ameyam

Dear all,

just wanted to know which engine is better for 3D and why. 4Stroke seem to be more prevelant than 2Stroke. Also, most planes are now installing the engine inverted for aesthetic reasons. Have had a bad time in the flying season with an inverted OS75AX.... it wouldnt remain tuned no matter what and kept cutting out even in straight and level flight. Are 2stroke engines really unsuitable for inverted installation? I want to know this because I have a Reactor 3D on order. If I am to put a 2stroke 55AX vertical or at 90 Deg in it, I will have to do major modifications to the cowl. My alternative is a OS 70Alpha which is twice as expensive. Saitos are not available and YS too expensive so I am stuck with these two, 46AX and 75AX

Ameyam

TruBlu02

You have opened up a can of worms here. The choice between two stroke and 4 stroke is normally a matter of opinion. I have both types in 3D aircraft. I have a Reactor as well and I use a Saito 82 in it. I know there are plenty of people who use the 55AX in the Reactor with no problems at all. I would not reccomend mounting it up-right either. I believe the plane have you mounting it at a 135 Degree angle so the muffler will go out the bottom. You will get alot of opinions about 2 and 4 stroke engine for 3D but you need to see what work best for you especially since engine availability is limited for you.

ameyam

I know this is a matter of opinion. The ratio of the two on my field is near 50% but most of the smaller engines are 2-Stroke. mainly becasue the trainees are more comfortable with them. I myself have never used a 4Stroke thus far.

To summarise my reading, I know that the 4S engine produce more torque as compared to the 2S, the 2S rev at higher RPM and a larger 4S is required instead of a comparable 2S. 2S require mainly high end needle manipulation, the low end is rarely required to be touched; atleast we never touched it in the 55AX; my instructor did some adjustment in the 75AX when we were trying to tune her. For the 4S, tappet adjustment is the main issue. My instructor indicated that the same is very difficult to get right during tuning. Also, 4S engine is very slightly heavier that comparable 2S. 4S requires smaller muffler and makes less noise. Obviously, the 4S is more expensive. 4S can swing larger props but I dont think that is a factor in engine selection

One of things that none of the posts are not answering clearly: is there an issue with installing the 2S engine inverted? Yes, the Reactor suggests 135Deg installation for 2S but if the engine cant retain fuel in the carb when inverted, I dont think 135deg wont be any better either.

And there is no data on the FS72Alpha either. With the 46AX / 55AX, I know these are very good engines. But no one here has any idea of the 72Alpha.

Ameyam

TruBlu02

Ameyam,

Ther is no an issue with running the 55AX inverted. The biggest issue is tank placement. If the tank is to high in realtion to the carburator it will cause fuel to run down into the carb when it does not need to. I have run a 55AX inverted several times in different planes and it is only a matter of taking the time to tune it properly.

As for the 4-strokes yes they do have more torques and most of your ideas are correct. The valve adjustment is very easy to do. The info can be found all over the internet on how to accomplish this. Most of the time you will only need to check the clearance. I have a old OS 91 4S that has never needed a valve adjustment in all thes years of flying. I just check it once a year or so to make sure it is holding its settings. As for props, the ability of the 4S to swing larger more efficient props is where they make up for their RPM disadvantage. They provide better throttle response on a more efficient prop whihc in turn creates amazing performance. I would probably use only 4S for 3D planes but the cost is just to much for me most of the time. $150 for a 55AX or $300 for a Saito 82. Not to hard of a choice for me.

TedMo

Right you will read many that have problems with running engines inverted, both 4s as well as 2s. I have both in several planes and do not have any problems with my engines when inverted or sidewise or upright. Ok, will modify that slightly from time to time there have been some that become troublesome but rarely and the problem is not due to how they are mounted. Just something inherent with model engines. sometimes they just become cantankerous. Main things are proper tank location and engine tuning. These are both well covered in other posts. Of course if you go electric none of these problems exist.

octanehuffer

Given both planes are the same, a 4 stroke will 3D better than a 2 stroke. The 4 stroke has much better throttle response and will swing a larger prop. The bigger prop will help throw more air over the surfaces and creating a slower flying, better manuvering 3D machine. It also mimicks a gas plane if you ever do make the jump to fly something real good. I have 3 planes on 2 strokes and 3 planes on 4 strokes for 3D nitro.

nitrofevr

It isnt about better or worse it is all about what kind of feal you like. As mentioned a 4 stroke will swing a bigger stick at lower rpms which will blow air over more of the controles. A 2 stroke will swing a smaller stick with more rpms. This will give you less control coverage but more air speed over where it does hit. These make a difference in the feal. The way they deliver torque and hourse power also has an effect on the feal. These variables have a lot to do with how the plane flies, maybe no better or worse just different. it is up to you to decide how you like it.

