over prime

[dvm]

Does anyone know if you can over prime (flood) the engine in the accusim mustang. I have looked in the manuals and can't find any info. There have been occasions when I am having trouble starting and am not sure if it is a fuel starvation problem or the opposite. As in the real world it is sometimes difficult to determine what is going on. When I am stumped in the real world with a small engine I just pull a spark plug and the condition is obvious. If this condition is modeled would you use the normal procedure to clear the engine ?

[Gypsy Baron]

I have apparently over-primed in the past. Usually I just let the aircraft sit for a few minutes then start
cranking it over again. After several blades I then hit the primer once and listen to the
engine. If it tries to 'catch' I'll hit the primer again.

Paul

[DHenriques_]

Does anyone know if you can over prime (flood) the engine in the accusim mustang. I have looked in the manuals and can't find any info. There have been occasions when I am having trouble starting and am not sure if it is a fuel starvation problem or the opposite. As in the real world it is sometimes difficult to determine what is going on. When I am stumped in the real world with a small engine I just pull a spark plug and the condition is obvious. If this condition is modeled would you use the normal procedure to clear the engine ?

Over priming the engine is possible as the primer system is modeled. The trick with starting the Mustang is in handling the primer properly. It's EXTREMELY sensitive. WE have it modeled as it is in the actual airplane as a momentary ON switch. In the real aircraft the primer pulls fuel directly from the engine driven fuel pump and from there right into the intake manifold. Done right it doesn't take a lot of primer fuel to start a Merlin.
The RIGHT way to use the primer is a bit tricky. In the real Mustang the RIGHT way to prime the engine is with the mixture in ICO and with the ENGINE TURNING. What makes this a bit difficult is that using a mouse as your hand you don't have the ability to split your fingers between the primer, the starter, and the mag switch so holding the primer in the ON position with a mouse as you use the starter and the primer is as one might say.......a bit tricky; unless you're an octopus that is, which helps in the real airplane as well )))
I believe what Scott ended up doing with the programming was to allow you to use the primer , THEN go to the starter which is a HOLD function once energized. This allows you to have the prop turning as you move the mouse on over to the mag switch and go to BOTH after 6 blades have passed.
Anyway, this is how I start the A2A Mustang.
Just remember, that primer is sensitive.
Perhaps Scott can chime in and inform you on exactly how we handled the over prime condition in Accusim.
Dudley Henriques

[dvm]

Thanks for the info Dudley & Paul,

I don't generally have much trouble starting. I have a switch panel and a toggle on/off switch for the primer and intermittent switch for the starter so it is easy to control these functions. I usually do as you suggested and crank the engine while priming. The times when I have a little trouble is when I let the engine die. Here is something I am not sure is correct. I just made a flight and after taxiing back to the tie down I attempted to shut down the engine by pulling the mixture to cutoff and the engine kept running. I cut the mags and the engine of course shut down. I then realized that I had left the prime switch energized for the entire flight and it was running on prime when I attempted to shut down. Would the engine perform normally in flight with the primer left on ?

[DHenriques_]

Thanks for the info Dudley & Paul,

I don't generally have much trouble starting. I have a switch panel and a toggle on/off switch for the primer and intermittent switch for the starter so it is easy to control these functions. I usually do as you suggested and crank the engine while priming. The times when I have a little trouble is when I let the engine die. Here is something I am not sure is correct. I just made a flight and after taxiing back to the tie down I attempted to shut down the engine by pulling the mixture to cutoff and the engine kept running. I cut the mags and the engine of course shut down. I then realized that I had left the prime switch energized for the entire flight and it was running on prime when I attempted to shut down. Would the engine perform normally in flight with the primer left on ?

