Extreme Speed Prop Planes Discuss the need for speed with fast prop planes (Screamin Demon, Diamond Dust, Shrikes or any REAL sound breakin'''' plane)

Oops, time to swap engines..

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Old 06-15-2009, 11:01 AM
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MJD
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Default Oops, time to swap engines..

Flight 2 Saturday night of the Screamin Demon / West .50V1 combo, which BTW is a rocket.

Durn thing. I balance my props quite obsessively, so I bet this is from a couple of Magnum flights a while back where the engine mounting bolts were apparently needing retorquing but I didn't know it yet, and there was a little bit of fretting at the mounts. I imagine that sealed the header's fate. It is/was mounted solidly in the delta and had not budged. Might have got bumped on the last "landing" of the Magnum too, dunno.

I didn't spot it on the ground. There were a couple of surges in flight 1 that had me raise an eyebrow, as otherwise it sounded okay and I saw smoke, and it had run like a watch the prior session and usually does. I remember thinking it was acting like tank pressure was low or spotty. I checked things over, fuel lines were okay, pressure tap and line seemed healthy, figured I went a click or two too far. So I opened the main a few clicks, refuled, restarted and retuned carefully. Engine seemed okay, pinch test showed a good rpm surge, so off we went again, launched slightly ratty on the edge of the pipe and lots of smoke, and it unloaded and took off smartly. Top speed seemed down, then a couple more surges during a climb, but smoke in level flight. I backed off and observed a bit, it was smooth, so I throttled up again, then pulled elevator into a vertical and "braaap" - quit. I knew that sound, figured the coupled had let go, and brought it in. Look what I found, gee it all seems obvious after you know the answer doesn't it? Must have developed a hairline crack but was running smoothly enough to sound fine on the ground and to tune normally when not contending with 9g pullups. Swapping engines.

MJD


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Old 06-15-2009, 11:18 AM
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combatpigg
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Default RE: Oops, time to swap engines..

It looks like the tubing broke, not the weld. I'll bet loose mount hardware didn't help, but even when everything is tight there is going to be a constant buzz looking for the weakest link.

I asked MACs once about their process, what their batting average was for turning out welded parts that last as long as they do. They said it took a long time with a lot of failures to get to where more pieces end up getting packed and shipped VS thrown in the reject pile.
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Old 06-15-2009, 11:31 AM
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Default RE: Oops, time to swap engines..

The Magnum had a much more solid fuse and wing. The SD like a DD has a more open structure and will vibrate more, or I guess a better way to say it is that it will not dampen the vibrations as well. I use the flight preserver from Hitec to cut a piece that I put between the pipe and mount to reduce the engine vibrations from traveling through the airframe to the pipes mount and to the end of the pipe.

Also looking back at your pics you supported the pipe only it it's tip so all the vibes were allowed to transfer to the header pipe at the coupler. It's much better to support the pipe somewhere nearer the middle. Hope you can tell by the pic
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Old 06-15-2009, 12:55 PM
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Default RE: Oops, time to swap engines..


ORIGINAL: evan-RCU

The Magnum had a much more solid fuse and wing. The SD like a DD has a more open structure and will vibrate more, or I guess a better way to say it is that it will not dampen the vibrations as well. I use the flight preserver from Hitec to cut a piece that I put between the pipe and mount to reduce the engine vibrations from traveling through the airframe to the pipes mount and to the end of the pipe.

Also looking back at your pics you supported the pipe only it it's tip so all the vibes were allowed to transfer to the header pipe at the coupler. It's much better to support the pipe somewhere nearer the middle. Hope you can tell by the pic
I know what you mean, good advice. The open pipe seemed so light and the mounting quite solid as it was, that the header would have no problem supporting it. Apparently not. It survived what, 30 plus? flights on a Magnum before I swapped it into here. This was the fourth flight since the move.

I'll change the support scheme next time around and take the load of the end of the header, or most of it anyhow. Number 2 is nearly ready for finishing, so the Jett can move over there and the West back into this one since it already has pipe mounting holes and evidence of flight. Hopefully I can bring them both down to NC. Even if I get nothing wicked and notorious complete in time, I still plan to come and bomb around with these and whatever else I can fit in the car. Blink #1 is coming for sure, and the Profi/Blink may see a surge of late night puttering since I just found the - firewall I had modified days ago then dropped somewhere and seemingly lost forever.

Mike D.
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Old 06-15-2009, 07:00 PM
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Default RE: Oops, time to swap engines..

Cool Mike, I hope to meet you if I make it to the speed day...
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Old 06-15-2009, 07:35 PM
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Default RE: Oops, time to swap engines..


ORIGINAL: evan-RCU

Cool Mike, I hope to meet you if I make it to the speed day...
"..if.."?? There's a question you're coming?

Mike D.
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Old 06-15-2009, 08:00 PM
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Default RE: Oops, time to swap engines..

Yeah, I was planning on jumping on a military flight space A to visit my kids in Spain....  I may put it off a few days but I'm undecided right now. You need to come down and fly where I do, the world famous Lowes motor speedway...  we have a much nicer flying area for the fast stuff, wide open....
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Old 06-15-2009, 08:36 PM
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Default RE: Oops, time to swap engines..


ORIGINAL: evan-RCU

Yeah, I was planning on jumping on a military flight space A to visit my kids in Spain.... I may put it off a few days but I'm undecided right now. You need to come down and fly where I do, the world famous Lowes motor speedway... we have a much nicer flying area for the fast stuff, wide open....

I have good places to fly, now that's no problem. Last model airplane event on a motor speedway I attended was at the Ford Utica test track in the early '80's. One of the rocket geeks put something sideways into the drygrass and burned off a huge chunk of the field with emergency vehicles wailing and the rocketeers of course getting the boot.

Mike D.
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Old 06-15-2009, 09:36 PM
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Default RE: Oops, time to swap engines..

You need to come down and fly where I do, the world famous Lowes motor speedway... we have a much nicer flying area for the fast stuff, wide open....
You are a funny man.
There is a nice long runway down there but as far as open space goes, it's hard to beat our feild. Mike, if you really want to I'm sure Evan would be glad to fly with you at Lowes on the Sunday following. I'm all set for our last meeting prior to the rally tomorrow night where we get everything all finalized and ready to go. The guys in the club are pretty geeked at having some out of town RC royalty show up...we always like hosting Evan at our field too.

If you guys are interested I don't mind having a 1/2a grudge race after we get done with the speed runs.

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