PDA

View Full Version : need a start up proceedure for negative G engine stallings



stugumby
03-11-2006, 04:51 PM
http://forums.ubi.com/groupee_common/emoticons/icon_frown.gif
I have been kiling myself due to too much negative G forces. The macchi 200 is becoming my favorite but it suffers from coughing and spluttering to a stop at Neg G. Is there a way to restart the engine in the air? It runs about 15 seconds and splutters off again.

Nimits
03-11-2006, 05:40 PM
Don't know the MC 200 for sure. I know some planes (I-16) can only be started on the ground (hand cranks and all that). Maybe if you dive to get the prop spinning fast?

x6BL_Brando
03-11-2006, 05:40 PM
You need to drop throttle back to zero. Nose gently down to pick up speed - hit ignition, probably twice. You can see this on the screen if you have it enabled - that is, you may see Engine: Off first press, press again you'll see Engine: Starting. So two presses needed for many planes.

Avoid neg-G by avoiding the bunt. Drop in by rolling left or right, using opposite rudder and pulling the stick back. Pushing the nose over from level (i.e. stick forward) to dive is a sure way to cut the engine.

May help...

B.

Zeus-cat
03-11-2006, 06:03 PM
Trying to start it right after the engine stalls usually doesn't work. I find giving it a few seconds helps.

NonWonderDog
03-11-2006, 06:26 PM
I actually find that hitting the 'I' key repeatedly will eventually start the engine, no matter what else you do. I'm not sure it's really as complex as we all make out.

Anyway, what you "should" do in the sim:

1. Throttle to idle
2. RPM to max/Prop to full fine (100%)
3. Mixture to full rich
4. (Check mags, supercharger, fuel pump, primer, yadda yadda yadda)
5. Dive to increase prop speed
6. Turn ignition while moving throttle forward to 15-30%
7. Throttle up and pull up before crashing and dying

In real life, though, if you have spark, you have fuel, and your prop is turning... your engine is on. All the starter does is turn the prop. Apparently our virtual I-16 pilot turns the ignition off when he pushes into negative Gs. http://forums.ubi.com/groupee_common/emoticons/icon_wink.gif

GMwrench
03-11-2006, 06:50 PM
""In real life, though, if you have spark, you have fuel, and your prop is turning... your engine is on. All the starter does is turn the prop. Apparently our virtual I-16 pilot turns the ignition off when he pushes into negative Gs.""

In real life, Neg. G's Would cause a fuel starvation in the carburator. This caused a lean condition and would eventually stall the engine. It would take a while to get the fuel flow going again...The Spitfire too had this problem, which is why the German planes, with the fuel injected engines, could go into a Neg. G dive to get away from any planes on their 6...

GM

TX-EcoDragon
03-11-2006, 07:39 PM
I regularly starve carbureted engines during aerobatics in the real world. . you wanna hear the fancy way we restart them?? Roll upright or restore at least a little positive G. Additionally it takes a bit longer in all aircraft I've flown for the starvation to begin, here it's near instantaneous. I€ve commented on this for years. I thought they changed the startup so that now +G was enough . . .don't tell me it's changed back!

As NonWonderDog said, the fuel flow resumes with +G, and the spark never stops provided the prop continues to windmill (which it generally does) so +G and the powerplant comes back alive without any thought or effort by the pilot. . . this pressing I stuff is silly. It used to require throttling back to around 10-15% and pressing the I key once upright.

I€m off to try it in 4.04.

NonWonderDog
03-11-2006, 10:09 PM
In the sim, if you push into negative G for only a couple seconds, your engine will be starved for fuel. Restoring positive G will restore fuel flow and engine power.

If you push into negative G for more than a couple seconds, your virtual avatar will secretly close the fuel c0ck and you'll have to throttle down below 15% to restore his confidence in the fuel lines and then press the I key repeatedly in an attempt to goad him into restoring the fuel flow. http://forums.ubi.com/images/smilies/53.gif

mortoma
03-12-2006, 10:09 AM
Originally posted by GMwrench:
""In real life, though, if you have spark, you have fuel, and your prop is turning... your engine is on. All the starter does is turn the prop. Apparently our virtual I-16 pilot turns the ignition off when he pushes into negative Gs.""

In real life, Neg. G's Would cause a fuel starvation in the carburator. This caused a lean condition and would eventually stall the engine. It would take a while to get the fuel flow going again...The Spitfire too had this problem, which is why the German planes, with the fuel injected engines, could go into a Neg. G dive to get away from any planes on their 6...

GM Ah baloney, A Cessna 172 ( like any other carb fed, reciprocating engine in GA ) will start up immediately if you accidentally pull out too far on the mixture knob and kill the engine. I did it once accidentally in the air. It was the first flight I embarked on after I got my PPL. I had gone up to high altitude and was not good at leaning the engine. Why was I not good at it?? Because flight instructors spend little or no time teaching it to you, which is plain wrong. They rarely take you over a few thousand feet AGL. Most are leery about trying to teach it ( proper leaning ) for some reason.

In any case, when I did that, the engine quit completely, no sound except wind noise. But the prop was still spinning and as soon as I pushed the mixture knob back in, it started up with no hesitation like you are sayig. It does not "take a while". The fuel starts flowing again instantly. I can duplicate this on the ground all day in a Cessna, which of course is safer and more responsible. I do it every now and then just for the hell of it.

