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Post  batjac Thu Jun 19, 2014 9:01 pm

Well, I took my son out flying this morning, and we had a good time.  He flew my BTC-2 once, and his Osbourne Platter four times.  Who knows, maybe it’ll take on this one.  It went pretty well.  On the fourth flight of his platter, the engine was singing along, but on the tenth or twelfth lap it went “Wheeeeeeeee – URK!”  Uh-oh…  So, we packed it in and came home.  Opening up the engine showed this:
An interesting morning of flying. DSCN1950_zps11f6fac0
An interesting morning of flying. DSCN1954_zps0799437e

I guess I over-compressed it a little.  That’s okay. I have an extra crank.  I’ll just lower the compression on it this time.

The URK! Mark
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Post  Cribbs74 Thu Jun 19, 2014 10:08 pm

How many shims and what % nitro?

Reason I ask is I have never seen a stock engine do that before. Usually they just won't run if over compressed.

Glad it's repairable!
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Post  batjac Thu Jun 19, 2014 10:24 pm

Cribbs74 wrote:How many shims and what % nitro?

Reason I ask is I have never seen a stock engine do that before. Usually they just won't run if over compressed.

Glad it's repairable!

Two head shims on a Dual Bypass, Dual Boost cylinder and high compression head. Sig 35%.  Started and ran fine.  Needled great, even with the crappy plastic backplate on the Babe Bee.  Was a little screamer.  We're going back out tomorrow morning, so we'll try it again.  I replaced the cylinder and head with a single bypass port cylinder and standard compression head.  I reset the piston rod in it to get rid of the slop.  My son said the plane was flying a little fast, so this should suit him better.  I'll save the cylinder and head for a flyer that better appreciates them (like Moi).

The Screaming Mark


Last edited by batjac on Fri Jun 20, 2014 1:35 am; edited 2 times in total
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Post  Cribbs74 Thu Jun 19, 2014 10:49 pm

Yeah, you were probably a bit over compressed. I would also think that the crank may have been flawed.

Reason being is I use bee cranks in performance builds and they stay together at speeds over 20K. That's with Nelson heads 3-4 shims, sometimes less sometimes more.

It is what it is I suppose. I just get curious when someone has a catastrophic failure.

Ron
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Post  getback Fri Jun 20, 2014 8:03 am

That's pretty strange you would think the pin or rod would have came apart first /// Mark cant tell in the pic but where the break is if there is any discoloration in it at a point this means that it was ready to break with a hair line crack in It . I am sure you probably already new this but reminders are always good . Getback
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Post  Kim Fri Jun 20, 2014 8:28 am

The cool part...OK, maybe there really ISN'T a 'cool part'...but you could make a "Cool Looking" paper weight for your desk by gluing the parts to a piece of nice ply.

Then, when asked it's story, you could non-nonchalantly, "Well, structural failure is just a fact of life with us Super-Engine-Tuner-Dudes..."
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Post  RknRusty Fri Jun 20, 2014 8:54 am

I'd bet that crank web had a weak spot in it from the time of manufacturing.
I do think that a hi comp head/dual port on 35% should have three shims unless the temperature was 100 degrees, then maybe two would be okay.
Salty Rusty

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Post  batjac Fri Jun 20, 2014 3:13 pm

Yeah, I'll go for 3 shims next time. This morning we flew the plane with the single bypass port. A little anemic for me, but it was okay by him. Next week when he's here we'll start a Sig Skyray for him, and I'll put the better cylinder back on the engine when it's ready to fly.

The Indulgent Mark
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Post  JPvelo Fri Jun 20, 2014 7:49 pm

Mark,
You will really enjoy the Skyray. It flies much better than a slab winger has a right to. I've about flown mine to death. I doubled the elevator on mine . I have a Skyray kit I need to build that will get the same elevator mod and probably flaps as well.

Jim
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Post  batjac Fri Jun 20, 2014 11:21 pm

JPvelo wrote:Mark,
You will really enjoy the Skyray. It flies much better than a slab winger has a right to. I've about flown mine to death. I doubled the elevator on mine . I have a Skyray kit I need to build that will get the same elevator mod and probably flaps as well.

Jim

Thanks, I'll try to remember to increase the elevator span. Knowing me, I'll probably charge straight forward and forget, though.  Rolling Eyes 

The Forgetful Mark
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Post  JPvelo Sat Jun 21, 2014 12:09 am

I didn't increase the span, I doubled the chord. Increasing the span would probably be better though.

Jim
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Post  batjac Sat Jun 21, 2014 3:47 am

JPvelo wrote:I didn't increase the span, I doubled the chord. Increasing the span would probably be better though.

Jim
What I meant. Read what I mean, not what I say.

The Feminine Side Mark
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