I have a sig SE that I just love to fly, in fact the other plane has been gathering a lot of dust since the SSE has become air worthy. I like this plane so much that I have gotten another SSE kit to build so I can have two of them in my fleet. The first plane was built to plans, but this one I would like to put my own touch to it. Okay, two questions. The first plane has a OS 46ax, but I would like to put a 4s on this one. Most of my flying is done at half throttle or less so I figure a 4s would have the torque curve closer to the speed I like to fly, plus the sound of a 4 stroke is sweet to my ears. But when I do open her up I don't want any less power than the 46 has. Also weight is a consideration, meaning I would like to stay as light as possible. Have been looking at the 50 size 4 strokes. The new OS is a 56 and have seen some older 52s. Would these engines be comparable to a 46ax or what size would be. Now for the second question, I would like to invert this engine so I can build a nice cowl without any big holes on the side, but the fuselage height and thrust line combination makes it impossible to drop the tank far enough to make the center of the tank close to the carberator. Wondering if a high as possible loop in the fuel line would work or am I stuck putting in a side mounted engine

a good rule of thumb on 2st-4st comparisons is move up 20 in engine size when going with a 4stroke, for comparable power a 70 4st engine is about equal to a 46AX in power.

you also going to need a little more power since the 4st is a bit heavier than the AX as well, got to love the low end torque of a 4st engine

Saiti .72, upright and naked!

I've heard you should multiply the displacement of a 2-stroke by 1.5X to find a suitable 4-stroke. That gives .69 . . . and I have swapped OS 70 IIs for Thunder Tiger Pro-46s in three airframes with very suitable results so I think it's a good rule of thumb.

I just looked and the 70's are only 1 or 2 ozs. heavier. The 72 aac saito is a little cheaper than the OS. Is a saito just as reliable of engine as OS?

Like every other engine, once tuned properly...saitos are great!

I dont know. I have a Saito 100 and it's bullet proof so far. Once you go Saito, you don't go back!

I suppose so. They're no Y&S but some like 'em.

If you can still find one, a YS-63 will fly that plane as well or better than the .46 2-stroke and still be lightweight. It is being replaced by the YS-70 however which of course would be even better.

Beyond that, any good .70-.82 4-stroke will be excellent. If you can find a discontinued OS .70 Surpass-2 it would be a great choice. There new ones would be too.

I used to have one of the OS .70s that I often used in 40 size planes. They had gobs of extra power. I regret I sold it because I never cared for the newer OS .70s. When you compare a YS then you may as well compare a .70 to a .70 because the YS is that strong compared to other four strokes. Saitos are a great engine but I like my four strokes to have a pump and I do tend to lean towards the YS engines. That is one way to forget where you install the fuel tank.

i would extend the rudder/elevator at least a inch. it will help make your flat spins flatter, KE easier and much more.

An O.S. 52 or Magnum 52 is really all you need. The Mag 70 is about 7 oz heaver than the Mag 52. I put one on my late Ruperts Dad because of the weight difference, I needed 7oz to balance out with the Mag 52 and it seemed logical to make the weight work, so I put in a 70 Way more power than I needed. The O.S. 52 has a better carb than the Mag 52, but both are good engines and for the price, the Mag 52 is your best buy in four strokes. Match a 52/56 four stroke with an APC 12 1/4 x 3 3/4 prop and you have a setup that pulls like a John Deere tractor. Not fast, but man does it pull. Unlimited vertical in a 5.5lb plane.

The Mag 70 is a rock solid engine, I've flown a Saito 45 and it is a bit weak in a 40 size plane.

I think a 90 size is just asking for trouble. Too much weight and too much power. It will want a 14 to 15 inch prop and ground clearance can be an issue.

The four strokes inverted can give some issues, but match the fuel tank height and run an O.S F plug and it should be OK. I"ve got an O.S. 52 in a Pheonix Fun Star and it is mounted with the head at about7;30 looking from the front. It has a nasty habbit in that the first run requires a long warmup before flying, It almost won't keep running at first, but once it is hot, it is rock solid. My theory is that the piston and rocker cover collects alot of oilwhen setting and until that oil is heated and dispersed in the air, it is a rough engine. I pulled the rocker cover off once and it contained about a teaspoon of oil in it.

