DarZeelon

Sorry, Tim, Terry...

In the past it was possible to open this application on the web site, input the figures and get the results on-line...


It seems this is no longer possible...


To use this excel file, one needs either Microsoft Office, Lotus 123, or the Google/Mozilla freeware (OpenOffice) that can do the same.

1fasthitman

all props on 30% fuel:

11x8 apc: 12500
11x6 apc: 13000
12x6 apc: 12000

martseger63

What exhaust are you using, not the stocker, right?

tony0707

hi the Tower Hobby expansion chamber exhaust for the 46 SF AX engine will bolt right up to the 55AX engine-at 15.00 plus s-h -pretty sure that it will improve performance and the RPMS over the stock box mufflervery similar design to the- Ulta Thrust -by Nelsoni have both expansion chambers and see little difference in there performance-and a big difference in price- hope that tip helps someones performance a bit - i am selling a new 55 AX -no fuel here on the engines for sale page TONY "the omega man "

tony0707

hi regarding a macs black exhaust pipei cut a 1/4 inch off it at a time the second 1/4 inch the internal baffel blew out-my rpms increased 1000 rpms over the reading i was getting prior to that timethe engine got loudbut i like LOUD-and i have left it that way sincean awsome sound and performace has been the result- TONY

helodrvr

My Feedback: (88)

You talking about this Black Macs exhaust pipe.

http://www3.towerhobbies.com/cgi-bin...?&P=8&I=LXXYM3

Do you have any back pressure problems??

freakingfast

My Feedback: (3)

Man,,,,, I don't know what to say to that one![sm=confused.gif] I guess he was confused between cutting a header down and the black muffler????????

georbeckha

My Feedback: (12)

Hi All,
I have some numbers off of my 55ax that I would find hard to believe if I hadn't seen them with my own eyes.
First is at 5000' altitude with 18% cool power in a Model Tech Mach Racer and an Ultrathrust Racing muffler...
APC 9x9 16,400 rpm
APC 9x10 16,200 rpm (Both these props pulled the racer at about 150 odd mph)

Now, at Sea level, 18% cool power with a Tower Hobbies 46 muffler
APC 11x7 Sounds like 110,115,200 but will confirm then weather permitting

George

Edited for Plain old Human Error (At least I admit I'm human)

DarZeelon

Quote:

ORIGINAL: georbeckha

First is at 5000' altitude...

Now, at Sea level...

George,


The altitude is irrelevant... as far as the RPM is concerned.


Sure, the power output will change as a linear function of the altitude density, but not the RPM.

This number will be retained, since power output and the effort required to spin the prop, are both linear functions of altitude density.

If altitude density is halved, power will be halved. But the power absorbed by the prop will also be halved, so RPM will remain about the same.


It is redundant to mention the altitude.

The acceleration of the prop and engine, however, will be affected.
In thinner air, the engine will not increase its rotational speed as fast as in thick air.

freakingfast

My Feedback: (3)

I think you need a new tach. The performance you show is up there with Jett 90LX on tuned pipe.

Altitude has little effect on rpm results on planes for the reasons Dar gave. Less air for power and less air for the blade to cut....they cancel each other.

georbeckha

My Feedback: (12)

LOL, I just knew I'd get reactions on those numbers up there. That's why at the time in Colorado I had someone else tach it.
Here at sea level I have just taken delivery of a new tach and when the weather is co-operative I'll try to get readings here. See what I get.

DarZeelon

Quote:

ORIGINAL: georbeckha

LOL, I just knew I'd get reactions on those numbers up there.

George,


While this is a social forum, where people chime in to discuss their experience with glow engines; I think no one here wants to read deceitful posts, claiming unreasonable RPM numbers, which were posted "just to get reactions"...

And right was Karl. the numbers you posted are unreasonable.

'Cruel-Power' is the wrong fuel for this engine. Both Morgan and Hobby Services say you should use fuel with castor oil in it, which this fuel hasn't.

15,200 RPM for this engine with the Tower muffler, is possible with a 10x6; but not with an 11x7... There is only a handful of full-length piped .61 engines that are capable of such a feat.