Into ICO and the engine not quitting would be an issue for sure.
Not sure how you have your mixture interfaced with your panel but the A2A Mustang should act like the real one so considering the A2A primer switch is a momentary ON switch, it should be releasing the primer unless held in the ON position.
For the Mustang, there should be no way the primer should be on unless something is amiss between FSX and your panel.
DH

[Kiwi Spitfire]

I jumped into the MkI Spitfire and was in a bit of a hurry the other day and didn't notice I had left the throttle at max.... Gave the usual 4-5 primes, then was busy turning it over and priming away trying to get it to catch, then I noticed the throttle. Needless to say it took a lot of turning over with the throttle closed before it would think about starting

Not exactly 'over priming' as such, but she def wasn't happy with cylinders full of fuel!

[Gypsy Baron]

I jumped into the MkI Spitfire and was in a bit of a hurry the other day and didn't notice I had left the throttle at max.... Gave the usual 4-5 primes, then was busy turning it over and priming away trying to get it to catch, then I noticed the throttle. Needless to say it took a lot of turning over with the throttle closed before it would think about starting

Not exactly 'over priming' as such, but she def wasn't happy with cylinders full of fuel!

The Mustang likes only about 10% open on the throttle. Any more and she tends to spit and sputter and
die in quick order.

I pretty much use that throttle setting on the other core aircraft as well when straring..

Paul

[DHenriques_]

I jumped into the MkI Spitfire and was in a bit of a hurry the other day and didn't notice I had left the throttle at max.... Gave the usual 4-5 primes, then was busy turning it over and priming away trying to get it to catch, then I noticed the throttle. Needless to say it took a lot of turning over with the throttle closed before it would think about starting

Not exactly 'over priming' as such, but she def wasn't happy with cylinders full of fuel!

The Mustang likes only about 10% open on the throttle. Any more and she tends to spit and sputter and
die in quick order.



I pretty much use that throttle setting on the other core aircraft as well when straring..

Paul

The spark advance is linked to the throttle. 1 inch is about right for the Merlin.
DH

[Kiwi Spitfire]

The spark advance is linked to the throttle. 1 inch is about right for the Merlin.
DH

Yep that's where I 'usually' have it in PV270 - when I am flying properly! Starts like a dream on the first cart most the time.

[dvm]

In regards to my leaving the primer on I have a on/off switch assigned to the primer rather than a momentary switch which frees up a hand during starting. I realize now you could not accidentally leave the prime on in the real Mustang. Still curious what would happen if you held the primer in flight. I assume it would just cause a slightly rich mixture as the amount of fuel delivered from the primer system would be miniscule as compared to the amount of fuel delivered with a reasonable power setting in flight. Nothing like coming up with theoretical foolishness.

[DHenriques_]

In regards to my leaving the primer on I have a on/off switch assigned to the primer rather than a momentary switch which frees up a hand during starting. I realize now you could not accidentally leave the prime on in the real Mustang. Still curious what would happen if you held the primer in flight. I assume it would just cause a slightly rich mixture as the amount of fuel delivered from the primer system would be miniscule as compared to the amount of fuel delivered with a reasonable power setting in flight. Nothing like coming up with theoretical foolishness.

Because of the momentary on switch I've naturally never considered this possibility. Considering the design of the fuel system my best guess without research would be that you are basically correct. Since the primer pulls fuel directly off the engine driven fuel pump and the pump is in operation with the engine running the result SHOULD be simply a slightly enriched mixture going into the intake manifold. I don't see that as a game changer.
DH

[dvm]

Thanks everyone for the input, good discussion and as always Dudley's experience is invaluable.
Vince

[dvm]

I was curious about what the manual says about the priming system so I took a look in one of several manuals I have and found this info. This manual was published in 1949 on the Packard Merlin 1650-3,-7. Here is what this manual says about over priming and a description of the system. This is of course for that particular engine. There were undoubtedly many mods made over the years. While researching I found out that the later Mustangs had tail wheel steering (1950s vintage USAF F-51D Manual) so you have to know what the vintage of your airplane/engine if you want the straight scoop.