So the next time know what you are talking about before you start blabbing. You are right on all points except the "taking a while" part. Once normal or positive G is restored, the engine will start up on it's own. And like TX-EcoDragon says, if the engine dies from neg Gs, it starts back up itself once you are no longer negative on Gs. No need to do anything at all. In my case it was not from neg. Gs but pulling the knob out too far, so I did have to do something to get it going again. Had to push the knob back in.

LEBillfish
03-12-2006, 10:53 AM
Mixture is not an empty fuel bowl......HUGE difference.....Now I know little of aircraft carburators yet if they are anything like many others then a float determines when to let fuel in and when not due to level...Naturally therefor in a negative G manuever I would "assume" the float has moved to an over fill condition, so shuts off fuel to the carb...At which point the carb drains dry and by the time you're to positive G's if the float is not stuck fuel is allowed back in.

Now, that sounds simple enough......IF the plane has electric fuel pumps that the electrical system allows to pump when the engine is not running (switch on or off).....Now IF it has a mechanical pump, or uses a mechanical pump as a regulator then the engine MUST be turning to pump the fuel.

IF the prop is clutched, or IF it cannot turn the engine over due to its pitch....Then the engine cannot be turned enough to run the mechanical pump.....

LASTLY......Many planes did NOT have starters as they were started by literally a truck pulling up and mounting to the engine turning the prop and engine with a seperate mounted motor....

A lot of IFs, and a lot of possible variables...Each dependant on the plane and the specific systems they used.......Now I do NOT know what of all that aplied to the planes we have here......Yet restarts in the sim are possible...IF you have time to do it.

AWL_Spinner
03-12-2006, 11:22 AM
As an aside, at the beginning of the film "Battle of Britain" there's a sequence with a Hurricane doing a roll, you hear the engine cough at the inverted point and then immediately re-catch.

In game, I tend to find I need the throttle significantly back for the engine to catch succesfully for a restart, and then a gradual application of power for it to hold.

Cobra427so
03-13-2006, 01:09 AM
I find if I go into a shallow dive to gain airspeed, when I attempt my re-start, a gentle pull on the stick to increase G helps re-start the engine faster. I've had a bit of practice as I test-flew my own BOB campaign with the older Hurricanes... http://forums.ubi.com/images/smilies/16x16_smiley-tongue.gif they seemed to be extremely sensitve to fuel starvation. On ocassion, if you're quick enough, you can add positive G when you hear that telltale sputter, it'll power itself back in.

Cobra427

mortoma
03-13-2006, 03:18 PM
Originally posted by LEBillfish:
Mixture is not an empty fuel bowl......HUGE difference.....Now I know little of aircraft carburators yet if they are anything like many others then a float determines when to let fuel in and when not due to level...Naturally therefor in a negative G manuever I would "assume" the float has moved to an over fill condition, so shuts off fuel to the carb...At which point the carb drains dry and by the time you're to positive G's if the float is not stuck fuel is allowed back in.

Now, that sounds simple enough......IF the plane has electric fuel pumps that the electrical system allows to pump when the engine is not running (switch on or off).....Now IF it has a mechanical pump, or uses a mechanical pump as a regulator then the engine MUST be turning to pump the fuel.

IF the prop is clutched, or IF it cannot turn the engine over due to its pitch....Then the engine cannot be turned enough to run the mechanical pump.....

LASTLY......Many planes did NOT have starters as they were started by literally a truck pulling up and mounting to the engine turning the prop and engine with a seperate mounted motor....

A lot of IFs, and a lot of possible variables...Each dependant on the plane and the specific systems they used.......Now I do NOT know what of all that aplied to the planes we have here......Yet restarts in the sim are possible...IF you have time to do it.
I'm afraid mixture indeed is an "empty bowl". ALMOST NO difference!! You are wrong.....
You increase the amount of air in proportion to the raw fuel so much by pulling the knob out too far that indeed you empty the bowl. Or at least empty it of fuel enough to kill the engine, which would differ little from starving it from negative Gs. It especially differs little in regards to how long it would take to restart. In either case it would be a very quick restart if the prop was still spinning, even slowly. Almost all air is going into the bowl if you pull it out far enough to kill the engine. As a matter of fact, that's that way us pilots kill our engines in recips, not by turning the key off like a car. You turn the igniton key off well after killing the engine with the mixture knob.

In any case, no matter the plane, if you pull out the mixture far enough to kill the engine, you have little fuel in the mixture ratio of fuel/air, just mostly air in the bowl!! Are you a pilot?? I am. Have you ever rebuilt a carb?? I have rebuilt many. Worked on engines and things all my life so few people can tell me anything about it besides people who do it for a living. I will usually bow to those. Are you a mechanic for a living LeBillfish?? If so I may listen to you and humble myself. However I think I'm right in this case.

And specifically in the case of what we are discussing here. My point was valid even if you are right about mixture not being an "empty bowl"!! My point was/is that that if a carb is starved for fuel ( regardless of why ) the engine it's connected to will indeed immediately restart if the fuel flow ( or proper mixture ratio thereof ) is restored and the prop is still spinning. That includes aircraft like you mentioned that have no starters but had to be started by another method, such as a truck
with a prop spinning motor on it like the Russians used with the I-16. All I know is that there is little difference between killing the engine by pulling out the mixture knob and killing it with negative Gs and therefore little difference in how long ( if any at all ) it would take to restart.

And LASTLY, clutches and all the variables and "ifs" you have mentioned really don't matter, it's that cut and dried. If the prop is still connected to the engine and the prop is spinning, then the engine is spinning, which is all any type of starter does. So the engine will restart ( barring other problems ) once the fuel flow or proper mixture of fuel is restored. And it should restart imediately if the plugs aren't fouled and everything else is intact.