Engine basics > Four strokes only
Would a Saito .72 be too much for a Top Flite Score ARF?
Mike Reed:
I've got a Saito .72 and was wondering if it'd be too much for a Top Flite Score. I was going to put an old Merco .61 on it but since I have the .72..... This would be my first four stoke plane.
The only other options I have four stroke wise is a Saito .56, .40, and a small case ASP FS.61AR.
Options two stroke wise are, besides the Merco is a K&B .61 ABC Twister, and a .61 SuperTiger V case. All my other two stroke would be too small but I do have a couple chinese .46bb R/C clones I could convert.
Thanks,
Mike
Brett Buck:
--- Quote from: Mike Reed on May 24, 2020, 04:57:53 PM ---I've got a Saito .72 and was wondering if it'd be too much for a Top Flite Score. I was going to put an old Merco .61 on it but since I have the .72..... This would be my first four stoke plane.
--- End quote ---
It would be fine, power-wise, for a score. I would be very concerned about how the pink hot-melt glue would hold up to the vibration, some of these giant 4-strokes are notorious for shaking airplanes apart.
Brett
Dan McEntee:
I have a Score with a Saito .56 in it and it has plenty of power. A .72 just needs proper size venturi and prop just like any other engine. As Brett alludes to, the Score was assembled with a hot melt glue gun at the factory. I got mine second hand, and it didn't have much time on it. I flew it on and off for two seasons trying to figure out what a decent run for a four stroke was and how to get it! I read everything I could find on the subject, and along the way I realized you have to forget everything you learned about running engines and props when it comes to a four stroke. They are a different animal and make a different kind of power, a pulsating type of power. you just don't notice it as much because it only thumps every four strokes, hence the name!. I finally found the information that Bob Reeves put up on the forums here and set my intake up like his and use a straight pressure, no uniflow tank, and I haven't had a bad run since. I flew the airplane for two more seasons pretty regularly. I took it along to Oshkosh one year to fly up there in the evenings and at the noon time C/L demo at KidVenture. I met Gilbert Berringer there, who is in the brake and hydraulic business in France (and proficient in running Saitos,) and had been getting feedback from him on running Saitos over the previous few years. He flew it in one demo and gave me a thumbs up on it. I flew it in the noon demo the next day and while flying the tank out after the pattern, the engine suddenly departed from the airplane! The engine missed the better part of the gathered crowd and the airplane just fluttered own in one piece. After gathering up the nose and the few other pieces, I could see that the entire nose just came apart at the seams. Every glue joint let loose, with the left side first, then it broke the right fuselage side. Once I got it home, it was easy to just take some tweezers and pull all of the glue off all the parts. Then I just reassembled the nose just like I was building a kit. I used CA for assembly, added a few gussets, then brushed thinned epoxy over the whole works and recovered the nose. When the engine pulled out, the prop was still turning and took a bit out of the right wing leading edge and I had to repair that. After recovering things with Monokote and installing the engine and tank, I was surprised to find that it weighed only 1/2 ounce more! The model was heavy anyway at 72 ounces but carries the weight well. The first flights were just like the hundreds of flight before it, (except for the previous one , obviously!) and it flew exactly the same. The only thing I noticed now was that I could feel engine vibration at the handle. No matter what, you always feel something at the handle, but I can remember thinking how smooth that Saito was when I first got it. I know realize why, and that was because the nose construction was like one giant rubber vibration isolater because of the hot melt glue! There really wasn't any oil soaked wood when I repaired it, so I don't think fuel had anything to do with the failure. The glue is just NOT permanent. If you search the forums for threads on the score you will find this story and a few others with similar experience. If you go with the Saito .72 I would make this recommendation. Pull the covering off the nose and remove all the exposed hot melt glue you can reach. Then flow in some thin CA along all the joints , and then coat with thin epoxy like I mentioned. Before you start, try twisting the nose in your hands just to get a feel for how rigid it ids or isn't. When finished, do it again and you will see what I mean. I think it's a pretty good airplane and you will enjoy it, but no matter what engine you put in it, I would thoroughly go through the nose section and reglue every joint.
