gene6029

I have been flying .049 C/L models w my grandson for the last year & want to move him up to a slightly larger size plane. I have lots of R/C motors in the .10-.19 size that i would like to put to use. Some have mufflers with out pressure taps, some were before mufflers were around. If i put the throttle in a fixed position ( wide open) should i expect any abnormal run problems?...... Gene

controlliner

They should run fine for just putting around the circle. Having a good venturi will benefit only if you want to do the AMA stunt pattern. I've used a Fox .45 R/C with no problem on a Sterling bearcat. Just remember to keep the tank centerline in line with the carb on a profile plane and all should be fine.

Boulder Dave

I've done that, and it's actually easier to tune an engine for full throttle operation, if you're not worried about idling. If your field allows it, you can leave off the muffler
completely, since you don't need the back pressure. You also don't need an idle-bar glow plug, if you're using one, improving full-throttle efficiency.

If you don't want to monkey with fixing a throttle pushrod, you can buy a venturi for most engines that eliminates the carburetor, thereby making it a C/L engine.

- Dave, Boulder

Boulder Dave

The centerline of the tank should be lined up, top to bottom, with the centerline of the crankshaft, with
the engine mounted profile-style. Looking from a wingtip, that is. Since in that position the engine is
always running "inverted" when flying, and that never changes, it's not as critical that the tank be in
line with the carb side-to-side (laterally). On an RC plane the tank centerline is in line with the carb
so it doesn't richen or lean when inverted or doing a push-over.

- Dave, Boulder

controlliner

That's what I said in fewer words.

gene6029

OK, thanks guys that only took a few minutes!! We are building a Sig "Buster" profile & im thinking of putting on a OS .10 or steel fin .15. I dont want it too fast for him, he's 10yrs old. Im thinking 52' lines & 1 oz tank ? Can allways put on a larger tank. Thanks again....Gene

controlliner

I flew the Shoestring version with an OS .10 FSR and it flew beautiful. If you use a .15 he will be spinning fast. I started out with an OS .15 FP and it was hot.

gene6029

Thanks for the heads up controlliner! I'll put the .10 on it & we'll see how that goes. Gene

Clean

Don't be afraid to put the prop on backwards either. Just enough initially to fly the plane. Later on, if you have the pilots/helpers, there an awful lot of fun to race.

gcb

Gene,

If you are considering the .10 ... which .10? I THINK the first MAX .10 RC came out about the time MAX switched from II to III (late '50's).

When you mentioned the "steelfin" Max .15, I am guessing the MAX-III .15 since the MAX-II still used a butterfly and exhaust restrictor as a crude throttle. Besides, they sold a LOT more III's. I don't remember the MAX-I being available with throttle. Mine was FF/CL.

I flew my MAX-III's on 52' x .012's.

Point is, if you are talking modern .10, it may equal the steelfin .15 in power, although the MAXes were strong .15's for the day.

Good idea on the tank. You might include a narrow line spacing on the handle too, to make it less sensitive while he is learning. Oh yes, preferably a 4" pitch on the prop...to keep it slow with good pulling power (for those awkward moments ).

Good luck with it.

George

gene6029

George, sorry it took so long to reply, but my OS.10 is not as old as most of the motors i have, but it has a 761 muffler on it with no pressure tap. The only other ID on the motor is on the backplate & it has the # 1107 on it. Not exactly sure of its time line....Gene

gcb

Gene,

The SIG Buster (CL-12) is a racing plane so if using it as a trainer I would go with the .10 and use a 7x3 or 7x4 prop to keep the speed down. I'm guessing that the .10 is lighter than the .15 so you can fly the plane slower. You can make the throttle adjustable to control the speed. The 52' lines will keep the RELATIVE speed rotation to a minimum. Fuel with 10%-15% nitro should keep the speed down yet provide reliability.

I would suggest you fly it at full throttle until you see how it handles, then throttle back some and turn it over to him. Make sure it is running fast enough that it will have sufficient pull and not fall out of the sky.

Good luck with it.

George

gene6029

Thanks George, but I might have to do it opposite from your suggestion & let the grandson turn it over to me! Its been awhile since i have flown circles & at my age I feel like im doing circles just watching him fly!!! Either way, im sure we will have a ball with it ( over tall grass at first)....Gene

gcb

I started to offer more advice, but reread your first entry. He already knows how to fly...just switching to a larger plane. To answer the original question, there should be no problems with throttle vs venturi.

Good luck. Enjoy!

If he wants something more maneuverable as a next step, there are several in the .15 size range...Flite Streak Jr., Flying Clown, Akromaster, to name a few.

George

gene6029

I wanted to post a picture, but its not working.....[&o]

gene6029

I'll try again... silkspan & 8 coats of nitrate so far....Gene

Jim Thomerson

The Sig Buster and Shoestring are too flimsy to survive the rigors of serious racing. My Son built a Buster from Sig plans, but with usual Goodyear construction, and raced it for a couple of years without incident.