What's the difference between OS 46 and the OS 55? The HP rating is not that much different I do see you can run 13x6 prop on the 55. Other than that it doesn't look like it has much more power.

O there is a big difference. I've seen them run side by side and even in the same plane.
The 55 seems to have the power of my OS 61 FX.
A buddy of mine flys a 55 on a value hobby sabre. it's a 3D machine

Wannabe,


They are both in OS' .40 size-frame bracket. I e. in the past, OS made the basic .40 cid (6.5 cc) engine in that bracket.
But over the last 30 years or so, engine manufacturers all began to increase the cubic displacement of their .40 engines, without making them any larger on the outside and they're not much heavier either.
They even drop into the same mounts.

OS.40FX engines had a 20.5 mm bore diameter and a piston stroke of 19.6 mm.
The .46FX and AX used the same stroke, but the bore diameter was increased by 1.5 mm to 22.
The OS.55AX still uses the same external dimensions, but the piston stroke is increased to 21.5 mm and the bore diameter is increased to 23 mm.

The OS.61FX has a 24 mm bore diameter and a piston stroke of 22 mm.
But it is in a larger frame... But OS has already crammed .95 cid within that frame, in the OS.95AX, with a 27.7 mm bore and a 25.8 mm stroke. And it is the same size and weight as the .61...

IN my experience when a manufacturer increases the displacement of their 46 to a 52,53 etc it is good for about 500 rpm on an 11X6.

I have an O.S. 46AX and 55AX both on 40 sized low wing sport planes. I can say that the 55 is much more fun to fly with. I can feel the extra power and about the horse power rating, I generally disregard that, I usually look at how many RPMs it can get up to on my intended prop for the model. Many say that "there is no replacement for displacement"

RCFlyyer,


It is not only you that cannot feel the 'horsepower rating'...
Your planes can't and not even the prop...

What you can feel is the actual HP output.
The .46AX on 15% nitro can spin an APC 10x6 at ~14,300 RPM, which translates into 1.14 actual HP.

The .55AX is more potent and spins the same prop faster; therefore its horsepower output is greater.

So it turns a larger prop at the same speed which generates more power.

Originally Posted by Want2B3D

So it turns a larger prop at the same speed which generates more power.

Wannabe,


It is a matter of physical definitions. One HP is defined as an output of 33,000 lbs. ft. per minute. It is not just a force, but a force applied over a distance per time unit.
Similarly, a force of one Newton applied over a distance of one meter per second, is defined as one Watt.

Claimed HP by model engine manufacturers, has become a cheap 'pissing contest'. There are but a couple that make a claim that can be realized.

OS for one claims 1.65 PS @ 16K RPM for their .46AX.
As you receive it, it cannot even come close to this figure.


Regarding the larger prop at the same RPM making more power... The engine produces the power output to spin the prop... The spinning prop produces thrust, which is a force; not power.
The power output is only realized in flight, since a force at speed, is a force over a distance per time unit - the definition of power output.

Originally Posted by DarZeelon

Claimed HP by model engine manufacturers, has become a cheap 'pissing contest'. There are but a couple that make a claim that can be realized.

OS for one claims 1.65 PS @ 16K RPM for their .46AX.
As you receive it, it cannot even come close to this figure.

This isn't really true, the ratings are mostly accurate, however they are measured using tiny props that are below the suggested range, so you'll never see that level of power in normal use.

However, as you pointed out, it is basically a pissing contest these days. So, if you look back at older engines, that are rated lower, they used more realistic props back then and should offer similar performance even with lower advertised power.

Originally Posted by ChillPhatCat

This isn't really true, the ratings are mostly accurate, however they are measured using tiny props that are below the suggested range, so you'll never see that level of power in normal use.

CPC,


No they are not and you are wrong.
This is simply a lie manufacturers (and magazines...) tell you...

With a friend, we took his engine (a low time OS.46AX) and ran it with a 15% nitro fuel and various 'toothpick' props, to get it up in the claimed HP RPM range.

