Hi I'm building a 16-18 pound aerobatic biplane and would like to put a gas engine on it...without spending the $400 price tag for a ready made engine. I've been eyeballing this cheap string trimmer at my local lowes. [link=http://www.lowes.com/lowes/lkn?action=productDetail&productId=183780-65481-BL100&lpage=none]trimmer[/link] , anyone have any experiance with this trimmer? Does it convert easily? Are there conversion kits out there that would work for it?

Thx for any help,
Collin K

Your link isn't working for me. I did find this string trimmer with the same item number as the one in your link.

http://www.lowes.com/lowes/lkn?actio...100&lpage=none

Thats a standard Ryobi 31cc engine. Much cheaper from Harbor Freight--but slow down--thats not enough HP for a 16-18 pound bipe.

You need a 40-50cc engine for an aerobatic biplane that weighs 16--18 pounds. I'd suggest a Poulan 46.

Here's a link to another trimmer with that same 31cc engine. Just for future reference if you ever want to build a bit lighter plane:
http://www.harborfreight.com/cpi/cta...emnumber=55008


Try this link and click on chainsaws on the left menu. There are 2 Poulan Pro chainsaws listed with 46cc engines. One is recondtioned for $140 and the new one is $220. I think some guys have even bought just the powerhead from lawnstation. Cheaper than buying the whole saw--which your going to throw away most of it anyway.
http://www.lawnstation.com/

So a "power head" is the entire engine? I'd seen several in the rcu classifieds and didnt know if that was just a part or the whole thing. And I'm afraid I've been a bit misleading...that 16-18 lbs includes the weight of a 4.5 pound engine.

Personally I prefer converting the Echo engines. 44 and 50cc s from chainsaws. Lots of power and torque. They also are much nicer looking as far as castings and overall quality go. You can buy the short blocks and add a prop hub, carb, muffler and ignition and go fly. I have done a few 42cc Poulans from Sears Craftsman saws. They too have decent power. If cost is a major issue the Poulan would be my choice. Ken at www.lambertsrc.com has most if not all the things you will need. I have a 50cc Echo ready to go if you are interested. PM me to discuss it.

Tim

I knew that you were talking about your all-up weight. A Ryobi 31cc engine is NOT going to haul 16-18 pounds around very well--not on a bipe that you want to do aerobatics with. It's just not. That would be like putting an OS 40LA on your 60 size Pitts. Will it fly? Yes. Will it be fun? Not in a million years.

I just wouldn't use the Ryobi on a bipe that you want to do aerobatics with. They just don't have that much poop. My 31cc Ryobi is mounted in a 4*120. It only weighs about 12 or 13 pounds. Thats a plane which is more suited to this engine. Bipes are draggy, and need a bit more power.

Maybe a better question would be-------How many square inches do you have on this plane?

I'm still thinking at least 35-40cc.

Another thing:
Weedies are about the lowest of the power range in these engines. They aren't ported for high output. They don't have high compression, or big transfer ports. They are made to lumkber along for 350hrs and then chuck them in the trash.

Chainsaws are ported to run better. They have higher compression, and can use bigger carbs. They put out more power per pound of engine than a weedie.

You can do a Poulan 38cc engine or a 40cc engine for just a little more money than the Ryobi, and the power will be quite a lot more without much weight gain.

As in frontal area or wing area? Its an 84" wingspan (18"chord) profile 85" long with aproximatly 16-18oz/sqft wing loading (this guess is on the high side...better safe than sorry)

In any case I don't really want to spend much more than $90 on the engine (before conversion)

After looking at other engines I found this poulan chainsaw with a 40cc engine...however it says that the powerhead weighs in at 10.5 lbs !? Is that info right?

Its the "poulan wild thing 2375LE"

This one comes in at 11.8 lbs for 42cc "PPB4218 SAS"

Somehow I dont really think thats right...In anycase is there someplace you can buy the engine only for these things? Preferably used.

look around on ebay for a deal on a conversion, I would agree with RCpilot in that you definately need upwards of 40cc. I flew my ultrastick today (Stihl 27cc that KEN LAMBERT did for me well over a year ago) and she still screams[>:] I switched props from a 16x8 to a 15x8 and it seemed to really open up some. At about 13 lbs I think it could still lose some weight but this thing is so damn fun to fly! Ken also converted a 65cc 4stroke Stihl backpack for me thats going in a 30% EDGE. I'll post pics when I get the engine mounted.

one question, What size props are you guys running in the 25-31cc range? 18x6 proved to be too much, 16x8 was good, 15x8 was better response and pretty fast too!! I like flying 3d but with the weight of this plane its better just fun flying so I was thinking about putting something like a 14x12 and making it really hall a**!

it seems I'm also limited by a governor in my ignition coil[:@] any suggestions here? C and H? how much?

Thanks guys and happy flying

Bottom line, how much static thrust can the 31cc produce?

Try this page www.duropower.com it has a 52CC engine for $79.99

Thanks it sounds good...If the man in my club thats going to help me with the conversion ok's this one..I think this is what I'll go with.

Eighteen pounds sounds light for an airplane with a 1500 sq in wing unless you have built the airplane previously. Twice the weight equals’ minimum cc is a reasonable rule of thumb.

Bill

a 54cc poulan would really talk to you on an 18# bipe I am building a new 60cc poulan for my wild hare ultimate , I just put one on a wild hare edge and it hovers all day and pulls straight up only thing this engine had a lot of time on it in the saw I was going to put a new cylinder kit on it but it flys great the way it is , just some other engine conversion to think about.

Its a very light profile I designed myself...However your right, with that larger engine on there it will probably come in around 21-23 lbs with the extra wood to beef it up a little...still a very good wing loading under 20 oz/sqft though. To break 20oz/sqft it would have to wind up weighing over 26lbs...which seems unlikley.