Hey all,
I think i've pretty much made up my mind on upgrading from my Avistar 40 to a Tower Kaos ARF. The dillema I am having is figuring out what a good engine for it would be. I was thinking an OS 55 however I was unsure if it was going to be too much power for that plane and also for my skill level?

I fly my Tower Kaos on a Thunder Tiger .46 Pro and it's plenty of power. The OS .46 AX with a Macs muffler will be all the power you'll need (my TT .46 doesn't like a Macs muffler and has to run on 10% fuel, but I think thats due to a lot of wear). I don't think the .55 will give you anything over the .46. Several planes I've flown with the .46 that had been converted to a .55 actually performed better with the .46.

Since my Kaos is worn out (covering held on with packing tape, and one of the elevators stripped the top plastic layer off the coloring/glue along with an engine that has just plain worn out from use), when I recondition/recover it I'll put a new .46 AX/Macs muffler on that is sitting NIB since I don't see any advantage to going with a .55.

Hogflyer

What IS your skill level?

If you've soloed then a Kaos is within the abilities of anyone ready to move on from a trainer depending...... depending on their confidence level.

As you progress, each model that pushes your envelope is a risk. Every one of them. The risk is greater when you're less confident and less when you're more confident. The Kaos is not a trainer that returns to neutral if you pull back the throttle and let go the sticks. But it's nowhere close to being edgy or touchy. It's actually a very comfortable to fly model with out any bad habits.

Any model that you're worried might be too much for you probably is. Any that you think might not be too much is a good next plane.

I've been flying solo for a couple months now. Im getting very comfortable with take off's and landings. I still plan on practicing with my Avistar for a while longer before I take a Kaos up.

Any .46 engine. If your buying new then the .55AX is a good choice because it can be used in a number of 60 size planes like the Pulse from Horizon or 4*. You won't over power the air frame of the little Kaos. However, the .55 isn't really enough power for planes like the 60 size Kaos. I have flown the 40 size Kaos with the .46 OS LA and that's all it needed. Any .46 to the .55 is a good choice.

The Tower Kaos is basically a .40 sized Kaos Jr. or Jr. Kaos (whichever it was called back in the early 70's ) and a K&B .40 was typical for the day. A friend had an HP .40 w/Tarno carb on his...made a very nice combination.
Both of those are very light engines...
I have a Webra .50 in my Tower Kaos, and it is way more than sufficient.

Any modern .46 would be plenty, and with the O.S..55 it would be quite fast...perhaps a bit more than you're ready for...but...there is a throttle on the engine...

Edit: Mine wound up quite nose heavy with the Webra .50 and TT spinner. A check of the weights of your potential engines is recommended. I had to move my battery pack back behind the wing...had to cut a hatch in the bottom of the fuselage just behind the wing.

I flew my Tower 40 KAOS with a OS .46 AX plenty of power for aerobatics able to compete in senior pattern competition. Nice airplane I won second in a senior pattern competition with mine have fun!

You will be very, very happy with the 55 AX. From what I've seen, where guys get into problems is when they actually read and follow the recommended prop list in the manual, which is aimed at noise reduction, not thrust, speed or ultimate power. Then there's the other extreme where guys want to rev the heck out of it like it's a Rossi or something. This engine's power range is in the 13 to 14,000 range on the ground and unloaded 15 to 16,000 in the air. For stock muffler or tuned muffler (RED! Jett muffler) the best props I have found are the 11X6 APC or Master Airscrew (S-2 series!)11x7 on sport planes like the Kaos. Other props for different needs are APC 10X9, 12X5, 13X4. With the stock muffler/baffle and the right prop for job this engine just sips fuel and it's not bad on a tuned system either so expect extended flight time.

I agree, if you have to buy an engine anyways you may as well get the 55. Keep it on the rich side and don't overload it and it will last forever while providing all the power you need.