A glow driver may be in order depending on your engine. It will ad a couple oz to the weight, but the piece of mind is worth the extra weight.

Don

PS. Ionlyhave one 2 stroke plane , and I love the sound and ease of cleanup of the 4 strokes.

That's a heck of a lot of power for a 40 sized airframe. May I suggest model rocketry?

I'd personally go with a Saito 56 and be done with it.

The SSE begs for a Saito .82. It is lighter than the .72, and really hauls the mail with this plane. I swing a 15X4 APC wide blade on mine.

Nah... A YS-1.10 would be overpowered. I've actually seen people suggest that sort of combo too on a 40 size plane. Makes no sense to me. The little .63 will be equivelant of something like a Saito .82. Maybe not exact of course but similar. Plus it is fairly compact and lightweight.

I also agree on the .52-.56 though depending on how you want to fly it. They'll do better than a person might think.

I'll gladly swap you any of my Saitos for an OS

If your tank is going to be substantially higher than your carburator, a Cline regulator will keep your engine from flooding. It's a demand regulator, which simply means that pressure from the tank can't push fuel into your engine, but your engine can pull as much fuel as it wants out. As long as you have some positive pressure on the tank side of the line to keep fuel going to the regulator, then you can put the tank anywhere you want.

Me too!!!

Same here.

Allright you guys! I have an OS F-S .30 that has two tanks through it and Ill make a trade with yall! I trust you guys, so Ill trade it for a "slightly more used" Saito 50-56!

Saito 82 all the way. Will give you a little more power!!!!!!!!!!!!!!!!!!

I love all my OS 4-strokers as well as my Saitos. Both are quality engines. To replace a .46AX the rule of thumb I use would dictate a .70 four stroke. The Saito .72 is a great engine, comparable to the old OS .70 Surpass of which I have 3.

However, I recently compared my Saito .72 to a new OS .56a in the same airframe. I did this because the specs looked similar on paper and the OS is much lighter. Guess what - that new little OS is about 99% as powerful as the Saito .72. This is with them both running inverted, unpumped. The new OS 'a' series seem to change all the rules as the new .82a is at LEAST as powerful as the old OS .91 Surpass.

The YS guys are right about the power of those engines but I've really never seen one that didn't ask for a lot of tinkering. With the OS or Saito it's set it and (almost) forget it.

Good luck with your choice. There's nothing like the sound and reliability of a four stroke-unless it's twin four strokers!!!!!

That's the problem.... people tinker with them. If you have a good leak-free fuel tank and plumb everything exactly as the instructions show, a YS should be almost trouble free. I always staid away from them after watching guys struggle and hearing horror stories. Once I had one though I realized there was nothing to fear. Those people struggling just didn't pay attention to detail and made it more complicated than it actually is in their own head. Yes there could be a regulator problem from time to time but that's only after a lot of use (years?) and it is easily replaced.

I also like those new OS alpha series 4-strokes too. There's just too much good stuff out there.

I'm going to have to go ahead and agree with Chuck as never having had a YS of my own I only get involved with the 'Hey can you help me get this thing to run?' scenarios. It always amazes me that folks neglect to read the manufacturers instructions.....they apparently know more about engines then the engineers who designed them. That's not to say we all don't have our own experiences and preferences.

I have a reputation as 'the guy who stills runs in his engines' and we get a lot of laughs out of that around the field. The other day I'm breaking in a new Saito 1.00 and I hear the usual 'You don't need to break them in any more .... it's not a Fox .35! I pulled out 'the book' and showed everyone page 1 where it says something to the effect that you had better get 40 minutes on the engine before you lean her out and adjust the low end. Of course the 'experts' said "That must be a misprint". Hahahahaha. Did I mention I've had some engines for 20 years and they run better than new?????