If you fly around in circles upright all day it matters to a certant extent how you mount any engine its just whats the cost and benefit. With the oriantation of the engine and 3d i dont think it matters just as long as you counter balance for it. You will be up side down, knife edge, vertical, and who knows what else. You need an engine that runs very reliable first and foremost. When your doing slow rollers head level you need to know it will be there for you. With that you also need to mount your tank and run your lines in such way that it doesnt favor any paticular attitude. It is all about symmetry.

Just my .02 and sorry about the spelling.

airborneSGT

My Feedback: (15)

I have flown 40 size planes all the way up to 40% planes. I can tell you that 4 strokes on smaller planes do fly circles around two strokes. The torque is what makes the difference. You can worry less about throttle management, giving throttle blips to get air over control surfaces, with a 4 stroke. Now large two strokes (Moki's and such) on tuned pipes do fly alright. Gas engines (mainly two strokes) also fly very well.

wind junkie

My Feedback: (1)

One other small item 4 strokes have in their favor is since they run lower RPMs, they tend to be easier on glo plugs. It's not uncommon to go several seasons on a single plug. I've never been able to get a 2 stroke plug to last beyond the first set of weather changes (and some tweaking). These were good plugs also solid platinum elements OS A3 and F plugs.

On the flip side, the 4 strokes DO vibrate more and this often shows up as tank foaming or fuselage integrity issues, so that needs to be dealt with properly.

Each has it's charms. When you see a good pilot flying his favorite setup, you can't really tell the difference except for the sound.

ameyam

So to summarise: I should have no problems with installing a 55AX at 135 deg on the Reactor...correct?

Ameyam

airborneSGT

My Feedback: (15)

You should not have an issue but I still think the ideal setup for planes this small is a good profile with either a 4 stroke or 2 stroke.

When I used to run small two strokes I recall using cool power 15% with an enya plug. I will also second the plug issue; on two strokes sometimes I could burn through them quickly during the summer time.

ameyam

I may be able to get the OS FS-70 Surpass-II or the OS FS-91 Surpass-II. Though it is expensive, as a one-off engine it is OK. The FL-70 is more readily available. What are your experiences with these engines?

Ameyam

airborneSGT

My Feedback: (15)

Both are good and there is an exact copy of both available made by magnum.

ameyam

No, I actually meant which one is better regardless of size class? I can only get one. If I get the 91FS, I will use with my Topstar. If I take the FS70, I will use it with my Reactor. So I can use either

Ameyam

airborneSGT

My Feedback: (15)

I cant' say either is better. Its what is best for your airframe.

wyo69cowboy

My Feedback: (2)

ameyam, the thread on the Reactor has lots of good info on these different engines in a Reactor but to surmise: a .46-size two stroke is marginal for 3D, as are the .70 class 4-strokes. The Saito .82 or OS .81 work well, as does the .91 Saito, in the Reactor anyway. If you have a lighter profile type plane, the .70 4 stroke would be fine. I have a Saito .82 in my Reactor, and it works well.

ameyam

Will check on the Reactor thread. I am looking at the 55AX that has slightly more power than the 46AX. Referring the FS82Alpha, the same actually works to be more expensive ordering direct from Tower than the 91FS available locally. If the 55AX is not sufficient, the 61FX 2Stroke will be required. However, that is almost as expensive and as heavy as the 75AX I already have. I feel the 61FX / 75AX / FS91SII will be a bit too heavy for 3D.

To summarise it is between the 55AX(Locally), FS-70SII(Locally), FS-70Alpha (locally) and FS-80Alpha (Tower). In pricing terms, the 55AX is the cheapest, FS-70 SII and FS-70Alpha are very similar and the FS-80 is the highest.

By the way, any one has any idea on the difference between the FS-70 SII nad the FS-70Alpha? There are no reviews or details on the same anywhere

Ameyam

airborneSGT

My Feedback: (15)

I had a friend with a U Can Do .46 on here. His with an OS .91 flew circles around mine with a Saito 82. His was even heavier as he had a NIMH rx pack and I had a lipo. Sometimes the rules of what flies well are not always clear. You might have to try a few setups.