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Scat Cat rebuild or Weston Magnum

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Old 01-12-2015, 01:47 PM
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westwind1124
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Default Scat Cat rebuild or Weston Magnum

So as some of you may remember, I have a clipped wing Scat Cat with a YS 45 rear exhaust. Its definetely getting old and loose. Lost an aileron to flutter the other day. It really needs to be rebuilt but I am having a hard time deciding what I want to do so I thought I would get all your thoughts. I currently am looking at a rebuild but maybe tapering the wings and reducing the tail feather sizes buy 10-15%. OR. Go with a Weston Magnum, but I know very little about the Magnum. How would one perform with a YS 45 Rear exhaust and tuned pipe? What kind of speeds would I possibly expect with said setup. Are they any good and how would a fella like me in the middle of Kansas get ahold of one? Thanks.
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Old 01-12-2015, 05:14 PM
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First, where in Kansas do you live? Second, how short did you clip the wings? The stock S'cat had a very generous tail surface, most likely above 20% of the wing area. You can drop that down to about 15% and still have plenty as long as you are not setup nose heavy.

Of course since the original was designed for the old K&B .40 with no muffler, any modern .40 or .45 with a muffler will cause certain balance issues. We used to chop about an inch off the nose, and much latter started mounting three servos and maybe the switch harness behind the wing.
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Old 01-12-2015, 05:46 PM
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I live in Wichita. I shortened the nose 1 inch, Clipped about 3 inches off each wing...ditched the canopy and gear and made it a hand launcher. Balance seems ok. Its fast as hell but its getting worn out. Can't decide if I want to rebuild it or go with a weston magnum or other...im open to suggestions.
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Old 01-12-2015, 07:51 PM
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A new Scat Cat fuse with a custom wing?
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Old 01-12-2015, 07:58 PM
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The Magnum is nowhere near as fast as any of the mfg claims, not sure if you know that. Nobody I know of has reported any better than about 165 on the West .50, which is no slouch of an engine. I think Q500's are better fliers and a modded Q500 would be more interesting, but that's just me. I had a spare Magnum R and I sold it. I put the West .50 on a delta and it was significantly faster.
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Old 01-12-2015, 07:59 PM
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Originally Posted by speedracerntrixie View Post
A new Scat Cat fuse with a custom wing?
And retracts.
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Old 01-12-2015, 09:50 PM
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The magnum must be a real dog if it will only do 165 with a .50. A stock race legal quickie with the full wing and landing gear can easily outrun 165 with an old 428 engine.
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Old 01-12-2015, 10:12 PM
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It could be happening, but I've never seen anyone post evidence. The highest radar checked numbers I've seen are 165-ish. There are some results in Vic's speed rally records, these are the top runs not the final average:

2014 Jett .50 8.8x8.75 160.5
2013 Jett .50 9x8 151.7, modified Magnum (I think it's a V-tail) Jett .50 9x8 170.4
2011 Jett .50 8.8x8.75 153

similar or lower before that. The SJ .50 is probably the closest analog to the West although timed a bit lower. I never clocked my Magnum/West, all I know for sure is the when I bolted the same engine/pipe combo onto a Screamin Demon, several people saw it who also were familiar with the Magnum, and all of us agreed it was somewhere in the 10-20 mph faster range to the eye. My thumbs said so too, but at a fraction the wing loading it's a different animal when low and slow.

The Magnum is a cool looking airplane and a real crowd pleaser, but the manufacturer's hyperbole is off the scale.
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Old 01-13-2015, 02:54 AM
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The Magnum is no slouch, but it's a matter of power. And the West engine just is not that powerful, not when compared to a Q500 or Q40 race engine (even an old one).
Also, in my experience, the West engines are not really up to the job when it comes to rpm. When you really start to set them up for peak power and rpm, they start to throw rods and wrist pin clips and what not. So you have to stay on the safe side (slow side).

There was a video somewhere on youtube where a guy had bolted a Q40 engine in a Magnum...it wasn't that much down from a Q40 racer from the looks of it. So IMO, it's just a matter of power.
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Old 01-13-2015, 07:03 AM
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I ran mine around the 21k mark and it was pretty fuss free. After, that is, the first run rod failure.. it was very promptly repaired under warranty.
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Old 01-13-2015, 07:15 AM
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My experiences differ, but then again, I could have just been unlucky. I think I blew 3 Wests over the years, and I have just about given up on them.

My engines were tight from the get go too, so I always preheated them first and ran them rich at full throttle immediately. The slower you run them, the colder they get and the more the rod suffers I think.

I break in all my ABC's like that: smallish prop load, preheated and running in at full throttle on a rich setting. Seems to work for other engines ranging from ASP's to Nelsons.
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Old 01-13-2015, 07:36 AM
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I had let mine run slowly for a bit to heat up, then advanced the throttle and tweaked the needle to break into a rich 2 cycle. Ka-pwang! They blamed it on the syn/cas fuel, it should have been Prosynth, although you can't get it in NA.
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Old 01-13-2015, 08:08 AM
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HEH, well thats interesting about the magnum....BTW, I don't need retracts as there is no gear on my Scat to begin with. Its a hand launch belly lander. So I am getting the idea that magnums are a big of a market bloat?
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Old 01-13-2015, 08:12 AM
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Originally Posted by MJD View Post
I had let mine run slowly for a bit to heat up, then advanced the throttle and tweaked the needle to break into a rich 2 cycle. Ka-pwang!
That's your problem right there. And the Prosynth argument is absolute bollocks.

