ripmax33

HI guys i need some advice here. i'm building a CAPICHE50 and soon i will have to make a decision which engine should i use. i am interested between a OS 55 AX or a 4 stroke SAITO72. since the model is intended to be used for 3D stuff, i would like to know some results with the OS 55 AX used for 3D.

any tips or prop readings, even experiences shared will be very usefull. i almost forgot ....i had i mind that if i will buy the 55ax i think i will fit a throttle pipe. (TUNED PIPES USED FOR 3D PLANES) are they called like this??...anyway any ideas?

regards
daniel

orstraycat

I prefer the 4 stroke engine over 2 stroke engines for 3D planes as the 4 stroke will swing a larger prop. My 2 cents !!!

freakingfast

My Feedback: (3)

The 55 AX on stock muffler w/baffle is stronger than the Saito 72 or about even with an 82.
A Macs "Quiet Pipe" will get you even more power yet broader than a typical tuned pipe.
The trick here is to set the pipe tuned a bit more favored for mid range (the header longer than normal peak setting) since your looking for "grunt" not top speed.
If you do it this way it will have a smother transition rather than a sudden hard pull at top end.

You can use less costly lower nitro with the OS as well.

DarZeelon

Daniel,


Any tuned exhaust system; even one that is in essence a tuned muffler, or a cone-and-disk pipe, will have a 'step' in the power curve...

Getting past that 'step' is never as smooth as just going up in RPM, even if that step is rather small...


If the 3D behavior you are looking for is smooth; i.e. linear engine behavior from low RPM to high RPM, most would suggest that you keep away from tuned exhausts...

Look into [link=http://www.jettengineering.com/engines/bse40.html]this Jett Engineering page[/link], where Dub Jett offers the Jett .76BSE 3D engine, with a non-tuned muffler.
One could opt for the JettStream, or the TurboJett and get more power at no extra cost, but for 3D the non-tuned Lite-Jett muffler is more than suggested and power is more than sufficient.

In any case; the wider the effective RPM range of a tuned exhaust system, the lower the available boost.

For your OS.55AX, you would probably want a tuned exhaust system, that begins to boost power below the typical hovering RPM...
It would typically become a 'rev-limiter' at ~150% of that figure... I.e. the engine would never exceed that RPM, even if spinning a toothpick...

NM2K

My Feedback: (14)

I would be looking into using the Mousse Can Pipe for 3D flying with the OS .55AX. The combination of weight savings and the slight increase in power output over the stock muffler might be more useful than a true tuned pipe. For Mousse Can Pipe construction information, do a Google Search of:

"rec.models.rc.air; Bob Adkins, Mousse Can Pipe"


Ed Cregger

ripmax33

so does the 55AX will be more then enough for a 4.5 to 5Ib 3D plane? will i get stifactory performance with about 10% nitro fuel and a 13x4 prop ? Or should i concentrate to get a saito 72. 4stroke are economical but expensive, 2 stroke cheaper and maybe lighter, but i think they burn more fuel...well its a 2 stroke., 1 power stroke every 1 revolution instead of 2

any ideas???

regards
daniel

ripmax33

Edited by Rcpilot

Reason: Double post

DarZeelon

Daniel,


Because a two-stroke engine usually has a heavy muffler, it is usually a bit heavier than a four-stroke that makes the same power and for sure heavier than a four-stroke engine of the same displacement.

The other attributes you mentioned are correct, but economy is not only about amounts...

A four-stroke engine would typically use higher nitro fuels that not only cost more per gallon, but are also used in greater amounts, due to their lower stoichiometric ratios...
The two-stroke OS.55AX would readily run very well on 5% nitro, so I don't think a four-stroke engine would cost you less to run.


This thread is in the RPM forum...
Discussions of 'which engine is better and for what purpose', should be carried on in the general discussion fora ('Glow Engines' in this case...).

NM2K

My Feedback: (14)

Just off the top of my head (guessineering), your projected model sounds too heavy at 5 lbs. Drop another pound and you might get some serious performance. This is just an old man jibber-jabbering, so take it for what it's worth.

In today's world, there is no reason to even think of buying the Saito .72. It was a great engine - for its day - but the engine to buy today (other than the YS .63) will be the new OS FS-81 or the slightly older Saito .82. I have a couple of the Saito .82 engines and haven't been sorry in the slightest way. I'd like to try an OS .81, but haven't yet. I still think that the YS .63 is the best in the contest.


Ed Cregger

freakingfast

My Feedback: (3)

With the stock muffler and baffle in place turning an APC 12.25X3.75 (these are wide blades, thou not listed as "W") at only 12000rpm on 15% will give you over 7lbs of "static" thrust.
With a " tuned" muffler or Macs Quiet Pipe* with same prop and fuel will get you over 14600 rpm and 11 lbs of static thrust. This will really make a Capiche jump!

