Topic Author
Posts: 3996
Joined: Wed May 23, 2001 10:43 am

Piston Engine Start...

Sun May 25, 2003 11:49 pm

Why do piston engines rotate two or three times before actually starting?
There is something special about planes....

RE: Piston Engine Start...

Mon May 26, 2003 2:06 am

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...
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...
Any "old timer" here to be more accurate in this explanation for our friend Captaink...?
Happy contrails...
(s) Skipper
Posts: 1589
Joined: Tue Nov 09, 1999 6:20 pm

RE: Piston Engine Start...

Mon May 26, 2003 3:26 am

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.

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RE: Piston Engine Start...

Mon May 26, 2003 7:10 am

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.

Posts: 1788
Joined: Mon Nov 12, 2001 10:34 am

RE: Piston Engine Start...

Mon May 26, 2003 8:03 am

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.

Posts: 698
Joined: Sun Oct 29, 2000 9:36 am

RE: Piston Engine Start...

Tue May 27, 2003 5:44 am

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