The new Tower Hobbies flyer advertises the new OS .46AX engine.

I don't intend to buy it, but the ad includes suggested prop sizes, which could be considered out of the ordinary.
The suggested sizes are 11x6 - 11x8 and 12x6 - 12x7...

This engine is supposed to be quite close in power, to the now defunct FX.


The OS.46FX that I had, with the muffler baffle removed on 5% nitro, used to spin an Master Airscrew 11x6 (black) at 12,300 RPM.

An 11x6 APC would bog the engine down into the 11s as would an 11.5x6 (Bolly and APC). I never dared trying an 11x7...

12x6??? 12x7??? Is this engine meant to be run (deep) into the 10s? Or should it be raced to utilize more of its available output, at around 14K?

The Tower web site, BTW, also lists the 10.5x6 (which is equal in load to a 10x7), but this size was not even mentioned in the flyer.

Those props do seem large to me also if this is roughly on par with the FX. I've ran quite a few of the .46 FXs, and have always thought they liked to be up in the 14k range better than bogged down.

11x5
10x6
11.5 x 4

All APC have worked well for me.

There list looks like props you would reccomend for the .61 not a .46.

This engine has more HP than the former FX......... this is my only guess why they would suggest those props.
I have an ASP .52 that really performs well with an APC 11x6. It hauls my plane around with authority.

Some sites recommend 10x6 to 11x6 for speed and 11x7 to 12x6 for aerobatics.......it is really you choice though by testing out various size props for your engine and plane combo.

Ask this question in a month, the weather should stay above freezing long enough for me to run mine and I'll post what I find. Our racing group will be watching this closely. We race quickee with just one engine, the FX. So as you can see we are up poopy creek. We hope it will be the same as the FX so we can just transition to the new motor as the FX's wear out

I am using an APC 11-5 on my 46 FX engines with good results. It should work even better with the new AX. With the higher power rating than the FX it should give you better speed with that prop and have lots of vertical.[8D]

anyone have any tach readings on the ax? i'm curious if it actually has more power or os just recalculated the numbers... 12x7 on a .46? that seems a little too excessive!

Ryan,

The Reivers prop calculator; when 1 HP is assumed at 10,190 RPM, a 12x7 prop can be spun at this speed.
I may even be optimistic.

If a large prop offers enough load to put the engine below its peak torque, it may even spin more slowly.

I guess someone who has this engine, should tach a 12x7 and tell us all the results and on what fuel they were obtained.

I always run an 11-5 APC on my 46 FX motors (except when I have the Ultrathrust muffler hooked up). I tested my new AX on my LT-40 with an 11-5 and the difference was very significant- the heavy trainer was almost unlimited with the AX! I put the same AX motor on my Nobler with the same prop and was surprised that there wasn't much of a difference. But the Nobler is a relatively light, fast plane.

My conclusion is that the motor has more torque and we will all have to learn how to prop it to get the most out of it. I'm going to try an 11-6, then an 11-7. I don't have enough ground clearance to run a 12" prop on this plane.

A 12-6 seems mighty big to me, but then who knows...

Walt

OS recommends too big of prop for all their engines.It has something to do with noise rules in Japan.Even the 46 fx manual recommends a 12x6-7.
Personally I would start with a 10x6 and let it spin.

Kelly,

Noise regulations would explain this, but only half the way.

When MVVS designed their larger glow engines (.61-.91), they intended them also, to be used for low RPM, low noise operation.
So they used a 15mm o/d crankshaft (like the OS.46FX/AX and much smaller than most high power .40-.53 engines, not to mention other .61-.91 engines), with a small gas passage, modest timing numbers and relatively small intake bypasses, to maximize low RPM torque.

Their tuned exhaust systems are likewise tuned for the below 10K to 13K (.61 - 12K for the .77 and 11K for the .91) RPM range.

And they do excel with very large props in the intended, low RPM range (the .61 out-revs the OS.61FX, on a 14x6, by 2,000(!!) RPM).

Even if you cut their header down, the engine's design would not allow it to make Rossi/Picco/OPS/YS/Jett type, 14K++ RPM power.


The OS.46FX/AX are still rated at 16,000 RPM, yet are intended to spin, as they come from the factory at only 10,000-10,700 RPM?
Isn't there something wrong here? Shouldn't they have been designed to maximize their low end power?


The AX is new (but utilizes many FX parts). This is (was?) a great chance to redesign the engine for its intended, low RPM purpose.
Yet OS failed to do so.

This is precisely what's done with all CL stunt engines plus they keep the weight as low as possible (I have a rear exhaust ABC .61 that weighs 12 ounces with muffler). The cheapest would be the CL version of the Super Tigre G51 (an exceptional engine BTW) and ranging up to things like the RO-Jett or PA (made by Nelson).

The problem with RC is that the market is driven by a fascination for high HP numbers. Take the Super Tigre G51 for example. The RC version develops around 1.6HP@ 16K but the CL version is 1.1HP@ 12K (or thereabouts, I'm going from memory here). Which one will the average RC flyer choose even though they usually prop for around 12K anyway? I know which one will swing a big prop the fastest.

When the weather gets better I will be finding out what an 11x4 can do with an Avistar with that engine.

APC 12.25 X 3.75 works so much better than any other prop on my TT .46 Pro that I don't bother using anything else. My plane is a Magic Extra 300.
regards
Ed

DarZeelon wrote :
The AX is new (but utilizes many FX parts).

Only prop nut and washer and maybe screws and connecting rod.
Carb. New design of spray bar.
Cilinder : new design of ports and
Cilinder Head: New
Crankshaft : the hole for intake is now (AX) round and location for drive washer isn't te same.
Crancase:new.
Drive washer: new
Cover plate : new.

Manuel,


I have not seen an AX in person yet and maybe the info I received was inaccurate.
These parts may not be exactly the same, but most are close enough to be interchangeable.

Most external parts are clearly different (the carburettor is entirely so; not just the spray-bar), but I was under the impression that most innards were not different.

The ABL process is what the more recent FX engines also had. It is just a new name for the same thing.

The design of the muffler may have more effect than anything, as far as power is concerned.


Until the engine's stats are changed, so it will peak at 12,000 RPM, or less, the 12x6/12x7 prop recommendation does not hold water.