The most appropriate was an APC pylon 8.75x8.25NN prop.
The engine spun it at 16,100 RPM, which is close enough to the rated 16,000.

Initially we were happy... but to our dismay, the calculated HP was only .92.
This is much lower than a 10x6 APC prop takes at 14,300 RPM (1.14 HP), as well as over 44% below OS' 1.65 HP claim!!!


There are few cases where an engine met and even exceeded the manufacturer's HP claim...

One such case in my own MVVS .49 engine, equipped with their standard #3248 tuned silencer and running on 5% nitro fuel. They claimed 1.4 HP for this engine.

It spun a Bolly Clubman 11.5x6 prop at 13,100 RPM, producing no less than 1.52 HP!

A Jett .50 BSE actually produces 1.92 HP, spinning an APC 10x6 at 17K RPM, but Dub makes no tall HP claims for people to challenge and guarantees this RPM.

First I would like to say that I ran up my AX .55 and it sounded pretty good as did my .46. Both were bargain swap meet items because I have heard so many bad things about peeling liners and bad bearings, I didn't want to put good money into bad. Maybe the power figures given for the OS stuff are given without the muffler installed. I know the beloved Jett and the MVVS have a very good muffler/pipe that increases or at least doesn't detract from the power. Also the 8-8, 9-9" etc. props and the high pitch props that work so well in speed planes will unload a lot in the air for more performance but it will be likely 3,000 rpm higher, making it possibly higher than the peak HP rating. As far as the OP is concerned, I haven't run the .46 and .55 together on the same day for tach. readings, yet.

Originally Posted by DarZeelon

[COLOR="Navy"]CPC,


No they are not and you are wrong.
This is simply a lie manufacturers (and magazines...) tell you...

With a friend, we took his engine (a low time OS.46AX) and ran it with a 15% nitro fuel and various 'toothpick' props, to get it up in the claimed HP RPM range.

The most appropriate was an APC pylon 8.75x8.25NN prop.
The engine spun it at 16,100 RPM, which is close enough to the rated 16,000.

Initially we were happy... but to our dismay, the calculated HP was only .92.

How were you calculating power? According to any of the online power calculators, that comes out to about 1.45 Hp static...

CPC,


The PropPower calculator spreadsheet by Pé Reivers can be downloaded here.

You need MS Office, Mozilla OpenOffice, or another spreadsheet program to use it.

But when you do you'll see it has many realistic and empirically tested prop indices, for virtually all makes and models of props. These were arrived at by actually measuring actual wattage required to overcome their drag, at various RPM values.

The N type APC has the factor 0.90, while the normal APC Sport props have it at 1.23.


Most on-line calculators are overly optimistic. This one isn't; period.
Just take a look at one of the APC Quickie props (not their C/F F1 types). Do you think they are even similar in load, with their thin tips, to the much wider Sport APCs?

Bailed out.

Originally Posted by aspeed

First I would like to say that I ran up my AX .55 and it sounded pretty good as did my .46. Both were bargain swap meet items because I have heard so many bad things about peeling liners and bad bearings, I didn't want to put good money into bad. Maybe the power figures given for the OS stuff are given without the muffler installed. I know the beloved Jett and the MVVS have a very good muffler/pipe that increases or at least doesn't detract from the power. Also the 8-8, 9-9" etc. props and the high pitch props that work so well in speed planes will unload a lot in the air for more performance but it will be likely 3,000 rpm higher, making it possibly higher than the peak HP rating. As far as the OP is concerned, I haven't run the .46 and .55 together on the same day for tach. readings, yet.

Aspeed,


You'd be happy to know that with a JettStream tuned muffler installed instead of its original PowerBox; the OS.46 engine produces no less than 1.57 HP @ 15,900 RPM... But that's not the configuration under which it was rated by OS, was it? And in this configuration it would utterly fail any noise test...

I found another, later reading for the MVVS .49 with the same prop and setup... 13,600 RPM, which equate to 1.7 HP...


For a glow two-stroke, its a great muffler, or else...