Low RPM after engine start

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Amollen
Airman Basic
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Joined: 10 Aug 2014, 22:38

Low RPM after engine start

Post by Amollen »

I've started the B-17 many times successfully using the sequence indicated on the checklist. Lately however I have experienced a number of times that the engine starts, but I can never get it above about 500 RPM even if I open the throttle. After some time, typically between 5-20 seconds, the engine dies. The hangar shows an engine without trouble.

- Is this a sign of fouled spark plugs?
- Anything else I might be doing wrong?
- Could this be caused by cold weather? Last night this occurred at a temperature of 0 C, I usually fly in warmer weather.

I finally did get the engines going after half an hour, I don't know what I did different. Any ideas?

alan CXA651
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Re: Low RPM after engine start

Post by alan CXA651 »

Hi.
If flying in cold climates , make sure you have the correct oil grade , also prior to shut down , do an oil dilution for a max of two minutes , else the engine may not start , or run rough , until it warms up , assuming you get it started in the first place , what was your outside temp on shutdown and startup.
regards alan. 8)
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Daube
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Location: Nice, France

Re: Low RPM after engine start

Post by Daube »

I think Alan found the origin of the problem.
You engine is probably suffering from carburetor icing. To prevent that, you have to set your turbo setting (the big rotating button) to a high value.

Tomas Linnet
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Re: Low RPM after engine start

Post by Tomas Linnet »

I sometimes have that problem, but I pretty sure it’s when I’ve feathered a prop.
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Amollen
Airman Basic
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Joined: 10 Aug 2014, 22:38

Re: Low RPM after engine start

Post by Amollen »

Thanks guys, in the end I got them started with a combination of your suggestions and then some.

I had used oil dilution, thank you. Temp was around 0 C
I changed the oil grade to 1080.
I set the dial to '8', I'm not sure that's allowed during start, I know that once flying that is a good way to heat up a cold carburetor
I also skipped the prime in between Start and Mesh, I was afraid I was drowning the engine in fuel, but honestly I don't believe that was the issue
I made one other change, I opened the throttle significantly during start, almost halfway instead of just cracked.

Just like before, the engines started at 500 RPM but now they slowly creeped up and started warming up rather than quitting.

So I don't really know what made the difference, but thanks guys!

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FireRescue85
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Location: New York

Re: Low RPM after engine start

Post by FireRescue85 »

I had a similar issue and it turned out to be carb ice. I fly in the northeast and face cold climates regularly, my advice would be to set your turbo to 3 after start. It keeps your carbs warmer so they won’t freeze. Also make sure you allow adequate warm up. I’ve taken off with cold CHT, oil temps, and carb temps and had engines freezing up shortly after flight. Nothing scarier than watching your oil temp fall into the 30’s, CHT hit 60, carbs fall below 0 and slowly watch your RPM’s drop off to 0 lol.
Fire Marshall, Firefighter/Emergency Medical Tech.

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Jacques
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Re: Low RPM after engine start

Post by Jacques »

I’m pretty sure that when you changed the oil from whatever it was to 1080 was really what helped the most in your scenario. If you changed the oil after you diluted the oil you had in previously, then you would have fresh, undiluted oil in your engines.
When you add fresh oil or change the grade of oil you are using, the fresh oil is simulated as pre-warmed. Engine starts are, as a consequence, much easier.

About oil dilution, perhaps someone can correct me, but I always understood that for that process to actually work in the sim, you need to dilute the oil, then save the scenario in FSX (P3Dv3) if you are going to shut down your computer between starts. I’m not sure if oil dilution is persistent when the sim is shut down and the scenario has not been saved and re-loaded upon restart.




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alan CXA651
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Joined: 15 Mar 2016, 08:23

Re: Low RPM after engine start

Post by alan CXA651 »

Hi Jacques.
I have not saved my flight after dilution , and it does appear to remember that you diluted , when you next fire up the sim , and on the occasions i forgot to dilute prior shut down , then i could not start the engines the next day , till i had changed the oil.
regards alan. 8)
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SJDobby
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Re: Low RPM after engine start

Post by SJDobby »

Hi

While on the subject of engine starting and cold weather, I did a flight last evening from Trondheim to Bergen and deliberately shut down engine 3 in the cruise (FL160). I then attempted a restart and the RPM started out at something over 700rpm (not climbing in the 10 or 15 secs I was looking at it) and (not having read this thread) I worried I was doing the engine some kind of harm so shut it down again and continued to Bergen for an uneventful landing.

Now that I have read the above I shall run a similar exercise on my next flight. However, in the meantime, is the method of restarting a shutdown and feathered engine [especially in cold conditions] the same as for a standard start i.e. fuel/mags/mixture-auto-rich/prop-high/throttle-about-10%/[ignore fire extinguisher]/start/prime/mesh/generator, but with the Turbo dial up to at least 3 or so (which it probably will be anyway to keep the already-operating carburettors warm)? I don't recall what I did with the feather button on the restart, but is there anything specific one needs to do there or does it auto "pop-out" on engine start?

Thanks
Simon
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alan CXA651
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Re: Low RPM after engine start

Post by alan CXA651 »

Hi SJDobby.
Prior to inflight restart , you need to un-feather the engine , this will start the dead engine windmilling , you then go through the normal start sequence , depending on the windmill speed , you might not need the boost pump , also prior to an atempt at a restart , check oat and engine temp , i did some practice at inflight shutdown restarts when i first got the B17 , and i did notice that it could be sometimes easy , sometimes not , now i fly with the 91st bombgroup , if my engine was shut down , like it was this saturday , then a restart was out of the question , becuase it took a direct hit by flak , and fire bottle used.
regards alan. 8)
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