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wm708

Active Member
I BELIEVE SOME OF THE ELECTRONIC IGNITIONS HAVE SPEED LIMITERS ON THEM.
As Magneto's do not have this feature. And you have a governor failure this might help stop a overspeed.
Maybe some of the electronic ignition vendors can chime in on this part .
Drag cars have had this feature for many years.
Bill J
 
Disabling the ignition automatically will not stop an engine overspeed caused by a governor failure driving the prop towards fine pitch.

The reason it works in a car is the engine is driving the vehicle independent of the gearing. IF you were to jam it into first gear at highway speeds then pop the clutch (simulating a governor failure in a plane), you'll overspeed your engine irrespective of your non-firing spark plugs.
 
wm708 said:
I BELIEVE SOME OF THE ELECTRONIC IGNITIONS HAVE SPEED LIMITERS ON THEM.
As Magneto's do not have this feature. And you have a governor failure this might help stop a overspeed.
Maybe some of the electronic ignition vendors can chime in on this part .
Drag cars have had this feature for many years.
Bill J
Click to expand...

Our CPI and EM-5 both have rev limiter functions. Could save you a heap of money in the event of a prop governor failure.
 
Adjusting the low pitch stop on your prop will prevent an overspeed, this should be done as part of your initial setup of pitch stop/governor setup.

Edit: this will require more investigation, although it may help it may not prevent in overspeed in cruise.
 
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It should be stated that electronic rev limiters will not save ALL overspeed events but will be helpful in a vast majority of cases outside of "downhill" flight events.

If your prop goes full fine at high power in cruise or with the nose down without a rev limiter, adjusting the pitch stops won't do much for you I don't think. The prop is unloaded considerably in flight compared to static so is never close to the low pitch stop in flight except at low power settings and low speeds like on approach.
 
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KRviator said:
Disabling the ignition automatically will not stop an engine overspeed caused by a governor failure driving the prop towards fine pitch.

The reason it works in a car is the engine is driving the vehicle independent of the gearing. IF you were to jam it into first gear at highway speeds then pop the clutch (simulating a governor failure in a plane), you'll overspeed your engine irrespective of your non-firing spark plugs.
Click to expand...

Well, not always. In an enroute climb, where the engine is supplying power to the propeller, an overspeed may be avoided if power is immediately shut down by an RPM limiter following a governor failure or loss of oil pressure to the prop hub. A limiter would be useless in cases where a low pitch propeller could drive the engine such as during a high speed descent.
 
Walt said:
Adjusting the low pitch stop on your prop will prevent an overspeed QUOTE]

Are you sure about this? With the low pitch stops set per manufacture for proper take-off RPM at rotation speed and then flying at over 175 knots TAS in a less dense air mass I don't see how the low speed stop can prevent overspeed. There is quite a bit of blade pitch angle difference.
Click to expand...
 
Weasel said:
Walt said:
Adjusting the low pitch stop on your prop will prevent an overspeed QUOTE]

Are you sure about this? With the low pitch stops set per manufacture for proper take-off RPM at rotation speed and then flying at over 175 knots TAS in a less dense air mass I don't see how the low speed stop can prevent overspeed. There is quite a bit of blade pitch angle difference.
Click to expand...

Hmmm, you have a good point, no I'm not sure and will need to look into this more now.
Click to expand...
 
rv6ejguy said:
If your prop goes full fine at high power in cruise or with the nose down without a rev limiter, adjusting the pitch stops won't do much for you I don't think. The prop is unloaded considerably in flight compared to static so is never close to the low pitch stop in flight except at low power settings and low speeds like on approach.
Click to expand...

I agree.
Not that it isn't a good idea to have the low pitch stops properly set up (because it is) but even if they are, if the prop abruptly jumps to the stops in cruise flight it is still going to over speed significantly.
 
Here the blade pitch at 500 ft MSL and 45 knots is ~ 15 degrees.

28918852522_9d1fb50836_c.jpg


Here at 10,000 ft MSL and 175 knots the angle is over 23 degrees I assumed 65% power at this altitude...just a guess. both 2700 RPM

28918982542_8c831ac952_c.jpg
 
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Lets talk about a few factors of overspeed, including the recent couple of events being discussed on other threads.
How many total events have occurred in the last 30 years?
Which configuration of constant speed propellers experienced overspeed? (all propellers were non counterweighted type? increase oil pressure to hub increases blade pitch)
What was the final determined cause? (usually governor?) (Which brands?)
How high did the RPM get? High enough to damage engine equipped with non counterweighted props? Propeller damaged also?
Damage to accessory drive gears and possible the crank gear / bolt & pin? (due to seized governor shaft?)
What was the pilot's reaction? (close throttle quickly?, Climb steeply to reduce airspeed?)
I agree automatic protection devise(s) might be a good idea, especially when they are included as a 'feature' as in an electronic ignition or electronic fuel injection or full electronic injection + ignition systems. These don't seem prone to causing engine shut down in normal use, which would be unacceptable. (Failure mode analysis) Obviously these reset when engine speed decreases to normal.
Counterweighted props are preferred for aerobatics, because loss of oil pressure to the propeller causes increased pitch. one poster did have a governor failure on a counterwieghted prop equipped IO-540. No overspeed, but he did lose over a quart of oil in about 10 minutes and may have had accessory gear damage.
 
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