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RV-12iS engine starting shudder

J

jveatch

Member
I find the initial shudder of the engine at startup to be very disconcerting. It can't be helping the gearbox have life longevity, I would think. The POH says to have both LANE A and B ON but only Fuel Pump 1 ON (fuel Pump 2 OFF) and the throttle at 50% at start. A discussion I think came from Rotax says to have only one Lane and one fuel Pump ON, and with the throttle at 50%. I tried both, and the engine/gearbox shudder is scary.

I got the least shudder so far by following the POH but with the throttle at minimum.

What is the reason for delaying turning ON the Fuel Pump 2?
 
jveatch said:
What is the reason for delaying turning ON the Fuel Pump 2?
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Jon and Rob have the answer for the starting procedure. My thought on why start using only one fuel pump is to have more wear on one fuel pump than the other so that only one fuel pump fails many hours down the airway leaving one to get you on the ground and replace both at same time.

One fuel pump gives enough fuel pressure to run so no need for the second just for start up. It exists for the purpose of backup redundancy when flying.
 
sansoneservices said:
I think rotax 912, 914 all seem to have a startup and shutdown "shudder" .. have you compared yours to another?
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I have no "shudder." Others have actually marveled at the quick start up and shut down of the engine. No "dieseling" or running on of the engine when shutting down.
 
Amadeus said:
I have no "shudder." Others have actually marveled at the quick start up and shut down of the engine. No "dieseling" or running on of the engine when shutting down.
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Not "dieseling" that I refer to, not hard starting either. Just a "shudder" upon startup and shutdown as the OP mentioned.
 
As others have mentioned crank until 1500 rpm. I had been starting it like a car with just a quick key turn and 99% of the time started right up. A few months ago on a cold morning I got a shuddering start and noticed a radiator leak later that day.
 
jveatch said:
I find the initial shudder of the engine at startup to be very disconcerting. It can't be helping the gearbox have life longevity, I would think. The POH says to have both LANE A and B ON but only Fuel Pump 1 ON (fuel Pump 2 OFF) and the throttle at 50% at start. A discussion I think came from Rotax says to have only one Lane and one fuel Pump ON, and with the throttle at 50%. I tried both, and the engine/gearbox shudder is scary.

I got the least shudder so far by following the POH but with the throttle at minimum.

What is the reason for delaying turning ON the Fuel Pump 2?
Click to expand...
The purpose for starting on a single fuel pump is explained in the FTS as being done to avoid causing damage to the engine. This potential damage is not clearly explained by Van's but is generally understood to be an avoidance of starting under reduced voltage. Running a single pump reduces the load on the electrical system during cranking and startup. Once the generators are online, pump 2 comes on.

This concept ties to others in this thread regarding slow/rough starts.
 
The verbiage in the FTS comes directly from the Rotax "Operators Manual" (OM_912 i Series_ED2_R1.pdf).

This is only one page of four outlining start up procedures.

912iS OM Start.png

NOTE: Item 6, "ACTIVATE START POWER SWITCH" is controlled automatically in the RV-12iS by the Ignition Module and the HIC Module using a feature called START BUTTON BYPASS, relieving the pilot from activating another switch during start up.
 
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jrtens said:
Make sure you hold the start switch on until 1500 rpm. Both lanes on.
Click to expand...

CessnaTPA said:
As others have mentioned crank until 1500 rpm. I had been starting it like a car with just a quick key turn and 99% of the time started right up. A few months ago on a cold morning I got a shuddering start and noticed a radiator leak later that day.
Click to expand...
I failed to mention that the overnight temperature here in the Puget Sound area of Washington (Bremerton) has been about 30º and slightly below that. That may be part of my present experience. The plane is new to me, so I don't really know how it acts when it is warmer.
 
N8DAV8R said:
The purpose for starting on a single fuel pump is explained in the FTS as being done to avoid causing damage to the engine. This potential damage is not clearly explained by Van's but is generally understood to be an avoidance of starting under reduced voltage. Running a single pump reduces the load on the electrical system during cranking and startup. Once the generators are online, pump 2 comes on.

This concept ties to others in this thread regarding slow/rough starts.
Click to expand...
Starting the engine with reduced battery voltage may cause kick back because of difficulty pulling through compression stroke. This is very hard on the starter motor one-way Sprag clutch bearing which can easily be damaged and difficult to replace...

I keep my battery fully charged with a 6-amp Odyssey battery charger. Odyssey chargers are designed to work with sealed AGM batteries. The charger is connected 24/7 when the plane is in the hanger. Odyssey says it is perfectly acceptable to keep battery connected to charger indefinately. The unit only charges when battery voltage falls below a set value. A fully charged battery assures fast powerful cranking...

1739542803416.jpeg 1739542843755.jpeg
 
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