4 Stroke engine vs. 2 Stroke
 

This question is related to a twin project I'm getting ready for.

Here's what I have, I have two Webra 1.2, two stroke engines, two Moki 1.8, two stroke engines, and two Enya 1.2 four stroke engines.

I'd like to turn a 14" three blade prop.

Best choice? Should I purchase two engines of something else?

Suggestions, advice?

Thanks

Charles

RE: 4 Stroke engine vs. 2 Stroke
 

Use the Moki engines. You'll have a hard time getting a 1.20 size engine to swing a 14" 3-blade prop at any decent RPM's.

RE: 4 Stroke engine vs. 2 Stroke
 

my YS 1.20 turns a 14x7 three blade quite well.

RE: 4 Stroke engine vs. 2 Stroke
 

More information needed.

What type of performance/flying do you want from the airplane?

What 14" dia x "pitch" prop do you intend to use?

Ed S

RE: 4 Stroke engine vs. 2 Stroke
 

Well, a YS ain't the same animal as your average engine. ;) Everybody knows they put out 20% more power. It's not surprising that engine would swing a 14" 3-blade prop. I know from experience an OS 120 Surpass won't swing a MA 14x7 3-blade prop at any RPMs you can fly with.

He hasn't got one of those anyway. The Enya is no more powerful than an OS. Certainly not enough to spin the prop he wants to use.

And a 120 2-stroke isn't going to do it either. At best you could turn a 13" 3-blade on a 120 engine.

A Saito 180 turns a MA 14-7 3-blade at 7500RPM on 15% Omega. Thats leaned out and then richened to drop about 300RPM off peak.

My rule of thumb is drop 2" off the diameter and leave the pitch alone.

A standard 120 engine turns a 15-6 or a 15-8 prop.
A 180 engine turns a 16-8 or a 16-10 prop.

I know there is a trend to overprop engines right now. People are using 16" props on 120 size engines and 18" props on 180 engines. Thats fine if you are using a 2-blade prop and looking for a quiet setup. But you aren't going to lug an engine down with a 3-blade prop and expect it to do any work.

Just my opinion.

RE: 4 Stroke engine vs. 2 Stroke
 

Both my OS 1.20 (2) and YS 1.10 (4) will spin 16x8 and 15x10 2-blades. I have not tried a 3-blade yet but don't see why OP's 1.20's can't spin a 14x7.

I would get one and try it, it's the best way to find out;)

RE: 4 Stroke engine vs. 2 Stroke
 

I guess that really is the best way, isn't it? [sm=thumbs_up.gif] Buy the prop you want and see which engine likes it the most.

RE: 4 Stroke engine vs. 2 Stroke
 

I would say that it's all preferance. I don't own any 2 strokes simply because I was sick of having to adjust them all the time. I set all my engines at 400 rpm under peak on the rich side at the start of every season. On 20% oil/20% nitro my Saito 125 will turn a Zinger 15X6 3 blade at 9000 in the air with no problem (8600 on the ground). I find that 9000 rpm is about peak power for 91 or larger four stroke. Remember that the max rpm doesnt mean the max horespower. With a four stroke you'll need to experiment with prop size, what the manufactor says and what the engine will actually swing are two different things.

RE: 4 Stroke engine vs. 2 Stroke
 

I really didn't want to buy two more engines.

The Enya 1.2 four strokes should deliver as much power as the Sato 1.25?

The pitch doesn't matter, I'll settle with any pitch, I need the 3 blade for scale apearance only. Same with the 14" prop.

I have one Enya 1.2R NIB. I would consider locating another.

Charles

RE: 4 Stroke engine vs. 2 Stroke
 

Sounds like it is going to be way overpowered for you to get the scale props; if the pitch is too high you might not slow it down to land. I would say if this plane would fly on 2 .40s-.60 2 strokes, I would go with lugging the Enyas with a 14-5s. What plane and what scale?

RE: 4 Stroke engine vs. 2 Stroke
 

Try the prop you want on the engine you want.

The model props performance is so unpredictable, you'd be surprised what works on what. I've run a 13x8(3) on a .75 two stroke with excellent results for over a year now.

Also, don't expect props of the same specs, but different mfg/shape to produce the same either.

RE: 4 Stroke engine vs. 2 Stroke
 

This is the project. The span is 80".

