M20K - Power Loss - In Flight Procedure Question

[FlyWalt]

While comparing procedures between my 1979 POH and a friend's 1983 manual, we noted that the 79 manual calls for turning on the High Bosst Pump.

Meanwhile, the 83 model calls for the Low Boost Pump.

Does anyone know why this changed?

[FlyWalt]

Wow, 73 views and no one takes a shot at the answer??

Ok let me rephrase the question: You are flying along in your M20K and your engine driven fuel pump fails thus shutting down the engine. Which boost pump are you going to switch on to try to restart the engine.

First one to respond wins the rubber nickel :-)

[Cruiser]

the one recommended in the POH

[Shadrach]

What kind of fuel pressure do you get from the mechanical pump in flight? I would use whatever level of boost approximated the mechanical pump. 

If that didn't work, then I'd try the other...

Edited October 19, 2015 by Shadrach

[ArtVandelay]

I would try low power, if no joy, I would try high power, if that didn't work I'd try both...if you lose power no point in not trying everything.

[jrwilson]

Wow, 73 views and no one takes a shot at the answer??

Ok let me rephrase the question: You are flying along in your M20K and your engine driven fuel pump fails thus shutting down the engine. Which boost pump are you going to switch on to try to restart the engine.

First one to respond wins the rubber nickel :-)

 

 

Per my 84 model, if engine driven pump quits, I go for high boost.  But mine is an 84 by serial number, built in 83, with a manual written in 83...Are you positive your friend's manual says what he thinks it says?

 

 

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Edited October 19, 2015 by jrwilson

[jrwilson]

Low boost is for fluctuating pressure

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[chrisk]

I seem to recall the high boost pump will cause an over rich ssue when operating the engine with low horse power.  

[kmyfm20s]

My non-turbo calls for trying the low first and if that doesn't work then try the high.

[nels]

Probably has to do with if the engine is running and turbo putting out boost. The pump does need to overcome boost pressure in order to deliver fuel.

[jrwilson]

Probably has to do with if the engine is running and turbo putting out boost. The pump does need to overcome boost pressure in order to deliver fuel.

But in this scenario, the engine isn't running.

[jrwilson]

Wow, 73 views and no one takes a shot at the answer??

Ok let me rephrase the question: You are flying along in your M20K and your engine driven fuel pump fails thus shutting down the engine. Which boost pump are you going to switch on to try to restart the engine.

First one to respond wins the rubber nickel :-)

 

So do I win the fabulous rubber nickel prize?  I don't know what that is, but I want it!

I didn't really answer the question fully, regarding why the manual changed...  To fully answer that part, I vote the manual probably didn't change and your friend may have misread the manual.  I base my well reasoned response on the fact that my manual written in 1983 says the same as your manual, written in 1979, go to high boost pump in the event of an engine failure. 

You can PM me for my address to send my winnings...   

[nels]

But in this scenario, the engine isn't running.

 

Edited October 20, 2015 by nels

[jrwilson]

Right, if it isn't running then use low boost pump. If it is running and turbos are putting out boost then turn on high boost pump. 

If there is an engine failure I guess your screwed no matter which pump you turn on.

well not to be picky, but if someone was reading this and trying to learn something about the proper engine operation, it might matter...the point is, if there is an engine failure, it most certainly does matter which pump you turn on, because one puts out the required fuel flow for a possible engine restart, while the other does not.

so again, if it isn't running, use HIGH boost, not low...if it is running and you have pressure fluctuations or roughness, the go for LOW boost pump.

as always, chech your POH because I'm just some guy on the Internet and my source is a specific year model POH...but the point of knowing this, and the reason the OP's question was a good one is because your not screwed in case of an engine failure...that's why there are restart procedures.

 

[Guest]

To clear up confusion, the plane has only one airframe boost pump.  It can run a two different speeds as indicated by a two position switch.  The speeds are adjustable through an electric fuel pressure regulator, this adjusts pump motor speed.

The engine driven pump on a TCM engine is a direct displacement pump, for every revolution it turns it delivers the same volume of fuel to the fuel injection system. Hence greater engine RPM results in greater fuel volume delivery.

I doubt the engine will run at the low setting.  The only way to test this is to remove the fuel pump drive shaft and run the boost pump and then start the engine 

Running the boost pump in the "high" setting with the engine at low RPM may result in a richer mixture, which can be leaned.  Far better than gliding to the crash with the pump on "low"

Clarence

[nels]

well not to be picky, but if someone was reading this and trying to learn something about the proper engine operation, it might matter...the point is, if there is an engine failure, it most certainly does matter which pump you turn on, because one puts out the required fuel flow for a possible engine restart, while the other does not.

so again, if it isn't running, use HIGH boost, not low...if it is running and you have pressure fluctuations or roughness, the go for LOW boost pump.

as always, chech your POH because I'm just some guy on the Internet and my source is a specific year model POH...but the point of knowing this, and the reason the OP's question was a good one is because your not screwed in case of an engine failure...that's why there are restart procedures.