*better transition than a tuned muffler.

DarZeelon

FF,


The performance you stated with the normal muffler seems substandard...

The 12.25x3.75 prop is in APC's control-line series and has always been described as a W prop, even in these pages...
I don't know why there is no 'W' there...
The normal APC 12x4 prop, is spun ~1,000 RPM faster, by any decent engine.

The 12K you stated on that prop, is typical for a standard OS.46AX...

The .50SX exceeds 13K, as does the MVVS .49, with the tuned silencer (14,100 RPM on the 12x4 APC).


The RPM figure with the Macs quiet pipe, however, is exaggerated and (with the W prop's 1.5 constant) translates to no less than 2.19 HP...

This is piped .91 power - not .55 power!

A typical, piped .60/.61 '80s pattern engine (pre 'long-stroke' Webra #1030/1024, Rossi .60, YS .60, Enya .61XF, OS.61FSR...), could only muster-up 1.87 HP, spinning an 11x7.5 @14K.
Nothing has actually changed in glow engine technology since. ...Virtually nothing in its power either.

I believe you should recheck that figure, with a better tachometer...

Besides, on 15% nitro and with the pipe's supercharging effect, this engine would be way over-compressed (burning plugs, Etc.).

Richard D Bahmann aka/Wrongway

My Feedback: (42)

Os-55 std muffler, 15% fuel APC 12.25x3.75 13,200
OS-55 std muffler, 15% fuel JC Super Prop (wood) 11,000
OS-55 E-composites tuned pipe (this is the same motor as above and fuel, has about 3 gallons in it) 13,000

Sea level, 80% Humidy, 85 degrees F.

DarZeelon

Quote:

ORIGINAL: Richard D Bahmann aka/Wrongway

...JC Super Prop (wood) 11,000...

Wrongway,


What pitch and diameter is your 'ivory wood' prop, you have quoted this RPM for?

Richard D Bahmann aka/Wrongway

My Feedback: (42)

Sorry 13x4

freakingfast

My Feedback: (3)

The performance with the stock muffler and baffle on a hot day is pathetic.
I just wanted to show that even with performance at this level a 5 lb plane wont tail slide
Pull out the baffle and you get 1000rpm jump.
Same HP number I get, is the 1.5 constant wrong???

I stand by my tach number and I’m not alone……

http://www.rcuniverse.com/forum/fb.asp?m=5374838
http://www.rcuniverse.com/forum/fb.asp?m=6515770

Never had a problem with K&B HDs or Enya #5 glow plugs.

DarZeelon

Quote:

ORIGINAL: freakingfast

The performance with the stock muffler and baffle on a hot day is pathetic.
I just wanted to show that even with performance at this level a 5 lb plane won't tail slide
Pull out the baffle and you get 1,000rpm jump.

Perhaps, FF, but an OS.46AX exceeds 12K, even in hot, Israel beachfront weather... With the P-Box baffle in place.

Quote:

Same HP number I get. Is the 1.5 constant wrong???

Maybe, but I believe it is more probably this prop deforms excessively, as a certain RPM level is exceeded...

It is in proper shape and rigid enough to offer the 1.5 constant drag, to engines that do about 13K, or a bit over that.

But when, say, 13,400 RPM are exceeded, this prop flattens out more and that constant is reduced significantly; allowing RPM to increase way beyond expectations.
As the P-factors is reduced, thrust is also... It will not produce the expected, calculated static thrust, if this is the case...


You can, however, agree that it is quite improbable (...) that this engine actually makes 2.19 HP at that 14,600 RPM, when at 12,000 it makes only (calculated) 1.21...

Quote:

Never had a problem with K&B HDs, or Enya #5 glow plugs.

This changes the issue.

Both of the above are cold plugs; much colder than than the OS #8, which this engine comes with and which most use...

freakingfast

My Feedback: (3)

This engine has never been happy making hp with the P box muffler and baffle, kinda like running a marathon with you mouth taped shut and one nostril plunged.
Not really fair to make any correlation of the stock muffler #'s to a tuned system. The P-box on the 55 is the same unit that is used on the 46. Some guys switch to a Tower muffler (much more volume) and are getting much better power, still less than a tuned system of course.

Here's another anomaly, APC 12X5 at 14,600 = 2.09HP (1.2 constant). http://www.rcuniverse.com/forum/fb.asp?m=6515770 There are other tach readings out there that bump the doors to 2Hp, too many to ignore. There seems to be a best peak around that rpm when tuned for it, (tuned mufflers, Jett or Ultras just happen to tune there) a tuned pipe will get a tad more power. I like to load my two engines so it's 13,800 to 14.000 on the ground but tuned for 14,600 so it has something to unload into (for max sport speed apps).

