeable way, compared to the change in rpm.   Although it was better said by   @Shadrach

The governor is not a pump, only a valve (unless someone jumps in and educates me otherwise).  It uses the engine oil pressure and regulates its flow to the prop.  That's why you see a decrease in oil pressure when you see a sudden and drastic decrease in RPM.  As RPM increases past its set point, oil from the engine is directed into the prop until the pitch increases and slows down to the set point at which point the governor closes the valve.  The RPM Decreases past the set point, the valve opens and allows oil to flow from the prop (under spring pressure in the prop) back to the reservoir, decreasing pitch and increasing RPM.

[takair]

43 minutes ago, bob865 said:

The governor is not a pump, only a valve (unless someone jumps in and educates me otherwise).  It uses the engine oil pressure and regulates its flow to the prop.  That's why you see a decrease in oil pressure when you see a sudden and drastic decrease in RPM.  As RPM increases past its set point, oil from the engine is directed into the prop until the pitch increases and slows down to the set point at which point the governor closes the valve.  The RPM Decreases past the set point, the valve opens and allows oil to flow from the prop (under spring pressure in the prop) back to the reservoir, decreasing pitch and increasing RPM.

The governor includes a high pressure gear driven pump that does boost oil pressure even higher for prop operation.  I forget the amount, but it is definitely there.  The condition of this pump can affect your prop governing ability as much as the fly weights can.

[Shadrach]

53 minutes ago, bob865 said:

The governor is not a pump, only a valve (unless someone jumps in and educates me otherwise).  It uses the engine oil pressure and regulates its flow to the prop.  That's why you see a decrease in oil pressure when you see a sudden and drastic decrease in RPM.  As RPM increases past its set point, oil from the engine is directed into the prop until the pitch increases and slows down to the set point at which point the governor closes the valve.  The RPM Decreases past the set point, the valve opens and allows oil to flow from the prop (under spring pressure in the prop) back to the reservoir, decreasing pitch and increasing RPM.

So your suggesting that the 60-90lbs (which decreases progressively down stream) is adequate to properly articulate the blades?  I do not think so. That's enough pressure to move them but not at the rate required for smooth constant speed operation. 

Also, it's not really a valve, it's an engine driven pump that that adjusts pressure to the prop in order to maintain the set RPM.  

Read the Deakin Column that Richard posted.  It's and oldy but a goody. 

 

Edited December 31, 2018 by Shadrach

[bob865]

9 minutes ago, Shadrach said:

So your suggesting that the 60-90lbs (which decreases progressively down stream) is adequate to properly articulate the blades?  I do not think so. That's enough pressure to move them but not at the rate required for smooth constant speed operation. 

Also, it's not really a valve, it's an engine driven pump that that adjusts pressure to maintain RPM.  

Read the Deakin Column that Richard posted.  It's and oldy but a goody. 

 

Got it!    Thanks!  In my mind, I'm was thinking the overly simplified schematics that you learn in school.  Here is the line from the article:

"Most governors also contain a high-pressure oil pump to boost engine oil pressure (which is typically around 50 PSI) up to the levels needed to control the prop (often around 200 PSI)."

Something to throw about about hydraulics (pneumatics) and pressure. If you're not paying attention the force multipliers in those systems will get away from you quickly.  For example, assuming the ram that is actuating the blades is only 3" in diameter (I obviously have no idea how big the ram is, but considering how big the spinner/hub is, 3" seems reasonable to me, or at least until I see one taken apart ).  At 60psi, it is exerting a force of 423.9 lbs and at 90psi, it's 637.9lbs.  Even at half the size the forces are 105.9 and 158.9 respectively.  But to your point at 200psi it is 353.25lbs for a 1.5" diameter ram and 1,413lbs at 3".  Just throwing it out becuase the factors in hydraulic systems can get away from you fast!  A few PSI on one side can be massive on the other depending on the size of the components.  This is true of the wings on your plane too.  The pressure differences are small, but the small pressure over the surface area of the wing is able to develop enough lift to carry us skyward at max gross weight at close to 1000ft/mi.  Obviously pressure is something I find intersting .

[Shadrach]

2 hours ago, Yetti said:

While the prop it's self may only hold a pint, the govenor and lines would also hold oil.   Mine was weeping a bit of grease, I read where if you do a couple of deep cycles it would reset the blades.  I did a couple of deep cycles and it fixed the grease weep.

It depends.  If the prop has been over serviced (with grease), the grease will enter the hub cavity on the spring side. Deep cycling the prop will cause the piston to force grease past the seals. Once the seals are herniated the prop will need to be removed and resealed.

[Guest]

13 hours ago, Shadrach said:

Thanks Clarence, would you kindly link the instruction if possible? This is the first I’ve heard of a Hartzell instruction regarding run-up operations.

I don't have a copy of it anymore.  The prop shop I use provided it to a client who had seepage issues with his overhaul.  It may be on the Hartzell site.

Clarence

[carusoam]

6 hours ago, bob865 said:

The governor is not a pump, only a valve (unless someone jumps in and educates me otherwise).  

Our governors are equipped with an internal gear pump to supply pressurized oil to the control valve....

So... we have two gear pumps for oil on our engines...

 

Why the engine’s oilP varies with rpm... the oil pump slows with engine rpm as well...

 

The problem I have... this is from old fuzzy memory...  anyone have a drawing of a governor? @Cody Stallings

PP thoughts only...

Best regards,

-a-

[Marauder]

Getting back to the original thread topic. Was the final determination that the parking brake somehow didn't release and that caused the issue? The reason I am asking is that having rebuilt my parking brake twice, I think it is a weak link in the system. I swear my mountain bike has a better braking system on it.

I started looking into alternatives to the Chinese made parking brake on my plane (and I mean that seriously)

 

Having some familiarity with folks who do weekend racing, I know there are hydraulic brake locks available. Like this one. Any reason why one of these couldn't be used?

https://www.jegs.com/i/JEGS/555/63028/10002/-1

 

 

[RLCarter]

33 minutes ago, Marauder said:

Any reason why one of these couldn't be used?

Add 2 zeros to the price and no one will question it

[carusoam]

20 minutes ago, RLCarter said:

Add 2 zeros to the price and no one will question it

Expect the fine print on the jegs model to still say made in China... 

Must be a different factory in China though...

Best regards,

-a-

 

[Skates97]

1 hour ago, Marauder said:

Getting back to the original thread topic. Was the final determination that the parking brake somehow didn't release and that caused the issue? The reason I am asking is that having rebuilt my parking brake twice, I think it is a weak link in the system. I swear my mountain bike has a better braking system on it.

I started looking into alternatives to the Chinese made parking brake on my plane (and I mean that seriously)

 

Having some familiarity with folks who do weekend racing, I know there are hydraulic brake locks available. Like this one. Any reason why one of these couldn't be used?

https://www.jegs.com/i/JEGS/555/63028/10002/-1

 

The brake valve was not the problem. The cable (which probably was never lubed in its life) got stuck about halfway in when I pushed to release it which was not enough to release the valve. With the cable unhooked from the valve it operated very smoothly. After some TLC the cable operates smoothly now. 

There was always quite a bit of resistance operating it from the time I got the plane a couple years ago. It would push in and it would sort of stick halfway and then pop through and go the rest of the way. I thought that was just the way the brake released (you don't know what you don't know). I didn't know that the valve is smooth throughout its range of operation.