LoneWolf wrote:I have a question about taxiing the Spitfire, I think I must be missing something because it feels wrong. After a while of what I would call a sensible taxiing speed the engine starts to choke a little and needs a bit more gas to clear it. Only problem is if I do that it wants to zoom off!
Slowing down the taxi speed when approaching curves in the taxiway it's normal for the engine to run a little rough. You need to clear the plugs by applying throttle a bit occasionally. Because you can't shut the throttle completely for a longer period, you really have to start slowing down very early so that you can keep it idling at lower end of stable idle rpm range.
So, maybe try a slower taxi speed or at least anticipate and act pro-actively very early. It's a difficult compromise between adequate taxi speeds (considering poor cooling while at low speeds, and increased time spent if taxing slow) and the risk of hitting the curve at too high speed and not managing to slow down to it without use of brakes. My suggestion would be that if you take off from airports that have long taxiways, start taxing earlier but don't hurry when doing the taxi. Using low idle rpm. You can take your time taxiing that way, no need hurry to avoid overheat.
LoneWolf wrote:Should I be running with lean mixture am I putting too much fuel into the engine?
Impossible. You cannot move the mixture lever further forward (to lean) than your throttle is. You need at least 1/3 of throttle before you can lean out the mixture. The mixture lever is physically forced to stay in rich position at low throttle. (This however is not modeled in Accusim. But for authenticity, do use rich mixture until you get airborne. Running the engine with 1/3 throttle required to put it into lean, is way too much throttle to have a properly slow taxi speed.)
LoneWolf wrote:Or and I running at the wrong RPM?
Yeah. If your engine runs rough on deceleration and increasing throttle to clear it up launches you forward, you need to find some middle ground between the two. A single millimeter of travel on your throttle quadrant can make a difference here. A low throttle setting just above rough running that can be sustained and would still allow the plane to slow down when approaching corners. On a paved taxiway, the rolling resistance is very low, so the required throttle setting to allow the plane to slow down even at a modest amount of deceleration is very close to being too closed for running well. Because of this, you should probably taxi slower. If temperatures are an issue, start your taxi before you finish warm up. Do your warm-up while taxing to take-off position. It requires very little power to taxi, so there's really no reason why you can't taxi with a cold engine. You don't need to rev it at all.
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I, myself, usually don't start taxi right away, even on airports with longer taxiways. I let it warm up to around 70 deg C before starting taxi, because this allows the taxiing to dissipate some heat away from the coolant (cold coolant wouldn't cool down) and I get my oil warmer by spending some extra time on the ground.
For people who are just getting used to Spitfire, I'd recommend starting taxi earlier so they don't need to hurry with the taxi. You may have a bit lower oil temperature (and thus higher oil pressure when taking off) if you do your warm up while taxiing to take-off position but this is usually
not a problem since it's normal for oil pressure to go off-the scale during take off. 15 deg C oil temp is absolute minimum and 30 deg C is highly recommended. Reaching 30 deg C is usually achievable even without any special tricks so feel free to taxi with a cold engine when in warm or mildly cool weather.
In cold weather, you may want to warm up stationary because likelihood of overheating is significantly reduced and even slow taxi speeds are adequate to cool down the engine. Starting taxi only after your engine coolant has risen to normal operating temperature (i.e the thermostat valve that blocks coolant flow to the cooler has opened) can give you an extra minute of warm-up time. It of course depends on the length of your taxiway.
In
very cold weather, or when you have no taxiway to use and have the plane in take-off position, you can consider starting the engine and shutting it down via normal shut down procedure once the coolant temperature has hit about 100 deg C. Let it cool down and restart (coolant cools down faster than the engine), and you get a second warm-up.