Type at you later and have a safe Memorial Day Holiday,
Dan McEntee
PS to add; If you go with the Saito.72, read up all you can on four strokes. This section of the forum should have everything you need in it. Proceed slowly with it and be ready for a different experience. If you have a muffler on it, and you should to provide pressure for the tank, it will be almost as quiet as an electric model. If you have been running two stroke engines for a long time, your ear and mind relate engine performance to a certain sound. At first, it won't sound like it has enough power to get out of it's own way, and it takes a while to get used to and get confidant with. I like the power plant a lot, but have not sold off all my Super Tigres, OS and Fox engines just yet!!
Mike Reed:
Brett and Dan,
Thanks for the heads up on the hotmelt glue. I'll make the necessary mods. Instead of epoxy to fuel proof I like to use Minwax oil based polyurethane varnish. Its lighter, flows into all the unseen cracks and nooks, and seems to soak into the wood better. Not to mention cheaper. Takes longer to dry though. But if your using the epoxy for strength are you laying in some fiberglass or something?
Dan,
Have been reading a lot of material about four strokes and ready to give it a try. One thing, I see Bob Reeves recommends to mount them on their sides. Did you do that on your Score? I gotta say though, that after hrs of watching Youtube videos, the ones mounted inverted didn't seem to be lacking.
Thanks,
Mike
Dan McEntee:
--- Quote from: Mike Reed on May 25, 2020, 03:54:22 AM ---Brett and Dan,
Thanks for the heads up on the hotmelt glue. I'll make the necessary mods. Instead of epoxy to fuel proof I like to use Minwax oil based polyurethane varnish. Its lighter, flows into all the unseen cracks and nooks, and seems to soak into the wood better. Not to mention cheaper. Takes longer to dry though. But if your using the epoxy for strength are you laying in some fiberglass or something?
Dan,
Have been reading a lot of material about four strokes and ready to give it a try. One thing, I see Bob Reeves recommends to mount them on their sides. Did you do that on your Score? I gotta say though, that after hrs of watching Youtube videos, the ones mounted inverted didn't seem to be lacking.
Thanks,
Mike
--- End quote ---
Hi Mike;
The epoxy is for strength. I added some gussets at the fire wall, I think, also. It's been long enough that I would have to pull the cowl and covering again to check. The original china-kote is just about all falling off, so I need to do that anyway. As for mounting, I got my Score second hand and it was originally built by Crist Riggoti who is a member here. He installed the engine inverted, changed the controls, and installed fuselage mounted landing gear. Along the way while I have owned it, I glued the wing in solid also with epoxy. The original mounting points were starting to get sloppy. Mounting on it's side may help with oiling, according to Bob, but after all the time I have on my .56, I haven't even checked the valves. it starts easy and runs well, so I don't feel the need to yet. Bob Reeves set up is a low RPM method of running the engine, limiting RPM to 8000 maximum, and this helps out a lot. I run Powermaster YS-20/20 fuel also. It's all synthetic and between that and the low RPM, my engine is as clean as a whistle and looks like new. I see all sorts of four strokes that are all coked up and look like a well worn Fox.35, and they shouldn't be. I've seen engine listed in the classifieds with bent push rods and no reason for that either other than over reving them. I run 13-6 and 13-7 props and I would start with those on your .72. After a life time of running two strokes it kind of goes against what is burned into your brain, but that is what works bests. I have not exactly mastered the art of hand starting mine yet, and still keep the electric started handy for those times it is difficult, but most times it's a one of two flip if I get it choked correctly and get a good bump. I have the venturi set up that the Moon brothers used to put out with their smallest venturi,. and a nylon 10-32 (I think) screw threaded into the throat of it and it's about half way in to get to the 8000 RPM limit. The screw lets you adapt to different weather conditions and air temps also. Once it's above 70 degrees and set, I usually don't have to adjust the screw, and the same for below 70 degrees. The needle may be one or two clicks one way or the other, and a four ounce tank is plenty big when the carb is adjusted correctly. I usually short tank it to 3 1/2 ounces to 3 3/4 ounces.I haven't flown it in a year or two since the covering started to come apart. If this virus induced vacation continues any longer I may get around to recovering it. Good luck with yours!
Type at you later,
Dan McEntee
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