water.boy
Posts: 78
Joined: 10/13/2005
From: Wichita,
KS, USA
Status: offline
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Reza, I know you've already warned about a 40cc on this rig and it's duly noted, but have you looked at the Brillelli 40GT? It's an improved version of the SPE 40, and among other things, Scott balances the crank and has a custom hub machined that runs true and has knurling for a better prop grip. Here's what Scott had to say in an email, and I hope he doesn't mind the reference:
"I usually do not bad mouth other engines, but I have a lot of experience with the SPE engines so I
feel I have the right  The stock 40 is a paint shaker for vibration. Also the
Chineese ignition is a pile of crap. I sent one to CH for testing and it failed
within 1 hour of run time. They have an electric motor they run them on and it
started arcing inside in about 40 min. Spark was jumping in the EI unit from
time to time after about 40 min and would have eventually failed as a carbon
path was made. I buy the engines with no EI, ballance the crankshaft, do some
polish work to them to dress them up, install pressure taps for smoke, replace
the way too small carb with a larger one, install a new single bolt prop hub,
and install CH EI. The origional prop hubs do not run true. Plus there is no
Knurling on them so the prop will spin on the hub pretty easy. Also the 40's I
do are a couple ounces lighter than a stock SPE 40. Mine are 3lbs 3oz with EI.
Most of that is due to my lighter prop hub. Power on ours is higher as well.
That is mainly due to the larger carb. As for the larger props they are
suggesting now, that is mainly due to the ignition unit not firing properly at
high rpm. If they get the rpm's down, then thier EI works better. CH will fire
at 10,000+ all day long. The 40 works best on a 20x8 for 3D, and an 18x8 or
18x10 for other types of flying."
Now I'm NOT saying this engine would be the BEST for this particular airframe, as my EVO w/muffler/ignition weighs 43oz and the Brillelli 40 weighs 51oz, but it seems to be a good performer for planes around that size. Since I don't know much about wingloading other than making sure my AUW is within what other people are getting and usually using the recommended motor, but I'd think 51oz would be at the high end for loading.
There's a couple of guys floating around (pun intended) here that have the 40's on their planes and think they're great. One is a 73" WH Edge and there's a good video of it here:
http://youtube.com/watch?v=-3qH_s9HycA&search=brillelli
The other guy has a CMP 140 size Giles 202 and he's very close to flying it but says it's very smooth running mounted on the plane. I'll have the same combo when my stuff gets here, so I'm crossing my fingers and if it doesn't shake a cheapo $160 kit apart, I'm thinking it might work fine on a quality QQ Yak.
To look at suitable replacements for those that agree they'd like faster pullout than the EVO 26, the next size EVO, the 35, weighs 53oz WITHOUT the muffler, and costs $450 without the muffler. Compare that to the 51oz Brillelli which costs $325 for everything, and you can see why I'm anxious to find out how well it works. I'm not versed on other options in this size range, so let me know if you're privy to something 
I guess in the end, we still have to find out how the Yak does w/ the Xoar or comparable prop in 18X6 (we're waiting guys), and possibly a tuned pipe (yes someone on here has one on this plane) and if you're still not happy with the pullout power of the EVO26 then you can try another engine, go back to glow, or step up to a 50cc rig.
I've just recently gotten into this size of plane, but it seems that things have REALLY taken off (again pun intended) here recently as far as options, so things are just going to get more exciting. As long as we have the support of the manufacturers who are willing to test things out for us, this segment will get pretty huge for the people who can't quite afford to build/transport a 50cc setup but still want to have the fun of a bigger plane.
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RE: 73" yak evolution 26gt - 
