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MikeyC
Joined: 24 Jan 2017
Posts: 22
Location: 1GA0
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 Posted: Sat Jul 03, 2021 3:10 am Post subject: Throttle Cable Support Incident |
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Thanks Mark. A benefit of taking so long to finish my project is that I can learn from others’ adventures. Just now finishing up, but will take a long look at securing my cables.
Best Regards, Mike Cowan
On Fri, Jul 2, 2021 at 3:00 PM Mark Fox <saafbusiness(at)gmail.com (saafbusiness(at)gmail.com)> wrote:
| Quote: | Hello group,
I am sharing this event in hopes it may help others from having the same situation.
I have a Pulsar XP, Rotax 912, built from 1994 -1996, SN 373 with 1050 hours on it. I am sure others have experienced this too, but when you do a 1- minute run up to check the engine and shut it down, it can sometimes want to continue to run/diesel (if you will) when it has only run for 1 minute.
I have learned if you add a little power over idle then quickly pull the power as you turn the key off it shuts down a lot cleaner. So that has been my procedure.
Here is what happened last week. I did the 1-minute run up, pulled the power and turned the key off at the same time as usual.
The engine went to full throttle instantly. Yikes !!!!!I
I tried to pull the power back to the stop (already there), applied full brakes, and turned the fuel selector off all in about 1-3 seconds. In that 3 second time frame, which happened so fast, I thought I would fly through the neighbor's hangar, destroy myself, the airplane and his helicopter...but luckily I didn't. In my mind I know the brakes can't hold it and the engine will run for 8 min with just the fuel in the carbs at idle...I have no idea how long at full power, that's what ran through my head in seconds. WTF do I do ?
It was 3 seconds of scary shit.
I (think) I turned the ignition key off multiple times then luckily it shut down.
Upon inspection here's what happened:
1 - Moving the throttle back relatively abruptly on shutdown broke the throttle cable support bracket on the side of the fuselage. It's the support bracket guide on the side of the fuselage forward of the throttle cable - built exactly to aerodesign specs.
2 - When the support broke, it allowed slack in the cable housings, allowing the engine to go to full throttle. I actually didn't know this would/could happen.
3 - FORTUNATELY, the sudden full power had so much left torque on the airplane the nose wheel turned 90 degrees to the left.
I believe now that the nose wheel being 90 degrees to the center line is the only thing that stopped me from flying through the neighbors hangar. It acted as a chock. (Yes I was pointed safely down the taxi way before this happened)
4 - While repairing the bracket, I was surprised it was only microed to the fuselage, no glass at all. That is what the aerodesigns called for apparently as I did not deviate at all from the manuals.
Bottom line, check your cable support brackets and reinforce with glass if you don't have it...mine has about 12 layers now 
Thanks
MLF
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Mike Cowan |
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sticky
Joined: 20 Mar 2021
Posts: 7
Location: at home
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| Posted: Sat Jul 03, 2021 5:19 am Post subject: Throttle Cable Support Incident |
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I am glad this worked out ok. The Pulsar manuals call for a lot of bonding with micro. I don't like that and in general have added plies to hold things together. Micro by itself, as you found out the hard way, is not so durable. It is brittle and can deteriorate over time. For example it can soak up moisture, and as a result just crumbles.Sonja
On Fri, Jul 2, 2021 at 12:00 PM Mark Fox <saafbusiness(at)gmail.com (saafbusiness(at)gmail.com)> wrote:
| Quote: | Hello group,
I am sharing this event in hopes it may help others from having the same situation.
I have a Pulsar XP, Rotax 912, built from 1994 -1996, SN 373 with 1050 hours on it. I am sure others have experienced this too, but when you do a 1- minute run up to check the engine and shut it down, it can sometimes want to continue to run/diesel (if you will) when it has only run for 1 minute.
I have learned if you add a little power over idle then quickly pull the power as you turn the key off it shuts down a lot cleaner. So that has been my procedure.
Here is what happened last week. I did the 1-minute run up, pulled the power and turned the key off at the same time as usual.
The engine went to full throttle instantly. Yikes !!!!!I
I tried to pull the power back to the stop (already there), applied full brakes, and turned the fuel selector off all in about 1-3 seconds. In that 3 second time frame, which happened so fast, I thought I would fly through the neighbor's hangar, destroy myself, the airplane and his helicopter...but luckily I didn't. In my mind I know the brakes can't hold it and the engine will run for 8 min with just the fuel in the carbs at idle...I have no idea how long at full power, that's what ran through my head in seconds. WTF do I do ?
It was 3 seconds of scary shit.
I (think) I turned the ignition key off multiple times then luckily it shut down.
Upon inspection here's what happened:
1 - Moving the throttle back relatively abruptly on shutdown broke the throttle cable support bracket on the side of the fuselage. It's the support bracket guide on the side of the fuselage forward of the throttle cable - built exactly to aerodesign specs.
2 - When the support broke, it allowed slack in the cable housings, allowing the engine to go to full throttle. I actually didn't know this would/could happen.
3 - FORTUNATELY, the sudden full power had so much left torque on the airplane the nose wheel turned 90 degrees to the left.
I believe now that the nose wheel being 90 degrees to the center line is the only thing that stopped me from flying through the neighbors hangar. It acted as a chock. (Yes I was pointed safely down the taxi way before this happened)
4 - While repairing the bracket, I was surprised it was only microed to the fuselage, no glass at all. That is what the aerodesigns called for apparently as I did not deviate at all from the manuals.
Bottom line, check your cable support brackets and reinforce with glass if you don't have it...mine has about 12 layers now
Thanks
MLF
|
| | - The Matronics Pulsar-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?Pulsar-List |
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