My first .36 seized up at anything less then 1/2 throttle in the air during the first flights, even after a couple of preheated break in runs on the ground. That's probably why the rod failed later on too.
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Old 01-13-2015, 08:18 AM
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Originally Posted by westwind1124 View Post
HEH, well thats interesting about the magnum....BTW, I don't need retracts as there is no gear on my Scat to begin with. Its a hand launch belly lander. So I am getting the idea that magnums are a big of a market bloat?
The 200mph claim is a market bloat for sure.
But they are faster than just about any sport ARF out there, with the WEST engine and an 8" prop.
At speed they fly great, but they glide like a brick.
The hand launch can be tricky, if you launch it like your typical foamie. If you have someone that can give it a decent shove, it is not a problem.
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Old 01-13-2015, 09:02 AM
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syn oil is good if you keep your engine cool and better than castor when engine stays cool.

Castor is a better oil if you run engines on the edge and get them hot, this is when castor is better than syn...

The Jett 50 isnt a very strong engine stock. a few mods and mine turns a 9x8 at 18,500 or a 8.8x8.0 at 21,000
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Old 01-13-2015, 09:07 AM
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That's pretty much my point too - it flies fast, looks cool, but it has some handling quirks. Launches on the West + 8x8 are okay, 8x9 sort of okay, 8x10 can be iffy. Glides like a brick is correct, and if you turn it too hard in the glide you'll quickly get some real life practice at recovering - rapidly I might add - from low altitude tip stalls, I know I did. Watch your throws. Big wide fast, a delta will eat it for lunch on handling in glide (well, and on top end too). I have also surprised myself by running out of energy on the approach and coming in short. I'm not normally plagued by such problems, but it consumes a lot of energy in turns. And you can run the CG way farther back than instructed which helps.. as instructed it is noticeably nose heavy, Weston says for point and shoot stability. They're the same company that claimed their factory demo models were flying at way over 200mph. All I know is that a few folks have decided Q500's and/or modded Q500's are more versatile and fun. Many do like the Magnums. I'm indifferent and box copy hype gets my nose way out of joint - I hate preying on people's gullibility, so that's why I have no career in advertising/marketing. Preying on their desires is okay if you're honest about it.
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Old 01-13-2015, 09:51 AM
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well a 8x10 from 3000 feet up with a pressurized fuel tank and they ould get 200 straight down lol.
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Old 01-13-2015, 12:17 PM
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Originally Posted by airraptor View Post
The Jett 50 isnt a very strong engine stock. a few mods and mine turns a 9x8 at 18,500 or a 8.8x8.0 at 21,000
Sport Jett? Which muffler?
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Old 01-13-2015, 12:31 PM
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Originally Posted by airraptor View Post


The Jett 50 isnt a very strong engine stock. a few mods and mine turns a 9x8 at 18,500 or a 8.8x8.0 at 21,000
More importantly: which mods?! Timing, compression volume, ... Spill!!!


8.8x8.0 at 21K is definitely Q500 racing engine territory. It would be sweet to have a sport engine that cranks out those numbers.
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Old 01-13-2015, 02:37 PM
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its been awhile since i messed with it. i will get some numbers for you today or tomorrow. I think its the gold or black not 100%. The 60LX was able to get 19,000 on the 9x8. I will say the 50 is very peaky though where its at. tough to get the needle right in the air.

you can fill the crank, radius the crank coming from the carb and do a general clean up and matching of the ports to see 500 or so.
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Old 01-13-2015, 02:38 PM
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its been awhile since i messed with it. i will get some numbers for you today or tomorrow. I think its the gold or black not 100%. The 60LX was able to get 19,000 on the 9x8. I will say the 50 is very peaky though where its at. tough to get the needle right in the air.

you can fill the crank, radius the crank coming from the carb and do a general clean up and matching of the ports to see 500 or so.
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Old 01-13-2015, 03:37 PM
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Sessholvlaru got his Magnum to do over 195 with [IIRC] a used Nelson Q40 engine and whatever Q40 prop APC has to offer. I think he used a piece of plastic sheet to hide the lower half of the engine.
If he had "gone all the way" by trying some Eliminator props and spending more time at it, he might have come pretty close to 200.
My 25 year old Webra .50 is on it's 2nd set of parts. Those parts weren't cheap, but cheaper than buying another engine. I raised the exhaust to 180, lightened the piston, oval shaped the rod, swapped carb for a 11mm venturi and used a MAC's tuned pipe to make it run well with a 7.5 x 8 prop.
The results on a Screamin' Demon Delta were in the 170 mph range. I think the limiting factor for these small crankshaft "40 size" engines is that the cranks do not have a big enough hole going through them to process as much air as a Nelson type .40
I opened up the Webra crank as far as I dared with a "power hone" tool.
To take this any further, I'd have to do a side by side comparison by running this engine on a Magnum for a couple of weeks with a hand full of props and another exhaust system that Mac's might recommend to extract more rpm with FAI type props.
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Old 01-13-2015, 04:42 PM
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CP that is key also most of the time you cant open the carbs up any more because the crank hole is so small so its pointless. these engines have to be kept torquer's.
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Old 01-13-2015, 05:38 PM
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http://youtu.be/J-KnwuBBH8E?list=UUv...G7PvspskjQLq9A

Here's my Webra .50 pulling a SD.........
Weston would need to improve what you see here by maybe 50% to have an engine that can do 200 mph on paper...?

Last edited by combatpigg; 01-13-2015 at 05:43 PM.
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