R44 Raven I priming system

[Peter3127]

Brains Trust,

A mate has a Raven 1 with the cylinder priming system (priming pump in the back, affixed to frame).

A couple of questions:

- I have not seen reference to this system in the R44 POH available online - in Systems Description, or Supplements. Am I being thick? (It is in the Cadet POH, but this is a Raven 1).
- Would the failure of one of the cylinder priming lines cause a loss of compression in that cylinder? Or do they have check valves in lines?
- And why only 4 cylinders primed?

My personal view is that it would be rarely used, and if failure of the system could cause degraded engine performance then I would take it out. Thoughts?

Pete

p.s. keep sending pics for calendar.

[aa777888]

AFAIK, you are not being thick, and the lack of documentation leaves me unable to answer your systems questions. FWIW, there is one on the Raven I the school has here. I've never used it and never seen it used, not even in the dead of winter. They don't even train it, other than to make sure it is locked during pre-flight.

[Robbiee]

The only reference I've ever seen to it is in the checklist where all it says is, "prime as necessary". I have used it once, but that was a long time ago. This is a question I would save for my next trip to the RHC Safety Course, or perhaps just email their maintenance guy, Pat Cox I believe is his name?

[Pat Cox]

Relevant description is in
-R44 POH Section 7, SYSTEMS DESCRIPTION, page 7-26 dated 21 FEB 2014, specifically ENGINE PRIMER SYSTEM (OPTIONAL)
-R44 IPC Ch 28 FUEL SYSTEM, Figure 28-33 on page 28.32 dated JAN 2014.
-R44 IPC Ch 28 FUEL SYSTEM, Figure 28-37 on page 28.36 dated JAN 2014 (early type, rarely seen due most having been upgraded to preceding).

There are two check valves within the primer pump itself: inlet & outlet. If, contrary to instructions, the primer pump handle is not locked after priming then a small amount of fuel can flow thru both check valves and cause rough idling; the engine with run smoother as MAP is increased (due to less fuel flow thru check valves).

Referenced documents freely available at https://robinsonheli.com under the Publications tab.

[Torquetalk]

Prime as needed:

Cold weather: five or six rolls of the throttle.
Warm weather: 1 or 2

No need to lift the collective whilst doing this. Opening and closing the throttle will open the butterfly valve and induce a fuel flow without cockpit gymnastics.

Close throttle, crack very slightly.

Don’t rev on start! (risks tearing teeth on the starter ring)

[aa777888]

Prime as needed:

Cold weather: five or six rolls of the throttle.
Warm weather: 1 or 2

No need to lift the collective whilst doing this. Opening and closing the throttle will open the butterfly valve and induce a fuel flow without cockpit gymnastics.

Close throttle, crack very slightly.

Don’t rev on start! (risks tearing teeth on the starter ring)
:ok: .

[Peter3127]

Relevant description is in
-R44 POH Section 7, SYSTEMS DESCRIPTION, page 7-26 dated 21 FEB 2014, specifically ENGINE PRIMER SYSTEM (OPTIONAL)
-R44 IPC Ch 28 FUEL SYSTEM, Figure 28-33 on page 28.32 dated JAN 2014.
-R44 IPC Ch 28 FUEL SYSTEM, Figure 28-37 on page 28.36 dated JAN 2014 (early type, rarely seen due most having been upgraded to preceding).

There are two check valves within the primer pump itself: inlet & outlet. If, contrary to instructions, the primer pump handle is not locked after priming then a small amount of fuel can flow thru both check valves and cause rough idling; the engine with run smoother as MAP is increased (due to less fuel flow thru check valves).

Referenced documents freely available at https://robinsonheli.com under the Publications tab.


Oooh, now I feel just a wee bit stooopid. Thanks Pat.

[Pat Cox]

Please don't feel embarrassed - many folks expect the tech documents to be behind a paywall, but I encouraged management to make them free ergo they are.:)

[bvgs]

https://cimg9.ibsrv.net/gimg/pprune.org-vbulletin/2000x1504/659d7047_33ef_4654_b42a_34ade052212d_e660e164c00a360333b6851 0acd103e00550e05d.jpeg
https://cimg1.ibsrv.net/gimg/pprune.org-vbulletin/2000x1504/5886f33f_ccea_4669_8407_53de6fd8b129_863206113516766c1f09869 41e03dbe0fdf9bd33.jpeg
Can someone advise the correct method for using this. I would normally twist the throttle several times to prime but seen this on a machine today and wondered if anyone can shine a light. Thanks.

[Luther Sebastian]

Got about 150 hours on the Raven 1 and to my shame can’t remember seeing that behind the flap - if it’s even there on the one I fly. Only ever primed with the throttle.

[Robbiee]

Hmm,..thought you just twisted it until it pops up, then just push it back down?

[mechpowi]

That prime pump is probably optional. I've flown one Raven I (in addition to Raven IIs) and it had that installed. I was shown how to use it on cold engine, maybe three strokes during the last pre-flight walkaround. Worked like charm, way better than Raven II, but can't compare it to Raven Is without the sysytem. IIRC only twist grip turns was the practice with warm engine.

[muermel]

It's an optional primer pump. Very useful when flying in the winter time in colder climates. Flew the 44 a lot for pipeline inspections and below 0°C it was a real pain to get the Raven 1 to fire up in the winter in the morning. With the primer pump you unlock it, pump it a couple of times until it draws fuel (you can feel it in the movement of the stroke) and after that pump 2-3 times. Much more efficient than twisting the throttle 40-50 times to get it to fire maybe once and die again straight away. When it's cold you don't have many attempts before the battery dies. Also very helpful to pull all the CBs of unnecessary electrical consumers for starting and to have a 2nd guy turn the tailrotor/ drivetrain whil you're cranking.

[lelebebbel]

The primer pump injects fuel directly onto the intake valves. Opening the throttle just dumps it into the carb, where it still has plenty of opportunity to condense anywhere along the intake runners. In very cold weather, the primer is far more effective and also reduces the chances of lighting your air filter on fire during start.

I believe the primer lines connect to the same fitting that the manifold pressure line is attached to, which is why it doesn't prime all 6 cylinders.

[as350nut]

I have used the primer in R44 1 and r22 , with a cold aircraft sometimes they can be hard to start; 3 to 5 primes then go to start and all is good, alternatively a small room heater under the carbi box for about 20 minutes works just as well but obviously only at home hangar. I think the primer is a good thing (still got a spare one in the shed somewhere)