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OS .46AX vs. Evo .46

Old 02-14-2005, 11:09 AM
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Ed_Moorman
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Default OS .46AX vs. Evo .46

In the February issue of R/C Report magazine, the publisher, Gordon Banks, did a test on the Tower muffler, showing the rpm gain over the stock muffler. He used 3 engines, OS .46AX, Evo .40 & Evo .46. I assume that like I did the first few times through, everyone looked at the gain in rpm from using the Tower muffler. Look again at the rpms of the engines on an 11-6 prop. 1,000 difference between engines. The AX was turning 1,000 rpm better with an 11-6 prop than the Evo .46. Anyone else noticed this big a difference?
Old 02-14-2005, 07:27 PM
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flipstart
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Default RE: OS .46AX vs. Evo .46

Ed-With the Tower muffler on my 46 FX I noticed a 800 rpm increase over the stock muffler, BUT on 2-AX's I was running the stock muffler w/o baffle. When I installed a Tower Muffler on one of them, there was no appreciable gain. I generally am getting 12,800-13,200 rpm with APC 11/6 on all 3 engines. OS calls the AX muffler a power box-so maybe it is (w/o baffle) as efficient as the Tower Muffler. I was surprised at these results.
Old 02-14-2005, 09:03 PM
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Ed_Moorman
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Default RE: OS .46AX vs. Evo .46

When I ran my tests that I documented here, I used the stock muffler without removing the baffle. I should probably try it with the baffle removed.

Did you notice any lowering of muffler pressure with the baffle out?

My main point of the post was the difference in the AX and the Evo, which I thought was a lot. I have an Evo and if most of my planes weren't in storage while I wait repairs for hurricane Ivan from last fall, I would try it myself.
Old 02-14-2005, 09:25 PM
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ChuckN
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Default RE: OS .46AX vs. Evo .46

A few years ago I compared the OS 46FX and the TT 46 Pro back to back with stock and Tower mufflers. With the 11x6 prop and Tower muffler the OS outperformed the TT by better than 1000rpm. Judging by how the engines sounded, it was clear that only the OS was getting up into the "tuned" operating realm of the Tower muffler. It seemed as though the TT missed it by a couple hundred RPM and never benefited from the muffler's performance boosting characteristics. Sure enough, with the stock OS muffler, the OS outperformed the TT by nearly 500 rpm. By falling short of the muffler's rpm range (appears to be 11,500rpm to 16,000rpm) the TT wasn't able to capitalize on it's tuning affects. Looking for reasons, I discovered that the TT's exhaust port timing was a little longer than that of the conservative OS FX. This would take away some bottom end that was needed with the 11x6 prop. Also measured cylinder pressures with one of those clever cylinder pressure guages. The OS had slightly better cylinder pressure. I suspect that you will find the same situation with the EVO 46 and the 46AX. Just my two cents
Old 02-14-2005, 10:28 PM
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Default RE: OS .46AX vs. Evo .46

Hi Ed.

I have an Evo .46NT with a Tower's muffler on the way. I'll tach the engine before and after the muffler to let you know. I always take out the baffles and I'll do that too. By the way, W8YE flies at our field and I will see if he is interested in being there. I'm running an APC 11x4 now and I think that I've tached it at over 13K in the past. I'll have to check my logbook.
Old 02-14-2005, 11:28 PM
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Harry Lagman
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Default RE: OS .46AX vs. Evo .46

Nice post ChuckN. I have also noticed with the TT 46 Pro that its ground revs are not that spectacular but once they get airborne they can really unload well, even in a draggy airframe like a typical trainer.

I have had first hand setup and tuning experience with several OS FXs, TT 46s and GMS .47s mounted on trainers owned by guys that I have been teaching to fly. Most of them are running 11x6 MA props. Even though static revs are pretty similar when comparing the three, the TTs have consistently outperformed the others once the load comes off them. Out of the three, I'd choose the TT for high performance sport flying based on that experience.

It just goes to show that static revs with one prop are not the be-all and end-all of performance.
Old 02-15-2005, 08:26 AM
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Default RE: OS .46AX vs. Evo .46

Harry-Just to substantiate what you found-a friend and I built 2 planes as identical as possible-he powered his with a ST 51 and mine with a OS 46 AX running either stock muffler (w/o baffle) or TM. I always out tached him on the ground by 1000 to 1200 rpms using the same APC 11/6 prop BUT he always out ran me in the air.

We even went to great lengths to make sure trims were close to same, weight (mine was 4 oz lighter) and on a thrust test with calibrated scale I had 1.5#-2# more thrust on the ground. So it was evident that the static test was not the final numbers that really mattered. We raced for over 20+ flights and I was never able to keep up with his plane despite trying everything I knew to do for better performance. I know there are subtle differences in planes, but this was frustrating. thought I would have blown him away. Same fuel by the way. Go figure. Even the gurus at the field are still puzzled.
Old 02-15-2005, 09:09 AM
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Ed_Moorman
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Default RE: OS .46AX vs. Evo .46

What you say is true that some engines unload in the air better than others. I remember this from racing in both CL & RC a hundred years ago or so.

What would be interesting would to make a large blower that you could roll up in front of your engine test stand. Something that would put 75 mph air or so over your engine would be adequate, I would think. This would allow the engine/prop combination to rev up like it was airborne and give you more realistic tach readings.
Old 02-16-2005, 09:25 PM
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ChuckN
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Default RE: OS .46AX vs. Evo .46

Try running an 11x7 prop on your ST 51 and see what happens. The ST51 has a longer stroke than the OS46 so it's peak power will be at a lower RPM. Stroke length and port timing have a very significant affect on how your engine unloads. It's quite probable that if you prop your ST to run the same ground rpm as the OS, you would beat the OS in the air. Try it and let us know.
Old 02-20-2005, 09:09 PM
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Default RE: OS .46AX vs. Evo .46

I gained about 1000 RPM to 14,300 when I installed the Tower muffler on my Evo .46NT with the same APC 11x4 prop. Howver, it's been quite a while since I tached the stock muffler and I didn't go a before and after check as I should have. From a strictly gut impression point of view, the engine screamed with the Tower muffler and displayed a power boost except for one puzzling profile- flying vertical. Maybe it is just faulty perception, but it did seem to lack a little on vertical uplines. Could be the temp-da for yesterday, maybe the cycle of the moon, or whatever.
Old 02-20-2005, 10:24 PM
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Ed_Moorman
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Default RE: OS .46AX vs. Evo .46

The ST .51 does have a longer stroke than the OS .46, but it is also larger in displacement. The .51 is a bored out ST .45. Compared to the OS .46, the ST .51 has a larger bore-stroke ratio so it is a shorter stroke engine, relatively speaking. As I recall, the ST .45 is a revving engine and it has the same stroke, 20 mm vs. the OS 19.6 mm.

A lot of the unloading may be the mufflers and the port timing.

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