Four Stroke Vs. Two Stroke
 

Hi All

I might buy a Seagull Dual Ace but looking through all the forums most people are having fun on OS .46la/ax size engines. I wanted to put a couple of small four strokes in mine and wondered what the equivilant size might be....... .52 four stroke ????????? :eek:

Thanks for any replies

Cymaz

RE: Four Stroke Vs. Two Stroke
 

Yes. The Magnum/ASP 52 four stroke would be fine.

The OS 52 four stroke has been discontinued

You might consider the Saito 56/62 engines

Or RCS 58

RE: Four Stroke Vs. Two Stroke
 

Hi just purchased a saito 56 I am a little confused when looking at engine requirements on many of the models out there. Some say 40/46 2c 70/91 4c did the 56 fall through the cracks what is a good rule of thum for my 56 can I use it in a 46 2c application and have enough power I dont fly fast iI just want to feel like I'm not under powering any help appreciated Bob A

RE: Four Stroke Vs. Two Stroke
 

I've flown two different Phoenix Models SeaBee .46 Sport/Pattern ARFs. The first I flew had an O.S. Max .46 FXi 2-stroke in it and it flew great with that engine. The second one I flew had a Magnum XL .52 RFS in it. The Magnum 4-stroke was turning an MA K-Series 12x6 prop at 10,000 RPMs and it flew just as fast as the .46 FXi turning an 11x6/11x7 APC prop.

Based on this experience, I am comfortable using a .52/.54/.56 4-stroke in place of a .46 2-stroke. When tuned and propped correctly, they're just as powerful for sport applications.

Four Stroke shoppers would do well to consider also the Thunder Tiger F-54s, F-75s, and F-91s. The F-54s is a solid value at $179.99, but with the F-75s selling around $169.99 to $174.99 at many TT dealers, it's not surprising most shoppers are opting for more displacement. Both of these engines are very similar in weight to other four strokes of the same displacement, only the TT F-91s is noticably heavier than offerings from other manufacturers.

RE: Four Stroke Vs. Two Stroke
 

A 91 four stork replacing a 46 two stroke. No way. My Mag 91's are monster engines size wise comparired to the O.S 46 I have. About twice the weight, and the dementions are quite different also The 91 is quite comfortable swinging a 15" prop and I'm sure the 46 would not be up to the job. A really hot 46 compaired to a 70 four stroke may be a valid compairson in power, but the weight and physical size is still an issue. Your Saito 56 would be a very good engine on a 40 size plane, maybe a bit over powered. If you are working with a cowl, check the dementions carefuly. Don't forget that the carb takes up a lot of room behind the engine and with some mounts you have to move even more to the front.

Don

RE: Four Stroke Vs. Two Stroke
 

What the ARF and kit manufacturers try to do is recommend a series of engines that have similar weight, mounting dimensions and power.

Engines can be divided into, for the want of a better term, block size categories. For example, the ".40 block" engines include modern .40, .46 and .52/.55 size two-stroke engines. Also, four-strokes like the .40 - .56 Saito/OS/Magnums, the Saito .72/82a and YS .63 fit into this category. They are all about 36mm between mounting beams and they weigh about 500 grams, give or take. You often see ARFs recommending ".40 - .46 two strokes or .52 - .72 four-strokes" for this reason.

Same goes for the ".60 block" engines:, hence: ".61 - .75 two-stroke and "91 - 100 four-strokes", because engines in this range are typically about 42 mm between beams and weigh about 600 - 700 grams.

In my experience, in very general simplified terms, a good .52 four-stroke performs about the same as an average .40 - .46. A good .70 four-stroke about the same as a .52 two-stroke and a good .91 FS about as good as good .61 - .75 two stroke. YS fourstrokes are a bit different - they pretty much match or slightly exceed a two stroke cube for cube.

Notwithstanding the above, four strokes have some tangible advantages (spoolup and linear throttling) in applications like 3D flying, where response and throttle control is critical.

RE: Four Stroke Vs. Two Stroke
 

I, like Harry, have never considered the "flying power" of fourstrokes and two strokes as having nearly the discrepancy that many people think. Most HP figures, (on most two strokes), are gotten using a prop that is unrealistic to fly with. I like Horizons idea of a prop range then a benchmark prop and rpm. The Saito .56 is a surprisingly powerful engine on a plane.

RE: Four Stroke Vs. Two Stroke
 

I dont mean to hijack this thread.... but my ST90 will swing a 15x4 @ about 10000 rpm with horrible spool up, and my 91 saito will swing it at about 9400 but with great throttle rsponse

RE: Four Stroke Vs. Two Stroke
 

Hi

Well I started this thread as the Seagull Dual Ace does not have much room for a large tank about 8-10oz at the most, and since the fuel economy of a 4 stroke is better then I will go for that. I dont want a dead stick on one engine because of lack of fuel.

By the way does anybody know the relative fuel economy of 2s vs. 4s..... say a .46 2s compared to a .56 4s ???????????,, How much time on say a 10oz tank for each.

This would be a great help. Thanks to one and all for the replies.

Cymaz:D

P.S. I don't mind who hijacks the thread MetallicaJunkie...we all get useful info and tips.

RE: Four Stroke Vs. Two Stroke
 

I'd opt for the TT75FS to replace a 46-52 sized 2-stroke.

Why buy a .52/54 4-stroke when, for just a hand-full of pocket change, you can get an engine that has more displacement and more power but no more weight.

If you're worried about "overpowering" your plane just remember that you can always throttle back :-)

As to fuel economy most 4-strokes are more fuel-efficient than comparable 2-strokes except perhaps the Saitos. Even when you tune them properly (which lots of folks don't) the Saitos seem to drink about the same amount of fuel as the equivalent 2-stroke. I'm not sure why that is but it may be related to their relatively low compression ratios (which is why they also *love* 30% nitro).

The TT 4-stroke engines seem *very* fuel efficient. My P51 Mustang (with TT91FS) had a 330ml tank in it and I'd get totally bored while flying it *long* before the tank got empty. In fact I replaced the tank with a 250cc one and I still get flight times of 10+ minutes, mostly at full throttle.