The other numbers are even more unreasonable (read: impossible lies)... That person in Colorado must be pulling your leg.

And... The number quoted for an APC 10x11 is a hoax, since there isn't such a prop.
Spinning a 10x10 at your quoted RPM would require 2.76 HP... Again, a tall tail...

You would be lucky to have this engine spinning a 10x6 at this RPM...

EDIT: Typo; grammar.

georbeckha

My Feedback: (12)

Nice... I am being 100% truthfull in my posts and someone that was not even there to witness the tach readings themselves shoots them down.
YOU believe what you want and I'll believe my eyes. Have YOU ever tried this combination of fuel, prop and muffler? No? And 'That person in Colorado was as stated in my post myself! That's why we went with a 2nd tach reading. As for the 10x11. I could have sword that this was one I put on there and maybe it was discontinued some months ago as this was some months ago. I will go thru my props and see if I still have one. Maybe I am on crack. Maybe I do need to stop smoking my bathwater.

georbeckha

My Feedback: (12)

Ok, I'll man up and apologise to all... I mistook the size on the prop. For some reason I had it in my mind I was using 10" props but I have come to find I was using 9" props...
9x9 and 9x10. (I checked my logs for June and July when it was mid to upper 90's farenheight outside.) I do however stand by the RPM numbers. And remember, I said those numbers were using an Ultrathrust RACING muffler NOT the one off of the Tower 46. That I still need to get a reading off of. (This is currently spinning an APC 10x7)

As for the Cool Power being the wrong fuel... Each to his own. Personally I have never had an issue with it but I have read of others here that have. Maybe it is because I have always put a splash of Castor in mine when I first get the fuel.

DarZeelon

George,


As to the fuel; "each to his own" is hardly an excuse to be using the wrong fuel...
But since you do add castor; make sure it is 4 ounces per gallon, to make it safer for your engine.

As to the props; in your post #158, you stated 15,200 RPM with the Tower muffler, on an 11x7 APC...
Would you wish to 'revise' this unreasonable figure?


As to the UltraThrust mufflers; I import and sell them in my country (Israel)...

RPM up to 17K is within the realm of the Std. UltraThrust UT-2.

The Racing version will not allow any .40-.55 engine, to spin an APC 10x6, or 10x7 any faster than the UT-2...
It is intended to spin smaller props; at higher RPM.

Smaller, meaning APC pylon racing props, or a sport 9x6 APC prop.
Higher RPM meaning 17K-21K.

...But in that range you will encounter a problem of a different kind...
The porting of the OS.55AX is too conservative and is not designed for this kind of RPM.

Its ports are typical .40 size and their timing in degrees is 'sport oriented'... Exhaust timing is ~155°.
This engine is not intended to 'sing' at such high RPM, so it will not be able to utilize the Racing UT's RPM potential.

georbeckha

My Feedback: (12)

Sounds like you have a great and full understanding of the engines performance and a full understanding of how they work and why.
Real world RPM vs prop size here taken today at 50 degrees F and a slight breeze blowing.
11x7 APC Prop - Unable to test as as the glow driver slipped out of my hand and fell unto the prop as I was removing it. Broke the prop.
10x7 apc - 14,800 rpm. (Tested on 2 seperate runs)
10x6 apc - 15,600 rpm. (Tested on 3 seperate runs)
Muffler off of a Tower Hobbies .46

Ok, Go ahead and rip these numbers appart. I know you want to. All I know is that I saw these numbers less than 2 hours ago and was seen by numerous people out there.

freakingfast

My Feedback: (3)

Those numbers are inline with stock muffler with baffle performance levels. The 11X7 would have been 12,100 at that rate.

freakingfast

My Feedback: (3)

The highest I've ever seen a 55AX turn an APC 11X7 with 15% is 13,900, and that was after going through a box of assorted correct sized tuned pipes and lots header trimming/spacing. Perhaps it would have turned another 400 on 30% with an OS A5 (#10) or K&B HP glow plug. Cool dry air will raise the numbers about 150 at the most. So 14,400 would be about the best case possible speed that you could ever see this engine turn with that prop and that's an incredible 1.9 hp.

