I posted this question in the gas engine forum by mistake. So I'll try here. I have the option of a 25cc poulan from a Weed Eater or a 28cc Ryobi from Wally World also from a string trimmer. They are to go on a Ziroli B25.

What do you guy's think?. What one would you choose?. The Ryobi is 30.00 cheaper. The Ryobi is the one with the rear induction carb, it has good poinys and bad.

Thanks Peter

I really wouldnt use either engine in the B25. Unless that 25cc is just like the Homelite engine. Even then I'd still want at least 30cc on each wing. The homelite 33cc from their chainsaws would fit the bill nicely I would think. Piper

Hi Piper;

Ziroli has two b25's. The smaller one he has uses zenoa g23's, do you still think a 30cc weed wacker engine is too small?

Thanks Peter

The G23 is a very powerfull engine for its size. Most of us using trimmer conversions are using 25cc-30cc Homelites or ryobi 31cc's in place of that engine. no , i dont think that a homelite 30cc is too small for that plane, just the smallest I would consider using. Piper

Hmmm;

Ok, lets say i choose to go for the 30cc Ryobi or the 25cc poulan, which one do you think is better.

I'll also do some more thinking on the size of the motors.......... Kind of puts a hex on what I had planned. I have two other weed wacker engines and a 54cc chainsaw engine conversion and was really impressed with them. The 54cc is in a Pica spit and puts out good power, it has not flown yet though. The other is a 28cc in a 1/4 scale cub and flies great. Another is in a Ziroli p47 (42cc industrial weed wacker) swings a 18x10 at 7000, but has not flown yet either, just finishing it up.

Again Im unsure of the 25cc poulan. Is the engine based on the homelite 25cc? Alot of these engines are in many models of trimmers because one company owns several brands. I'll let you in on a secret, If you havent bought any motor yet, buy the homelite 30cc. They arent made anymore but you can get them for cheap on ebay. Look for homelite pressure washers, they are all 30cc and they stink as pressure washers but the motor is almost the same in weight as the 25cc but can make almost 1000rpm more with the same prop over the 25cc. I bought one new and one used but slightly both for $26 each. The 30cc were in some of the trimmers also but there model numbers arent always clear but any washer has the 30cc. I've got all I want so I dont mind letting it out on how to get them. If they were in the r/c boat section of ebay they go for upwards of $100 in any running shape. If you get any engine you know you have to free up the exaust and get a larger carb, Pete at www.wackerengines.com can set you up on the cheap with carb, mount ,muffler and prop hub for most any engine. Give him a call, his number is on his site and he likes to talk on the phone rather than play email tag anyway. Piper

OH! On the ryobi 31cc. There great motors for the right install. Im using one on my 1/4 scale Cub because they lug a huge prop and everything is in cowl, but for brute thrust I think the homelite is a tad bit better.

I'm not familiar with the Poulens but I personally wouldn't trust a twin to two Ryobis. The Homelite 25s with the bigger carb (#28 stamped inside) are equivalent to a G23, but heavier, which could be a good thing on a B-25.

Jim

Peter, I'll repost my response from the Scale Aircraft thread just for the discussion:

"The Ryobi 31cc is a popular choice and should power your B-25 well in a scale manner. I recommend getting CH Ignitions for them so that you can have to two engine counter-rotate. The Ryobi 31cc is reed valve intake and will happily run "backwards" if you set the ignition timing correctly. The rear intake rear exhaust also make it very easy to conceal inside smaller cowls"

The reliability of these conversion engines lies in the ignition system and the carb. The basic engine blcok itself isn't likely to develop problems in RC use, which is super light duty compared to the weedie and chainsaw environment, for which they were originally designed. Now the carb: sometimes these pumper carbs will have problems with getting a steady atmospheric pressure to the diaphrams to pump and meter fuel properly. With the Ryobi, the carb sits behind the crankcase and so will typically be shielded from much of the turbulence up front in the prop wash. I would consider that a plus for reliable operation.

As for the ignition, the stock magneto ignition is just about bullet-proof. Provided you set the air gap correctly, not much could go wrong with them for hundreds of hours of operation. In case you upgrade to CH Ignition, well..., then you have identical system to some of the best gas engine available for RC use (BME, FPE, Brison, Taurus, etc.)

Power from the newer twin-ring Ryobi 31ccc engines are substantially greater than a G23. I have a Ryobi 31cc, Homelite 30cc, and a G23, all twin-ring, and all on CH Synchrospark ignition. The Ryobi 31cc has the most power. The reed valve allows the Ryobi to swing a larger prop than the piston-ported ones. This might be important to you on a scale aircraft. A B-25 should not be expected to perform aerobatics, so the too often overblown overpowering mentality should be kept in check. I'm sure you may already have read this article, but it does give you great starting point:

http://flyinglindy.homestead.com/b25construction.html

In short, I would not be afraid to use any of these popular conversion engines on a giant scale B-25, as long as the conversion is done well. I do recommend that you purchase brand new engines, instead of trying to save a few buck with refurbished ones though.

Thanks Volfy;

I had not purchased the engines yet. I was going to buy brand new weed wackers from wally world. The cost Can. is $97.00. each. Glad to hear you think the Ryobi's are a stronger engine, I am not one of those guy's who likes to overpower everything just as long it is comfortably enough. Being underpowered can cause lots of problems as well.

As far as reliability, hey they are a lot more reliable than glow, knock on wood, I have not had a dead stick on my conversions.

Thanks again Volfy, I needed to hear another opinion that was in support.

How much will the B-25 weigh? I agree with the above post. The Ryobi will pull a B-25 from Ziroli around pretty well I think. A friend and I both have converted twin ring Ryobi's on Hanger 9 PT-19 Arfs and have flown them for two plus years. Neither of us has ever had one so much as hiccup. They were properly converted and adjusted to run properly before ever leaving the ground the first time, which helps in my opinion. Between the two planes they have probably 100 or more flights. They are currently turning Master Airscrew 18x8 wood props at around 7200 rpms. We fly at 5200' elevation here and this engine will pull my 14.5 lb. plane from full throttle level flight to 300-400 high at near verticle climb before powering out. Two of them on a B-25 would be more than adequate I would think. We are currently building two Great Planes Ryan ST-M arfs for the same engines but with CH ignitions . Should be done by summer.

Later,

Maximus

Thanks Maximus;

I too have a couple conversions. No troubles yet. As far as how much the plane will weigh........... depends how scale I go. I am thinking of fiberglassing the fuse and then applying some aluminium covering, (like the Executive Sweet) in essence a double covering job, but we will see, could change my mind. In any event the plane could weigh 38 lbs. I have a cub with a 26cc on it. Before adding smoke it weighed 14lbs and would hover for several seconds before tail sliding. Twins are supposed to be more efficient, but then I have never flown a B25.

Hey Pete! If you havent seen it yet, check out the new post of a B-25 on ryobi 31cc power.

Hey thanks for looking out for me Mr. Pipercub