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Piston Engine Start...  
User currently offlineCaptaink From Mexico, joined May 2001, 5108 posts, RR: 12
Posted (10 years 11 months 6 days 12 hours ago) and read 4496 times:

Why do piston engines rotate two or three times before actually starting?


There is something special about planes....
5 replies: All unread, jump to last
 
User currently offlineB747Skipper From , joined Dec 1969, posts, RR:
Reply 1, posted (10 years 11 months 6 days 10 hours ago) and read 4403 times:

Car engines do the same, the starter does require to rotate the engine a few revolutions before starting. I never flew the "props" when I started with the airlines, but "old timers" told me that they had, i.e. to "count the blades" (when rotating the starter to start engines) - count 9 blades could be 3 complete engine rotations, for a 3 bladed R-2800 engine, or 12 blades for a R-3350 with 4 bladed propellers...
xxx
Obviously, it takes the carburetor (or engine gas injection system) to fill the cylinders of the air and fuel mixture to permit ignition and start... and this can only be achieved by a couple of rotations...
xxx
Any "old timer" here to be more accurate in this explanation for our friend Captaink...?
Happy contrails...
(s) Skipper


User currently offlineRalgha From United States of America, joined Nov 1999, 1614 posts, RR: 6
Reply 2, posted (10 years 11 months 6 days 9 hours ago) and read 4348 times:

That's a good question, they don't always rotate much either, often they'll start in half a turn. I'll ask a mechanic.

 Big thumbs up



09 F9 11 02 9D 74 E3 5B D8 41 56 C5 63 56 88 C0
User currently offlineSllevin From United States of America, joined Jan 2002, 3376 posts, RR: 6
Reply 3, posted (10 years 11 months 6 days 5 hours ago) and read 4319 times:

I was always told that you rotated the big radials, as Skipper described, in order to clear the bottom cylinders of any fuel and oil buildup -- worst case, if you were going to get a hydraulic lock, better to only hit it with the starter's force without adding the torque of firing cylinders. A secondary reason was to start the oil flowing.

Modern GA aircraft are flat (opposed) and thus, hydraulic lock isn't a big issue.

Steve


User currently offline411A From United States of America, joined Nov 2001, 1826 posts, RR: 8
Reply 4, posted (10 years 11 months 6 days 4 hours ago) and read 4312 times:

Starting large radial engines require a definate procedure.

Will be running the R2800 engines on a friends Lockheed PV2 aircraft next week and the start sequence is (cold engine)...

Engage start and start safety switch simultaneously.

Rotate engine a MINIMUM of 12 blades.

Switch mags to 'both', and at the same time hold down the ignition boost and prime switches until the engine fires, release the start, start safety and ignition boost switches, and keep the engine running with the engine prime until the mixture control can be moved to the auto/lean position.

Use prime as necessary to keep the engine running, then move mixture to auto/rich.

Warm engine is the same except initial rotation is only nine blades.





User currently offlineFlightSimFreak From United States of America, joined Oct 2000, 720 posts, RR: 0
Reply 5, posted (10 years 11 months 5 days 6 hours ago) and read 4235 times:

Does this thread help?

http://www.airliners.net/discussions/tech_ops/read.main/53370/4/


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