Guys: A heads up on a potentially hazardous ground incident. Yesterday, I turned on the master switch in the hangar to check something and the propellar started turning. It startled me but I reacted immediately but not before the prop made a couple of revolutions. After investigation, it turned out the starter solenoid was stuck in the closed position, continuity through both poles with the start switch wire removed. I had flown the day before for .8 and the starter was not in the start mode for that flight, I have a starter engage warning light on the my panel. Additionally, there is no evidence on the starter ring or starter teeth of any abnormal wear. I have never heard of a solenoid failing in the closed position, only in the open position. Anyone else out there ever experienced this problem? Anyway, the point here is to be aware that the prop can turn when you turn on the master. It's probably another good reason check the prop clear or holler "clear prop" or both before turning on the master. Dan
Van's Air Force
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Starter Solenoid
- Thread starter guccidude1
- Start date
Yes, the diode was installed and functional. I'm trying to get info on how this condition could occur. One would expect the last time the starter was engaged, the solenoid "stuck" in the closed position. However, the starter would continue to operate with resultant starter drive and ring damage appartent, after a .8 hour flight. No such damage is evident, and as I mentioned in the original post, I have a starter engage warn light, which checks good. How and when did the solenoid stick closed? Dan.
How hard was your last landing? I know, that sounds like a smart-*** question, but if the solenoid shaft is vertical, and you gave it a good bang (and it was defective in some way) - maybe it moved and stuck?
As you can see, I am out of ideas....
Paul
As you can see, I am out of ideas....
Paul
I've heard from some aerobatic pilots that pulling hard G's can overcome the spring in the solenoid and engage the starter. These pilots also said that some aerobatic aircraft have the starter solenoid mounted sideways so this cannot happen.
Karl
Now in Sandpoint, ID
If the solenoid is wired like the Cessnas, it is there to absorb the back emf from the coil being switched off and has nothing to do with the solenoid sticking.....
What kind of starter solenoid do you have?
When I tore down my RV-4 for its refit, I found that the builder had used a continuous duty solenoid for the starter. It never gave me any trouble but it could have. The continuous duty solenoids have a weaker spring and consume less coil current than the standard, intermittent-duty, kind. That makes them more prone to sticking on as yours did.
BTW, I've redesigned my starter circuit to eliminate all single points of failure that can cause the starter to stick on. I'm planning to post the schematic here when I get around to drawing it.
When I tore down my RV-4 for its refit, I found that the builder had used a continuous duty solenoid for the starter. It never gave me any trouble but it could have. The continuous duty solenoids have a weaker spring and consume less coil current than the standard, intermittent-duty, kind. That makes them more prone to sticking on as yours did.
BTW, I've redesigned my starter circuit to eliminate all single points of failure that can cause the starter to stick on. I'm planning to post the schematic here when I get around to drawing it.
hgerhardt
Well Known Member
For Skytec starters
If you have the standard Lycoming Skytec starter, which has a built-in solenoid like your car has, why use a starter contactor at all? Just use an automotive-style cube relay, like an Eaton VF4, to activate the solenoid. The cube relay will handle the 20-amp current inrush of the starter solenoid easily and still protect your key switch or pushbutton or whatever you're using to start your bird.
This is the way every modern car does it, and it's worked great for my RV-6 for the 144 hours it's flown so far.
If you can't figure out how to wire it, send me a PM and I'll send you a diagram.
Heinrich Gerhardt
If you have the standard Lycoming Skytec starter, which has a built-in solenoid like your car has, why use a starter contactor at all? Just use an automotive-style cube relay, like an Eaton VF4, to activate the solenoid. The cube relay will handle the 20-amp current inrush of the starter solenoid easily and still protect your key switch or pushbutton or whatever you're using to start your bird.
This is the way every modern car does it, and it's worked great for my RV-6 for the 144 hours it's flown so far.
If you can't figure out how to wire it, send me a PM and I'll send you a diagram.
Heinrich Gerhardt
frankh
Well Known Member
And
If you used a double pole starter switch you could activate the Skytech solenoid and the solenoid on the firewall independantly....So if the firewall ssolenoid engaged it still wouldn't engage the starter.
Hmm..I think I like this idea, now where to find a double pole starter push button?..
Frank
If you used a double pole starter switch you could activate the Skytech solenoid and the solenoid on the firewall independantly....So if the firewall ssolenoid engaged it still wouldn't engage the starter.
Hmm..I think I like this idea, now where to find a double pole starter push button?..
Frank
hgerhardt
Well Known Member
So, WHY would you do that? You've just introduced another potential failure point...
What does the firewall-mounted solenoid do for you that the built-in starter solenoid doesn't do?
The whole idea is to is to make things more reliable, and you do that by eliminating potential failure points.
And by eliminating the firewall-mounted solenoid, you also eliminate two more big crimp fittings by running the fat wire directly from the master contactor to the starter.
Heinrich Gerhardt
hgerhardt
Well Known Member
And by having that always-hot cable two feet shorter is how much safer? It's still going through the firewall hot, so you have the risk of it being compromised by a sharp edge of the stainless, and you have a big, fat always-hot terminal on the firewall-mounted solenoid that only has a thin silicone boot covering it, just waiting for some errant engine part (or even the whole engine) to hit it during a crash.
In an impending crash scenario, you're supposed to shut off the master anyway before you crash.
HOWEVER, and I just now thought about this, is: why not mount the start solenoid adjacent to the master solenoid on the cold side of the firewall? Then you eliminate all potential hazards to the fat wire of passing through the firewall.
Oh, wait, here's another HOWEVER: you still have the #6 (fat) wire coming from the alternator that's always hot, just waiting to make sparks somewhere. You're pretty much stuck with that.
SO, considering all of that, I'm sticking to my original way of using a cube relay to activate the built-in starter solenoid. Also, my #6 alternator wire is only 1 foot long and goes from the alternator directly to the fat terminal on the starter (with an 80-amp fuse inline) eliminating yet more complexity and weight. You can only wire it this way if you don't use an external solenoid.
Heinrich Gerhardt