I currently have an OS 55AX with APC 11-7 on my Tower Kaos & its ballistic on 30% heli fuel!....Gene

The 55AX maybe a bit overkill for the 40 KAOS, but it will certainly will give you performance. Just remember throttle control will be important with that much power.

Well I am not an O.S. guy I flew a scratch built Koas 40 with a Super Tigre .45 and it was a really good setup Not unlimited vertical, but close. I then put a Magnum .52 in it. That was more vertical then I imagined.

Any of the current .45, .46 engines will have more then enough power for it. If you want more power then the .52 to 55 will make you smile every flight.


Buzz.

I have flown mine with OS 70 and 52 four strokes. I like the 52 better as I did not have to add any weight. With the 70 I had to add about 6-8 ounces on the tail if I remember correctly. With the 70some creative installation work had to be done to get the throttle servo to work out, also.Whatever you decide to use, the Kaos is simple, reliable, dependable and predicitable and you will enjoy it. Good luck

Much as I like my Saito and OS 4-strokes, a Kaos is not that kind of plane. Almost any .40-.46 will fly it like it was meant to be flown. I've had one with a piped .46SF and one with a piped .55AX. The .55AX was wretched excess, but lots of fun! Your biggest concern, however, is not power. It is the lousy covering that will be falling off by the first flight. Do yourself a favor and strip the garbage factory covering and recover with Ultracote or Monokote. I prefer Ultracote, but either will be fine. Once you've done that you will have one of the finest flying sport models ever designed.

I fly mine with a Rossi 45. Because I had it. It will do anything I want. On FAI 0% fuel.

Instead of spending the big bucks on an OS go with a Magnum or ASP 46 or 52. (Both are old OS engines that OS sold the castings for years ago.) You will not be disappointed. Put a 10x6 prop on it run it a little rich and you will have all the power you will ever need.

I know I will catch flak for that comment. But it is the truth. If/when my Rossi wears out I will put a Magnum 52 with a 10x6 prop with the Rossi mini pipe. If the plane survives.

No flak from me. Those "other" engines get better all the time and OS's haven't gotten any cheaper. Are you listening, OS?

I fly mine with the 46AX and love it. When I put on a Jett muffler and tuned it, it would sustain knife edge with a 10 x 6 APC. I have the CG about a quarter inch behind the recommended and have 5 points of down elevator mixed in with rudder, it has NO roll coupling at all.......great flying plane. Check out this review and build, it has some good ideas for the Tower Kaos build.
http://masportaviator.com/2007/11/16/kaos-40-mk-ii-arf/

My bad, my last post should read 5 points of UP elevator mixed with rudder, mine pulled a little to the wheels in knife edge.

Propped a bit differently, the .40 in your old Avistar will probably work. Almost any recent schnurle ported .40 would be a match for the best of the ubiquitous loop scavenged .40-.45's of the era when the Kaos was born.

If you have an LA .40 in the Avistar, you can get a cheap boost in power by fitting it with a Fox Stunt .35's muffler (the holes and exhaust port openings line up just fine and the Fox muffler is fairly cheap) and sawing off the back end of the Fox muffler so the opening is in the 1/2" diameter range. It'll be louder, but the power boost is something you'll feel visibly. OS's stock mufflers are fairly restrictive, but you can't just lop the rear end with a hacksaw like you can with Fox muffler due to that goofy through-bolt design of OS's.

Special bonus - the Fox muffler's don't seem to fall apart in flight with the frequency of that through-bolt design. Our field is littered with the back half of OS mufflers that fell apart in flight.

Magnum .52 XLS Two Stroke. WOW...

K@B 61 !!! POWER lol..

Hey!! That's a very nice looking bird ya have there!!

I wonder how a very strong Enya 53-4c 4 cycle would do in it ??

Git er done lol !! I have been there whit the tape.. Hey It works !!

From Tower Hobbies web site:
OS 46AX - 130
OS 55AX - 170
TT Pro 46 - 110

You decide. I would never pay even $20 more to get an OS over the Thunder Tiger.