Priming inflight

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badmash
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Priming inflight

#1 Post by badmash » Sun Aug 27, 2017 1:07 pm

What are the possible consequences of priming a piston engine in flight when the engine is running?
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JasonE
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Re: Priming inflight

#2 Post by JasonE » Sun Aug 27, 2017 1:19 pm

It runs rich momentarily & you waste fuel.
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Re: Priming inflight

#3 Post by Cat Driver » Sun Aug 27, 2017 3:56 pm

Why would you even think of priming in flight?
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Re: Priming inflight

#4 Post by Big Pistons Forever » Sun Aug 27, 2017 4:26 pm

If the engine has failed and you have checked all the obvious things, and have time for more troubleshooting, it is worth trying a shot of prime to see if the engine will run. I have heard of a case where the pilot was able to use the primer to get enough engine power extend the glide enough to make it to a nearby airport.

One issue that does not seem to be well known in flight schools is that an unlocked primer could bypass enough extra fuel to to give the engine such an over rich mixture that it will run rough. If the engine is running rough and you have checked for carb ice and the mixture control, it would be worth giving the primer knob a pull to see if it was locked in.
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Re: Priming inflight

#5 Post by PilotDAR » Sun Aug 27, 2017 4:55 pm

I have heard of a case where the pilot was able to use the primer to get enough engine power extend the glide ...
'Been there, done that... I was able to stretch the glide and warm the engine enough and use carb heat, that at a lower altitude I could continue with great caution (it was a night flight, so I was well motivated to remain airborne). Carb air temperature indicator installed shortly after! It is necessary to find a partial throttle setting appropriate to pumping the primer steadily.
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Re: Priming inflight

#6 Post by crazyaviator » Sun Aug 27, 2017 9:43 pm

One might want to go to altitude, ( over an airport or lake ) pull the mixture and feed in primer to keep the engine going at cruise, you will loose some power as you reach the bottom of the stroke ,,,,,
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Re: Priming inflight

#7 Post by badmash » Mon Aug 28, 2017 1:28 pm

Cat Driver wrote:Why would you even think of priming in flight?
Because every checklist involves checking the primer being locked. Hence, the question, what would happen if the primer were unlocked or an accidental shot of primer was sprayed!
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Re: Priming inflight

#8 Post by badmash » Mon Aug 28, 2017 1:29 pm

PilotDAR wrote:
I have heard of a case where the pilot was able to use the primer to get enough engine power extend the glide ...
'Been there, done that... I was able to stretch the glide and warm the engine enough and use carb heat, that at a lower altitude I could continue with great caution (it was a night flight, so I was well motivated to remain airborne). Carb air temperature indicator installed shortly after! It is necessary to find a partial throttle setting appropriate to pumping the primer steadily.
You suspected carb ice? and priming helped warm the engine?
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Re: Priming inflight

#9 Post by Cat Driver » Thu Aug 31, 2017 3:37 pm

what would happen if the primer were unlocked or an accidental shot of primer was sprayed!
And how does one accidentally give the engine a shot of prime in flight?
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Re: Priming inflight

#10 Post by digits_ » Thu Aug 31, 2017 3:47 pm

Cat Driver wrote:
what would happen if the primer were unlocked or an accidental shot of primer was sprayed!
And how does one accidentally give the engine a shot of prime in flight?
Primer wasn't locked, moves slowly out due to vibrations, you notice it and push it back in to where it belongs in a reflex.
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Re: Priming inflight

#11 Post by Cat Driver » Thu Aug 31, 2017 4:01 pm

Primer wasn't locked, moves slowly out due to vibrations, you notice it and push it back in to where it belongs in a reflex.
I should not have asked.

So what you are saying is the pilot did not check the primer was locked before take off and while flying noticed it was unlocked and had vibrated out so instead of slowly pushing it back in and locking it the pilot jammed it back in and temporarily increased the mixture to over rich?

