Mac conversion questions
 

Hello fellas,

I am currently building my first big airplane:a Byron Christen Eagle. I am new to large scale airplanes, and I have a limited budget.

I have a brand new Mac weedie engine sitting at home in the garage, but it is not labeled as to it's size (displacement) and I am wondering if it is big enough for the Eagle. She should weigh 14-17 pounds when finished. If the engine is in fact big enough, is it a worthy conversion? What prop should I use? Will I be able to hand start it without the use of an electric starter? Will I have to re-carb it? Will I have to use a prop shaft extension? So many questions, sorry. I will try to get some pics of it this evening and post them here to ease in the identification of it's size. I appreciate the help, thanks.

Tommy

A bit small...
 

Hi,

The Macs are easy to convert, especially if you are going to use battery ignition which I recommend for ease of starting, and lighter weight. Yours is probably either a 28 or 32cc. This would be a touch small for your plane I would say. Better find something in the 40 to 50cc range. The engine weight won't be much different, and you could use the extra thrust on that Eagle. Lawnstation has good deals on Poulan chain saws that have engines that are fairly easy to convert.

Good luck,
AV8TOR

Mac conversion questions
 

Thanks AV8TOR. I was unable to get pics of it this evening, but these are the numbers that appear on the data plate:

MOD......40005102
SER.......15-014736

hope this helps, I will try again tomorrow evening for the pics.

Tommy

Mac conversion questions
 

The 28 and 32 Mac weedies look indentical on the outside. I'm on the other side of the nation right now but I'm thinking that there is a 28 or 32 somewhere on the cylinder. I'm thinking its on the edge of the base? I have a 28 that I converted to a 32 with the addition of a 32 cylinder.

They look nice with the C-H ignition. They look like they were supposed to be a model engine all along.

They work better with a larger carb like the one fron a Zenoah G23 Walbro WA167 but I understand that they are no longer available. I bought mine from Carr Precision. They have a 28 molded into the venturi on the air inlet side. That's a 7/16" venturi. I've also used a 32 (1/2") Walbro carb on them.

The newer Homelite and Poulan chain saws make nice conversions too. Though you will be forced to use the C-H ignition with some models. The original carb is big enough on these providing you don't get a new type 4 Poulan with the non adjustable sealed carb. The 33 through 46cc sizes all weigh the same. A source for the Homelite would be Cummings Tool. Lawn Station often has sales and they also play the game on Ebay.

Enjoy,

Jim

Mac conversion questions
 

I think these guys are heading you in the right direction. You will need something larger than a weeder for the Eagle. Lawnstation.com is a good place to buy Poulan saws at a good price, but do not forget to check the local small engine shops. That is where I buy most of my engines for converting. You would be surprised how many saws get hit with a splitting mall or run over by a truck/tractor. It doesn't take much damage to total a saw, usually a broken gas tank or handle will be to expensive to fix, so they end up in the junk pile. These are the ones I look for, usually $20.00 buys them.
Tim

Hmmm.
 

Jim,

I will double check the cylinder for any markings. Looks like it is going to be too small, either way, so I may go out hunting for a 45cc or bigger to convert. Are the conversions easy to accomplish? I am an aircraft sheet metal guy, so working with metal is no big deal, however, when it comes to ignitions, I are dumm. :>) What manufacturers make these engines 45cc or bigger that are acceptable powerplants? Thanks for all of your help, guys.

Tommy

Mac conversion questions
 

Forgot to mention, this Mac weedie of mine has a 'stub shaft' exiting what would be the back of the engine. Mounted on this shaft is a ratchet mechanism for the pull start. If I choose to convert this engine for another project, will I have to cut this extension off, or leave it and cut a hole in the firewall to accomodate it? Thanks again.

Tommy

Mac conversion questions
 

You are making your MAc sound like an even smaller engine. I cannot remember the size but seems like it was a 25? I've never seen anything about converting these. The 28 and 32 have cantilever cranks. There's nothing sticking out the back.

Look at www.rcfaq.com and you may find some of the answers with pictures of what you are looking for.

There are two popular electronic ignition outfits around. One is C-H ignition and the other has been Ralph Cunningham in Williams AZ. Find C-H with Google and Ralph with the Explorer white pages.

Read around on here in the conversions and gas sections and you will find these people mentioned as well as pictures and a wealth of info regarding your interest.

Your existing engine as well as the chainsaw types have this shaft sticking out the back. Some people saw them off and others let them wiggle back into the fuselage. The choice is yours.

The electronic ignitions we are referring to are the type that have a Hall effect sensor on the front of the engine that detects a magnet at a certain location in the front hub as a timing reference. They are powered by a conventional NiCd or NiMh 4 cell battery but with 1100+ mah capacity. All this is available from the two companies mentioned or you can send your engine to them and they will take care of everything.

Enjoy,

Jim

Mac conversion questions
 

Check out lawnstation.com for their Poulan chainsaw offerings. For around $100.00 or so you can get a 42 or 46cc saw. These are easy to convert as the engine has nothing to cut off to use for a model engine. The 46cc requires a special carb adapter available from several suppliers. The ignition is simple to do and I recommend Ch ignition. Their site is www.ch-ignitions.com. I'm in the process of ordering a 42cc for myself, because it is about the right size for my project, and nothing needs to be done about the carb mounting on that model. If you want, contact Lawnstation by phone or e-mail, and they will sell you the engine alone; without the chainsaw trappings. Price doesn't drop much this way, but you won't have parts to throw away!

