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Vapor Lock


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Could you provide us with more specific details as to when this occurs?

Such as: during a "hot" or "cold" engine start procedure?

 

Fuel injected aircraft engines are prone to "vapor lock" while accomplishing an engine start during hot weather and hot engine conditions, therefore "hot" engine start procedures as per the flight manual must utilized to remedy this condition!

 

All Enstrom piston engine models, (A, C, C-2, F and FX), are fuel injected.

:cheers:

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Ga Chopper

 

You think vapor lock would be a good explanation for engine failure with hot engine after an hour flight and then idling for a few minutes and then pulling in power/pitch to come up in a hover? (engine failure in hover) Apparently the "newer" models have the fuel lines "wrapped" in foil tape for this reason, seems they get a little hot and positioning  of the lines has a lot to do with it. Any thoughts?

 

rotorheadsmiley

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birdog,

 

I don't know for sure if the "A" models had foil wrapped fuel lines such as on the "C" and "F" models, since the latter models have turbo chargers that generate more heat. I imagine that with the lack of this foil wrapping it could cause a problem to occur, especially in a hover because the temperature in the engine compartment is much higher than in forward flight due to the lack of ambient airflow. But I would check the mainteneance manual to find out; or call Buyard DuPont at the Enstrom factory since he is the Enstrom expert.

 

However your problem may not be due to vapor lock. Vapor lock does not generally occur when these particular engines are up to operating RPM since the fuel quickly flows thru the lines to the injectors. Shuting down a hot engine in hot weather will cause the stagnant fuel to vaporize in the the fuel lines above the cylinders, or when at idle RPM/low fuel flow conditions. Thus, utilizing the "hot" engine start procedure will address this issue.

 

I would begin troubleshooting from the simplest to the more complex items first:

 

1. Check and test the fuel, our local airport recently had a bad batch of fuel that contained too much "blue dye" that caused starting problems with all the various piston powered helicopters. It caused our fuel screens to gum up and restrict fuel flow.

 

2. Check the fuel screen in the fuel servo for contamination.

 

3. If the engine quit after reducing power below 2,000 RPM, or trying to maintain the throttle at intermediate positions between fully closed and 2,000 engine RPM; the problem may due to improper idle mixture settings or a faulty fuel servo.

 

4. I would perform a "idle mixture check" as outlined in the flight manual to find out if it is set properly. If it's not, transitioning from the idle mixture to the main mixture can cause the engine to quit.

 

5. If required, adjust the idle mixture as per the maintenance manual.

 

6. If the engine still quits when operating under those contitions, the servo may be faulty or have scored mixture plates.

 

7. A reputable fuel servo overhaul shop such as "Precision" in Miami, can bench check and overhaul your servo. 

 

These items are just a few of many possiblities, a graphic engine anaylizer would be very useful in troublshooting the problem; I have one in my ship which has proven to be worth it's weight in gold!

 

Best of luck.

 

rotorheadsmiley

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Ga Chopper,

 

Thanks a ton for the info!!!

 

I never even imagined the issue about the "blue dye" interesting!!

Our A&P called Buyard, I think he did pretty much what you suggested. The lines are now wrapped and it is doing great.

About your graphic engine analyzer, who makes it?? They have a website?

 

Also,  another "tip" from Enstrom was to put some 2" x 3/8" foam-type tape around the fan shroud which would create a better seal providing more cooling.

 

 

birddog

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birddog,

 

Glad to hear that you were able to contact Buyard and hope your problem has been resoved.

 

My graphic engine anaylizer is manufactured by "Insight". It will also store the last 30 hours of engine data in it's memory which can latter be downloaded into a PDA or computer and a excel spreadsheet can be created to track the history and provide trend information. This can help to head off any developing problem before it becomes more serious.

 

Once I had an AN plug fitting back out of a cylinder in flight which created an intake leak. That particular cylinder's mixture went lean and the display in the cockpit immediately got my attention as it started to flash and it showed which cylinder's EGT had suddenly spiked. Without the anayizer that clyinder could have eventually failed and might have caused an incident or accident. This is the best insurance policy you can buy for your engine!  If you call Enstrom, they may also reccommend another manufacturer.

 

The foam tape around the inside of the cooling shroud is very effective in reducing the oil temperature and also helps with the CHT, since it eliminates the gap between the fan and the shroud. It's amazing the airflow is effected by the tip loss around the fan to the oil cooler and cylinders. The shroud can also be adjusted to provide equal spacing betweeen the fan and the shroud, all the way around it's circumfrance. This can be accomplished by "loosenig" the shroud's attaching hardware and using little wooded wedges between the fan and shroud. Once there is equal spacing all the way around, re-tighten the loosened hardware. This will eliminate gaps "all the way around", once the foam tape is installed.

 

Good luck and safe flying!

 

 

rotorheadsmiley

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