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OS 25AX vs 25FX. What am I missing?

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Old 11-08-2012, 08:21 PM
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jwottowa
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Default OS 25AX vs 25FX. What am I missing?

So I am looking for a new small OS for a combat/fun fly plane and I am a bit confused....

The OS FX25 sells for $130 and weighs 248 grams, and makes.84 hp at 18,000 rpm
The OS AX25 sells for $160 and weighs 357 grams, and makes. 79 hp at 15,000 rpm

Why does the heavier engine that makes less power cost $30 more? To further complicate the issue,

The OS AX35 sells for $155 and weighs 363 grams and makes 1.28 hp at 16000 rpm

Again, the 35 is $5 bucks cheaper only weighs 6 grams more and makes a ton more horsepower than the AX25.

So I guess my question is, What is so special about the AX25 compared to these other two offerings to justify the higher price? It seems if I wanted to go light, the FX25 is a better choice and if I am after power, the AX35 is the better choice.

What am I missing????? Thanks in advance for your input!


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Old 11-08-2012, 09:14 PM
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Default RE: OS 25AX vs 25FX. What am I missing?

Let me know when you figure it out.
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Old 11-08-2012, 09:21 PM
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Default RE: OS 25AX vs 25FX. What am I missing?

.25 FX kicks A!
Based on empirical data. No questions answered.[8D]
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Old 11-08-2012, 11:51 PM
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Default RE: OS 25AX vs 25FX. What am I missing?

It seems all sizes of those AX-engines are cheaper new generation which was designed to make more money for the Owners of OS with a compromise on the performance...and that was posible because the other brands are even going worse, so why shouldn't OS save some money... [>:]
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Old 11-09-2012, 01:55 AM
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Default RE: OS 25AX vs 25FX. What am I missing?

The .25 FX was brought back by O.S. due to demand from a certain class of control line competitive racing where lightness and power are paramount.
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Old 11-09-2012, 06:33 AM
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Default RE: OS 25AX vs 25FX. What am I missing?

Thanks all for the input. I think I'll build light and go with the FX25.

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Old 11-09-2012, 09:19 AM
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Default RE: OS 25AX vs 25FX. What am I missing?

The latest magnum are apparently stronger than the FX, and true ABC etc...
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Old 11-09-2012, 02:15 PM
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Default RE: OS 25AX vs 25FX. What am I missing?

Hi!
The .25 AX is probably "stronger" (develops more usable power (at lower rews)) 0,79 bhp at 15000rpm compared to .25FX 0,84bhp at 18000rpm.
The .25 AX would probably the better engine to have in Aircombat swinging 9x6 props (RAM and Graupner Sonic)
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Old 11-10-2012, 02:43 AM
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Default RE: OS 25AX vs 25FX. What am I missing?

...after all it seems that the other major 'players' (frame, weight, propeller etc) than the engine should be considered
very profoundly, right ?

So what is really the set-up:

- to find the best engine for a given airframe,
OR
- to desing the optimum combination of frame+propeller+engine etc...)

Frankly, it looks to me the Aircombat (I have been playing with it time to time it since 1977... 'good' old times... )
is the WORSE one can think of designing Frame for it unless you fly without a tail...and the tail kills every thing
after is in place .

The best Engines I had are those whose body is for 2.5cc but the liner is for 3.5cc and then put her 'Magesty'
the TAIL and find the best propeller for Aerobatics WITH that 'bloody' tail and that is it...go practicing and make
sure yo have one more engine exactly the same in the bag redy to fire.

Sounds simple, but...what do you think for the 'Whole Thing', combat is after all more similar to Slow
Aerobatics than to Fast Pilon Racing, isn't it ? - If you agree, then Low RPM and Huge Torque is better,
isn't it.

And ONE more funny (or not) thing: - Remove the tail and load with just lead in the center of gravity
the Combat plane to come to the performance which the plane had while with tail. The horrible
descovery is that the Equivalent load to the Tail is in the order of 200 grams on horisonal fight!!!
(I had no nerves to measure it on combined aerobatics and horsonal; still was climing similarly)

That led me to the conclusion: Biggest Possible Displacement Engine is the universal best, and
the rest it to the Pilot hands....

I.e. if possible, place there OS .91FX and you will be the winner, that one is about 550g.
So for Fun I fly only OS.91FX which is in fact 0.61 body with 15cc displacement...and 3.2 bhp
at 13,000 rpm !!


Cheers,
Nick
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Old 11-10-2012, 04:51 AM
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Default RE: OS 25AX vs 25FX. What am I missing?

Hi!
?
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Old 11-21-2012, 07:30 AM
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Default RE: OS 25AX vs 25FX. What am I missing?


Quote:
ORIGINAL: fiery

The .25 FX was brought back by O.S. due to demand from a certain class of control line competitive racing where lightness and power are paramount.
I don't think it was control line, it was R/C combat. The 25FX was the "go to" engine for the combat guys and OS discontinued it. When the AX was brought out at a higher price, a lot of the combat guys went to the Magnum XLS 25 for $75 and liked them. OS said, "Uh oh!" and brought back the FX cheaper than the AX to try to offset their Magnum losses. At least that's what *I* read. Power wise, I've read that the AX engines like bigger props at lower RPM's and that's the disrepancy you see. I've not flown the .25's, but I've flown the .46FX and AX and that seems to be the case. I like the FX's better, but that's probably just me, not from some scientific data. And I couldn't tell you if that translates to the 25's or not.

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Old 11-21-2012, 11:54 AM
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Default RE: OS 25AX vs 25FX. What am I missing?

I see absolutely no use for a .25 that weighs 12 1/2 oz. That's an ounce heavier than a TT .36! I just can't imagine how OS sells any of them.
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Old 11-21-2012, 12:41 PM
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Default RE: OS 25AX vs 25FX. What am I missing?

For the life of me I can't understand why people use nickel plated bore engines,
if you want a real performer try a NV.
http://www.nvengines.com/index.php?page=shop.product_details&flypage=flypag e.tpl&product_id=29&category_id=1&option=com_virtu emart&Itemid=65
Happy flyin', Oscar
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Old 11-22-2012, 07:46 AM
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Default RE: OS 25AX vs 25FX. What am I missing?

The horse power ratings that different engine makers use can be very misleading, so I would not go by that. Most of the 25 size engines made by most manufacturers are good and strong, but some are a little stronger and or last longer. I like OS and have a lot of their older 25 and 28 FSR engines, and a few of their FX and SF. If you are not regulated by any rules, and depending on plane, go with the 35. If you want to save a lot of money look into the Magnum and Thunder Tiger. Here are a couple of planes I still run the older 25 and 28 FSR's on -

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