The best higher end I’ve personally seen is 10X8 at 15700 about 1.91hp, http://www.rcuniverse.com/forum/fb.asp?m=6903674 but the engine hits a wall at about 16,000 and won’t make worthwhile power above that regardless of pipe tuning, its reached its limits of its porting.
With a tuned exhaust, I think it’s a better idea for most applications is to utilize/fly this engine in the 14600 range….what ever hp it’s really making it seems to be best there.

Yes, it's hard to fathom that kind of power out of that engine.

Blade47

I have two OS55ax one on a f-16 and the other on a F-18 ...both run Jett muffler with a 11x7 Master Air Screw 2 scimitar 10% fuel Hanger 9 super plug and local field at 2300' Ground tach to 14,500 with room to spare on the top end ..you can hear them both unload in the air ...but ground run at 14,500 should be 2.232 HP is this about right?

freakingfast

My Feedback: (3)

11X7 MA S-2 (scimitar .95 prop constant) @ 14500 I get 1.53 hp.

It looks like you are trying to use the Thrusthp calculator, it's a bit too optimistic.
That program has issues, try changing the pitch and see if the thrust numbers change.

I get 14000 with same prop with an Ultrathust muffler so you are doing good.

DarZeelon

Quote:

ORIGINAL: freakingfast

Here's another anomaly, APC 12X5 at 14,600 = 2.09HP (1.2 constant). http://www.rcuniverse.com/forum/fb.asp?m=6515770 There are other tach readings out there that bump the doors to 2Hp, too many to ignore. There seems to be a best peak around that rpm when tuned for it, (tuned mufflers, Jett or Ultras just happen to tune there) a tuned pipe will get a tad more power. I like to load my two engines so it's 13,800 to 14.000 on the ground but tuned for 14,600 so it has something to unload into (for max sport speed apps).

The best higher end I’ve personally seen is 10X8 at 15700 about 1.91hp, http://www.rcuniverse.com/forum/fb.asp?m=6903674 but the engine hits a wall at about 16,000 and won’t make worthwhile power above that regardless of pipe tuning, its reached its limits of its porting.
With a tuned exhaust, I think it’s a better idea for most applications is to utilize/fly this engine in the 14600 range….what ever hp it’s really making it seems to be best there.

Yes, it's hard to fathom that kind of power out of that engine.

Karl,


I still believe most 'extravagant' readings are cases of prop deformation...

Typically, a muffled tuned pipe is capable of raising the BMEP of a two-stroke engine, by ~20% over the open-exhaust value and 25-30% over the muffled numbers.


Getting over 2 HP out of a .55 cid engine, at 14.5K, would require too great a BMEP value.
A rudimentary supercharger that a tuned exhaust is, cannot possibly get the engine up to such values...

A bent-over prop is much more likely to.


As to the porting becoming the bottleneck; I installed an APC 8.75x8.25NN Q500 prop, on an OS.46AX, with a debaffled P-Box muffler, on a Diamond Dust.

The engine managed to spin 16,100 RPM on the ground... With the model flying at full speed and even diving, the engine unloaded, maybe, 100-200 RPM...
You would expect an engine to unload to around 18K and beyond, but this simply did not happen. The RPM sounded the same as it did on the ground.


The calculated HP number with that prop was a lame-duck 0.91. Just to compare, the 14,300 RPM this engine can reach with a 10x6 APC, is 1.1 HP.

There is indeed a porting induced 'brick wall' there...

Blade47

FF ... you are right that is what I used ... I did check with another program and do get what you have at 1.53 hp ... to bad [&o] oh well it still performs well.

DarZeelon

Pete,


Please go to Pé Reivers' web site and download the [link=http://mvvs.nl/prop-power-calculator.xls]Prop-Power calculator[/link].

This software is based on REAL research and dynamometer readings; not on manufacturers' claims (read; 'tall tales').


You can also work it on the web site.

Richard D Bahmann aka/Wrongway

My Feedback: (42)

That MVVS.nl calculator is very accurate. I was able to verify thrust reading on a 50cc engine in the past to an accurate amount.

R

anuthabubba

My Feedback: (102)

Dar says, "You can also work it on the web site."

Please explain. Every time I try to use the tool I get a "You don't have the right software to use this tool" notice. How can it be used "on the site" without having to download a bazillionK of software?

Thanks,

Terry in LP

TimC

Same here. I tried this a few years back. I even downloaded the software and still couldn't get it to work. I blamed it on my lack of computer savvy.