View Single Post
  #473  
Old 10-01-2010, 06:43 AM
WTE_Galway WTE_Galway is offline
Approved Member
 
Join Date: Jul 2008
Posts: 1,201
Default

Quote:
Originally Posted by Blackdog_kt View Post
Would be nice if it was modelled according to the amount of priming.

Since different ambient temperatures demand different amounts of priming (more priming for cold weather starts), it is entirely possible to over-prime if you misjudge the effect of atmospheric temperature and get the flames.

Apart from experience with operating the engine, the other way to prevent unburnt fuel from dripping out the exhaust is to slightly under-prime before turning the engine, then as it's turning prime further until it starts and seems to stabilize in RPM. However, you can't do that in most fighters because they lack the capacity to run their starters for a long time.

Multi-engined aircraft had continuous direct drive starters or hybrid inertia and direct drive starters. The B17 had the latter, the inertia starter would spin up (energize phase) and then coupled to the engine to start turning it (start phase) but if it failed to start instantly the starter kept turning the engine, albeit at a lower RPM, driven by battery power.

However, most batteries of the time couldn't reach a sufficient capacity to run a continuous starter without the battery weight becoming prohibitive for use on fighters. That's why most fighters used pure inertia starters or even cartridge starters (blank shotgun shells that when fired, provided the energy to turn the engine). I think cartridge starters were more common on RAF types.

US and German ones mostly used battery driven inertia starters. Instead of spinning the entire engine the battery is used to spin a metal disk to very high RPM and then that disk is connected to the engine via a clutch mechanism, transferring its rotational motion to the engine's axis (the crankshaft, isn't this what this is called?) and turning the engine for start. Since the metal disk is essentially a free spinning flywheel that doesn't have to work against piston compression, it's easier to spin it without draining the battery. Of course, the amount of energy transferred between each system is the same (minus the friction/heat loss), but for brief periods of turning the engine (assuming it will start within 2-3 attempts with the inertia starter) the drain on battery would probably be less than using a direct drive mechanism.

Some of the German planes even used hand-cranked inertia starters. This is widely visible on videos of aircraft using the DB engines, like 109s and 110s, where the mechanic is manually winding up the starter.

However, in the videos posted by Richie we can see the 109 G-10 starting on its own. I'm not sure if it was like that originally, or the mechanics at EADS took advantage of modern technology and installed a battery capable of powering the inertia starter without the need for hand-cranking.
The other common one was compressed air. See the Fiat at 0:58 here:

Reply With Quote