 

I know what you are saying but I guess it depends on your definition of engine failure. I think he is talking an engine still running but not correctly. 

I guess I don't understand the logic of high pump pressure for an engine not running versus low pressure for one that is running? Not being sarcastic but would like to understand.

[jrwilson]

I know what you are saying but I guess it depends on your definition of engine failure. I think he is talking an engine still running but not correctly. 

I guess I don't understand the logic of high pump pressure for an engine not running versus low pressure for one that is running? Not being sarcastic but would like to understand.

HIGH boost puts out more fuel flow, which is needed for restart, or is sufficient for standing in for a failed fuel pump.  LOW boost puts out less flow, which is not sufficient to restart or run the engine, but can help if the fuel pressure is low or fluctuating.  Using HIGH boost when the engine is running, when it isn't called for, will cause an over-rich situation, which can cause an engine failure.  That is why the HIGH boost pump has a switch guard.

[nels]

I didn't realize the two pumps were purposed to deliver different flow. I was assuming they delivered different pressure.

I'm really not familiar with the turbo Mooney as such. I do know a supercharged engine on the ground that has a mechanical pump delivering say, 6 psi to the induction system,  will only run up to 6 psi boost pressure. Anything above that the engine will quite as the boost will start to blow the fuel back into the tank. I thought the turboed Mooney may have a high and low pressure pump to accommodate this type of problem at high altitude.

[jrwilson]

I didn't realize the two pumps were purposed to deliver different flow. I was assuming they delivered different pressure.

I'm really not familiar with the turbo Mooney as such. .

Then perhaps turbo mooney procedural questions aren't the best topics for you to reply. Telling people which pumps to use in critical phases of an emergency procedure are probably best left to those with a POH to reference and passing familiarity with the plane type.

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[Guest]

I didn't realize the two pumps were purposed to deliver different flow. I was assuming they delivered different pressure.

I'm really not familiar with the turbo Mooney as such. I do know a supercharged engine on the ground that has a mechanical pump delivering say, 6 psi to the induction system,  will only run up to 6 psi boost pressure. Anything above that the engine will quite as the boost will start to blow the fuel back into the tank. I thought the turboed Mooney may have a high and low pressure pump to accommodate this type of problem at high altitude.

There are not 2 electric fuel pumps in a Mooney.  One pump with 2 speeds.

Clarence

[nels]

 

Then perhaps turbo mooney procedural questions aren't the best topics for you to reply. Telling people which pumps to use in critical phases of an emergency procedure are probably best left to those with a POH to reference and passing familiarity with the plane type.

 

 

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That's an odd response!  I'd like to know how and why it works as it does and I would imagine the originator of this thread would like to know also. Not trying to step on any toes, just trying to learn something.

And if FlyWalt is correct saying there are two different procedures from the early model to the later then what do you have to say? Again, I could be wrong but wasn't there an induction change in that model in 1983?

[nels]

There are not 2 electric fuel pumps in a Mooney.  One pump with 2 speeds.

Clarence

Thanks Clarence. Makes sense.

[jrwilson]

Right, if it isn't running then use low boost pump. If it is running and turbos are putting out boost then turn on high boost pump. 

If there is an engine failure I guess your screwed no matter which pump you turn on.

That's an odd response!  I'd like to know how and why it works as it does and I would imagine the originator of this thread would like to know also. Not trying to step on any toes, just trying to learn something.

And if FlyWalt is correct saying there are two different procedures from the early model to the later then what do you have to say? Again, I could be wrong but wasn't there an induction change in that model in 1983?

Yeah, the first post just came across as very opinionated and I worry these types of posts could lead people astray, thinking that the person posting is knowledgeable on the subject.  It probably just came out wrong or I have a predisposed bias to it, either one.  I used to have a C model, with only one setting boost pump, and I hope I wouldn't have went blasting around with an opinion on this topic when I really would have no idea.

It would be nice if everyone would post what type of plane they fly, so we can have some idea where their opinion comes from.  Nels, nothing personal about you of course.

[nels]

 

Yeah, the first post just came across as very opinionated and I worry these types of posts could lead people astray, thinking that the person posting is knowledgeable on the subject.  It probably just came out wrong or I have a predisposed bias to it, either one.  I used to have a C model, with only one setting boost pump, and I hope I wouldn't have went blasting around with an opinion on this topic when I really would have no idea.

It would be nice if everyone would post what type of plane they fly, so we can have some idea where their opinion comes from.  Nels, nothing personal about you of course.

I thought about it and you are right. Not intentional but might be perceived as fact. So, I deleted it. 

By the way, I own an E model. For what it's worth, I also collect and restore old supercharged Studebaker's. A far cry from a K Mooney but similarities in induction systems to some degree.

 

Edited October 20, 2015 by nels

[jrwilson]

I thought about it and you are right. Not intentional but might be perceived as fact. So, I deleted it.

 

  You seem like a reasonable person and if only everyone on the internet was more like you, it would be a great place!