Have fun,

AV8TOR

Mac conversion questions
 

I have a Byron Cristen Eagle with a 60 cc Homelite. A good combination. Bipes need a little more power than the average aerobatic monoplane. Just food for thought.

Mac conversion questions
 

Ok Guys, here is what I found......there is a '10' stamped on one of the lower mounting flange on the jug. Does this mean it is 10cc? I find that hard to believe, since the piston is easily three times as big as any .40 size glow engine. I visited the C-H website, but I am still a little fuzzy on the spark issue. How do these engines maintain spark? I thought a magneto was something driven off of a crankshaft, there doesn't seem to be anything driven off the crank on this little Mac. There is a 'flywheel' with what appear to be magnets embedded in it, and a pickup of some sort suspended above it. How does this all work?

By the way, this Mac of mine has a Champion #DJ8J plug in it, if this helps. Thanks for everyone's help, truly a great forum!

Tommy

Mac conversion questions
 

Flypaper,

With that engine, how is the vertical performance? I'm not really looking for unlimited vertical, but does it have enough power to get you out of trouble, if necessary? Thanks,

Tommy

Mac conversion questions
 

Tommy:
The magneto is made up of the magnets on the flywheel and the coil sitting above it which puts out the high voltage to the plug. You would have to use a RCJ7Y plug for RC use. The Eagle is not overpowered at all. Just Enough power for good aerobatics.

Your ignition questions...
 

Hi,

Here's some basic igniton info. Your magneto consists of the flywheel with the magnets in it, and the coil mounted close by as you noticed. This unit generates it's own electricity and fires the coil to produce spark. Works fine, except it's heavy and hard to hand start. (Likes to be "winged" over pretty good to generate a good spark.)

Your other option is the CH Ignitions battery system. With this system, you do not use the flywheel nor the original coil. This is a battery operated system. You will have a special hub with a magnet in it in place of the original flywheel. This is also where you will mount the prop. The prop hub with magnet in it will also have a sensor mounted close by. When the magnet passes by the sensor, it will trigger the ignition. The rest of the system will consist of a battery, a switch, and the ignition module. The ignition module will have the spark plug wire coming out of it.

This all sounds more complicated than it is. The box, (ignition module) has a three wire bundle with a connector on it. This connector plugs into the corresponding connector on the wire from the sensor mounted near the magnet hub. The other two wire set goes to your battery/switch setup. That's it! You will have to have a separate battery solely for the ignition; you can't use your radio battery for the ignition.

Hope this helps,
AV8TOR

Mac conversion questions
 

Ah ha. Now I understand. The magnets flying by the coil generates it's own electricity for the spark, got it. Hard to start and heavy. So the electronic ignitions are lighter, except for the battery pack you must have to operate it, but makes for easier starting. After searching the forums here for conversion pics, I think this little engine belongs in the trimmer, not in an airplane! I may have to go shopping at Lawnstation! Thanks for everyone's help, much appreciated!

Tommy

Mac conversion questions
 

Well, the little engines are fine for some planes, just not a 14 lb. aerobatic biplane. I just converted a little 16cc trimmer engine for a 9.5 lb. "Stick" and it does just fine. But you will want something that makes a lot more than the 7 or 8 lbs. of thrust I got out of that! As I said, I'm going to use a Poulan for my next (bigger) project, as it is reasonably priced and easy to convert.

BTW... many people do use the magneto systems, and either use a pull rope setup to start the engine, or a starter. You still have the weight penalty however.

Have fun,

AV8TOR

Mac conversion questions
 

Sounds like my little Mac would be okay on an ugly sick, maybe. I have read a lot of the posts in this forum, enough to get myself thoroughly confused, but which engines are the ones that seem like they 'were designed to be model engines'? Do the Poulans make for easy conversions? I acquired a old 20+ year old Huskie 45cc chainsaw and looked it over, only to find that the crankcase is also the saw case, and it also has shaftage sticking out both sides of the case! Not to mention that the flywheel weighs almost 2lbs by itself!

So here's the bottom line: I am going to need 16+ pounds of thrust. I don't mind converting a chainsaw engine. I will probably have to buy a new one. So....which one?

I am going to post another thread with this same question, so I can get everyone's opinion and make some sort of educated guess.

Tommy

I'm for the Poulan...
 

The Poulan's have a separate magneto, and the engine completely unbolts. There is no case cutting involved. It really does look like a model airplane motor when you get it all removed from the saw. You even use beam type mounts like a model airplane engine. If you look around, there are some pictures in this forum of them. You can also go to the Poulan site and look up the parts schematics. It shows how simple the engine is to use for aircraft conversions.

Good luck,

AV8TOR

Mac conversion questions
 

Look strongly at the Poulan 46 from Lawn Station without the bar. Also the Homelite 45 Timbermaster 20" saw from Cummins is a good canidate. Both engine seem to turn a 20X8 at 7200 rpm.

Enjoy

Jim