Tach-ing an engine into a strong head wind will raise the numbers dramatically.....of course that doesn't count

DarZeelon

Quote:

ORIGINAL: georbeckha

10x7 APC - 14,800 RPM (tested in 2 separate runs).
10x6 APC - 15,600 RPM (tested in 2 separate runs).
Muffler is off of a Tower Hobbies .46.

George,


I will not mess with these numbers, simply because they seem reasonable and probably attainable.

That 11x7 number was something even a 'super-duper' piped .61 from Rossi/Jett/OPS/Picco... is not capable of.
The Jett .90L can only spin an APC 11x8 at 15K; and yours is just a 'plain Jane' OS.55...

Harry Lagman

Freakingfast's numbers pretty much align with my rpm point expectations for the APC 11 x 7 on an engine such as the 55 AX.

I haven't yet played with an OS .55 but I have seen an ASP .52 and an OS SX .50 both spin an APC 11 x 7 at about 13,600 with a tuned pipe on 15% fuel.

Other rpm points for the APC 11 x 7 I have got with my own engines (all 15% nitro) are:

Jett .90L with stock Jettstream pipe: 15,000
OS VF .61 with Macs unmuffled tuned pipe: 14,500
OS VF .61 with open face (no pipe at all): 13,200
OS FSR .60 with stock muffler: 12,600

Eganwp

My Feedback: (1)

Apparently I've put off posting my tach results on this thread... I posted them on the extreme prop speed forum awhile back, but that my have been before this thread existed. Back then the only info on the Tower .46 muffler and a 55ax on the web was a guy using one on a 55ax and saying it was an "improvement" lol.

Here's my info from flying this engine on 2 planes since last March. Did TONS of testing on different prop types and sizes, but I can't recall some of the numbers so I've omitted them if I didn't have them written down. Also note that moving to 15% Omega fuel only ever netted me about 100-150rpm on the top end with almost every prop. It's not worth the extra $$ though 1 click lower idle is kinda nice.

15*C, 3500ft ASL (and yes Dar I realize this isn't needed haha), 10% Omega fuel; 3 gallons so "broken-in"; testing on ground on short grass

Stock muffler w/ baffle:
12,840 rpm 11x7 MA G/F S2
12,000 rpm 11x7 APC

Stock muffler w/out baffle:
13,100 rpm 11x7 MA G/F S2
12,220 rpm 11x7 APC
13,100 rpm 10x8 APC

Tower .46 muffler for $15:
14,200 rpm 10x8 APC - the prop I now fly with all the time on my Super Sportster 40. Absolutely insane speed for this plane and still unlimited vertical on 10".


Best $15 I've ever spent lol! I prefer the 11x7 MA G/F S2 prop the best on the stock pipe w/ or w/out the baffle if anyone's considering between the two.

Ernie Misner

Hi Dar, is that "last piece cut off of the header" similar in appearance to say, a wedding band? Could you tune the length of the assembly simply by pulling the pipe back slightly in the coupler before tightening the nylon zip ties? Or would the internal flow tend to be disrupted too much by the gap inside?

Thanks,

Ernie

DarZeelon

Hi, Ernie.


Using that last 'wedding band' in the header and not just leaving the bare silicone tube, achieves three objectives...

It protects the coupler from the heat, by exposing minimal lengths if it to the hot flow, it minimizes the flow disturbance that can result from 'waisting' of the coupler and it minimizes the absorption of the 'pressure pulses' by the tubing, by being more rigid than silicone... leaving more of the pulse for maximal boost.

freakingfast

My Feedback: (3)

The first issue Dar addressed is the most important, protection. The more the exposed gap, the shorter the coupling life. For example if you have a gap of 1/4", the silicone coupling will most likely be compromised in under a gallon of run time. Even with minimum gaps, high performance applications don't last long. One trick I've found is to add a central tie strap right over the joint(s), not too tight. This keeps the coupling from ballooning when hot and letting the hot gasses and caustics have more access to interior surface area of the coupling.

Ernie Misner

Does it help to use the expensive gray couplers from Mac's?

Thanks,

Ernie