Yeh, that sounds believable and reflects on poor airmanship and poor training more than anything else.
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Re: Priming inflight

#12 Post by Zaibatsu » Thu Aug 31, 2017 4:56 pm

He was asking hypothetically.

I know what happens. Nothing, really. Engine will run rough for a few seconds, then continue on. Was that so hard?
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Re: Priming inflight

#13 Post by Cat Driver » Thu Aug 31, 2017 5:02 pm

I know what happens. Nothing, really. Engine will run rough for a few seconds, then continue on. Was that so hard?
No it was not so hard.

There are many types of engine priming.

Some are more effective than others.

Which method of priming do you think is most effective and will induce more fuel into the engine, throat priming or cylinder priming?
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Re: Priming inflight

#14 Post by Zaibatsu » Thu Aug 31, 2017 5:11 pm

You forgot the third kind, manifold priming.

Each has its advantages and disadvantages. Cylinder priming gets the fuel right into the intake port, but usually not all cylinders have primers. Throat primers will supply all cylinders, but you have to get the charge into the cylinders with cranking otherwise the fuel can condense and drain into the air box. Manifold priming is in between, closer to the cylinders than a throat primer, but able to supply more than one cylinder.

With the engine running, things are moving so fast it doesn't matter where the primer is. Either you really rich out a few cylinders or partially rich out all of them.
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Re: Priming inflight

#15 Post by JasonE » Thu Aug 31, 2017 5:56 pm

I noticed my Lycoming only has primers on 3 cylinders. What is the purpose of 3 instead of 4?
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Re: Priming inflight

#16 Post by ahramin » Thu Aug 31, 2017 8:36 pm

Is there anything plugged into the 4th cylinder? Manifold pressure gauge?
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Re: Priming inflight

#17 Post by JasonE » Fri Sep 01, 2017 5:33 am

Just a solid plug.
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Re: Priming inflight

#18 Post by ahramin » Fri Sep 01, 2017 6:27 am

The purpose then would be it's cheaper (or for a homebuilt, less work). I flew one last month that only had two cylinders primed.
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Re: Priming inflight

#19 Post by digits_ » Fri Sep 01, 2017 9:04 am

Cat Driver wrote: So what you are saying is the pilot did not check the primer was locked before take off and while flying noticed it was unlocked and had vibrated out so instead of slowly pushing it back in and locking it the pilot jammed it back in and temporarily increased the mixture to over rich?

Yeh, that sounds believable and reflects on poor airmanship and poor training more than anything else.
So what you are saying is that no (student) pilot ever made the mistake of not properly locking the primer? I've seen it happen, so yes, it is believable. Even if you push it back in slowly, you are still priming the engine in flight. It's something you are not supposed to do, which makes the question of "what would happen if..." very interesting.
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Re: Priming inflight

#20 Post by Cat Driver » Fri Sep 01, 2017 4:48 pm

So what you are saying is that no (student) pilot ever made the mistake of not properly locking the primer? I've seen it happen, so yes, it is believable.
Without sounding pedantic on this issue I was merely stating that the use of the primer if one is in the airplane is something that the student should understand and use properly during basic training, reflex actions are not a sign of proper training, thinking before acting is.

The correct use of engine controls was one of the most frustrating problems I had with instructors when I owned a flight school.

It was common for them to set a power setting and then control taxi speed with the brakes, then on take off they just slammed the throttle full in like it was some kind of contest to see how fast they could get it from taxi RPM to full power.
Primer wasn't locked, moves slowly out due to vibrations, you notice it and push it back in to where it belongs in a reflex.
When I read the above it said " you " not the student.
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Re: Priming inflight

#21 Post by crazyaviator » Sun Sep 03, 2017 5:37 pm

If there is a spot for a 4th primer on a lyc engine, I almost always install one for better ( quicker ) starting. For a homebuilt, I would imagine one could install a variable fuel boost pump to prime ( lakes have an electric primer) AND to use it in case of carburetor failure to fly to an airport !
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