RE: 4 Stroke engine vs. 2 Stroke
 

My Saito 120 Turned a Graupner 14-7 without any trouble when it was in my Skybolt. Now it's swinging a 16-6 2 blade in my Funtana100

RE: 4 Stroke engine vs. 2 Stroke
 

Cool plane. Widgeon right? At 80" it is not going to be big and heavy; probably 14-17 pounds. An engine that can truly spin the scale props is going to hammer the airframe. The moki could tale that plane vertical on one engine. You matching the engines is just as important as Grumman doing the same. It would be like you taking one of those planes and saying I want 2 P&W 3350s installed. I would say the Enyas with the correct props would make a better plane.

RE: 4 Stroke engine vs. 2 Stroke
 

Does it really matter that much to have a scale prop for flying? Scale size props, generally do not equate well to our engines. Why not use static props for display and change them out for flying to optimize performance? You cannot see them when they are spinning anyway, but you will certainly feel the lack of performance in the air.

RE: 4 Stroke engine vs. 2 Stroke
 

G'day Mate,
If you only want scale appearance, you can put any prop you want on it, but if you want it to fly, then you must experiment with different props.
And an Enya 120, won't deliver as much power as a Saito 125.

RE: 4 Stroke engine vs. 2 Stroke
 

When I mentioned the prop, I said "scale appearance only". Any 3 blade at 14" would give me my scale appearance. I may round the tips and see if that changes RPM, but my guess is it won't.

I'm trying to work with what I have. I forgot I have two NIB, OS 80 two strokes, the ones with the double plugs. Old but never run.

I do expect the model to weigh more than 17 lbs. I'm drawing up scale retracts, that could be a pound in itself.

Keep in mind that full throttle isn't necessary, But it does have to get out of the water.

What's necessary is the 14" prop. I do need a fare percentage of prop greater than the size of the nacelles. At least to match the look of the actual airplane.

Don't forget the Webra 1.2. I have two Jen .57's also, but I think they could only spin a two blade prop and not at 14".

I would have to look for and purchase a Enya 120R.

Charles

RE: 4 Stroke engine vs. 2 Stroke
 

I run a moki 1.8 in my 80in 18lb P-51 mustang. It turns an 18x12 apc prop close to 9000rpm, it's fast and darn near unlimited vertical... The moki would be an extreme over kill in weight and performance, and I think 14in props... unless you have serious pitch would be severly underpropping the moki. From what I remember the old webra 120's were some pretty strong engines.. I think that it puts out more power than the supertiger 2300, and could possible be very comfortable running the 14x7 or 14x8 3 blades. Now that I think about it I remember running 13x6 or 13x7 3 blade prop on a supertiger 90, that I had on a 60 size zero several years ago, and I had no issues what so ever.

RE: 4 Stroke engine vs. 2 Stroke
 

Hi!
For a 80" Grumman Widgeon a .52-.62 four stroke is what I would choose. Those engines swing either a 12x6APC or 13x6 APC two blade prop. Choosing a 3-blade and you can try a 11x6 for the .52-.56 and a 12x6 for the .62.
Any larger engine and it will just be too heavy and not fly good!

An OS 1.20 four stroke runs good on a 16x6 or a 15x8 2-blade prop. The correct size 3-blade is then a 15x6, 14x7, 14x8 prop. That is if you fly at sea level and use 5%-15%nitro.

RE: 4 Stroke engine vs. 2 Stroke
 

I guess for flying, I would not bother with a 3 blade prop. Very inefficient. Then you will get your diameter to clear the nacelles.

RE: 4 Stroke engine vs. 2 Stroke
 

Webra 120 will spin this prop very easily, probably at around 8500-9000 rpm, it spin apc 16/8@9300rpm, that is more them any four cycle engine could put with this prop. Moki 180 is just over kill.

RE: 4 Stroke engine vs. 2 Stroke
 

To balance this model, weight has to be placed in the nose. Understandably. The larger engines will help with balancing, depending on how it's viewed.

The nacelles are large! 14"s the least I can spin in a prop. 1/6 scale is 14" of prop, three blade. I could swin 14" two blade props?

What about the older OS 80's?

Charles

RE: 4 Stroke engine vs. 2 Stroke
 

Hi!
Don't be afraid of the big nacelles! A prop doesn't have to stick out much from the nacelles to work!
Build the tail light and you don't have to use such heavy (way too large engines) engines.
Using .91 or worse...1.20 engines in a such a small (220cm span) scale model is asking for trouble.

RE: 4 Stroke engine vs. 2 Stroke
 

The .80s are cool engines but not powerhouses. They will swing a big prop but power is about equal to a modern .40-.46 engine.

RE: 4 Stroke engine vs. 2 Stroke
 

Should I stop living in the past with my older but not used engines?

Should I just consider new engines which are made better, lighter, and are more reliable. Or are they?

Charles